Power Conversion Device

Abstract

To prevent deterioration of a switching element of a power conversion apparatus by protecting a body diode of the switching element of the power conversion apparatus while suppressing overcurrent when the overcurrent flows through the switching element.SOLUTION: A power conversion apparatus includes arms of three phases in each of which a positive electrode-side switching element connected to a DC power source, a negative electrode-side switching element, and an external connection point connecting the positive electrode-side switching element and the negative electrode-side switching element in series and being connected to a winding wire of a rotary electric machine, are disposed, a phase current detection unit that detects currents in the respective phases, and a switching control device that controls the rotary electric machine by performing on-off control of the positive electrode-side switching elements and the negative electrode-side switching elements, and that determines that overcurrent is generated when a current detected by the phase current detection unit is greater than a predetermined threshold, and turns on all the positive electrode-side switching elements and turns off all the negative electrode-side switching elements, or vice versa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Recently, automobiles equipped with electric powertrains such as hybrid automobiles, plug-in hybrid automobiles, electric automobiles, and fuel cell automobiles (hereinafter referred to as "electric vehicles") have become widespread. These electric vehicles are equipped with a rotating electric machine for driving the wheels and an inverter, which is a power conversion device for driving the rotating electric machine, in addition to or instead of the configuration of an automobile powered by a conventional gasoline engine.

[0003] Inverters convert DC power from a DC power source into AC power by turning multiple semiconductor switching elements on and off at a predetermined switching frequency, and adjust the torque and rotation speed of the rotating electrical machine that serves as the load. The semiconductor switching elements must allow current to flow in both forward and reverse directions. When using field effect transistors (FETs) as semiconductor switching elements, the body diode (also known as a parasitic diode) built into the FET can be used without connecting a freewheeling diode in parallel. For this reason, FETs are often used in small, high-performance inverters.

[0004] However, the body diode of an FET can deteriorate due to the passage of large currents. Like a general diode, the body diode of an FET has a specified continuous current capacity and a larger short-term rated current capacity. If the current passing through it exceeds the short-term rated current of the body diode, the life of the FET may be shortened.

[0005] In particular, when an overcurrent flows through a switching element in a power conversion device, a control that shuts off all switching elements is widely adopted as a measure to prevent the overcurrent. However, in such a case, current flows through the body diode. In this case, it is necessary to protect the body diode and prevent the switching element from deteriorating.

[0006] As a countermeasure against current flowing into the body diode, a technique has been proposed in which another diode is connected in anti-parallel to the semiconductor switching element. In this case, a method has been disclosed in which an additional free wheel diode is provided, the on-voltage of which when current is conducted being set lower than the conduction start voltage of the body diode (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-305836 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the technology of Patent Document 1 requires the provision of an additional free wheel diode in addition to the semiconductor switching element. The provision of an additional free wheel diode contradicts the miniaturization and cost reduction required for power conversion devices. In order to increase the allowable current of the body diode of the FET and improve the withstand capability without providing an additional free wheel diode, the semiconductor size of the FET must be increased, which also contradicts the miniaturization and cost reduction of power conversion devices.

[0009] The present application has been made to solve the above-mentioned problems in power conversion devices, and aims to provide a power conversion device that, when an overcurrent flows through a switching element of the power conversion device, can suppress the overcurrent while protecting the body diode of the switching element of the power conversion device, thereby preventing the switching element from deteriorating. [Means for solving the problem]

[0010] The power conversion device disclosed in the present application comprises: a three-phase arm provided with a positive-side switching element connected to a positive side of a DC power supply, a negative-side switching element connected to a negative side of the DC power supply, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and connected to a winding of a rotating electric machine; a phase current detection unit that detects a current for each phase flowing between the external connection point and the winding; and a switching control device that controls the rotating electric machine by controlling the on / off of the positive-side switching elements and the negative-side switching elements, and determines that an overcurrent has occurred when the current detected by the phase current detection unit exceeds a predetermined threshold value, and turns on either all of the positive-side switching elements or all of the negative-side switching elements and turns off the other. In the power conversion device, the phase current detection unit detects a direction and a value of a current for each phase flowing between the external connection point and the winding; The switching control device detects whether an overcurrent has occurred in the positive-side switching element and the negative-side switching element based on the direction of the current detected by the phase current detection unit when the occurrence of the overcurrent is detected, and when the occurrence of the overcurrent is detected, turns on one of the positive-side switching element and the negative-side switching element in which the occurrence of the overcurrent was first detected, and turns off the other switching element. It is something. [Effects of the Invention]

[0011] According to the power conversion device of the present application, when an overcurrent flows through a switching element of the power conversion device, by turning on either all of the positive-side switching elements or all of the negative-side switching elements and turning off the other, it is possible to suppress the overcurrent while preventing a large current from flowing through the body diode of the switching element. This makes it possible to obtain a power conversion device that can protect the body diode and prevent deterioration of the switching elements while promoting miniaturization and cost reduction without requiring the installation of additional freewheeling diodes or enlarging the semiconductor size. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a configuration diagram of a power conversion device according to a first embodiment. [Figure 2]1 is a hardware configuration diagram of a switching control device of a power conversion device according to a first embodiment. [Figure 3] FIG. 10 is a block diagram of overcurrent response control of a power conversion device according to a comparative example. [Figure 4] FIG. 10 is a diagram illustrating the operation logic of a signal blocking circuit of a power conversion device according to a comparative example. [Figure 5] 10 is a time chart showing overcurrent response control of a power conversion device according to a comparative example. [Figure 6] 3 is a diagram showing a current flow during normal operation of the power conversion device according to the first embodiment. FIG. [Figure 7] FIG. 10 is a diagram showing a current flow in overcurrent response control of a power conversion device according to a comparative example. [Figure 8] 1 is a block diagram of overcurrent response control of a power conversion device according to a first embodiment. [Figure 9] 3 is a diagram showing the operation logic of a positive-side three-phase short-circuit processing circuit of the power conversion device according to the first embodiment. FIG. [Figure 10] 4 is a diagram showing the operation logic of a negative-side three-phase short-circuit processing circuit of the power conversion device according to the first embodiment. FIG. [Figure 11] 4 is a first diagram showing the relationship between the direction of current and overcurrent detection in the power conversion device according to the first embodiment. FIG. [Figure 12] FIG. 10 is a second diagram showing the relationship between the direction of current and overcurrent detection in the power conversion device according to the first embodiment. [Figure 13] 4 is a time chart showing overcurrent response control of the power conversion device according to the first embodiment. [Figure 14] 4 is a diagram showing a current flow in overcurrent response control of the power conversion device according to the first embodiment. FIG. [Figure 15] FIG. 10 is a configuration diagram of a power conversion device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a power conversion device according to the present invention will be described with reference to the drawings.

