Power conversion device

Abstract

To provide a power conversion device capable of reducing risk of damage on a switching element, while improving power consumption by making its switching speed variable.SOLUTION: A power conversion device 4 includes: a MOSFET 13 which is a switching element; an ECU 30 which is a control device for commanding switching speed of the switching element; and a driving circuit 20 for performing on / off drive of the switching element with switching speed according to a command speed. The power conversion device 4 further includes: a feedback circuit 23 as a feedback part; and a monitoring part 36 as abnormality determination part. The feedback circuit 23 outputs a signal correlated with actual switching speed as a feedback signal to the control device. The monitoring part 36 determines whether or not the actual switching speed is in an abnormal state contrary to the command speed by comparing the feedback signal and the command speed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The disclosure herein relates to power conversion devices. [Background technology]

[0002] Patent Document 1 discloses a power conversion device capable of changing the switching speed of a switching element, and is incorporated by reference as an explanation of the technical elements in this specification. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-65742 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned variable switching speed device, the power consumption can be improved by increasing the switching speed. However, the faster the switching speed, the larger the surge voltage becomes, which may damage the switching element.

[0005] One disclosed object is to provide a power conversion device that can reduce the risk of damage to switching elements while improving power consumption by making the switching speed variable. [Means for solving the problem]

[0006] One disclosed power conversion device is: A plurality of switching elements (13) that convert and output electric power; A control device (30) for commanding the switching speed of the switching element; a drive circuit (20) for driving the switching element to turn on and off at a switching speed corresponding to a command speed from a control device; a feedback unit (23, 40) that outputs a signal correlated with an actual switching speed as a feedback signal to a control device; The control device further includes an abnormality determination unit (36) that determines whether or not the actual switching speed is in an abnormal state contrary to the command speed by comparing the feedback signal with the command speed.

[0007] According to the disclosed power conversion device, since the switching elements are turned on and off at a switching speed corresponding to the command speed, the switching speed can be changed. Therefore, it is possible to improve the power consumption by increasing the switching speed. At the same time, since the abnormality determination unit determines whether the actual switching speed is in an abnormal state contrary to the command speed, it is possible to realize a fail-safe control or other measures to deal with an abnormality. Therefore, it is possible to reduce the concern of damage to the switching elements.

[0008] The various aspects disclosed in this specification employ different technical means to achieve their respective objectives. The claims and the parenthetical symbols described in this section are merely illustrative of the corresponding relationships with the embodiments described below, and are not intended to limit the technical scope. The objectives, features, and advantages disclosed in this specification will become more apparent by referring to the detailed description of the invention and the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a circuit configuration and a drive system of a power conversion device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing the configuration of a drive circuit and an ECU. [Diagram 3] FIG. 13 is a diagram showing differences in voltage waveforms according to switching speeds. [Figure 4] FIG. 11 is a diagram showing the relationship between surge voltage and power loss. [Diagram 5] 4 is a flowchart showing a process executed by a microcomputer of an ECU. [Figure 6]10 is a flowchart showing a process executed by a microcomputer according to the second embodiment. [Figure 7] 13 is a flowchart showing a process executed by a microcomputer according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, several embodiments will be described with reference to the drawings. In addition, by assigning the same reference numerals to corresponding components in each embodiment, duplicated explanations may be omitted. When only a part of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to the other parts of the configuration. In addition to the combination of configurations explicitly stated in the description of each embodiment, configurations of several embodiments can be partially combined together even if not explicitly stated, as long as there is no particular problem with the combination.

[0011] The power conversion device of this embodiment is applied to, for example, a moving body using a rotating electric machine as a drive source. The moving body is, for example, an electric vehicle such as a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), an electric flying object such as a drone or an electric vertical take-off and landing aircraft (eVTOL), a ship, a construction machine, or an agricultural machine. An example of application to a vehicle will be described below.

[0012] (First embodiment) First, a schematic configuration of a drive system of a vehicle will be described with reference to FIG.

[0013] <Vehicle drive system 1> As shown in FIG. 1, a vehicle drive system 1 includes a DC power supply 2, a motor generator 3, and a power conversion device 4.

[0014] The DC power supply 2 is a DC voltage source composed of a chargeable and dischargeable secondary battery. The secondary battery is, for example, a lithium ion battery, a nickel metal hydride battery, an organic radical battery, or the like. The motor generator 3 is a three-phase AC rotating electric machine. The motor generator 3 functions as a drive source for the vehicle, that is, an electric motor. The motor generator 3 functions as a generator during regeneration. The power conversion device 4 performs power conversion between the DC power supply 2 and the motor generator 3.

