Power conversion device

Abstract

A power conversion device (4) is provided with: a MOSFET (13) as a switching element; an ECU (30) as a control device for commanding the switching speed of the switching element; and a drive circuit (20) that drives the switching element to turn on and off at a switching speed corresponding to the command speed. The power conversion device (4) further comprises: a feedback circuit (23) as a feedback unit; and a monitoring unit (36) as an abnormality determination unit. The feedback circuit (23) outputs a signal related to the actual switching speed as a feedback signal to the control device. The monitoring unit (36) determines whether or not the actual switching speed is in an abnormal state opposite to the command speed by comparing the feedback signal and the command speed.

Description

[0001] Mutual citation of related applications

[0002] This application is based on Japanese Patent Application No. 2023-131628 filed on August 10, 2023, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The disclosure in this specification relates to an electric power conversion device. Background Technology

[0004] Patent Document 1 discloses a power conversion device capable of changing the switching speed of a switching element. Reference is made hereto as an explanation of technical elements herein.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-65742 Summary of the Invention

[0008] In devices with variable switching speeds as described above, power consumption can be improved by increasing the switching speed. However, the faster the switching speed, the larger the surge voltage, which may damage the switching elements.

[0009] One of the disclosed objectives is to provide a power conversion device that can set the switching speed to be variable to improve power consumption and reduce the possibility of damage to switching elements.

[0010] One of the disclosed power conversion devices includes: Multiple switching elements, which convert and output electrical power; The control device commands the switching speed of the switching elements; The drive circuit drives the switching element to turn on and off at a switching speed corresponding to the command speed of the control device. The feedback unit outputs a signal related to the actual switching speed to the control device as a feedback signal; and The anomaly determination unit compares the feedback signal and the command speed to determine whether the actual switching speed is an abnormal state opposite to the command speed.

[0011] According to the disclosed power conversion device, since the switching element is switched on and off at a switching speed corresponding to the commanded speed, the switching speed can be changed. Therefore, by increasing the switching speed, power consumption can be improved. Furthermore, since the anomaly determination unit determines whether the actual switching speed constitutes an abnormal state opposite to the commanded speed, it is possible to handle anomalies such as fault safety control. Therefore, the possibility of damage to the switching element can be reduced.

[0012] This specification discloses multiple methods that employ different technical means to achieve various objectives. The claims and the symbols enclosed in parentheses within them illustratively indicate a correspondence with portions of the embodiments described later and are not intended to limit the scope of the technology. The objectives, features, and effects disclosed in this specification will become clearer upon reference to the following detailed description and accompanying drawings. Attached Figure Description

[0013] Figure 1 This is a diagram showing the circuit structure and drive system of the power conversion device according to the first embodiment.

[0014] Figure 2 This is a diagram showing the structure of the drive circuit and ECU.

[0015] Figure 3 This is a graph showing the difference in voltage waveforms corresponding to switching speed.

[0016] Figure 4 This is a graph showing the relationship between surge voltage and power loss.

[0017] Figure 5 This is a flowchart illustrating the processes performed by the microcomputer in the ECU.

[0018] Figure 6 This is a flowchart illustrating the process performed by the microcomputer in the second embodiment.

[0019] Figure 7 This is a flowchart illustrating the process performed by the microcomputer in the third embodiment. Detailed Implementation

[0020] Hereinafter, several embodiments will be described based on the accompanying drawings. Furthermore, in each embodiment, repeated descriptions are sometimes omitted by using the same symbols to denote corresponding constituent elements. When only a portion of the structure is described in each embodiment, structures from other previously described embodiments can be applied to the remaining parts of that structure. Moreover, not only combinations of structures explicitly described in the descriptions of each embodiment are possible, but also combinations of structures from multiple embodiments can be partially combined with each other, provided that such combinations do not particularly hinder them.

[0021] The power conversion device of this embodiment is applicable, for example, to mobile bodies driven by a rotary electric motor. Examples of mobile bodies include electric vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric aircraft such as drones or electric vertical takeoff and landing (eVTOL) aircraft, ships, construction machinery, and agricultural machinery. Hereinafter, examples applicable to vehicles will be described.

[0022] (First Implementation)

[0023] First, based on Figure 1 The schematic structure of the vehicle's drive system is explained.

[0024] <Vehicle Drive System 1>

[0025] like Figure 1 As shown, the vehicle's drive system 1 includes a DC power supply 2, an electric generator 3, and a power conversion device 4.

