Power Conversion Device

Abstract

To reduce overcurrent that flows in a power semiconductor element in overcurrent protection operation of the power semiconductor element.SOLUTION: A power conversion device 100 comprises a control unit 10 for controlling a drive circuit 14 including an overcurrent protection circuit 41 and an element drive circuit 40 for outputting an element drive signal sd to power semiconductor elements 3a to 3f. The control unit 10 outputs a correction command signal sc generated on the basis of previously stored voltage correction amounts 86a, 86b or voltage correction amounts 86a, 86b calculated from previously stored voltage correction amount data 55 to the overcurrent protection circuit 41. When overcurrent flows, the overcurrent protection circuit 41 compares overcurrent threshold voltage Vthp, Vthn generated on the basis of the correction command signal sc with detection voltage Viu, Viv, Viw output by current sensors 21a, 21b, 21c to generate an overcurrent stop signal st.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to a power conversion device. [Background technology]

[0002] In recent years, power semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) have been widely used in power conversion devices used in electric powertrains of hybrid vehicles, electric vehicles, and the like. The power semiconductor elements are mounted on a power semiconductor module, either individually or in a configuration in which multiple elements are connected in parallel. Such power semiconductor modules are mounted on power conversion devices.

[0003] Power semiconductor elements generally have a tolerance for voltage and current, and may be destroyed if the voltage and current exceed the allowable limits. For this reason, power conversion devices are equipped with current sensors that detect the value of the current flowing through the path, and can protect the power semiconductor elements from overcurrent by detecting excessive current and stopping the current flowing through the power semiconductor elements.

[0004] Generally, the switching speed (di / dt) of a power semiconductor device is designed so that it does not exceed the device's breakdown voltage (voltage tolerance). Typically, when an overcurrent occurs, which is the condition that maximizes surges, the control circuit of a power semiconductor device, for example, whose control terminal is a gate terminal, sets control parameters such as the turn-on switching speed, drive voltage, and control terminal resistance so that the surge voltage is below the breakdown voltage. For example, in a power semiconductor device whose control terminal is a gate terminal, the gate resistance, or gate constant, is often used as a control parameter. For this reason, when the control circuit of a power semiconductor device sets a high overcurrent tolerance, it is necessary to increase the gate constant and suppress the switching speed. Setting a high gate constant increases the switching loss of the power semiconductor device even in the normal operating range. Therefore, to improve the efficiency of a power conversion device, it is necessary to minimize the overcurrent value itself.

[0005] A typical overcurrent protection circuit is one in which the output value detected and output by a current sensor is input to a comparator or other such device, which constantly compares the output value of the current sensor with a threshold value set as the overcurrent value, and the comparator stops the power conversion device when the output value of the current sensor exceeds the overcurrent threshold. This method can be configured with a relatively simple circuit, but if the output value of the current sensor varies due to variations in the current sensor, temperature characteristics, etc., the power conversion device may stop at a current value greater than the expected overcurrent value, i.e., the preset overcurrent value.

[0006] Patent Document 1 discloses an overcurrent detection circuit including the configuration of a general overcurrent protection circuit. The overcurrent detection circuit in Patent Document 1 includes a series circuit of a current detection MOSFET and a resistor connected in parallel to a drive MOSFET, and compares a detection voltage obtained by detecting the current of the drive MOSFET using the resistor in the series circuit with a threshold voltage obtained by detecting the current of a temperature characteristic correction MOSFET, which has the same temperature characteristic as the drive MOSFET, using the resistor. If the detection voltage exceeds the threshold voltage, a gate control unit outputs an overcurrent detection signal that stops driving the drive MOSFET. The overcurrent detection circuit in Patent Document 1 improves overcurrent detection accuracy by canceling out the temperature characteristics of the detection voltage and the threshold voltage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-154669 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the overcurrent detection circuit of Patent Document 1 adjusts for temperature-related threshold variations by including a temperature-compensation MOSFET with the same temperature characteristics as the drive MOSFET. However, even when using MOSFETs of the same size and structure, variations in each device, such as on-resistance, can cause errors in the adjusted threshold. Furthermore, the overcurrent detection circuit of Patent Document 1 only adjusts the threshold for temperature variations and fails to consider output variations, such as gain error and offset error, of the series circuit of the current detection MOSFET and resistor, which corresponds to the current sensor. Furthermore, magnetic field detection current sensors with a coreless configuration have large errors due to dimensional tolerances and layout variations. Therefore, when detecting overcurrents using a current sensor, temperature compensation of the threshold cannot sufficiently absorb errors due to current sensor output variations, and an unexpected overcurrent may flow.

[0009] The technology disclosed in the present specification aims to reduce the overcurrent flowing through a power semiconductor element during overcurrent protection operation of the power semiconductor element. [Means for solving the problem]

[0010] An example of a power conversion device disclosed herein controls a power conversion unit having multiple power semiconductor elements to convert DC power to AC power or AC power to DC power. The power conversion unit includes a drive circuit that outputs an element drive signal to drive the multiple power semiconductor elements, a control unit that controls the drive circuit, and a current sensor that detects AC current in the power conversion unit. The drive circuit includes an element drive circuit that outputs the element drive signal to the power semiconductor elements, and an overcurrent protection circuit that determines whether an overcurrent has flowed through the power semiconductor elements and outputs an overcurrent stop signal to the element drive circuit, causing the element drive circuit to output an element drive signal that switches the power semiconductor elements from an ON state to an OFF state. The overcurrent protection circuit includes a comparator that determines whether an overcurrent has flowed through the power semiconductor elements by comparing a detection voltage output by the current sensor with an overcurrent threshold voltage and generates the overcurrent stop signal, a threshold output unit that outputs the overcurrent threshold voltage, and a threshold voltage adjustment unit that generates an adjustment voltage that causes the threshold output unit to output the overcurrent threshold voltage based on a correction command signal output from the control unit and outputs the adjustment voltage to the threshold output unit. The difference between the first voltage of the current sensor at the time of design and the second voltage of the installed current sensor with respect to a predetermined overcurrent setting value that turns the power semiconductor element into an off state is set as the voltage correction amount, and the control unit generates a correction command signal based on the voltage correction amount that has been stored in advance or the voltage correction amount calculated from the voltage correction amount data that has been stored in advance. [Effects of the Invention]

[0011] In one example of a power conversion device disclosed in the present specification, a control unit outputs a correction command signal to an overcurrent protection circuit, the correction command signal being generated based on a voltage correction amount stored in advance or a voltage correction amount calculated from pre-stored voltage correction amount data, and when an overcurrent flows, the overcurrent protection circuit generates an overcurrent stop signal by comparing the overcurrent threshold voltage generated based on the correction command signal with the detection voltage output by the current sensor, and switches a power semiconductor element in which it is determined that an overcurrent is flowing from an ON state to an OFF state, thereby making it possible to reduce the overcurrent flowing in the power semiconductor element during the overcurrent protection operation of the power semiconductor element. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of a first power conversion device according to a first embodiment. [Figure 2] 10A and 10B are diagrams illustrating the operation of a power conversion device of a comparative example when an overcurrent occurs. [Figure 3] FIG. 10 is a diagram showing a current waveform in a power conversion device of a comparative example. [Figure 4] FIG. 2 is a diagram showing the configuration of a drive circuit in FIG. [Figure 5] FIG. 5 is a diagram illustrating a configuration of the protection circuit of FIG. [Figure 6] 2 is a diagram showing a first example of sensor characteristics of the current sensor of FIG. 1. FIG. [Figure 7] 1. FIG. 4 is a diagram showing a second example of the sensor characteristics of the current sensor of FIG. [Figure 8] 1. FIG. 4 is a diagram showing a third example of the sensor characteristics of the current sensor of FIG. [Figure 9] 4 is a diagram showing a first example of correction of an overcurrent threshold value of the overcurrent protection circuit according to the first embodiment; FIG. [Figure 10] 6 is a diagram showing a second example of correction of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment; FIG. [Figure 11] 10 is a diagram illustrating a third example of correction of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment. FIG. [Figure 12] 5A to 5C are diagrams illustrating a method for checking the sensor characteristics of the current sensor according to the first embodiment. [Figure 13] 10 is a diagram illustrating a fourth example of correction of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment. FIG. [Figure 14] FIG. 3 is a diagram showing a schematic configuration of a second power conversion device according to the first embodiment. [Figure 15] 10 is a diagram showing a fifth example of correction of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment. FIG. [Figure 16] FIG. 10 is a diagram showing a configuration of a drive circuit according to a second embodiment. [Figure 17] FIG. 17 is a diagram showing a configuration of a first protection circuit in FIG. [Figure 18] FIG. 17 is a diagram showing the configuration of a second protection circuit in FIG. [Figure 19] FIG. 10 is a diagram illustrating a duty ratio. [Figure 20] FIG. 19 is a diagram showing the output voltage characteristics of a smoothing circuit that smooths the pulse signal Vpi of FIGS. 17 and 18. [Figure 21] 19 is a diagram showing the output voltage characteristics of a smoothing circuit that smooths the pulse signal Vpia of FIG. 18. [Figure 22] FIG. 10 is a diagram showing a first example of an overcurrent threshold characteristic of the first protection circuit according to the second embodiment. [Figure 23] FIG. 10 is a diagram showing a second example of the overcurrent threshold characteristics of the first protection circuit according to the second embodiment. [Figure 24] FIG. 10 is a diagram showing a third example of the overcurrent threshold characteristic of the first protection circuit according to the second embodiment. [Figure 25] FIG. 10 is a diagram showing a first example of an overcurrent threshold characteristic of a second protection circuit according to the second embodiment. [Figure 26] FIG. 10 is a diagram showing a second example of the overcurrent threshold characteristic of the second protection circuit according to the second embodiment. [Figure 27] FIG. 10 is a diagram showing a third example of the overcurrent threshold characteristic of the second protection circuit according to the second embodiment. [Figure 28] 10 is a diagram illustrating a first correction example of an overcurrent threshold value of the protection circuit according to the second embodiment. FIG. [Figure 29] 10 is a diagram illustrating a second example of correction of the overcurrent threshold of the protection circuit according to the second embodiment. FIG. [Figure 30]10 is a diagram illustrating a second example of correction of the overcurrent threshold of the protection circuit according to the second embodiment. FIG. [Figure 31] 10 is a diagram illustrating a second example of correction of the overcurrent threshold of the protection circuit according to the second embodiment. FIG. [Figure 32] FIG. 10 is a diagram showing a configuration of a drive circuit according to a third embodiment. [Figure 33] FIG. 33 is a diagram illustrating a configuration of the protection circuit of FIG. 32. [Figure 34] FIG. 34 is a diagram showing a first example of the overcurrent threshold characteristic of the protection circuit of FIG. 33. [Figure 35] FIG. 34 is a diagram showing a second example of the overcurrent threshold characteristic of the protection circuit of FIG. 33. [Figure 36] FIG. 34 is a diagram showing a third example of the overcurrent threshold characteristic of the protection circuit of FIG. 33. [Figure 37] FIG. 34 is a diagram showing a fourth example of the overcurrent threshold characteristic of the protection circuit of FIG. 33. [Figure 38] FIG. 34 is a diagram showing a fifth example of the overcurrent threshold characteristic of the protection circuit of FIG. 33. [Figure 39] FIG. 34 is a diagram showing a sixth example of the overcurrent threshold characteristic of the protection circuit of FIG. 33. [Figure 40] FIG. 10 is a diagram showing a configuration of a first driving circuit according to a fourth embodiment. [Figure 41] FIG. 41 is a diagram illustrating a configuration of the overcurrent protection circuit of FIG. 40. [Figure 42] FIG. 10 is a diagram showing a configuration of a second drive circuit according to the fourth embodiment. [Figure 43] FIG. 43 is a diagram illustrating a configuration of the overcurrent protection circuit of FIG. 42. [Figure 44] 44 is a diagram illustrating an example of correction of the overcurrent threshold of the overcurrent protection circuit of FIG. 43. [Figure 45] 42 is a diagram illustrating an example of correction of the overcurrent threshold of the overcurrent protection circuit of FIG. 41. [Figure 46] FIG. 10 is a diagram showing a configuration of a first driving circuit according to a fifth embodiment. [Figure 47] FIG. 47 is a diagram showing the configuration of the protection circuit of FIG. 46. [Figure 48] FIG. 13 is a diagram showing a configuration of a second driving circuit according to the fifth embodiment. [Figure 49]FIG. 49 is a diagram illustrating a configuration of the overcurrent protection circuit of FIG. 48. [Figure 50] FIG. 2 is a diagram illustrating an example of a hardware configuration that realizes the functions of a control unit by digital calculation. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the power conversion device of the present application will be described with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0014] Embodiment 1 FIG. 1 is a diagram illustrating a schematic configuration of a first power conversion apparatus according to the first embodiment. FIG. 2 is a diagram illustrating the operation of a power conversion apparatus according to a comparative example when an overcurrent occurs, and FIG. 3 is a diagram illustrating a current waveform in the power conversion apparatus according to the comparative example. FIG. 4 is a diagram illustrating the configuration of a drive circuit of FIG. 1, and FIG. 5 is a diagram illustrating the configuration of a protection circuit of FIG. 4. FIGS. 6, 7, and 8 are diagrams illustrating first, second, and third examples of sensor characteristics of the current sensor of FIG. 1, respectively. FIGS. 9, 10, and 11 are diagrams illustrating first, second, and third correction examples of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment, respectively. FIG. 12 is a diagram illustrating a method for checking the sensor characteristics of the current sensor according to the first embodiment, and FIG. 13 is a diagram illustrating a fourth correction example of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment. FIG. 14 is a diagram illustrating a schematic configuration of a second power conversion apparatus according to the first embodiment, and FIG. 15 is a diagram illustrating a fifth correction example of the overcurrent threshold of the overcurrent protection circuit according to the first embodiment. The power conversion device 100 of the first embodiment controls a power conversion unit 110 having a plurality of power semiconductor elements 3a, 3b, 3c, 3d, 3e, and 3f to convert DC power to AC power or AC power to DC power. FIG. 1 shows an example of the power conversion device 100 that converts DC power to AC power, i.e., an inverter circuit. The power conversion device 100 includes a drive circuit 14 that outputs an element drive signal sd that drives the plurality of power semiconductor elements 3a to 3f, a control unit 10 that controls the drive circuit 14, and current sensors 21a, 21b, and 21c that detect the AC current of the power conversion unit 110. While the following mainly describes an example in which the power conversion device 100 is an inverter circuit, the following also describes an example in which the power conversion device 100 is a converter circuit that converts AC power to DC power, as appropriate.

[0015] In the power conversion device 100, a DC power supply 1 is connected to DC terminals 16p and 16n on the input side, and a motor 9 is connected to AC terminals 17u, 17v, and 17w on the output side via AC wiring 19u, 19v, and 19w. The DC power supply 1 is, for example, a battery, and outputs DC power, i.e., DC voltage and DC current. Here, when the power conversion device 100 of the first embodiment is applied to an automobile equipped with an electric powertrain, such as an electric vehicle or a hybrid vehicle, the DC power supply 1 is a secondary battery typified by a nickel-metal hydride battery or a lithium-ion battery. The motor 9 is, for example, a generator, an electric motor, or a generator-motor. When the power conversion device 100 outputs AC power to the motor 9, the motor 9 functions as a load. When the power conversion device 100 receives AC power from the motor 9, converts it, and outputs the converted DC power to the DC power supply 1, the motor 9 functions as a generator.

[0016] Power conversion unit 110 is, for example, a three-phase inverter equipped with capacitor 2 on the DC side for removing and smoothing voltage ripple and noise, and power semiconductor elements 3a to 3f which are semiconductor switching elements, and converts the output power of capacitor 2 into three-phase AC power and outputs it from AC terminals 17u, 17v, and 17w to motor 9. AC terminals 17u, 17v, and 17w of power conversion unit 110 supply the three-phase AC power to motor 9 via AC wiring 19u, 19v, and 19w.

[0017] The control unit 10 and the drive circuit 14 output an element drive signal sd to the power semiconductor elements 3a-3f, which are switching elements, to control the on and off states of the power semiconductor elements 3a-3f. The element drive signal sd includes a predetermined dead time to prevent the series-connected power semiconductor elements of the power conversion unit 110 from simultaneously turning on. The control unit 10 outputs a drive control signal scg to the drive circuit 14 based on an externally input torque command value Trq* and a DC voltage command value Vdc* for the motor 9, a DC voltage Vdc between the high-power side wiring 18p and the low-power side wiring 18s of the power conversion unit 110 detected by a voltage sensor 20, and a rotation angle θm detected by a rotation sensor 25. Furthermore, the control unit 10 generates the correction command signal sc based on pre-stored voltage correction amounts 83a, 83b (see FIGS. 9 to 11) or pre-stored voltage correction amount data, i.e., voltage correction amounts 86a, 86b (see FIG. 13), calculated from the corrected sensor characteristic 55. Note that the pre-stored voltage correction amounts may be the voltage correction amounts 86a, 86b calculated in advance from the corrected sensor characteristic 55 without storing the corrected sensor characteristic 55 in the control unit 10.

[0018] The drive circuit 14 includes an element drive circuit 40 that outputs an element drive signal sd to the power semiconductor elements 3a-3f, and an overcurrent protection circuit 41 that determines when an overcurrent has flowed through the power semiconductor elements 3a-3f and outputs an overcurrent stop signal st to the element drive circuit 40, causing the element drive signal sd to be output, switching the power semiconductor elements 3a-3f from an ON state to an OFF state. The voltage correction amounts 83a and 83b are the difference between the first voltage (positive side overcurrent threshold Vth0p, negative side overcurrent threshold Vth0n) of the current sensor at the time of design and the second voltage (positive side overcurrent threshold Vthap, negative side overcurrent threshold Vthan) of the installed current sensor, relative to the predetermined overcurrent setting values ​​(positive side overcurrent setting value Iocp, negative side overcurrent setting value Iocn) that switch the power semiconductor elements 3a-3f to an OFF state. The terms "positive side" and "negative side" used consecutively in the voltage correction amounts 83a, 83b, 86a, and 86b will be described later.

[0019] The element drive signal sd is input to the power semiconductor elements 3a to 3f via six signal lines 32a to 32f. The element drive signal sda is input to the power semiconductor element 3a via signal line 32a, and the element drive signal sdb is input to the power semiconductor element 3b via signal line 32b. The element drive signal sdc is input to the power semiconductor element 3c via signal line 32c, and the element drive signal sdd is input to the power semiconductor element 3d via signal line 32d. The element drive signal sde is input to the power semiconductor element 3e via signal line 32e, and the element drive signal sdf is input to the power semiconductor element 3f via signal line 32f. Where appropriate, the element drive signals will be generically referred to as sd, and will be distinguished by the symbols sda to sdf. The voltage sensor 20 outputs the detected DC voltage Vdc to the control unit 10 via signal line 31a.

[0020] Current sensors 21a, 21b, and 21c are disposed on AC wirings 19u, 19v, and 19w, respectively. AC wirings 19u, 19v, and 19w are U-phase, V-phase, and W-phase AC wirings, respectively. Current sensor 21a detects U-phase AC current Iu flowing through AC wiring 19u and outputs a detected voltage Viu corresponding to AC current Iu to drive circuit 14 via signal line 31b. Similarly, current sensor 21b detects V-phase AC current Iv flowing through AC wiring 19v and outputs a detected voltage Viv corresponding to AC current Iv to drive circuit 14 via signal line 31c. Current sensor 21c detects V-phase AC current Iw flowing through AC wiring 19w and outputs a detected voltage Viw corresponding to AC current Iw to drive circuit 14 via signal line 31d.

[0021] The power semiconductor elements 3a to 3f of the power conversion unit 110 form a full-bridge circuit. The power semiconductor elements 3a, 3c, and 3e connected to the high-voltage side wiring 18p form an upper arm, and the power semiconductor elements 3b, 3d, and 3f connected to the low-voltage side wiring 18s form a lower arm. The legs, each formed by connecting the upper arm and the lower arm in series, are a series body formed by connecting the power semiconductor elements 3a and 3b in series, a series body formed by connecting the power semiconductor elements 3c and 3d in series, and a series body formed by connecting the power semiconductor elements 3e and 3f in series. The connection point between the upper arm and the lower arm is connected to an AC terminal. The connection point between the power semiconductor elements 3a and 3b is connected to AC terminal 17u. The connection point between the power semiconductor elements 3c and 3d is connected to AC terminal 17v, and the connection point between the power semiconductor elements 3e and 3f is connected to AC terminal 17w. In FIG. 1, an example of MOSFETs having a transistor Tr and a diode Di is shown as the power semiconductor elements 3a to 3f. The diode Di may be a parasitic diode of a MOSFET or a diode of a separate element. The power semiconductor elements 3a to 3f are not limited to MOSFETs and may be configured, for example, with an IGBT, which is a transistor Tr, and a diode Di connected in antiparallel to the IGBT.

[0022] The control unit 10 is a circuit that controls the power conversion unit 110 via the drive circuit 14, and is realized by, for example, electronic components including a configuration in which a processor 98 executes a program stored in a memory 99 shown in FIG. 50. FIG. 50 is a diagram showing an example of a hardware configuration in which the functions of the control unit are realized by digital calculations. The electronic components that make up the control unit 10 are, for example, a microcontroller, a system LSI (Large Scale Integration), etc. FIG. 50 is a diagram showing an example of a hardware configuration in which the functions of the control unit 10 are realized by digital calculations. The functions realized by the digital calculations of the control unit 10 are realized by the processor 98 and the memory 99. Furthermore, multiple processors 98 and multiple memories 99 may cooperate to execute each function.

[0023] The control unit 10 and the drive circuit 14 control the power semiconductor elements 3a-3f of the power conversion unit 110 so that the desired power is supplied to the motor 9. Specifically, the control unit 10 calculates the time (on time) for each of the power semiconductor elements 3a-3f of the power conversion unit 110 to be in the on state based on the power to be supplied to the motor 9. For example, the control unit 10 can control the power conversion unit 110 using PWM (Pulse Width Modulation) control, which modulates the on time of the power semiconductor elements 3a-3f according to the voltage to be output. The control unit 10 then outputs a drive control signal scg, which is a control command, to the drive circuit 14 so that an on signal is output to the power semiconductor elements that should be in the on state at each time point, and an off signal is output to the power semiconductor elements that should be in the off state at each time point. The drive circuit 14 outputs an on signal or an off signal as an element drive signal sd to the control electrodes of each of the power semiconductor elements 3a-3f in accordance with the drive control signal scg.

[0024] The upper-arm power semiconductor elements 3a, 3c, and 3e, which are connected to the positive side of DC power supply 1 and high-voltage side wiring 18p, and the lower-arm power semiconductor elements 3b, 3d, and 3f, which are connected to the negative side of DC power supply 1 and low-voltage side wiring 18s, are not turned on simultaneously due to the dead time described above. The upper-arm power semiconductor elements 3a, 3c, and 3e can also be referred to as positive-side power semiconductor elements. The lower-arm power semiconductor elements 3b, 3d, and 3f can also be referred to as negative-side power semiconductor elements. When power conversion device 100 is an inverter circuit, i.e., when power conversion unit 110 is an inverter, when upper-arm power semiconductor elements 3a, 3c, and 3e are turned on, AC currents Iu, Iv, and Iw flow in the positive direction (the direction of the arrows Iu, Iv, and Iw in FIG. 1 ) from AC terminals 17u, 17v, and 17w to motor 9. When the power semiconductor elements 3b, 3d, and 3f of the lower arm are turned on, AC currents Iu, Iv, and Iw flow in the negative direction, which is opposite to the positive direction, from the motor 9 to the AC terminals 17u, 17v, and 17w. When the power conversion device 100 is a converter circuit, i.e., when the power conversion unit 110 is a converter, when the power semiconductor elements 3a, 3c, and 3e of the upper arm are turned on, AC currents Iu, Iv, and Iw flow from the motor 9 to the AC terminals 17u, 17v, and 17w. When the power semiconductor elements 3b, 3d, and 3f of the lower arm are turned on, AC currents Iu, Iv, and Iw flow from the AC terminals 17u, 17v, and 17w to the motor 9. Since the current flows from the side with higher potential to the side with lower potential, the direction changes between the inverter and the converter. Here, in cases where the terms "positive side" and "negative side" differ from the general usage such as the positive side and negative side of DC power supply 1, the term "positive side" used consecutively in the name refers to the power semiconductor elements 3a, 3c, and 3e of the upper arm, and the term "negative side" used consecutively in the name refers to the power semiconductor elements 3b, 3d, and 3f of the lower arm.