[0014] 1. First Embodiment <Configuration of power conversion device> FIG. 1 is a configuration diagram of a power conversion device 1 according to a first embodiment. The power conversion device 1 is connected to a DC power supply 4 via DC buses 3a and 3b. The power conversion device 1 receives driving power from the DC power supply 4 or transmits regenerative power to the DC power supply 4. The power conversion device 1 is connected to a rotating electric machine 6 via an AC bus 5. The power conversion device 1 transmits driving power to the rotating electric machine 6 or receives regenerative power from the rotating electric machine 6.

[0015] The rotating electric machine 6 is equipped with a U-phase winding 10a, a V-phase winding 10b, and a W-phase winding 10c. The rotating electric machine 6 also has a rotation angle sensor 7 that detects the rotation angle of the rotating electric machine 6. The rotating electric machine 6 rotates a load and is capable of regenerating the rotational energy of the load as electrical energy. The rotating electric machine 6 may be an electric motor with a permanent magnet in the rotor, an electric motor with an electromagnet in the rotor, a brush electric motor, a brushless electric motor, or the like.

[0016] The power conversion device 1 includes an inverter circuit 8 and a switching control device 9. The inverter circuit 8 includes a capacitor 2 connected between DC buses 3a and 3b on the power supply input side, a voltage detection circuit 11 that detects the DC bus voltage of the inverter circuit 8, a power conversion circuit 12 that is composed of multiple switching elements and performs DC / AC power conversion, and a current sensor 13 that detects the current that flows between the inverter circuit 8 and the rotating electric machine 6 via the AC bus 5.

[0017] The switching element of the power conversion circuit 12 may be, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as shown in Fig. 1. A diode is formed in the MOSFET in an anti-parallel configuration, which is called a body diode (also called a parasitic diode).

[0018] The power conversion circuit 12 is a commonly known inverter with six switching elements connected in a full bridge configuration. U-phase switching elements 14 and 15, V-phase switching elements 16 and 17, and W-phase switching elements 18 and 19 are connected in series in pairs. These pairs are called arms.

[0019] The U-phase arm, the V-phase arm, and the W-phase arm are each connected in parallel to the DC power supply 4. An external connection point, which is the midpoint of switching elements 14 and 15, which are U-phase arms, is connected to a U-phase input of the rotating electric machine 6. An external connection point, which is the midpoint of switching elements 16 and 17, which are V-phase arms, is connected to a V-phase input of the rotating electric machine 6. An external connection point, which is the midpoint of switching elements 18 and 19, which are W-phase arms, is connected to a W-phase input of the rotating electric machine 6.

[0020] Here, the switching elements 14, 16, and 18 connected to the DC bus 3a on the positive side of the DC power supply 4 are referred to as upper switching elements or upper arms. The switching elements 15, 17, and 19 connected to the DC bus 3b on the negative side of the DC power supply 4 are referred to as lower switching elements or lower arms.

[0021] Capacitor 2 of inverter circuit 8 functions to suppress ripples in the DC bus voltage. Capacitor 2 also functions to reduce the power supply impedance of inverter circuit 8, thereby improving the AC current driving capability of inverter circuit 8. Capacitor 2 also functions to absorb surge voltages. Voltage detection circuit 11 divides the DC bus voltage using voltage dividing resistors or the like to a voltage that can be read by switching control device 9. Switching control device 9 receives DC bus voltage information from voltage detection circuit 11.

[0022] Current sensor 13 detects the phase current of rotating electric machine 6 flowing through AC bus 5. Current sensor 13 converts the current value into a voltage and outputs it to switching control device 9. Fig. 1 shows a configuration in which U-phase current sensor 13a detects U-phase current, V-phase current sensor 13b detects V-phase current, and W-phase current sensor 13c detects W-phase current. Note that shunt resistors may be used for current sensor 13.

[0023] Here, the current flowing from the power conversion device 1 to the rotating electric machine 6 is defined as a positive current, and the current flowing in the opposite direction is defined as a negative current. The current flowing between the external connection point of switching elements 14 and 15 and the U-phase input of the rotating electric machine 6 is defined as a phase current Iu. The current flowing between the external connection point of switching elements 16 and 17 and the V-phase input of the rotating electric machine 6 is defined as a phase current Iv. The current flowing between the external connection point of switching elements 18 and 19 and the W-phase input of the rotating electric machine 6 is defined as a phase current Iw.

[0024] The rotation angle sensor 7 is a sensor that detects the rotor rotation angle of the rotating electric machine 6. A resolver encoder, an optical encoder, or the like can be used as the rotation angle sensor 7. The detected rotor rotation angle is output to the switching control device 9. The rotor rotation angle θm is converted into an electrical angle θe based on the number of pole pairs of the permanent magnet of the rotating electric machine 6.

[0025] <Hardware configuration of switching control device> FIG. 2 is a hardware configuration diagram of the switching control device 9 of the power conversion device 1 according to the first embodiment. The hardware configuration diagram in FIG. 2 can also be applied to the switching control device 9a. Here, the switching control device 9 will be used as a representative example for explanation. In this embodiment, each function of the switching control device 9 is realized by a processing circuit provided in the switching control device 9. Specifically, as shown in FIG. 2, the switching control device 9 includes, as processing circuits, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 that exchanges data with the arithmetic processing device 90, an input circuit 92 that inputs external signals to the arithmetic processing device 90, and an output circuit 93 that outputs signals from the arithmetic processing device 90 to the outside.