[0026] DC power supply 2 is a DC voltage source composed of rechargeable and discharging secondary batteries. Examples of secondary batteries include lithium-ion batteries, nickel-metal hydride batteries, and organic free radical batteries. Electric generator 3 is a three-phase AC rotating electric motor. Electric generator 3 functions as the vehicle's driving force, i.e., an electric motor. During regeneration, electric generator 3 functions as a generator. Power conversion device 4 performs power conversion between DC power supply 2 and electric generator 3.

[0027] <Circuit Structure of Power Conversion Device 4>

[0028] Figure 1 The circuit structure of the power conversion device 4 is shown. The power conversion device 4 includes at least a power conversion circuit. In this embodiment, the power conversion circuit is an inverter 5. Furthermore, the power conversion device 4 includes a smoothing capacitor 6, a drive circuit 20, an ECU 30 (control device), etc. ECU is short for Electronic Control Unit.

[0029] The smoothing capacitor 6 primarily smooths the DC voltage supplied from the DC power supply 2. The smoothing capacitor 6 is connected to the P-line 8 (high-potential side) and the N-line 9 (low-potential side). The P-line 8 is connected to the positive terminal of the DC power supply 2, and the N-line 9 is connected to the negative terminal of the DC power supply 2. The positive terminal of the smoothing capacitor 6 is connected to the P-line 8 between the DC power supply 2 and the inverter 5. The negative terminal 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 with the DC power supply 2.

[0030] Inverter 5 is a DC-AC conversion circuit. Under the switching control of ECU 30, inverter 5 converts DC voltage into three-phase AC voltage and outputs it to the electric generator 3. Thus, the electric generator 3 is driven to produce a specified torque. Inverter 5 also converts the three-phase AC voltage generated by the electric generator 3 during regenerative braking of the vehicle (receiving rotational force from the wheels) into DC voltage and outputs it to line P 8. In this way, inverter 5 performs bidirectional power conversion between DC power supply 2 and electric generator 3.

[0031] Inverter 5 is configured to include upper and lower arm circuits 10 corresponding to the three. The upper and lower arm circuits 10 are sometimes referred to as bridge branches. The upper and lower arm circuits 10 have an upper arm 10H and a lower arm 10L, respectively. The upper arm 10H and the lower arm 10L set the upper arm 10H on the P line 8 side and are connected in series between the P line 8 and the N line 9.

[0032] 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 electric generator 3 via the output line 11. The U-phase upper and lower arm circuit 10U in the upper and lower arm circuit 10 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.

[0033] The upper and lower arm circuits 10 (10U, 10V, 10W) ​​have series circuits 12. The series circuits 12 in the upper and lower arm circuits 10 can be one or more. In many cases, the series circuits 12 are connected in parallel to form a corresponding 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 connects the switching elements on the upper arm 10H side and the lower arm 10L side in series between the P line 8 and the N line 9.

[0034] The number of switching elements on the high side and the low side constituting the series circuit 12 is not particularly limited. There can be one or more. In this embodiment, the series circuit 12 has one switching element on the high side and one switching element on the low side.

[0035] In this embodiment, n-channel MOSFETs 13 are used as switching elements. MOSFET is short for Metal Oxide Semiconductor Field Effect Transistor. MOSFET 13 is turned on and off by a drive signal (gate voltage).

[0036] A return diode 14 (hereinafter referred to as FWD14) is connected in reverse parallel to each MOSFET 13. In the case of MOSFET 13, FWD1 can be a parasitic diode (body diode) or an external diode. In the upper arm 10H, the drain of MOSFET 13 is connected to P-line 8. In the lower arm 10L, the source of MOSFET 13 is connected to N-line 9. Moreover, the drains of MOSFET 13 in the upper arm 10H and the drains of MOSFET 13 in the lower arm 10L are connected to each other. The anode of FWD14 is connected to the source of the corresponding MOSFET 13, and the cathode is connected to the drain.

[0037] Furthermore, the switching element is not limited to MOSFET 13. For example, an IGBT can also be used. IGBT is short for Insulated Gate Bipolar Transistor. In the case of an IGBT, FWD 14 is also connected in reverse parallel. MOSFET 13 acts as the switching element.

[0038] The drive circuit 20 drives the switching elements that constitute the power conversion circuit of the inverter 5. Based on the drive command from the ECU 30, the drive circuit 20 supplies gate voltage to the gate of the corresponding MOSFET 13. The drive circuit drives the corresponding MOSFET 13 by applying the gate voltage, that is, turns the drive on and off. The drive circuit is sometimes referred to as a driver.

