Power conversion device

Abstract

A power conversion device according to the present invention comprises: a power conversion circuit that connects a switching element on the positive electrode side and a switching element on the negative electrode side in series and that derives an AC output; a DC voltage detector; a phase current detector; and a control device having a control unit that outputs a control signal and a speed instruction signal, an overvoltage protection unit, an overcurrent protection unit, and a gate drive unit that drives the switching element on the basis of the control signal and the speed instruction signal and stops the switching element on the basis of an overvoltage cutoff signal and an overcurrent cutoff signal. A power conversion device is capable of changing at least one of an overvoltage determination threshold and an overcurrent determination threshold while changing a speed instruction signal.

Description

Technical Field

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

[0002] As a control device for a rotating motor (motor) applied to an electric vehicle such as a hybrid vehicle or an electric vehicle, a power conversion device is often used. As a power conversion device, there are AC / DC converters (Alternate Current / Direct Current Converter) that converts AC power to DC power, inverters (Inverter) that convert DC power to AC power, and DC / DC converters (Direct Current / Direct Current Converter) that change the level of the input voltage and output voltage of DC power. Most of these power conversion devices have a structure with semiconductor switching elements.

[0003] As an example of a power conversion device, an inverter mounted on an electric vehicle is used to convert the DC power output from a DC power supply into the desired AC power and supply it to the rotating motor, thereby controlling the rotating motor. The power conversion device is composed of a switching circuit composed of a combination of switching elements, a control circuit that controls the switching elements, a current sensor for detecting the current flowing through a load such as a rotating motor, a capacitor for taking measures against switching noise, and the like. For example, in the case of controlling a three-phase synchronous rotating motor, the power conversion device has a switching circuit in each of the upper arm (the arm on the positive side) and the lower arm (the arm on the negative side) of the three phases (U phase, V phase, W phase).

[0004] The switching elements of each phase of the inverter are turned on or off in sequence, thereby supplying AC power with a phase difference of 120 degrees to each phase of the rotating electric machine to drive the rotating electric machine. The efficiency of such on-board electrical components is directly related to the fuel consumption and power consumption of the vehicle, so it is important to reduce losses.

[0005] In order to reduce the switching loss of the power conversion device, it is effective to increase the switching speed. However, if the switching speed is increased, the surge voltage when the switching element is energized and cut off will increase, and the driving noise will also increase. Therefore, the increase in switching speed must be implemented within a range that can prevent the degradation of the switching element caused by the surge voltage and the voltage exceeding the withstand voltage.

[0006] A technology is disclosed for calculating an expected surge voltage based on the temperature of a switching element, a current command, and a DC power supply voltage, and increasing the switching speed when there is a margin for the surge voltage relative to the withstand voltage of the switching element. In order to increase the switching speed, for example, a method is provided for reducing the switching loss by increasing the gate voltage of an IGBT (Insulated Gate Bipolar Transistor) used as a switching element, while keeping the surge voltage of the switching element below the withstand voltage (for example, Patent Document 1). Prior art literature Patent Literature

[0007] Patent Document 1: Japanese Patent No. 4333802 Summary of the invention Technical problem to be solved by the invention

[0008] In the technology of Patent Document 1, the gate voltage corresponding to the appropriate switching speed is set according to the surge voltage calculated based on the command current and the battery voltage. However, there is no mention of the method for setting the judgment threshold of overcurrent or overvoltage when the switching speed is changed. Therefore, the change of current and voltage after the overcurrent or overvoltage is detected is not considered. When the current and voltage rise sharply in an abnormal situation, the switching action may be higher than expected. Then, the surge voltage may exceed the withstand voltage value of the switching element, causing the switching element to fail or the performance to deteriorate, thereby shortening the life.

[0009] When the power conversion device is operated by increasing the switching speed, if the current or voltage changes sharply and exceeds the overcurrent judgment threshold or the overvoltage judgment threshold, it is necessary to consider the large surge voltage when the switching element stops turning on and off. Therefore, it is necessary to set the overcurrent judgment threshold or the overvoltage judgment threshold to a smaller value. As a result, the maximum operating current and the maximum operating voltage when the switching speed is not increased are also limited, and the operating range of the power conversion device is limited.

[0010] The present application discloses a technology for solving the above-mentioned problems. Its purpose is to obtain a power conversion device that can change the switching speed according to the operating state of the power conversion device, taking into account both efficient power conversion operation and power conversion operation in a wider range, and preventing failure, performance degradation and shortened life of the switching element. Technical means for solving technical problems

[0011] The power conversion device involved in the present disclosure includes: A power conversion circuit including a switching element on the positive side connected to the positive electrode of a DC power source, a switching element on the negative side connected to the negative electrode of the DC power source, and an external connection point for connecting the switching element on the positive side and the switching element on the negative side in series and deriving an AC output; 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 an external connection point of the power conversion circuit and an AC output; and A control device, the control device comprising: a control unit, the control unit outputting a control signal for controlling a switching element based on an external command value, and outputting a speed indication signal indicating a switching speed of the switching element; an overvoltage protection unit, the overvoltage protection unit outputting an overvoltage cutoff signal when a voltage detected by a voltage detector is larger than a predetermined overvoltage determination threshold; an overcurrent protection unit, the overcurrent protection unit outputting an overcurrent cutoff signal when a phase current detected by a phase current detector is larger than a predetermined overcurrent determination threshold; and a gate driving unit, the gate driving unit turning on and off the switching element based on a control signal output by the control unit, and changing the on and off speed of the switching element based on the speed indication signal, and stopping the on and off of the switching element based on the overvoltage cutoff signal output by the overvoltage protection unit and the overcurrent cutoff signal output by the overcurrent protection unit, The control device changes at least one of the overvoltage determination threshold value and the overcurrent determination threshold value while changing the speed instruction signal. Effects of the Invention

[0012] According to the present disclosure, a power conversion device can be obtained, which can change the switching speed according to the operating state of the power conversion device, and at the same time change at least one of the overcurrent judgment threshold and the overvoltage judgment threshold, so as to take into account both efficient power conversion action and power conversion action in a wider range, and prevent failure, performance degradation and shortened life of the switching element. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a configuration diagram of a power conversion device according to Embodiment 1. Figure 2 This is a first hardware configuration diagram of the control device for the power conversion device according to the first embodiment. Figure 3 1 is a first diagram showing the response to overcurrent detection in the power conversion device according to the comparative example. Figure 4 This is a second diagram showing the response to overcurrent detection in the power conversion device according to the comparative example. Figure 5This is a flowchart showing a process of changing the switching speed of the control device of the power conversion device according to the first embodiment. Figure 6 This is a diagram showing the setting of the overcurrent determination threshold value of the power conversion device according to the first embodiment. Figure 7 It is a diagram showing the response to overcurrent detection in the power conversion device according to the first embodiment. Figure 8 This is a second hardware configuration diagram of the control device for the power conversion device according to the first embodiment. Fig. 9 This is a configuration diagram of a power conversion device according to the second embodiment. Fig.10 This is a flowchart showing a process of changing the switching speed of the control device of the power conversion device according to the second embodiment. Fig.11 This is a diagram showing the setting of the overcurrent determination threshold value and the overvoltage determination threshold value of the power conversion device according to the second embodiment. Fig.12 This is a diagram showing the setting of the switching speed of the power conversion device according to the second embodiment. DETAILED DESCRIPTION

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

[0015] 1. Implementation Method 1 <Structure of power conversion device> Figure 1 1 is a block diagram of a power conversion device 1 according to Embodiment 1. The power conversion device 1 can be used in electric vehicles such as electric vehicles and plug-in hybrid vehicles. It can be assumed that the power conversion device uses a DC power supply such as a battery as a power supply and is used to drive a rotating motor (motor) as a load by AC. The load is not limited to the rotating motor, and may be a load other than the rotating motor.