[0026] The arithmetic processing device 90 may be an application-specific integrated circuit (ASIC), an integrated circuit (IC), a digital signal processor (DSP), a field programmable gate array (FPGA), various logic circuits, various signal processing circuits, etc. Furthermore, a plurality of the same or different types of arithmetic processing devices 90 may be provided, with each device performing a different process. The storage device 91 may be a random access memory (RAM) configured to be able to read and write data from the arithmetic processing device 90, a read-only memory (ROM) configured to be able to read data from the arithmetic processing device 90, a flash memory, etc. The input circuit 92 is connected to various sensors and switches and includes an A / D converter and the like that inputs output signals from the sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads and includes a drive circuit and the like that converts and outputs control signals from the arithmetic processing device 90 to the electrical loads.

[0027] Each function of the switching control device 9 is realized by an arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM, and cooperating with other hardware of the switching control device 9, such as the storage device 91, an input circuit 92, and an output circuit 93. Setting data such as thresholds and judgment values ​​used by the switching control device 9 is stored in the storage device 91 such as a ROM as part of the software (program). The functions of the components of the switching control device 9 will be described below. Each function of the switching control device 9 may be configured as a software module, or may be configured as a combination of software and hardware.

[0028] <Functions of switching control devices> The switching control device 9 is responsible for overall control of the power conversion device 1. The process by which the switching control device 9 calculates the on / off control signals for the switching elements 14 to 19 will be described. A torque command value Trqc to be generated by the rotating electric machine 6 is input from a control device or control program (not shown) that is higher than the switching control device 9. In response to this, the switching control device 9 determines a d-axis current command value Id1c and a q-axis current command value Iq1c.

[0029] Here, the d-axis indicates the direction of the magnetic pole position (magnetic flux) of the rotating electric machine, and the q-axis indicates the direction electrically perpendicular to the d-axis, forming a dq-axis coordinate system. When the rotor of an electric motor with magnets rotates, the dq-axis coordinate system also rotates.

[0030] Current value signals of the U-phase current Iu, V-phase current Iv, and W-phase current Iw are input to the switching control device 9 from the current sensor 13. The rotor rotation angle θm, which is to be converted into an electrical angle θe, is input to the switching control device 9 from the rotation angle sensor 7. A voltage value signal of the DC bus voltage Vpn is then input to the switching control device 9 from the voltage detection circuit 11. The current values ​​of the U-phase current Iu, V-phase current Iv, and W-phase current Iw are converted into a d-axis current detection value Id and a q-axis current detection value Iq by coordinate transformation by the switching control device 9. The electrical angle θe is time-differentiated by the switching control device 9 to calculate an electrical angular velocity ω (rotational speed ω).

[0031] The switching control device 9 calculates the d-axis current deviation between the d-axis current command value Idc and the d-axis current detection value Id, and the q-axis current deviation between the q-axis current command value Iqc and the q-axis current detection value Iq. The switching control device 9 calculates the d-axis voltage command value Vdc and the q-axis voltage command value Vqc for each current deviation through proportional-integral control calculation.

[0032] The switching control device 9 calculates three-phase voltage command values ​​Vuc, Vvc, and Vwc in a stationary coordinate system from the d-axis voltage command value Vdc, the q-axis voltage command value Vqc, and the electrical angle θe. The switching control device 9 calculates duty command values ​​Du, Dv, and Dw from the three-phase voltage command values ​​Vuc, Vvc, and Vwc and the DC bus voltage Vpn. Using a triangular wave comparison method, which is widely and commonly used in inverter drive, the switching control device 9 calculates on-off control signals for each switching element 14 to 19 from the duty command values ​​Du, Dv, and Dw for each phase. The switching control device 9 then outputs on-off control signals UU, UL, VU, VL, WU, and WL to each drive circuit. Hereinafter, for convenience, the outputs of the drive circuits will also be referred to as UU, UL, VU, VL, WU, and WL.

[0033] The drive circuit turns on and off switching elements 14 to 19 in accordance with on-off control signals UU, UL, VU, VL, WU, and WL. The power conversion circuit 12 converts DC power to AC power by passing a U-phase current Iu, a V-phase current Iv, and a W-phase current Iw, and supplies the AC power to the rotating electric machine 6. The power conversion circuit 12 also converts regenerative power generated by the rotating electric machine 6 in a regenerative state from AC power to DC power, and charges the DC power supply 4. Here, of the above symbols, the electrical angle θe, torque command value Trqc, d-axis current command values ​​Idc and Id1c, q-axis current command values ​​Iqc and Iq1c, d-axis voltage command value Vdc, q-axis voltage command value Vqc, three-phase voltage command values ​​Vuc, Vvc, and Vwc, and duty command values ​​Du, Dv, and Dw are symbols used to make the explanation easier to understand and are not shown in the figures or formulas.

[0034] <Overcurrent response control> The power conversion device 1 exchanges power with the rotating electric machine 6 using the torque command value Trqc, the U-phase current Iu, the V-phase current Iv, the W-phase current Iw, the electrical angle θe, and the DC bus voltage Vpn. However, it is conceivable that the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw may reach excessively large values ​​that exceed the normal control range due to a malfunction of the rotation angle sensor 7 or the current sensor 13, a short circuit or ground fault in the AC bus 5, or a transient malfunction of the arithmetic processing device 90 (transient fixation of the on / off control signal).

[0035] To protect against such excessive currents, thresholds can be set for the U-phase current Iu, V-phase current Iv, and W-phase current Iw to determine whether an overcurrent has occurred. A possible protection circuit would then turn off all switching elements when each current exceeds a threshold, thereby preventing overcurrents.