[0039] ECU 30 generates drive commands to operate MOSFET 13 and outputs them to drive circuit 20. ECU 30 generates drive commands, for example, based on torque requests input from a host ECU (not shown) or signals detected by various sensors. Furthermore, ECU 30 generates speed commands to change the switching speed of MOSFET 13 and outputs them to drive circuit 20. ECU 30 may also be located within a host ECU.

[0040] Next, use Figure 2 The structure of the drive circuit 20 and ECU 30 will be explained in more detail.

[0041] The drive circuit 20 includes 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 the function of switching the magnitude of the gate voltage and outputting it. The switching circuit 22 outputs the drive signal Vg and the switching signals VH and VL to the output circuit 24.

[0042] The drive signal Vg is a voltage signal generated based on the drive command from ECU 30. For example... Figure 3 As shown by the solid line, the drive signal Vg is a square waveform signal that changes voltage in a pulse-like manner over time. When the drive signal Vg pulse is turned on, MOSFET 13 is turned on, and the motor current Im flows through winding 3a. When the drive signal Vg pulse is turned off, MOSFET 13 is turned off, and the motor current Im becomes zero.

[0043] The switching signals VH and VL are voltage signals generated based on the speed command from ECU 30. The switching signals VH and VL instruct the waveform shape to which the drive signal Vg should be converted. Figure 3 The dashed line in the diagram represents the drive signal used to convert the waveform to a high-speed switch, and it is the high-speed drive signal VgH. Figure 3 The single-dot dashed line in the diagram is the drive signal for converting the waveform to a low-speed switch, and it is the low-speed drive signal VgL.

[0044] Output circuit 24 converts the drive signal Vg to a high-speed drive signal VgH when the command switching signal VH is applied, and converts it to a low-speed drive signal VgL when the command switching signal VL is applied. In the high-speed drive signal VgH, the slope of the pulse edges is greater than that in the low-speed drive signal VgL. By switching the gate voltage waveform in this way, the waveform of the voltage (motor voltage) for the motor current Im flowing through MOSFET 13 also changes. In the case of the high-speed drive signal VgH, the rise and fall slopes of the motor voltage are greater than those in the case of the low-speed drive signal VgL.

[0045] The switching speed in this specification refers to the rate of increase and decrease (i.e., the slope) 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 is generated during the switching of MOSFET 13. On the other hand, the faster the switching speed, the greater the surge voltage generated when MOSFET 13 switches on and off. That is, the height of the surge waveform appearing in the motor voltage increases.

[0046] For example, in this embodiment, a MOS transistor is used in the output circuit 24, and switching signals VH and VL are input to the gate of the MOS transistor. The drive signal Vg input to the MOS transistor 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 high voltage compared to 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 MOSFET 13 becomes high-speed. 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 MOSFET 13 becomes low-speed.

[0047] Feedback circuit 23 outputs a signal related to the actual switching speed of MOSFET 13 to ECU 30 as a feedback signal. Feedback circuit 23 acts as a feedback unit. The feedback signal output by feedback circuit 23 indicates the type of switching signals VH and VL output by switching circuit 22 to output circuit 24. For example, when a switching signal VH is output to set the switching speed to high speed, the high-speed signal VH is output as a feedback signal. When a switching signal VL is output to set the switching speed to low speed, the low-speed signal VL is output as a feedback signal.

[0048] The driver IC 21 and the output circuit 24 are respectively located in MOSFET 13. Therefore, for each of MOSFET 13, a feedback signal is input to ECU 30. That is, multiple feedback signals are input to ECU 30.

[0049] Furthermore, in this embodiment, in addition to the high-speed signal VH and the low-speed signal VL, the component temperature T is also input to the ECU 30 as a feedback signal. The component temperature T is the temperature of the MOSFET 13 detected by the temperature sensor 40. The faster the switching speed, the higher the component temperature T becomes. That is, the component temperature T is a signal related to the actual switching speed of the MOSFET 13. When the ECU 30 uses the component temperature T as a feedback signal, the temperature sensor 40 acts as a feedback unit.

[0050] The ECU 30 includes a microcomputer (microcomputer 31). The microcomputer 31 is configured to include a processor 32 and a memory 33. By executing programs stored in the memory 33 through the processor 32, the microcomputer 31 performs various functions. These functions include a power-on command unit 34, a speed command unit 35, and a monitoring unit 36, etc.

[0051] The power-on command unit 34 generates the aforementioned drive command based on the torque request and signals detected by various sensors. As the drive command, the power-on command unit 34 outputs, for example, a PWM signal. PWM is short for Pulse Width Modulation.