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

[0017] Figure 1In the embodiment, the power conversion circuit 200 has three-phase positive side switching elements 11, 12, 13, three-phase negative side switching elements 14, 15, 16, and three external connection points in which the positive side switching elements and the negative side switching elements are connected in series in each phase and connected to the rotating electric machine 3. A plurality of transistors can be connected in parallel to form each switching element. In addition, Figure 1 Although the case where the power conversion device 1 has a three-phase output is described in FIG. 1 , it may have a two-phase output or a four-phase or more output.

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

[0019] In addition, the command value is transmitted to the control unit 17 from the outside of the power conversion device 1, and the control unit 17 outputs a signal for controlling the switching elements 11 to 16 based on the command value. The control of the switching elements 11 to 16 by the control unit 17 can use the detection values ​​of the rotation angle sensor 4, the voltage detector 21, the phase current detectors 22, 23, 24, etc. As the command value input from the outside, a target speed, a target torque, a target current, a target voltage, etc. can be assumed. The control unit 17 can be a computing device that executes software to calculate input data and determines an output value.

[0020] <Switching elements> As switching elements, diodes that allow current to flow in only one direction, thyristors that are suitable for handling large currents, and power transistors that are power semiconductor switching elements that can operate at high switching frequencies are commonly used. Among semiconductor switching elements, power transistors are particularly used in a wide range of fields such as automobiles, refrigerators, and air conditioners. Among power transistors, there are IGBTs (Insulated Gate Bipolar Transistors) and MOS-FETs (Metal-oxide―Semiconductor Field-Effect Transistors), and these power transistors are used differently according to their various uses.

[0021] As materials for semiconductor switching elements, semiconductors using silicon (Si: Silicon) are mostly used. However, in recent years, silicon carbide (SiC: Silicon Carbide) and gallium nitride (GaN: Gallium Nitride) have attracted attention. Compared with semiconductor switching elements using conventional silicon, semiconductor switching elements formed of these wide-bandgap semiconductor materials have lower resistance values ​​in the on state, which can reduce power loss. In addition, the electron saturation speed is high, and the on and off states can be switched quickly.

[0022] As the switching elements 11 to 16, Figure 1 An example using IGBTs is shown in . In each of the IGBTs of the switching elements 11 to 16 , a free wheel diode (FWD) is connected in parallel with the direction from the negative electrode side to the positive electrode side of the DC power supply 2 , that is, from the lower side to the upper side as the forward direction.

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

[0024] <Change of switching speed> In the case of an IGBT, the value of the current flowing into the gate can be adjusted by changing the value of the gate resistor, thereby changing the switching speed of the switching element. By increasing the amount of current flowing into the gate, the switching speed increases.

[0025] In addition, for IGBT, the gate voltage can be changed by adjusting the voltage of the gate drive circuit, thereby changing the switching speed. If the gate voltage is increased, the switching speed increases, the switching efficiency improves, but the surge voltage and switching noise become larger. Conversely, if the gate voltage is reduced, the switching speed decreases, the switching efficiency decreases, but the surge voltage and noise can be reduced.

[0026] MOS-FET also has the characteristic that the rise time slows down when the gate current decreases. Therefore, the gate current can be adjusted by changing the value of the gate resistor, thereby adjusting the switching speed.

[0027] <Overvoltage protection, overcurrent protection> When the DC voltage value Vdc exceeds the overvoltage determination threshold value VTHOV, the overvoltage protection unit 19 outputs an overvoltage detection signal 19a to the gate drive unit 18 and the control unit 17. The gate drive unit 18 receives the overvoltage detection signal 19a and stops the on / off of the switching elements 11 to 16. In addition, the control unit 17 recognizes the generation of overvoltage by receiving the overvoltage detection signal 19a. The overvoltage protection circuit 19 can be composed of, for example, a circuit that compares a voltage value obtained from the DC voltage value Vdc through a voltage-dividing resistor with a voltage corresponding to a predetermined overvoltage determination threshold value VTHOV using a comparator.

[0028] When the absolute values ​​of the phase current values ​​iu, iw, and iv exceed the overcurrent determination threshold value ITHOC, the overcurrent protection unit 20 outputs an overcurrent detection signal 20a to the gate drive unit 18 and the control unit 17. The gate drive unit 18 receives the overcurrent detection signal 20a and stops the on / off of the switching elements 11 to 16. In addition, the control unit 17 recognizes the generation of overcurrent by receiving the overcurrent detection signal 20a.

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

[0030] If the overvoltage protection unit 19 and the overcurrent protection unit 20 are configured as described above, the overvoltage and overcurrent can be detected by the control unit 17, which is a computing device that executes software, and can be dealt with in a shorter time than issuing a control instruction. This is because the overvoltage and overcurrent are detected by using the analog circuit and digital circuit of the overvoltage protection unit 19 and the overcurrent protection unit 20, and the on and off of the switching elements 11 to 16 can be stopped quickly.

[0031] <Hardware Structure of Control Device> Figure 2 1 is a hardware configuration diagram of the control device 100 of the power conversion device 1 according to Embodiment 1. In this embodiment, each function of the control device 100 is implemented by a processing circuit included in the control device 100. Specifically, the control device 100 is configured as follows: Figure 2As shown, as a processing circuit, it has an operation processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 for exchanging data with the operation processing device 90, an input circuit 92 for inputting external signals to the operation processing device 90, and an output circuit 93 for outputting signals from the operation processing device 90 to the outside. Figure 1 The control unit 17 may include a processing device 90 .

[0032] The operation processing device 90 may include an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits. In addition, the operation processing device 90 may include a plurality of the same or different operation processing devices to share the execution of each process. The storage device 91 may include a RAM (Random Access Memory) configured to read and write data from the operation processing device 90, a ROM (Read Only Memory) configured to read data from the operation processing device 90, a flash memory, and the like. The input circuit 92 is connected to various sensors such as the voltage detector 21, the phase current detectors 22, 23, 24, and the rotation angle sensor 4, and a switch, and includes an A / D converter (Analog / Digital Converter) that inputs the output signals of these sensors and switches to the operation processing device 90. The output device 93 includes a gate driving unit 18 and the like, is connected to electric loads such as the switching elements 11 to 16 , and converts a control signal from the arithmetic processing unit 90 and outputs the converted signal to the electric loads.

[0033] Each function of the control device 100 is realized by the operation processing unit 90 executing the software (program) stored in the storage device 91 such as ROM, and cooperating with other hardware of the control device 100 such as the storage device 91, the input circuit 92 and the output circuit 93. In addition, the setting data such as the threshold value and the judgment value used by the control device 100 is stored in the storage device 91 such as ROM as part of the software (program). The functions of the structural elements of the control device 100 are described. Each function of the control device 100 can be composed of a software module, or can be composed of a combination of software and hardware.

[0034] <Switching speed and overcurrent cutoff (1)> In order to reduce the switching loss in the power conversion device, it is effective to increase the switching speed. However, if the switching speed is increased, the surge voltage when the switching element is energized and cut off will increase, and the driving noise will also increase. Therefore, the increase in switching speed must be implemented within the range where the surge voltage does not exceed the withstand voltage of the switching element.

[0035] The surge voltage expected when the on-off of the switching element stops can be calculated based on the command value (current command value) for the power conversion device, the battery voltage, etc. Then, only when the calculated expected surge voltage is sufficiently low relative to the withstand voltage of the switching element, the control to increase the switching speed is considered. For example, the following case is considered: when the current command value of the power conversion device or the detected phase current is below the predetermined switching speed switching current value, the switching speed is set to high speed, and when it is greater than the switching speed switching current value, the switching speed is set to low speed.