[0036] 3 is a block diagram of overcurrent response control of a power conversion device 1a according to a comparative example (the power conversion device 1a is not shown). The power conversion device 1a according to the comparative example can be configured by changing the hardware or software of the switching control device 9 of the power conversion device 1 according to the first embodiment. Here, an example in which the circuit for overcurrent response control of the switching control device 9 is changed will be described as a switching control device 9a.

[0037] 3 shows the output portion to the upper switching element 14 and the lower switching element 15 for the U phase in the block diagram of the overcurrent response control. A current detection unit 41 receives a signal from the current sensor 13 and detects the current of each phase of the power conversion device 1a. The current detection unit 41 is configured with a positive side overcurrent detection circuit 24 and a negative side overcurrent detection circuit 25. The positive side overcurrent detection circuit 24 and the negative side overcurrent detection circuit 25 compare the output of the current sensor 13 with a threshold value indicating an overcurrent, and output a signal indicating the occurrence of an overcurrent if the output exceeds the threshold value.

[0038] For example, the positive-side overcurrent detection circuit 24 outputs an H signal when the phase current Iu, Iv, or Iw of any of the U, V, or W phases flows in the positive direction and becomes larger than the threshold value Ioc, and outputs an L signal otherwise. The negative-side overcurrent detection circuit 25 outputs an H signal when the phase current Iu, Iv, or Iw of any of the U, V, or W phases flows in the negative direction and the absolute value of the phase current becomes larger than the threshold value Ioc, and outputs an L signal otherwise. The current detection unit 41 maintains the L output when no overcurrent is flowing.

[0039] The rotating electric machine drive unit 21 outputs a signal DUU that drives the U-phase upper switching element 14 and a signal DUL that drives the U-phase lower switching element 15 to drive the normal rotating electric machine 6. When the overcurrent detection signal OC is L, the signal cutoff circuit 27 outputs the drive signal D as is. Therefore, when the output of the current detection unit 41 is L, the switching control device 9a transmits the output of the rotating electric machine drive unit 21 as is to the switching elements 14 and 15 via the drive circuits 22a and 22b.

[0040] When the overcurrent detection signal OC is H, the signal cutoff circuit 27 maintains the output signal at L regardless of the state of the drive signal D. Therefore, when the output of the current detection unit 41 is H, the switching control device 9a turns off the switching elements 14 and 15 via the drive circuits 22a and 22b to cut off the current.

[0041] 4 is a diagram showing the operation logic of the signal cutoff circuit 27 of the switching control device 9a according to the comparative example. It shows the logic of the output signal O in response to the overcurrent detection signal OC and drive signal D, which are inputs to the signal cutoff circuit 27. As described above, the logic of the signal cutoff circuit 27 is determined by giving priority to the overcurrent detection signal OC.

[0042] 3 has been described with reference to the logic of the signal blocking circuit 27 for the U-phase switching elements 14 and 15. Although not shown in FIG. 3, the rotary electric machine drive unit 21 also outputs a signal DVU for driving the V-phase upper switching element 16, a signal DVL for driving the V-phase lower switching element 17, a signal DWU for driving the W-phase upper switching element 18, and a signal DWL for driving the W-phase lower switching element 19. For the V-phase and W-phase, the signal blocking circuit 27 and drive circuits 22a and 22b are provided for the upper switching elements 16 and 18 and the lower switching elements 17 and 19, respectively. In the switching control device 9a according to the comparative example, as overcurrent response control, all of the switching elements 15 to 19 are blocked when the absolute value of the phase current Iu, Iv, or Iw of any of the U-phase, V-phase, or W-phase becomes larger than a threshold value Ioc.

[0043] <Shutoff control> Fig. 5 is a time chart showing overcurrent response control of a power conversion device 1a according to a comparative example. Fig. 6 is a diagram showing a current flow during normal operation of the power conversion device 1 according to embodiment 1. Fig. 7 is a diagram showing a current flow during overcurrent response control of the power conversion device 1a according to the comparative example. The current flow during normal operation of the power conversion device 1a according to the comparative example is the same as that of the power conversion device 1 according to embodiment 1 shown in Fig. 6.

[0044] The current that flows through the power conversion circuit 12 when an overcurrent is detected and all of the switching elements 14 to 19 are turned off will be described with reference to Figures 5 to 7. Figure 5 shows the waveforms of the phase currents Iu, Iv, and Iw. The lower time chart in Figure 5 is an enlarged version of the time axis of the upper time chart. The power conversion device 1a operates normally up to time Ta. At time Ta, the U-phase upper switching element 14, the V-phase lower switching element 17, and the W-phase lower switching element 19 are on. The U-phase lower switching element 15, the V-phase upper switching element 16, and the W-phase upper switching element 18 are off.

[0045] The normal current paths at this time are indicated by arrows in Figure 6. Current flows from the positive DC bus 3a through U-phase upper switching element 14 to U-phase winding 10a. The current then splits into two paths at the junction of the three-phase windings: one path passing through V-phase winding 10b and V-phase lower switching element 17, and the other path passing through W-phase winding 10c and W-phase lower switching element 19, before flowing to the negative DC bus 3b.

[0046] Consider a case where a temporary fixation occurs in the switching control device 9a, and the on / off states of the switching elements 14 to 19 are fixed. In this case, the current changes without being controlled as it should be.

[0047] At time Tb in Figure 5, the U-phase current Iu becomes excessive and exceeds the threshold value Ioc. The switching control device 9a detects the overcurrent and turns off all control signals for the switching elements 14 to 19, thereby cutting off the current. This prevents the overcurrent.

[0048] At this time, current flows as shown in Figure 7. The current passes through U-phase lower switching element 15 and flows to U-phase winding 10a. The current is then divided into two at the junction of the three-phase windings. The current flows through a path that passes through V-phase winding 10b and V-phase upper switching element 16, and a path that passes through W-phase winding 10c and W-phase upper switching element 18.

[0049] When current flows through switching elements 15, 16, and 18, each switching element is in the off state, so current flows through the respective body diodes. If the current flowing at this time is excessively large due to an overcurrent, it may cause degradation of the body diodes.

