Power conversion device

Abstract

To change switching speed according to an operation state, to prevent fault of a switching element, degradation of performance, and shortening of lifespan while achieving both efficient power conversion operation and power conversion operation in a wide range.SOLUTION: A power conversion device comprises: a power conversion circuit in which positive-pole side switching elements and negative-pole side switching elements are connected in series, and AC output is derived; a DC voltage detector; a phase current detector; and a control device having a control unit for outputting a control signal and a speed instruction signal, an overvoltage protection unit, an overcurrent protection unit, and a gate driving unit for driving the switching elements on the basis of the control signal and the speed instruction signal, and stopping the switching elements on the basis of an over voltage blocking signal and an overcurrent blocking signal. The power conversion device can change at least one of an overvoltage determination threshold value and an overcurrent determination threshold value at the same time as changing the speed instruction signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Power conversion devices are often used as control devices for rotating machines (motors) applied to electrically powered vehicles such as hybrid vehicles and electric cars. Examples of power conversion devices include AC / DC (Alternate Current / Direct Current Converters) that convert AC power to DC power, inverters that convert DC power to AC power, and DC / DC (Direct Current / Direct Current Converters) that change the levels of the input and output voltages of DC power. These power conversion devices are often configured with semiconductor switching elements.

[0003] As an example of a power conversion device, an inverter mounted on an electric vehicle is used to convert DC power output from a DC power source into desired AC power and supply it to a rotating machine to control the rotating machine. A power conversion device is composed of a switching circuit formed by combining switching elements, a control circuit for controlling the switching elements, a current sensor for detecting the current flowing through a load such as a rotating machine, a capacitor for reducing switching noise, etc. When controlling a three-phase synchronous rotating machine, for example, a power conversion device may be provided with a switching circuit in each of the upper arm (positive arm) and lower arm (negative arm) of the three phases (U phase, V phase, W phase).

[0004] By sequentially turning on and off the switching elements provided for each phase of the inverter, AC power with a phase difference of 120 degrees is supplied to each phase of the rotating machine to drive the rotating machine. Since the efficiency of such on-board electrical equipment is directly linked to the fuel and power consumption of the vehicle, reducing losses is important.

[0005] Increasing the switching speed is an effective way to reduce the switching loss of a power conversion device. However, increasing the switching speed increases the surge voltage when the switching element is turned on and off, and also increases the driving noise. For this reason, the switching speed must be increased within a range that can prevent the deterioration of the switching element due to the surge voltage and the exceeding of the withstand voltage.

[0006] A technique is disclosed in which an expected surge voltage is calculated based on the temperature of a switching element, a current command, and a DC power supply voltage, and the switching speed is increased when the surge voltage has a margin relative to the withstand voltage of the switching element. In order to increase the switching speed, for example, a method has been proposed in which the gate voltage of an IGBT (Insulated Gate Bipolar Transistor) used as the switching element is increased, thereby reducing switching loss while keeping the surge voltage of the switching element below the withstand voltage (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 433802 Summary of the Invention [Problem to be solved by the invention]

[0008] In the technology of Patent Document 1, a gate voltage corresponding to an appropriate switching speed is set from a surge voltage calculated based on a command current and a battery voltage. However, there is no mention of a method for setting a threshold value for judging an overcurrent or overvoltage when the switching speed is changed. For this reason, the change in current and voltage after detecting an overcurrent or overvoltage is not taken into consideration, and when the current and voltage rise sharply in an abnormality, the switching operation may be performed at a current and voltage higher than expected. Then, the surge voltage may exceed the withstand voltage value of the switching element, causing the switching element to break down, or the performance may be degraded, resulting in a shortened lifespan.

[0009] When the switching speed is increased and the power conversion device is operated, if the current or voltage suddenly changes and exceeds the overcurrent judgment threshold or the overvoltage judgment threshold, it is necessary to consider the large surge voltage that occurs when turning on and off the switching element is stopped. For this reason, it is necessary to set the overcurrent judgment threshold or the overvoltage judgment threshold small. In that case, the maximum operating current and maximum operating voltage when the switching speed is not increased are also limited, limiting the operating range of the power conversion device.

[0010] The present disclosure discloses a technique for solving the above-mentioned problems. It is an object of the present invention to provide a power conversion device that can change the switching speed according to the operating state of the power conversion device, and can achieve both efficient power conversion operation and power conversion operation over a wide range while preventing failure, performance degradation, and shortened lifespan of switching elements. [Means for solving the problem]

[0011] The power conversion device according to the present disclosure comprises: a power conversion circuit including a positive-side switching element connected to a positive electrode of a DC power supply, a negative-side switching element connected to a negative electrode of the DC power supply, and an external connection point that connects the positive-side switching element and the negative-side switching element in series and from which an AC output is derived; a voltage detector for detecting a voltage between the positive and negative poles of the power conversion circuit; a phase current detector for detecting a phase current flowing between an external connection point of the power conversion circuit and an AC output; and a control device having: a control unit that outputs a control signal for controlling a switching element based on an external command value and outputs a speed instruction signal for instructing a switching speed of the switching element; an overvoltage protection unit that outputs an overvoltage cut-off signal when a voltage detected by a voltage detector is greater than a predetermined overvoltage determination threshold; an overcurrent protection unit that outputs an overcurrent cut-off signal when a phase current detected by a phase current detector is greater than a predetermined overcurrent determination threshold; and a gate drive unit that turns on and off the switching element based on the control signal output by the control unit, changes the on / off speed of the switching element based on the speed instruction signal, and stops the on / off of the switching element based on the overvoltage cut-off signal output by the overvoltage protection unit and the overcurrent cut-off signal output by the overcurrent protection unit, The control device changes at least one of the overvoltage determination threshold and the overcurrent determination threshold simultaneously with the change in the speed instruction signal. Effect of the Invention

[0012] According to the present disclosure, it is possible to obtain a power conversion device that can change at least one of an overcurrent determination threshold and an overvoltage determination threshold in accordance with the operating state of the power conversion device while changing the switching speed, thereby achieving both efficient power conversion operation over a wide range, while preventing failure, performance degradation, and shortened lifespan of switching elements. [Brief description of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a power conversion device according to a first embodiment. [Diagram 2] 2 is a first hardware configuration diagram of a control device for a power conversion device according to the first embodiment. FIG. [Diagram 3] 10 is a first diagram showing a response at the time of overcurrent detection of a power conversion device according to a comparative example. FIG. [Figure 4] FIG. 11 is a second diagram showing how the power conversion device according to the comparative example responds when an overcurrent is detected. [Diagram 5]5 is a flowchart showing a process for changing a switching speed of the control device for the power conversion device according to the first embodiment. [Figure 6] 5 is a diagram illustrating setting of an overcurrent determination threshold value of the power conversion device according to the first embodiment. FIG. [Figure 7] 5 is a diagram showing how the power conversion device according to the first embodiment responds when an overcurrent is detected. FIG. [Figure 8] 4 is a second hardware configuration diagram of the control device for the power conversion device according to the first embodiment. FIG. [Figure 9] FIG. 11 is a configuration diagram of a power conversion device according to a second embodiment. [Figure 10] 10 is a flowchart showing a process for changing a switching speed of a control device for a power conversion device according to a second embodiment. [Figure 11] 13 is a diagram showing settings of an overcurrent determination threshold and an overvoltage determination threshold of a power conversion device according to the second embodiment. FIG. [Figure 12] FIG. 11 is a diagram illustrating setting of a switching speed of a power conversion device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a power conversion device according to the present disclosure will be described with reference to the drawings.

[0015] 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 may be used in an electrically powered vehicle such as an electric vehicle or a plug-in hybrid vehicle. It is possible to imagine a power conversion device for driving a rotating machine (motor) serving as a load with an AC current using a DC power source such as a battery. The load is not limited to a rotating machine, and may be something other than a rotating machine.

[0016] The power conversion device 1 is connected to a DC power source 2 and a rotating machine 3, and is composed of a smoothing capacitor 10, a power conversion circuit 200 having positive side switching elements 11, 13, 15 and negative side switching elements 12, 14, 16, and a control device 100 that controls the switching elements 11 to 16. The DC power source 2 supplies power to the power conversion circuit 200 via a positive side DC bus bar and a negative side DC bus bar. The smoothing capacitor 10 plays a role in smoothing fluctuations in DC power generated by the power conversion circuit 200.