[0015] <Circuit configuration of power conversion device 4> 1 shows a circuit configuration of a power conversion device 4. The power conversion device 4 includes at least a power conversion circuit. The power conversion circuit in this embodiment is an inverter 5. The power conversion device 4 further includes a smoothing capacitor 6, a drive circuit 20, an ECU 30 (control device), and the like. ECU is an abbreviation for Electronic Control Unit.

[0016] The smoothing capacitor 6 mainly smoothes the DC voltage supplied from the DC power supply 2. The smoothing capacitor 6 is connected to a P line 8 which is a power supply line on the high potential side and an N line 9 which is a power supply line on the low potential side. The P line 8 is connected to the positive electrode of the DC power supply 2, and the N line 9 is connected to the negative electrode of the DC power supply 2. The positive electrode of the smoothing capacitor 6 is connected to the P line 8 between the DC power supply 2 and the inverter 5. The negative electrode of the smoothing capacitor 6 is connected to the N line 9 between the DC power supply 2 and the inverter 5. The smoothing capacitor 6 is connected in parallel to the DC power supply 2.

[0017] The inverter 5 is a DC-AC conversion circuit. The inverter 5 converts a DC voltage into a three-phase AC voltage in accordance with switching control by the ECU 30 and outputs the voltage to the motor generator 3. This drives the motor generator 3 to generate a predetermined torque. During regenerative braking of the vehicle, the inverter 5 converts the three-phase AC voltage generated by the motor generator 3 upon receiving rotational force from the wheels into a DC voltage in accordance with switching control by the ECU 30 and outputs the DC voltage to the P line 8. In this way, the inverter 5 performs bidirectional power conversion between the DC power source 2 and the motor generator 3.

[0018] The inverter 5 is configured to include upper and lower arm circuits 10 for three phases. The upper and lower arm circuits 10 are sometimes referred to as legs. The upper and lower arm circuits 10 each have an upper arm 10H and a lower arm 10L. The upper arm 10H and the lower arm 10L are connected in series between the P line 8 and the N line 9, with the upper arm 10H on the P line 8 side.

[0019] A connection point between the upper arm 10H and the lower arm 10L, i.e., a midpoint of the upper and lower arm circuits 10, is connected to a corresponding phase winding 3a of the motor generator 3 via an output line 11. Of the upper and lower arm circuits 10, a U-phase upper and lower arm circuit 10U is connected to the U-phase winding 3a via an output line 11. A V-phase upper and lower arm circuit 10V is connected to the V-phase winding 3a via an output line 11. A W-phase upper and lower arm circuit 10W is connected to the W-phase winding 3a via an output line 11.

[0020] The upper and lower arm circuits 10 (10U, 10V, 10W) ​​have a series circuit 12. The upper and lower arm circuits 10 may have one or more series circuits 12. When there are more than one series circuits 12, the series circuits 12 are connected in parallel to each other to configure one phase of the upper and lower arm circuits 10. In this embodiment, each of the upper and lower arm circuits 10 has one series circuit 12. The series circuit 12 is configured by connecting a switching element on the upper arm 10H side and a switching element on the lower arm 10L side in series between the P line 8 and the N line 9.

[0021] The number of high-side switching elements and low-side switching elements constituting the series circuit 12 is not particularly limited. There may be one or more. The series circuit 12 of this embodiment has one switching element on the high-side side and one switching element on the low-side side.

[0022] In this embodiment, each switching element is an n-channel MOSFET 13. MOSFET is an abbreviation for Metal Oxide Semiconductor Field Effect Transistor. The MOSFET 13 is turned on and off by a drive signal (gate voltage).

[0023] A free wheel diode 14 (hereinafter referred to as FWD 14) is connected in anti-parallel to each of the MOSFETs 13. In the case of the MOSFETs 13, the FWD 1 may be a parasitic diode (body diode) or an external diode. In the upper arm 10H, the drain of the MOSFET 13 is connected to a P line 8. In the lower arm 10L, the source of the MOSFET 13 is connected to an N line 9. The drain of the MOSFET 13 in the upper arm 10H and the drain of the MOSFET 13 in the lower arm 10L are connected to each other. The anode of the FWD 14 is connected to the source of the corresponding MOSFET 13, and the cathode is connected to the drain.

[0024] The switching element is not limited to the MOSFET 13. For example, an IGBT may be used. IGBT is an abbreviation for Insulated Gate Bipolar Transistor. In the case of an IGBT, the FWD 14 is also connected in inverse parallel. The MOSFET 13 corresponds to a switching element.

[0025] The drive circuit 20 drives switching elements constituting a power conversion circuit such as the inverter 5. The drive circuit 20 supplies a gate voltage to the gate of the corresponding MOSFET 13 based on a drive command from the ECU 30. The drive circuit drives the corresponding MOSFET 13, i.e., drives it on and off, by applying the gate voltage. The drive circuit is sometimes referred to as a driver.