[0050] Currently, the use of field-effect transistors made of silicon carbide (SiC) (hereinafter referred to as SiC semiconductor FETs) is being promoted in order to miniaturize power conversion equipment, including inverters. However, even when using SiC semiconductor FETs, the current flowing through the body diode can be a problem. Bipolar operation by the body diode can accelerate crystal degradation of the SiC semiconductor FET. Continuous current flow through the body diode accelerates crystal degradation of the SiC semiconductor, causing the on-voltage of the body diode to rise. As a result, loss in the SiC semiconductor FET increases and the device's functionality deteriorates. This makes it difficult for the power conversion circuit to operate in a stable state.

[0051] <Three-phase short circuit treatment> In order to solve the above problems, the power conversion device 1 according to the first embodiment performs three-phase short-circuit processing when an overcurrent occurs. The three-phase short-circuit processing refers to turning on all of the upper switching elements 14, 16, and 18 and turning off all of the lower switching elements 15, 17, and 19 among the switching elements 14 to 19, or turning on all of the lower switching elements 15, 17, and 19 and turning off all of the upper switching elements 14, 16, and 18.

[0052] <Motor voltage equation> Here, we will explain how to calculate the d-axis current value Id3ps and the q-axis current value Iq3ps in the steady state after three-phase short circuit processing has been performed. First, the voltage equation of the motor is expressed as the following equation (1) using the d-axis voltage Vd, the q-axis voltage Vq, the d-axis current detection value Id, the q-axis current detection value Iq, the armature winding resistance R of the motor, the d-axis inductance Ld of the motor, the q-axis inductance Lq of the motor, the d-axis armature flux linkage number Φm of the motor, and the rotational speed ω of the motor.

[0053]

number

[0054]

number

[0055]

number

[0056]

number

[0057] Furthermore, the effective values ​​Irms of the U-phase current Iu, V-phase current Iv, and W-phase current Iw can be calculated using the d-axis current value Id3ps and the q-axis current value Iq3ps according to the following equation (5).

[0058]

number

[0059] <Operation logic for three-phase short circuit processing> Fig. 8 is a block diagram of overcurrent response control of the power conversion device 1 according to the first embodiment. Fig. 8 shows the portion of the overcurrent response control block diagram that relates to the U phase and outputs to the upper switching element 14 and the lower switching element 15. The current detection unit 41 is the same as the block diagram of Fig. 3 according to the comparative example, and is configured to include a positive side overcurrent detection circuit 24 and a negative side overcurrent detection circuit 25.

[0060] The positive side overcurrent detection circuit 24 or the negative side overcurrent detection circuit 25 compares the output of the current sensor 13 with a threshold value Ioc indicating an overcurrent. If the absolute value of the phase current Iu, Iv, or Iw of any of the U phase, V phase, or W phase detected by the current sensor 13 exceeds the threshold value Ioc, a signal indicating the occurrence of an overcurrent is output.

[0061] The outputs of both the positive side overcurrent detection circuit 24 and the negative side overcurrent detection circuit 25 are transmitted to both the positive side three-phase short circuit processing circuit 26a for the upper switching elements and the negative side three-phase short circuit processing circuit 26b for the lower switching elements. The positive side three-phase short circuit processing circuit 26a and the negative side three-phase short circuit processing circuit 26b determine their outputs depending on whether an overcurrent is detected in the positive side overcurrent detection circuit 24 or the negative side overcurrent detection circuit 25. Under normal conditions where no overcurrent is detected, the positive side three-phase short circuit processing circuit 26a and the negative side three-phase short circuit processing circuit 26b transmit the output of the rotating electric machine drive unit 21 directly to the drive circuits 22a and 22b.

[0062] When a positive-side overcurrent is detected by the positive-side overcurrent detection circuit 24, the positive-side three-phase short-circuit processing circuit 26a transmits an ON instruction signal to the drive circuit 22a, turning on the switching element 14. At this time, the negative-side three-phase short-circuit processing circuit 26b transmits an OFF instruction signal to the drive circuit 22b, turning off the switching element 15.

[0063] When a negative overcurrent is detected by the negative overcurrent detection circuit 25, the positive three-phase short circuit processing circuit 26a transmits an OFF instruction signal to the drive circuit 22a, turning off the switching element 14. At this time, the negative three-phase short circuit processing circuit 26b transmits an ON instruction signal to the drive circuit 22b, turning on the switching element 15.

[0064] 9 is a diagram showing the operation logic of the positive-side three-phase short-circuit processing circuit 26a of the power conversion device 1 according to embodiment 1. The diagram shows the logic of the output signal O with respect to the positive-side overcurrent detection signal OCU, the negative-side overcurrent detection signal OCL, and the drive signal D, which are inputs to the positive-side three-phase short-circuit processing circuit 26a.

[0065] The logic of the positive three-phase short circuit processing circuit 26a is determined by giving priority to the positive overcurrent detection signal OCU. H may be interpreted as an on signal, and L as an off signal. When the positive overcurrent detection signal OCU is H, the output signal O remains in the H state regardless of the states of other input signals. When the positive overcurrent detection signal OCU is L, the logic is determined by giving priority to the negative overcurrent detection signal OCL. In this case, when the negative overcurrent detection signal OCL is H, the output signal O remains in the L state regardless of the state of the drive signal D. When the positive overcurrent detection signal OCU is L and the negative overcurrent detection signal OCL is L, the state of the drive signal D is transmitted as is to the output signal O.

[0066] 10 is a diagram showing the operation logic of the negative three-phase short circuit processing circuit 26b of the power conversion device 1 according to embodiment 1. The diagram shows the logic of the output signal O with respect to the positive overcurrent detection signal OCU, the negative overcurrent detection signal OCL, and the drive signal D, which are inputs to the negative three-phase short circuit processing circuit 26b.