[0017] In Fig. 1, the power conversion circuit 200 has three-phase positive pole side switching elements 11, 12, 13, three-phase negative pole side switching elements 14, 15, 16, and three external connection points where the positive pole side switching elements and the negative pole side switching elements are connected in series for each phase and are connected to the rotating machine 3. Each switching element may be configured by connecting multiple transistors in parallel. Also, although Fig. 1 shows a case where the power conversion device 1 has a three-phase output, it may have a two-phase or four or more phase output.

[0018] The rotating machine 3 is provided with a rotation angle sensor 4 using a resolver, a Hall element, etc., and a rotation angle θ of the rotating machine 3 is transmitted to a control unit 17. The power conversion device 1 is provided with a voltage detector 21 that detects a DC voltage between a positive DC bus bar and a negative DC bus bar, and a DC voltage value Vdc is transmitted to the control unit 17 and an overvoltage protection unit 19. The power conversion device 1 is also provided with phase current detectors 22, 23, 24 that detect phase currents flowing from an external connection point of the power conversion circuit 200 to each phase of the rotating machine 3, and phase current values ​​iu, iv, iw are transmitted to the control unit 17 and an overcurrent protection unit 20.

[0019] Furthermore, a command value is transmitted to the control unit 17 from outside the power conversion device 1, and the control unit 17 outputs a signal to control the switching elements 11 to 16 based on the command value. Detection values ​​of the rotation angle sensor 4, the voltage detector 21, the phase current detectors 22, 23, 24, etc. may be used for the control of the switching elements 11 to 16 by the control unit 17. Possible command values ​​input from outside include a target rotation speed, a target torque, a target current, a target voltage, etc. The control unit 17 may be a calculation device that executes software to calculate input data and determine an output value.

[0020] <Switching element> As switching elements, diodes that pass current in only one direction, thyristors that are suitable for handling large currents, and power transistors, which are power semiconductor switching elements that can operate at high switching frequencies, are often used. Among semiconductor switching elements, power transistors in particular are used in a wide range of fields, such as automobiles, refrigerators, and air conditioners. Power transistors include IGBTs (Insulated Gate Bipolar Transistors) and MOS-FETs (Metal-oxide-Semiconductor Field-Effect Transistors), and these power transistors are used for various purposes.

[0021] Semiconductors using silicon (Si) are often used as the material for semiconductor switching elements. However, in recent years, silicon carbide (SiC) and gallium nitride (GaN) have been attracting attention. Semiconductor switching elements made from these wide band gap semiconductor materials have a lower resistance in the on-state compared to conventional semiconductor switching elements using silicon, and can reduce power loss. In addition, they have a high electron saturation velocity, allowing them to quickly switch between on and off states.

[0022] 1 shows an example in which IGBTs are used as the switching elements 11 to 16. A free wheel diode (FWD) is connected in parallel to each of the IGBTs of the switching elements 11 to 16, with the forward direction being the direction from the negative side to the positive side of the DC power supply 2, i.e., the direction from the lower stage to the upper stage.

[0023] A control terminal of each switching element is connected to a gate driver 18 of the control device 100. The gate driver 18 receives a control signal (on / off signal) 17a from the control unit 17 and transmits drive signals 111, 121, 131, 141, 151, and 161 to the control terminals of each switching element 11 to 16. The gate driver 18 receives a switching speed signal 17b from the control unit 17 and changes the switching speed of the switching element.

[0024] <Switching speed change> The switching speed of the switching element can be changed by adjusting the value of the gate current flowing into the gate in the case of an IGBT by changing the value of the gate resistance. By increasing the amount of current flowing into the gate, the switching speed increases.

[0025] Also, for IGBTs, the switching speed can be changed by adjusting the voltage of the gate drive circuit to change the gate voltage. Increasing the gate voltage increases the switching speed and improves switching efficiency, but increases surge voltage and switching noise. Conversely, lowering the gate voltage decreases the switching speed and decreases switching efficiency, but both surge voltage and noise can be reduced.

[0026] MOS-FETs also have the characteristic that the rise time slows down as the gate current decreases. Therefore, by changing the value of the gate resistor, the gate current can be adjusted, and the switching speed can be adjusted.

[0027] <Overvoltage protection, overcurrent protection> When the DC voltage value Vdc exceeds the overvoltage determination threshold VTHOV, the overvoltage protection unit 19 outputs an overvoltage detection signal 19a to the gate drive unit 18 and the control unit 17. Upon receiving the overvoltage detection signal 19a, the gate drive unit 18 stops turning on and off the switching elements 11 to 16. Furthermore, upon receiving the overvoltage detection signal 19a, the control unit 17 recognizes the occurrence of an overvoltage. The overvoltage protection unit 19 may be formed, for example, of a circuit that uses a comparator to compare a voltage value obtained by resistive voltage division from the DC voltage value Vdc with a voltage corresponding to a predetermined overvoltage determination threshold VTHOV.

[0028] When the absolute values ​​of the phase current values ​​iu, iv, iw exceed the overcurrent determination threshold ITHOC, the overcurrent protection unit 20 outputs an overcurrent detection signal 20a to the gate driver 18 and the control unit 17. Upon receiving the overcurrent detection signal 20a, the gate driver 18 stops turning on and off the switching elements 11 to 16. Furthermore, upon receiving the overcurrent detection signal 20a, the control unit 17 recognizes the occurrence of an overcurrent.

[0029] The overcurrent protection unit 20 may be configured, for example, by a circuit that uses a comparator to compare the output voltage of a Hall-type current detection circuit with a voltage corresponding to the overcurrent determination threshold ITHOC. The adjustment of the overcurrent determination threshold ITHOC of the overcurrent protection unit 20 may be achieved by switching a voltage dividing resistor of a reference voltage of the circuit using a transistor. The adjustment of the overcurrent determination threshold ITHOC of the overcurrent protection unit 20 may be achieved by generating a voltage to be compared using a D / A converter (Digital / Analog Converter) based on the overcurrent threshold signal 17c received as an H / L (High / Low) signal, an analog voltage signal, or a digital signal indicating a voltage value.

[0030] By configuring overvoltage protection unit 19 and overcurrent protection unit 20 as described above, it is possible to detect overvoltage and overcurrent and respond in a shorter time than if control unit 17, which is a calculation device that executes software, were to detect and issue control instructions. This is because overvoltage and overcurrent can be detected using the analog and digital circuits of overvoltage protection unit 19 and overcurrent protection unit 20, and the on / off switching of switching elements 11 to 16 can be stopped quickly.

[0031] <Control device hardware configuration> Fig. 2 is a hardware configuration diagram of the control device 100 of the power conversion device 1 according to the first embodiment. In this embodiment, each function of the control device 100 is realized by a processing circuit provided in the control device 100. Specifically, as shown in Fig. 2, the control device 100 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 an external signal to the arithmetic processing device 90, and an output circuit 93 that outputs a signal from the arithmetic processing device 90 to the outside. The control unit 17 in Fig. 1 may include the arithmetic processing device 90.

[0032] 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. Also, the arithmetic processing device 90 may be a plurality of devices of the same type or different types, and each process may be shared and executed. 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 such as the voltage detector 21, the phase current detectors 22, 23, 24, and the rotation angle sensor 4, and includes an analog / digital converter (A / D converter) that inputs output signals of these sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads such as the switching elements 11 to 16, and includes a gate driver 18 that converts control signals from the arithmetic processing device 90 and outputs them to these electrical loads.

[0033] Each function of the control device 100 is realized by the arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM, and cooperating with other hardware of the control device 100 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 control device 100 are stored in the storage device 91 such as a ROM as part of the software (programs). The functions of the components of the control device 100 will be described. Each function of the control device 100 may be configured as a software module, or may be configured as a combination of software and hardware.

[0034] <Switching speed change and overcurrent interruption (1)> In power conversion devices, it is effective to increase the switching speed in order to reduce switching losses. However, increasing the switching speed increases the surge voltage when the switching element is turned on and off, and also increases the driving noise. For this reason, the switching speed must be increased within a range that does not exceed the withstand voltage of the switching element due to the surge voltage.

[0035] A surge voltage predicted when the switching element is turned on and off can be calculated based on a command value (current command value) to the power conversion device, a battery voltage, etc. Then, a control that increases the switching speed can be considered only when the predicted surge voltage calculated with respect to the withstand voltage of the switching element is sufficiently low. For example, consider a case where the switching speed is made high when the current command value of the power conversion device or the detected phase current is equal to or lower than a predetermined switching speed switching current value, and is made low when the current command value is higher than the switching speed switching current value.

