Power conversion device

Abstract

This power conversion device (4) comprises: a MOSFET (13) that is a switching element; an ECU (30) that is a control device for commanding the switching speed of the switching element; and a drive circuit (20) that carries out on / off driving of the switching element at a switching speed corresponding to a command speed. The power conversion device (4) furthermore comprises a feedback circuit (23) serving as a feedback unit, and a monitoring unit (36) serving as an abnormality determination unit. The feedback circuit (23) outputs, to the control device, a signal correlated with the actual switching speed as a feedback signal. The monitoring unit (36) compares the feedback signal with the command speed, thereby determining whether the actual switching speed is in an abnormal state against the command speed.

Description

Power Conversion Device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2023-131628 filed in Japan on August 10, 2023, and the contents of the original application are incorporated by reference in their entirety.

[0002] TECHNICAL FIELD The disclosure herein relates to power conversion devices.

[0003] 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.

[0004] JP 2015-65742 A

[0005] In the variable switching speed devices described above, power consumption can be improved by increasing the switching speed, but the faster the switching speed, the larger the surge voltage becomes, which raises concerns about damage to the switching elements.

[0006] 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.

[0007] One of the disclosed power conversion devices includes a plurality of switching elements that convert and output power, a control device that commands the switching speed of the switching elements, a drive circuit that drives the switching elements to turn on and off at a switching speed according to the command speed from the control device, a feedback unit that outputs a signal that is correlated with the actual switching speed as a feedback signal to the control device, and an abnormality determination unit that compares the feedback signal with the command speed to determine whether the actual switching speed is in an abnormal state that is contrary to the command speed.

[0008] According to the disclosed power conversion device, the switching elements are turned on and off at a switching speed corresponding to the command speed, making it possible to change the switching speed. Therefore, by increasing the switching speed, it is possible to improve power consumption. At the same time, the abnormality determination unit determines whether the actual switching speed is in an abnormal state that is contrary to the command speed, so that fail-safe control and other measures can be implemented to deal with abnormalities. This reduces the risk of damage to the switching elements.

[0009] The various aspects disclosed in this specification employ different technical means to achieve their respective objectives. The reference numerals in parentheses in the claims and in this section are intended to exemplify the correspondence with the following embodiments and are not intended to limit the technical scope. The objectives, features, and advantages disclosed in this specification will become more apparent by reference to the detailed description of the invention and the accompanying drawings.

[0010] 1 is a diagram showing a circuit configuration and a drive system of a power conversion device according to a first embodiment; FIG. 2 is a diagram showing the configuration of a drive circuit and an ECU; FIG. 3 is a diagram showing differences in voltage waveforms according to switching speeds; FIG. 4 is a diagram showing the relationship between surge voltage and power loss; FIG. 5 is a flowchart showing processing executed by a microcomputer of an ECU; FIG. 6 is a flowchart showing processing executed by a microcomputer according to a second embodiment; and FIG. 7 is a flowchart showing processing executed by a microcomputer according to a third embodiment.

[0011] Hereinafter, several embodiments will be described with reference to the drawings. Note that in each embodiment, corresponding components are designated by the same reference numerals, and redundant description may be omitted. When only a portion of the configuration is described in each embodiment, the configuration of another embodiment previously described may be applied to the remaining portion of the configuration. Furthermore, in addition to the combinations of configurations explicitly stated in the description of each embodiment, configurations of several embodiments may be partially combined together even if not explicitly stated, provided that there is no particular problem with the combination.

[0012] The power conversion device of this embodiment is applied to, for example, a mobile body that uses a rotating electric machine as a drive source. Examples of the mobile body include electric vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric flying bodies such as drones and electric vertical take-off and landing (eVTOL) aircraft, ships, construction machinery, and agricultural machinery. An example of application to a vehicle will be described below.

[0013] First Embodiment First, a schematic configuration of a vehicle drive system will be described with reference to FIG.