[0036] However, when the switching speed is increased to operate the power conversion device, if the current or voltage changes sharply and exceeds the overcurrent judgment threshold or the overvoltage judgment threshold, it is necessary to consider the large surge voltage when the switching element stops turning on and off. Therefore, considering the situation of increasing the switching speed, it is necessary to set the overcurrent judgment threshold and the overvoltage judgment threshold to be smaller. As a result, 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, resulting in the limitation of the operating range of the power conversion device.

[0037] Figure 3 1 is a first diagram showing the response to overcurrent detection of the power conversion device involved in the comparative example. Here, the structure of the power conversion device 1 involved in the first embodiment is described with reference to the structure of the power conversion device 1. When the switching speed is low and exceeds the overcurrent judgment threshold ( Figure 3 At this time, due to the delay of the overcurrent protection unit 20, it cannot be cut off immediately, and actually generates a cut-off current higher than the overcurrent judgment threshold ( Figure 3 The black triangle (▲) is shown in the figure.

[0038] It is necessary to prevent the surge voltage when the current is cut off from exceeding the withstand voltage of the switching elements 11 to 16. For this purpose, it is necessary to set the switching speed on the low speed side so that Figure 3 The surge voltage generated by cutting off the current shown by the middle dotted line does not exceed the withstand voltage of the switching elements 11 to 16.

[0039] Consider the case where the switching speed is high. Assume that a problem occurs and an overcurrent occurs when the switching speed is high. 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 speed signal 17b is transmitted from the control unit 17 to the gate drive unit 18 to switch the switching speed.

[0040] The control unit 17 controls the power conversion operation based on the 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] Even if the switching frequency of the switching elements 11 to 16 of the power conversion device 1 mounted on the vehicle is relatively high, it is mostly around 10kHz. For example, when PWM (Pulse Width Modulation) control is implemented at a switching frequency of 10kHz, a current command is generated at a period of 100μs, and sensor information such as voltage, temperature, and angular velocity is sampled, and the PWM output is calculated using the sensor information. Switching the switching speed based on the current command value of the power conversion device 1 or the detected phase current will produce a delay of about 100μs. That is, the set switching speed is based on the parameters 100μs ago. When parameters such as the current command value, phase current, and voltage change, a situation occurs in which switching is performed at a switching speed that is not suitable for the parameters at that moment.

[0042] exist Figure 3 When the switching speed is high and power conversion is performed, if an abnormality occurs and the phase current rises sharply, at the moment when the phase current exceeds the overcurrent judgment threshold ( Figure 3 The white circle (0) of FIG. 1 determines the generation of overcurrent, and the overcurrent protection unit 20 outputs the overcurrent detection signal 20a to the gate driving unit 18. Then, the gate driving unit 18 receives the overcurrent detection signal 20a and stops the on and off of the switching elements 11 to 16.

[0043] At this time, the overcurrent protection unit 20 cannot be immediately cut off due to the delay, and actually generates a cut-off current ( Figure 3 The white triangle (△) of the figure shows the current increase before the switching speed of the switching element switches from the high speed setting to the low speed setting. Therefore, the current is cut off while the switching speed is kept at the high speed setting at the cut-off current shown by the dotted line. The higher the switching speed, the higher the surge voltage. Therefore, Figure 3 Under such a setting, the surge voltage may exceed the withstand voltage of the switching element and cause a failure when the cut-off current increases during an abnormality or the like.

[0044] <Switching speed and overcurrent cutoff (2)> Figure 4 The second figure shows the response of the power conversion device involved in the comparative example when overcurrent is detected. Figure 3 Problems such as Figure 4 As shown in FIG. 1 , the problem is solved by reducing the switching speed switching current value. By setting in this way, the time from the detected phase current rising from the switching speed switching current value to the current cut-off is extended, and during this period, the switching speed of the switching element is switched to a low speed.

[0045] Therefore, when the current reaches the point where the current is cut off during abnormality ( Figure 4 The white triangle (△) of the switch changes from high speed to low speed. Therefore, the surge voltage is within the range that does not exceed the withstand voltage of the switching element.

[0046] In adopting Figure 4 In such a setting, the following problems arise: the current range in which the switching speed can be set to high speed becomes narrower. The operating range in which the switching loss can be reduced by setting the switching speed to high speed is limited. Specifically, in electric vehicles, in addition to the areas where the load of the rotating motor is large and the phase current is large, such as when starting and accelerating, it is expected that the switching loss can be reduced in the area where the phase current is medium or below. However, the area in which the switching loss can be reduced by reducing the switching speed switching current value becomes narrower, and the loss reduction related to the fuel consumption and power consumption of the vehicle cannot be fully implemented.

[0047] In addition, in the control unit 17, the timing of calculating the driving timing, driving time, and switching speed of the switching elements 11 to 16 is performed, for example, in a 100 μs cycle. Therefore, when the current rises in a shorter time during an abnormality, it can be considered that the switching speed cannot be switched to the low speed side in time, and when the switching speed is high, the surge voltage at the time of disconnection exceeds the withstand voltage, and the overcurrent protection is not established.

[0048] <Simultaneous changes in switching speed and overcurrent judgment threshold> Figure 5 This 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 1. The process of simultaneously changing the switching speed and the overcurrent determination threshold value, which is a feature of Embodiment 1 of the present disclosure, will be described.

[0049] Figure 5 The processing shown is executed by the arithmetic processing unit 90 of the control device 100 . Figure 5 The processing may be executed at predetermined time intervals (for example, every 100 μs). Alternatively, the processing may not be executed at predetermined time intervals, but may be executed for each event, such as each time predetermined input information is detected, each time communication is performed, etc.

[0050] The process starts. In step S101, the control unit 17 receives command values ​​such as torque command and speed command from the outside of the power conversion device 1 to calculate the current command value IC. The current command value IC can be directly received from the outside. The current command value is, for example, a d-axis current command value and a q-axis current command value. The current command value calculated here is used to determine the timing of the on and off of the PWM drive of the switching element.

[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 compared with the switching speed switching current value ITHCHGS as the current command value IC, the switching speed can be determined stably.

[0052] At this time, the phase current detected by the phase current detectors 22, 23, and 24 instead of the current command value IC can be compared with the switching speed switching current value ITHCHGS. However, the phase current slightly changes around the current command value IC due to current feedback. When the phase current is used, the average value of the phase current over a predetermined period can be calculated and used. In addition, when comparing with the switching speed switching current value ITHCHGS, hysteresis can be set 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. When the current command value IC is less than the switching speed switching current value ITHCHGS (determined as YES), the process proceeds to step S103. When the current command value IC is not less than the switching speed switching current value ITHCHGS (determined as NO), the process proceeds to step S104.

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

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

[0056] In step S105, the control unit 17 outputs the set switching speed SPSP as the switching speed signal 17b to the gate drive unit 18. Then, the control unit 17 outputs the set overcurrent determination threshold value ITHOC to the gate drive unit 18 as the 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 follow-up control calculation of the current command value IC, and the gate driving unit drives the switching elements 11 to 16 to perform the current command follow-up control. The process ends after step S106.

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

[0059] As a premise, a surge voltage is generated when the IGBT is switched. However, due to parasitic inductance in the circuit and the recovery characteristics of a diode connected in reverse parallel to the IGBT, the surge voltage tends to increase as the on-current during switching increases.

[0060] In addition, by adjusting the gate resistance of the IGBT, the current change rate di / dt of the on-current of the IGBT, that is, the switching speed, can be adjusted. The lower the gate resistance of the IGBT and the higher the switching speed, the higher the surge voltage. When the current and voltage during switching are the same, the higher the switching speed, the lower the switching loss. The same tendency is also shown when the gate voltage of the IGBT is increased to increase the switching speed.