[0025] Using FIG. 2, the mechanism by which an overcurrent occurs in the power conversion unit 160 of the power conversion device 150 of the comparative example will be described. The power conversion unit 160 of the comparative example has the same configuration as the power conversion unit 110 of the first embodiment, but the element drive signal sd input when an overcurrent occurs in the power semiconductor elements 3a to 3f is different from that of the power conversion unit 110 of the first embodiment. In FIG. 2, a control unit such as a microcomputer and an element drive unit are omitted. In the power conversion device 150 of the comparative example, consider a case where the pulse width that turns on the power semiconductor elements 3a to 3f under PWM control, i.e., the on-duty width, widens due to an abnormality in the control unit or exceeds the control period and becomes temporarily stuck in the on state. FIG. 2 shows a case where the power semiconductor elements 3a, 3d, and 3f are stuck. A current 91a flows from the upper arm power semiconductor element 3a to the AC wiring 19u, a current 91b flows from the AC wiring 19v to the lower arm power semiconductor element 3d, and a current 91c flows from the AC wiring 19w to the lower arm power semiconductor element 3f.

[0026] At this time, as shown in FIG. 3, the current value deviates from the steady-state operating range and enters the overcurrent region at time t1. The vertical axis in FIG. 3 represents the phase current of each phase, and the horizontal axis represents time. The element drive unit of the comparative example is provided with a comparator for each phase, similar to the overcurrent detection circuit of Patent Document 1. The comparators compare the detection voltages Viu, Viv, and Viw detected by the U-phase current sensor 21a, the V-phase current sensor 21b, and the W-phase current sensor 21c with threshold values. When the detection voltages Viu, Viv, and Viw exceed the threshold values, the comparators for each phase output an overcurrent stop signal st to the element drive circuit to shut off the power semiconductor elements 3a to 3f.

[0027] Here, current sensors 21a, 21b, and 21c have variations. For example, a magnetic field detection current sensor uses a magnetic core or other device to detect magnetic fields generated by currents flowing through bus bars and board wiring connecting power semiconductor elements 3a-3f of power conversion unit 110 and power conversion unit 160. The magnetic flux density is then converted into voltage. These magnetic field detection current sensors produce variations in the output voltage corresponding to the current value due to Hall element variations, such as the influence of surrounding magnetic flux and circuit variations. In Figure 3, the steady-state operating range is from time t0 to time t1, the overcurrent region is from time t1 to time t3, and the interruption region is from time t3 to time t4. Time t2 is the time when the phase current reaches the designed overcurrent threshold Ith, and time t3 is the time when the phase current is actually interrupted at the interruption current value Ioff. Figure 3 also shows the rated current Ira and current ripple Irp.

[0028] As shown in FIG. 3, a current greater than expected flows from the overcurrent threshold Ith (design value) during the design period until the detection voltages Viu, Viv, and Viw output by the current sensors 21a, 21b, and 21c reach the threshold (from time t2 to time t3), and the interruption current value Ioff, which is the current value at the time of interruption, exceeds the overcurrent threshold Ith by the current difference ΔIdt. For example, when detecting an overcurrent of 1000 A, variations in the current sensors may prevent the power semiconductor elements 3a-3f from stopping at the set value, causing an overcurrent of 1200-1300 A to flow through the power semiconductor elements 3a-3f. Therefore, the power conversion device 150 of the comparative example increases the risk of failure of the power semiconductor elements 3a-3f due to excessive current and surge voltage at the time of interruption. Therefore, in the power conversion device 150 of the comparative example, in order to suppress surges due to excessive current and surge voltage, it is necessary to increase the gate constant, which is a control parameter related to the control terminals of the MOSFETs and IGBTs, and it is necessary to suppress the switching speed of the power semiconductor elements 3a to 3f. As a result, in the power conversion device 150 of the comparative example, the switching loss of the power semiconductor elements 3a to 3f increases.

[0029] The power conversion device 100 of the first embodiment can reduce the current difference ΔIdt, which is the difference between the interruption current value Ioff and the overcurrent threshold Ith described in the comparative example, by correcting the variation in the output values ​​output by the current sensors 21a, 21b, and 21c. That is, the power conversion device 100 of the first embodiment can reduce the overcurrent flowing through the power semiconductor elements 3a to 3f during overcurrent protection operation for the power semiconductor elements 3a to 3f by correcting the variation in the output values ​​output by the current sensors 21a, 21b, and 21c. Furthermore, since the power conversion device 100 of the first embodiment reduces the overcurrent during overcurrent protection operation, it is not necessary to increase the gate constant of the power semiconductor elements 3a to 3f and it is not necessary to suppress the switching speed of the power semiconductor elements 3a to 3f. Therefore, the power conversion device 100 of embodiment 1 can improve the switching speed of the power semiconductor elements 3a to 3f compared to the power conversion device 150 of the comparative example by reducing the overcurrent during overcurrent protection operation, and can reduce the switching loss of the power semiconductor elements 3a to 3f.

[0030] The overcurrent protection operation of the power conversion device 100 and the overcurrent protection circuit 41 of the first embodiment will be described. The overcurrent protection circuit 41 shown in FIG. 4 is an example in which a protection circuit 59 is provided for each phase of a three-phase AC. The overcurrent protection circuit 41 of the first embodiment includes a U-phase protection circuit 59u, a V-phase protection circuit 59v, and a W-phase protection circuit 59w. The protection circuits 59u, 59v, and 59w have the configuration shown in FIG. 5. Where appropriate, the protection circuits will be collectively referred to as 59, and 59u, 59v, and 59w will be used to distinguish between them. The protection circuit 59 includes a threshold voltage adjuster 60 and an overcurrent stop signal output unit 62. The overcurrent stop signal output unit 62 includes a comparator 42p that outputs a positive-side overcurrent stop signal stp to the element drive circuit 40 via an output terminal 47p, and a comparator 42n that outputs a negative-side overcurrent stop signal stn to the element drive circuit 40 via an output terminal 47p. The detection voltage Vi output from the current sensors 21a, 21b, and 21c via the input terminal 48 is input to a negative terminal, which is one end of the comparators 42p and 42n, a positive overcurrent threshold Vthp is input to a positive terminal, which is the other end of the comparator 42p, and a negative overcurrent threshold Vthn is input to a positive terminal, which is the other end of the comparator 42n. The positive overcurrent threshold Vthp and the negative overcurrent threshold Vthn are reference voltages for comparison with the detection voltage Vi in the comparators 42p and 42n, respectively. The positive overcurrent threshold Vthp is a reference voltage for determining whether an overcurrent is flowing through the upper arm power semiconductor elements 3a, 3c, and 3e, and the negative overcurrent threshold Vthn is a reference voltage for determining whether an overcurrent is flowing through the lower arm power semiconductor elements 3b, 3d, and 3f. As appropriate, the signs of the detected voltages output from the current sensors 21a, 21b, and 21c are collectively referred to as Vi, and when they need to be distinguished, Viu, Viv, and Viw are used.

[0031] When an excessive current flows through the positive-side or negative-side power semiconductor element, comparators 42p, 42n of overcurrent stop signal output unit 62 output overcurrent stop signals stp, stn indicating a shutdown when the detection voltage Vi output from current sensors 21a, 21b, 21c exceeds a threshold voltage (positive-side overcurrent threshold Vthp, negative-side overcurrent threshold Vthn). When no overcurrent is detected, overcurrent stop signals stp, stn indicating a non-shutdown are output. For example, a high-level signal is output to indicate a shutdown, and a low-level signal is output to indicate a non-shutdown. When the overcurrent stop signals stp, stn indicating a shutdown are input, element drive circuit 40 operates, as described above, to turn off power semiconductor elements 3a-3f in which an overcurrent is determined to be flowing in power conversion device 100. The positive overcurrent threshold Vthp is adjusted based on the positive-side regulated voltage Vap output from the threshold voltage adjusting unit 60 and the threshold output unit 61a. The negative overcurrent threshold Vthn is adjusted based on the negative-side regulated voltage Van output from the threshold voltage adjusting unit 60 and the threshold output unit 61b. The threshold voltage adjusting unit 60 outputs the positive-side regulated voltage Vap from the positive output terminal 43p and the negative-side regulated voltage Van from the negative output terminal 43n based on a positive-side correction command signal scp input from the positive input terminal 49p and a negative-side correction command signal scn input from the negative input terminal 49n. The correction command signals scp and scn are command signals output from the control unit 10.

[0032] The threshold output unit 61a is connected to a wiring connecting the output terminal 43p of the threshold voltage adjuster 60 and the positive terminal of the comparator 42p, and the threshold output unit 61b is connected to a wiring connecting the output terminal 43n of the threshold voltage adjuster 60 and the positive terminal of the comparator 42n. The threshold output unit 61a is a series circuit in which multiple resistors Ra1 and Ra2 are connected in series between a power supply voltage Vpp generated inside the power conversion device 100 and ground GND, and a connection point na between the resistors Ra1 and Ra2 is connected to the output terminal 43p and the positive terminal of the comparator 42p. The threshold output unit 61b is a series circuit in which multiple resistors Ra3 and Ra4 are connected in series between the power supply voltage Vpp and ground GND, and a connection point nb between the resistors Ra3 and Ra4 is connected to the output terminal 43n and the positive terminal of the comparator 42n. Ground GND is a voltage reference for the overcurrent protection circuit 41. The value of the power supply voltage Vpp is a predetermined constant value. The positive overcurrent threshold Vthp changes according to the value of the positive regulated voltage Vap output from the threshold voltage adjusting unit 60. The negative overcurrent threshold Vthn changes according to the value of the negative regulated voltage Van output from the threshold voltage adjusting unit 60.

[0033] The protection circuit 59 for each phase of the overcurrent protection circuit 41 is outlined below. The protection circuit 59 includes comparators 42p, 42n that determine that an overcurrent has flowed through the corresponding power semiconductor elements 3a-3f by comparing the detection voltage Vi output by the corresponding current sensor 21a, 21b, 21c with overcurrent threshold voltages, i.e., a positive side overcurrent threshold Vthp and a negative side overcurrent threshold Vthn, and generate overcurrent stop signals stp, stn indicating a shutdown; threshold output units 61a, 61b that output the overcurrent threshold voltages (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn); and a threshold voltage adjustment unit 60 that generates adjustment voltages (positive side adjustment voltage Vap, negative side adjustment voltage Van) that cause the threshold output units 61a, 61b to output the overcurrent threshold voltages (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn) based on a correction command signal sc output from the control unit 10, and outputs the adjustment voltages (positive side adjustment voltage Vap, negative side adjustment voltage Van) to the threshold output units 61a, 61b.

[0034] In the overview of the protection circuit 59 for each phase of the overcurrent protection circuit 41 described above, the overcurrent threshold voltage, comparator, threshold output unit, adjustment voltage, and correction command signal for the "positive side" of the upper arm power semiconductor elements 3a, 3c, and 3e, and the overcurrent threshold voltage, comparator, threshold output unit, adjustment voltage, and correction command signal for the "negative side" of the lower arm power semiconductor elements 3b, 3d, and 3f are collectively expressed, but if the "positive side" for the upper arm power semiconductor elements 3a, 3c, and 3e and the "negative side" for the lower arm power semiconductor elements 3b, 3d, and 3f are expressed separately, the result is as follows. The protection circuit 59 includes a first comparator 42p that determines that an overcurrent has flowed through the upper arm power semiconductor elements 3a, 3c, and 3e by comparing the detection voltage Vi output by the corresponding current sensor 21a, 21b, and 21c with a positive overcurrent threshold Vthp that is a positive overcurrent threshold voltage, and generates a positive overcurrent stop signal stp that indicates a stop of the power semiconductor elements 3a, 3c, and 3e. The protection circuit 59 includes a first comparator 42p that determines that an overcurrent has flowed through the upper arm power semiconductor elements 3a, 3c, and 3e by comparing the detection voltage Vi output by the corresponding current sensor 21a, 21b, and 21c with a negative overcurrent threshold Vthn that is a negative overcurrent threshold voltage, and generates a positive overcurrent stop signal stp that indicates a stop of the power semiconductor elements 3b, 3d, and The inverter 42 includes a second comparator 42n that determines that an overcurrent has flowed through the inverter 3f and generates a negative overcurrent stop signal stn indicating a stop, a first threshold output unit 61a that outputs a positive overcurrent threshold Vthp, which is a positive overcurrent threshold voltage, a second threshold output unit 61b that outputs a negative overcurrent threshold Vthn, which is a negative overcurrent threshold voltage, and a threshold voltage adjuster 60 that outputs a positive regulated voltage Vap, which is a first regulated voltage, to the first threshold output unit 61a and a negative regulated voltage Van, which is a second regulated voltage, to the second threshold output unit 61b. The threshold voltage adjuster 60 generates the positive regulated voltage Vap, which is a first regulated voltage, based on a first correction command signal scp output from the control unit 10, and generates the negative regulated voltage Van, which is a second regulated voltage, based on a second correction command signal scn output from the control unit 10.

[0035] In addition, if the power semiconductor elements 3a, 3c, and 3e of the upper arm and the power semiconductor elements 3b, 3d, and 3f of the lower arm have different resistance to overcurrent, the power conversion device 100 of embodiment 1 may be configured to perform overcurrent protection operation only on the upper arm or lower arm that has the weaker resistance.

[0036] The overcurrent protection circuit 41 and element drive signal sd of the first embodiment will be described with reference to FIG. 4. The overcurrent protection circuit 41 of the first embodiment includes a U-phase protection circuit 59u, a V-phase protection circuit 59v, and a W-phase protection circuit 59w. The U-phase element drive signal sda is generated based on the drive control signal scgup output from the output terminal 44 of the control unit 10 and the overcurrent stop signal stup output from the U-phase protection circuit 59u. The U-phase element drive signal sdb is generated based on the drive control signal scgun output from the output terminal 44 of the control unit 10 and the overcurrent stop signal stun output from the U-phase protection circuit 59u. The element drive signals sda and sdb each turn on the power semiconductor elements 3a and 3b when at a high level, and turn off the power semiconductor elements 3a and 3b when at a low level, for example. When an overcurrent flows through power semiconductor element 3a in the ON state, and if the positive overcurrent stop signal stup indicates a stop, element drive circuit 40 changes element drive signal sda from high to low to turn power semiconductor element 3a into the OFF state. Also, when an overcurrent flows through power semiconductor element 3b in the ON state, and if the negative overcurrent stop signal stun indicates a stop, element drive circuit 40 changes element drive signal sdb from high to low to turn power semiconductor element 3b into the OFF state.

[0037] In U-phase protection circuit 59u, detected voltage Viu output from current sensor 21a is input to input terminal 48, correction command signal scup output from output terminal 45a of control unit 10 is input to input terminal 49p, and correction command signal scun output from output terminal 45b of control unit 10 is input to input terminal 49n. Protection circuit 59u outputs a positive-side overcurrent stop signal stup to element drive circuit 40 from output terminal 47p, and outputs a negative-side overcurrent stop signal stun to element drive circuit 40 from output terminal 47n.

[0038] The V-phase element drive signal sdc is generated based on the drive control signal scgvp output from the output terminal 44 of the control unit 10 and the overcurrent stop signal stvp output from the V-phase protection circuit 59v. The V-phase element drive signal sdd is generated based on the drive control signal scgvn output from the output terminal 44 of the control unit 10 and the overcurrent stop signal stvn output from the V-phase protection circuit 59v. The operation of the element drive circuit 40 for the V-phase is the same as that of the element drive circuit 40 for the U-phase. For example, when the element drive signals sdc and sdd are at a high level, they turn on the power semiconductor elements 3c and 3d, and when they are at a low level, they turn off the power semiconductor elements 3c and 3d. When an overcurrent flows through the power semiconductor element 3c that is in the on state, and the positive-side overcurrent stop signal stvp indicates a stop, the element drive circuit 40 changes the element drive signal sdc from a high level to a low level, turning off the power semiconductor element 3c. In addition, when an overcurrent flows through the power semiconductor element 3d in the ON state, if the negative side overcurrent stop signal stvn indicates a stop, the element drive circuit 40 changes the element drive signal sdd from high level to low level, thereby turning off the power semiconductor element 3d.

[0039] V-phase protection circuit 59v receives at input terminal 48 the detected voltage Viv output from current sensor 21b, at input terminal 49p the correction command signal scvp output from output terminal 45c of control unit 10, and at input terminal 49n the correction command signal scvn output from output terminal 45d of control unit 10. Protection circuit 59v outputs a positive-side overcurrent stop signal stvp to element drive circuit 40 from output terminal 47p, and outputs a negative-side overcurrent stop signal stvn to element drive circuit 40 from output terminal 47n.

[0040] The W-phase element drive signal sde is generated based on the drive control signal scgwp output from the output terminal 44 of the control unit 10 and the overcurrent stop signal stwp output from the W-phase protection circuit 59w. The W-phase element drive signal sdf is generated based on the drive control signal scgwn output from the output terminal 44 of the control unit 10 and the overcurrent stop signal stwn output from the W-phase protection circuit 59w. The operation of the element drive circuit 40 for the W phase is the same as the operation of the element drive circuit 40 for the U phase. For example, when the element drive signals sde and sdf are at a high level, they turn on the power semiconductor elements 3e and 3f, and when they are at a low level, they turn off the power semiconductor elements 3e and 3f. When an overcurrent flows through the power semiconductor element 3e that is in the on state, and the positive-side overcurrent stop signal stwp indicates a stop, the element drive circuit 40 changes the element drive signal sde from a high level to a low level, turning off the power semiconductor element 3e. In addition, when an overcurrent flows through the power semiconductor element 3f in the ON state, if the negative side overcurrent stop signal stwn indicates a stop, the element drive circuit 40 changes the element drive signal sdf from high level to low level, thereby turning the power semiconductor element 3f into the OFF state.

[0041] W-phase protection circuit 59w receives at input terminal 48 the detected voltage Viw output from current sensor 21c, at input terminal 49p the correction command signal scwp output from output terminal 45e of control unit 10, and at input terminal 49n the correction command signal scwn output from output terminal 45f of control unit 10. Protection circuit 59w outputs a positive-side overcurrent stop signal stwp to element drive circuit 40 from output terminal 47p, and outputs a negative-side overcurrent stop signal stwn to element drive circuit 40 from output terminal 47n.

[0042] Where appropriate, the symbols of the drive control signals are collectively referred to as scg, with scgup, scgun, scgvp, scgvn, scgwp, and scgwn being used when distinguishing between them. The symbols of the correction command signals are collectively referred to as sc, with scup, scun, scvp, scvn, scwp, scwn, scp, and scn being used when distinguishing between them. The correction command signal scp is a positive-side correction command signal that does not distinguish between the U, V, and W phases, and the correction command signal scn is a negative-side correction command signal that does not distinguish between the U, V, and W phases. The symbols of the overcurrent stop signals are collectively referred to as st, with stup, stun, stvp, stvn, stwp, stwn, stp, and stn being used when distinguishing between them. The overcurrent stop signal stp is a positive-side overcurrent stop signal that does not distinguish between the U, V, and W phases, and the overcurrent stop signal stn is a negative-side overcurrent stop signal that does not distinguish between the U, V, and W phases.

[0043] The above-mentioned variations in the current sensors will now be described in detail. FIGS. 6 to 8 show three examples of sensor characteristics, which are the output characteristics of the current sensors 21a, 21b, and 21c. The current sensors 21a, 21b, and 21c are adjusted so that, with the arrows of the AC currents Iu, Iv, and Iw shown in FIG. 1 pointing in the positive direction, the current values ​​flowing on the negative side (<0 A) and the current values ​​flowing on the positive side (>0 A) are output as positive voltage values ​​only. In FIGS. 6 to 8, the horizontal axis represents current and the vertical axis represents voltage. Regarding current, the power conversion unit 110 is illustrated as an inverter. However, even when the power conversion unit 110 is a converter, the current sensors 21a, 21b, and 21c are adjusted so that the current values ​​flowing on the negative side (<0 A) and the current values ​​flowing on the positive side (>0 A) are output as positive voltage values ​​only. For example, as shown in sensor characteristic 50, the output voltage range of the current sensor is 0 to 5 V, with 2.5 V in the middle set as the output voltage when the current value is 0 A. Sensor characteristic 50 is the sensor characteristic of current sensors 21a, 21b, and 21c at the time of design. In Figures 6 to 8, the horizontal axis represents current and the vertical axis represents voltage. Variations in the current sensor include offset variation and gain variation. Sensor characteristic 50a shown in Figure 6 is an example that includes offset variation, sensor characteristic 50b shown in Figure 7 is an example that includes gain variation, and sensor characteristic 50c shown in Figure 8 is an example that includes offset variation and gain variation.

[0044] Offset variation is a variation in which the output voltage is offset by a certain value to the positive side (increase) or negative side (decrease) with respect to the current, as shown in sensor characteristic 50a in Figure 6, i.e., an example of characteristic deviation. Figure 6 shows an example of an offset to the positive side (increase). Gain variation is a variation in the gain (slope of the sensor characteristic) of the current sensor during design, as shown in sensor characteristic 50b in Figure 7, i.e., an example of characteristic deviation. The current sensor outputs a voltage value that is amplified so that the voltage value corresponding to the current value to be detected becomes an appropriate value. Figure 7 shows an example in which the gain of the current sensor is smaller than the design value. When offset variation and gain variation are included, i.e., an example in which offset variation and gain variation are combined, it becomes sensor characteristic 50c in Figure 8.

[0045] In the designed sensor characteristic 50, when the current to be detected is the positive side overcurrent setting value Iocp, the output voltage of the current sensor becomes the positive side overcurrent threshold Vthp, and when the current to be detected is the negative side overcurrent setting value Iocn, the output voltage of the current sensor becomes the negative side overcurrent threshold Vthn. In the sensor characteristic 50a including offset variation, when the output voltage is the positive side overcurrent threshold Vthp, the current value is the positive side cut-off current value Iocfp, and when the output voltage is the negative side overcurrent threshold Vthn, the current value is the negative side cut-off current value Iocfn. In the case of an overcurrent protection circuit 41 using a current sensor whose sensor characteristic is sensor characteristic 50a, when the current becomes the positive side cut-off current value Iocfp or the negative side cut-off current value Iocfn, the corresponding power semiconductor element of power semiconductor elements 3a to 3f is turned off.

[0046] As shown in FIG. 6, in the comparative example power conversion device 150 using the sensor characteristic 50a offset to the positive side, the overcurrent value determined by the negative overcurrent threshold Vthn on the negative side of the current becomes the negative overcurrent set value Iocn in the design, which becomes the negative cutoff current value Iocfn, resulting in a current deviation 80b. On the positive side of the current, the overcurrent value determined by the positive overcurrent threshold Vthp becomes the positive overcurrent set value Iocp in the design, which becomes the positive cutoff current value Iocfp, resulting in a current deviation 80a. Therefore, on the negative side of the current, the absolute value of the current increases from the designed cutoff set value (i.e., the negative overcurrent set value Iocn) to the negative cutoff current value Iocfn, resulting in a large surge at the time of cutoff. Furthermore, on the positive side of the current, the absolute value of the current decreases from the designed cutoff set value (i.e., the positive overcurrent set value Iocp) to the positive cutoff current value Iocfp, which may result in the power semiconductor elements 3a to 3f being turned off within the normal operating range, i.e., the steady-state range shown in FIG. 3.

[0047] As shown in FIG. 7 , in the comparative example power conversion device 150 using sensor characteristic 50c, in which sensor characteristic 50 has a gain smaller than the design value, the overcurrent value determined by the negative-side overcurrent threshold Vthn becomes the negative-side overcurrent set value Iocn in the design, resulting in a current discrepancy 81b. On the positive side of the current, the overcurrent value determined by the positive-side overcurrent threshold Vthp becomes the positive-side overcurrent set value Iocp in the design, resulting in a current discrepancy 81a. Therefore, on the negative side of the current, the absolute value of the current increases from the designed cutoff set value (i.e., the negative-side overcurrent set value Iocn) to the negative-side cutoff current value Iocfn, resulting in a larger surge at the time of cutoff. On the positive side of the current, the absolute value of the current increases from the designed cutoff set value (i.e., the positive-side overcurrent set value Iocp) to the positive-side cutoff current value Iocfp, resulting in a larger surge at the time of cutoff.