[0014] <Vehicle Drive System 1> As shown in FIG. 1, the vehicle drive system 1 includes a DC power supply 2, a motor generator 3, and a power conversion device 4.

[0015] The DC power supply 2 is a DC voltage source composed of a chargeable and dischargeable secondary battery. The secondary battery may be, for example, a lithium-ion battery, a nickel-metal hydride battery, or an organic radical battery. 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 converts power between the DC power supply 2 and the motor generator 3.

[0016] <Circuit Configuration of Power Conversion Device 4> Fig. 1 shows the circuit configuration of the power conversion device 4. The power conversion device 4 includes at least a power conversion circuit. In this embodiment, the power conversion circuit 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.

[0017] 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.

[0018] The inverter 5 is a DC-AC conversion circuit. In accordance with switching control by the ECU 30, the inverter 5 converts a DC voltage into a three-phase AC voltage and outputs it 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 in response to rotational force from the wheels into a DC voltage in accordance with switching control by the ECU 30 and outputs it 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.

[0019] The inverter 5 is configured with upper and lower arm circuits 10 for three phases. The upper and lower arm circuits 10 are sometimes referred to as legs. Each upper and lower arm circuit 10 has 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.

[0020] The connection point between the upper arm 10H and the lower arm 10L, i.e., the midpoint of the upper and lower arm circuit 10, is connected to the corresponding phase winding 3a of the motor generator 3 via an output line 11. Of the upper and lower arm circuits 10, the U-phase upper and lower arm circuit 10U is connected to the U-phase winding 3a via the output line 11. The V-phase upper and lower arm circuit 10V is connected to the V-phase winding 3a via the output line 11. The W-phase upper and lower arm circuit 10W is connected to the W-phase winding 3a via the output line 11.

[0021] Each of the upper and lower arm circuits 10 (10U, 10V, 10W) ​​has a series circuit 12. The upper and lower arm circuits 10 may have one or more series circuits 12. When there are multiple series circuits 12, the series circuits 12 are connected in parallel to each other to form one phase of the upper and lower arm circuit 10. In this embodiment, each of the upper and lower arm circuits 10 has one series circuit 12. The series circuit 12 is formed 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.

[0022] The number of high-side switching elements and the number of low-side switching elements constituting the series circuit 12 are not particularly limited. They may be one or more. The series circuit 12 of this embodiment has one switching element on the high-side and one switching element on the low-side.

[0023] 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).

[0024] A freewheeling 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 the P line 8. In the lower arm 10L, the source of the MOSFET 13 is connected to the 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.

[0025] 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 antiparallel. The MOSFET 13 corresponds to the switching element.

[0026] 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., turns it on and off, by applying the gate voltage. The drive circuit is sometimes referred to as a driver.

[0027] 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 host ECU (not shown) and signals detected by various sensors. The ECU 30 also 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 within the host ECU.

[0028] Next, the configuration of the drive circuit 20 and the ECU 30 will be described in more detail with reference to FIG.

[0029] 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.

[0030] The drive signal Vg is a voltage signal generated in response to a drive command from the ECU 30. As shown by the solid line in Figure 3, the drive signal Vg is a square waveform signal whose voltage changes in a pulsed manner over time. When the drive signal Vg pulses on, the MOSFET 13 is turned on, causing the motor current Im to flow through the winding 3a. When the drive signal Vg pulses off, the MOSFET 13 is turned off, causing the motor current Im to become zero.

[0031] 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 the type of waveform to convert the drive signal Vg into. The dashed line in Figure 3 represents the drive signal converted into a waveform for high-speed switching, which is the high-speed drive signal VgH. The dashed line in Figure 3 represents the drive signal converted into a waveform for low-speed switching, which is the low-speed drive signal VgL.

