Motor drive device, motor drive method, and motor drive program

Abstract

To provide a motor drive device, motor drive method and motor drive program that prevent a switching element from generating a large surge voltage.SOLUTION: In an electric machine system 200, a motor drive device 220 comprises: gate drive circuits 12a-c and 21a-c for driving upper arm side switching elements 4a-c and lower arm side switching elements 5a-c provided in an inverter 210 for driving a motor; and fail safe circuits 8 and 14 for performing a fail safe control including at least one of all ON of the upper arm side switching elements or all ON of the lower arm side switching elements. The gate drive circuits reduce an ON-resistance of at least one switching element that is turned ON among the upper arm side switching elements and the lower arm side switching elements in at least one period during which the fail safe control is performed, than an ON-resistance in at least one period during which the fail safe control is not performed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a motor drive device, a motor drive method, and a motor drive program.

Background Art

[0002] An electric machine system having a motor and an inverter for driving the motor is used in electric vehicles such as hybrid vehicles and electric vehicles. In such an electric machine system, a technique is known in which, when an abnormality occurs, all the upper arm side switching elements or all the lower arm side switching elements in the inverter are turned on to short-circuit the motor (Patent Documents 1 to 4). For example, Patent Document 3 states that "in a motor that operates up to high speeds using a permanent magnet for field excitation, when an abnormality occurs in the inverter at high speeds, the induced voltage generated by the rotation of the motor becomes an excessive voltage" (paragraph 0004). Therefore, "normally, the motor is driven by PWM, but when any abnormality occurs in the inverter, by switching the three-phase switching elements from PWM drive to three-phase short-circuit drive, the DC power supply voltage is suppressed within a predetermined voltage range" (paragraph 0009). Also, Patent Documents 5 to 7 describe that when short-circuiting the motor, all the upper arm side switching elements and all the lower arm side switching elements are alternately turned on. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-14184 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2017-147806 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2015-198503 [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2009-284747 [Patent Document 5] International Publication No. 2016 / 136815 [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2012-65425 [Patent Document 7] Japanese Unexamined Patent Application Publication No. 2018-152986

Summary of the Invention

Problems to be Solved by the Invention

[0003] When a motor winding short - circuit occurs due to a three - phase short - circuit of the upper - arm - side switching element or the lower - arm - side switching element in a state where the motor is under high load, a current exceeding the current flowing during normal motor driving may transiently flow through the switching element. When switching between a three - phase short - circuit of the upper arm and a three - phase short - circuit of the lower arm in such a state, a large surge voltage may be generated.

Means for Solving the Problems

[0004] In a first aspect of the present invention, a motor drive device is provided. The motor drive device may include a gate drive unit that drives a plurality of upper - arm - side switching elements and a plurality of lower - arm - side switching elements included in an inverter for driving a motor. The motor drive device may include a fail - safe unit that performs fail - safe control including at least one of all - on of the plurality of upper - arm - side switching elements or all - on of the plurality of lower - arm - side switching elements. The gate drive unit may reduce the on - resistance of at least one switching element to be turned on among the plurality of upper - arm - side switching elements and the plurality of lower - arm - side switching elements during at least a part of the period in which the fail - safe control is performed, as compared with the on - resistance during at least a part of the period in which the fail - safe control is not performed.

[0005] Each of the plurality of upper - arm - side switching elements and the plurality of lower - arm - side switching elements may turn on in response to a gate drive voltage exceeding a threshold voltage being supplied to the gate. The gate drive unit may increase the gate drive voltage supplied to the gate of at least one switching element during at least a part of the period in which the fail - safe control is performed, as compared with the gate drive voltage during at least a part of the period in which the fail - safe control is not performed.

[0006] The motor drive device may include a first power source and a second power source that outputs a power supply voltage higher than the first power source. The gate drive unit may supply a gate drive voltage supplied to the gate of at least one switching element using the power supply voltage from the second power source during at least a part of the period in which fail-safe control is performed. The gate drive unit may supply a gate drive voltage supplied to the gate of at least one switching element using the power supply voltage from the first power source during at least a part of the period in which fail-safe control is not performed.

[0007] The second power source may be connected to the DC bus of the inverter.

[0008] The fail-safe unit may perform fail-safe control in response to the power supply voltage output by the first power source being equal to or lower than the threshold voltage.

[0009] The gate drive unit may reduce the on-resistance of at least one switching element during at least a part of the period in which fail-safe control is performed to be lower than the on-resistance during the period in which fail-safe control is not performed.

[0010] The gate drive unit may reduce the on-resistance of at least one switching element during at least a part of the period in which fail-safe control is performed to be lower than the on-resistance during at least a part of the period in which fail-safe control is not performed, on the condition that the current flowing through at least one switching element exceeds the threshold current.