[0036] However, when the switching speed is increased and the power conversion device is operated, if the current or voltage suddenly changes and exceeds the overcurrent judgment threshold or the overvoltage judgment threshold, it is necessary to consider a large surge voltage that occurs when turning on and off the switching element is stopped. For this reason, it is necessary to set the overcurrent judgment threshold and the overvoltage judgment threshold small, taking into consideration the case where the switching speed is increased. In that case, the maximum operating current and the maximum operating voltage when the switching speed is not increased are also limited by the overcurrent judgment threshold and the overvoltage judgment threshold, and the operating range of the power conversion device is limited.

[0037] Fig. 3 is a first diagram showing a response when an overcurrent is detected in a power conversion device according to a comparative example. Here, an explanation will be given with reference to the configuration of the power conversion device 1 according to the first embodiment. When the switching speed is slow and exceeds an overcurrent determination threshold (indicated by a black circle (●) in Fig. 3), an overcurrent is determined. At this time, an immediate cutoff is not possible due to a delay in the overcurrent protection unit 20, and a cutoff current higher than the overcurrent determination threshold actually occurs (indicated by a black triangle (▲) in Fig. 3).

[0038] It is necessary to prevent the surge voltage generated when an interruption is performed at this current from exceeding the withstand voltage value of switching elements 11 to 16. To achieve this, it is necessary to set the switching speed on the slow side so that the surge voltage generated by the interruption current shown by the dashed line in Figure 3 does not exceed the withstand voltage of switching elements 11 to 16.

[0039] Consider the case where the switching speed is high. Assume that a problem occurs when the switching speed is high, causing an overcurrent. When the current command value of the power conversion device 1 or the detected phase current is larger than the switching speed switching current value, the switching speed is switched to a low speed. However, the switching of the switching speed is performed by transmitting a switching speed signal 17b from the control unit 17 to the gate drive unit 18.

[0040] The control unit 17 controls the power conversion operation based on a command value received from the outside. In this case, a delay time occurs until the control unit 17 calculates the current command value or the detected phase current and outputs the switching speed signal 17b based on the processing result.

[0041] In many cases, the switching frequency of the switching elements 11 to 16 of the power conversion device 1 mounted on a vehicle is at most about 10 kHz. For example, when PWM (Pulse Width Modulation) control is performed at a switching frequency of 10 kHz, a current command is generated at a period of 100 μs, and sensor information such as current, voltage, temperature, and angular velocity is sampled, and the PWM output is calculated using the sensor information. A delay of about 100 μs occurs when switching the switching speed based on the current command value of the power conversion device 1 or the detected phase current. In other words, the set switching speed is based on parameters 100 μs ago, and when parameters such as the current command value, phase current, and voltage change, switching may not be performed at an appropriate switching speed for the parameters at that time.

[0042] When power conversion is being performed at a high switching speed in Fig. 3, if an abnormality occurs and the phase current suddenly rises, the occurrence of an overcurrent is determined at the point in time when the phase current exceeds the overcurrent determination threshold (white circle (◯) in Fig. 3), and the overcurrent protection unit 20 outputs an overcurrent detection signal 20a to the gate drive unit 18. Then, the gate drive unit 18 stops turning on and off the switching elements 11 to 16 upon receiving the overcurrent detection signal 20a.

[0043] At this time, delays in overcurrent protection unit 20 prevent immediate shutdown, and in fact a shutdown current higher than the overcurrent determination threshold occurs (white triangle (△) in Figure 3). Because the current increases before the switching speed of the switching element is switched from a high-speed setting to a low-speed setting, shutdown occurs with the switching speed still set to high at the shutdown current shown by the dashed line. Since the higher the switching speed, the higher the surge voltage, with settings such as those in Figure 3, there is a risk that the surge voltage will exceed the withstand voltage of the switching element at the increased shutdown current in the event of an abnormality, causing a breakdown.

[0044] <Switching speed change and overcurrent interruption (2)> Fig. 4 is a second diagram showing the response of the power conversion device according to the comparative example when an overcurrent is detected. In order to improve the problem shown in Fig. 3, the switching speed switching current value is reduced as shown in Fig. 4. By setting it in this way, the time during which the detected phase current rises from the switching speed switching current value to the cutoff current is extended, and the switching speed of the switching element is switched to a low speed during this time.

[0045] In this way, the switching speed is switched from high to low at the point when the abnormal current reaches the cutoff current (white triangle (△) in Figure 4). Therefore, the surge voltage is kept within a range that does not exceed the withstand voltage of the switching element.

[0046] When the switching speed is set as shown in Fig. 4, a problem occurs in that the current range in which the switching speed can be set to high is narrowed. The operating range in which the switching speed can be set to high and switching loss can be reduced is limited. Specifically, in an electric vehicle, it is expected that switching loss will be reduced in the range in which the load of the rotating machine is small, such as during cruising, and the phase current is medium or lower, excluding the range in which the load of the rotating machine is large and the phase current is large, such as when starting and accelerating. However, the range in which switching loss can be reduced by reducing the switching speed switching current value is narrowed, and loss reduction that is directly linked to the fuel consumption and power consumption of the vehicle cannot be sufficiently implemented.

[0047] Furthermore, the timing for calculating the drive timing, drive time, and switching speed of the switching elements 11 to 16 in the control unit 17 is, for example, executed in a cycle of 100 μs. Therefore, if the current rises in a shorter time during an abnormality, the switching speed may not be switched to the slower speed in time, and if the switching speed is high, the surge voltage at the time of cutoff may exceed the withstand voltage, and overcurrent protection may not be established.

[0048] <Simultaneous change of switching speed and overcurrent threshold> 5 is a flowchart showing the process of changing the switching speed of the control device 100 of the power conversion device 1 according to embodiment 1. A process of simultaneously changing the switching speed and the overcurrent determination threshold, which is a feature according to embodiment 1 of the present disclosure, will be described.

[0049] The process shown in Fig. 5 is executed by the arithmetic processing device 90 of the control device 100. The process in Fig. 5 may be executed at predetermined time intervals (for example, every 100 μs). Alternatively, instead of at predetermined time intervals, the process may be executed for each event, such as each time predetermined input information is detected or communication is performed.

[0050] After starting the process, in step S101, the control unit 17 receives command values ​​such as a torque command and a rotation speed command from outside the power conversion device 1 and calculates a current command value IC. The current command value IC may be received directly from outside. The current command value is, for example, a d-axis current command value or a q-axis current command value. The current command value calculated here is used to determine the on / off timing of PWM driving of the switching elements.

[0051] In step S102, the current command value IC is compared with the switching speed switching current value ITHCHGS to determine the switching speed. By setting the value to be compared with the switching speed switching current value ITHCHGS as the current command value IC, it is possible to stabilize the determination of the switching speed.

[0052] At this time, the phase current detected by the phase current detectors 22, 23, 24 may be compared with the switching speed switching current value ITHCHGS instead of the current command value IC. However, the phase current fluctuates slightly around the current command value IC due to current feedback. When using the phase current, the average value of the phase current over a predetermined period may be calculated and used. Also, when comparing with the switching speed switching current value ITHCHGS, hysteresis may be provided to stabilize the determination of the switching speed.

[0053] The current command value IC may be a current command effective value calculated from the d-axis current command value and the q-axis current command value. If the current command value IC is equal to or less than the switching speed switching current value ITHCHGS (determination is YES), the process proceeds to step S103. If the current command value IC is not equal to or less than the switching speed switching current value ITHCHGS (determination is NO), the process proceeds to step S104.

[0054] In step S103, the switching speed SPSW is set to a switching speed H (higher side switching speed) SPSWH, and the overcurrent determination threshold ITHOC is set to an overcurrent determination threshold L (lower side overcurrent determination threshold) ITHOCL, and the process proceeds to step S105.

[0055] In step S104, the switching speed SPSW is set to a switching speed L (lower switching speed) SPSWL, and the overcurrent determination threshold ITHOC is set to an overcurrent determination threshold H (upper overcurrent determination threshold) ITHOCH, and the process proceeds to step S105.

[0056] In step S105, the control unit 17 outputs the set switching speed SPSW as a switching speed signal 17b to the gate driving unit 18. Then, the control unit 17 outputs the set overcurrent determination threshold ITHOC to the gate driving unit 18 as an overcurrent threshold signal 17c.

[0057] In step S106, the control unit 17 outputs a control signal 17a to the gate driving unit 18 based on the tracking control calculation for the current command value IC, and the gate driving unit drives the switching elements 11 to 16 to perform the current command tracking control. The post-processing of step S106 is terminated.