[0026] The ECU 30 generates a drive command for operating the MOSFET 13 and outputs it to the drive circuit 20. The ECU 30 generates the drive command based on, for example, a torque request input from a higher-level ECU (not shown) and signals detected by various sensors. Furthermore, the ECU 30 generates a speed command for changing the switching speed of the MOSFET 13 and outputs it to the drive circuit 20. The ECU 30 may be provided in the higher-level ECU.

[0027] Next, the configurations of the drive circuit 20 and the ECU 30 will be described in more detail with reference to FIG.

[0028] The drive circuit 20 has a drive IC 21 and an output circuit 24. The drive IC 21 functions as a switching circuit 22 and a feedback circuit 23. The output circuit 24 outputs a gate voltage to the gate terminal of the MOSFET 13. The output circuit 24 has a function of switching the magnitude of the gate voltage and outputting it. The switching circuit 22 outputs a drive signal Vg and switching signals VH and VL to the output circuit 24.

[0029] The drive signal Vg is a voltage signal generated in response to a drive command from the ECU 30. The drive signal Vg is a square waveform signal whose voltage changes in a pulse shape over time, as shown by the solid line in Fig. 3. When the drive signal Vg pulses on, the MOSFET 13 is turned on and the motor current Im flows through the winding 3a. When the drive signal Vg pulses off, the MOSFET 13 is turned off and the motor current Im becomes zero.

[0030] The switching signals VH and VL are voltage signals generated in response to a speed command from the ECU 30. The switching signals VH and VL are signals that command what shape of waveform the drive signal Vg should be converted into. The dashed line in Fig. 3 is the drive signal converted into a waveform for high-speed switching, which is the high-speed drive signal VgH. The dashed line in Fig. 3 is the drive signal converted into a waveform for low-speed switching, which is the low-speed drive signal VgL.

[0031] The output circuit 24 converts the drive signal Vg into a high-speed drive signal VgH when the switching signal VH is commanded, and converts the drive signal Vg into a low-speed drive signal VgL when the switching signal VL is commanded. The high-speed drive signal VgH has a steeper pulse edge inclination than the low-speed drive signal VgL. By switching the waveform of the gate voltage in this way, the waveform of the voltage (motor voltage) of the motor current Im flowing through the MOSFET 13 also changes. The slope of the rising and falling edges of the motor voltage is steeper in the case of the high-speed drive signal VgH than in the case of the low-speed drive signal VgL.

[0032] In this specification, the switching speed refers to the speed of change (i.e., the slope) of the rise and fall of the motor voltage. The faster this change speed is, that is, the greater the slope, the faster the switching speed is, and the less power loss occurs with the on / off driving of the MOSFET 13. On the other hand, the faster the switching speed is, the greater the surge voltage that occurs when the MOSFET 13 is switched on and off. In other words, the height of the surge waveform that appears in the motor voltage becomes greater.

[0033] For example, in this embodiment, a MOS transistor is adopted in the output circuit 24, and the switching signals VH and VL are input to the gates of the MOS transistors. The drive signal Vg input to the MOS transistors is converted into a signal corresponding to the switching signals VH and VL and output. For example, the switching signal VH is set to a higher voltage than the switching signal VL. When the switching signal VH is input to the output circuit 24, the high-speed drive signal VgH is output from the output circuit 24. As a result, the switching speed of the MOSFET 13 becomes high. When the switching signal VL is input to the output circuit 24, the low-speed drive signal VgL is output from the output circuit 24. As a result, the switching speed of the MOSFET 13 becomes low.

[0034] The feedback circuit 23 outputs a signal correlated with the actual switching speed of the MOSFET 13 as a feedback signal to the ECU 30. The feedback circuit 23 corresponds to a feedback unit. The feedback signal output by the feedback circuit 23 is a signal indicating the type of the switching signals VH, VL output by the switching circuit 22 to the output circuit 24. For example, when the switching signal VH is output to increase the switching speed, the high-speed signal VH is output as the feedback signal. When the switching signal VL is output to decrease the switching speed, the low-speed signal VL is output as the feedback signal.

[0035] The driving IC 21 and the output circuit 24 are provided for each MOSFET 13. Therefore, a feedback signal for each MOSFET 13 is input to the ECU 30. That is, a plurality of feedback signals are input to the ECU 30.

[0036] Furthermore, in this embodiment, in addition to the high-speed signal VH and the low-speed signal VL, the element temperature T is also input to the ECU 30 as a feedback signal. The element temperature T is the temperature of the MOSFET 13 detected by the temperature sensor 40. The element temperature T becomes higher as the switching speed becomes faster. In other words, the element temperature T is a signal correlated with the actual switching speed of the MOSFET 13. When the ECU 30 uses the element temperature T as a feedback signal, the temperature sensor 40 corresponds to a feedback unit.