[0052] like Figure 4 As shown, the more effort is put into increasing the switching speed to reduce power loss, the larger the surge voltage becomes. When the surge voltage exceeds the withstand voltage (component withstand voltage) of MOSFET 13, damage to MOSFET 13 may occur. Damage to MOSFET 13 may also prevent the vehicle from moving. Therefore, the speed command unit 35 generates a speed command to increase the switching speed to a level where the surge voltage does not exceed the component withstand voltage, thereby reducing power loss while avoiding component damage.

[0053] However, even at the same switching speed, the larger the current flowing through MOSFET 13, the larger the surge voltage becomes. Therefore, when a large current flows through MOSFET 13, the speed command unit 35 generates a speed command to slow down the switching speed to avoid damage to the device.

[0054] In view of the above-mentioned problems, 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 windings 3a of each phase. The speed command is generated in such a way that the larger the motor current Im, the slower the switching speed. In this embodiment, the switching speed is switched between two stages: high speed and low speed. The speed command unit 35 outputs one of the high-speed signal and the low-speed signal as the speed command. The speed command unit 35 commands a common switching speed for multiple MOSFETs 13.

[0055] The monitoring unit 36 ​​compares the speed command output by the power-on command unit 34 with the actual switching speed, i.e., the feedback signal, to monitor whether an abnormal state has occurred. If the state is normal, the speed command and the feedback signal should be consistent; if they are inconsistent, it is determined to be an abnormal state. The feedback signal used for this monitoring can be a low-speed signal VL and a high-speed signal VH, or it can be the component temperature T. The monitoring unit 36 ​​is equivalent to an abnormality determination unit.

[0056] In this embodiment, the monitoring unit 36 ​​uses a low-speed signal VL and a high-speed signal VH as feedback signals for monitoring. As an abnormal state, there are two modes. One mode is that although the speed command unit 35 outputs a high-speed signal, the feedback signal becomes the low-speed signal VL. The other mode is that although the speed command unit 35 outputs a low-speed signal, all feedback signals become the high-speed signal VH.

[0057] One possible cause of the anomaly is a fault in MOSFET 13 itself, such as component damage, poor connection, open circuit, or short circuit. Other possible causes include faults in signal lines L1, L2, and L3 that connect the ECU 30 to the drive circuit 20, such as open circuits or short circuits.

[0058] 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 sent via different signal lines L1 and L2, but they can also be sent using a common signal line. The low-speed signal VL and high-speed signal VH, which serve as feedback signals, are sent from the drive circuit 20 to the ECU 30 via signal line L4. In this embodiment, the feedback signal corresponding to each of the MOSFETs 13 is sent via a different signal line L3, but they can also be sent using a common signal line.

[0059] Temperature sensor 40 and ECU 30 are connected via signal line L4. Using signal line L4, the component temperature T is transmitted from temperature sensor 40 to ECU 30. Alternatively, the component temperature T can also be transmitted from temperature sensor 40 to ECU 30 via drive circuit 20. In this case, the low-speed signal VL, high-speed signal VH, and component temperature T can also be transmitted from drive circuit 20 to ECU 30 using a common signal line. In this configuration, since a feedback signal can be transmitted from drive circuit 20 to ECU 30 using the signal line for component temperature T, the number of signal lines can be reduced.

[0060] <Control Flow of Microcomputer 31>

[0061] Figure 5 The control flow shown is repeatedly executed by the microcomputer 31 at a predetermined operation cycle during the driving period of the electric generator 3.

[0062] First, in step S10, the detected value of the motor current Im is obtained. Next, in step S20, it is determined whether the obtained motor current Im is greater than the threshold Ith. If it is determined that Im > Ith, it is considered to be in a state of... Figure 4 When the current is high. Then, in the next step S30, the speed command unit 35 outputs a low-speed signal as a speed command. As a result, the surge voltage is reduced, and damage to the MOSFET 13 can be avoided.

[0063] On the other hand, if it is determined that Im is not greater than Ith, it is considered to be in the state of Figure 4 When the current is low, the speed command unit 35 then outputs a high-speed signal as a speed command. This increases the switching speed and reduces power loss.

[0064] If a low-speed command is issued in step S30, in the next step S40, the monitoring unit 36 ​​determines whether the feedback signal is a low-speed signal VL. If it is determined to be a low-speed signal VL in step S40, since the commanded speed and the feedback signal are consistent, the process is considered to be in a normal state and ends. Figure 5 The processing.

[0065] If a high-speed command is issued in step S31, in the next step S41, the monitoring unit 36 ​​determines whether the feedback signal is a high-speed signal VH. If it is determined to be a high-speed signal VH in step S41, since the command speed and the feedback signal are consistent, the process is considered to be in a normal state and ends. Figure 5 The processing.