[0058] <Relationship between switching speed and overcurrent threshold> 6 is a diagram showing the setting of the overcurrent determination threshold of the power conversion device 1 according to the embodiment 1. A method of setting the switching speed SPSW and the overcurrent determination threshold ITHOC will be described.

[0059] As a premise, a surge voltage occurs when the IGBT is switched, but due to the parasitic inductance in the circuit and the recovery characteristics of the diode connected inversely in parallel to the IGBT, the surge voltage tends to increase as the conduction current during switching increases.

[0060] In addition, the rate of change of the IGBT's conduction current, di / dt, i.e., the switching speed, can be adjusted by adjusting the gate resistance of the IGBT. The higher the switching speed is by lowering the IGBT's gate resistance, the higher the surge voltage will be. If the current and voltage during switching are the same, the higher the switching speed, the lower the switching loss will be. The same tendency is observed when increasing the IGBT's gate voltage to increase the switching speed.

[0061] The overcurrent determination threshold H(ITHOCH) shown in Fig. 6 is set for the case where the switching speed SPSW is switching speed L (lower speed switching speed) SPSWL. It is set to a value that does not detect an overcurrent when the power conversion device 1 operates at the maximum rated current at switching speed L. That is, the overcurrent determination threshold H(ITHOCH) is set to a value larger than the maximum rated current of the power conversion device 1. In addition, the overvoltage determination threshold VTHOV is set to a value larger than the maximum voltage that can be obtained during normal operation.

[0062] 6, instantaneous cutoff is not possible due to a delay in the overcurrent protection unit 20, and a cutoff current H that is actually higher than the overcurrent determination threshold is generated. It is necessary to determine the switching speed L (low-speed switching speed) SPSWL so that the surge voltage (cutoff voltage) generated when cutting off is performed at this current does not exceed the withstand voltage value of the switching element.

[0063] Next, the case where the switching speed SPSW is the switching speed H (high-speed switching speed) SPSWH is set. The switching speed switching current value ITHCHGS at the point indicated by B2 in FIG. 6 is determined. For example, based on the current that occurs frequently in a driving mode for regulating the power consumption of an electric vehicle, the switching speed switching current value ITHCHGS is determined so that the operating state in which the switching efficiency should be improved is below the point indicated by B2. By doing so, it is possible to perform power conversion operation at the switching speed H (high-speed switching speed) SPSWH in the operating mode in which the switching efficiency is desired to be improved. For convenience, the voltage at the point indicated by B2 in FIG. 6 is set to be the same as the point indicated by A.

[0064] The overcurrent determination threshold L (ITHOCL) is determined by the point shown by B1 in Fig. 6, which is not reached during normal power conversion operation at the switching speed H (high-speed switching speed) SPSWH. The overcurrent determination threshold L (ITHOCL), which is the point shown by B1 in Fig. 6, is not reached during normal operation at the switching speed H (high-speed switching speed) SPSWH, but is determined so that an early overcurrent determination is performed during abnormal operation and the surge voltage at the time of cutoff does not exceed the withstand voltage value of the switching element.

[0065] When an overcurrent occurs during abnormal operation, the switching speed SPSW should be switched to switching speed L (low-speed switching speed) SPSWL at the point when the current command value IC or the detected phase current becomes larger than the switching speed switching current value ITHCHGS. However, there are cases where the switching of the switching speed SPSW is delayed due to the PWM calculation timing. In this case, the switching speed remains at H (high-speed switching speed) SPSWH, and the detected phase current becomes larger than the overcurrent judgment threshold L, and an overcurrent is judged.

[0066] At the point indicated by B1 in Figure 6, an overcurrent is detected, and the on / off switching of the switching element is stopped, interrupting current conversion. At this time, power conversion is stopped at switching speed H (high-speed switching speed) SPSWH, causing the surge voltage to increase. However, since the phase current when the current is interrupted is at overcurrent detection threshold L (ITHOCL), which is smaller than overcurrent detection threshold H (ITHOCH), the current value only rises to the interruption current L in Figure 6, even if there is a delay until the actual current interruption. Therefore, the surge voltage due to the interruption current L does not exceed the withstand voltage value of the switching element.

[0067] At points A, B1, and B2, the voltage is the same, but the current value has the relationship A>B1>B2. The switching speed can be increased in the region where the current value is smaller than that of point B2. Therefore, it is possible to reduce loss in the switching element in the current region that is assumed to be normally used frequently in electric vehicles.

[0068] The switching speed switching current value ITHCHGS is set to a value smaller than the overcurrent determination threshold value L (ITHOCL). Specifically, the switching speed switching current value ITHCHGS is a value based on the effective value of the AC current to be compared with the current command value IC (effective value). For this reason, the current value obtained by adding control fluctuations to the peak current and current ripple calculated by switching speed switching current value x √2 is set to be lower than the overcurrent determination threshold value L (ITHOCL).

[0069] As a result, under normal circumstances, when the current command value IC (effective value) exceeds the switching speed switching current value ITHCHGS, the switching speed SPSW is switched to switching speed L (lower switching speed) SPSWL, and at the same time, the overcurrent determination threshold ITHOC is switched from the overcurrent determination threshold L (ITHOCL) to the overcurrent determination threshold H (ITHOCH).

[0070] Therefore, it is possible to expand the region in which the power conversion device 1 can be operated without detecting the occurrence of an overcurrent. Therefore, setting the switching speed switching current value ITHCHGS to a value smaller than the overcurrent determination threshold L(ITHOCL) is useful for expanding the operable region of the power conversion device 1.

[0071] FIG. 7 is a diagram showing the response of the power conversion device 1 according to the first embodiment at the time of overcurrent detection. Compared with the case of FIG. 4 according to the comparative example, the switching speed switching current value ITHCHGS can be set to a necessary degree large. Therefore, it is understood that it is possible to set the switching speed at a high speed to improve the switching efficiency and sufficiently secure the running region. Even if an abnormality occurs and the phase current suddenly rises when the switching speed is set at a high speed, the overcurrent determination can be quickly performed by detecting the overcurrent determination threshold value L (ITHOCL) (white circle (◯) in FIG. 7). Since the on / off of the switching element can be quickly stopped, even if there is a delay until the actual current interruption, the phase current increases only to the interruption current L (white triangle (△) in FIG. 7). Therefore, it is clear that it is possible to prevent the failure, performance degradation, and shortening of the life of the switching element due to the surge voltage at the time of interruption of the switching element in this case.

[0072] As described above, according to the power conversion device 1 of the first embodiment, even if there is a delay in the setting of the switching speed, switching can be stopped by overcurrent protection with a short delay time for a steep current increase during an abnormality. Therefore, it is not necessary to set the switching speed switching current value ITHCHGS low in consideration of the delay in the switching speed. In addition, a high switching speed can be set while considering a steep current increase during an abnormality and the current dependency of the surge voltage, making it possible to reduce losses.

[0073] In addition, since the values ​​of the overcurrent determination threshold L (ITHOCL) and the overcurrent determination threshold H (ITHOCH) can be freely set, the overcurrent determination thresholds can be appropriately changed and set according to the performance of the power conversion device 1, the performance of the rotating machine as the load, and the running characteristics of the electric vehicle. Since this can be achieved simply by changing the software (changing the parameters), it is possible to obtain a power conversion device 1 with a high degree of freedom.

[0074] In the above embodiment, the method of adjusting the switching speed by changing the gate resistance has been described, but the present invention is not limited to this, and the same effect can be obtained by adjusting the switching speed by changing the gate drive voltage or gate drive current. The switching speed can be increased by lowering the gate resistance, increasing the gate drive voltage, or increasing the gate drive current.

[0075] <Overvoltage and overcurrent protection without software intervention> 8 is a second hardware configuration diagram of the control device 100 of the power conversion device 1 according to the embodiment 1. If the overcurrent protection unit 20, the overvoltage protection unit 19, and the gate drive unit 18 are configured with analog circuits and digital circuits such as voltage dividing resistors, comparators, and logic circuits, it is possible to quickly detect and respond to overcurrents and overvoltages.

[0076] Compared with a case where the overcurrent protection unit 20, the overvoltage protection unit 19, and the gate driver 18 are configured as functions of a computing device that executes software, it is possible to quickly detect overvoltages and overcurrents and to stop turning on and off the switching elements 11 to 16 without delay. An example of the hardware configuration of the control device 100 when such a configuration is adopted is shown in Fig. 8.