[0048] As shown in FIG. 8 , in a power conversion device 150 of the comparative example, in which sensor characteristic 50b is used and sensor characteristic 50b has a gain smaller than the design value, the overcurrent value determined by the negative overcurrent threshold Vthn on the negative side of the current becomes the negative overcurrent set value Iocn in the design, resulting in a current deviation 82b. On the positive side of the current, the overcurrent value determined by the positive overcurrent threshold Vthp becomes the positive overcurrent set value Iocp in the design, resulting in a current deviation 82a. Therefore, on the negative side of the current, the absolute value of the current increases from the designed cutoff set value (i.e., the negative overcurrent set value Iocn) to the negative cutoff current value Iocfn, resulting in a larger surge at the time of cutoff. On the positive side of the current, the absolute value of the current increases from the designed cutoff set value (i.e., the positive overcurrent set value Iocp) to the positive cutoff current value Iocfp, resulting in a larger surge at the time of cutoff.

[0049] Unlike the power conversion device 150 of the comparative example, the power conversion device 100 of the first embodiment generates the positive-side regulated voltage Vap and the negative-side regulated voltage Van so that the threshold voltage adjuster 60 outputs a corrected positive-side overcurrent threshold Vthp from the threshold output unit 61a and a corrected negative-side overcurrent threshold Vthn from the threshold output unit 61b in accordance with the sensor characteristics of the installed current sensors 21a to 21c. Examples of correction of the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn according to the first embodiment are shown in FIGS. 9 to 11. The first example of correction of the overcurrent threshold shown in FIG. 9 is a correction example for the sensor characteristic 50a including the offset variation shown in FIG. 6. The second example of correction of the overcurrent threshold shown in FIG. 10 is a correction example for the sensor characteristic 50b including the gain variation shown in FIG. 7. The third example of correction of the overcurrent threshold shown in FIG. 11 is a correction example for the sensor characteristic 50c including the offset variation and the gain variation shown in FIG. 8.

[0050] 9 to 11, the horizontal axis represents current and the vertical axis represents voltage. The positive side overcurrent threshold and negative side overcurrent threshold during design are Vth0p and Vth0n, respectively. During design, the positive side overcurrent threshold Vth0p is set for the positive side overcurrent setting value Iocp, and the negative side overcurrent threshold Vth0n is set for the negative side overcurrent setting value Iocn in the sensor characteristics 50. The initial positive side overcurrent threshold Vth0p is corrected to the positive side overcurrent threshold Vthap by voltage correction amount 83a, and the initial negative side overcurrent threshold Vth0n is corrected to the negative side overcurrent threshold Vthan by voltage correction amount 83b. FIGS. 9 to 11 will be described in detail.

[0051] In the first correction example of FIG. 9, sensor characteristic 50a is offset from sensor characteristic 50 to the positive side, so voltage correction amount 83a and voltage correction amount 83b are the differential voltages from sensor characteristic 50 to sensor characteristic 50a at each current value. Voltage correction amount 83a and voltage correction amount 83b have a positive (+) sign when they increase and a negative (-) sign when they decrease. In FIG. 9, the signs of voltage correction amount 83a and voltage correction amount 83b are both positive. By correcting positive side overcurrent threshold Vthp from the initial positive side overcurrent threshold Vth0p to positive side overcurrent threshold Vthap, power conversion device 100 of the first embodiment can turn off target power semiconductor elements through which an overcurrent flows at the positive side overcurrent setting value Iocp during design. Similarly, the negative side overcurrent threshold Vthn is corrected from the initial negative side overcurrent threshold Vth0n to the negative side overcurrent threshold Vthan, so that the power conversion device 100 of embodiment 1 can turn off the target power semiconductor element through which an overcurrent is flowing at the negative side overcurrent setting value Iocn at the time of design.

[0052] In the second correction example of FIG. 10 , the gain of sensor characteristic 50b is smaller than that of sensor characteristic 50, so the signs of voltage correction amounts 83a and 83b are different for the positive and negative currents. The sign of voltage correction amount 83a is negative, and the sign of voltage correction amount 83b is positive. In the second correction example of FIG. 10 , similar to the first correction example, the positive-side overcurrent threshold Vthp is corrected from the initial positive-side overcurrent threshold Vth0p to the positive-side overcurrent threshold Vthap, allowing the power conversion device 100 of the first embodiment to turn off the target power semiconductor device through which an overcurrent is flowing at the positive-side overcurrent setting value Iocp as designed. Similarly, the negative-side overcurrent threshold Vthn is corrected from the initial negative-side overcurrent threshold Vth0n to the negative-side overcurrent threshold Vthan, allowing the power conversion device 100 of the first embodiment to turn off the target power semiconductor device through which an overcurrent is flowing at the negative-side overcurrent setting value Iocn as designed.

[0053] In the third correction example of FIG. 11 , sensor characteristic 50c is offset from sensor characteristic 50 to the positive side, and the gain is reduced. Therefore, the signs of voltage correction amounts 83a and 83b are different for the positive and negative currents. The sign of voltage correction amount 83a is negative, and the sign of voltage correction amount 83b is positive. In the third correction example of FIG. 11 , similar to the first and second correction examples, the positive-side overcurrent threshold Vthp is corrected from the initial positive-side overcurrent threshold Vth0p to the positive-side overcurrent threshold Vthap, allowing the power conversion device 100 of the first embodiment to turn off the target power semiconductor device through which an overcurrent is flowing at the positive-side overcurrent setting value Iocp as designed. Similarly, the negative-side overcurrent threshold Vthn is corrected from the initial negative-side overcurrent threshold Vth0n to the negative-side overcurrent threshold Vthan, allowing the power conversion device 100 of the first embodiment to turn off the target power semiconductor device through which an overcurrent is flowing at the negative-side overcurrent setting value Iocn as designed.

[0054] The power conversion device 100 of the first embodiment corrects the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn in accordance with the sensor characteristics of the current sensors 21a-21c, and therefore, unlike the power conversion device 150 of the comparative example, can reduce the overcurrent flowing through the power semiconductor elements 3a-3f during overcurrent protection operation for the power semiconductor elements 3a-3f without greatly exceeding the overcurrent setting value set at the time of design. Furthermore, the power conversion device 100 of the first embodiment corrects the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn in accordance with the sensor characteristics of the current sensors 21a-21c, and therefore, unlike the power conversion device 150 of the comparative example, can prevent the power semiconductor elements 3a-3f from being turned off within a normal operating range during overcurrent protection operation for the power semiconductor elements 3a-3f.

[0055] In the power conversion device 100 of the first embodiment, the threshold voltage adjuster 60 of the overcurrent protection circuit 41 receives a correction command signal sc from the controller 10 and corrects the regulated voltages (positive-side regulated voltage Vap, negative-side regulated voltage Van) so that overcurrent thresholds (positive overcurrent threshold Vthp, negative overcurrent threshold Vthn) corresponding to the sensor characteristics of each of the current sensors 21a to 21c are output from the threshold output units 61a, 61b. This prevents the current value during overcurrent protection operation from deviating from the design value, i.e., the set value at the time of design. For this reason, the controller 10 pre-stores voltage correction amounts 83a, 83b (see FIGS. 9 to 11) for correcting the overcurrent thresholds (positive overcurrent threshold Vthp, negative overcurrent threshold Vthn) or corrected sensor characteristics 55 (see FIG. 13), which is voltage correction amount data.

[0056] A method for checking sensor characteristics including variations among current sensors 21a to 21c will be described. Sensor variations are checked during shipping inspection of power conversion device 100 according to the first embodiment. For example, in the case of current sensors, a predetermined current is applied to each current sensor or a predetermined current is applied to the wiring to be detected, and the output voltage at that time is recorded. For example, in FIG. 12, output voltages at three predetermined current values ​​(positive and negative) including 0 A are recorded, thereby obtaining corrected sensor characteristics 55 that have been measured in advance. In FIG. 12, the horizontal axis represents current and the vertical axis represents voltage. Corrected current value I1 is the positive-side specified current value for calibration, and corrected current value I2 is the negative-side specified current value for calibration. Measurement data 53a, 53b, and 53c are the output voltages of the current sensors when the currents are corrected current value I1, 0 A, and I2, respectively. Corrected sensor characteristics 55 can be expressed by the relationship between voltage V and current I, expressed as V = αI + β. α and β are constants, with constant α corresponding to the gain amount and constant β corresponding to the offset amount when the current I is 0 A. Therefore, the gain amount and offset amount can be estimated from corrected sensor characteristic 55. Note that FIG. 12 also shows sensor characteristic 54 at the time of design. The relationship between voltage V and current I in sensor characteristic 54 can be expressed by the equation V=aI+b. a and b are constants, with constant a corresponding to the gain amount and constant b corresponding to the offset amount when the current I is 0 A.

[0057] Each of the magnetic field detection current sensors 21a-21c is a hardware configuration consisting of a core and a circuit, and it is not practical to individually change the constants, components, etc. whenever variations occur. Therefore, the current sensors 21a-21c of the power conversion device 100 each have a characteristic such as a corrected sensor characteristic 55. By grasping this characteristic in advance, the control unit 10, such as a microcomputer, can generate a corrected command signal sc so that the threshold output units 61a, 61b of the overcurrent protection circuit 41 output overcurrent thresholds (positive overcurrent threshold Vthp, negative overcurrent threshold Vthn) that correspond to the sensor characteristics of each of the current sensors 21a-21c. Because the positive overcurrent set value Iocp and the negative overcurrent set value Iocn are preset, if the corrected sensor characteristic 55, which is the voltage correction amounts 86a, 86b or voltage correction amount data shown in FIG. 13, is stored, the control unit 10 generates the corrected command signal sc based on the voltage correction amounts 86a, 86b or the voltage correction amounts 86a, 86b calculated from the voltage correction amount data. The threshold voltage adjuster 60 of the overcurrent protection circuit 41 generates regulated voltages (positive-side regulated voltage Vap, negative-side regulated voltage Van) based on the corrected command signal sc so that the threshold output units 61a, 61b output overcurrent thresholds (positive-side overcurrent threshold Vthp, negative-side overcurrent threshold Vthn) that correspond to the sensor characteristics of each of the current sensors 21a-21c. For example, the threshold voltage adjuster 60 generates regulated voltages (positive-side regulated voltage Vap, negative-side regulated voltage Van) so that the overcurrent thresholds (positive-side overcurrent threshold Vthp, negative-side overcurrent threshold Vthn) approach the command values ​​of the corrected command signal sc. For example, the threshold voltage adjuster 60 includes a DA converter (digital-to-analog converter) and generates regulated voltages (positive-side regulated voltage Vap, negative-side regulated voltage Van) based on the input digital corrected command signal sc.

[0058] If corrected sensor characteristic 55 is stored, control unit 10 such as a microcomputer can accurately estimate the current value by converting the analog voltages of current sensors 21a to 21c into analog voltages using an AD converter (analog-digital converter) included in control unit 10. In this case, control unit 10 can change drive control signal scg based on signs of overcurrent flowing in AC currents Iu, Iv, Iw, thereby avoiding or reducing the overcurrent.

[0059] Up to now, the first power conversion device 100 of the first embodiment has been described, but is not limited to this example. Factors that can cause the overcurrent to become larger than the set value during overcurrent protection operation of the power semiconductor elements 3a to 3f include gain variations and offset variations in the output characteristics of the current sensors 21a to 21c, as well as temperature-related changes in the output characteristics of the current sensors 21a to 21c, i.e., temperature dependency. Next, a second power conversion device 100 that takes into account the temperature dependency of the output characteristics of the current sensors 21a to 21c will be described.

[0060] 14 is different from the first power conversion apparatus 100 in that it includes a temperature sensor 22 that detects the temperatures of the current sensors 21a to 21c, and the control unit 10 generates a correction command signal sc based on a temperature detection value Ta that is temperature information detected by the temperature sensor 22. The following mainly describes the parts that are different from the first power conversion apparatus 100.

[0061] Temperature sensor 22 is disposed near current sensors 21a to 21c. FIG. 14 shows an example in which temperature sensor 22 is disposed near current sensor 21c. AC wiring 19u, AC wiring 19v, and AC wiring 19w are usually disposed close to each other, so there is not much difference in temperature between current sensors 21a to 21c. Temperature sensor 22 outputs detected temperature information, or temperature detection value Ta, to control unit 10 via signal line 31e. FIG. 15 shows sensor characteristics 56a, 56b, and 56c at multiple temperatures. In FIG. 15, the horizontal axis represents current and the vertical axis represents voltage. For example, sensor characteristic 56a represents characteristics at room temperature, which is a reference temperature (reference temperature). Sensor characteristic 56b represents characteristics at a high temperature, such as 105°C. Sensor characteristic 56c represents characteristics at a low temperature, such as -40°C. Room temperature is the standard temperature used to measure the temperature characteristics of current sensors, and is between 5°C and 35°C. This room temperature range is specified as the standard condition for a test location in the JIS standard JIS Z8703. Sensor characteristic 56a shown in FIG. 15 is, for example, a characteristic at 25°C. Three sensor characteristics 56a, 56b, and 56c form a temperature map 75. In other words, temperature map 75 has multiple sensor characteristics 56a, 56b, and 56c. Sensor characteristics 56a, 56b, and 56c also serve as corrected sensor characteristics 55 at each temperature. The number of sensor characteristics in temperature map 75 is not limited to three, and may be two, four, or more. The reference temperature is not limited to 25°C, and may be another temperature within the room temperature range.

[0062] Sensor characteristic 56a shown in FIG. 15 represents a characteristic obtained by correcting gain variations and offset variations in the output characteristics of current sensors 21a to 21c. Therefore, the overcurrent threshold voltages at positive overcurrent setting value Iocp and negative overcurrent setting value Iocn are set to positive overcurrent threshold Vthap and negative overcurrent threshold Vthan, respectively. At positive overcurrent setting value Iocp, the voltage of sensor characteristic 56a is positive overcurrent threshold Vthap, the voltage of sensor characteristic 56b is positive overcurrent threshold Vthap1, and the voltage of sensor characteristic 56c is positive overcurrent threshold Vthap2. When temperature detection value Ta of temperature sensor 22 changes from room temperature to a high temperature, correcting the positive overcurrent threshold to Vthap1 allows the power semiconductor element to be turned off by an overcurrent at positive overcurrent setting value Iocp. When the temperature detection value Ta of the temperature sensor 22 changes from room temperature to a low temperature, the power semiconductor element can be turned off by an overcurrent of the positive side overcurrent setting value Iocp by correcting the positive side overcurrent threshold to Vthap2.

[0063] At the negative overcurrent setting value Iocn, the voltage of sensor characteristic 56a is the negative overcurrent threshold Vthan, the voltage of sensor characteristic 56b is the negative overcurrent threshold Vthan1, and the voltage of sensor characteristic 56c is the negative overcurrent threshold Vthan2. When the temperature detection value Ta of temperature sensor 22 changes from room temperature to a high temperature, the power semiconductor element can be turned off with an overcurrent of the negative overcurrent setting value Iocn by correcting the positive overcurrent threshold to Vthan1. When the temperature detection value Ta of temperature sensor 22 changes from room temperature to a low temperature, the power semiconductor element can be turned off with an overcurrent of the negative overcurrent setting value Iocn by correcting the positive overcurrent threshold to Vthan2.

[0064] When the temperature detection value Ta changes from room temperature (25°C) to a high temperature (105°C), the temperature-dependent correction amount of the positive overcurrent threshold Vthp is temperature correction amount 87a, and the temperature-dependent correction amount of the negative overcurrent threshold Vthn is temperature correction amount 88a. When the temperature detection value Ta changes from room temperature (25°C) to a low temperature (-40°C), the temperature-dependent correction amount of the positive overcurrent threshold Vthp is temperature correction amount 87b, and the temperature-dependent correction amount of the negative overcurrent threshold Vthn is temperature correction amount 88b. The temperature correction amount can also be referred to as the temperature-dependent voltage correction amount.

[0065] The control unit 10 in the second power conversion device 100 includes an internal temperature map 75, and estimates the output characteristics of the current sensors 21a-21c at each temperature based on the detected temperature value Ta. The control unit 10 then outputs a correction command signal sc to the threshold voltage adjuster 60 of the overcurrent protection circuit 41 to adjust the overcurrent threshold voltages (positive overcurrent threshold Vthp, negative overcurrent threshold Vthn). In this case, the correction command signal sc is generated based on the sum of the temperature correction amount and voltage correction amounts 86a, 86b (see FIG. 13) that correct gain variations and offset variations, i.e., the difference between the first voltages (positive overcurrent threshold Vth0p, negative overcurrent threshold Vth0n) of the current sensors 21a-21c at the time of design and the second voltages (positive overcurrent threshold Vthap, negative overcurrent threshold Vthan) of the installed current sensors 21a-21c. The sensor characteristics 56a, 56b, and 56c of the temperature map 75 are the characteristics of each temperature in the corrected sensor characteristic 55 that is actually measured.

[0066] As described above, in the second power conversion device 100 of the first embodiment, the control unit 10 stores, as the temperature map 75, characteristic data (sensor characteristics 56a, 56b, 56c) of the output voltage versus the current detected by the current sensors 21a to 21c, which are measured in advance at a plurality of temperatures. The control unit 10 generates a correction command signal sc based on a total correction amount obtained by adding together the temperature correction amount and the voltage correction amount extracted based on the temperature detection value Ta, which is temperature information detected by the temperature sensor 22, and the temperature map 75. The total correction amount for the positive overcurrent setting value Iocp is the sum of the voltage correction amount 86a and the temperature correction amounts 87a and 87b. The total correction amount for the negative overcurrent setting value Iocn is the sum of the voltage correction amount 86b and the temperature correction amounts 88a and 88b. The temperature correction amount may also be the amount of change in the detected voltage output by the current sensors 21a to 21c relative to the overcurrent setting value (positive overcurrent setting value Iocp, negative overcurrent setting value Iocn) relative to a preset reference temperature (the above-mentioned room temperature). The temperature correction amounts for the positive-side overcurrent setting value Iocp are temperature correction amounts 87a and 87b, and the temperature correction amount for the negative-side overcurrent setting value Iocn is temperature correction amounts 88a and 88b. Even if the second power conversion device 100 of the first embodiment is equipped with current sensors 21a to 21c that have high temperature dependency, it is possible to reduce the overcurrent flowing through the power semiconductor elements during the overcurrent protection operation for the power semiconductor elements 3a to 3f.

[0067] The overcurrent detection circuit of Patent Document 1 requires a temperature characteristic correction MOSFET for each current sensor. Therefore, if a series circuit of a current detection MOSFET and a resistor corresponding to a current sensor is provided for each of the U, V, and W phases, as in a three-phase inverter, and a comparator is provided for each of the positive-side and negative-side current detection MOSFETs, the circuit size of the current sensors and overcurrent detection circuit may become large. In contrast, the power conversion device 100 of the first embodiment, unlike the overcurrent detection circuit of Patent Document 1, can use a threshold voltage adjustment unit 60 with a relatively small circuit size for the positive-side comparator 42p and the negative-side comparator 42n. This prevents the circuit size of the overcurrent protection circuit 41 and the current sensors 21a-21c from becoming larger than that of the overcurrent detection circuit and current sensors of Patent Document 1. For example, when a threshold voltage adjustment unit 60 including two resistors R1 and R2 shown in FIG. 33 (described later) is used and an analog correction command signal sc is output from the control unit 10 to the threshold voltage adjustment unit 60, the circuit size of the overcurrent protection circuit 41 can be effectively reduced.

[0068] As described above, the power conversion device 100 of the first embodiment controls the power conversion unit 110 having the plurality of power semiconductor elements 3a, 3b, 3c, 3d, 3e, and 3f to convert DC power to AC power or AC power to DC power. The power conversion device 100 includes a drive circuit 14 that outputs an element drive signal sd to drive the plurality of power semiconductor elements 3a-3f, a control unit 10 that controls the drive circuit 14, and current sensors 21a, 21b, and 21c that detect AC currents Iu, Iv, and Iw of the power conversion unit 110. The drive circuit 14 includes an element drive circuit 40 that outputs the element drive signal sd to the power semiconductor elements 3a-3f, and an overcurrent protection circuit 41 that determines that an overcurrent has flowed through the power semiconductor elements 3a-3f and outputs an overcurrent stop signal st to the element drive circuit 40 to cause the element drive signal sd to be output, changing the power semiconductor elements from an ON state to an OFF state. The overcurrent protection circuit 41 includes comparators 42p and 42n that determine that an overcurrent has flowed through the power semiconductor elements 3a to 3f by comparing the detection voltages Vi (Viu, Viv, Viw) output by the current sensors 21a to 21c with overcurrent threshold voltages (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn) and generate an overcurrent stop signal st; threshold output units 61a and 61b that output the overcurrent threshold voltages (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn); and a threshold voltage adjustment unit 60 that generates adjustment voltages (positive side adjustment voltage Vap, negative side adjustment voltage Van) that cause the threshold output units 61a and 61b to output the overcurrent threshold voltages (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn) based on a correction command signal sc output from the control unit 10, and outputs the adjustment voltages (positive side adjustment voltage Vap, negative side adjustment voltage Van) to the threshold output units 61a and 61b.The difference between the first voltage (positive side overcurrent threshold Vth0p, negative side overcurrent threshold Vth0n) of the current sensors 21a to 21c at the time of design and the second voltage (positive side overcurrent threshold Vthap, negative side overcurrent threshold Vthan) of the installed current sensors 21a to 21c for a predetermined overcurrent setting value (positive side overcurrent setting value Iocp, negative side overcurrent setting value Iocn) that turns off the power semiconductor elements 3a to 3f is set as voltage correction amounts 86a, 86b, and the control unit 10 generates a correction command signal sc based on the voltage correction amounts 86a, 86b that are stored in advance or the voltage correction amounts 86a, 86b calculated from the voltage correction amount data (correction sensor characteristic 55) that are stored in advance. With this configuration, the power conversion device 100 of embodiment 1 outputs to the overcurrent protection circuit 41 a corrected command signal sc generated by the control unit 10 based on pre-stored voltage correction amounts 86a, 86b or voltage correction amounts 86a, 86b calculated from pre-stored voltage correction amount data (corrected sensor characteristic 55).When an overcurrent flows, the overcurrent protection circuit 41 compares the overcurrent threshold voltages (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn) generated based on the corrected command signal sc with the detection voltages Viu, Viv, Viw output by the current sensors 21a to 21c to generate an overcurrent stop signal st, and switches the power semiconductor element in which it is determined that an overcurrent is flowing from the on state to the off state.As a result, the overcurrent flowing in the power semiconductor elements can be reduced during the overcurrent protection operation of the power semiconductor elements 3a to 3f.

[0069] Embodiment 2 FIG. 16 is a diagram illustrating a configuration of a drive circuit according to embodiment 2. FIG. 17 is a diagram illustrating a configuration of a first protection circuit of FIG. 16, and FIG. 18 is a diagram illustrating a configuration of a second protection circuit of FIG. 16. FIG. 19 is a diagram illustrating a duty ratio. FIG. 20 is a diagram illustrating output voltage characteristics of a smoothing circuit that smooths the pulse signal Vpi of FIGS. 17 and 18, and FIG. 21 is a diagram illustrating output voltage characteristics of a smoothing circuit that smooths the pulse signal Vpia of FIG. 18. FIGS. 22, 23, and 24 are respectively diagrams illustrating first, second, and third examples of overcurrent threshold characteristics of the first protection circuit according to embodiment 2. FIGS. 25, 26, and 27 are respectively diagrams illustrating first, second, and third examples of overcurrent threshold characteristics of the second protection circuit according to embodiment 2. FIG. 28 is a diagram illustrating a first correction example of the overcurrent threshold of the protection circuit according to embodiment 2. FIGS. 29, 30, and 31 are respectively diagrams illustrating second correction examples of the overcurrent threshold of the protection circuit according to embodiment 2.

[0070] The power conversion device 100 of the second embodiment differs from the power conversion device 100 of the first embodiment in that a positive-side overcurrent threshold Vthp and a negative-side overcurrent threshold Vthn are output from one threshold output unit 61 to two comparators 42p, 42n, respectively, and in that the number of output terminals for outputting the correction command signal sc of the control unit 10 is reduced. The following mainly describes the parts that are different from the power conversion device 100 of the first embodiment.

[0071] The components of the power conversion device 100 of the second embodiment are the same as those of the power conversion device 100 of the first embodiment shown in FIGS. 1 and 14. However, the configuration of the protection circuit 59 and the number of output terminals of the control unit 10 are different. In the power conversion device 100 of the first embodiment, the power conversion unit 110 of a three-phase inverter was described. To interrupt a positive overcurrent and a negative overcurrent in the U-phase, V-phase, and W-phase AC currents, six correction command signals sc are required to correct the respective overcurrent thresholds, and the control unit 10 needs six output terminals 45a to 45f to output the six correction command signals sc, respectively. For example, if the control unit 10 is an existing microcomputer, it is possible that the number of output terminals for outputting the correction command signals sc is insufficient. In the second embodiment, an overcurrent protection circuit 41 is described that reduces the number of output terminals for outputting the correction command signals sc and can correct multiple threshold voltages with a single correction command signal sc. This overcurrent protection circuit 41 allows the power conversion device 100 of embodiment 2 to achieve the same effect as the power conversion device 100 of embodiment 1, and also reduces power consumption as the number of output terminals of the control unit 10 decreases, making it possible to reduce the cost of the control unit 10.