[0066] Here, for each of the MOSFETs 13, a feedback signal is input from the feedback circuit 23 to the ECU 30 as described above. In the determinations of steps S40 and S41, if at least one of the multiple feedback signals input to the ECU 30 is inconsistent with the command speed, a negative determination is made, and the process proceeds to step S50.

[0067] If, in step S40, it is determined that the signal is not a low-speed signal VL, the commanded speed and the feedback signal are inconsistent. Similarly, if, in step S41, it is determined that the signal is not a high-speed signal VH, the commanded speed and the feedback signal are inconsistent. In these cases, it is considered an abnormal state, and the process proceeds to the next step, S50.

[0068] In step S50, an abnormal state is diagnosed, and the abnormality flag is set to "on". When the abnormality flag is set to "on", the power-on command unit 34 performs fault safety control, such as limiting the output of the electric generator 3. Additionally, when the abnormality flag is set to "on", the ECU 30 notifies the upper-level ECU. Upon receiving the notification of the abnormal state, the upper-level ECU informs the vehicle occupants of the abnormal state via a warning display or warning sound output.

[0069] <Summary of the First Implementation>

[0070] In this embodiment, the MOSFET 13 is switched on and off at a switching speed corresponding to the commanded speed, thus allowing the switching speed to be varied. Therefore, by increasing the switching speed, power consumption can be improved. Furthermore, since a feedback signal related to the actual switching speed is fed back to the ECU 30, the ECU 30 can monitor whether the actual switching speed becomes an abnormal state opposite to the commanded speed. Therefore, fault-tolerant control, such as limiting the output of the electric generator 3, or handling abnormal situations such as warning notifications can be implemented. Based on the above, power consumption can be improved while reducing the possibility of surge voltage exceeding the component's withstand voltage due to the actual switching speed becoming faster than intended.

[0071] In this embodiment, the ECU 30 commands a common switching speed for multiple MOSFETs 13. The feedback circuit 23 outputs a feedback signal for each of the multiple MOSFETs 13. The monitoring unit 36 ​​determines that an abnormal state is incurred if at least one of the multiple feedback signals is opposite to the command speed. As a result, the computational processing load on the microcomputer 31 can be reduced.

[0072] Here, when the component temperature T is used as the feedback signal, even if an abnormal state occurs, the component temperature T requires time to change to the abnormal temperature. Therefore, it is difficult to detect the abnormality quickly. 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. Furthermore, the drive circuit 20 has a switching circuit 22 that commands the magnitude of the gate voltage to the output circuit 24. Moreover, the feedback signal used in the monitoring of the monitoring unit 36 ​​includes switching signals VH and VL that represent the command content of the switching circuit 22. Therefore, even if an abnormal state occurs where the content of the speed command is inconsistent with the content of the feedback signal, it can be detected quickly.

[0073] (Second Implementation)

[0074] This embodiment is a variation based on the previous embodiment, and the description of the previous embodiment can be referenced. In the previous embodiment, even when an abnormality is detected, the command speed is determined based on the magnitude of the motor current Im. Instead, in this embodiment, when an abnormality is detected, regardless of the magnitude of the motor current Im, the command speed for subsequent commands is set in the following manner.

[0075] Specifically, in Figure 6 If a negative determination is made in step S41, in step S51, the abnormality flag is activated and an abnormality warning is issued, similar to 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 by decreasing it.

[0076] If the actual speed then normally becomes low speed, a positive determination is made in step S40. If the motor current Im remains below the threshold Ith, the high speed command is switched back in step S31.

[0077] Furthermore, in this embodiment, if a negative determination is made in step S40, an abnormal warning is issued in step S50, and then in the following step S70, the speed command unit 35 is prohibited from outputting high-speed commands.

[0078] <Summary of the Second Implementation>

[0079] According to this embodiment, the same effect as the structure described in the previous embodiment can be achieved. In addition, the ECU 30 changes the command speed when an abnormal state is determined. More specifically, if a high-speed command is given but the actual speed is low—that is, if a negative determination is made in step S41—it changes to a low-speed command. By changing from a high-speed command to a low-speed command in this way, it is possible to avoid abnormal states. Therefore, according to this embodiment, it is sometimes possible to switch to the state of driving the electric generator 3 normally.