[0067] The logic of the negative three-phase short circuit processing circuit 26b is determined by giving priority to the positive overcurrent detection signal OCU. H may be interpreted as an on signal, and L as an off signal. When the positive overcurrent detection signal OCU is H, the output signal O remains in the L state regardless of the states of other input signals. When the positive overcurrent detection signal OCU is L, the logic is determined by giving priority to the negative overcurrent detection signal OCL. In this case, when the negative overcurrent detection signal OCL is H, the output signal O remains in the H state regardless of the state of the drive signal D. When the positive overcurrent detection signal OCU is L and the negative overcurrent detection signal OCL is L, the state of the drive signal D is transmitted as is to the output signal O.

[0068] Here, negative side overcurrent detection may be disabled during positive side overcurrent detection, and positive side overcurrent detection may be disabled during negative side overcurrent detection. Also, the threshold for determining whether an overcurrent has occurred and the threshold for determining whether an overcurrent has disappeared may be set to different values ​​to provide hysteresis. This can suppress unstable conditions due to vibrations and jitter in the overcurrent detection.

[0069] 8 has described the logic of the positive-side three-phase short-circuit processing circuit 26a and the negative-side three-phase short-circuit processing circuit 26b for the U-phase switching elements 14, 15. Although not shown in Fig. 8, the rotating electric machine drive unit 21 also outputs a signal DVU that drives the V-phase upper switching element 16, a signal DVL that drives the V-phase lower switching element 17, a signal DWU that drives the W-phase upper switching element 18, and a signal DVL that drives the W-phase lower switching element 19.

[0070] For the V phase and the W phase, a positive-side three-phase short-circuit processing circuit 26a, a negative-side three-phase short-circuit processing circuit 26b, and drive circuits 22a and 22b are provided for the upper switching elements 16 and 18 and the lower switching elements 17 and 19, respectively. In the switching control device 9 according to the first embodiment, three-phase short-circuit processing is performed as overcurrent response control when the absolute value of the phase current Iu, Iv, or Iw of any of the U phase, V phase, and W phase becomes larger than a threshold value Ioc. That is, all of the upper switching elements 14, 16, and 18 are turned on and all of the lower switching elements 15, 17, and 19 are turned off, or all of the lower switching elements 15, 17, and 19 are turned on and all of the upper switching elements 14, 16, and 18 are turned off.

[0071] <Identifying the switching element where an overcurrent has occurred> Fig. 11 is a first diagram showing the relationship between the direction of current and overcurrent detection in power conversion device 1 according to embodiment 1. Fig. 12 is a second diagram showing the relationship between the direction of current and overcurrent detection. Here, a method for determining the switching element in which an overcurrent is occurring based on the direction of current detected by U-phase current sensor 13a, V-phase current sensor 13b, and W-phase current sensor 13c will be described.

[0072] 11 shows an example in which upper switching element 14 and lower switching element 17 are on, and phase current Iu flows in the positive direction and phase current Iv flows in the negative direction. At this time, DC bus voltage is applied to U-phase winding 10a and V-phase winding 10b, and excitation current flows through them. Phase current Iu detected by U-phase current sensor 13a increases in the positive direction, and phase current Iv detected by V-phase current sensor 13b increases in the negative direction.

[0073] An overcurrent is detected when the current increases and exceeds the threshold value Ioc. Therefore, if an overcurrent occurs when U-phase current sensor 13a detects a current in the positive direction, it can be determined that upper switching element 14 is in the on state and the overcurrent has occurred in switching element 14. Similarly, if an overcurrent is detected when V-phase current sensor 13b detects a current in the negative direction, it can be determined that lower switching element 17 is in the on state and the overcurrent has occurred in switching element 17.

[0074] 12 shows a case where the upper switching element 14 and the lower switching element 17 are in the on state, and the phase current Iu flows in the negative direction and the phase current Iv flows in the positive direction. At this time, the U-phase winding 10a and the V-phase winding 10b generate a back electromotive force, and a free-wheeling current flows. In other words, this shows a state where the DC power supply 4 is being charged by the power generated by the rotating electric machine 6.

[0075] At this time, the phase current Iu detected by the U-phase current sensor 13a decreases in the negative direction, and the phase current Iv detected by the V-phase current sensor 13b decreases in the positive direction. Because the currents decrease, it can be said that no overcurrent occurs in the state shown in Figure 12.

[0076] The above is not limited to the combination of switching element 14 and switching element 17. The same can be said for the relationship between current and voltage in other combinations of switching elements. That is, if an overcurrent is detected when the phase currents Iu, Iv, and Iw are in the positive direction, it can be determined that an overcurrent has occurred in the upper switching elements 14, 16, and 18, respectively. If an overcurrent is detected when the phase currents Iu, Iv, and Iw are in the negative direction, it can be determined that an overcurrent has occurred in the lower switching elements 15, 17, and 19, respectively.

[0077] <Current during three-phase short circuit treatment> Fig. 13 is a time chart showing the overcurrent response control of the power conversion device 1 according to embodiment 1. Fig. 14 is a diagram showing the current flow of the overcurrent response control of the power conversion device 1 according to embodiment 1. The operation when a three-phase short circuit is performed by the positive-side three-phase short-circuit processing circuit 26a for the upper switching elements and the negative-side three-phase short-circuit processing circuit 26b for the lower switching elements will be described with reference to Figs. 13 and 14.

[0078] Figure 13 shows the waveforms of phase currents Iu, Iv, and Iw. The lower time chart in Figure 13 is an enlarged version of the time axis of the upper time chart. Power conversion device 1 operates normally up to time Ta. At time Ta, U-phase high-side switching element 14, V-phase low-side switching element 17, and W-phase low-side switching element 19 are on. U-phase low-side switching element 15, V-phase high-side switching element 16, and W-phase high-side switching element 18 are off.

[0079] In this case, current flows along the path shown in Figure 6. It passes through U-phase upper switching element 14 and then to U-phase winding 10a. The current then splits into two paths at the junction of the three-phase windings: one path passing through V-phase winding 10b and V-phase lower switching element 17, and the other path passing through W-phase winding 10c and W-phase lower switching element 19.

[0080] Consider a case where a temporary fixation occurs in the switching control device 9a, and the on / off states of the switching elements 14 to 19 are fixed. In this case, the current changes without being controlled as it should be.