[0032] 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 slope than the low-speed drive signal VgL. By switching the gate voltage waveform in this way, the waveform of the voltage (motor voltage) of the motor current Im flowing through the MOSFET 13 also changes. The slopes of the rising and falling edges of the motor voltage are steeper when the high-speed drive signal VgH is used than when the low-speed drive signal VgL is used.

[0033] In this specification, the switching speed refers to the rate of change (i.e., the slope) of the rise and fall of the motor voltage. The faster this rate of change, i.e., the greater the slope, the faster the switching speed, and the less power loss occurs when the MOSFET 13 is turned on and off. On the other hand, the faster the switching speed, 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.

[0034] For example, in this embodiment, MOS transistors are used in the output circuit 24, and 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, a 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, a low-speed drive signal VgL is output from the output circuit 24. As a result, the switching speed of the MOSFET 13 becomes low.

[0035] 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 that indicates 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.

[0036] The drive 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.

[0037] 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 as a feedback signal to the ECU 30. 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 that correlates 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.

[0038] The ECU 30 includes a microcomputer (microcomputer 31). The microcomputer 31 includes a processor 32 and a memory 33. The processor 32 executes programs stored in the memory 33, causing the microcomputer 31 to perform a variety of functions. These functions include a current supply command unit 34, a speed command unit 35, and a monitoring unit 36.

[0039] The energization command unit 34 generates the drive command described above based on the torque request and signals detected by the 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.

[0040] As shown in Figure 4, the surge voltage increases as the switching speed is increased to reduce power loss. If the surge voltage exceeds the breakdown voltage (element breakdown voltage) of MOSFET 13, there is a concern that MOSFET 13 may be damaged. If MOSFET 13 is damaged, the vehicle may not be able to run. Therefore, the speed command unit 35 generates a speed command to increase the switching speed to a degree that prevents the surge voltage from exceeding the element breakdown voltage, thereby reducing power loss and avoiding element damage.

[0041] However, even if the switching speed is the same, the surge voltage increases as the current flowing through the MOSFET 13 increases. Therefore, the speed command unit 35 generates a speed command to slow down the switching speed when a large current flows through the MOSFET 13, thereby avoiding damage to the element.

[0042] 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 decreases 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 the speed command. The speed command unit 35 commands a common switching speed to the multiple MOSFETs 13.

[0043] The monitoring unit 36 ​​compares the content 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 content of the speed command and the content of 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 the element temperature T. The monitoring unit 36 ​​corresponds to an abnormality determination unit.

[0044] 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.

[0045] One of the causes of the abnormality is a failure of the MOSFET 13 itself, such as damage to the element, 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.

[0046] The ECU 30 and the drive circuit 20 can communicate with each other via signal lines L1, L2, and L3. In this embodiment, drive commands and speed commands are transmitted via separate signal lines L1 and L2, but they may be transmitted using a common signal line. The low-speed signal VL and the high-speed signal VH, which serve as feedback signals, are transmitted from the drive circuit 20 to the ECU 30 via signal line L4. In this embodiment, feedback signals corresponding to each of the MOSFETs 13 are transmitted via separate signal line L3, but they may be transmitted using a common signal line.

[0047] The temperature sensor 40 and the ECU 30 are connected by a signal line L4. The temperature sensor 40 transmits the element temperature T 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.

[0048] <Control Flow by Microcomputer 31> The control flow shown in FIG. 5 is repeatedly executed by the microcomputer 31 at a predetermined calculation cycle while the motor generator 3 is being driven.

[0049] First, in step S10, a detected value of the motor current Im is acquired. In the following step S20, it is determined whether the acquired motor current Im is greater than a threshold value Ith. If it is determined that Im > Ith, it is considered that the current is high as shown 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, thereby preventing damage to the MOSFET 13.

[0050] On the other hand, if it is determined that Im>Ith is not true, it is considered to be the low current state shown in Fig. 4. Then, the speed command unit 35 outputs a high-speed signal as a speed command, thereby increasing the switching speed and reducing power loss.