[0080] Furthermore, according to this embodiment, when an abnormal state is determined, the ECU 30 fixes the command speed at a predetermined speed and prohibits any changes. More specifically, if a low-speed command is given but the actual speed becomes high—that is, if a negative determination is made in step S40—the command is fixed as a low-speed command and changes to a high-speed command are prohibited. This reduces the possibility that the switching speed may become faster than intended, and reduces the possibility of damage to the MOSFET 13 caused by surge voltage.

[0081] (Third implementation method)

[0082] This embodiment is a variation based on the previous embodiment, and the description of the previous embodiment can be referenced. In the previous embodiment, one feedback signal was used to diagnose the anomaly. Alternatively, two or more feedback signals may be used to diagnose the anomaly.

[0083] Specifically, in this embodiment, such as Figure 7 As shown, in Figure 6 Step S60 is added to the flowchart. This step S60 is executed when the actual speed becomes high even though it is a low-speed command, i.e., when a negative determination is made in step S40. In step S60, the monitoring unit 36 ​​uses a second feedback signal to determine an anomaly. Specific examples of the second feedback signal include the component 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 winding 3a. In this embodiment, the component temperature T is used as the second feedback signal. The first feedback signal is the switching signal VH, VL, and in contrast, the component temperature T as the second feedback signal is equivalent to a detection signal.

[0084] The first feedback signal is the feedback signal used in steps S40 and S41, namely the switching signals VH and VL. The second feedback signal is a signal of a different type from the first feedback signal that is related to the actual switching speed.

[0085] Steps S40 and S41 correspond to a first determination unit that uses a first feedback signal to determine an abnormal state. Step S60 corresponds to a second determination unit that uses a second feedback signal to determine an abnormal state. Temperature sensor 40 corresponds to a detection unit that detects the second feedback signal. This detection unit and feedback circuit 23 correspond to a feedback unit that outputs a feedback signal related to the actual switching speed.

[0086] Here, the faster the switching speed, the higher the component temperature T becomes. Therefore, if the speed command is switched from high speed to low speed and this state is maintained for a specified time or more, the component temperature T should decrease. Similarly, if the speed command is switched from low speed to high speed and this state is maintained for a specified time or more, the component temperature T should increase. In view of this, in step S60, it is determined whether the actual speed is low speed or high speed based on the component temperature T. Specifically, the actual speed is determined based on the value of the component temperature T at the current time point and the change of the component temperature T up to the current time point.

[0087] If a low-speed command is output in step S30 but is determined not to be low-speed in step S40, the exception flag is set to on in step S50. However, even under such exception diagnosis, if it is determined to be low-speed in step S50, the high-speed command is not prohibited in step S70, but the process returns to step S10. Moreover, if it is determined not to be low-speed in step S50, just like in step S40, the high-speed command is prohibited in step S70. Step S70 is equivalent to a limiting unit that imposes a speed restriction on the command to prohibit the high-speed command when the second determination unit determines that an exception is in place.

[0088] <Summary of the Third Implementation>

[0089] According to this embodiment, the same effect as the structure described in the previous embodiment can be achieved. In addition, the power conversion device 4 includes a temperature sensor 40, and the feedback signal includes, in addition to the switching signals VH and VL, the element temperature T detected by the temperature sensor 40. The anomaly determination unit of the monitoring unit 36 ​​has a first determination unit in steps S40 and S41 and a second determination unit in step S60. In the first determination unit, an abnormal state is determined by comparing the switching signals VH and VL with the command speed. In the second determination unit, an abnormal state is determined by comparing the element temperature T detected by the temperature sensor 40 with the command speed. Therefore, since two feedback signals are used for anomaly determination, the accuracy of anomaly determination can be improved.

[0090] Here, the first determination unit can quickly detect abnormalities, but there is also a possibility of false detection due to an abnormality in signal line L3. In view of this, in this embodiment, even if the first determination unit determines it to be an abnormal state, the speed limit in the limiting unit of step S70 is prohibited if the second determination unit does not determine it to be an abnormal state. Therefore, the possibility of insufficient improvement in power consumption due to excessive speed limiting can be reduced. Thus, fault avoidance of MOSFET 13 and improvement in power consumption can be achieved simultaneously.

[0091] (Other implementation methods)

[0092] The disclosure in this specification and accompanying drawings is not limited to the illustrated embodiments. This disclosure includes illustrated embodiments and modifications made by those skilled in the art based thereon. For example, this disclosure is not limited to the combinations of components and / or elements shown in the embodiments. This disclosure can be implemented in various combinations. This disclosure may have additional portions that can be added to the embodiments. This disclosure includes embodiments in which components and / or elements of the embodiments are omitted. This disclosure includes substitutions or combinations of components and / or elements between one embodiment and other embodiments. The technical scope of this disclosure is not limited to the description of the embodiments. Several technical scopes of this disclosure should be understood to be expressed by the description of the claims, and also include all modifications within the meaning and scope of equivalents to the description of the claims.