[0011] In fail-safe control, the fail-safe unit may alternately turn on all of the plurality of upper-arm side switching elements and the plurality of lower-arm side switching elements.

[0012] The gate drive unit may reduce the on-resistance of each switching element to be turned on completely among the plurality of upper-arm side switching elements and the plurality of lower-arm side switching elements during at least a part of the period in which fail-safe control is performed to be lower than the on-resistance during at least a part of the period in which fail-safe control is not performed.

[0013] The gate drive unit may reduce the switching speed of at least one switching element during at least a part of the period in which fail-safe control is performed, as compared with the switching speed during at least a part of the period in which fail-safe control is not performed.

[0014] The gate drive unit may increase the gate resistance connected to the gate of at least one switching element during at least a part of the period in which fail-safe control is performed, as compared with the gate resistance during at least a part of the period in which fail-safe control is not performed.

[0015] In a second aspect of the present invention, a motor drive device is provided. The motor drive device may include a gate drive unit that drives a plurality of upper-arm-side switching elements and a plurality of lower-arm-side switching elements included in an inverter for driving a motor. The motor drive device may include a fail-safe unit that performs fail-safe control including at least one of all-on of the plurality of upper-arm-side switching elements or all-on of the plurality of lower-arm-side switching elements. The gate drive unit may reduce the switching speed of at least one switching element to be turned on among the plurality of upper-arm-side switching elements and the plurality of lower-arm-side switching elements during at least a part of the period in which fail-safe control is performed, as compared with the switching speed during at least a part of the period in which fail-safe control is not performed.

[0016] The gate drive unit may increase the gate resistance connected to the gate of at least one switching element during at least a part of the period in which fail-safe control is performed, as compared with the gate resistance during at least a part of the period in which fail-safe control is not performed.

[0017] Note that the above summary of the invention does not enumerate all the features of the present invention. Also, sub-combinations of these feature groups may also be inventions.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

MODE FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution means of the invention.

[0020] FIG. 1 shows the configuration of the electric machine system 200 according to this embodiment. When a current exceeding the current flowing during motor drive transiently flows during a full-phase short circuit of the upper arm side switching elements 4a to 4c or the lower arm side switching elements 5a to 5c, the electric machine system 200 reduces the on-voltage generated between the main terminals of the switching element to be turned on, thereby reducing the power loss due to the switching element. As a result, the electric machine system 200 can suppress the power loss within the allowable value range even when a large current flows through the switching element to be turned on.

[0021] The electric motor system 200 includes a main battery 1, a switch 2, a DC bus capacitor 3, an auxiliary battery 6, a power supply circuit 13, a motor PM, one or more current sensors 100, an angle sensor 101, an inverter 210, and a motor drive device 220. The main battery 1 is a power supply of, for example, 400 V, and is connected between the positive side and the negative side of the DC bus of the inverter 210 to generate power to be supplied to the motor PM.

[0022] The switch 2 is provided between the main battery 1, the DC bus capacitor 3, and the inverter 210, and switches whether to connect the main battery 1 to the DC bus capacitor 3 and the inverter 210. As an example, the switch 2 is switched to the on state according to, for example, the start of the electric motor system 200 or the vehicle equipped with the electric motor system 200, and a failure or abnormality of the electric motor system 200 or the vehicle equipped with the electric motor system 200 occurs, or the voltage between the DC buses exceeds the upper limit voltage due to regeneration from the motor PM side. It may be switched to the off state according to such circumstances. Further, the switch 2 may be switched to the off state according to the interruption of the power supply from the auxiliary battery 6, that is, for example, when the voltage supplied from the auxiliary battery 6 becomes equal to or lower than a predetermined lower limit voltage.

[0023] The DC bus capacitor 3 is connected between the positive and negative DC buses on the inverter 210 side with respect to the switch 2. The DC bus capacitor 3 stabilizes the DC bus voltage and absorbs fluctuations in the current supplied to the inverter 210 side.

[0024] The auxiliary battery 6 is a power supply of, for example, 12 V, and generates power to be supplied to the motor drive device 220. The auxiliary battery 6 may be connected to other devices (such as a cell motor and electrical components) provided in a vehicle or the like equipped with the electric motor system 200, and supply power to these devices. The ground GND_N1, which is the negative side of the auxiliary battery 6, may be grounded to the vehicle body and is insulated from the main battery 1 and the DC bus capacitor 3.