[0077] <Reducing delay times through interrupt processing> However, it is also possible to perform A / D conversion on the output of the voltage detector 21 and the outputs of the phase current detectors 22, 23, and 24 at short intervals and execute an input capture interrupt process each time an A / D conversion is completed. During the input capture interrupt process, the occurrence of an overvoltage or overcurrent is confirmed.

[0078] This makes it possible to respond to overvoltage and overcurrent occurrences with a shorter delay time, without having to wait for the timing to generate a current command and calculate the PWM output in the usual 100 μs cycle. In this case, it is possible to configure the overcurrent protection unit 20, the overvoltage protection unit 19, and the gate driver 18 as functions of a computing device that executes software.

[0079] The power conversion device 1 mounted on a vehicle must detect overcurrent and overvoltage and immediately stop the power conversion operation when the connected DC power source 2, rotating machine 3, and other electrical equipment connected to the DC power source 2 start to operate abnormally, and when the power conversion device 1 itself temporarily malfunctions due to noise or the like. It is required to protect the switching element from a surge voltage during switching that exceeds its withstand voltage by stopping the on / off of the switching element. Assuming a sudden change in current and voltage, it may be desirable to detect overcurrent and overvoltage and stop the power conversion within a few μs.

[0080] In such cases, it is necessary to deal with the problem in a time shorter than the delay time set for the normal switching speed. Even if an input capture interrupt process is executed each time an A / D conversion is completed and the occurrence of an overvoltage or overcurrent is confirmed, it is difficult to complete the process within a few microseconds.

[0081] To deal with such cases, there is an advantage in configuring the overvoltage protection unit 19, overcurrent protection unit 20, and gate driver to execute the switching element stop function in response to overcurrent and overvoltage without going through software processing. By configuring the switching elements to be stopped in response to overcurrent and overvoltage by the operation of analog and digital circuits, high-speed measures against overcurrent and overvoltage can be realized.

[0082] 2. Second embodiment <Configuration of power conversion device> 9 is a configuration diagram of a power conversion device 1 according to embodiment 2. In embodiment 1, the power conversion device 1 that changes the overcurrent determination threshold ITHOC simultaneously with the switching speed SPSW is described. In embodiment 2, the power conversion device 1 that changes the overcurrent determination threshold ITHOC and the overvoltage determination threshold VTHOV simultaneously with the switching speed SPSW is described.

[0083] The power conversion device 1 in FIG. 9 differs from the power conversion device in FIG. 1 according to the first embodiment only in that the overvoltage protection unit 19 has an additional function of receiving an overvoltage threshold signal 17d from the control unit 17 and changing the overvoltage determination threshold VTHOV. The adjustment of the overvoltage determination threshold VTHOV of the overvoltage protection unit 19 may be achieved by switching a voltage dividing resistor of a reference voltage of a circuit with a transistor. The adjustment of the overvoltage determination threshold VTHOV of the overvoltage protection unit 19 may be achieved by generating a voltage to be compared by a D / A converter (Digital / Analog Converter) based on the overvoltage threshold signal 17d received as an H / L (High / Low) signal, an analog voltage signal, or a digital signal indicating a voltage value. Only the parts different from the first embodiment will be described below.

[0084] <Simultaneous change of switching speed, overcurrent judgment threshold, and overvoltage judgment value> 10 is a flowchart showing a process of changing the switching speed of the control device 100 of the power conversion device 1 according to embodiment 2. A process of simultaneously changing the switching speed, the overcurrent determination threshold, and the overvoltage determination value, which is a feature according to embodiment 2 of the present disclosure, will be described.

[0085] The process shown in Fig. 10 is executed by the arithmetic processing device 90 of the control device 100. The process shown in Fig. 10 may be executed at predetermined time intervals (for example, every 100 μs). Alternatively, instead of at predetermined time intervals, the process may be executed for each event, such as each time predetermined input information is detected or communication is performed.

[0086] After starting the process, in step S201, the control unit 17 reads out the DC voltage value Vdc detected by the voltage detector 21. In step S202, the control unit 17 receives command values ​​such as a torque command and a rotation speed command from outside the power conversion device 1 and calculates a current command value IC. The current command value IC may be received directly from outside. The current command value is, for example, a d-axis current command value or a q-axis current command value. The current command value calculated here is used to determine the on / off timing of PWM driving of the switching elements.

[0087] In step S203, the current command value IC is compared with the switching speed switching current value ITHCHGS to determine the switching speed. By setting the value to be compared with the switching speed switching current value ITHCHGS as the current command value IC, it is possible to stabilize the determination of the switching speed.

[0088] At this time, the phase current detected by the phase current detectors 22, 23, 24 may be compared with the switching speed switching current value ITHCHGS instead of the current command value IC. However, the phase current fluctuates slightly around the current command value IC due to current feedback. When using the phase current, the average value of the phase current over a predetermined period may be calculated and used. Also, when comparing with the switching speed switching current value ITHCHGS, hysteresis may be provided to stabilize the determination of the switching speed.

[0089] The current command value IC may be a current command effective value calculated from the d-axis current command value and the q-axis current command value. If the current command value IC is equal to or less than the switching speed switching current value ITHCHGS (determination is YES), the process proceeds to step S204. If the current command value IC is not equal to or less than the switching speed switching current value ITHCHGS (determination is NO), the process proceeds to step S205.

[0090] In step S204, it is determined whether the DC voltage value Vdc is equal to or less than the switching-speed switching voltage value VTHCHGS. If the DC voltage value Vdc is equal to or less than the switching-speed switching voltage value VTHCHGS (determination is YES), the process proceeds to step S206. If the DC voltage value Vdc is not equal to or less than the switching-speed switching voltage value VTHCHGS (determination is NO), the process proceeds to step S207.

[0091] In step S206, the switching speed SPSW is set to a switching speed H (high-speed switching speed) SPSWH, the overcurrent determination threshold ITHOC is set to an overcurrent determination threshold L (lower overcurrent determination threshold) ITHOCL, and the overvoltage determination threshold VTHOV is set to an overvoltage determination threshold L (lower overvoltage determination threshold) VTHOVL.Then, the process proceeds to step S210.

[0092] In step S207, the switching speed SPSW is set to a switching speed M (medium switching speed) SPSWM, the overcurrent determination threshold ITHOC is set to an overcurrent determination threshold L (lower overcurrent determination threshold) ITHOCL, and the overvoltage determination threshold VTHOV is set to an overvoltage determination threshold H (upper overvoltage determination threshold) VTHOVH. Then, the process proceeds to step S210.

[0093] In step S205, it is determined whether the DC voltage value Vdc is equal to or less than the switching-speed switching voltage value VTHCHGS. If the DC voltage value Vdc is equal to or less than the switching-speed switching voltage value VTHCHGS (determination is YES), the process proceeds to step S208. If the DC voltage value Vdc is not equal to or less than the switching-speed switching voltage value VTHCHGS (determination is NO), the process proceeds to step S209.

[0094] In step S208, the switching speed SPSW is set to a switching speed M (medium switching speed) SPSWM, the overcurrent determination threshold ITHOC is set to an overcurrent determination threshold H (upper overcurrent determination threshold) ITHOCH, and the overvoltage determination threshold VTHOV is set to an overvoltage determination threshold L (lower overvoltage determination threshold) VTHOVL. Then, the process proceeds to step S210.

[0095] In step S209, the switching speed SPSW is set to a switching speed L (low-speed switching speed) SPSWL, the overcurrent determination threshold ITHOC is set to an overcurrent determination threshold H (upper overcurrent determination threshold) ITHOCH, and the overvoltage determination threshold VTHOV is set to an overvoltage determination threshold H (upper overvoltage determination threshold) VTHOVH. Then, the process proceeds to step S210.

[0096] In step S210, the control unit 17 outputs the set switching speed SPSW as a switching speed signal 17b to the gate driving unit 18. The control unit 17 outputs the set overcurrent determination threshold ITHOC as an overcurrent threshold signal 17c to the gate driving unit 18. Then, the control unit 17 outputs the set overvoltage determination threshold VTHOV to the gate driving unit 18 as an overvoltage threshold signal 17d.

[0097] In step S211, the control unit 17 outputs a control signal 17a to the gate driving unit 18 based on the tracking control calculation for the current command value IC, and the gate driving unit drives the switching elements 11 to 16 to perform the current command tracking control. The post-processing of step S211 is terminated.