[0061] Figure 6 The overcurrent determination threshold value H (ITHOCH) shown is set when the switching speed SPSW is the switching speed L (low-speed side switching speed) SPSWL. When the power conversion device 1 operates at the maximum rated current at the switching speed L, it is set to a value that does not detect overcurrent. That is, the overcurrent determination threshold value H (ITHOCH) is set to a value greater than the maximum rated current of the power conversion device 1. In addition, the overvoltage determination threshold value VTHOV is set to a value greater than the maximum voltage that can be obtained under normal operation.

[0062] Then, in Figure 6 When the occurrence of overcurrent is detected at the point shown in A, the overcurrent protection unit 20 cannot be immediately cut off due to the delay, and a cut-off current H higher than the overcurrent judgment threshold is actually generated. The switching speed L (slow-speed switching speed) SPSWL needs to be determined so that the surge voltage (cut-off voltage) generated when the cut-off is performed at this current does not exceed the withstand voltage value of the switching element.

[0063] Next, the switching speed SPSW is set to the switching speed H (high-speed switching speed) SPSWH. Figure 6The switching speed switching current value ITHCHGS at the point shown in B2 is determined. For example, the switching speed switching current value ITHCHGS is determined based on the current that occurs at a high frequency in the driving mode for regulating the power consumption of the electric vehicle, so that the operating state in which the switching efficiency should be improved comes below the point shown in B2. Thus, in the operating mode in which the switching efficiency is to be improved, the power conversion action can be performed at the switching speed H (high-speed side switching speed) SPSWH. For convenience, Figure 6 The voltage at the point indicated by B2 is set to be the same as that at the point indicated by A.

[0064] The overcurrent judgment threshold L (ITHOCL) is not reached during the normal power conversion operation at the switching speed H (high-speed switching speed) SPSWH. Figure 6 The point shown in B1 is used to determine the Figure 6 The point shown in B1, i.e., the overcurrent judgment threshold L (ITHOCL), is not reached during normal operation at the switching speed H (high-speed side switching speed) SPSWH, but an early overcurrent judgment is implemented during abnormal operation, and it is determined that the surge voltage during cut-off does not exceed the withstand voltage value of the switching element.

[0065] When an overcurrent is generated during abnormal operation, the switching speed SPSW should be switched to the switching speed L (low-speed switching speed) SPSWL when the original current command value IC or the detected phase current is larger than the switching speed switching current value ITHCHGS. However, due to the PWM calculation timing, there is a case where the switching speed SPSW is delayed. In this case, when the switching speed H (high-speed switching speed) SPSWH is maintained, the detected phase current becomes larger than the overcurrent determination threshold L, and an overcurrent is determined.

[0066] By Figure 6 The overcurrent judgment is performed at the point shown in B1 of FIG. 1 , the on-off of the switch element is stopped, and the current conversion is interrupted. At this time, the power conversion is stopped at the switching speed H (high-speed switching speed) SPSWH, so the surge voltage becomes larger. However, the phase current when the current is cut off is the overcurrent judgment threshold L (ITHOCL), which is smaller than the overcurrent judgment threshold H (ITHOCH). Therefore, even if there is a delay until the actual current is cut off, the current value only rises to Figure 6 As a result, the surge voltage caused by the cut-off current L does not exceed the withstand voltage value of the switching element.

[0067] For the points shown in A, B1, and B2, the voltage is common, and the relationship of A>B1>B2 for the current value holds. In the region where the current value is smaller than the point shown in B2, the switching speed can be increased. Therefore, in the current region that is generally considered to be used at a high frequency in electric vehicles, the loss of the switching element can be reduced.

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

[0069] Therefore, if the current command value IC (effective value) exceeds the switching speed switching current value ITHCHGS under normal circumstances, the switching speed SPSW is switched to the switching speed L (low-speed side switching speed) SPSWL, and at the same time, the overcurrent judgment threshold ITHOC is switched from the overcurrent judgment threshold L (ITHOCL) to the overcurrent judgment threshold H (ITHOCH).

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

[0071] Figure 7 1 is a diagram showing the response to overcurrent detection of the power conversion device 1 according to the first embodiment. Figure 4 Compared with the case of , the switching speed switching current value ITHCHGS can be made larger than the required degree. Therefore, it can be known that the switching efficiency can be improved by setting the switching speed to a high speed, and the driving area can be fully secured. In addition, even if an abnormality occurs when the switching speed is set to a high speed and the phase current rises sharply, the overcurrent judgment threshold L (ITHOCL) can be detected ( Figure 7 The white circle (0) of the switch element can be quickly stopped from turning on and off. Therefore, even if there is a delay until the actual current is cut off, the phase current only increases to the cut-off current L ( Figure 7 The white triangle (△) of FIG. 1 shows a schematic diagram of a switching device. This can prevent the switching device from being damaged, causing a surge voltage when the switching device is turned off, and preventing the switching device from being damaged or having a shorter lifespan.

[0072] As described above, according to the power conversion device 1 involved in the first embodiment, even if the setting of the switching speed has a delay, the switch can be stopped by overcurrent protection with a short delay time for the rapid current increase during an abnormality. Therefore, it is not necessary to set the switching speed switching current value ITHCHGS to a low value in consideration of the delay of the switching speed. The rapid current increase during an abnormality and the current dependence of the surge voltage can be considered and a high switching speed can be set, which can reduce the loss.

[0073] In addition, the values ​​of the overcurrent determination threshold L (ITHOCL) and the overcurrent determination threshold H (ITHOCH) can be freely set, so the overcurrent determination threshold can be appropriately changed and set according to the performance of the power conversion device 1, the performance of the rotating electrical machine as a load, and the driving characteristics of the electric vehicle. It can be dealt with only by changing the software (changing the parameters), so a power conversion device 1 with a high degree of freedom can be obtained.

[0074] In addition, in the above embodiment, a method of adjusting the switching speed by changing the gate resistance is described, but the present invention is not limited thereto, and the same effect can be obtained even if the switching speed is adjusted by changing the gate drive voltage or the gate drive current. The switching speed can be increased by reducing the gate resistance, increasing the gate drive voltage or increasing the gate drive current.

[0075] <Overvoltage and overcurrent response without software> Figure 8 This is a second hardware configuration diagram of the control device 100 of the power conversion device 1 according to Embodiment 1. If the overcurrent protection unit 20, the overvoltage protection unit 19, and the gate drive unit 18 are composed of analog circuits such as voltage-dividing resistors, comparators, and logic circuits, and digital circuits, overcurrent and overvoltage can be detected and dealt with quickly.

[0076] Compared with the case where the overcurrent protection unit 20, the overvoltage protection unit 19, and the gate driving unit 18 are configured as functions of a computing device that executes software, overvoltage and overcurrent can be detected quickly, and the on and off of the switching elements 11 to 16 can be stopped without delay. Figure 8 2 shows an example of the hardware configuration of the control device 100 when such a configuration is adopted.

[0077] <Reducing the delay time due to interrupt processing> However, it is also possible to perform A / D conversion on the output of the voltage detector 21 and the output of the phase current detectors 22, 23, and 24 in a short cycle and execute input capture interrupt processing at the end of each A / D conversion. In the input capture interrupt processing, the generation of overvoltage and overcurrent is confirmed.

[0078] Therefore, there is no need to wait for the timing of calculating the PWM output by generating a current command in a normal 100 μs cycle, and the generation of overvoltage and overcurrent can be dealt with with a shorter delay time. In this case, the overcurrent protection unit 20, the overvoltage protection unit 19, and the gate drive unit 18 can be configured as functions of a computing device that executes software.