[0025] The power supply circuit 13 is connected to the DC bus of the inverter 210, receives power supply from the DC bus capacitor 3, and outputs a power supply voltage VHV_2 with the voltage of the positive DC bus dropped. The power supply circuit 13 is an example of a second power supply and may be included in the motor drive device 220. Here, the power supply voltage VHV_2 may have a potential of, for example, the potential of the ground GND_N2 + 16V, with the potential of the negative DC bus (i.e., the potential of the ground GND_N2 in the figure) as the reference potential. The power supply circuit 13 is a DC voltage converter such as a DC / DC converter, for example, and may not be insulated from the main battery 1 and the DC bus capacitor 3.

[0026] The motor PM is, as an example, a three-phase permanent magnet (PM: Permanent Magnet) motor. Alternatively, the motor PM may have a different number of phases and may be another type of motor that rotates upon receiving power supply. In the present embodiment, the motor PM rotates the wheels of a vehicle on which the electric machine system 200 is mounted.

[0027] One or more current sensors 100 are provided on a part or all of one or more wirings connected to the motor PM to detect the current flowing through the corresponding wiring. The current sensor 100 may be a current sensor that measures the current in a non-contact manner with the wiring to be measured, such as a CT (Current Transformer) method. The angle sensor 101 receives power supply from the auxiliary battery 6 and detects the rotation of the motor PM. The angle sensor 101 may be a rotation angle sensor such as a resolver method that detects the rotation angle of the motor PM.

[0028] The inverter 210 is connected between the DC buses, converts the DC bus voltage into an AC voltage (a three-phase AC voltage in this embodiment) for driving the motor PM, and supplies it to the motor PM. The inverter 210 has, corresponding to each phase of the motor PM, each of a plurality of upper-arm side switching elements 4a to 4c (hereinafter, also referred to as "upper-arm side switching elements 4") and each of a plurality of lower-arm side switching elements 5a to 5c (hereinafter, also referred to as "lower-arm side switching elements 5"). Each upper-arm side switching element 4 and each lower-arm side switching element 5 may be power semiconductor elements. As an example, they are IGBTs (Insulated Gate Bipolar Transistors) having a collector and an emitter as main terminals and a gate as a control terminal. Instead of this, each upper-arm side switching element 4 and each lower-arm side switching element 5 may be MOSFETs having a drain and a source as main terminals and a gate as a control terminal. In this embodiment, each of the plurality of upper-arm side switching elements 4a to 4c and each of the plurality of lower-arm side switching elements 5a to 5c turn on in response to a gate drive voltage exceeding the threshold voltage being supplied to the gate.

[0029] The upper-arm side switching element 4a and the lower-arm side switching element 5a are connected in this order in parallel with the DC bus capacitor 3 between the positive-side DC bus and the negative-side DC bus with their main terminals connected therebetween, and the first-phase terminal (U-phase terminal) of the motor PM is connected between the upper-arm side switching element 4a and the lower-arm side switching element 5a. The upper-arm side switching element 4b and the lower-arm side switching element 5b, and the upper-arm side switching element 4c and the lower-arm side switching element 5c are connected with their main terminals between the DC buses in the same manner as the upper-arm side switching element 4a and the lower-arm side switching element 5a, the second-phase terminal (V-phase terminal) of the motor PM is connected between the upper-arm side switching element 4b and the lower-arm side switching element 5b, and the third-phase terminal (W-phase terminal) of the motor PM is connected between the upper-arm side switching element 4c and the lower-arm side switching element 5c.

[0030] Each upper arm side switching element 4 and each lower arm side switching element 5 may have a freewheel diode connected in reverse to the switching element body. Here, when each upper arm side switching element 4 and each lower arm side switching element 5 are MOSFETs, the freewheel diode may be a parasitic diode.

[0031] The motor drive device 220 is connected to the inverter 210 and controls the inverter 210 by receiving power supply from the power supply circuit 13 and the auxiliary battery 6. The motor drive device 220 includes a control circuit 7, a first fail-safe circuit 8, a failure detection circuit 15, a plurality of upper arm power supply circuits 9a to 9c, a plurality of upper arm gate drive circuits 12a to 12c, a lower arm power supply circuit 10, an insulation circuit 17, a second fail-safe circuit 14, and a plurality of lower arm gate drive circuits 21a to 21c. Note that the circuit configuration including the plurality of upper arm power supply circuits 9a to 9c, the plurality of upper arm gate drive circuits 12a to 12c, and the plurality of lower arm gate drive circuits 21a to 21c is also referred to as a "gate drive unit". Also, the circuit configuration including the first fail-safe circuit 8 and the second fail-safe circuit 14 is also referred to as a "fail-safe unit".