[0098] <Relationship between switching speed and overcurrent / overvoltage threshold> Fig. 11 is a diagram showing settings of an overcurrent determination threshold and an overvoltage determination threshold of the power conversion device 1 according to the embodiment 1. Fig. 12 is a diagram showing settings of the switching speed of the power conversion device according to the embodiment 2. Fig. 12 is a diagram explaining the switching of the switching speed between low speed, medium speed, and high speed in Fig. 11. A method of setting the switching speed SPSW, the overcurrent determination threshold ITHOC, and the overvoltage determination threshold VTHOV will be described below.

[0099] In Fig. 11, the surge voltage establishment line is a line showing the relationship between voltage and current where the surge voltage at switching speeds defined as high, medium, and low speeds coincides with the element withstand voltage. It is a line showing the combination of maximum current and maximum voltage allowed at a specified switching speed in a switching element, and although it is drawn as a straight line for convenience, it is actually expressed as a curved line.

[0100] If the current and voltage are lower than the surge voltage establishment line, the surge voltage will not exceed the withstand voltage of the switching element and it will be in an operable range. The figure shows three surge voltage establishment lines corresponding to high, medium, and low switching speeds. For example, when the switching speed is high, the surge voltage will be high, so this line shows the lowest allowable current.

[0101] 11 is set to a value at which an overcurrent is not detected when the power conversion device 1 operates at the maximum rated current. Also, an overvoltage determination threshold H (upper overvoltage determination threshold) VTHOVH is set to a value at which an overvoltage is not detected when the power conversion device 1 operates at the maximum voltage that the DC power supply 2 can normally have.

[0102] When setting the overcurrent determination threshold H and the overvoltage determination threshold H, they must be set so that overcurrent protection and overvoltage protection are possible during abnormal operation. They should be set so that the surge voltage when an overcurrent is detected and the on / off of the switching element is stopped, under conditions of a slow switching speed, does not exceed the withstand voltage value of the switching element. They should be set so that the surge voltage when an overvoltage is detected and the on / off of the switching element is stopped, under conditions of a slow switching speed, does not exceed the withstand voltage value of the switching element.

[0103] The overcurrent determination threshold H and overvoltage determination threshold H must be set so that the surge voltage when the switching element is stopped at an interruption current of H and an interruption voltage of H does not exceed the withstand voltage of the switching element. The point indicated by E in Figure 11 is the maximum operating point at which operation can continue when the switching speed is low. Conversely, a switching speed that satisfies the above conditions may be set as the switching speed for low speed.

[0104] The overcurrent determination threshold L (lower overcurrent determination threshold) ITHOCL is set to a value that does not exceed the overcurrent determination threshold L when operating at a current value that occurs frequently in a driving mode for regulating the power consumption of an electric vehicle, for example. Also, the overvoltage determination threshold L (lower overvoltage determination threshold) VTHOVL is set to a value that does not detect an overvoltage during normal driving in the same driving mode. For example, if the DC power source 2 is a lithium-ion battery, the voltage range of a single cell is 2.8V to 4.2V, and the rated voltage is 3.7V, so the overvoltage is set to a value that does not detect an overvoltage when operating at a rated voltage that is lower than the maximum voltage of the battery pack and is used frequently.

[0105] In Fig. 11, the switching speed switching current value ITHCHGS, which switches the switching speed, is set to the lower current side than the overcurrent determination threshold value L. Specifically, since the switching speed switching current value is a value based on the effective value of the AC current to be compared with the current command value IC (effective value), it is set so that the current value obtained by adding control fluctuations to the peak current and current ripple calculated by switching speed switching current value × √2 is lower than the overcurrent determination threshold value L.

[0106] The switching speed switching voltage value VTHCHGS is set to a lower voltage side than the overvoltage determination threshold value L. Specifically, since the switching speed switching voltage value is a value to be compared with the detected DC voltage value Vdc, the voltage value taking into account the voltage ripple and detection error for the DC voltage value Vdc is set to be lower than the overvoltage determination threshold value L.

[0107] By doing so, when the current or voltage rises in a normal operating state, it becomes possible to continue operation while changing the switching speed without detecting overcurrent or overvoltage. Furthermore, even if the switching speed is delayed and the switching speed remains high when the current value or voltage value rises suddenly due to the occurrence of an abnormality, it becomes possible to quickly detect overcurrent or overvoltage by exceeding the overcurrent judgment threshold L or the overvoltage judgment threshold L. As a result, it becomes possible to quickly stop turning on and off the switching element by detecting overcurrent or overvoltage. Although the surge voltage when the power conversion operation is stopped becomes large due to the high switching speed, by setting the overcurrent judgment threshold L and the overvoltage judgment threshold L to appropriately small values, the withstand voltage value of the switching element is not exceeded. As a result, it is possible to obtain a power conversion device that can prevent failure, performance degradation, and shortened life of the switching element while achieving both efficient power conversion operation and power conversion operation over a wide range.

[0108] 11 and 12, the switching speed is set to high when the current command value IC is equal to or less than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is equal to or less than the switching speed switching voltage value VTHCHGS. The switching speed is set to low when the current command value IC is greater than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is greater than the switching speed switching voltage value VTHCHGS. Otherwise, the switching speed is set to medium.

[0109] The overcurrent threshold L and overvoltage threshold L must be set so that overcurrent protection and overvoltage protection are possible during abnormal operation. The surge voltage when an overcurrent is detected and the on / off switching of the switching element is stopped is set so as not to exceed the withstand voltage value of the switching element.The surge voltage when an overvoltage is detected and the on / off switching of the switching element is stopped under high-speed switching speed conditions is set so as not to exceed the withstand voltage value of the switching element.

[0110] Under high-speed switching conditions, the overcurrent determination threshold L and the overvoltage determination threshold L must be set so that the cut-off current L and cut-off voltage L do not exceed the withstand voltage value of the switching element when a surge voltage is applied. The point indicated by D in Figure 11 is the maximum operating point for continuing operation when the switching speed is high. Conversely, a switching speed that satisfies the above conditions may be set as the switching speed for high speed.

[0111] Additionally, when setting the combination of overcurrent determination threshold H and overvoltage determination threshold L, and the combination of overcurrent determination threshold L and overvoltage determination threshold H, the case where the switching speed is medium will be considered. As above, the settings must be made so that overcurrent protection and overvoltage protection are possible during abnormal operation. When the switching speed is medium, the settings must be made so that the surge voltage when an overcurrent is detected and the on / off of the switching element is stopped does not exceed the withstand voltage value of the switching element. When the switching speed is medium, the settings must be made so that the surge voltage when an overvoltage is detected and the on / off of the switching element is stopped does not exceed the withstand voltage value of the switching element.

[0112] When the switching speed is medium, the speed can be set so that the combination of cut-off current H and cut-off voltage L when a surge voltage is applied when the switching element is stopped from being turned on and off, and the combination of cut-off current L and cut-off voltage H do not exceed the withstand voltage value of the switching element. The point indicated by C in Figure 11 is the maximum operating point when the current value for continuing operation is large when the switching speed is medium. The point indicated by F in Figure 11 is the maximum operating point when the voltage value for continuing operation is large when the switching speed is medium.

[0113] In this way, the switching speeds H, M, and L and the overcurrent determination thresholds H, L, H and L can be appropriately set. As a result, the switching speed is set to high in the current and voltage ranges assumed to be used frequently in an electric vehicle, and switching loss can be reduced. Even if either the current or the voltage exceeds the switching speed switching current value or the switching speed switching voltage value, the switching speed can be set to medium speed for operation. Furthermore, by setting the switching speed to low speed for low-frequency operation where the current and voltage are at the maximum in the operating range, it becomes possible to continuously operate the power conversion device 1.

[0114] In addition, the values ​​of the overcurrent judgment threshold H (upper overcurrent judgment threshold) ITHOCH, the overcurrent judgment threshold L (lower overcurrent judgment threshold) ITHOCL, the overvoltage judgment threshold H (upper overvoltage judgment threshold) VTHOVH, the overvoltage judgment threshold L (lower overvoltage judgment threshold) VTHOVL, the switching speed H (high-speed switching speed) SPSWH, the switching speed M (medium-speed switching speed) SPSWM, the switching speed L (low-speed switching speed) SPSWL, the switching speed switching current value ITHCHGS, and the switching speed switching voltage value VTHCHGS can be freely set, so that the switching speed and the overcurrent judgment threshold can be appropriately changed and set according to the performance of the power conversion device 1, the performance of the rotating machine which is the load, and the running characteristics of the electric vehicle. Since this can be achieved only by changing the software (changing the parameters), it is possible to obtain a power conversion device 1 with a high degree of freedom.