[0079] In the case of abnormal operation of the connected DC power supply 2, the rotating motor 3, and other electrical components connected to the DC power supply 2, and in the case of temporary malfunction of the power conversion device 1 itself due to noise, etc., the power conversion device 1 mounted on the vehicle needs to detect overcurrent and overvoltage and quickly stop the power conversion operation. It is required to protect by stopping the on and off of the switching element so that the surge voltage during switching does not exceed the withstand voltage of the switching element. Assuming a sharp change in current and voltage, the time until the overcurrent and overvoltage are detected and the power conversion is stopped is sometimes preferably about several μs.

[0080] In this case, a shorter response time than the setting delay of the normal switching speed is required. In addition, even if the input capture interrupt processing is executed every time the A / D conversion is completed to confirm the overcurrent or the occurrence of the overcurrent, it is difficult to complete the processing within a few μs.

[0081] In order to cope with this situation, it is advantageous that the overvoltage protection unit 19, the overcurrent protection unit 20, and the gate drive unit are configured to execute the stop function of the switching element for overcurrent and overvoltage without software processing. By configuring the switching element for overcurrent and overvoltage to be stopped by the operation of the analog circuit and the digital circuit, a high-speed overcurrent and overvoltage countermeasure can be achieved.

[0082] 2. Implementation Method 2 <Structure of power conversion device> Fig. 9 1 is a block diagram of a power conversion device 1 according to Embodiment 2. Embodiment 1 describes a power conversion device 1 that changes the overcurrent determination threshold value ITHOC simultaneously with the switching speed SPSW. Embodiment 2 describes a power conversion device 1 that changes the overcurrent determination threshold value ITHOC and the overvoltage determination threshold value VTHOV simultaneously with the switching speed SPSW.

[0083] Fig. 9 The power conversion device 1 and the embodiment 1 involved Figure 1The only difference between the power conversion device of the embodiment 1 and the embodiment 1 is that the overvoltage protection unit 19 has a function of transmitting the overvoltage threshold signal 17d from the control unit 17 to change the overvoltage judgment threshold VTHOV. The adjustment of the overvoltage judgment threshold VTHOV of the overvoltage protection unit 19 can be achieved by using a voltage-dividing resistor method of a reference voltage of a transistor switching circuit. The adjustment of the overvoltage judgment threshold VTHOV of the overvoltage protection unit 19 can be achieved by generating a comparison voltage by a D / A converter (Digital / Analog Converter) based on an H / L (High / Low) signal, an analog voltage signal, or an overvoltage threshold signal 17d received as a digital signal representing a voltage value. In the following, only the parts that are different from the embodiment 1 are described.

[0084] <Simultaneous changes in switching speed, overcurrent judgment threshold, and overvoltage judgment value> Fig.10 This is a flowchart showing the switching speed change process of the control device 100 of the power conversion device 1 according to Embodiment 2. The feature according to Embodiment 2 of the present disclosure, namely, the simultaneous change process of the switching speed, the overcurrent determination threshold value, and the overvoltage determination value will be described.

[0085] Fig.10 The processing shown is executed by the arithmetic processing unit 90 of the control device 100 . Fig.10 The processing may be executed at predetermined time intervals (for example, every 100 μs). Alternatively, the processing may not be executed at predetermined time intervals, but may be executed for each event, such as each time predetermined input information is detected, each time communication is performed, etc.

[0086] The process starts. In step S201, the control unit 17 reads the DC voltage value Vdc detected by the voltage detector 21. In step S202, the control unit 17 receives command values ​​such as torque command and speed command from the outside of the power conversion device 1 to calculate the current command value IC. The current command value IC can be directly received from the outside. The current command value is, for example, a d-axis current command value and a q-axis current command value. The current command value calculated here is used to determine the timing of the on and off of the PWM drive of the switching element.

[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 compared with the switching speed switching current value ITHCHGS as the current command value IC, the switching speed can be determined stably.

[0088] At this time, the phase current detected by the phase current detectors 22, 23, and 24 instead of the current command value IC can be compared with the switching speed switching current value ITHCHGS. However, the phase current slightly changes around the current command value IC due to current feedback. When the phase current is used, the average value of the phase current over a predetermined period can be calculated and used. In addition, when comparing with the switching speed switching current value ITHCHGS, hysteresis can be set 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. When the current command value IC is less than the switching speed switching current value ITHCHGS (determined as YES), the process proceeds to step S204. When the current command value IC is not less than the switching speed switching current value ITHCHGS (determined as NO), the process proceeds to step S205.

[0090] In step S204, it is determined whether the DC voltage value Vdc is less than the switching speed switching voltage value VTHCHGS. If the DC voltage value Vdc is less than the switching speed switching voltage value VTHCHGS (the determination is yes), the process proceeds to step S206. If the DC voltage value Vdc is not less than the switching speed switching voltage value VTHCHGS (the 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 L (lower overcurrent determination threshold) ITHOCL is set to the overcurrent determination threshold ITHOC, and the overvoltage determination threshold L (lower overvoltage determination threshold) VTHOVL is set to the overvoltage determination threshold VTHOV. 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 L (lower overcurrent determination threshold) ITHOCL is set to an overcurrent determination threshold ITHOC, and the overvoltage determination threshold H (upper overvoltage determination threshold) VTHOVH is set to an overvoltage determination threshold VTHOV. Then, the process proceeds to step S210.

[0093] In step S205, it is determined whether the DC voltage value Vdc is less than the switching speed switching voltage value VTHCHGS. If the DC voltage value Vdc is less than the switching speed switching voltage value VTHCHGS (the determination is yes), the process proceeds to step S208. If the DC voltage value Vdc is not less than the switching speed switching voltage value VTHCHGS (the 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 value ITHOC is set to an overcurrent determination threshold value H (upper overcurrent determination threshold value) ITHOCH, and the overvoltage determination threshold value VTHOV is set to an overvoltage determination threshold value L (lower overvoltage determination threshold value) 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 value ITHOC is set to an overcurrent determination threshold value H (upper overcurrent determination threshold value) ITHOCH, and the overvoltage determination threshold value VTHOV is set to an overvoltage determination threshold value H (upper overvoltage determination threshold value) VTHOVH. Then, the process proceeds to step S210.

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

[0097] In step S211, the control unit 17 outputs a control signal 17a to the gate drive unit 18 based on the follow-up control calculation of the current command value IC, and the gate drive unit drives the switching elements 11 to 16 to perform the current command follow-up control. The process ends after step S211.

[0098] <Relationship between switching speed and overcurrent judgment threshold and overvoltage judgment threshold> Fig.11 It is a diagram showing the setting of the overcurrent determination threshold value and the overvoltage determination threshold value of the power conversion device 1 according to the first embodiment. Fig.12 This is a diagram showing the setting of the switching speed of the power conversion device according to the second embodiment. Fig.12 It focuses on Fig.11 The following is a diagram for explaining the switching of the switching speed SPSW and the setting method of the overcurrent determination threshold value ITHOC and the overvoltage determination threshold value VTHOV.

[0099] Fig.11 In the figure, the surge voltage establishment line is a line showing the relationship between the surge voltage and the voltage and current at the switching speeds defined as high, medium, and low speeds, which is consistent with the component withstand voltage. In the case of a switching element, it is a line showing the combination of the maximum current and the maximum voltage allowed at a specified switching speed. Although it is drawn as a straight line for convenience, it is actually expressed as a curve.

[0100] If the current and voltage are on the lower side of the surge voltage establishment line, the surge voltage becomes a region where the operation can be performed without exceeding the withstand voltage of the switching element. The figure shows three surge voltage establishment lines corresponding to the switching speeds of high speed, medium speed, and low speed. For example, when the switching speed is high, the surge voltage becomes high, so the allowable current becomes the lowest line.