[0037] The ECU 30 includes a microcomputer (microcomputer 31). The microcomputer 31 includes a processor 32 and a memory 33. The processor 32 executes a program stored in the memory 33, causing the microcomputer 31 to perform various functions. These functions include a current supply command unit 34, a speed command unit 35, a monitoring unit 36, and the like.

[0038] The energization command unit 34 generates the drive command described above based on the torque request and signals detected by various sensors. The energization command unit 34 outputs, for example, a PWM signal as the drive command. PWM is an abbreviation for Pulse Width Modulation.

[0039] As shown in Fig. 4, the surge voltage increases as the switching speed is increased to reduce power loss. If the surge voltage exceeds the withstand voltage (element withstand voltage) of MOSFET 13, damage to MOSFET 13 becomes a concern. If MOSFET 13 is damaged, it may become impossible to run the vehicle. Thus, speed command unit 35 generates a speed command to increase the switching speed to a degree that the surge voltage does not exceed the element withstand voltage, thereby reducing power loss and avoiding element damage.

[0040] However, even with the same switching speed, the surge voltage increases as the current flowing through the MOSFET 13 increases. Therefore, when a large current flows through the MOSFET 13, the speed command unit 35 generates a speed command to slow down the switching speed to avoid damage to the element.

[0041] In consideration of the above, the speed command unit 35 generates a speed command based on the magnitude of the motor current Im detected by a current sensor (not shown). The motor current Im is the current flowing through the winding 3a of each phase. The speed command is generated so that the switching speed is slower as the motor current Im increases. In this embodiment, the switching speed is switched between two levels, high speed and low speed. The speed command unit 35 outputs either a high speed signal or a low speed signal as a speed command. The speed command unit 35 commands a common switching speed to the multiple MOSFETs 13.

[0042] The monitoring unit 36 ​​compares the contents of the speed command output by the energization command unit 34 with the actual switching speed, i.e., the feedback signal, to monitor whether an abnormal state has occurred. In a normal state, the contents of the speed command and the feedback signal should match, and if they do not match, it is determined that an abnormal state has occurred. The feedback signal used for this monitoring may be the low speed signal VL and the high speed signal VH, or may be the element temperature T. The monitoring unit 36 ​​corresponds to an abnormality determination unit.

[0043] The monitoring unit 36 ​​according to this embodiment performs monitoring using the low speed signal VL and the high speed signal VH as feedback signals. There are two patterns of abnormal states. One is a pattern in which the feedback signal is the low speed signal VL even though the speed command unit 35 outputs a high speed signal. The other is a pattern in which the feedback signal is the high speed signal VH even though the speed command unit 35 outputs a low speed signal.

[0044] One of the causes of the abnormality is a failure of the MOSFET 13 itself, such as element damage, sticking, disconnection, or short circuit of the MOSFET 13. Another cause is a failure of the signal lines L1, L2, and L3 connecting the ECU 30 and the drive circuit 20, such as a disconnection or short circuit of the signal lines L1, L2, and L3.

[0045] The ECU 30 and the drive circuit 20 can communicate with each other through signal lines L1, L2, and L3. In this embodiment, the drive command and the speed command are transmitted through separate signal lines L1 and L2, but may be transmitted using a common signal line. The low speed signal VL and the high speed signal VH as feedback signals are transmitted from the drive circuit 20 to the ECU 30 through a signal line L4. In this embodiment, the feedback signals corresponding to each of the MOSFETs 13 are transmitted through separate signal lines L3, but may be transmitted using a common signal line.

[0046] The temperature sensor 40 and the ECU 30 are connected by a signal line L4. The element temperature T is transmitted from the temperature sensor 40 to the ECU 30 using this signal line L4. Alternatively, the element temperature T may be transmitted from the temperature sensor 40 to the ECU 30 via the drive circuit 20. In this case, the low speed signal VL, the high speed signal VH, and the element temperature T may be transmitted from the drive circuit 20 to the ECU 30 using a common signal line. In this case, the signal line for the element temperature T can be used to transmit a feedback signal from the drive circuit 20 to the ECU 30, thereby reducing the number of signal lines.

[0047] <Control flow by microcomputer 31> The control flow shown in FIG. 5 is repeatedly executed by the microcomputer 31 at a predetermined calculation period during the driving period of the motor generator 3.

[0048] First, in step S10, a detection value of the motor current Im is obtained. In the following step S20, it is determined whether or not the obtained motor current Im is greater than a threshold value Ith. If it is determined that Im>Ith, it is considered to be a high current state in FIG. 4. Then, in the following step S30, the speed command unit 35 outputs a low speed signal as a speed command. This reduces the surge voltage, and damage to the MOSFET 13 is prevented.

[0049] On the other hand, if it is determined that Im>Ith is not true, it is considered to be in the low current state shown in Fig. 4. Then, the speed command unit 35 outputs a high-speed signal as a speed command. This increases the switching speed, thereby reducing power loss.