[0115] 12, the switching speed is switched between three speeds, high speed, medium speed, and low speed, but the switching speed may be switched between four speeds as follows.

[0116] When the current command value IC is equal to or less than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is equal to or less than the switching speed switching voltage value VTHCHGS, the switching speed is set to a first speed. When the current command value IC is greater than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is equal to or less than the switching speed switching voltage value VTHCHGS, the switching speed is set to a second speed. When the current command value IC is equal to or less than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is greater than the switching speed switching voltage value VTHCHGS, the switching speed is set to a third speed. When the current command value IC is greater than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is greater than the switching speed switching voltage value VTHCHGS, the switching speed is set to a fourth speed.

[0117] The second speed and the third speed may be set to different speeds, with the first speed>the second speed and the third speed>the fourth speed. The effect of delay associated with switching of the switching speed, the effect of an increase in the current value due to a delay in current interruption when an overcurrent is detected, and the behavior of the interruption surge voltage in those cases may be experimentally determined to set an optimal switching speed and switching determination value within a range that does not exceed the withstand voltage value of the switching element. By setting in this way, the switching speed, the switching determination value, and the overcurrent determination threshold can be changed and set more appropriately according to the performance of the power conversion device 1, the performance of the rotating machine that is the load, and the running characteristics of the electric vehicle.

[0118] <Temperature characteristics of switching elements> In the first and second embodiments, the switching speed and the overcurrent determination threshold or the overvoltage determination threshold are changed based on the current and the voltage. In addition to this, the switching speed or the overcurrent determination threshold or the overvoltage determination threshold may be changed based on the temperature of the switching element.

[0119] In IGBTs, MOSFETs, etc., the lower the temperature of the switching element, the higher the gate threshold value becomes, shortening the switching time at turn-off, which in turn increases the switching speed and increases the surge voltage. Furthermore, the lower the temperature, the lower the element breakdown voltage becomes, so the allowable surge voltage becomes lower.

[0120] In addition, the higher the temperature of the switching element, the worse the recovery characteristics of the diode connected in inverse parallel to the IGBT and the body diode of the MOSFET become, and the higher the surge voltage becomes when the element is turned on. In this way, it is possible that the surge voltage becomes higher at lower and higher temperatures. Also, at low temperatures, the withstand voltage of the element decreases.

[0121] Therefore, the switching speed or the overcurrent determination threshold and the overvoltage determination threshold may be adjusted based on the temperature characteristics. This makes it possible to calculate the appropriate withstand current and withstand voltage values ​​of the switching elements based on the temperature characteristics. This makes it possible to reduce losses over a wider operating range while preventing degradation of the switching elements.

[0122] When the surge voltage increases due to temperature, the switching speed may be adjusted to be reduced while maintaining the overcurrent determination threshold and overvoltage determination threshold shown in the above embodiment. Also, the overcurrent determination threshold and overvoltage determination threshold may be adjusted while maintaining the switching speed. Alternatively, both the switching speed and the overcurrent determination threshold and overvoltage determination threshold may be adjusted. Also, the temperature of the switching element may be detected by directly detecting the temperature of the switching element using a temperature detector, or the temperature near the switching element in the power module may be detected by a temperature detector.

[0123] In the first and second embodiments, the power converter 1 using the IGBT made of silicon semiconductor is exemplified. However, the power converter is not limited to this. For example, wide band gap semiconductors using silicon carbide, gallium nitride material, or diamond may be used. These wide band gap semiconductors are expensive compared to silicon semiconductors, but are used to reduce loss, and are therefore effective in further promoting loss reduction.

[0124] In the first and second embodiments, a method of adjusting the overvoltage determination threshold of the overvoltage protection unit 19 and the overcurrent determination threshold of the overcurrent protection unit 20 has been described. However, a method of suppressing a steep current / voltage rise during an abnormality by providing a plurality of protection circuits and activating a protection circuit corresponding to a region where the current value or voltage value is small may also be used.

[0125] In the above, a method has been shown in which the switching speed, the overcurrent determination threshold, and the overvoltage determination threshold are simultaneously switched by comparing the switching speed switching current value with the current, or the switching speed switching voltage value with the voltage. However, a plurality of switching thresholds for switching the switching speed may be used for the current or the voltage. Alternatively, a method may be used in which the switching speed, the overcurrent determination threshold, and the overvoltage determination threshold are constantly adjusted so that the surge voltage calculated based on the current and voltage in consideration of the behavior during an abnormality does not exceed the element withstand voltage.

[0126] Also, the method of adjusting the switching speed, the overcurrent determination threshold, and the overvoltage determination threshold based on the current command value has been described, but the present disclosure may be applied to a DC / DC converter instead of the current command value.

[0127] For example, a similar effect can be obtained with a DC / DC converter in which a reactor is connected to the junction of a series circuit of upper and lower arm switching elements and which is controlled by detecting the reactor current and the voltage across the series circuit.

[0128] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not exemplified are assumed within the scope of the disclosed technology, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment.

[0129] Various aspects of the present disclosure are summarized below as appendices.

[0130] (Appendix 1) a power conversion circuit including a positive-side switching element connected to a positive electrode of a DC power supply, a negative-side switching element connected to a negative electrode of the DC power supply, and an external connection point that connects the positive-side switching element and the negative-side switching element in series and from which an AC output is derived; a voltage detector for detecting a voltage between a positive electrode and a negative electrode of the power conversion circuit; a phase current detector for detecting a phase current flowing between the external connection point of the power conversion circuit and the AC output; and a control unit that outputs a control signal to control the switching element based on an external command value and outputs a speed instruction signal to instruct a switching speed of the switching element; an overvoltage protection unit that outputs an overvoltage cut-off signal when a voltage detected by the voltage detector is greater than a predetermined overvoltage determination threshold; an overcurrent protection unit that outputs an overcurrent cut-off signal when a phase current detected by the phase current detector is greater than a predetermined overcurrent determination threshold; and a gate drive unit that turns on and off the switching element based on the control signal output by the control unit, changes the on / off speed of the switching element based on the speed instruction signal, and stops the on / off of the switching element based on the overvoltage cut-off signal output by the overvoltage protection unit and the overcurrent cut-off signal output by the overcurrent protection unit, The control device is a power conversion device that changes at least one of the overvoltage determination threshold and the overcurrent determination threshold simultaneously with the change in the speed instruction signal. (Appendix 2) The power conversion device according to claim 1, wherein the control device changes the speed instruction signal and the overcurrent determination threshold based on a current command value calculated from the command value or the phase current. (Appendix 3) The power conversion device according to claim 2, wherein the control device changes the speed instruction signal so as to decrease the switching speed of the switching element as the current command value or the phase current increases, and changes the overcurrent determination threshold so as to increase. (Appendix 4) The power conversion device according to claim 2, wherein the control device changes the speed instruction signal so as to decrease the switching speed of the switching element and changes the overcurrent determination threshold so as to increase when the current command value or the phase current becomes larger than a predetermined speed switching current value. (Appendix 5) The power conversion device according to claim 4, wherein the speed switching current value is always smaller than the overcurrent determination threshold value. (Appendix 6) The power conversion device according to any one of Supplementary claims 2 to 6, wherein the control device changes the speed instruction signal and the overcurrent determination threshold based on the current command value. (Appendix 7) 2. The power conversion device according to claim 1, wherein the control device changes the speed indication signal and the overvoltage determination threshold based on the voltage detected by the voltage detector. (Appendix 8) 8. The power conversion device according to claim 7, wherein the control device changes the speed instruction signal so that a switching speed of the switching element decreases as the voltage increases, and changes the overvoltage determination threshold so that it increases. (Appendix 9) The power conversion device according to claim 7, wherein the control device changes the speed instruction signal so as to decrease the switching speed of the switching element and changes the overvoltage determination threshold so as to increase when the voltage becomes greater than a predetermined speed switching voltage value. (Appendix 10) 10. The power conversion device according to claim 9, wherein the control device is configured such that the speed switching voltage value is always smaller than the overvoltage determination threshold value. (Appendix 11) the control device outputs the speed instruction signal for setting a switching speed of the switching element to a first speed when the current command value or the phase current is equal to or less than a predetermined speed switching current value and the voltage is equal to or less than a predetermined speed switching voltage value, sets the overcurrent determination threshold to a first overcurrent determination threshold, and sets the overvoltage determination threshold to a first overvoltage determination threshold; when the current command value or the phase current is greater than the speed switching current value and the voltage is equal to or less than the speed switching voltage value, outputting the speed instruction signal for setting the switching speed of the switching element to a second speed slower than the first speed, setting the overcurrent determination threshold to a second overcurrent determination threshold greater than the first overcurrent determination threshold, and setting the overvoltage determination threshold to the first overvoltage determination threshold; when the current command value or the phase current is equal to or less than the speed switching current value and the voltage is greater than the speed switching voltage value, outputting the speed instruction signal for setting the switching speed of the switching element to a third speed slower than the first speed, setting the overcurrent determination threshold to the first overcurrent determination threshold, and setting the overvoltage determination threshold to a second overvoltage determination threshold greater than the first overvoltage determination threshold; The power conversion device according to Appendix 1, wherein, when the current command value or the phase current is greater than the speed switching current value and the voltage is greater than the speed switching voltage value, the speed instruction signal is output to set the switching speed of the switching element to a fourth speed slower than the second speed and the third speed, the overcurrent determination threshold is set to the second overcurrent determination threshold, and the overvoltage determination threshold is set to the second overvoltage determination threshold. (Appendix 12) a temperature sensor for detecting a temperature of the switching element; The power conversion device according to any one of claims 1 to 11, wherein the control device changes at least one of the overvoltage determination threshold and the overcurrent determination threshold simultaneously with changing the speed instruction signal based on a temperature of the switching element. (Appendix 13) The power conversion device according to any one of appendixes 1 to 12, wherein the control device is configured so that the speed indication signal and at least one of the overvoltage determination threshold and the overcurrent determination threshold are set so that a surge voltage generated when the gate driver stops turning on and off the switching element based on the overvoltage cut-off signal or the overcurrent cut-off signal is equal to or lower than a withstand voltage of the switching element. (Appendix 14) The power conversion device according to any one of appendix 1 to 13, wherein the control device changes an on / off speed of the switching element by changing at least one of a gate drive voltage, a gate drive current, and a gate drive resistance of the gate drive unit. (Appendix 15) 15. The power conversion device according to any one of claims 1 to 14, wherein the control device outputs the overvoltage cut-off signal by the overvoltage protection unit when the voltage is greater than the overvoltage determination threshold, the overcurrent protection unit outputs the overcurrent cut-off signal when the phase current is greater than the overcurrent determination threshold, and the gate drive unit stops turning on and off the switching element based on the overvoltage cut-off signal or the overcurrent cut-off signal, without software processing. (Appendix 16) 16. The power conversion device according to claim 1, wherein the switching element uses a wide-gap semiconductor. [Explanation of symbols]