[0101] Fig.11 The overcurrent determination threshold value H (upper overcurrent determination threshold value) ITHOCH is set to a value at which the power conversion device 1 does not perform overcurrent detection when operating at the maximum rated current. In addition, the overvoltage determination threshold value H (upper overvoltage determination threshold value) VHTOVH is set to a value at which the power conversion device 1 does not perform overvoltage detection when operating at the maximum voltage that can be obtained when the DC power supply 2 is normal.

[0102] When setting the overcurrent judgment threshold H and overvoltage judgment threshold H, it is necessary to set them so that overcurrent protection and overvoltage protection can be performed in the event of abnormal operation. Set them so that the surge voltage when detecting overcurrent and stopping the on / off of the switch element under the condition of low switching speed does not exceed the withstand voltage value of the switch element. Set them so that the surge voltage when detecting overvoltage and stopping the on / off of the switch element under the condition of low switching speed does not exceed the withstand voltage value of the switch element.

[0103] The overcurrent determination threshold value H and the overvoltage determination threshold value H must be set so that the surge voltage when the switching element is stopped when the current H and the voltage H are cut off does not exceed the withstand voltage value of the switching element. Fig.11 The point E shown in FIG. 1 is the maximum operating point for continued operation when the switching speed is low. Conversely, the switching speed that satisfies the above conditions can be set as the switching speed when the speed is low.

[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 this current value, based on, for example, the current generated at a high frequency in the driving mode for defining the power consumption of the electric vehicle. In addition, the overvoltage determination threshold L (lower overvoltage determination threshold) VTHOVL is set to a value that does not perform overvoltage detection during normal driving in the same driving mode. For example, if the DC power supply 2 is a lithium-ion battery, since the voltage range of a single cell is 2.8V to 4.2V and the rated voltage is 3.7V, it is set to a value that does not perform overvoltage detection when operating at a rated voltage that is lower than the maximum voltage in the battery and is used at a high frequency.

[0105] Fig.11In the example, the switching speed switching current value ITHCHGS for switching the switching speed is set to the low current side of the overcurrent judgment threshold value L. Specifically, the switching speed switching current value is a value based on the effective value of the AC current compared with the current command value IC (effective value), and therefore, it is set so that the current value obtained by adding the control variation to the peak current and current ripple obtained by the switching speed switching current value × √2 is lower than the overcurrent judgment threshold value L.

[0106] Then, the switching speed switching voltage value VTHCHGS is set to the lower voltage side of the overvoltage judgment threshold value L. Specifically, the switching speed switching voltage value is a value to be compared with the detected DC voltage value Vdc, and therefore, is set so that the voltage value obtained by adding the voltage ripple and the detection error to the DC voltage value Vdc is lower than the overvoltage judgment threshold value L.

[0107] Thus, in the case where the current or voltage rises under normal operating conditions, the switching speed can be changed and the operation can be continued without overcurrent detection or overvoltage detection. Moreover, in the case where the current value or voltage value rises sharply due to the occurrence of an abnormality, even if the switching speed is delayed and the switching speed remains high, overcurrent detection or overvoltage detection can be quickly performed due to exceeding the overcurrent judgment threshold L or the overvoltage judgment threshold L. As a result, the on-off stop of the switching element can be quickly performed through overcurrent detection or overvoltage detection. Since the switching speed is high, the surge voltage when the power conversion action stops becomes larger, but by appropriately setting the overcurrent judgment threshold L and the overvoltage judgment threshold L to a smaller value, the withstand voltage value of the switching element will not be exceeded. Thus, a power conversion device can be obtained, which can take into account both efficient power conversion action and power conversion action in a wide range, and can prevent failure of the switching element, performance degradation, and shortened life.

[0108] Fig.11 , 12 In the case where the current command value IC is less than the switching speed switching current value ITHCHGS and the DC voltage value Vdc is less than the switching speed switching voltage value VTHCHGS, the switching speed is set to high speed. In the case where 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 low speed. In other cases, the switching speed is set to medium speed.

[0109] It must be set so that overcurrent protection and overvoltage protection can be performed in the event of abnormal operation in the settings of the overcurrent judgment threshold L and the overvoltage judgment threshold L. It is set so that the surge voltage when detecting overcurrent and stopping the on / off of the switching element under the condition of high switching speed does not exceed the withstand voltage value of the switching element. It is set so that the surge voltage when detecting overvoltage and stopping the on / off of the switching element under the condition of high switching speed does not exceed the withstand voltage value of the switching element.

[0110] Under the condition of high switching speed, the overcurrent judgment threshold L and the overvoltage judgment threshold L must be set so that the cutoff current L and the cutoff voltage L when the surge voltage is applied do not exceed the withstand voltage value of the switching element. Fig.11 The point shown in D becomes the maximum operating point for continued operation when the switching speed is high. Conversely, the switching speed that satisfies the above conditions can be set as the switching speed when the switching speed is high.

[0111] In addition, in the settings under the combination of the overcurrent determination threshold value H and the overvoltage determination threshold value L, and the combination of the overcurrent determination threshold value L and the overvoltage determination threshold value H, the case where the switching speed is medium speed is discussed. As described above, it is necessary to set it so that overcurrent protection and overvoltage protection can be performed in the event of abnormal operation. The setting is made so that when the switching speed is medium speed, the surge voltage when the overcurrent is detected and the conduction and switching of the switch element are stopped does not exceed the withstand voltage value of the switch element. The setting is made so that when the switching speed is medium speed, the surge voltage when the overvoltage is detected and the conduction and switching of the switch element are stopped does not exceed the withstand voltage value of the switch element.

[0112] When the switching speed is medium, the speed at which the switching speed is medium can be set so that the combination of the cut-off current H and the cut-off voltage L when a surge voltage is applied when the conduction and switching of the switching element are stopped, and the combination of the cut-off current L and the cut-off voltage H do not exceed the withstand voltage value of the switching element. Fig.11 The point indicated by C is the maximum operating point when the current value of the continuous operation is large when the switching speed is medium. Fig.11 The point indicated by F is the maximum operating point when the switching speed is medium and the voltage value for continued operation is large.

[0113] Thus, the switching speed H, the switching speed M, the switching speed L and the overcurrent judgment threshold H, the overcurrent judgment threshold L, the overvoltage judgment threshold H, and the overvoltage judgment threshold L can be appropriately set. As a result, the switching loss can be reduced by setting the switching speed to high speed within the current and voltage range assumed to be used at high frequencies in electric vehicles. Even if one of the current or voltage exceeds the switching speed switching current value or the switching speed switching voltage value, the switching speed can be set to medium speed to operate. In addition, for low-frequency operations in which the current and voltage are the largest within the operating range, the power conversion device 1 can continue to operate by setting the switching speed to low speed.

[0114] In addition, the overcurrent determination threshold H (upper overcurrent determination threshold) ITHOCH, the overcurrent determination threshold L (lower overcurrent determination threshold) ITHOCL, the overvoltage determination threshold H (upper overvoltage determination threshold) VTHOVH, the overvoltage determination threshold L (lower overvoltage determination 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 the switching speed and the overcurrent determination threshold can be appropriately changed and set according to the performance of the power conversion device 1, the performance of the rotating electrical machine as a load, and the driving characteristics of the electric vehicle. It can be handled only by changing the software (changing the parameters), so a power conversion device 1 with a high degree of freedom can be obtained.

[0115] Fig.12 In the above description, the case where the switching speed is set to three types, namely, high speed, medium speed, and low speed, is explained. However, as shown below, the switching speed may be set to four types.