[0050] When a low speed command is issued in step S30, the monitoring unit 36 ​​determines in the following step S40 whether the feedback signal is the low speed signal VL. If it is determined in step S40 that the feedback signal is the low speed signal VL, the command speed and the feedback signal match, so it is considered to be in a normal state and the process in FIG. 5 is terminated.

[0051] When a high speed command is issued in step S31, in the following step S41, the monitoring unit 36 ​​judges whether the feedback signal is the high speed signal VH or not. If it is judged in step S41 that the feedback signal is the high speed signal VH, the command speed and the feedback signal match, so it is considered to be in a normal state and the process in FIG. 5 is terminated.

[0052] As described above, a feedback signal is input from the feedback circuit 23 to the ECU 30 for each of the MOSFETs 13. In the determinations of steps S40 and S41, if at least one of the multiple feedback signals input to the ECU 30 does not match the command speed, a negative determination is made and the process proceeds to step S50.

[0053] If it is determined in step S40 that the low-speed signal VL has not been reached, the command speed and the feedback signal do not match. Similarly, if it is determined in step S41 that the high-speed signal VH has not been reached, the command speed and the feedback signal do not match. In these cases, it is determined that an abnormal state has occurred, and the process proceeds to the next step S50.

[0054] In step S50, an abnormal state is diagnosed and an abnormality flag is set to ON. When the abnormality flag is set to ON, the power supply command unit 34 executes fail-safe control such as limiting the output of the motor generator 3. When the abnormality flag is set to ON, the ECU 30 notifies a higher-level ECU. Upon receiving the notification of the abnormal state, the higher-level ECU notifies the vehicle occupants of the abnormal state by outputting a warning display or a warning sound.

[0055] <Summary of the First Embodiment> In this embodiment, the MOSFET 13 is turned on and off at a switching speed corresponding to the command speed, so the switching speed can be changed. Therefore, by increasing the switching speed, it is possible to improve the power consumption. At the same time, a feedback signal correlated with the actual switching speed is fed back to the ECU 30, so the ECU 30 can monitor whether the actual switching speed is in an abnormal state contrary to the command speed. Therefore, it is possible to realize a fail-safe control such as limiting the output of the motor generator 3, a warning, or other measures to deal with an abnormality. As a result, it is possible to reduce the concern that the surge voltage will exceed the element withstand voltage due to the actual switching speed becoming faster than intended, while improving the power consumption.

[0056] In this embodiment, the ECU 30 commands a common switching speed to the multiple MOSFETs 13. The feedback circuit 23 outputs a feedback signal to each of the multiple MOSFETs 13. The monitoring unit 36 ​​determines an abnormal state when at least one of the multiple feedback signals is not in line with the command speed. This can reduce the computation load on the microcomputer 31.

[0057] Here, when the element temperature T is used as a feedback signal, even if an abnormal state occurs, it takes time for the element temperature T to change to an abnormal temperature. Therefore, it is difficult to quickly detect an abnormality. In contrast, in this embodiment, the drive circuit 20 has an output circuit 24 that switches the magnitude of the gate voltage and outputs it to the gate terminal of the MOSFET 13. The drive circuit 20 further has a switching circuit 22 that commands the magnitude of the gate voltage to the output circuit 24. The feedback signal used for monitoring by the monitoring unit 36 ​​includes switching signals VH and VL that indicate the command contents by the switching circuit 22. Therefore, even if an abnormal state occurs in which the contents of the speed command and the contents of the feedback signal do not match, it can be quickly detected.

[0058] Second embodiment This embodiment is a modification of the previous embodiment as a basic form, and the description of the previous embodiment can be used. In the previous embodiment, even if an abnormality is detected, the command speed is determined according to the magnitude of the motor current Im. Instead, in this embodiment, when an abnormality is detected, the command speed from the next time onwards is set as follows, regardless of the magnitude of the motor current Im.

[0059] Specifically, if a negative determination is made in step S41 in Fig. 6, in step S51, an abnormality flag is turned on to warn of an abnormality in the same manner as in step S50. Then, in step S30, a low speed signal is output as a speed command. In other words, if an abnormal state is determined because the switching speed corresponding to the feedback signal is slower than the command speed, the speed command unit 35 changes the command speed to decrease it.

[0060] Thereafter, if the actual speed becomes normally low, an affirmative determination is made in step S40, and if the motor current Im remains equal to or less than the threshold value Ith thereafter, the command is switched again to a high speed command in step S31.

[0061] Furthermore, in this embodiment, if a negative determination is made in step S40, an abnormality warning is issued in step S50, and then in the following step S70, the speed command unit 35 is prohibited from outputting a high speed command.