[0051] If 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 processing in FIG. 5 is terminated.

[0052] If a high-speed command is issued in step S31, the monitoring unit 36 ​​determines in the following step S41 whether the feedback signal is the high-speed signal VH. If it is determined 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 processing in FIG. 5 is terminated.

[0053] 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.

[0054] 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, an abnormal state is assumed, and the process proceeds to the next step S50.

[0055] 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 host ECU. Upon receiving the notification of the abnormal state, the host ECU notifies the vehicle occupants of the abnormal state by outputting a warning display or warning sound.

[0056] Summary of the First Embodiment In this embodiment, the MOSFET 13 is driven on and off at a switching speed corresponding to the command speed, making it possible to change the switching speed. Therefore, by increasing the switching speed, it is possible to improve power consumption. Furthermore, a feedback signal correlated with the actual switching speed is fed back to the ECU 30, allowing the ECU 30 to monitor whether the actual switching speed is in an abnormal state that is contrary to the command speed. Therefore, it is possible to implement fail-safe control, such as limiting the output of the motor-generator 3, or to issue a warning or other response to an abnormality. As a result, it is possible to improve power consumption while reducing the risk of a surge voltage exceeding the element breakdown voltage due to an unintended increase in the actual switching speed.

[0057] 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 different from the commanded speed. This reduces the processing load on the microcomputer 31.

[0058] Here, when the element temperature T is used as a feedback signal, it takes time for the element temperature T to rise to an abnormal temperature even if an abnormal state occurs. 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 also 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 represent the command content from the switching circuit 22. Therefore, even if an abnormal state occurs in which the content of the speed command and the content of the feedback signal do not match, it can be quickly detected.

[0059] Second Embodiment This embodiment is a modification of the preceding embodiment as a basic form, and the description of the preceding embodiment can be used. In the preceding 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, if 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.

[0060] 6, if a negative determination is made in step S41, an abnormality flag is set to ON in step S51 to issue an abnormality warning, as in step S50. Then, in step S30, a low-speed signal is output as a speed command. That is, 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.

[0061] Thereafter, if the actual speed becomes normally low, an affirmative determination is made in step S40, and if the motor current Im remains below the threshold value Ith thereafter, the command is switched again to a high speed command in step S31.

[0062] 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.

[0063] Summary of the Second Embodiment This embodiment can achieve the same effects as the configuration described in the preceding embodiment. In addition, the ECU 30 changes the command speed when an abnormal state is determined. More specifically, when the actual speed is low despite a high-speed command, that is, when a negative determination is made in step S41, the ECU 30 changes the command speed to a low-speed command. By changing from a high-speed command to a low-speed command in this manner, it is possible to avoid the abnormal state. Therefore, this embodiment may be able to switch to a state in which the motor-generator 3 is normally driven.

[0064] Furthermore, according to this embodiment, if an abnormal state is determined, the ECU 30 fixes the command speed to a predetermined speed and prohibits any change. More specifically, if the actual speed is high despite the low speed command, that is, if a negative determination is made in step S40, the ECU 30 fixes the command speed to a low speed and prohibits any change to a high speed command. This reduces the risk of the switching speed being increased unintentionally and reduces the risk of damage to the MOSFET 13 due to a surge voltage.

[0065] Third Embodiment This embodiment is a modification of 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.

[0066] Specifically, in this embodiment, as shown in FIG. 7, step S60 is added to the flowchart of FIG. 6. This step S60 is executed when the actual speed is high despite the low-speed command, that is, when a negative determination is made in step S40. In step S60, the monitoring unit 36 ​​determines an abnormality using a 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 the surge voltage waveform generated in the MOSFET 13 or the winding 3a. In this embodiment, the element temperature T is used as the second feedback signal. While the first feedback signal is the switching signals VH and VL, the element temperature T as the second feedback signal corresponds to a detection signal.

[0067] 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.

[0068] 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.