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

[0117] The relationship can be set to be the first speed> the second speed, the third speed> the fourth speed, and the second speed and the third speed can be set to different speeds. The influence of the delay in switching the switching speed, the influence of the increase in the current value caused by the delay in current cutoff during overcurrent detection, the behavior of the surge voltage in these cases, etc. can be obtained through experiments, and the optimal switching speed and switching judgment value can be set within the range that does not exceed the withstand voltage value of the switching element. By setting in this way, the switching speed, switching judgment value and overcurrent judgment threshold can be further appropriately changed and set according to the performance of the power conversion device 1, the performance of the rotating motor as a load, and the driving characteristics of the electric vehicle.

[0118] <Temperature characteristics of switching elements> In Embodiments 1 and 2, an example of switching the switching speed and the overcurrent determination threshold or the overvoltage determination threshold based on the current and voltage is described. Alternatively, 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 IGBT, MOSFET, etc., the lower the temperature of the switching element, the higher the gate threshold, which shortens the switching time when turning off. As a result, the switching speed increases and the surge voltage increases. In addition, the lower the temperature, the lower the component withstand voltage, so the allowable value of the surge voltage decreases.

[0120] In addition, the higher the temperature of the switching element, the worse the recovery characteristics of the diode connected in reverse parallel to the IGBT and the body diode of the MOSFET, and the higher the surge voltage when it is turned on. Therefore, it can be considered that the lower the temperature and the higher the temperature, the higher the surge voltage. In addition, the component withstand voltage decreases at low temperatures.

[0121] Therefore, the switching speed or overcurrent judgment threshold and overvoltage judgment threshold can be adjusted based on the temperature characteristics. Thus, the appropriate current resistance value and voltage resistance value of the switching element can be calculated based on the temperature characteristics. Thus, the degradation of the switching element can be prevented and the loss can be reduced in a wider operating range.

[0122] When the surge voltage increases due to temperature, the switching speed can be reduced while the overcurrent determination threshold and the overvoltage determination threshold shown in the above embodiment remain unchanged. In addition, the overcurrent determination threshold and the overvoltage determination threshold can be adjusted while the switching speed remains unchanged. In addition, the method of adjusting the switching speed and the overcurrent determination threshold and the overvoltage determination threshold can be used to correspond. In addition, in addition to directly detecting the temperature of the switching element by a temperature detector, the temperature near the switching element in the power module can also be detected by a temperature detector.

[0123] In the first and second embodiments, a power conversion device 1 using an IGBT composed of a silicon semiconductor is shown as an example. However, the power conversion device is not limited to this. For example, a wide bandgap semiconductor using silicon carbide, gallium nitride-based materials, or diamond can be used. These wide bandgap semiconductors are more expensive than silicon semiconductors, but they are used to achieve low loss, so they can further promote loss reduction, so they are effective.

[0124] In the first and second embodiments, the method of adjusting the overvoltage determination threshold of the overvoltage protection unit 19 and the overcurrent determination threshold of the overcurrent protection unit 20 is described. However, the following method may be adopted: a plurality of protection circuits are provided, and the sharp current and voltage rise in an abnormal situation is suppressed by making the protection circuit corresponding to the area with a small current value or voltage value effective.

[0125] The above content discloses a method of comparing the switching speed switching current value with the current, or the switching speed switching voltage value with the voltage, and switching the switching speed and the overcurrent judgment threshold and the overvoltage judgment threshold at the same time. However, a plurality of switching thresholds for switching the switching speed may be used for the current or voltage. Alternatively, a method of always adjusting the switching speed and the overcurrent judgment threshold and the overvoltage judgment threshold may be adopted so that the surge voltage calculated based on the current and voltage in consideration of the abnormal behavior does not exceed the component withstand voltage.

[0126] In addition, a method for adjusting the switching speed and the overcurrent determination threshold and the overvoltage determination threshold based on the current command value is shown, but it is not limited to this. For example, they can be adjusted based on the instantaneous value of the phase current. The power conversion circuit 200 of the power conversion device 1 is described as an example of an inverter. However, the power conversion device is not limited to this, and the technology disclosed in this disclosure can also be applied to a DC / DC converter.

[0127] For example, a DC / DC converter in which a reactor is connected to a connection point of a series circuit of switching elements of the upper and lower arms and the reactor current and the voltage across the series circuit are detected for control can achieve the same effect.

[0128] The present disclosure describes various exemplary embodiments and examples, but various features, forms, and functions described in one or more embodiments are not limited to application in specific embodiments and can be applied to the embodiments alone or in various combinations. Therefore, it is considered that numerous modifications not shown in the examples are also included in the disclosed technical scope, including, for example, the case where at least one component is modified, added, or omitted, and the case where at least one component is extracted and combined with components of other embodiments.

[0129] Hereinafter, each aspect of the present disclosure will be collectively described as a supplementary note.

[0130] (Supplementary Note 1) A power conversion device comprising: A power conversion circuit including a switching element on the positive side connected to the positive electrode of a DC power source, a switching element on the negative side connected to the negative electrode of the DC power source, and an external connection point for connecting the switching element on the positive side and the switching element on the negative side in series and deriving an AC output; 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 device, the control device comprising: a control unit, the control unit outputting a control signal for controlling the switching element based on an external command value, and outputting a speed indication signal indicating a switching speed of the switching element; an overvoltage protection unit, the overvoltage protection unit outputting an overvoltage cutoff signal when the voltage detected by the voltage detector is larger than a predetermined overvoltage judgment threshold; an overcurrent protection unit, the overcurrent protection unit outputting an overcurrent cutoff signal when the phase current detected by the phase current detector is larger than a predetermined overcurrent judgment threshold; and a gate driving unit, the gate driving unit turning on and off the switching element based on the control signal output by the control unit, and changing the on and off speed of the switching element based on the speed indication signal, and stopping the on and off of the switching element based on the overvoltage cutoff signal output by the overvoltage protection unit and the overcurrent cutoff signal output by the overcurrent protection unit, The control device changes at least one of the overvoltage determination threshold and the overcurrent determination threshold while changing the speed instruction signal. (Supplement 2) The power conversion device as described in Supplement 1, The control device changes the speed instruction signal and the overcurrent determination threshold value based on the current command value calculated from the command value or the phase current. (Supplementary Note 3) The power conversion device as described in Supplementary Note 2, The control device changes the speed instruction signal so that the switching speed of the switching element decreases as the current command value or the phase current increases, and changes so that the overcurrent determination threshold value increases. (Supplement 4) The power conversion device as described in Supplement 2, When the current command value or the phase current is larger than a predetermined speed switching current value, the control device changes the speed instruction signal so as to reduce the switching speed of the switching element and changes so as to increase the overcurrent determination threshold value. (Supplementary Note 5) The power conversion device as described in Supplementary Note 4, In the control device, the speed switching current value is always smaller than the overcurrent determination threshold value. (Supplement 6) A power conversion device as described in any one of Supplements 2 to 6, The control device changes the speed instruction signal and the overcurrent determination threshold value based on the current command value. (Supplementary Note 7) The power conversion device as described in Supplementary Note 1, The control device changes the speed instruction signal and the overvoltage determination threshold value based on the voltage detected by the voltage detector. (Supplementary Note 8) The power conversion device as described in Supplementary Note 7, The control device changes the speed instruction signal so that the switching speed of the switching element decreases as the voltage increases, and changes the speed instruction signal so that the overvoltage determination threshold value increases. (Supplementary Note 9) The power conversion device as described in Supplementary Note 7, When the voltage is larger than a predetermined speed switching voltage value, the control device changes the speed instruction signal so as to reduce the switching speed of the switching element and changes so as to increase the overvoltage determination threshold value. (Supplement 10) The power conversion device as described in Supplement 9, In the control device, the speed switching voltage value is always smaller than the overvoltage determination threshold. (Supplement 11) The power conversion device as described in Supplement 1, The control device outputs the speed instruction signal for setting the switching speed of the switching element to a first speed, 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 below a predetermined speed switching current value and the voltage is below a predetermined speed switching voltage value, When the current command value or the phase current is larger than the speed switching current value and the voltage is lower than the speed switching voltage value, the speed instruction signal is outputted to set the switching speed of the switching element to a second speed slower than the first speed, the overcurrent determination threshold is set to a second overcurrent determination threshold larger than the first overcurrent determination threshold, and the overvoltage determination threshold is set to the first overvoltage determination threshold, When the current command value or the phase current is below the speed switching current value and the voltage is greater than the speed switching voltage value, the speed instruction signal is outputted to set the switching speed of the switching element to a third speed that is slower than the first speed, the overcurrent determination threshold is set to the first overcurrent determination threshold, and the overvoltage determination threshold is set to a second overvoltage determination threshold that is greater than the first overvoltage determination threshold, When the current command value or the phase current is larger than the speed switching current value and the voltage is larger than the speed switching voltage value, the speed indication signal is output to set the switching speed of the switching element to a fourth speed that is slower than the second speed and the third speed, the overcurrent judgment threshold is set to the second overcurrent judgment threshold, and the overvoltage judgment threshold is set to the second overvoltage judgment threshold. (Supplement 12) A power conversion device as described in any one of Supplements 1 to 11, A temperature sensor is provided, the temperature sensor detecting the temperature of the switching element, The control device changes the speed instruction signal based on the temperature of the switching element, and at the same time changes at least one of the overvoltage determination threshold value and the overcurrent determination threshold value. (Supplement 13) A power conversion device as described in any one of Supplements 1 to 12, In the control device, the speed indication signal and at least one of the overvoltage judgment threshold and the overcurrent judgment threshold are set so that the surge voltage when the gate drive unit stops the conduction and switching of the switching element based on the overvoltage cutoff signal or the overcurrent cutoff signal is below the withstand voltage of the switching element. (Supplement 14) A power conversion device as described in any one of Supplements 1 to 13, The control device changes the on / off speed of the switching element by changing at least one of a gate driving voltage, a gate driving current, and a gate driving resistance of the gate driving unit. (Supplement 15) A power conversion device as described in any one of Supplements 1 to 14, In the control device, the overvoltage protection unit outputs the overvoltage cutoff signal when the voltage is larger than the overvoltage judgment threshold, the overcurrent protection unit outputs the overcurrent cutoff signal when the phase current is larger than the overcurrent judgment threshold, and the gate drive unit stops the on and off of the switching element based on the overvoltage cutoff signal or the overcurrent cutoff signal without software processing. (Supplement 16) A power conversion device as described in any one of Supplements 1 to 15, The switching element uses a wide bandgap semiconductor. Description of symbols