[0131] REFERENCE SIGNS LIST 1 power conversion device, 2 DC power supply, 11, 12, 13, 14, 15, 16 switching element, 17 control unit, 18 gate drive unit, 19 overvoltage protection unit, 20 overcurrent protection unit, 21 voltage detector, 22, 23, 24 phase current detector, 100 control device, 200 power conversion circuit

Claims

1. a power conversion circuit including a positive-side switching element connected to a positive electrode of a DC power supply, a negative-side switching element connected to a negative electrode of the DC power supply, and an external connection point that connects the positive-side switching element and the negative-side switching element in series and from which an AC output is derived; a voltage detector for detecting a voltage between a positive electrode and a negative electrode of the power conversion circuit; a phase current detector for detecting a phase current flowing between the external connection point of the power conversion circuit and the AC output; and a control unit that outputs a control signal to control the switching element based on an external command value and outputs a speed instruction signal to instruct a switching speed of the switching element; an overvoltage protection unit that outputs an overvoltage cut-off signal when a voltage detected by the voltage detector is greater than a predetermined overvoltage determination threshold; an overcurrent protection unit that outputs an overcurrent cut-off signal when a phase current detected by the phase current detector is greater than a predetermined overcurrent determination threshold; and a gate drive unit that turns on and off the switching element based on the control signal output by the control unit, changes the on / off speed of the switching element based on the speed instruction signal, and stops the on / off of the switching element based on the overvoltage cut-off signal output by the overvoltage protection unit and the overcurrent cut-off signal output by the overcurrent protection unit, The control device is a power conversion device that changes at least one of the overvoltage determination threshold and the overcurrent determination threshold simultaneously with the change in the speed instruction signal.

2. The power conversion device according to claim 1 , wherein the control device changes the speed instruction signal and the overcurrent determination threshold based on a current command value calculated from the command value or the phase current.

3. 3. The power conversion device according to claim 2, wherein the control device changes the speed instruction signal so that a switching speed of the switching element decreases and changes the overcurrent determination threshold so that the overcurrent determination threshold increases as the current command value or the phase current increases.

4. 3. The power conversion device according to claim 2, wherein the control device changes the speed instruction signal so as to reduce a switching speed of the switching element and changes the overcurrent determination threshold so as to increase when the current command value or the phase current becomes larger than a predetermined speed switching current value.

5. The power conversion device according to claim 4 , wherein the control device always has the speed switching current value smaller than the overcurrent determination threshold value.

6. The power conversion device according to claim 2 , wherein the control device changes the speed instruction signal and the overcurrent determination threshold value based on the current command value.

7. The power conversion device according to claim 1 , wherein the control device changes the speed indication signal and the overvoltage determination threshold based on the voltage detected by the voltage detector.

8. The power conversion device according to claim 7 , wherein the control device changes the speed instruction signal so that a switching speed of the switching element decreases as the voltage increases, and changes the overvoltage determination threshold so that it increases.

9. 8. The power conversion device according to claim 7, wherein the control device changes the speed instruction signal so as to reduce the switching speed of the switching element and changes the overvoltage determination threshold so as to increase when the voltage becomes greater than a predetermined speed switching voltage value.

10. The power conversion device according to claim 9 , wherein the control device always has the speed switching voltage value smaller than the overvoltage determination threshold value.

11. the control device outputs the speed instruction signal for setting a switching speed of the switching element to a first speed when a current command value calculated from the command value or the phase current is equal to or less than a predetermined speed switching current value and the voltage is equal to or less than a predetermined speed switching voltage value, sets the overcurrent determination threshold to a first overcurrent determination threshold, and sets the overvoltage determination threshold to a first overvoltage determination threshold; when the current command value or the phase current is greater than the speed switching current value and the voltage is equal to or less than the speed switching voltage value, outputting the speed instruction signal for setting the switching speed of the switching element to a second speed slower than the first speed, setting the overcurrent determination threshold to a second overcurrent determination threshold greater than the first overcurrent determination threshold, and setting the overvoltage determination threshold to the first overvoltage determination threshold; when the current command value or the phase current is equal to or less than the speed switching current value and the voltage is greater than the speed switching voltage value, outputting the speed instruction signal for setting the switching speed of the switching element to a third speed slower than the first speed, setting the overcurrent determination threshold to the first overcurrent determination threshold, and setting the overvoltage determination threshold to a second overvoltage determination threshold greater than the first overvoltage determination threshold; 2. The power conversion device according to claim 1, wherein, when the current command value or the phase current is greater than the speed switching current value and the voltage is greater than the speed switching voltage value, the speed instruction signal is output to set the switching speed of the switching element to a fourth speed slower than the second speed and the third speed, the overcurrent determination threshold is set to the second overcurrent determination threshold, and the overvoltage determination threshold is set to the second overvoltage determination threshold.

12. a temperature sensor for detecting a temperature of the switching element; The power conversion device according to claim 1 , wherein the control device changes at least one of the overvoltage determination threshold and the overcurrent determination threshold simultaneously with the change of the speed instruction signal based on the temperature of the switching element.

13. 2. The power conversion device according to claim 1, wherein the control device sets the speed instruction signal and at least one of the overvoltage determination threshold and the overcurrent determination threshold so that a surge voltage generated when the gate drive unit stops turning on and off the switching element based on the overvoltage cut-off signal or the overcurrent cut-off signal is equal to or lower than a withstand voltage of the switching element.

14. The power conversion device according to claim 1 , wherein the control device changes the on / off speed of the switching element by changing at least one of a gate drive voltage, a gate drive current, and a gate drive resistance of the gate drive unit.

15. 15. The power conversion device according to claim 1, wherein the control device outputs the overvoltage cut-off signal by the overvoltage protection unit when the voltage is greater than the overvoltage determination threshold, the overcurrent protection unit outputs the overcurrent cut-off signal when the phase current is greater than the overcurrent determination threshold, and the gate drive unit stops turning the switching element on and off based on the overvoltage cut-off signal or the overcurrent cut-off signal, without software processing.

16. The power conversion device according to claim 1 , wherein the switching elements are made of wide-gap semiconductors.

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