[0093] The disclosures in the specification and drawings are not limited by the claims. The disclosures in the specification and drawings include the technical ideas described in the claims, and involve more diverse and broader technical ideas than those described in the claims. Therefore, it is possible to extract various technical ideas from the disclosures in the specification and drawings without being limited by the claims.

[0094] In the third embodiment, the first feedback signal and the second feedback signal are used for anomaly detection, but the first feedback signal can also be discarded and the second feedback signal can be used for anomaly detection.

[0095] In the above embodiments, the switching speed is switched between two stages: high speed and low speed. In contrast, the switching speed can be switched between three or more stages, or it can be changed steplessly to linearly.

[0096] In the second embodiment described above, under abnormal conditions, the ECU 30 fixes the command speed to a predetermined speed. Specifically, assuming the switching speed is switched between high and low speed stages, in an abnormal situation where the actual speed becomes high despite being a low-speed command, the ECU 30 fixes the command to low speed. Conversely, assuming the switching is between high, medium, and low speed stages, the ECU 30 can also fix the command to low speed or medium speed under the aforementioned abnormal conditions. Furthermore, assuming the switching speed is changed linearly and steplessly, the speed can be fixed at a level that will not damage the MOSFET 13, and the ECU 30 issues the speed command. Specific examples of damage in this situation include damage caused by excessive current flowing through the MOSFET 13, damage caused by excessive temperature of the MOSFET 13, and damage caused by applying excessive voltage to the MOSFET 13.

[0097] In the above embodiments, if a negative determination is made in step S41, the low-speed command in step S30 is allowed if the motor current Im is greater than the threshold Ith. Conversely, if a negative determination is made in step S41, the low-speed command may be prohibited regardless of the magnitude of the subsequent motor current Im.

[0098] In the above embodiments, if a negative determination is made in step S40, the switching speed is also determined in step S20 based on the magnitude of the motor current Im. Conversely, if a negative determination is made in step S40, the high-speed command can be fixed regardless of the subsequent magnitude of the motor current Im.

[0099] In the embodiments described above, the switching speed is varied based on the motor current Im. Conversely, the switching speed can also be varied based on the temperature of the MOSFET 13 and the temperature of the cooling water cooling the MOSFET 13. For example, it is desirable that higher temperatures result in faster switching speeds and reduced power losses. Furthermore, the switching speed can also be varied based on the voltage supplied to the MOSFET 13 or the voltage supplied to the drive circuit 20. For example, it is desirable that lower voltages result in faster switching speeds and reduced power losses. Additionally, the switching speed can also be varied based on the voltage of the power supply used as the gate signal for the MOSFET 13. For example, it is desirable that lower voltages used for the gate signal result in faster switching speeds and reduced power losses. Furthermore, the switching speed can be varied by combining the aforementioned parameters such as the motor current Im, various temperatures, various voltages, or atmospheric pressure.

[0100] The power conversion device 4 can also include a converter as a power conversion circuit. The converter is a DC-DC conversion circuit that converts DC voltage into DC voltages of different values. The converter is located between the DC power supply 2 and the smoothing capacitor 6. The converter can be configured, for example, to include a reactor and the aforementioned upper and lower arm circuits 10. With this configuration, step-up and step-down voltage conversion is possible. The power conversion device 4 can also include a filter capacitor to remove power supply noise from the DC power supply 2. The filter capacitor is located between the DC power supply 2 and the converter.

[0101] (The disclosure of technical ideas)

[0102] This specification discloses several technical ideas described in the following list of items. Some items are sometimes described by selectively referencing a multiple dependent form of a previous item in a subsequent item. Furthermore, some items are sometimes described by referring to a multiple dependent form of another multiple dependent form. These items described in multiple dependent forms define several technical ideas.

[0103] (Technical Idea 1)

[0104] A power conversion device, comprising: Multiple switching elements (13) convert and output electrical power; Control device (30), the control device commands the switching speed of the switching element; The drive circuit (20) drives the switching element to turn on and off at a switching speed corresponding to the command speed of the control device. Feedback units (23, 40) output a signal related to the actual switching speed to the control device as a feedback signal; and The anomaly determination unit (36) determines whether the actual switching speed is an abnormal state opposite to the command speed by comparing the feedback signal and the command speed.