[0131] 1 Power conversion device 2 DC power supply 11, 12, 13, 14, 15, 16 Switching elements 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 devices 200 power conversion circuits.

Claims

1. A power conversion device, characterized in that: include: A power conversion circuit including a switching element on the positive side connected to the positive electrode of a DC power source, a switching element on the negative side connected to the negative electrode of the DC power source, and an external connection point for connecting the switching element on the positive side and the switching element on the negative side in series and deriving an AC output; 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; as well as A control device, the control device comprising: a control unit, the control unit outputting a control signal for controlling the switching element based on an external command value, and outputting a speed instruction signal for indicating a switching speed of the switching element; an overvoltage protection unit, the overvoltage protection unit outputting an overvoltage cutoff signal when the voltage detected by the voltage detector is greater than a predetermined overvoltage determination threshold; an overcurrent protection unit that outputs an overcurrent cutoff signal when the phase current detected by the phase current detector is larger than a predetermined overcurrent determination threshold; and a gate driving unit that turns on and off the switching element based on a control signal output by the control unit, changes the on and off speed of the switching element based on the speed instruction signal, and stops the on and off of the switching element based on an overvoltage cutoff signal output by the overvoltage protection unit and the overcurrent cutoff signal output by the overcurrent protection unit, The control device changes at least one of the overvoltage determination threshold and the overcurrent determination threshold while changing the speed instruction signal.

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

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

4. The power conversion device according to claim 2, characterized in that: When the current command value or the phase current is larger than a predetermined speed switching current value, the control device changes the speed instruction signal so as to reduce the switching speed of the switching element and changes so as to increase the overcurrent determination threshold value.

5. The power conversion device according to claim 4, characterized in that: In the control device, the speed switching current value is always smaller than the overcurrent determination threshold value.

6. The power conversion device according to claim 2, characterized in that: 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, characterized in that: The control device changes the speed instruction signal and the overvoltage determination threshold value based on the voltage detected by the voltage detector.

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

9. The power conversion device according to claim 7, characterized in that: When the voltage is larger than a predetermined speed switching voltage value, the control device changes the speed instruction signal so as to reduce the switching speed of the switching element and changes so as to increase the overvoltage determination threshold value.

10. The power conversion device according to claim 9, characterized in that: In the control device, the speed switching voltage value is always smaller than the overvoltage determination threshold.

11. The power conversion device according to claim 1, characterized in that: The control device outputs the speed instruction signal for setting the switching speed of the switching element to a first speed, 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 calculated based on the command value or the phase current is below a predetermined speed switching current value and the voltage is below a predetermined speed switching voltage value, When the current command value or the phase current is larger than the speed switching current value and the voltage is lower than the speed switching voltage value, the speed instruction signal is outputted to set the switching speed of the switching element to a second speed slower than the first speed, the overcurrent determination threshold is set to a second overcurrent determination threshold larger than the first overcurrent determination threshold, and the overvoltage determination threshold is set to the first overvoltage determination threshold, When the current command value or the phase current is below the speed switching current value and the voltage is greater than the speed switching voltage value, the speed instruction signal is outputted to set the switching speed of the switching element to a third speed that is slower than the first speed, the overcurrent determination threshold is set to the first overcurrent determination threshold, and the overvoltage determination threshold is set to a second overvoltage determination threshold that is greater than the first overvoltage determination threshold, When the current command value or the phase current is larger than the speed switching current value and the voltage is larger than the speed switching voltage value, the speed indication signal is output to set the switching speed of the switching element to a fourth speed that is slower than the second speed and the third speed, the overcurrent judgment threshold is set to the second overcurrent judgment threshold, and the overvoltage judgment threshold is set to the second overvoltage judgment threshold.

12. The power conversion device according to claim 1, characterized in that: A temperature sensor is provided, the temperature sensor detecting the temperature of the switching element, The control device changes the speed instruction signal based on the temperature of the switching element, and at the same time changes at least one of the overvoltage determination threshold value and the overcurrent determination threshold value.

13. The power conversion device according to claim 1, characterized in that: In the control device, the speed indication signal and at least one of the overvoltage judgment threshold and the overcurrent judgment threshold are set so that the surge voltage when the gate drive unit stops the conduction and switching of the switching element based on the overvoltage cutoff signal or the overcurrent cutoff signal is below the withstand voltage of the switching element.

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

15. The power conversion device according to any one of claims 1 to 14, characterized in that: In the control device, the overvoltage protection unit outputs the overvoltage cutoff signal when the voltage is larger than the overvoltage judgment threshold, the overcurrent protection unit outputs the overcurrent cutoff signal when the phase current is larger than the overcurrent judgment threshold, and the gate drive unit stops the on and off of the switching element based on the overvoltage cutoff signal or the overcurrent cutoff signal without software processing.

16. The power conversion device according to claim 1, characterized in that: The switching element uses a wide bandgap semiconductor.

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