[0062] <Summary of the second embodiment> According to this embodiment, it is possible to achieve the same effect as the configuration described in the preceding embodiment. In addition, the ECU 30 changes the command speed when it is determined that an abnormal state exists. More specifically, when the actual speed is low despite the high speed command, that is, when a negative determination is made in step S41, the command speed is changed to a low speed command. By changing from the high speed command to the low speed command in this manner, it is possible to avoid an abnormal state. Therefore, according to this embodiment, it is possible to switch to a state in which the motor generator 3 is normally driven.

[0063] Furthermore, according to this embodiment, when it is determined that an abnormal state exists, the ECU 30 fixes the command speed to a predetermined speed and prohibits any change. More specifically, when the actual speed is high despite the low speed command, that is, when a negative determination is made in step S40, the command speed is fixed to the low speed command and any change to a high speed command is prohibited. This reduces the possibility that the switching speed will be unintentionally increased, and reduces the risk of damage to the MOSFET 13 due to a surge voltage.

[0064] Third embodiment This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be used. In the preceding embodiment, one type of feedback signal is used to diagnose an abnormality. Alternatively, two or more types of feedback signals may be used to diagnose an abnormality.

[0065] Specifically, in this embodiment, as shown in FIG. 7, step S60 is added to the flowchart in FIG. 6. This step S60 is executed when the actual speed is high despite the low speed command, that is, when the negative determination is made in step S40. In step S60, the monitoring unit 36 ​​determines an abnormality using the second feedback signal. Specific examples of the second feedback signal include the element temperature T, the magnitude of the gate voltage applied to the gate terminal of the MOSFET 13, and a surge voltage waveform occurring in the MOSFET 13 or the winding 3a. In this embodiment, the element temperature T is used as the second feedback signal. The first feedback signal is the switching signals VH and VL, while the element temperature T as the second feedback signal corresponds to a detection signal.

[0066] The first feedback signal is the feedback signal used in steps S40 and S41, i.e., the switching signals VH and VL. The second feedback signal is a signal that is correlated with the actual switching speed and is different from the first feedback signal.

[0067] Steps S40 and S41 correspond to a first determination unit that determines an abnormal state using the first feedback signal. Step S60 corresponds to a second determination unit that determines an abnormal state using the second feedback signal. The temperature sensor 40 corresponds to a detection unit that detects the second feedback signal. This detection unit and the feedback circuit 23 correspond to a feedback unit that outputs a feedback signal that is correlated with the actual switching speed.

[0068] Here, the faster the switching speed, the higher the element temperature T. Therefore, when the speed command is switched from high to low and this state continues for a predetermined time or more, the element temperature T should decrease. Similarly, when the speed command is switched from low to high and this state continues for a predetermined time or more, the element temperature T should increase. In view of this, in step S60, it is determined whether the actual speed is low or high based on the element temperature T. In detail, the actual speed is determined based on the current value of the element temperature T and the change in the element temperature T up to the present time.

[0069] If it is determined in step S40 that the speed is not low even though a low speed command is output in step S30, an abnormality flag is set to ON in step S50. However, even if an abnormality is diagnosed in this way, if it is determined in step S50 that the speed is low, the process returns to step S10 without prohibiting a high speed command in step S70. Then, if it is determined in step S50 that the speed is not low as in step S40, the high speed command is prohibited in step S70. Step S70 corresponds to a regulating unit that limits the command speed so as to prohibit a high speed command when an abnormal state is determined by the second judging unit.

[0070] <Summary of the third embodiment> According to this embodiment, it is possible to achieve the same effect as the configuration described in the preceding embodiment. In addition, the power conversion device 4 includes a temperature sensor 40, and the feedback signal includes the element temperature T detected by the temperature sensor 40 in addition to the switching signals VH and VL. The abnormality determination unit by the monitoring unit 36 ​​has a first determination unit by steps S40 and S41 and a second determination unit by step S60. The first determination unit determines an abnormal state by comparing the switching signals VH and VL with the command speed. The second determination unit determines an abnormal state by comparing the element temperature T detected by the temperature sensor 40 with the command speed. According to this, since an abnormality is determined using two types of feedback signals, the accuracy of the abnormality determination can be improved.

[0071] Here, the first determination unit can quickly detect an abnormality, but there may be cases where an abnormality in the signal line L3 causes an erroneous detection. In consideration of this point, in this embodiment, even if the first determination unit determines that an abnormal state exists, if the second determination unit does not determine that an abnormal state exists, the speed limiting unit is prohibited from limiting the speed in step S70. This reduces the concern that excessive speed limiting will prevent sufficient improvement in electricity efficiency. This makes it possible to achieve both avoidance of failure of the MOSFET 13 and improvement in electricity efficiency.