[0105] (Technical Idea 2)

[0106] As described in technical concept 1, the power conversion device, in which, The control device changes the command speed when it determines that the above-mentioned abnormal state has occurred.

[0107] (Technical Idea 3)

[0108] As described in technical concept 2, the power conversion device, in which, If the abnormal state is determined to be caused by the switching speed corresponding to the above feedback signal being slower than the above command speed, the control device changes by reducing the command speed.

[0109] (Technical Idea 4)

[0110] As described in technical concept 1, the power conversion device, in which, When the aforementioned control device determines that the above-mentioned abnormal state has occurred, it will fix the above-mentioned command speed at the specified speed and prohibit any changes.

[0111] (Technical Idea 5)

[0112] As described in any of the technical ideas 1 to 4, the power conversion device, wherein, The aforementioned driving circuit includes: 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 switch to a specific gate voltage. The aforementioned feedback signal includes a switching signal that represents the instruction content of the aforementioned switching circuit.

[0113] (Technical Idea 6)

[0114] As described in technical concept 5, the power conversion device, in which... The aforementioned feedback unit includes a detection unit (40), which detects at least one of the temperature of the switching element, the gate voltage applied to the switching element, and the surge voltage waveform of the switching element. In addition to the switching signal, the feedback signal also includes the detection signal detected by the detection unit. The above-mentioned abnormality determination unit includes: a first determination unit (S40, S41), which determines the abnormality state by comparing the switching signal and the command speed; and a second determination unit (S60), which determines the abnormality state by comparing the detection signal and the command speed.

[0115] (Technical Idea 7)

[0116] As described in technical concept 6, the power conversion device, in which... The system includes a limiting unit (S70) that limits the command speed of the control device when the second determination unit determines that an abnormal state has occurred. Even if the first determination unit determines that the above-mentioned abnormal state is present, the speed limit of the above-mentioned limiting unit is prohibited if the second determination unit does not determine that the above-mentioned abnormal state is present.

[0117] (Technical Idea 8)

[0118] As described in any of the technical ideas 1 to 7, the power conversion device, wherein, The aforementioned control device commands a common switching speed to multiple of the aforementioned switching elements. The aforementioned feedback unit outputs the aforementioned feedback signal to each of the plurality of aforementioned switching elements. If at least one of the multiple feedback signals is opposite to the speed of the command, the above-mentioned abnormality determination unit determines that the above-mentioned abnormality is true.

Claims

1. A power conversion device, comprising: Multiple switching elements (13) convert and output electrical power; Control device (30), the control device instructs the switching speed of the switching element; Drive circuit (20), the drive circuit drives the switching element to turn on and off at a switching speed corresponding to the command speed of the control device; Feedback unit (23, 40), which outputs a signal related to the actual switching speed to the control device as a feedback signal; as well as Anomaly determination unit (36) determines whether the actual switching speed is an abnormal state opposite to the command speed by comparing the feedback signal and the command speed.

2. The power conversion device as described in claim 1, characterized in that, The control device changes the command speed when it determines that the abnormal state has occurred.

3. The power conversion device as described in claim 2, characterized in that, If an abnormal state is determined to occur when the switching speed corresponding to the feedback signal is slower than the command speed, the control device changes the command speed by reducing it.

4. The power conversion device as described in claim 1, characterized in that, When the control device determines that the abnormal state is present, it will fix the command speed at the specified speed and prohibit any changes.

5. The power conversion device as described in any one of claims 1 to 4, characterized in that, The driving circuit includes: 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 switch to which gate voltage. The feedback signal includes a switching signal that represents the instruction content of the switching circuit.

6. The power conversion device as described in claim 5, characterized in that, 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 the surge voltage waveform of the switching element. In addition to the switching signal, the feedback signal also includes the detection signal detected by the detection unit. The anomaly determination unit includes: a first determination unit (S40, S41), which determines the anomaly state by comparing the switching signal and the command speed; And a second determination unit (S60), which determines the abnormal state by comparing the detection signal and the command speed.

7. The power conversion device as described in claim 6, characterized in that, The system includes a limiting unit (S70) that limits the command speed of the control device when the second determination unit determines that an abnormal state has occurred. Even if the first determination unit determines that the abnormal state is abnormal, the speed limit of the limiting unit is prohibited if the second determination unit does not determine that the abnormal state is abnormal.

8. The power conversion device as described in any one of claims 1 to 4, characterized in that, The control device commands a common switching speed to the multiple switching elements. The feedback unit outputs the feedback signal to each of the plurality of switching elements. The anomaly determination unit determines the anomaly state when at least one of the multiple feedback signals is opposite to the command speed.

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