[0072] The control unit 10 and drive circuit 14 of the second embodiment shown in FIG. 16 will be described below in terms of differences from the control unit 10 and drive circuit 14 of the first embodiment shown in FIG. The control unit 10 of the second embodiment has three output terminals 45a, 45c, and 45e. The control unit 10 outputs a correction command signal scu to a U-phase protection circuit 59u from the output terminal 45a, a correction command signal scv to a V-phase protection circuit 59v from the output terminal 45c, and a correction command signal scw to a W-phase protection circuit 59w from the output terminal 45e. The input terminals to which the correction command signal sc is input in the protection circuits 59u, 59v, and 59w have been reduced from two input terminals 49p and 49n to a single input terminal 49. As mentioned above, the symbol for the correction command signal is generally sc. When distinguishing between the correction command signals, the symbols scu, scv, and scw are used.

[0073] The protection circuits 59u, 59v, and 59w each have the configuration shown in FIG. 17 or the configuration shown in FIG. 18. The first protection circuit 59 shown in FIG. 17 is configured for a case where offset variations among the current sensors 21a to 21c are dominant, while the second protection circuit 59 shown in FIG. 18 is configured for a case where gain variations among the current sensors 21a to 21c are dominant. First, the first protection circuit 59 shown in FIG. 17 will be described. The threshold voltage adjuster 60 includes two smoothing circuits 65a and 65b that smooth the pulse signal Vpi, resistors R1 and R2, an input terminal 49 to which a correction command signal sc is input, an output terminal 43p that outputs a positive-side regulated voltage Vap, and an output terminal 43n that outputs a negative-side regulated voltage Van. The smoothing circuit 65a that outputs the adjustment source voltage Vsp is referred to as the first smoothing circuit, and the smoothing circuit 65b that outputs the adjustment source voltage Vsn is referred to as the second smoothing circuit. The correction command signal sc in the second embodiment is a pulse signal Vpi having a duty ratio Du. The duty ratio Du is the ratio of the high period Th of the pulse signal Vpi to the pulse period Tf, ie, it can be expressed as Th / Tf.

[0074] The first smoothing circuit 65a smooths the pulse signal Vpi to generate the adjustment source voltage Vsp. The second smoothing circuit 65b smooths the pulse signal Vpi to generate the adjustment source voltage Vsn. The first smoothing circuit 65a and the second smoothing circuit 65b output a voltage ranging from 0 V to a maximum voltage value Vsa according to the duty ratio Du of the pulse signal Vpi. In FIG. 17, the first smoothing circuit 65a is an RC filter circuit including a resistor Rb1 and a capacitor C1, and the second smoothing circuit 65b is an RC filter circuit including a resistor Rb2 and a capacitor C2. The number of RC filter circuits is not limited to one, and multiple RC filter circuits may be connected.

[0075] The adjustment source voltages Vsp and Vsn are proportional to the duty ratio Du of the pulse signal Vpi and range from 0V to the maximum voltage value Vsa, as shown in output voltage characteristic 67 in Fig. 20. In Fig. 20, the horizontal axis represents the duty ratio Du of the pulse signal Vpi, and the vertical axis represents voltage. For example, if the maximum voltage value Vsa is 5V, the adjustment source voltages Vsp and Vsn will be 0V when the duty ratio Du is 0, and will be 5V when the duty ratio Du is 1.

[0076] One end of resistor R1 is connected to a connection point n1 between resistor Rb1 and capacitor C1, and the other end is connected to output terminal 43p. One end of resistor R2 is connected to a connection point n2 between resistor Rb2 and capacitor C2, and the other end is connected to output terminal 43n. The connection point n1 of first smoothing circuit 65a is an output point that outputs adjustment source voltage Vsp, and the connection point n2 of second smoothing circuit 65b is an output point that outputs adjustment source voltage Vsn. The adjustment source voltage Vsp output from the output point of first smoothing circuit 65a is output from output terminal 43p via resistor R1 as positive-side regulated voltage Vap (see FIG. 5). The adjustment source voltage Vsn output from the output point of second smoothing circuit 65b is output from output terminal 43n via resistor R2 as negative-side regulated voltage Van (see FIG. 5).

[0077] The overcurrent stop signal output unit 62 includes a comparator 42p that outputs a positive-side overcurrent stop signal stp to the element drive circuit 40, a comparator 42n that outputs a negative-side overcurrent stop signal stn to the element drive circuit 40, and a threshold output unit 61 that outputs a positive-side overcurrent threshold Vthp and a negative-side overcurrent threshold Vthn based on a positive-side regulated voltage Vap and a negative-side regulated voltage Van. The detection voltage Vi output from the current sensors 21a, 21b, and 21c via the input terminal 48 is input to the negative terminal of one end of the comparators 42p and 42n. The positive-side overcurrent threshold Vthp is input to the positive terminal of the other end of the comparator 42p, and the negative-side overcurrent threshold Vthn is input to the positive terminal of the other end of the comparator 42n. The threshold output unit 61 is a series circuit in which multiple resistors R3, R4, and R5 are connected in series between a power supply voltage Vpp generated inside the power conversion device 100 and ground GND. Resistors R3, R4, and R5 of the threshold output unit 61 are referred to as a first resistor, a second resistor, and a third resistor, respectively. A connection point n3, which is a first connection point where the first resistor (resistor R3) and the second resistor (resistor R4) on the power supply voltage Vpp side are connected, is connected to an output terminal 43p of the threshold voltage adjustment unit 60 and a positive-side comparator 42p. A connection point n4, which is a second connection point where the third resistor (resistor R5) and the second resistor (resistor R4) on the ground GND side are connected, is connected to an output terminal 43n of the threshold voltage adjustment unit 60 and a negative-side comparator 42n.

[0078] 17, the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn output from the threshold output unit 61 of the first protection circuit 59 will be described. The positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn are generated by resistors R3, R4, and R5 of the threshold output unit 61, the power supply voltage Vpp of the threshold output unit 61, and the adjustment source voltages Vsp and Vsn. Specifically, the resistors R3, R4, and R5 are connected in series between the power supply voltage Vpp and the ground GND, and the positive-side overcurrent threshold Vthp output from a connection point n3 between the resistors R3 and R4 is generated by a resistor-divided value of the resistors R3, R4, and R5 and a positive-side adjustment voltage Vap, which is an adjustment source voltage Vsp determined by a duty ratio Du of a pulse signal Vpi output from the control unit 10 and output to the connection point n3 via the resistor R1. Furthermore, the negative overcurrent threshold Vthn output from the connection point n4 between resistors R4 and R5 is generated by the resistor-divided value of resistors R3, R4, and R5, and the negative regulated voltage Van, which is the regulation source voltage Vsn determined by the duty ratio Du of the pulse signal Vpi output from the control unit 10 and output to the connection point n4 via resistor R2. The positive overcurrent threshold Vthp changes in response to changes in the regulation source voltage Vsp and the positive regulated voltage Vap, as the duty ratio Du of the pulse signal Vpi changes. Similarly, the negative overcurrent threshold Vthn changes in response to changes in the regulation source voltage Vsn and the negative regulated voltage Van, as the duty ratio Du of the pulse signal Vpi changes.

[0079] 22 to 24 show first to third examples of the overcurrent threshold characteristic of the first protection circuit 59, respectively. In FIGS. 22 to 24, the horizontal axis represents the duty ratio Du of the pulse signal Vpi, and the vertical axis represents voltage. FIGS. 22 to 24 show an example in which the maximum voltage value Vsa is 5.0 V. In FIGS. 22 to 24, the resistors R1 and R2 of the threshold voltage adjustment unit 60 and the resistors R3, R4, and R5 of the threshold output unit 61 have different magnitudes. The resistance values ​​of the resistors R1, R2, R3, R4, and R5 are simply referred to as R1, R2, R3, R4, and R5 where appropriate. The first example of the overcurrent threshold characteristic in FIG. 22 corresponds to the case in which R1=R2 and R1, R2>>R3, R4, and R5 (first resistance condition). The second example of the overcurrent threshold characteristic in Figure 23 is when R1 = R2 and R1, R2 ≈ R3, R4, R5 (second resistance condition). The third example of the overcurrent threshold characteristic in Figure 24 is when R1 >> R3, R4, R5 and R2 ≈ R3, R4, R5 (third resistance condition). The relationship between the positive-side overcurrent threshold Vthp and the duty ratio Du is shown as positive-side overcurrent threshold characteristics 92a, 92b, and 92c. The relationship between the negative-side overcurrent threshold Vthn and the duty ratio Du is shown as negative-side overcurrent threshold characteristics 93a, 93b, and 93c.

[0080] 22 to 24, it can be seen that the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn change depending on the values ​​of the resistors R1 and R2 of the threshold voltage adjusting unit 60. As shown in Fig. 23, when the values ​​of the resistors R1 and R2 of the threshold voltage adjusting unit 60 are equivalent to the values ​​of the resistors R3 and R4 of the threshold output unit 61, the slopes of the positive side overcurrent threshold characteristic 92b and the negative side overcurrent threshold characteristic 93b with respect to the duty ratio Du become larger, and the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn are significantly affected by the adjustment source voltages Vsp and Vsn. In contrast, when the values ​​of resistors R1 and R2 of threshold voltage adjuster 60 are increased, as shown in FIG. 22, the slopes of positive side overcurrent threshold characteristic 92a and negative side overcurrent threshold characteristic 93a with respect to duty ratio Du become smaller than those of positive side overcurrent threshold characteristic 92b and negative side overcurrent threshold characteristic 93b in FIG. 23, and the positive side overcurrent threshold Vthp and negative side overcurrent threshold Vthn are not significantly affected by adjustment source voltages Vsp and Vsn.

[0081] The positive overcurrent threshold Vthp can be corrected from the initial positive overcurrent threshold Vth0p to the positive overcurrent threshold Vthap by changing the duty ratio Du. Similarly, the negative overcurrent threshold Vthn can be corrected from the initial negative overcurrent threshold Vth0n to the negative overcurrent threshold Vthan by changing the duty ratio Du. Furthermore, the slopes of the positive overcurrent threshold characteristic and the negative overcurrent threshold characteristic can be adjusted by adjusting the values ​​of the resistors R1 and R2 of the threshold voltage adjuster 60. Because the correction command signal sc output from the controller 10 is a pulse signal Vpi having the duty ratio Du, it is necessary to realize the voltage correction amount 86a (see FIG. 13) for the positive overcurrent threshold Vthp and the voltage correction amount 86b (see FIG. 13) for the negative overcurrent threshold Vthn simply by changing the duty ratio Du. By adjusting the values ​​of resistors R1 and R2 of the threshold voltage adjuster 60 in advance for each of the current sensors 21a to 21c, the voltage correction amount 86a for the positive overcurrent threshold Vthp and the voltage correction amount 86b for the negative overcurrent threshold Vthn can be realized by changing the duty ratio Du.

[0082] Next, the second protection circuit 59 shown in FIG. 18 will be described. The second protection circuit 59 shown in FIG. 18 differs from the first protection circuit 59 shown in FIG. 17 in that an inverter 63 is added to the threshold voltage adjustment unit 60, and the smoothing circuit 65b that outputs the negative-side adjustment source voltage Vsn is changed to a smoothing circuit 66 that outputs the negative-side adjustment source voltage Vsn in response to the pulse signal Vpia output from the inverter 63. Note that the smoothing circuit 65a that smooths the pulse signal Vpi is designated by the reference numeral 65. As appropriate, the smoothing circuit 65 that outputs the adjustment source voltage Vsp will be referred to as the first smoothing circuit, and the smoothing circuit 66 that outputs the adjustment source voltage Vsn will be referred to as the second smoothing circuit. Differences from the first protection circuit 59 will be mainly described. The first smoothing circuit 65 smooths the pulse signal Vpi to generate the adjustment source voltage Vsp from the connection point n1, which is the output point. The second smoothing circuit 66 smooths the pulse signal Vpia, which is obtained by inverting the pulse signal Vpi by the inverter 63, and generates the adjustment source voltage Vsn from the connection point n2, which is the output point.

[0083] The adjustment source voltage Vsp varies from 0 V to the maximum voltage value Vsa in proportion to the duty ratio Du of the pulse signal Vpi, as shown in output voltage characteristic 67 in Fig. 20. On the other hand, the adjustment source voltage Vsn generated by the inverter 63 from the pulse signal Vpia, which is an inverted pulse of the pulse signal Vpi, varies as shown in output voltage characteristic 68 in Fig. 21, in which the output voltage characteristic 67 in Fig. 20 is inverted left and right.

[0084] FIGS. 25 to 27 show first to third examples of overcurrent threshold characteristics in the second protection circuit 59, respectively. FIGS. 25 to 27 use the same horizontal and vertical axes as FIGS. 22 to 24, and show an example where the maximum voltage value Vsa is 5.0 V. The first example of the overcurrent threshold characteristics in FIG. 25 is for the same first resistance condition as in FIG. 22. The second example of the overcurrent threshold characteristics in FIG. 26 is for the same second resistance condition as in FIG. 23. The third example of the overcurrent threshold characteristics in FIG. 27 is for the same third resistance condition as in FIG. 24. The relationship between the positive-side overcurrent threshold Vthp and the duty ratio Du is shown as positive-side overcurrent threshold characteristics 92d, 92e, and 92f. The relationship between the negative-side overcurrent threshold Vthn and the duty ratio Du is shown as negative-side overcurrent threshold characteristics 93d, 93e, and 93f.

[0085] 22 to 24, Figures 25 to 27 also show that the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn change depending on the values ​​of the resistors R1 and R2 of the threshold voltage adjusting unit 60. As shown in Figure 26, when the values ​​of the resistors R1 and R2 of the threshold voltage adjusting unit 60 are equivalent to the values ​​of the resistors R3 to R4 of the threshold output unit 61, the slopes of the positive side overcurrent threshold characteristic 92e and the negative side overcurrent threshold characteristic 93e with respect to the duty ratio Du become larger, and the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn are significantly affected by the adjustment source voltages Vsp and Vsn. In contrast, when the values ​​of resistors R1 and R2 of threshold voltage adjustment unit 60 are increased, as shown in FIG. 25, the slopes of positive side overcurrent threshold characteristic 92d and negative side overcurrent threshold characteristic 93d with respect to duty ratio Du become smaller than those of positive side overcurrent threshold characteristic 92e and negative side overcurrent threshold characteristic 93e in FIG. 26, and the positive side overcurrent threshold Vthp and negative side overcurrent threshold Vthn are not significantly affected by adjustment source voltages Vsp and Vsn.

[0086] In the second protection circuit 59, similar to the first protection circuit 59, the positive overcurrent threshold Vthp can be corrected from the initial positive overcurrent threshold Vth0p to the positive overcurrent threshold Vthap by changing the duty ratio Du. Similarly, the negative overcurrent threshold Vthn can be corrected from the initial negative overcurrent threshold Vth0n to the negative overcurrent threshold Vthan by changing the duty ratio Du. Furthermore, the slopes of the positive overcurrent threshold characteristics and the negative overcurrent threshold characteristics can be adjusted by adjusting the values ​​of the resistors R1 and R2 of the threshold voltage adjuster 60. In the second protection circuit 59, similar to the first protection circuit 59, the values ​​of the resistors R1 and R2 of the threshold voltage adjuster 60 are adjusted in advance for each of the current sensors 21a to 21c, thereby realizing a voltage correction amount 86a for the positive overcurrent threshold Vthp and a voltage correction amount 86b for the negative overcurrent threshold Vthn by changing the duty ratio Du.

[0087] The overcurrent protection circuit 41 of the second embodiment includes a protection circuit 59 corresponding to each phase of the three-phase AC. The protection circuit 59 includes a first comparator 42p that determines that an overcurrent has flowed through the upper-arm power semiconductor elements 3a, 3c, and 3e by comparing the detection voltage Vi output by the current sensors 21a to 21c with a positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp) and outputs a positive-side overcurrent stop signal stp; a second comparator 42n that determines that an overcurrent has flowed through the lower-arm power semiconductor elements 3b, 3d, and 3f by comparing the detection voltage Vi output by the current sensors 21a to 21c with a negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn) and outputs a negative-side overcurrent stop signal stn; a threshold output unit 61 that outputs the positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp) and the negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn); and a threshold voltage adjustment unit 60 that outputs a first regulated voltage (positive-side regulated voltage Vap) and a second regulated voltage (negative-side regulated voltage Van) to the threshold output unit 61. Threshold voltage adjuster 60 generates a first regulated voltage (positive-side regulated voltage Vap) and a second regulated voltage (negative-side regulated voltage Van) based on a correction command signal sc output from controller 10. In power conversion device 100 of the second embodiment, protection circuit 59 can generate two overcurrent stop signals stp and stn based on one correction command signal sc, so that the number of output terminals of controller 10 can be reduced, and the reduction in the number of output terminals of controller 10 can reduce power consumption and also reduce the cost of controller 10.

[0088] The method of correcting the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn in each protection circuit 59 of the overcurrent protection circuit 41 of the second embodiment and the operation of the power conversion device 100 of the second embodiment will be described with reference to FIGS. 28 to 31. The method of correcting the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn is the same for both the first protection circuit 59 and the second protection circuit 59, but the second protection circuit 59 will be described as a representative example. FIGS. 28 to 31 show an example of the overcurrent value characteristics of the second protection circuit 59 similar to those of FIG. 26, in which gain variation is dominant, resistors R1 to R5 are in the second resistance condition, and the maximum voltage value Vsa is 5.0 V. In FIGS. 28 to 31, the horizontal axis represents the duty ratio Du of the pulse signal Vpi, and the vertical axis represents voltage. 28 to 31, the relationship between the positive overcurrent threshold Vthp and the duty ratio Du is shown as positive overcurrent threshold characteristics 94a and 94b, and the relationship between the negative overcurrent threshold Vthn and the duty ratio Du is shown as negative overcurrent threshold characteristics 95a and 95b.

[0089] Consider a case where the default positive overcurrent threshold Vthp and negative overcurrent threshold Vthn input to comparators 42p and 42n, i.e., the positive overcurrent threshold Vthp and negative overcurrent threshold Vthn at the time of design, are positive overcurrent threshold Vth0p and negative overcurrent threshold Vth0n, and correction is required to set them to positive overcurrent threshold Vthap and negative overcurrent threshold Vthan. The positive overcurrent threshold Vthap and negative overcurrent threshold Vthan are calculated using corrected sensor characteristic 55 shown in FIG. 13. Alternatively, as described in the first embodiment, they may be calculated using voltage correction amounts 86a and 86b calculated in advance from corrected sensor characteristic 55 and stored. The control unit 10 calculates the positive overcurrent threshold Vthap by adding voltage correction amount 86a to the positive overcurrent threshold Vth0p, and calculates the negative overcurrent threshold Vthan by subtracting voltage correction amount 86b from the negative overcurrent threshold Vth0n. First, a first correction example will be described with reference to FIG. 28. To change the positive side overcurrent threshold Vth0p to the positive side overcurrent threshold Vthap, the positive side overcurrent threshold Vthp must be lowered by the voltage correction amount 79a, and to change the negative side overcurrent threshold Vth0n to the negative side overcurrent threshold Vthan, the negative side overcurrent threshold Vthn must be raised by the voltage correction amount 79b.

[0090] The control unit 10 changes the duty ratio Du from an initial duty ratio value d1 to a duty ratio value d2. The amount of change from the duty ratio value d1 to the duty ratio value d2 is a duty ratio change amount 78. The control unit 10 outputs a pulse signal Vpi, in which the duty ratio Du is the duty ratio value d2, as a correction command signal sc to the protection circuit 59 of the overcurrent protection circuit 41. The duty ratio change amount 78 is set in accordance with each of the current sensors 21a to 21c. The control unit 10 generates a pulse signal Vpi having a duty ratio Du corresponding to each of the current sensors 21a to 21c as correction command signals scu, scv, and scw, and outputs the correction command signals scu, scv, and scw to the protection circuits 59u, 59v, and 59w, respectively. In this way, even if the power conversion device 100 of embodiment 2 is equipped with current sensors 21a to 21c having variations in sensor characteristics, it can turn off the power semiconductor elements 3a to 3f at predetermined overcurrent setting values ​​(positive side overcurrent setting value Iocp, negative side overcurrent setting value Iocn) during overcurrent protection operation.

[0091] Next, consider a case where the positive overcurrent threshold Vthap and the negative overcurrent threshold Vthan cannot be achieved with the same duty ratio change amount 78 due to variations in the sensor characteristics of the current sensors. An example of this case is shown in FIGS. 29 to 31. A second correction example will be described using FIGS. 29 to 31. FIGS. 29 to 31 show an example in which the positive overcurrent threshold Vthp can only be lowered to the lower-limit positive overcurrent threshold Vthpmin. If the positive overcurrent threshold Vthp falls below the lower-limit positive overcurrent threshold Vthpmin, causing the power semiconductor elements 3a to 3f to enter the OFF state in the steady-state operating range, the positive overcurrent threshold Vthp is set to the lower-limit positive overcurrent threshold Vthpmin. Similarly, if the negative overcurrent threshold Vthn increases beyond the upper-limit negative overcurrent threshold Vthnmax, causing the power semiconductor elements 3a to 3f to enter the OFF state in the steady-state operating range, the negative overcurrent threshold Vthn is set to the upper-limit negative overcurrent threshold Vthnmax. Note that the case where the negative overcurrent threshold Vthn exceeds the upper limit negative overcurrent threshold Vthnmax occurs when the differential voltage of the negative overcurrent threshold Vthn drops below a limit value when considered in terms of the differential voltage from the median value of 2.5 V described in Figures 6 to 8. Therefore, both the lower limit positive overcurrent threshold Vthpmin and the upper limit negative overcurrent threshold Vthnmax are limit values ​​of the overcurrent threshold at which the steady operation of the power conversion device 100 is not hindered.

[0092] 29 to 31 assume a case where the positive-side voltage correction amount 83a is smaller than the negative-side voltage correction amount 83b, as in the example of FIG. 11. In this case, the control unit 10 of the power conversion device 100 of the second embodiment adjusts the value of the duty ratio Du according to either the smaller voltage correction amount or the limit value of the overcurrent threshold (positive-side overcurrent threshold Vthap, negative-side overcurrent threshold Vthan). FIGS. 29 to 31 show examples of the overcurrent threshold characteristics of the second protection circuit 59 shown in FIG. 18. The characteristics of the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn are positive-side overcurrent threshold characteristic 94b and negative-side overcurrent threshold characteristic 95b, respectively. The positive-side overcurrent threshold Vthp and negative-side overcurrent threshold Vthn set as defaults, i.e., the initial positive-side overcurrent threshold Vthp0 and the initial negative-side overcurrent threshold Vthn0, are set by the correction command signal sc in which the value of the duty ratio Du of the pulse signal Vpi is the duty ratio value d3. That is, the control unit 10 sets the default positive side overcurrent threshold Vthp0 and negative side overcurrent threshold Vthn0 by outputting to the protection circuit 59 a correction command signal sc in which the value of the duty ratio Du of the pulse signal Vpi is the duty ratio value d3.

[0093] The threshold voltage of the lower limit line 35 is the lower limit positive overcurrent threshold Vthpmin, and the threshold voltage of the upper limit line 36 is the upper limit negative overcurrent threshold Vthnmax. The duty ratio value lower limit line 34 is the line where the positive overcurrent threshold characteristic 94b becomes the lower limit positive overcurrent threshold Vthpmin. The positive side threshold settable range 39a is between the positive side overcurrent threshold Vthp0 and the lower limit positive overcurrent threshold Vthpmin indicated by the lower limit line 35. The negative side threshold settable range 39b is between the negative side overcurrent threshold Vthn0 and the upper limit negative overcurrent threshold Vthnmax indicated by the upper limit line 36. The duty ratio value lower limit line 34 indicates that the value of the duty ratio Du is duty ratio value d4. The value of the duty ratio Du where the negative side overcurrent threshold characteristic 95b of the negative overcurrent threshold Vthn intersects with the upper limit line 36 is duty ratio value d5. The range of duty ratio Du from duty ratio value d3 to duty ratio value d4 is a duty ratio adjustment range 38 in which duty ratio Du can actually be adjusted.