[0072] (Other embodiments) The disclosure in this specification and drawings, etc. is not limited to the exemplified embodiments. The disclosure includes the exemplified embodiments and modifications by those skilled in the art based thereon. For example, the disclosure is not limited to the combination of parts and / or elements shown in the embodiments. The disclosure can be implemented by various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure includes the omission of parts and / or elements of the embodiments. The disclosure includes the substitution or combination of parts and / or elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiments. Some disclosed technical scopes are indicated by the description of the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the description of the claims.

[0073] The disclosure in the specification and drawings is not limited by the claims. The disclosure in the specification and drawings includes the technical ideas described in the claims, and extends to more diverse and broader technical ideas than the technical ideas described in the claims. Therefore, various technical ideas can be extracted from the disclosure in the specification and drawings without being bound by the claims.

[0074] In the third embodiment, the first feedback signal and the second feedback signal are used to determine whether an abnormality has occurred. However, the first feedback signal may be eliminated, and the second feedback signal may be used to determine whether an abnormality has occurred.

[0075] In each of the above-described embodiments, the switching speed is switched between two stages, high speed and low speed, but the switching speed may be switched between three or more stages, or may be changed linearly without stages.

[0076] In the second embodiment described above, in the case of an abnormal state, the ECU 30 fixes the command speed to a predetermined speed. Specifically, on the premise that the switching speed is switched in two stages, high speed and low speed, in the case of an abnormality in which the actual speed is high despite the low speed command, the ECU 30 fixes it to the low speed command. On the other hand, on the premise that the switching speed is switched in three stages, high speed, medium speed, and low speed, in the case of the abnormality described above, the ECU 30 may fix it to the low speed command or the medium speed command. Also, on the premise that the switching speed is changed linearly in a stepless manner, the ECU 30 may issue a speed command by fixing it to a speed at which the MOSFET 13 is not damaged. Specific examples of damage in this case include damage caused by an excessive current flowing through the MOSFET 13, damage caused by an excessive temperature of the MOSFET 13, and damage caused by an excessive voltage being applied to the MOSFET 13.

[0077] In each of the above-described embodiments, when a negative determination is made in step S41, if the motor current Im is greater than the threshold Ith thereafter, the low speed command is permitted in step S30. In contrast, when a negative determination is made in step S41, the low speed command may be prohibited regardless of the magnitude of the motor current Im thereafter.

[0078] In each of the above-described embodiments, if a negative determination is made in step S40, the switching speed is determined in step S20 according to the magnitude of the motor current Im thereafter. In contrast, if a negative determination is made in step S40, the switching speed may be fixed to the high speed command regardless of the magnitude of the motor current Im thereafter.

[0079] In each of the above-described embodiments, the switching speed is changed according to the motor current Im. In contrast, the switching speed may be changed according to the temperature of the MOSFET 13 or the temperature of the cooling water for cooling the MOSFET 13. For example, it is desirable to increase the switching speed as these temperatures increase to reduce power loss. The switching speed may be changed according to the voltage supplied to the MOSFET 13 or the voltage supplied to the drive circuit 20. For example, it is desirable to increase the switching speed as these voltages decrease to reduce power loss. The switching speed may be changed according to the voltage of the power supply used as the gate signal of the MOSFET 13. For example, it is desirable to increase the switching speed as the voltage for the gate signal decreases to reduce power loss. The switching speed may be changed by combining parameters such as the motor current Im, various temperatures, various voltages, and atmospheric pressure described above.

[0080] The power conversion device 4 may include a converter as a power conversion circuit. The converter is a DC-DC conversion circuit that converts a DC voltage, for example, into a DC voltage of a different value. The converter is provided between the DC power source 2 and the smoothing capacitor 6. The converter is configured to include, for example, a reactor and the above-mentioned upper and lower arm circuits 10. With this configuration, voltage can be increased and decreased. The power conversion device 4 may include a filter capacitor that removes power supply noise from the DC power source 2. The filter capacitor is provided between the DC power source 2 and the converter.

[0081] (Disclosure of technical ideas) This specification discloses multiple technical ideas described in the following multiple dependent claims. Some of the claims may be described in a multiple dependent form, where the subsequent claim alternatively refers to the preceding claim. Furthermore, some of the claims may be described in a multiple dependent form, where the subsequent claim alternatively refers to the preceding claim. The claims described in these multiple dependent forms define multiple technical ideas.

[0082] (Technical thought 1) A plurality of switching elements (13) that convert and output electric power; a control device (30) for commanding the switching speed of the switching element; a drive circuit (20) that drives the switching element to turn on and off at a switching speed corresponding to a command speed from the control device; a feedback unit (23, 40) that outputs a signal correlated with an actual switching speed as a feedback signal to the control device; an abnormality determination unit (36) that determines whether or not an actual switching speed is in an abnormal state contrary to the command speed by comparing the feedback signal with the command speed; A power conversion device comprising:

[0083] (Technical thought 2) The power conversion device according to Technical Idea 1, wherein the control device changes the command speed when the abnormal state is determined.