[0081] At time Tb in Figure 13, the U-phase current Iu becomes excessive and exceeds the threshold value Ioc. The switching control device 9 detects the overcurrent in the upper switching elements and performs three-phase short-circuit processing, turning on all of the upper switching elements 14, 16, and 18. At the same time, the lower switching elements 15, 17, and 19 are all turned off.

[0082] 14, at this time, current flows through U-phase winding 10a via U-phase upper switching element 14. This current is divided into two at the junction of the three-phase windings, and flows through a path that passes through V-phase winding 10b and V-phase upper switching element 16, and a path that passes through W-phase winding 10c and W-phase upper switching element 18.

[0083] Here, switching element 14 remains on, preventing excessive current from flowing to the body diode of the opposite switching element 15. Switching elements 16 and 18 are on, which results in a small resistance value called on-resistance, so current does not flow through the body diode portion, but flows through the transistor portion of the switching element.

[0084] If a three-phase short circuit occurs, the current will temporarily increase, but over time it will converge to the effective current value shown in equation (5). This prevents overcurrent. During this time, the switching elements 14, 16, and 18 that are passing current are on, so no current flows through the body diodes.

[0085] In this way, when an overcurrent flows through the switching elements of the power conversion device 1, it is possible to suppress the overcurrent while preventing a large current from flowing through the body diodes of the switching elements by turning on either all of the positive-side switching elements or all of the negative-side switching elements and turning off the other. This makes it possible to obtain a power conversion device 1 that can protect the body diodes and prevent degradation of the switching elements while promoting miniaturization and cost reduction without requiring the installation of additional freewheeling diodes or enlarging the semiconductor size.

[0086] In the above description, the positive-side three-phase short-circuit processing circuit 26a and the negative-side three-phase short-circuit processing circuit 26b are provided to switch the on / off signal of the rotary electric machine drive unit 21 between continuous on and continuous off. However, in addition to the normal on / off signal input, an input for forcibly instructing on / off may be provided to the drive circuit, and a signal instructing based on the result of overcurrent detection may be input.

[0087] After the three-phase short-circuit process is performed, the current converges to the effective current value shown in equation (5). After the absolute value of the current has decreased to the required level due to current convergence and becomes smaller than a second threshold value that is smaller than the threshold value Ioc, the three-phase short-circuit process can be canceled and all switching elements can be turned off. By doing so, the phase currents flowing to the windings can be changed to zero. In addition, during this process, the current flowing through the body diode can be reduced after all switching elements are turned off.

[0088] In this case, by releasing the three-phase short-circuit process at a current value equal to or less than the allowable current value of the body diode, it is possible to prevent deterioration and shortening of the lifespan of the body diode. For this reason, it is effective to determine the second threshold value based on the characteristics of the body diode of the switching element.

[0089] Alternatively, the three-phase short circuit processing may be cancelled by setting the second threshold to a current value that reduces the surge voltage generated when the switching elements are turned off to a tolerable voltage or less. To do so, it is effective to determine the second threshold based on the characteristics of the rotating electric machine 6. This makes it possible to prevent breakdowns of the switching elements due to their exceeding the withstand voltage.

[0090] Furthermore, when turning off the switching element, the off transition time may be set to be longer than the normal off transition time, which further suppresses the occurrence of surge voltage and prevents breakdowns due to the switching element exceeding its withstand voltage.

[0091] 2. Second Embodiment Fig. 15 is a configuration diagram of a power conversion device 1b according to embodiment 2. The configuration diagram of Fig. 15 differs from the configuration of the power conversion device 1 of Fig. 1 according to embodiment 1 in that the power conversion device 1b is connected to a second DC power source 44 in addition to the DC power source 4.

[0092] By providing a power supply circuit that generates power from the DC power supply 4 and the second DC power supply 44, three-phase short-circuit processing can be performed even when the DC power supply 4 fails, allowing for more reliable operation. The second DC power supply 44 may be a storage battery that is charged from the DC power supply 4. The second DC power supply 44 may also be a power supply that generates power by stepping down a voltage from a higher-voltage power supply using a DC-DC converter. Furthermore, the second DC power supply 44 may also be a power supply that generates power by stepping up a voltage from a lower-voltage power supply using a DC-DC converter.

[0093] Furthermore, in general, the switching control device 9, voltage detection circuit 11, current sensor 13, rotation angle sensor 7, and the like often generate their respective power sources from a low-voltage DC power source such as a lead battery to operate. If this low-voltage DC power source fails, the above-mentioned three-phase short-circuit processing cannot be performed. To prevent such a situation, a power supply circuit 45 may be provided that can generate power from the higher-voltage DC power source 4 in addition to the low-voltage DC power source. In this way, even if the low-voltage DC power source fails, power can be generated from the DC power source 4, making it possible to perform three-phase short-circuit processing.

[0094] 15, power supply circuit 45 is capable of supplying 5V power supply 47 to switching control device 9, voltage detection circuit 11, current sensor 13, rotation angle sensor 7, etc. from either DC power supply 4 or low-voltage DC power supply 46. Here, the case where DC power supply 4 is a power supply separate from a lead battery has been described, but DC power supply 4 may also be a power supply that uses a lead battery.

[0095] In this embodiment, wide bandgap semiconductors, such as SiC semiconductor FETs, may be used as the switching elements 14 to 19. Wide bandgap semiconductors can operate at voltages, frequencies, and temperatures much higher than conventional semiconductor materials such as silicon and gallium arsenide. This allows the switching elements to be made smaller and lighter while still achieving high performance. When using SiC semiconductor FETs, the three-phase short-circuiting process of the present invention is more suitable because it can suppress the progression of crystal degradation.

[0096] 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.

[0097] Various aspects of the present disclosure are summarized below as appendices.