[0094] The positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthap) for the duty ratio Du at the positive-side overcurrent setting value (positive-side overcurrent setting value Iocp) is set as first threshold data (positive-side overcurrent threshold characteristic 94b), and the negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthan) for the duty ratio Du at the negative-side overcurrent setting value (negative-side overcurrent setting value Iocn) is set as second threshold data (negative-side overcurrent threshold characteristic 95b). This first threshold data and second threshold data are stored in advance in the control unit 10 as voltage correction amount data, together with the correction sensor characteristic 55 or the voltage correction amounts 86a and 86b. The control unit 10 calculates a first overcurrent threshold V1, which is a positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp) for a positive-side overcurrent setting value (positive-side overcurrent setting value Iocp), from the corrected sensor characteristic 55, which is the first characteristic data, within a positive-side settable range (threshold settable range 39a), and calculates a second overcurrent threshold V2, which is a negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn) for a negative-side overcurrent setting value (negative-side overcurrent setting value Iocn), from the corrected sensor characteristic 55, which is the first characteristic data, within a negative-side settable range (threshold settable range 39b). Note that the control unit 10 may calculate the first overcurrent threshold V1, which is the positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp), and the second overcurrent threshold V2, which is the negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn), using voltage correction amounts 86a and 86b stored in advance. In this case, the control unit 10 calculates a first overcurrent threshold V1, which is a positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp) for a positive-side overcurrent setting value (positive-side overcurrent setting value Iocp), within a positive-side settable range (threshold settable range 39a), using voltage correction amounts 86a and 86b calculated and stored in advance based on the corrected sensor characteristic 55. The control unit 10 also calculates a second overcurrent threshold V2, which is a negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn) for a negative-side overcurrent setting value (negative-side overcurrent setting value Iocn), within a negative-side settable range (threshold settable range 39b). The first overcurrent threshold V1 is obtained by adding the voltage correction amount 86a to the positive-side overcurrent threshold Vth0p, and the second overcurrent threshold V2 is obtained by subtracting the voltage correction amount 86b from the negative-side overcurrent threshold Vth0n.

[0095] Thereafter, the control unit 10 calculates a first voltage correction amount ΔV1, which is a voltage correction amount for the calculated first overcurrent threshold V1, and a second voltage correction amount ΔV2, which is a voltage correction amount for the calculated second overcurrent threshold V2. When generating the correction command signal sc, in the case of condition A, where either a first limit condition is met in which the first overcurrent threshold V1 is the limit value (lower-limit positive overcurrent threshold Vthpmin) of the positive-side settable range (threshold settable range 39a) or a second limit condition is met in which the second overcurrent threshold V2 is the limit value (upper-limit negative overcurrent threshold Vthnmax) of the negative-side settable range (threshold settable range 39b), the control unit 10 determines the value of the duty ratio Du of the pulse signal Vpi, which is the correction command signal sc, to be the selected duty ratio value ds, as follows: If only one of the first limit condition and the second limit condition is satisfied, the duty ratio value (duty ratio value d4) derived based on the limit value (lower-limit positive overcurrent threshold Vthpmin) and one of the first threshold data (positive-side overcurrent threshold characteristic 94b) and the second threshold data (negative-side overcurrent threshold characteristic 95b) corresponding to the limit value (lower-limit positive overcurrent threshold Vthpmin) is determined as the selected duty ratio value ds. If the first limit condition and the second limit condition are satisfied, the limit value corresponding to the smaller correction amount between the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 is set as the selected limit value, and the duty ratio value derived based on the selected limit value and one of the first threshold data (positive-side overcurrent threshold characteristic 94b) and the second threshold data (negative-side overcurrent threshold characteristic 95b) corresponding to the selected limit value is determined as the selected duty ratio value ds.

[0096] The example shown in FIG. 29 illustrates the case of condition A, in which the first limit condition is satisfied. When the duty ratio Du becomes smaller than the duty ratio value d4, the positive overcurrent threshold Vthp becomes lower than the lower-limit positive overcurrent threshold Vthpmin, which is the positive limit. In this case, even if the power conversion unit 110 of the power conversion device 100 is operating normally, the overcurrent protection circuit 41 may determine that an overcurrent has flowed through the power semiconductor elements 3a-3f and turn off the determined power semiconductor elements 3a-3f. To achieve the desired functionality of the power conversion device 100, the limit values ​​of the overcurrent thresholds are not reduced more than necessary. That is, the lower-limit positive overcurrent threshold Vthpmin, which is the positive limit, is not lowered more than necessary, and the upper-limit negative overcurrent threshold Vthnmax, which is the negative limit, is not raised more than necessary. In a normal power conversion device (a power conversion device of the comparative example), a large margin is required due to variations in the output characteristics of the current sensors 21a to 21c, but in the power conversion device 100 of embodiment 2, the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn can be corrected, so a smaller margin can be provided than in the power conversion device of the comparative example.

[0097] 29, because duty ratio Du is set to duty ratio value d4, the negative overcurrent threshold Vthan that is set becomes the negative overcurrent threshold indicated by dashed line 121 where negative overcurrent threshold characteristic 95b intersects with duty ratio lower limit line 34. The negative overcurrent threshold Vthan that is set becomes a value smaller than upper limit negative overcurrent threshold Vthnmax, which is the limit value, as indicated by arrow 122, and although the overcurrent detected during overcurrent protection operation increases slightly, this is an improvement over the default setting value of negative overcurrent threshold Vth0n, and therefore power conversion device 100 of embodiment 2 can also suppress surge voltage during overcurrent protection operation to some extent.

[0098] FIG. 29 illustrates the case of condition A, in which the first limit condition is satisfied. Next, an example will be described in which the control unit 10 adjusts the duty ratio Du to match the smaller voltage correction amount. FIG. 30 illustrates the case of condition B, in which the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are different, other than condition A. FIG. 31 illustrates the case of condition C, in which the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are the same, other than condition A and condition B. While the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 may be different under condition A, condition A is a case in which the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are at their limit values. Using FIG. 30, an example will be described in which condition B, in which condition A is excluded, is excluded. In FIG. 30, the calculated first voltage correction amount ΔV1 for the first overcurrent threshold V1 is smaller than the calculated second voltage correction amount ΔV2 for the second overcurrent threshold V2. The value of the duty ratio Du of the first threshold data (positive-side overcurrent threshold characteristic 94b) that becomes the first overcurrent threshold V1 is duty ratio value d6. The value of the duty ratio Du of the second threshold data (negative-side overcurrent threshold characteristic 95b) that becomes the second overcurrent threshold V2 is duty ratio value d7. In the case of condition B other than condition A, in which the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are different, the control unit 10 sets the smaller correction amount (first voltage correction amount ΔV1 in FIG. 30) as the selected voltage correction amount ΔVs, and determines, as the selected duty ratio value ds, the value of the duty ratio Du (duty ratio value d6 in FIG. 30) that is derived based on the selected voltage correction amount ΔVs and one of the first threshold data (positive-side overcurrent threshold characteristic 94b) and the second threshold data (negative-side overcurrent threshold characteristic 95b) that corresponds to the selected voltage correction amount ΔVs (positive-side overcurrent threshold characteristic 94b in FIG. 30).

[0099] An example of condition C, which excludes conditions A and B, will be described using FIG. 31. In FIG. 31, the calculated first voltage correction amount ΔV1 for the first overcurrent threshold V1 and the calculated second voltage correction amount ΔV2 for the second overcurrent threshold V2 are the same. The value of the duty ratio Du of the first threshold data (positive side overcurrent threshold characteristic 94b) that corresponds to the first overcurrent threshold V1 is the first duty ratio value da1. The value of the duty ratio Du of the second threshold data (negative side overcurrent threshold characteristic 95b) that corresponds to the second overcurrent threshold V2 is the second duty ratio value da2. The voltage correction amount calculated from the voltage value V2a of the second threshold data (negative side overcurrent threshold characteristic 95b) for the first duty ratio value da1 is the third voltage correction amount ΔV3. The voltage correction amount calculated from the voltage value V1a of the first threshold data (positive side overcurrent threshold characteristic 94b) for the second duty ratio value da2 is the fourth voltage correction amount ΔV4. 31 , when changing from the first duty ratio value da1 to the second duty ratio value da2, the positive-side overcurrent threshold Vthap changes from the first overcurrent threshold V1 to a voltage value V1a, and the voltage correction amount increases from the first voltage correction amount ΔV1 to a fourth voltage correction amount ΔV4. When changing from the second duty ratio value da2 to the first duty ratio value da1, the negative-side overcurrent threshold Vthan changes from the second overcurrent threshold V2 to a voltage value V2a, and the voltage correction amount decreases from the second voltage correction amount ΔV2 to a third voltage correction amount ΔV3. In this case, the control unit 10 determines the first duty ratio value da1, which is the duty ratio value for which the correction amount is decreasing, as the selected duty ratio value ds, and generates a pulse signal Vpi having the determined selected duty ratio value ds as the correction command signal sc.

[0100] In the case of condition C, excluding conditions A and B, the control unit 10 determines the selected duty ratio value ds as follows. In the case of condition C, other than conditions A and B, in which the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are the same, the control unit 10 compares a first duty ratio value da1, which is the value of the duty ratio Du derived based on the first voltage correction amount ΔV1 and the first threshold data (positive-side overcurrent threshold characteristic 94b), with a second duty ratio value da2, which is the value of the duty ratio Du derived based on the second voltage correction amount ΔV2 and the second threshold data (negative-side overcurrent threshold characteristic 95b). If the first duty ratio value da1 and the second duty ratio value da2 are the same, the control unit 10 determines the duty ratio Du of this value as the selected duty ratio value ds. If the first duty ratio value da1 and the second duty ratio value da2 are different, the control unit 10 compares a third voltage correction amount ΔV3, which is a voltage correction amount calculated from the voltage value V2a of the second threshold data (negative side overcurrent threshold characteristic 95b) for the first duty ratio value da1, with a fourth voltage correction amount ΔV4, which is a voltage correction amount calculated from the voltage value V1a of the first threshold data (positive side overcurrent threshold characteristic 94b) for the second duty ratio value da2, and determines the duty ratio value with the smaller correction amount (the first duty ratio value da1 in Figure 31) as the selected duty ratio value ds.

[0101] Even in the case of condition C, the duty ratio Du with the smaller correction amount is ultimately used. In the overcurrent protection circuit 41 of the power conversion device 100 according to the second embodiment, when the calculated first voltage correction amount ΔV1, which is the positive-side correction amount, and the calculated second voltage correction amount ΔV2, which is the negative-side correction amount, differ, the duty ratio Du with the smaller correction amount is used. Furthermore, when the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are at their limit values, the duty ratio Du with the limit value correction amount is used. As a result, in the examples of FIGS. 29 to 31, the values ​​of duty ratio Du are selected as duty ratio values ​​d4, d6, and da1, respectively. Therefore, although the negative overcurrent threshold Vthan is set to a slightly increased level of overcurrent detected during overcurrent protection operation, it is still improved compared to the default negative overcurrent threshold Vth0n. Therefore, the power conversion device 100 according to the second embodiment can suppress surge voltages during overcurrent protection operation to some extent. Of course, depending on variations in current sensors 21a to 21c, it is necessary to select the most appropriate one from the examples in Figures 28 to 31. In the example in Figure 29, when the value of duty ratio Du is changed to a smaller value, the positive side overcurrent threshold Vthap reaches the limit value earlier than the negative side overcurrent threshold Vthan.

[0102] Embodiment 3 FIG. 32 is a diagram showing the configuration of a drive circuit according to embodiment 3, and FIG. 33 is a diagram showing the configuration of the protection circuit of FIG. 32. FIGS. 34, 35, 36, 37, 38, and 39 are diagrams showing first, second, third, fourth, fifth, and sixth examples of overcurrent threshold characteristics of the protection circuit of FIG. 33, respectively. In embodiment 2, an example of power conversion device 100 was described in which protection circuit 59 of overcurrent protection circuit 41 generates adjustment source voltages Vsp and Vsn based on correction command signal sc. In embodiment 3, an example is described in which voltage values ​​corresponding to adjustment source voltages Vsp and Vsn of embodiment 2 are input to protection circuit 59 of overcurrent protection circuit 41 as correction command signal sc, which is an analog signal. The power conversion device 100 of the third embodiment differs from the power conversion device 100 of the second embodiment in that a positive-side overcurrent threshold Vthp and a negative-side overcurrent threshold Vthn are output from one threshold output unit 61 to two comparators 42p, 42n, respectively, based on a corrected command signal sc, which is an analog signal output from a control unit 10. The following mainly describes the parts that are different from the power conversion device 100 of the second embodiment.

[0103] The components of the power conversion device 100 of the third embodiment are the same as the components of the power conversion device 100 of the first embodiment shown in FIGS. 1 and 14. However, the configuration of the protection circuit 59 is different from the configuration of the protection circuit 59 of the first and second embodiments. The control unit 10 of the third embodiment has six output terminals 45a to 45f. The control unit 10 outputs analog correction command signals vsup and vsun from output terminals 45a and 45b to a U-phase protection circuit 59u, outputs analog correction command signals vsvp and vsvn from output terminals 45c and 45d to a V-phase protection circuit 59v, and outputs analog correction command signals vswp and vswn from output terminals 45e and 45f to a W-phase protection circuit 59w. The protection circuits 59u, 59v, and 59w each have two input terminals to which the correction command signal sc is input, namely, two input terminals 46p and 46n, similar to the protection circuits 59u, 59v, and 59w in the first embodiment. As described above, the signs of the correction command signals are collectively referred to as sc. When the correction command signals are to be distinguished, the signs of the correction command signals are used as vsup, vsun, vsvp, vsvn, vswp, and vswn. When the U-phase, V-phase, and W-phase are not to be distinguished, the positive side correction command signal of the analog correction command signal sc is referred to as the correction command signal vsp, and the negative side correction command signal of the analog correction command signal sc is referred to as the correction command signal vsn.

[0104] Protection circuits 59u, 59v, and 59w have the configuration shown in FIG. 33. Protection circuits 59u, 59v, and 59w of embodiment 3 differ from protection circuits 59u, 59v, and 59w of embodiment 2 in that they do not have smoothing circuits 65a, 65b, 65, and 66. A positive correction command signal vsp of an analog correction command signal sc is input from input terminal 46p, and a negative correction command signal vsn of an analog correction command signal sc is input from input terminal 46n. The correction command signal vsp corresponds to adjustment source voltage Vsp of embodiment 2, and the correction command signal vsn corresponds to adjustment source voltage Vsn of embodiment 2. Threshold voltage adjuster 60 of embodiment 3 outputs adjustment source voltage Vsp from output terminal 43p as positive-side adjustment voltage Vap via resistor R1, and outputs adjustment source voltage Vsn from output terminal 43n as negative-side adjustment voltage Van via resistor R2. The overcurrent stop signal output unit 62 of the third embodiment is the same as the overcurrent stop signal output unit 62 of the second embodiment.

[0105] 34 to 39 show first to sixth examples of the overcurrent threshold characteristic of the protection circuit 59, respectively. The first to third examples of the overcurrent threshold characteristic correspond to the first to third examples of the overcurrent threshold characteristic of the first protection circuit 59 of the second embodiment. The fourth and fifth examples of the overcurrent threshold characteristic correspond to the first to third examples of the overcurrent threshold characteristic of the second protection circuit 59 of the second embodiment. In FIGS. 34 to 38, the horizontal axis represents the voltage of the input correction command signal sc, and the vertical axis represents the voltage of the overcurrent threshold. FIGS. 34 to 39 show an example in which the maximum voltage value Vsa is 5.0 V. FIGS. 34 to 36 show overcurrent threshold characteristics when offset variations in the current sensors 21a to 21c are dominant, and the resistors R1 and R2 of the threshold voltage adjuster 60 and the resistors R3, R4, and R5 of the threshold output unit 61 have different magnitudes. 37 to 39 show overcurrent threshold characteristics when gain variations in current sensors 21a to 21c are dominant, and the resistances R1 and R2 of threshold voltage adjuster 60 and resistances R3, R4, and R5 of threshold output unit 61 are different in magnitude. In FIGS. 34 and 37, R1=R2 and R1, R2>>R3, R4, and R5 (first resistance condition). In FIGS. 35 and 38, R1=R2 and R1, R2≈R3, R4, and R5 (second resistance condition). In FIGS. 36 and 39, R1>>R3, R4, and R5 and R2≈R3, R4, and R5 (third resistance condition).

[0106] The relationship between the positive-side overcurrent threshold Vthp and the adjustment source voltage Vsp is shown as positive-side overcurrent threshold characteristics 96a, 96b, 96c, 96d, 96e, and 96f. The relationship between the negative-side overcurrent threshold Vthn and the adjustment source voltage Vsn is shown as negative-side overcurrent threshold characteristics 97a, 97b, 97c, 97d, 97e, and 97f. The adjustment source voltage Vsn in Figures 37 to 39 is the voltage obtained by subtracting the adjustment source voltage Vsp from the maximum voltage value Vsa.

[0107] The power conversion device 100 of the third embodiment can reduce the overcurrent flowing through the power semiconductor elements 3a to 3f when the power conversion device 100 performs an overcurrent protection operation for the power semiconductor elements 3a to 3f, similar to the power conversion devices 100 of the first and second embodiments. Moreover, in the power conversion device 100 of the third embodiment, the protection circuit 59 of the overcurrent protection circuit 41 does not include the smoothing circuits 65a, 65b, 65, and 66, so that the overcurrent protection circuit 41 can be made smaller than that of the power conversion device 100 of the second embodiment.

[0108] The analog correction command signal sc can also be applied to the power conversion device 100 of the first embodiment. In this case, threshold voltage adjustment unit 60 of the first embodiment shown in FIG. 5 receives a positive correction command signal of the analog correction command signal sc from input terminal 49p and a negative correction command signal of the analog correction command signal sc from input terminal 49n, similar to threshold voltage adjustment unit 60 of the third embodiment. The positive correction command signal corresponds to adjustment source voltage Vsp of the second embodiment, and the negative correction command signal corresponds to adjustment source voltage Vsn of the second embodiment. Adjustment source voltage Vsp is output from output terminal 43p as positive-side regulated voltage Vap via resistor R1, and adjustment source voltage Vsn is output from output terminal 43n as negative-side regulated voltage Van via resistor R2.

[0109] Embodiment 4 FIG. 40 is a diagram showing the configuration of a first drive circuit according to embodiment 4, and FIG. 41 is a diagram showing the configuration of the overcurrent protection circuit of FIG. 40. FIG. 42 is a diagram showing the configuration of a second drive circuit according to embodiment 4, and FIG. 43 is a diagram showing the configuration of the overcurrent protection circuit of FIG. 42. FIG. 44 is a diagram showing an example of correction of the overcurrent threshold of the overcurrent protection circuit of FIG. 43, and FIG. 45 is a diagram showing an example of correction of the overcurrent threshold of the overcurrent protection circuit of FIG. 41. In the power conversion device 100 of embodiment 2, an example has been described in which the control unit 10 outputs a correction command signal sc for each phase of a three-phase AC, i.e., three correction command signals scu, scv, and scw. The power conversion device 100 of embodiment 4 is an example in which the number of correction command signals sc of the control unit 10 is reduced compared to the power conversion device 100 of embodiment 2. The power conversion device 100 of the fourth embodiment differs from the power conversion device 100 of the second embodiment in that the overcurrent protection circuit 41 includes six comparators 42a to 42f corresponding to the positive and negative sides of each phase, one threshold output unit 61, and one threshold voltage adjustment unit 60. The following mainly describes the parts that differ from the power conversion device 100 of the second embodiment.

[0110] The components of the power conversion device 100 of the fourth embodiment are the same as the components of the power conversion device 100 of the first embodiment shown in FIGS. 1 and 14. However, a first drive circuit 14 is shown when the control unit 10 outputs one correction command signal sc, and a second drive circuit 14 is shown when the control unit 10 outputs two correction command signals sc. The control unit 10 and the first drive circuit 14 shown in FIG. 40 are an example in which the control unit 10 outputs one correction command signal sc to the first drive circuit 14 from one output terminal 26. The control unit 10 and the second drive circuit 14 shown in FIG. 42 are an example in which the control unit 10 outputs correction command signals scp and scn to the first drive circuit 14 from two output terminals 26a and 26b, respectively. The power conversion device 100 of the fourth embodiment achieves the same effects as the power conversion devices 100 of the first and second embodiments, and can reduce power consumption due to the reduction in the number of output terminals of the control unit 10, thereby enabling a reduction in the cost of the control unit 10.

[0111] The overcurrent protection circuit 41 of the first drive circuit 14 includes input terminals 48a, 48b, 48c to which detection voltages Viu, Viv, Viw of current sensors 21a-21c of the respective phases are input, an input terminal 27 to which a correction command signal sc is input, and output terminals 47a-47f to which six overcurrent stop signals st are output. The U-phase overcurrent stop signals stup, stun are output from the output terminals 47a, 47b, the V-phase overcurrent stop signals stvp, stvn are output from the output terminals 47c, 47d, and the W-phase overcurrent stop signals stwp, stwn are output from the output terminals 47e, 47f. The overcurrent protection circuit 41 of the second drive circuit 14 includes input terminals 48a, 48b, and 48c to which the detection voltages Viu, Viv, and Viw of the current sensors 21a to 21c of the respective phases are input, input terminals 27a and 27b to which the positive-side correction command signal scp and the negative-side correction command signal scn are input, respectively, and output terminals 47a to 47f for outputting six overcurrent stop signals st. The U-phase overcurrent stop signals stup and stun are output from the output terminals 47a and 47b, the V-phase overcurrent stop signals stvp and stvn are output from the output terminals 47c and 47d, and the W-phase overcurrent stop signals stwp and stwn are output from the output terminals 47e and 47f.

[0112] As shown in FIG. 41, the configuration of the first drive circuit 14 is such that the threshold voltage adjuster 60 is the same as the threshold voltage adjuster 60 in the second protection circuit 59 shown in FIG. 18, and the overcurrent stop signal output unit 62 includes six comparators 42a-42f and one threshold output unit 61. The positive overcurrent threshold Vthp output from the threshold output unit 61 is input to the positive terminals of the comparators 42a-42f. The detection voltage Viu output from the current sensor 21a is input from an input terminal 48a to the negative terminals of the comparators 42a and 42b. The detection voltage Viv output from the current sensor 21b is input from an input terminal 48b to the negative terminals of the comparators 42c and 42d. The detection voltage Viw output from the current sensor 21c is input from an input terminal 48c to the negative terminals of the comparators 42e and 42f. Threshold voltage adjusting section 60 and threshold output section 61 in first driving circuit 14 are the same as second protection circuit 59 of the second embodiment shown in FIG. 18, and therefore description thereof will not be repeated.

[0113] As shown in Fig. 43, the second drive circuit 14 has a configuration in which the threshold voltage adjuster 60 includes two smoothing circuits 65a and 65b similar to those of the first protection circuit 59 shown in Fig. 17, and the overcurrent stop signal output unit 62 includes six comparators 42a to 42f and two threshold output units 61a and 61b. The smoothing circuits 65a and 65b in the second drive circuit 14 of the fourth embodiment differ from the smoothing circuits 65a and 65b shown in Fig. 17 in that a positive-side correction command signal scp is input from an input terminal 27a and a negative-side correction command signal scn is input from an input terminal 27b, respectively. The correction command signal scp is a pulse signal Vpi1 having a duty ratio Du, and the correction command signal scn is a pulse signal Vpi2 having a duty ratio Du. Because the duty ratio Du of pulse signal Vpi1 and the duty ratio Du of pulse signal Vpi2 can be changed independently, the regulated voltage Vsp output by smoothing circuit 65a and the regulated voltage Vsn output by smoothing circuit 65b can be independent voltages. The regulated voltage Vsp output from the output point (connection point n1) of smoothing circuit 65a is output as a positive-side regulated voltage Vap (see FIG. 5) from output terminal 43p via resistor R1. The regulated voltage Vsn output from the output point of smoothing circuit 65b (connection point n2) is output as a negative-side regulated voltage Van (see FIG. 5) from output terminal 43n via resistor R2.