[0084] (Technical Thought 3) A power conversion device according to technical idea 2, in which when the abnormal state is determined because the switching speed corresponding to the feedback signal is slower than the command speed, the control device changes the command speed to be lower.

[0085] (Technical Thought 4) The power conversion device according to Technical Idea 1, wherein the control device fixes the command speed to a predetermined speed and prohibits any change thereto when the abnormal state is determined.

[0086] (Technical Thought 5) The drive circuit includes an output circuit (24) that switches the magnitude of a gate voltage and outputs the switched voltage to the switching element, and a switching circuit (22) that switches a switching speed by instructing the output circuit to which gate voltage to switch to, The power conversion device according to any one of Technical Concepts 1 to 4, wherein the feedback signal includes a switching signal representing a command content by the switching circuit.

[0087] (Technical Thought 6) The feedback unit includes a detection unit (40) that detects at least one of a temperature of the switching element, a gate voltage applied to the switching element, and a surge voltage waveform of the switching element, the feedback signal includes, in addition to the switching signal, a detection signal detected by the detection unit; The power conversion device described in Technical Idea 5, wherein the abnormality judgment unit has a first judgment unit (S40, S41) that judges the abnormal state by comparing the switching signal with the command speed, and a second judgment unit (S60) that judges the abnormal state by comparing the detection signal with the command speed.

[0088] (Technical Thought 7) a regulating unit (S70) that limits a command speed by the control device when the second judging unit judges that the abnormal state exists; A power conversion device as described in technical idea 6, in which even if the first judgment unit judges that an abnormal state exists, if the second judgment unit does not judge that an abnormal state exists, the speed limit by the regulating unit is prohibited.

[0089] (Technical Thought 8) The control device commands a common switching speed to the plurality of switching elements, the feedback unit outputs the feedback signal for each of the plurality of switching elements; The power conversion device according to any one of Technical Concepts 1 to 7, wherein the abnormality determination unit determines that the abnormal state exists when at least one of a plurality of feedback signals deviates from the command speed. [Explanation of symbols]

[0090] 13 switching element, 20 drive circuit, 22 switching circuit, 23 feedback section, 24 output circuit, 30 control device, 36 abnormality determination section, 40 feedback section, 40 detection section, S40, S41 first determination section, S60 second determination section, S70 regulation section.

Claims

1. A plurality of switching elements (13) that convert and output electric power; A control device (30) for commanding the switching speed of the switching element; A drive circuit (20) that drives the switching element to turn on and off at a switching speed corresponding to a command speed from the control device; A feedback unit (23, 40) that outputs a signal correlated with an actual switching speed as a feedback signal to the control device; and an abnormality determination unit (36) that determines whether or not an actual switching speed is in an abnormal state contrary to the command speed by comparing the feedback signal with the command speed.

2. The power conversion device according to claim 1 , wherein the control device changes the command speed when the abnormal state is determined.

3. 3. The power conversion device according to claim 2, wherein when the abnormal state is determined as a result of the switching speed corresponding to the feedback signal being slower than the command speed, the control device changes the command speed so as to decrease it.

4. The power conversion device according to claim 1 , wherein the control device fixes the command speed to a predetermined speed and prohibits any change thereto when the abnormal state is determined.

5. The drive circuit has an output circuit (24) that switches the magnitude of a gate voltage and outputs it to the switching element, and a switching circuit (22) that switches a switching speed by instructing the output circuit to which gate voltage to switch to, 5. The power conversion device according to claim 1, wherein the feedback signal includes a switching signal representing a command issued by the switching circuit.

6. The feedback unit includes a detection unit (40) that detects at least one of a temperature of the switching element, a gate voltage applied to the switching element, and a surge voltage waveform of the switching element, the feedback signal includes, in addition to the switching signal, a detection signal detected by the detection unit; 6. The power conversion device according to claim 5, wherein the abnormality determination unit has a first determination unit (S40, S41) that determines the abnormal state by comparing the switching signal with the command speed, and a second determination unit (S60) that determines the abnormal state by comparing the detection signal with the command speed.

7. a regulating unit (S70) that limits a command speed by the control device when the second judging unit judges that the abnormal state exists; 7. The power conversion device according to claim 6, wherein even if the first determination unit determines that the abnormal state exists, if the second determination unit does not determine that the abnormal state exists, the speed limit by the regulating unit is prohibited.

8. The control device commands a common switching speed to the plurality of switching elements, the feedback unit outputs the feedback signal for each of the plurality of switching elements; 5. The power conversion device according to claim 1, wherein the abnormality determination unit determines that the abnormal state exists when at least one of a plurality of feedback signals is contrary to the command speed.

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