[0098] (Appendix 1) a three-phase arm provided with a positive-side switching element connected to a positive side of a DC power supply, a negative-side switching element connected to a negative side of the DC power supply, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and connected to a winding of a rotating electric machine; a phase current detection unit that detects a current for each phase flowing between the external connection point and the winding; and a switching control device that controls a rotating electric machine by controlling the on / off of the positive-side switching elements and the negative-side switching elements, respectively, and determines that an overcurrent has occurred when the current detected by the phase current detection unit exceeds a predetermined threshold, and turns on either all of the positive-side switching elements or all of the negative-side switching elements and turns off the other. (Appendix 2) the phase current detection unit detects a direction and a value of a current for each phase flowing between the external connection point and the winding; The power conversion device according to claim 1, wherein the switching control device determines whether the overcurrent has occurred in the positive-side switching element or the negative-side switching element based on the direction of the current detected by the phase current detection unit when it is determined that the overcurrent has occurred. (Appendix 3) The power conversion device according to claim 2, wherein, when it is determined that the overcurrent has occurred, the switching control device turns on one of the positive-side switching element and the negative-side switching element in which the overcurrent has occurred, and turns off the other switching element. (Appendix 4) The power conversion device according to any one of appendixes 1 to 3, wherein when determining that the overcurrent has occurred, the switching control device turns on one of the positive-side switching element and the negative-side switching element in which the overcurrent has occurred, and turns off the other switching element, and then turns off all of the switching elements when the current value detected by the phase current detection unit becomes equal to or less than a predetermined second threshold. (Appendix 5) The power conversion device according to claim 4, wherein the second threshold value with which the switching control device compares the current value detected by the phase current detection unit to determine whether to turn off all of the switching elements is specified based on characteristics of the rotating electric machine. (Appendix 6) The power conversion device according to claim 4 or 5, wherein the second threshold value with which the current values ​​detected by the phase current detection units are compared to determine whether the switching control device should turn off all of the switching elements is specified based on characteristics of body diodes of the switching elements. (Appendix 7) 7. The power conversion device according to claim 4, wherein the second threshold value with which the current values ​​detected by the phase current detection unit are compared to determine whether the switching control device should turn off all of the switching elements is specified based on switching characteristics of the switching elements. (Appendix 8) The power conversion device according to any one of appendixes 4 to 7, wherein the switching control device turns off all of the switching elements in an off transition time that is longer than a normal off time. (Appendix 9) 9. The power conversion device according to claim 1, further comprising a power supply circuit capable of generating power from both the DC power supply and a second DC power supply. (Appendix 10) 10. The power conversion device according to claim 9, wherein the phase current detection unit receives power supply from the power supply circuit. (Appendix 11) 11. The power conversion device according to claim 1, wherein the switching element uses a wide bandgap semiconductor. [Explanation of symbols]

[0099] 1, 1a Power conversion device, 4 DC power supply, 6 Rotating electric machine, 8 Inverter circuit, 9, 9a Switching control device, 10a, 10b, 10c Winding, 12 Power conversion circuit, 13 Current sensor, 13a U-phase current sensor, 13b V-phase current sensor, 13c W-phase current sensor, 14, 15, 16, 17, 18, 19 Switching element, 41 Current detection unit, 44 Second DC power supply, 45 Power supply circuit

Claims

1. a three-phase arm provided with a positive-side switching element connected to a positive side of a DC power supply, a negative-side switching element connected to a negative side of the DC power supply, and an external connection point connecting the positive-side switching element and the negative-side switching element in series and connected to a winding of a rotating electric machine; a phase current detection unit that detects a current for each phase flowing between the external connection point and the winding; and a switching control device that controls a rotating electric machine by controlling the on / off of the positive pole side switching elements and the negative pole side switching elements, and determines that an overcurrent has occurred when a current detected by the phase current detection unit exceeds a predetermined threshold value, and turns on either all of the positive pole side switching elements or all of the negative pole side switching elements and turns off the other, the phase current detection unit detects a direction and a value of a current for each phase flowing between the external connection point and the winding; The switching control device detects whether an overcurrent has occurred in the positive pole side switching element and the negative pole side switching element based on the direction of the current detected by the phase current detection unit when the occurrence of the overcurrent is detected, and when the occurrence of the overcurrent is detected, turns on one of the positive pole side switching element and the negative pole side switching element in which the occurrence of the overcurrent was first detected, and turns off the other switching element.

2. The power conversion device described in Claim 1, wherein the switching control device turns on the positive side switching element and turns off the negative side switching element when overcurrent occurrence in the positive side switching element and the negative side switching element is detected simultaneously.

3. 3. The power conversion device according to claim 1, wherein when determining that the overcurrent has occurred, the switching control device turns on one of the positive-side switching element and the negative-side switching element in which the overcurrent has occurred, and turns off the other switching element, and then turns off all of the switching elements when the current value detected by the phase current detection unit becomes equal to or less than a predetermined second threshold.

4. 4. The power conversion device according to claim 3, wherein the second threshold value with which the switching control device compares the current values ​​detected by the phase current detection unit to determine whether to turn off all of the switching elements is defined based on characteristics of the rotating electric machine.

5. 4. The power conversion device according to claim 3, wherein the second threshold value with which the current values ​​detected by the phase current detection units are compared to determine whether the switching control device should turn off all of the switching elements is defined based on characteristics of body diodes of the switching elements.

6. 4. The power conversion device according to claim 3, wherein the second threshold value with which the switching control device compares the current values ​​detected by the phase current detection units to determine whether to turn off all of the switching elements is defined based on the switching characteristics of the switching elements.

7. The power conversion device according to claim 3 , wherein the switching control device turns off all of the switching elements in an off transition time that is longer than a normal off time.

8. A second DC power supply is provided, 3. The power conversion device according to claim 1, wherein the positive-side switching element is connected to both the DC power source and the second DC power source.

9. A power supply circuit capable of generating power from both the DC power supply and the second DC power supply, The power conversion device according to claim 8 , wherein the phase current detection unit and the switching control device receive power supply from the power supply circuit.

10. 3. The power conversion device according to claim 1, wherein the switching elements are made of wide bandgap semiconductors.

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