[0114] The threshold output unit 61a is connected to a wiring that connects an output terminal 43p of the threshold voltage adjuster 60 and the positive terminals of the positive-side comparators 42a, 42c, and 42e of each phase, and the threshold output unit 61b is connected to a wiring that connects an output terminal 43n of the threshold voltage adjuster 60 and the positive terminals of the negative-side comparators 42b, 42d, and 42f of each phase. The threshold output unit 61a is a series body in which a plurality of resistors Ra1 and Ra2 are connected in series between a power supply voltage Vpp generated inside the power conversion device 100 and the ground GND, and a connection point na between the resistors Ra1 and Ra2 is connected to the output terminal 43p and the positive terminals of the positive-side comparators 42a, 42c, and 42e of each phase. The threshold output unit 61b is a series circuit in which multiple resistors Ra3 and Ra4 are connected in series between a power supply voltage Vpp generated inside the power conversion device 100 and ground GND. A junction point nb between the resistors Ra3 and Ra4 is connected to an output terminal 43n and the positive terminals of the negative-side comparators 42b, 42d, and 42f. The detection voltage Viu output from the current sensor 21a is input to the negative terminals of the comparators 42a and 42b via an input terminal 48a. The detection voltage Viv output from the current sensor 21b is input to the negative terminals of the comparators 42c and 42d via an input terminal 48b. The detection voltage Viw output from the current sensor 21c is input to the negative terminals of the comparators 42e and 42f via an input terminal 48c. Ground GND serves as a reference voltage for the overcurrent protection circuit 41. The value of the power supply voltage Vpp is a predetermined constant value. The positive overcurrent threshold Vthp changes according to the value of the positive regulated voltage Vap output from the threshold voltage adjusting unit 60. The negative overcurrent threshold Vthn changes according to the value of the negative regulated voltage Van output from the threshold voltage adjusting unit 60.

[0115] As described above, the variations in the current sensors 21a to 21c can be corrected by one correction command signal sc or two correction command signals sc. In Fig. 41, an example including an inverter 63 is shown as a representative example of the threshold voltage adjusting unit 60, but the threshold voltage adjusting unit 60 of the first protection circuit 59 shown in Fig. 17 may also be used.

[0116] A method for correcting the positive-side overcurrent threshold Vthp and the negative-side overcurrent threshold Vthn of the overcurrent protection circuit 41 according to the fourth embodiment and the operation of the power conversion device 100 according to the fourth embodiment will be described with reference to FIGS. 44 and 45. FIGS. 44 and 45 show sensor characteristics 57a, 57b, and 57c of the current sensors 21a to 21c. In FIGS. 44 and 45, the horizontal axis represents current and the vertical axis represents voltage. Sensor characteristic 57a is the sensor characteristic of the U-phase current sensor 21a, sensor characteristic 57b is the sensor characteristic of the V-phase current sensor 21b, and sensor characteristic 57c is the sensor characteristic of the W-phase current sensor 21c. The sensor characteristics 57a, 57b, and 57c differ in voltage values ​​that result in the positive-side overcurrent setting value Iocp and the negative-side overcurrent setting value Iocn. The sensor characteristics 57a, 57b, and 57c also serve as the corrected sensor characteristics 55 for each phase. The voltage values ​​at reference point P1 of sensor characteristic 57a, reference point P2 of sensor characteristic 57b, and reference point P3 of sensor characteristic 57c, which correspond to the positive overcurrent setting value Iocp, are thresholds Vth1, Vth2, and Vth3, respectively. The voltage values ​​at reference point P4 of sensor characteristic 57b, reference point P5 of sensor characteristic 57a, and reference point P6 of sensor characteristic 57c, which correspond to the negative overcurrent setting value Iocn, are thresholds Vth4, Vth5, and Vth6, respectively. The order of reference points P1, P2, and P3 is determined by the order of decreasing voltage values ​​at the positive overcurrent setting value Iocp. The order of reference points P4, P5, and P6 is determined by the order of decreasing voltage values ​​at the negative overcurrent setting value Iocn. The positive overcurrent threshold and negative overcurrent threshold at the time of design are Vth0p and Vth0n, respectively. In the sensor characteristics of current sensors 21a to 21c for each phase, if an overcurrent is determined using the positive overcurrent threshold Vth0p and negative overcurrent threshold Vth0n as designed, a positive overcurrent will be a current that greatly exceeds the positive overcurrent setting value Iocp, and a negative overcurrent will be a current that greatly exceeds the negative overcurrent setting value Iocn. Therefore, in order for a positive overcurrent to be determined using the positive overcurrent setting value Iocp and a negative overcurrent to be determined using the negative overcurrent setting value Iocn, the thresholds of current sensors 21a to 21c must be corrected.

[0117] The first overcurrent protection circuit 41 of the fifth embodiment shown in FIG. 41 and the second overcurrent protection circuit 41 of the fifth embodiment shown in FIG. 43 determine positive overcurrents in the current sensors 21a-21c using a common positive overcurrent threshold Vthp, and determine negative overcurrents in the current sensors 21a-21c using a common negative overcurrent threshold Vthn. As described in the second embodiment, for example, assume that the positive overcurrent threshold Vthap on the positive side of the overcurrent is adjusted to match the V or W phase rather than the U phase, which has a smaller correction amount. In this case, as can be seen from the U-phase sensor characteristic 57a in FIG. 44, the voltage of the threshold Vth2 or Vth3 is reached at a current lower than the positive overcurrent setting value Iocp in the U phase, which may cause the U-phase power semiconductor device 3a to stop operating within its normal operating range. Similarly, assume that the negative overcurrent threshold Vthan on the negative side of the overcurrent is adjusted to match the U or V phase rather than the W phase, which has a smaller correction amount. In this case, as can be seen from the W-phase sensor characteristic 57c in FIG. 44, the W-phase voltage reaches threshold value Vth5 or threshold value Vth4 at a current lower than the negative overcurrent setting value Iocn, potentially causing the U-phase power semiconductor device 3a to shut down within its normal operating range. Therefore, the positive-side overcurrent threshold Vthap and the negative-side overcurrent threshold Vthan, which are the reference values ​​for overcurrent determination, are selected from the sensor characteristics of the current sensors with the smallest correction amounts on the positive and negative sides, respectively. In the example of FIG. 44, the U-phase has the highest threshold value Vth1 in the positive-side overcurrent setting value Iocp, and the W-phase has the lowest threshold value Vth6 in the negative overcurrent setting value Iocn. Therefore, the positive-side overcurrent threshold Vthap is corrected to threshold value Vth1, and the negative-side overcurrent threshold Vthan is corrected to threshold value Vth6. In FIG. 44, the voltage correction amount for the positive-side overcurrent threshold Vthp is voltage correction amount 89a, and the voltage correction amount for the negative overcurrent threshold Vthn is voltage correction amount 89c. In FIG. 45, the voltage correction amount for the positive overcurrent threshold Vthp is a voltage correction amount 89a, and the voltage correction amount for the negative overcurrent threshold Vthn is a voltage correction amount 89b.

[0118] Figure 44 corresponds to the correction method in the second overcurrent protection circuit 41 in Figure 43, and Figure 45 corresponds to the correction method in the first overcurrent protection circuit 41 in Figure 41. The difference between Figure 44 and Figure 45 is whether the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn are independently adjustable or whether the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn are related to each other, and therefore the voltage correction amount for the positive side overcurrent threshold Vthp and the voltage correction amount for the negative side overcurrent threshold Vthn are different. Figure 44 shows an example in which the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn are independently adjustable, and therefore the voltage correction amount 89a for the positive side overcurrent threshold Vthp and the voltage correction amount 89c for the negative side overcurrent threshold Vthn are different. In Fig. 45, since the positive side overcurrent threshold Vthp and the negative side overcurrent threshold Vthn are related to each other, an example is shown in which the magnitude of the voltage correction amount 89a for the positive side overcurrent threshold Vthp is the same as the magnitude of the voltage correction amount 89c for the negative side overcurrent threshold Vthn. Note that in Fig. 45, the positive side threshold settable range 39a, the negative side threshold settable range 39b, the lower limit positive side overcurrent threshold Vthpmin, and the upper limit negative side overcurrent threshold Vthnmax are omitted.

[0119] In the power conversion device 100 equipped with the first overcurrent protection circuit 41 of the fifth embodiment shown in Fig. 41, in the case of the sensor characteristics 57a, 57b, and 57c shown in Fig. 44 and Fig. 45, the value of the duty ratio Du of the pulse signal Vpi, which is the correction command signal sc, is adjusted to match the smaller of the positive side correction amount and the negative side correction amount, or the limit value correction amount, as in the second correction example of the second embodiment. When applying the method of the second correction example of the second embodiment, the symbols used in Figs. 29 to 31 are used.

[0120] The operation of generating the correction command signal sc of the power conversion device 100 including the first overcurrent protection circuit 41 of the fifth embodiment shown in Fig. 41 will be described. The control unit 10 stores the following voltage correction amount data. This voltage correction amount data includes first characteristic data (sensor characteristics 57a, 57b, 57c) of the output voltage versus the current detected by the current sensors 21a to 21c for each phase, which is measured in advance, first threshold data (positive side overcurrent threshold characteristic 94b) of the positive side overcurrent threshold voltage (positive side overcurrent threshold Vthap) versus the duty ratio Du at the positive side overcurrent setting value (positive side overcurrent setting value Iocp), and second threshold data (negative side overcurrent threshold characteristic 95b) of the negative side overcurrent threshold voltage (negative side overcurrent threshold Vthan) versus the duty ratio Du at the negative side overcurrent setting value (negative side overcurrent setting value Iocn).

[0121] The control unit 10 calculates a first overcurrent threshold V1, which is a positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp) for each phase relative to a positive-side overcurrent setting value (positive-side overcurrent setting value Iocp), from the first characteristic data (sensor characteristics 57a, 57b, 57c) within a positive-side settable range (threshold setting range 39a). The control unit 10 also calculates a second overcurrent threshold V2, which is a negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn) for each phase relative to a negative-side overcurrent setting value (negative-side overcurrent setting value Iocn), from the first characteristic data (sensor characteristics 57a, 57b, 57c) within a negative-side settable range (threshold setting range 39b). The first overcurrent threshold V1 is obtained by adding a voltage correction amount 86a to the positive-side overcurrent threshold Vth0p, and the second overcurrent threshold V2 is obtained by subtracting a voltage correction amount 86b from the negative-side overcurrent threshold Vth0n.

[0122] Thereafter, the control unit 10 calculates a first voltage correction amount ΔV1, which is a voltage correction amount for the calculated first overcurrent threshold V1, and a second voltage correction amount ΔV2, which is a voltage correction amount for the calculated second overcurrent threshold V2. When generating the correction command signal sc, in the case of condition A where the three (U-phase, V-phase, W-phase) first overcurrent thresholds V1 include the limit value (lower-limit positive overcurrent threshold Vthpmin) of the positive-side settable range (threshold settable range 39a) or the three (U-phase, V-phase, W-phase) second overcurrent thresholds V2 include the limit value (upper-limit negative overcurrent threshold Vthnmax) of the negative-side settable range (threshold settable range 39b), the control unit 10 determines the value of the duty ratio Du of the pulse signal Vpi, which is the correction command signal sc, to be the selected duty ratio value ds as follows:

[0123] If one of the three (U phase, V phase, W phase) first overcurrent thresholds V1 and the three (U phase, V phase, W phase) second overcurrent thresholds V2 is a limit value, the value of the duty ratio Du derived based on the limit value and one of the first threshold data (positive side overcurrent threshold characteristic 94b) and second threshold data (negative side overcurrent threshold characteristic 95b) corresponding to the limit value is determined to be the selected duty ratio value ds. Furthermore, if two or more of the three (U phase, V phase, W phase) first overcurrent thresholds V1 and three (U phase, V phase, W phase) second overcurrent thresholds V2 are limit values, the limit value corresponding to the smallest of the first voltage correction amount ΔV1 or second voltage correction amount ΔV2 corresponding to the candidate limit value is set as the selected limit value, and the value of the duty ratio Du derived based on the selected limit value and one of the first threshold data (positive side overcurrent threshold characteristic 94b) and second threshold data (negative side overcurrent threshold characteristic 95b) corresponding to the selected limit value is determined as the selected duty ratio value ds.

[0124] In the case of a condition B other than the condition A, in which the first voltage correction amount ΔV1 for the three phases (U phase, V phase, W phase) and the second voltage correction amount ΔV2 for the three phases (U phase, V phase, W phase) are not the same, the control unit 10 sets the smallest correction amount (the first voltage correction amount ΔV1 in FIG. 30) as the selected voltage correction amount ΔVs, and determines the value of the duty ratio Du derived based on the selected voltage correction amount ΔVs and one (the positive side overcurrent threshold characteristic 94b in FIG. 30) of the first threshold data (positive side overcurrent threshold characteristic 94b) and the second threshold data (negative side overcurrent threshold characteristic 95b) corresponding to the selected voltage correction amount ΔVs as the selected duty ratio value ds.

[0125] In the case of condition C, other than condition A and condition B, in which the first voltage correction amount ΔV1 for the three phases (U, V, and W) and the second voltage correction amount ΔV2 for the three phases (U, V, and W) are the same, the control unit 10 compares a first duty ratio value da1, which is the value of the duty ratio Du derived based on the first voltage correction amount ΔV1 and the first threshold data (positive-side overcurrent threshold characteristic 94b), with a second duty ratio value da2, which is the value of the duty ratio Du derived based on the second voltage correction amount ΔV2 and the second threshold data (negative-side overcurrent threshold characteristic 95b). If the first duty ratio value da1 and the second duty ratio value da2 are the same, the control unit 10 determines the duty ratio Du as the selected duty ratio value ds. If the first duty ratio value da1 and the second duty ratio value da2 are different, the control unit 10 compares a third voltage correction amount ΔV3, which is a voltage correction amount calculated from the voltage value V2a of the second threshold data (negative-side overcurrent threshold characteristic 95b) for the first duty ratio value da1, with a fourth voltage correction amount ΔV4, which is a voltage correction amount calculated from the voltage value of the first threshold data (positive-side overcurrent threshold characteristic 94b) for the second duty ratio value da2, and determines the duty ratio value resulting in a smaller correction amount (the first duty ratio value da1 in FIG. 31) as the selected duty ratio value ds. The control unit 10 generates a pulse signal Vpi having the determined selected duty ratio value ds as the correction command signal sc.

[0126] The operation of generating the correction command signal sc, i.e., the positive-side correction command signal scp and the negative-side correction command signal scn, of the power conversion device 100 including the second overcurrent protection circuit 41 of the fifth embodiment shown in Fig. 43 will be described. The control unit 10 stores the following voltage correction amount data. This voltage correction amount data includes first characteristic data (sensor characteristics 57a, 57b, 57c) of the output voltage versus current detected by the current sensors 21a to 21c for each phase, which is measured in advance; first threshold data (positive-side overcurrent threshold characteristic 94b) of the positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthap) versus the duty ratio Du at the positive-side overcurrent setting value (positive-side overcurrent setting value Iocp); and second threshold data (negative-side overcurrent threshold characteristic 95b) of the negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthan) versus the duty ratio Du at the negative-side overcurrent setting value (negative-side overcurrent setting value Iocn). The duty ratio Du of the positive-side correction command signal scp and the duty ratio Du of the negative-side correction command signal scn can be changed independently. The positive-side overcurrent thresholds Vthp for the U, V, and W phases are set to the same value by the positive-side correction command signal scp, so the first threshold data has one positive-side overcurrent threshold characteristic 94b common to the U, V, and W phases. Similarly, the negative-side overcurrent thresholds Vthn for the U, V, and W phases are set to the same value by the negative-side correction command signal scn, so the second threshold data has one negative-side overcurrent threshold characteristic 95b common to the U, V, and W phases.

[0127] The control unit 10 calculates, for each phase, a first overcurrent threshold V1, which is a positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthp) for a positive-side overcurrent setting value (positive-side overcurrent setting value Iocp), from the first characteristic data (sensor characteristics 57a, 57b, 57c) within a positive-side settable range (threshold setting range 39a). The control unit 10 also calculates, for each phase, a negative-side overcurrent threshold voltage (negative-side overcurrent threshold Vthn) for a negative-side overcurrent setting value (negative-side overcurrent setting value Iocn) from the first characteristic data (sensor characteristics 57a, 57b, 57c) within a negative-side settable range (threshold setting range 39b). The first overcurrent threshold V1 is obtained by adding a voltage correction amount 86a to the positive-side overcurrent threshold Vth0p. If the first overcurrent threshold V1 exceeds the limit of the positive-side settable range (threshold setting range 39a), the first overcurrent threshold V1 is set to a lower-limit positive-side overcurrent threshold Vthpmin. Similarly, on the negative side, the second overcurrent threshold V2 is obtained by subtracting the voltage correction amount 86b from the negative overcurrent threshold Vth0n, but if it exceeds the limit value of the negative settable range (threshold settable range 39b), it is set to the upper limit negative overcurrent threshold Vthnmax.

[0128] In the example of Figure 44, the lower limit positive side overcurrent threshold Vthpmin is between reference point P2 and reference point P3, and the positive side threshold settable range 39a is set between the initial positive side overcurrent threshold Vth0p and the lower limit positive side overcurrent threshold Vthpmin. Furthermore, the upper limit negative side overcurrent threshold Vthnmax is between reference point P5 and reference point P6, and the negative side threshold settable range 39b is set between the initial negative side overcurrent threshold Vth0n and the upper limit negative side overcurrent threshold Vthnmax. In the example of Figure 44, when determining the first overcurrent threshold V1, the control unit 10 sets the first overcurrent threshold V1 for the W phase to the lower limit positive side overcurrent threshold Vthpmin because the W phase reference point P3 exceeds the positive side threshold settable range 39a. In addition, when determining the second overcurrent threshold V2, the control unit 10 sets the second overcurrent threshold V2 of the U phase and the second overcurrent threshold V2 of the V phase as the upper limit negative overcurrent threshold Vthnmax because the U phase reference point P5 and the V phase reference point P4 exceed the negative threshold settable range 39b.

[0129] The control unit 10 calculates, for each phase, a first voltage correction amount ΔV1, which is a voltage correction amount relative to the calculated first overcurrent threshold V1, and a second voltage correction amount ΔV2, which is a voltage correction amount relative to the calculated second overcurrent threshold V2. In the example of FIG. 44, the first voltage correction amount ΔV1 and the second voltage correction amount ΔV2 are calculated as follows: On the positive side, the control unit 10 calculates the first voltage correction amount ΔV1 for the U phase as Vth0p-Vth1, the first voltage correction amount ΔV1 for the V phase as Vth0p-Vth2, and the first voltage correction amount ΔV1 for the W phase as Vth0p-Vthpmin. On the negative side, the control unit 10 calculates the second voltage correction amount ΔV2 for the U and V phases as |Vth0n-Vthnmax|, and the second voltage correction amount ΔV2 for the W phase as |Vth0n-Vth6|. In FIG. 44, since the initial negative overcurrent threshold Vth0n is lower than the upper limit negative overcurrent threshold Vthnmax and the threshold Vth6, an absolute value is used in the explanation of the calculation of the second voltage correction amount ΔV2.

[0130] When generating the first correction command signal scp, which is the positive-side correction command signal sc, the control unit 10 determines the smallest correction amount among the three first voltage correction amounts ΔV1 as the selected voltage correction amount ΔVs, and determines the value of the duty ratio Du derived based on the selected voltage correction amount ΔVs and the first threshold data (positive-side overcurrent threshold characteristic 94b) corresponding to the selected voltage correction amount ΔVs as the first selected duty ratio value (selected duty ratio value ds). In the example of FIG. 44, the positive-side selected voltage correction amount ΔVs is the first voltage correction amount ΔV1 of the U phase calculated using Vth0p-Vth1, which is the voltage correction amount 89a. The control unit 10 generates a pulse signal Vpi1 having the determined first selected duty ratio value (selected duty ratio value ds) as the first correction command signal scp.

[0131] When generating the second correction command signal scn, which is the negative-side correction command signal sc, the control unit 10 determines the smallest correction amount among the three second voltage correction amounts ΔV2 as the selected voltage correction amount ΔVs, and determines the value of the duty ratio Du derived based on the selected voltage correction amount ΔVs and the second threshold data (negative-side overcurrent threshold characteristic 95b) corresponding to the selected voltage correction amount ΔVs as the second selected duty ratio value (selected duty ratio value ds). In the example of FIG. 44, the negative-side selected voltage correction amount ΔVs is the second voltage correction amount ΔV2 of the W phase calculated using |Vth0n-Vth6|, which is the voltage correction amount 89c. The control unit 10 generates a pulse signal Vpi2 having the determined second selected duty ratio value (selected duty ratio value ds) as the second correction command signal scn.

[0132] Embodiment 5 FIG. 46 is a diagram showing the configuration of a first drive circuit according to a fifth embodiment, and FIG. 47 is a diagram showing the configuration of the protection circuit of FIG. 46. FIG. 48 is a diagram showing the configuration of a second drive circuit according to the fifth embodiment, and FIG. 49 is a diagram showing the configuration of the overcurrent protection circuit of FIG. 48. Even if there is variation in the current sensors 21a to 21c, the power conversion device 100 according to the first to fourth embodiments can reduce the overcurrent flowing through the power semiconductor elements 3a to 3f during overcurrent protection operation by correcting the overcurrent thresholds (positive-side overcurrent threshold Vthp and negative-side overcurrent threshold Vthn) used to determine the overcurrent and bringing the current flowing during overcurrent protection closer to the design value. However, due to malfunction of the control unit 10 caused by noise or variation in the internal circuit of the control unit 10, the corrected command signal sc output from the control unit 10 may deviate from the set value, have an increased error, or become an unexpected value. Furthermore, due to variation in the threshold voltage adjustment unit 60, the overcurrent threshold may become a value different from the expected value, i.e., a value different from the design value. In this case, if the overcurrent threshold value becomes a value different from the expected value, i.e., a value different from the design value, the effect of the power conversion device 100 of Embodiments 1 to 4 may be reduced. In Embodiment 5, an example will be described in which the normal operation of the overcurrent protection circuit 41 is confirmed by detecting the voltages of the overcurrent thresholds (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn), and the voltages of the overcurrent thresholds (positive side overcurrent threshold Vthp, negative side overcurrent threshold Vthn) can be maintained within the allowable range.

[0133] The components of the power conversion device 100 of the fifth embodiment are the same as those of the power conversion device 100 of the first embodiment shown in FIGS. 1 and 14. The power conversion device 100 of the fifth embodiment differs from the power conversion devices 100 of the first to fourth embodiments in that the overcurrent protection circuit 41 includes a voltage detection circuit 70 that detects the voltage of at least one overcurrent threshold (positive overcurrent threshold Vthp, negative overcurrent threshold Vthn), and the control unit 10 adjusts the correction command signal sc using threshold detection voltage information Vm output from the voltage detection circuit 70. The following mainly describes the differences from the power conversion devices 100 of the first to fourth embodiments. As a representative example, an example will be described in which the correction command signal sc is a pulse signal Vpi having a duty ratio Du. Examples of the first drive circuit 14 and the second drive circuit 14 of the fifth embodiment will be described below.

[0134] The overcurrent protection circuit 41 in the first drive circuit 14 of the fifth embodiment shown in Figures 46 and 47 includes a U-phase protection circuit 59u, a V-phase protection circuit 59v, and a W-phase protection circuit 59w, similar to the overcurrent protection circuit 41 in the second embodiment. The overcurrent protection circuit 41 in the second drive circuit 14 of the fifth embodiment shown in Figures 48 and 49 includes six comparators 42a to 42f, one threshold output unit 61, and one threshold voltage adjuster 60, corresponding to the positive and negative sides of each phase, similar to the overcurrent protection circuit 41 in the fourth embodiment.

[0135] First, the first drive circuit 14 of the fifth embodiment will be described. The first drive circuit 14 of the fifth embodiment is an example modified from the drive circuit 14 and protection circuit 59 shown in FIGS. 16 and 18. Differences from the drive circuit 14 and protection circuit 59 shown in FIGS. 16 and 18 will be mainly described. The U-phase protection circuit 59u, the V-phase protection circuit 59v, and the W-phase protection circuit 59w each include a voltage detection circuit 70 that detects at least one overcurrent threshold, for example, a positive-side overcurrent threshold Vthp, and outputs the detected voltage Vm0 as threshold detection voltage information Vm. The monitor point nm to which the voltage detection circuit 70 is connected is provided on the wiring connecting the connection point n3 of the threshold output unit 61 and the positive terminal of the positive-side comparator 42p. For example, the voltage detection circuit 70 is an AD converter. In this case, the voltage detection circuit 70 converts the detected voltage Vm0, which is an analog signal, into threshold detection voltage information Vm, which is a digital signal, and outputs the threshold detection voltage information Vm from the output terminal 71 of the protection circuit 59 to the control unit 10. The control unit 10 receives U-phase threshold detection voltage information Vmu from input terminal 72a, V-phase threshold detection voltage information Vmv from input terminal 72b, and W-phase threshold detection voltage information Vmw from input terminal 72c. Where appropriate, the threshold detection voltage information will be generically referred to as Vm, and will be distinguished by Vmu, Vmv, and Vmw.