[0069] Here, the faster the switching speed, the higher the element temperature T. Therefore, if 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, if 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 consideration 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.

[0070] If it is determined in step S40 that the speed is not low despite the low-speed command being 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, a 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.

[0071] Summary of the Third Embodiment This embodiment can achieve the same effects as the configurations described in the preceding embodiments. Additionally, the power conversion device 4 includes a temperature sensor 40, and the feedback signal includes the switching signals VH and VL as well as the element temperature T detected by the temperature sensor 40. The abnormality determination unit of the monitoring unit 36 ​​includes a first determination unit based on steps S40 and S41 and a second determination unit based on 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. This configuration improves the accuracy of abnormality determination by using two types of feedback signals to determine an abnormality.

[0072] Although the first determination unit can quickly detect an abnormality, there may be cases where an erroneous detection occurs due to an abnormality in the signal line L3. In consideration of this, 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 risk of insufficient improvement in electricity efficiency due to excessive speed limiting. Therefore, it is possible to avoid failure of the MOSFET 13 and improve electricity efficiency at the same time.

[0073] (Other Embodiments) The disclosure in this specification and drawings, etc. is not limited to the exemplified embodiments. The disclosure encompasses the exemplified embodiments and modifications thereto by those skilled in the art. For example, the disclosure is not limited to the combinations of parts and / or elements shown in the embodiments. The disclosure can be implemented in various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure encompasses the omission of parts and / or elements from the embodiments. The disclosure encompasses 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 defined by the claims, and should be interpreted as including all modifications within the meaning and scope equivalent to the claims.

[0074] The disclosure in the specification, drawings, etc. is not limited by the claims. The disclosure in the specification, drawings, etc. encompasses 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, drawings, etc. without being bound by the claims.

[0075] 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.

[0076] In 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 any stages.

[0077] In the second embodiment described above, in the event of an abnormality, the ECU 30 fixes the command speed to a predetermined speed. Specifically, assuming that the switching speed is switched between two levels, high and low, and in the event of an abnormality where the actual speed is high despite the low-speed command, the ECU 30 fixes the command speed to the low-speed command. In contrast, assuming that the switching speed is switched between three levels, high, medium, and low, the ECU 30 may fix the command speed to the low-speed command or the medium-speed command in the event of the abnormality. Furthermore, assuming that the switching speed is changed linearly and continuously, the ECU 30 may fix the command speed to a speed that does not damage the MOSFET 13. Specific examples of damage in this case include damage caused by excessive current flowing through the MOSFET 13, damage caused by excessive temperature of the MOSFET 13, and damage caused by excessive voltage application to the MOSFET 13.

[0078] In each of the above-described embodiments, when a negative determination is made in step S41, the low speed command is permitted in step S30 if the motor current Im is thereafter greater than the threshold value Ith. 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.

[0079] In each of the above-described embodiments, if a negative determination is made in step S40, the switching speed is subsequently determined in step S20 according to the magnitude of the motor current Im. 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.

[0080] In each of the above-described embodiments, the switching speed is changed according to the motor current Im. However, the switching speed may also be changed according to the temperature of the MOSFET 13 or the temperature of the cooling water that cools 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 also 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 also be changed according to the voltage of the power supply used as a gate signal for 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 also be changed by combining parameters such as the motor current Im, various temperatures, various voltages, and atmospheric pressure.

[0081] 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 with, for example, a reactor and the above-mentioned upper and lower arm circuits 10. This configuration allows for voltage step-up and step-down. The power conversion device 4 may also 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.

[0082] (Disclosure of Technical Ideas) This specification discloses multiple technical ideas described in the following multiple clauses. Some clauses may be described in a multiple dependent form, with the subsequent clause alternatively referring to the preceding clause. Furthermore, some clauses may be described in a multiple dependent form, with the subsequent clause referring to another multiple dependent clause. These multiple dependent clauses define multiple technical ideas.