[0136] The control unit 10 corrects the voltage correction amount 86a (see FIG. 13) so as to reduce the difference between the voltage indicated by the threshold detection voltage information Vm (detection voltage Vm0) and the overcurrent threshold voltage (positive overcurrent threshold Vthap) calculated from the voltage correction amount 86a, and adjusts the duty ratio Du of the pulse signal Vpi based on the corrected voltage correction amount 86a. The control unit 10 also adjusts the duty ratio Du of the pulse signal Vpi so as to reduce the difference between the positive overcurrent threshold voltage (positive overcurrent threshold Vthap) calculated from the first characteristic data (corrected sensor characteristic 55) (see FIG. 13) and the voltage indicated by the threshold detection voltage information Vm (detection voltage Vm0) or to keep the difference within a predetermined difference range. The difference range is an allowable difference range.

[0137] In the example of the overcurrent protection circuit 41 in the first drive circuit 14 of embodiment 5, the voltage detection circuit 70 detects the voltages of the positive-side overcurrent threshold Vthap for the U phase, V phase, and W phase. However, the voltage detection circuit 70 may also detect the voltages of the negative-side overcurrent threshold Vthan for the U phase, V phase, and W phase.

[0138] Next, a second drive circuit 14 according to a fifth embodiment will be described. The second drive circuit 14 according to the fifth embodiment is an example modified from the drive circuit 14 and overcurrent protection circuit 41 shown in FIGS. 40 and 41. Differences from the drive circuit 14 and overcurrent protection circuit 41 shown in FIGS. 40 and 41 will be mainly described. The overcurrent protection circuit 41 includes a voltage detection circuit 70 that detects at least one overcurrent threshold, for example, a positive overcurrent threshold Vthp, and outputs the detected voltage Vm0 as threshold detection voltage information Vm. The monitor point nm to which the voltage detection circuit 70 is connected is provided on the wiring connecting the connection point n3 of the threshold output unit 61 to the positive terminals of the positive-side comparators 42a, 42c, and 42e. For example, the voltage detection circuit 70 is an AD converter. In this case, the voltage detection circuit 70 converts the detected voltage Vm0, which is an analog signal, into threshold detection voltage information Vm, which is a digital signal, and outputs the threshold detection voltage information Vm from an output terminal 71 of the overcurrent protection circuit 41 to the control unit 10. The control unit 10 receives the threshold detection voltage information Vm from the input terminal 72 .

[0139] The control unit 10 corrects a voltage correction amount 89a (see FIG. 44) corresponding to a positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthap) so as to reduce the difference between the voltage (detection voltage Vm0) indicated by the threshold detection voltage information Vm, and adjusts the duty ratio Du of the pulse signal Vpi based on the corrected voltage correction amount 89a. The control unit 10 also adjusts the duty ratio Du of the pulse signal Vpi so as to reduce the difference between the positive-side overcurrent threshold voltage (positive-side overcurrent threshold Vthap) determined based on the first characteristic data (sensor characteristics 57a, 57b, 57c) of each phase and the voltage (detection voltage Vm0) indicated by the threshold detection voltage information Vm, or so as to fall within a predetermined difference range.

[0140] In the example of the overcurrent protection circuit 41 in the second drive circuit 14 of embodiment 5, the voltage detection circuit 70 detects the voltage of the positive-side overcurrent threshold Vthap common to the U phase, V phase, and W phase. However, the voltage detection circuit 70 may also detect the voltage of the negative-side overcurrent threshold Vthan common to the U phase, V phase, and W phase.

[0141] In the past, when input terminals 72, 72a to 72c for inputting threshold detection voltage information Vm, Vmu, Vmv, and Vmw were provided in control unit 10, a large number of input terminals for inputting threshold detection voltage information Vm were required in the case of a full-bridge inverter circuit or the like because the input terminals were also provided on the positive and negative sides (conventional example). However, in the control unit 10 of the power conversion device 100 according to the second and fourth embodiments, the number of output terminals for outputting correction command signals sc can be reduced. Therefore, even if the voltage detection circuit 70 described in the power conversion device 100 according to the fifth embodiment is provided, the increase in the number of wirings connecting overcurrent protection circuit 41 and control unit 10 can be reduced compared to the conventional example, where the number of wirings is the same as the number of input terminals for inputting threshold detection voltage information. This makes it possible to monitor whether the overcurrent protection circuit 41 is functioning normally from the threshold detection voltage information Vm while preventing the control unit 10 and the overcurrent protection circuit 41 from becoming large and complex. As a result, even if the overcurrent threshold deviates due to a deviation in the correction command signal sc of the control unit 10, variations in the threshold voltage adjustment unit 60, etc., the control unit 10 can adjust the duty ratio Du of the pulse signal Vpi using the threshold detection voltage information Vm of the voltage detection circuit 70 so that the overcurrent threshold falls within a predetermined difference range.

[0142] In the power conversion device 100 of the fifth embodiment, the ground GND of the overcurrent protection circuit 41 and the ground GND of the control unit 10 are common, so an isolation amplifier is not required. While the example in which the voltage detection circuit 70 is provided in the overcurrent protection circuit 41 has been described, the control unit 10 may also include an AD converter, and the threshold detection voltage information Vm may be generated by the AD converter of the control unit 10. When the control unit 10 includes an AD converter, if the ground GND of the overcurrent protection circuit 41 and the ground GND of the control unit 10 are different, the ground GND of the overcurrent protection circuit 41 and the ground GND of the control unit 10 are separated by an isolation amplifier or the like to prevent noise leakage. If the analog signal line from the monitor point nm to the AD converter of the control unit 10 is long, a noise-cutting RC filter may be provided in the area of ​​the voltage detection circuit 70 shown in Figures 47 and 49.

[0143] In each embodiment, the sensor characteristics of current sensors 21a-21c are shown as an example in which the output voltage increases as the current value goes from negative to positive, i.e., the slope of the sensor characteristics is positive, but this is not limited thereto and the output voltage may also increase as the current value goes from positive to negative, i.e., the slope of the sensor characteristics may be negative. Even in this case, the threshold voltage adjuster 60 of overcurrent protection circuit 41 corrects the deviation of the overcurrent threshold value associated with the deviation of current sensors 21a-21c when an overcurrent occurs, thereby achieving the same effect as that of power conversion device 100 of the embodiment.

[0144] 18, 41, 47, and 49 show an example in which the correction command signal sc is input via the inverter 63 to the smoothing circuit 66 that generates the negative adjustment source voltage Vsn, but the present invention is not limited to this, and the correction command signal sc may be input via the inverter 63 to the smoothing circuit 65 that generates the positive adjustment source voltage Vsp. In this case, the relationship between the duty ratio Du and voltage adjustment is simply reversed, and the same effect is achieved.

[0145] In recent years, silicon carbide (SiC) elements, which offer low loss and high-speed operation, have been used as power semiconductor elements to improve the performance of power conversion equipment. SiC elements have a wide bandgap and a dielectric breakdown voltage approximately 10 times higher than that of Si (Silicon) elements. Therefore, when designed with the same dielectric breakdown voltage, SiC elements can have a thinner semiconductor layer, which serves as the current path, than Si elements, achieving extremely low on-resistance during conduction. Furthermore, when compared at the same dielectric breakdown voltage, SiC elements have a depletion layer width that is approximately 1 / 10 that of Si elements, and the shortened carrier travel length enables switching approximately 10 times faster than Si elements.

[0146] By applying SiC elements to power conversion devices used in electric powertrains, it is possible to reduce losses during vehicle operation, leading to improvements in electric efficiency, which is equivalent to the vehicle's fuel economy. When the power conversion device is an inverter, the loss in the power semiconductor elements is directly linked to the loss of the entire inverter, so reducing loss in power conversion devices such as inverters is essential to realizing environmentally friendly and competitive electric vehicles.

[0147] The power conversion device 100 of embodiments 1 to 5 has a greater effect than when using Si elements, since the lower the switching loss of a device, such as a SiC element, which is a semiconductor element using a wide bandgap semiconductor material, the greater the effect of the difference in switching loss due to the switching speed at turn-on.

[0148] In the first to fifth embodiments, an example has been described in which the overcurrent protection circuit 41 disclosed in the present application, which protects a power semiconductor element from an overcurrent, is applied to a two-level three-phase inverter. However, the overcurrent protection circuit 41 of the present application is not limited to this and can be applied to various power conversion devices. For example, although the two-level power conversion device has been described, a three-level or multi-level power conversion device may also be used. In addition, when supplying power to a motor 9 in the case of a single-phase load, the overcurrent protection circuit 41 of the present application may also be applied to a single-phase inverter. Furthermore, when supplying power to a DC load such as the motor 9 or a battery, the overcurrent protection circuit 41 of the present application can also be applied to a DC / DC converter, an AC / DC converter, or the like. When the power conversion device is a DC / DC converter, the current sensor is disposed in the wiring on the input or output side of the power conversion unit 110.

[0149] Although various exemplary embodiments and examples are described in this application, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are contemplated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0150] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0151] Various aspects of the present disclosure are summarized below as appendices.

[0152] (Appendix 1) A power conversion device that controls a power conversion unit having a plurality of power semiconductor elements to convert DC power into AC power or AC power into DC power, a drive circuit that outputs an element drive signal that drives the plurality of power semiconductor elements; a control unit that controls the drive circuit; and a current sensor that detects an AC current in the power conversion unit, The drive circuit an element drive circuit that outputs the element drive signal to the power semiconductor element; an overcurrent protection circuit that determines that an overcurrent has flowed through the power semiconductor element and outputs an overcurrent stop signal to the element drive circuit to cause the element drive signal to be output to change the power semiconductor element from an on state to an off state, The overcurrent protection circuit includes: a comparator that determines that an overcurrent has flowed through the power semiconductor element by comparing a detection voltage output by the current sensor with an overcurrent threshold voltage, and generates the overcurrent stop signal; a threshold output unit that outputs the overcurrent threshold voltage; a threshold voltage adjustment unit that generates an adjustment voltage that causes the threshold output unit to output the overcurrent threshold voltage based on a correction command signal output from the control unit, and outputs the adjustment voltage to the threshold output unit, a voltage correction amount that is a difference between a first voltage of a current sensor at the time of design and a second voltage of the current sensor that is mounted, with respect to a predetermined overcurrent setting value that turns off the power semiconductor element; The control unit generating the correction command signal based on the voltage correction amount stored in advance or the voltage correction amount calculated from voltage correction amount data stored in advance; Power conversion device. (Appendix 2) The control unit The voltage correction amount data includes characteristic data of an output voltage relative to a current detected by the current sensor, the characteristic data being measured in advance, generating the correction command signal based on the voltage correction amount calculated from the voltage correction amount data; 2. The power conversion device of claim 1. (Appendix 3) the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; the threshold voltage adjusting unit that outputs the first adjusted voltage and the second adjusted voltage to the threshold output unit, The threshold voltage adjustment unit generating the first adjusted voltage and the second adjusted voltage based on the correction command signal output from the control unit; 3. The power conversion device according to claim 1 or 2. (Appendix 4) the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; a first threshold output unit that outputs the positive overcurrent threshold voltage; a second threshold output unit that outputs the negative overcurrent threshold voltage; a threshold voltage adjusting unit that outputs the first adjusted voltage to a first threshold output unit and outputs the second adjusted voltage to a second threshold output unit, the control unit outputs the first correction command signal and the second correction command signal to the overcurrent protection circuit; The threshold voltage adjustment unit generating a first adjusted voltage based on the first corrected command signal, and generating a second adjusted voltage based on the second corrected command signal; 3. The power conversion device according to claim 1 or 2. (Appendix 5) a temperature sensor for detecting a temperature of the current sensor; The control unit The temperature map includes characteristic data of an output voltage relative to a current detected by the current sensor, the characteristic data having been measured in advance at a plurality of temperatures, generating the correction command signal based on a total correction amount obtained by adding together the temperature correction amount extracted based on the temperature information detected by the temperature sensor and the temperature map and the voltage correction amount; 3. The power conversion device according to claim 1 or 2. (Appendix 6) The temperature correction amount is a change amount of the detected voltage output by the current sensor with respect to the overcurrent setting value, with a preset reference temperature as a reference. 6. The power conversion device of claim 5. (Appendix 7) the correction command signal is a pulse signal whose duty ratio is changeable, the threshold voltage adjusting unit includes a smoothing circuit that smoothes the pulse signal or an inverted pulse signal obtained by inverting the pulse signal and outputs an adjustment source voltage, the threshold output unit is a series circuit in which a plurality of resistors are connected in series between a power supply voltage and ground, a connection point between the resistors in the series body is connected to the comparator, and an output point from which the regulated source voltage is output is connected to the connection point via a resistor; 7. The power conversion device according to claim 1, 2, 5, or 6. (Appendix 8) the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; the threshold voltage adjusting unit that outputs the first adjusted voltage and the second adjusted voltage to the threshold output unit, The threshold voltage adjustment unit a first smoothing circuit that smoothes the pulse signal and outputs a first regulated source voltage, and a second smoothing circuit that smooths the pulse signal and outputs a second regulated source voltage, the threshold output unit is a series circuit in which a first resistor, a second resistor, and a third resistor are connected in series between a power supply voltage and ground, a first connection point at which the first resistor and the second resistor on the power supply voltage side are connected is connected to the first comparator; an output point of the first smoothing circuit, from which the first adjustment source voltage is output, is connected to the first connection point via a resistor; a second connection point at which the third resistor on the ground side and the second resistor are connected is connected to a second comparator; an output point of the second smoothing circuit, from which the second regulated source voltage is output, and the second connection point are connected via a resistor; 8. The power conversion device of claim 7. (Appendix 9) the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; the threshold voltage adjusting unit that outputs the first adjusted voltage and the second adjusted voltage to the threshold output unit, The threshold voltage adjustment unit the first smoothing circuit smoothing the pulse signal and outputting the first regulated source voltage, and the second smoothing circuit smoothing the inverted pulse signal obtained by inverting the pulse signal by an inverter and outputting the second regulated source voltage, the threshold output unit is a series circuit in which a first resistor, a second resistor, and a third resistor are connected in series between a power supply voltage and ground, a first connection point at which the first resistor and the second resistor on the power supply voltage side are connected is connected to the first comparator; an output point of the first smoothing circuit, from which the first adjustment source voltage is output, is connected to the first connection point via a resistor; a second connection point at which the third resistor on the ground side and the second resistor are connected is connected to a second comparator; an output point of the second smoothing circuit, from which the second regulated source voltage is output, and the second connection point are connected via a resistor; 8. The power conversion device of claim 7. (Appendix 10) The voltage correction amount data is a first characteristic data of an output voltage relative to a current detected by the current sensor, which is measured in advance; a first threshold data of the positive side overcurrent threshold voltage relative to the duty ratio at the positive side overcurrent setting value; and a second threshold data of the negative side overcurrent threshold voltage relative to the duty ratio at the negative side overcurrent setting value, The control unit a first overcurrent threshold, which is the positive side overcurrent threshold voltage for the positive side overcurrent setting value, is calculated from the first characteristic data within a positive settable range, and a second overcurrent threshold, which is the negative side overcurrent threshold voltage for the negative side overcurrent setting value, is calculated from the first characteristic data within a negative settable range; calculating a first voltage correction amount, which is the voltage correction amount for the first overcurrent threshold value obtained by calculation, and a second voltage correction amount, which is the voltage correction amount for the second overcurrent threshold value obtained by calculation; When generating the correction command signal, In the case of condition A, a first limit condition in which the first overcurrent threshold is the limit value of the positive side settable range or a second limit condition in which the second overcurrent threshold is the limit value of the negative side settable range is satisfied. If only one of the first limit condition and the second limit condition is satisfied, the duty ratio value derived based on the limit value and one of the first threshold data and the second threshold data corresponding to the limit value is determined as a selected duty ratio value; If the first limit condition and the second limit condition are satisfied, a limit value corresponding to the smaller correction amount of the first voltage correction amount or the second voltage correction amount is set as a selected limit value, and the duty ratio value derived based on the selected limit value and one of the first threshold data and the second threshold data corresponding to the selected limit value is determined as a selected duty ratio value; In the case of a condition B other than the condition A, in which the first voltage correction amount and the second voltage correction amount are different, the smaller correction amount is set as a selected voltage correction amount, and the value of the duty ratio derived based on the selected voltage correction amount and one of the first threshold data and the second threshold data corresponding to the selected voltage correction amount is determined as a selected duty ratio value; In the case of a condition C other than the conditions A and B in which the first voltage correction amount and the second voltage correction amount are the same, a first duty ratio value which is the value of the duty ratio derived based on the first voltage correction amount and the first threshold data, and a second duty ratio value which is the value of the duty ratio derived based on the second voltage correction amount and the second threshold data, If the first duty ratio value and the second duty ratio value are the same, the duty ratio of this value is determined as a selected duty ratio value; If the first duty ratio value and the second duty ratio value are different, a third voltage correction amount, which is the voltage correction amount calculated from the voltage value of the second threshold data for the first duty ratio value, and a fourth voltage correction amount, which is the voltage correction amount calculated from the voltage value of the first threshold data for the second duty ratio value, are compared, and the duty ratio value which results in a smaller correction amount is determined as a selected duty ratio value; generating the pulse signal having the determined selected duty ratio value as the correction command signal; 10. The power conversion device according to claim 8 or 9. (Appendix 11) the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; a threshold voltage adjusting unit that outputs the first adjusted voltage to a first threshold output unit and outputs the second adjusted voltage to a second threshold output unit, the control unit outputs the first adjustment source voltage and the second adjustment source voltage to the overcurrent protection circuit as the first correction command signal and the second correction command signal, respectively; The threshold voltage adjustment unit a first input resistor that sets the first regulated source voltage to the first regulated voltage, and a second input resistor that sets the second regulated source voltage to the second regulated voltage, the threshold output unit is a series circuit including a first resistor, a second resistor, and a third resistor connected in series between a power supply voltage and ground, a first connection point at which the first resistor and the second resistor on the power supply voltage side are connected is connected to the first comparator; an end of the first input resistor at a side where the first regulated voltage is output is connected to the first connection point; a second connection point at which the third resistor on the ground side and the second resistor are connected is connected to a second comparator; One end of the second input resistor at a side where the second regulated voltage is output is connected to the second connection point. 7. The power conversion device according to claim 1, 2, 5, or 6. (Appendix 12) the AC power handled by the power conversion unit is three-phase AC power, the current sensors are three current sensors that detect each phase of a three-phase AC current of the power conversion unit, The overcurrent protection circuit includes: a first comparator and a second comparator are provided for each phase of a three-phase AC current; the three first comparators receive the same positive overcurrent threshold voltage output from the threshold output unit; the three second comparators are input with the same negative overcurrent threshold voltage output from the threshold output unit; 10. The power conversion device according to claim 8 or 9. (Appendix 13) the AC power handled by the power conversion unit is three-phase AC power, the current sensors are three current sensors that detect each phase of a three-phase AC current of the power conversion unit, the first correction command signal and the second correction command signal are pulse signals whose duty ratios are changeable, The overcurrent protection circuit includes: a first comparator and a second comparator are provided for each phase of a three-phase AC current; the three first comparators are input with the same positive overcurrent threshold voltage output from the first threshold output unit, the three second comparators are input with the same negative overcurrent threshold voltage output from the second threshold output unit, The threshold voltage adjustment unit a first smoothing circuit that smoothes the pulse signal of the first correction command signal and outputs a first adjustment source voltage, and a second smoothing circuit that smoothes the pulse signal of the second correction command signal and outputs a second adjustment source voltage, the first threshold output unit is a first series circuit in which a plurality of resistors are connected in series between a power supply voltage and ground, the second threshold output unit is a second series circuit in which a plurality of resistors are connected in series between a power supply voltage and ground, a first connection point, which is a connection point between the resistors in the first series body, is connected to three first comparators, and an output point from which the first regulated source voltage is output is connected to the first connection point via a resistor; a second connection point, which is a connection point between the resistors in the second series body, is connected to three second comparators, and an output point from which the second regulated source voltage is output is connected to the second connection point via a resistor; 5. The power conversion device of claim 4. (Appendix 14) The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; the control unit corrects the voltage correction amount so that a difference between the voltage indicated by the threshold detection voltage information and the overcurrent threshold voltage calculated from the voltage correction amount becomes small, and adjusts the duty ratio of the pulse signal based on the corrected voltage correction amount. 10. The power conversion device according to claim 8 or 9. (Appendix 15) The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; the control unit adjusts the duty ratio of the pulse signal so that a difference between the positive overcurrent threshold voltage calculated from the first characteristic data and the voltage indicated by the threshold detection voltage information becomes small or falls within a predetermined difference range. 11. The power conversion device of claim 10. (Appendix 16) the AC power handled by the power conversion unit is three-phase AC power, the current sensors are three current sensors that detect each phase of a three-phase AC current of the power conversion unit, The overcurrent protection circuit includes: The control circuit includes the first comparator, the second comparator, the threshold output unit, and the threshold voltage adjustment unit for each phase of a three-phase AC current. 16. The power conversion device according to claim 14 or 15. (Appendix 17) The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; the control unit corrects the voltage correction amount so that a difference between the voltage indicated by the threshold detection voltage information and the voltage correction amount corresponding to the positive overcurrent threshold voltage becomes small, and adjusts the duty ratio of the pulse signal based on the corrected voltage correction amount. 14. The power conversion device according to claim 12 or 13. (Appendix 18) The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; The voltage correction amount data is First characteristic data of an output voltage versus a current detected by the current sensor for each phase, which is actually measured in advance; first threshold data of the overcurrent threshold voltage on a positive side relative to the duty ratio at the overcurrent setting value on a positive side, and second threshold data of the overcurrent threshold voltage on a negative side relative to the duty ratio at the overcurrent setting value on a negative side; the control unit adjusts the duty ratio of the pulse signal so that a difference between the positive overcurrent threshold voltage determined based on the first characteristic data of each phase and a voltage indicated by the threshold detection voltage information becomes small or falls within a predetermined difference range. 14. The power conversion device according to claim 12 or 13. (Appendix 19) The voltage correction amount data is first characteristic data of an output voltage versus a current detected by the current sensor for each phase, which are measured in advance; first threshold data of the positive side overcurrent threshold voltage versus the duty ratio at the positive side overcurrent setting value; and second threshold data of the negative side overcurrent threshold voltage versus the duty ratio at the negative side overcurrent setting value, The control unit a first overcurrent threshold, which is the positive side overcurrent threshold voltage for the positive side overcurrent setting value, is calculated from the first characteristic data within a positive side settable range, and a second overcurrent threshold, which is the negative side overcurrent threshold voltage for the negative side overcurrent setting value, is calculated from the first characteristic data within a negative side settable range, for each phase; calculating, for each phase, a first voltage correction amount that is the voltage correction amount for the first overcurrent threshold value obtained by calculation, and a second voltage correction amount that is the voltage correction amount for the second overcurrent threshold value obtained by calculation; When generating the first correction command signal, determining the smallest of the first voltage correction amounts for each phase as a selected voltage correction amount, and determining the value of the duty ratio derived based on the selected voltage correction amount and the first threshold data corresponding to the selected voltage correction amount as a first selected duty ratio value; generating the pulse signal having the determined first selected duty ratio value as a first correction command signal; When generating the second correction command signal, determining the smallest of the second voltage correction amounts for each phase as a selected voltage correction amount, and determining the value of the duty ratio derived based on the selected voltage correction amount and the second threshold data corresponding to the selected voltage correction amount as a second selected duty ratio value; generating the pulse signal having the determined second selected duty ratio value as a second corrected command signal; 14. The power conversion device of claim 13. (Appendix 20) The voltage correction amount data is first characteristic data of an output voltage versus a current detected by the current sensor for each phase, which are measured in advance; first threshold data of the positive side overcurrent threshold voltage versus the duty ratio at the positive side overcurrent setting value; and second threshold data of the negative side overcurrent threshold voltage versus the duty ratio at the negative side overcurrent setting value, The control unit a first overcurrent threshold, which is the positive side overcurrent threshold voltage for the positive side overcurrent setting value, is calculated from the first characteristic data within a positive side settable range for each phase, and a second overcurrent threshold, which is the negative side overcurrent threshold voltage for the negative side overcurrent setting value, is calculated from the first characteristic data within a negative side settable range for each phase; calculating a first voltage correction amount, which is the voltage correction amount for the first overcurrent threshold value obtained by calculation, and a second voltage correction amount, which is the voltage correction amount for the second overcurrent threshold value obtained by calculation; When generating the correction command signal, In the case of condition A, the three first overcurrent thresholds include the limit value of the positive side settable range or the three second overcurrent thresholds include the limit value of the negative side settable range, If one of the three first overcurrent thresholds and the three second overcurrent thresholds is a limit value, the duty ratio value derived based on the limit value and one of the first threshold data and the second threshold data corresponding to the limit value is determined as a selected duty ratio value; If two or more of the three first overcurrent thresholds and the three second overcurrent thresholds are limit values, the limit value corresponding to the smallest of the first voltage correction amount or the second voltage correction amount corresponding to the candidate limit value is set as a selected limit value, and the duty ratio value derived based on the selected limit value and one of the first threshold data and the second threshold data corresponding to the selected limit value is determined as a selected duty ratio value; In the case of a condition B other than the condition A, in which the three first voltage correction amounts and the three second voltage correction amounts are not the same, the smallest correction amount is determined as the selected voltage correction amount, and the value of the duty ratio derived based on the selected voltage correction amount and one of the first threshold data and the second threshold data corresponding to the selected voltage correction amount is determined as the selected duty ratio value; In the case of a condition C other than the condition A and the condition B, in which the three first voltage correction amounts and the three second voltage correction amounts are the same, among a first duty ratio value which is the value of the duty ratio derived based on the first voltage correction amount and the first threshold data, and a second duty ratio value which is the value of the duty ratio derived based on the second voltage correction amount and the second threshold data, If the first duty ratio value and the second duty ratio value are the same, the duty ratio of this value is determined as a selected duty ratio value; If the first duty ratio value and the second duty ratio value are different, a third voltage correction amount, which is the voltage correction amount calculated from the voltage value of the second threshold data for the first duty ratio value, and a fourth voltage correction amount, which is the voltage correction amount calculated from the voltage value of the first threshold data for the second duty ratio value, are compared, and the duty ratio value which results in a smaller correction amount is determined as a selected duty ratio value; generating the pulse signal having the determined selected duty ratio value as the correction command signal; 13. The power conversion apparatus of claim 12. (Appendix 21) 21. The power conversion device according to any one of appendixes 1 to 20, wherein the power semiconductor element is a power semiconductor element using a wide bandgap semiconductor material. [Explanation of symbols]

[0153] 3a, 3b, 3c, 3d, 3e, 3f...power semiconductor element, 10...control unit, 14...drive circuit, 21a, 21b, 21c...current sensor, 22...temperature sensor, 39a, 39b...threshold value settable range, 40...element drive circuit, 41...overcurrent protection circuit, 42a, 42b, 42c, 42d, 42e, 42f, 42n, 42p...comparator, 55...corrected sensor characteristics (voltage correction amount data, first characteristic data), 56a, 56b, 56c...sensor characteristics (voltage correction amount data), 57a, 57b, 57c...sensor characteristics (voltage correction amount data, first characteristic data), 59, 59u, 59v, 59w...overcurrent protection circuit, 60...threshold voltage adjustment unit, 61, 61a, 61b...threshold output unit, 63...inverter, 65...smoothing circuit (first smoothing circuit), 65a...smoothing circuit (first smoothing circuit), 65b...smoothing circuit (second smoothing circuit), 66...smoothing circuit (second smoothing circuit), 70...voltage detection circuit, 75...temperature map, 83a, 83b, 86a, 86b...voltage correction amount, 87a, 87b, 88a, 88b...temperature correction amount, 89a, 89b, 89c...voltage correction amount, 92a, 92b, 92c, 92d, 92e, 92f...positive side overcurrent threshold characteristics (voltage correction amount data), 93a, 93b, 93c, 93d, 93e, 93f...Negative side overcurrent threshold characteristics (voltage correction amount data), 94a...Positive side overcurrent threshold characteristics (voltage correction amount data), 94b...Positive side overcurrent threshold characteristics (voltage correction amount data, first threshold data), 95a...Negative side overcurrent threshold characteristics (voltage correction amount data), 95b...Negative side overcurrent threshold characteristics (voltage correction amount data, second threshold data), 96a, 96b, 96c, 96d, 96e, 96f...Positive side overcurrent threshold characteristics (voltage correction amount data), 97a, 97b, 97c, 97d, 97e, 97f...Negative side overcurrent threshold characteristics (voltage correction amount data), 100...Power conversion device, 110...Power Conversion section, d4...duty ratio value, Du...duty ratio, da1...first duty ratio value, da2...second duty ratio value, ds...selected duty ratio value, GND...ground, Iocn...negative overcurrent setting value, Iocp...positive overcurrent setting value, Iu, Iv, Iw...AC current, n1, n2...connection point (output point), n3...connection point (first connection point), n4...connection point (second connection point), R1, R2...resistor, R3...resistor (first resistor), R4...resistor (second resistor), R5...resistor (third resistor), Ra1, Ra2, Ra3, Ra4...resistor, Ta...temperature detection value (temperature information), sc, scup,scun, scvp, scvn, scwp, scwn...correction command signals, scp, scn, scu, scv, scw...correction command signals, sd, sda, sdb, sdc, sdd, sde, sdf...element drive signals, st, stp, stn...overcurrent stop signals, stup, stun, stvp, stvn, stwp, stwn...overcurrent stop signals, V1...first overcurrent threshold, V2...second overcurrent threshold, Vi, Viu, Viv, Viw...detection voltage, Vm, Vmu, Vmv, Vmw...threshold detection voltage information, Vm0...detection voltage, Vpi...pulse signal, Vpia...pulse signal (inverted pulse signal), Vpp...power supply voltage, Vsp...adjustment source voltage, Vsn...adjustment source voltage, vsp, vsn, vsup, vsun, vsvp , vsvn, vswp, vswn...correction command signal, Vthn...negative side overcurrent threshold (overcurrent threshold voltage), Vthp...positive side overcurrent threshold (overcurrent threshold voltage), Vth0n...negative side overcurrent threshold (overcurrent threshold voltage, first voltage), Vth0p...positive side overcurrent threshold (overcurrent threshold voltage, first voltage), Vthan...negative side overcurrent threshold (overcurrent threshold voltage, second voltage), Vthap...positive side overcurrent threshold (overcurrent threshold voltage, second voltage), Van...negative side adjustment voltage, Vap...positive side adjustment voltage, Vthnmax...upper limit negative side overcurrent threshold (limit value), Vthpmin...lower limit positive side overcurrent threshold (limit value), ΔV1...first voltage correction amount, ΔV2...second voltage correction amount, ΔV3...third voltage correction amount, ΔV4...fourth voltage correction amount, ΔVs...selected voltage correction amount,

Claims

1. A power conversion device that controls a power conversion unit having a plurality of power semiconductor elements to convert DC power into AC power or AC power into DC power, a drive circuit that outputs an element drive signal that drives the plurality of power semiconductor elements; a control unit that controls the drive circuit; and a current sensor that detects an AC current in the power conversion unit, The drive circuit an element drive circuit that outputs the element drive signal to the power semiconductor element; an overcurrent protection circuit that determines that an overcurrent has flowed through the power semiconductor element and outputs an overcurrent stop signal to the element drive circuit to cause the element drive signal to be output to change the power semiconductor element from an on state to an off state, The overcurrent protection circuit includes: a comparator that determines that an overcurrent has flowed through the power semiconductor element by comparing a detection voltage output by the current sensor with an overcurrent threshold voltage, and generates the overcurrent stop signal; a threshold output unit that outputs the overcurrent threshold voltage; a threshold voltage adjustment unit that generates an adjustment voltage that causes the threshold output unit to output the overcurrent threshold voltage based on a correction command signal output from the control unit, and outputs the adjustment voltage to the threshold output unit, a voltage correction amount that is a difference between a first voltage of a current sensor at the time of design and a second voltage of the current sensor that is mounted, with respect to a predetermined overcurrent setting value that turns off the power semiconductor element; The control unit generating the correction command signal based on the voltage correction amount stored in advance or the voltage correction amount calculated from voltage correction amount data stored in advance; Power conversion device.

2. The control unit The voltage correction amount data includes characteristic data of an output voltage relative to a current detected by the current sensor, the characteristic data being measured in advance, generating the correction command signal based on the voltage correction amount calculated from the voltage correction amount data; The power conversion device according to claim 1 .

3. the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; the threshold voltage adjusting unit that outputs the first adjusted voltage and the second adjusted voltage to the threshold output unit, The threshold voltage adjustment unit generating the first adjusted voltage and the second adjusted voltage based on the correction command signal output from the control unit; The power conversion device according to claim 1 or 2.

4. the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; a first threshold output unit that outputs the positive overcurrent threshold voltage; a second threshold output unit that outputs the negative overcurrent threshold voltage; a threshold voltage adjusting unit that outputs the first adjusted voltage to a first threshold output unit and outputs the second adjusted voltage to a second threshold output unit, the control unit outputs the first correction command signal and the second correction command signal to the overcurrent protection circuit; The threshold voltage adjustment unit generating a first adjusted voltage based on the first corrected command signal, and generating a second adjusted voltage based on the second corrected command signal; The power conversion device according to claim 1 or 2.

5. a temperature sensor for detecting a temperature of the current sensor; The control unit The temperature map includes characteristic data of an output voltage relative to a current detected by the current sensor, the characteristic data having been measured in advance at a plurality of temperatures, generating the correction command signal based on a total correction amount obtained by adding together the temperature correction amount extracted based on the temperature information detected by the temperature sensor and the temperature map and the voltage correction amount; The power conversion device according to claim 1 or 2.

6. The temperature correction amount is a change amount of the detected voltage output by the current sensor with respect to the overcurrent setting value, with a preset reference temperature as a reference. The power converter according to claim 5.

7. the correction command signal is a pulse signal whose duty ratio is changeable, the threshold voltage adjusting unit includes a smoothing circuit that smoothes the pulse signal or an inverted pulse signal obtained by inverting the pulse signal and outputs an adjustment source voltage, the threshold output unit is a series circuit in which a plurality of resistors are connected in series between a power supply voltage and ground, a connection point between the resistors in the series body is connected to the comparator, and an output point from which the regulated source voltage is output is connected to the connection point via a resistor; The power conversion device according to claim 1 or 2.

8. the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; the threshold voltage adjusting unit that outputs the first adjusted voltage and the second adjusted voltage to the threshold output unit, The threshold voltage adjustment unit a first smoothing circuit that smoothes the pulse signal and outputs a first regulated source voltage, and a second smoothing circuit that smooths the pulse signal and outputs a second regulated source voltage, the threshold output unit is a series circuit in which a first resistor, a second resistor, and a third resistor are connected in series between a power supply voltage and ground, a first connection point at which the first resistor and the second resistor on the power supply voltage side are connected is connected to the first comparator; an output point of the first smoothing circuit, from which the first adjustment source voltage is output, is connected to the first connection point via a resistor; a second connection point at which the third resistor on the ground side and the second resistor are connected is connected to a second comparator; an output point of the second smoothing circuit, from which the second regulated source voltage is output, and the second connection point are connected via a resistor; The power converter according to claim 7.

9. the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; the threshold voltage adjusting unit that outputs the first adjusted voltage and the second adjusted voltage to the threshold output unit, The threshold voltage adjustment unit the first smoothing circuit smoothing the pulse signal and outputting the first regulated source voltage, and the second smoothing circuit smoothing the inverted pulse signal obtained by inverting the pulse signal by an inverter and outputting the second regulated source voltage, the threshold output unit is a series circuit in which a first resistor, a second resistor, and a third resistor are connected in series between a power supply voltage and ground, a first connection point at which the first resistor and the second resistor on the power supply voltage side are connected is connected to the first comparator; an output point of the first smoothing circuit, from which the first adjustment source voltage is output, is connected to the first connection point via a resistor; a second connection point at which the third resistor on the ground side and the second resistor are connected is connected to a second comparator; an output point of the second smoothing circuit, from which the second regulated source voltage is output, and the second connection point are connected via a resistor; The power converter according to claim 7.

10. The voltage correction amount data is a first characteristic data of an output voltage relative to a current detected by the current sensor, which is measured in advance; a first threshold data of the positive side overcurrent threshold voltage relative to the duty ratio at the positive side overcurrent setting value; and a second threshold data of the negative side overcurrent threshold voltage relative to the duty ratio at the negative side overcurrent setting value, The control unit a first overcurrent threshold, which is the positive side overcurrent threshold voltage for the positive side overcurrent setting value, is calculated from the first characteristic data within a positive settable range, and a second overcurrent threshold, which is the negative side overcurrent threshold voltage for the negative side overcurrent setting value, is calculated from the first characteristic data within a negative settable range; calculating a first voltage correction amount, which is the voltage correction amount for the first overcurrent threshold value obtained by calculation, and a second voltage correction amount, which is the voltage correction amount for the second overcurrent threshold value obtained by calculation; When generating the correction command signal, In the case of condition A, a first limit condition in which the first overcurrent threshold is the limit value of the positive side settable range or a second limit condition in which the second overcurrent threshold is the limit value of the negative side settable range is satisfied. If only one of the first limit condition and the second limit condition is satisfied, the duty ratio value derived based on the limit value and one of the first threshold data and the second threshold data corresponding to the limit value is determined as a selected duty ratio value; If the first limit condition and the second limit condition are satisfied, a limit value corresponding to the smaller correction amount of the first voltage correction amount or the second voltage correction amount is set as a selected limit value, and the duty ratio value derived based on the selected limit value and one of the first threshold data and the second threshold data corresponding to the selected limit value is determined as a selected duty ratio value; In the case of a condition B other than the condition A, in which the first voltage correction amount and the second voltage correction amount are different, the smaller correction amount is set as a selected voltage correction amount, and the duty ratio value derived based on the selected voltage correction amount and one of the first threshold data and the second threshold data corresponding to the selected voltage correction amount is determined as a selected duty ratio value; In the case of a condition C other than the conditions A and B, in which the first voltage correction amount and the second voltage correction amount are the same, a first duty ratio value which is the value of the duty ratio derived based on the first voltage correction amount and the first threshold data, and a second duty ratio value which is the value of the duty ratio derived based on the second voltage correction amount and the second threshold data, If the first duty ratio value and the second duty ratio value are the same, the duty ratio of this value is determined as a selected duty ratio value; If the first duty ratio value and the second duty ratio value are different, a third voltage correction amount, which is the voltage correction amount calculated from the voltage value of the second threshold data for the first duty ratio value, and a fourth voltage correction amount, which is the voltage correction amount calculated from the voltage value of the first threshold data for the second duty ratio value, are compared, and the duty ratio value which results in a smaller correction amount is determined as a selected duty ratio value; generating the pulse signal having the determined selected duty ratio value as the correction command signal; The power converter according to claim 9.

11. the power conversion unit is a full bridge circuit in which the power semiconductor element of an upper arm and the power semiconductor element of a lower arm are connected in series, The overcurrent protection circuit includes: a first comparator that determines that an overcurrent has flowed through the power semiconductor element of the upper arm by comparing a detection voltage output by the current sensor with the overcurrent threshold voltage on a positive side, and generates the overcurrent stop signal on a positive side; a second comparator that determines that an overcurrent has flowed through the power semiconductor element of the lower arm by comparing a detection voltage output by the current sensor with the negative overcurrent threshold voltage, and generates the negative overcurrent stop signal; the threshold output unit that outputs the positive side overcurrent threshold voltage and the negative side overcurrent threshold voltage; a threshold voltage adjusting unit that outputs the first adjusted voltage to a first threshold output unit and outputs the second adjusted voltage to a second threshold output unit, the control unit outputs the first adjustment source voltage and the second adjustment source voltage to the overcurrent protection circuit as the first correction command signal and the second correction command signal, respectively; The threshold voltage adjustment unit a first input resistor that sets the first regulated source voltage to the first regulated voltage, and a second input resistor that sets the second regulated source voltage to the second regulated voltage, the threshold output unit is a series circuit including a first resistor, a second resistor, and a third resistor connected in series between a power supply voltage and ground, a first connection point at which the first resistor and the second resistor on the power supply voltage side are connected is connected to the first comparator; an end of the first input resistor at a side where the first regulated voltage is output is connected to the first connection point; a second connection point at which the third resistor on the ground side and the second resistor are connected is connected to a second comparator; One end of the second input resistor at a side where the second regulated voltage is output is connected to the second connection point. The power conversion device according to claim 1 or 2.

12. the AC power handled by the power conversion unit is three-phase AC power, the current sensors are three current sensors that detect each phase of a three-phase AC current of the power conversion unit, The overcurrent protection circuit includes: a first comparator and a second comparator are provided for each phase of a three-phase AC current; the three first comparators are input with the same positive overcurrent threshold voltage output from the threshold output unit, the three second comparators are input with the same negative overcurrent threshold voltage output from the threshold output unit; The power converter according to claim 9.

13. the AC power handled by the power conversion unit is three-phase AC power, the current sensors are three current sensors that detect each phase of a three-phase AC current of the power conversion unit, the first correction command signal and the second correction command signal are pulse signals whose duty ratios are changeable, The overcurrent protection circuit includes: a first comparator and a second comparator are provided for each phase of a three-phase AC current; the three first comparators are input with the same positive overcurrent threshold voltage output from the first threshold output unit, the three second comparators are input with the same negative overcurrent threshold voltage output from the second threshold output unit, The threshold voltage adjustment unit a first smoothing circuit that smoothes the pulse signal of the first correction command signal and outputs a first adjustment source voltage, and a second smoothing circuit that smoothes the pulse signal of the second correction command signal and outputs a second adjustment source voltage, the first threshold output unit is a first series circuit in which a plurality of resistors are connected in series between a power supply voltage and ground, the second threshold output unit is a second series circuit in which a plurality of resistors are connected in series between a power supply voltage and ground, a first connection point, which is a connection point between the resistors in the first series body, is connected to three first comparators, and an output point from which the first regulated source voltage is output is connected to the first connection point via a resistor; a second connection point, which is a connection point between the resistors in the second series body, is connected to three second comparators, and an output point from which the second regulated source voltage is output is connected to the second connection point via a resistor; The power converter according to claim 4.

14. The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; the control unit corrects the voltage correction amount so that a difference between the voltage indicated by the threshold detection voltage information and the overcurrent threshold voltage calculated from the voltage correction amount becomes small, and adjusts the duty ratio of the pulse signal based on the corrected voltage correction amount. The power converter according to claim 9.

15. The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; the control unit adjusts the duty ratio of the pulse signal so that a difference between the positive overcurrent threshold voltage calculated from the first characteristic data and the voltage indicated by the threshold detection voltage information becomes small or falls within a predetermined difference range. The power converter according to claim 10.

16. the AC power handled by the power conversion unit is three-phase AC power, the current sensors are three current sensors that detect each phase of a three-phase AC current of the power conversion unit, The overcurrent protection circuit includes: The control circuit includes the first comparator, the second comparator, the threshold output unit, and the threshold voltage adjustment unit for each phase of a three-phase AC current. The power converter according to claim 15.

17. The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; the control unit corrects the voltage correction amount so that a difference between the voltage indicated by the threshold detection voltage information and the voltage correction amount corresponding to the positive overcurrent threshold voltage becomes small, and adjusts the duty ratio of the pulse signal based on the corrected voltage correction amount. The power converter according to claim 12.

18. The overcurrent protection circuit includes: a voltage detection circuit that detects the positive overcurrent threshold voltage and outputs the detected voltage as threshold detection voltage information; The voltage correction amount data is First characteristic data of an output voltage versus a current detected by the current sensor for each phase, which is actually measured in advance; first threshold data of the overcurrent threshold voltage on a positive side relative to the duty ratio at the overcurrent setting value on a positive side, and second threshold data of the overcurrent threshold voltage on a negative side relative to the duty ratio at the overcurrent setting value on a negative side; the control unit adjusts the duty ratio of the pulse signal so that a difference between the positive overcurrent threshold voltage determined based on the first characteristic data of each phase and a voltage indicated by the threshold detection voltage information becomes small or falls within a predetermined difference range. The power converter according to claim 12.

19. The voltage correction amount data is first characteristic data of an output voltage versus a current detected by the current sensor for each phase, which are measured in advance; first threshold data of the positive side overcurrent threshold voltage versus the duty ratio at the positive side overcurrent setting value; and second threshold data of the negative side overcurrent threshold voltage versus the duty ratio at the negative side overcurrent setting value, The control unit a first overcurrent threshold, which is the positive side overcurrent threshold voltage for the positive side overcurrent setting value, is calculated from the first characteristic data within a positive side settable range, and a second overcurrent threshold, which is the negative side overcurrent threshold voltage for the negative side overcurrent setting value, is calculated from the first characteristic data within a negative side settable range, for each phase; calculating, for each phase, a first voltage correction amount that is the voltage correction amount for the first overcurrent threshold value obtained by calculation, and a second voltage correction amount that is the voltage correction amount for the second overcurrent threshold value obtained by calculation; When generating the first correction command signal, determining the smallest of the first voltage correction amounts for each phase as a selected voltage correction amount, and determining the value of the duty ratio derived based on the selected voltage correction amount and the first threshold data corresponding to the selected voltage correction amount as a first selected duty ratio value; generating the pulse signal having the determined first selected duty ratio value as a first correction command signal; When generating the second correction command signal, determining the smallest of the second voltage correction amounts for each phase as a selected voltage correction amount, and determining the value of the duty ratio derived based on the selected voltage correction amount and the second threshold data corresponding to the selected voltage correction amount as a second selected duty ratio value; generating the pulse signal having the determined second selected duty ratio value as a second corrected command signal; The power converter according to claim 13.

20. The voltage correction amount data is first characteristic data of an output voltage versus a current detected by the current sensor for each phase, which are measured in advance; first threshold data of the positive side overcurrent threshold voltage versus the duty ratio at the positive side overcurrent setting value; and second threshold data of the negative side overcurrent threshold voltage versus the duty ratio at the negative side overcurrent setting value, The control unit a first overcurrent threshold, which is the positive side overcurrent threshold voltage for the positive side overcurrent setting value, is calculated from the first characteristic data within a positive side settable range for each phase, and a second overcurrent threshold, which is the negative side overcurrent threshold voltage for the negative side overcurrent setting value, is calculated from the first characteristic data within a negative side settable range for each phase; calculating a first voltage correction amount, which is the voltage correction amount for the first overcurrent threshold value obtained by calculation, and a second voltage correction amount, which is the voltage correction amount for the second overcurrent threshold value obtained by calculation; When generating the correction command signal, In the case of condition A, the three first overcurrent thresholds include the limit value of the positive side settable range or the three second overcurrent thresholds include the limit value of the negative side settable range, If one of the three first overcurrent thresholds and the three second overcurrent thresholds is a limit value, the duty ratio value derived based on the limit value and one of the first threshold data and the second threshold data corresponding to the limit value is determined as a selected duty ratio value; If two or more of the three first overcurrent thresholds and the three second overcurrent thresholds are limit values, the limit value corresponding to the smallest of the first voltage correction amount or the second voltage correction amount corresponding to the candidate limit value is set as a selected limit value, and the duty ratio value derived based on the selected limit value and one of the first threshold data and the second threshold data corresponding to the selected limit value is determined as a selected duty ratio value; In the case of a condition B other than the condition A, in which the three first voltage correction amounts and the three second voltage correction amounts are not the same, the smallest correction amount is determined as the selected voltage correction amount, and the value of the duty ratio derived based on the selected voltage correction amount and one of the first threshold data and the second threshold data corresponding to the selected voltage correction amount is determined as the selected duty ratio value; In the case of a condition C other than the condition A and the condition B, in which the three first voltage correction amounts and the three second voltage correction amounts are the same, a first duty ratio value which is the value of the duty ratio derived based on the first voltage correction amount and the first threshold data, and a second duty ratio value which is the value of the duty ratio derived based on the second voltage correction amount and the second threshold data, If the first duty ratio value and the second duty ratio value are the same, the duty ratio of this value is determined as a selected duty ratio value; If the first duty ratio value and the second duty ratio value are different, a third voltage correction amount, which is the voltage correction amount calculated from the voltage value of the second threshold data for the first duty ratio value, and a fourth voltage correction amount, which is the voltage correction amount calculated from the voltage value of the first threshold data for the second duty ratio value, are compared, and the duty ratio value which results in a smaller correction amount is determined as a selected duty ratio value; generating the pulse signal having the determined selected duty ratio value as the correction command signal; The power converter according to claim 12.

21. 3. The power conversion device according to claim 1, wherein the power semiconductor element is a power semiconductor element using a wide bandgap semiconductor material.

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