[0083] (Technical Idea 1) A power conversion device comprising: a plurality of switching elements (13) that convert and output electric power; a control device (30) that commands the switching speeds of the switching elements; a drive circuit (20) that drives the switching elements to turn on and off at a switching speed according to the command speed from the control device; a feedback unit (23, 40) that outputs a signal that is correlated with the actual switching speed as a feedback signal to the control device; and an abnormality determination unit (36) that compares the feedback signal with the command speed to determine whether the actual switching speed is in an abnormal state that is contrary to the command speed.

[0084] (Technical Concept 2) The power conversion device according to Technical Concept 1, wherein the control device changes the command speed when the abnormal state is determined.

[0085] (Technical Idea 3) The power conversion device according to Technical Idea 2, wherein 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 decrease it.

[0086] (Technical Concept 4) The power conversion device according to Technical Concept 1, wherein the control device fixes the command speed to a predetermined speed and prohibits any change when the abnormal state is determined.

[0087] (Technical Idea 5) The power conversion device according to any one of Technical Ideas 1 to 4, wherein the drive circuit has an output circuit (24) that switches the magnitude of the gate voltage and outputs it to the switching element, and a switching circuit (22) that switches the switching speed by instructing the output circuit to which gate voltage to switch, and the feedback signal includes a switching signal that indicates the content of the instruction from the switching circuit.

[0088] (Technical Idea 6) The power conversion device according to Technical Idea 5, wherein 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 a detection signal detected by the detection unit in addition to the switching signal, and 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.

[0089] (Technical Idea 7) A power conversion device according to Technical Idea 6, further comprising a regulating unit (S70) that limits the command speed by the control device when the second judgment unit judges that the abnormal state exists, and even when the first judgment unit judges that the abnormal state exists, if the second judgment unit does not judge that the abnormal state exists, the speed limit by the regulating unit is prohibited.

[0090] (Technical Idea 8) A power conversion device according to any one of Technical Ideas 1 to 7, wherein 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, and the abnormality determination unit determines that an abnormal state has occurred when at least one of the plurality of feedback signals is contrary to the command speed.

Claims

1. A power conversion device comprising: a plurality of switching elements (13) that convert and output power; a control device (30) that commands the switching speed of the switching elements; a drive circuit (20) that drives the switching elements on and off at a switching speed corresponding to the command speed by the control device; a feedback unit (23, 40) that outputs a signal correlated with the actual switching speed as a feedback signal to the control device; and an abnormality determination unit (36) that compares the feedback signal with the command speed to determine whether the actual switching speed is in an abnormal state that is contrary to 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. 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 to a lower speed.

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

5. A power conversion device as described in any one of claims 1 to 4, wherein the drive circuit has an output circuit (24) that switches the magnitude of the gate voltage and outputs it to the switching element, and a switching circuit (22) that switches the switching speed by instructing the output circuit to which gate voltage to switch, and the feedback signal includes a switching signal that indicates the content of the instruction by the switching circuit.

6. The power conversion device according to claim 5, wherein the feedback unit includes a detection unit (40) that detects at least one of the temperature of the switching element, the gate voltage applied to the switching element, and a surge voltage waveform of the switching element, and the feedback signal includes, in addition to the switching signal, a detection signal detected by the detection unit, and 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 power conversion device as described in claim 6, further comprising a regulating unit (S70) which, when the second judgment unit judges that an abnormal state exists, limits the command speed by the control device, and even if the first judgment unit judges that an abnormal state exists, when the second judgment unit does not judge that an abnormal state exists, prohibits the speed limit by the regulating unit.

8. A power conversion device as described in any one of claims 1 to 4, wherein the control device commands a common switching speed to a plurality of the switching elements, the feedback unit outputs the feedback signal for each of the plurality of the switching elements, and the abnormality determination unit determines that an abnormal state has occurred when at least one of the plurality of feedback signals is contrary to the command speed.

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