[0032] The control circuit 7 uses the potential of the ground GND_N1 on the negative side of the auxiliary battery 6 as the reference potential and receives power supply from the auxiliary battery 6. The control circuit 7 may be realized by causing a CPU such as a microcontroller or a processor for motor control, or a computer including the CPU to execute a motor drive program. Alternatively, the control circuit 7 may be realized by a hardware circuit. The control circuit 7 receives a torque command τ* that specifies the torque for driving the motor PM from a computer (not shown) such as an ECU (Electric Control Unit) of the vehicle, and generates gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 for driving the motor PM so as to generate a torque corresponding to the torque command τ*, and outputs them. Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 are gate drive commands corresponding to the upper arm side switching elements 4a, 4b, 4c, lower arm side switching elements 5a, 5b, and 5c in order. In the present embodiment, the control circuit 7 outputs a gate drive command for instructing the inverter 210 to generate a three-phase alternating current for rotating the motor PM with the torque specified by the torque command τ*.

[0033] The first fail-safe circuit 8 uses the potential of the ground GND_N1 as a reference potential and receives power supply from the auxiliary battery 6. Similar to the control circuit 7, the first fail-safe circuit 8 may be implemented by a computer or the like, or may be implemented by a hardware circuit. The first fail-safe circuit 8 performs fail-safe control on at least one of the upper arm gate drive circuits 12a to 12c or the lower arm gate drive circuits 21a to 21c using at least one of the detection signal from the angle sensor 101 and the signal from the failure detection circuit 15. The first fail-safe circuit 8 obtains the rotation speed of the motor PM by time-differentiating the detection signal from the angle sensor 101. The first fail-safe circuit 8 may perform fail-safe control in response to the rotation speed of the motor PM exceeding a predetermined upper limit speed. Further, the first fail-safe circuit 8 may perform fail-safe control in response to receiving a signal indicating that an abnormality or failure of the control circuit 7 has been detected from the failure detection circuit 15. In the present embodiment, the first fail-safe circuit 8 performs both the fail-safe control of the upper arm gate drive circuits 12a to 12c and the fail-safe control of the lower arm gate drive circuits 21a to 21c.

[0034] Specifically, the first fail-safe circuit 8 inputs the gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 from the control circuit 7, and outputs them as the gate drive commands Gu_LV2, Gv_LV2, Gw_LV2, Gx_LV2, Gy_LV2, and Gz_LV2 without changing the values of the gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 in normal operation. Thereby, the inverter 210 drives the motor PM according to the control of the control circuit 7.

[0035] In the fail-safe operation, the first fail-safe circuit 8 sets the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 to logic L (low), causing all the upper-arm switching elements 4a to 4c to be turned off by the upper-arm gate drive circuits 12a to 12c, and sets the gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2, as well as the lower-arm short-circuit command Short_ON, to logic H (high), causing all the lower-arm switching elements 5a to 5c to be turned on by the lower-arm gate drive circuits 21a to 21c. The fail-safe control including these operations may be performed on the inverter 210.

[0036] The fault detection circuit 15 is connected to the control circuit 7 and receives power supply from the auxiliary battery 6. The fault detection circuit 15 monitors the control circuit 7 to detect a fault or abnormality in the control circuit 7, and resets and restarts the control circuit 7 according to the type of the fault or abnormality. Further, depending on the type of the fault or abnormality, the fault detection circuit 15 instructs the first fail-safe circuit 8 to perform fail-safe control.

[0037] Each of the upper-arm power supply circuits 9a to 9c receives power supply from the auxiliary battery 6 and converts the power supply voltage from the auxiliary battery 6 into a power supply voltage for controlling each of the upper-arm switching elements 4a to 4c. Here, the upper-arm power supply circuit 9a outputs, as a power supply voltage for controlling the upper-arm switching element 4a (for example, the potential of GND_U + 12V), a voltage with the main terminal on the lower-arm switching element 5a side (the emitter terminal of the upper-arm switching element 4a in the present embodiment) of the upper-arm switching element 4a as the reference potential (ground GND_U). Similarly, the upper-arm power supply circuit 9b outputs, as a power supply voltage for controlling the upper-arm switching element 4b, a voltage with the ground GND_V as the reference potential. The upper-arm power supply circuit 9c outputs, as a power supply voltage for controlling the upper-arm switching element 4c, a voltage with the ground GND_W as the reference potential. Each of the upper-arm power supply circuits 9a to 9c may be an isolated DC / DC converter including an isolation transformer as an example.

[0038] The upper arm gate drive circuits 12a to 12c are connected to the first fail-safe circuit 8 and receive power supply from the auxiliary battery 6 and the upper arm power supply circuits 9a to 9c. Then, the upper arm gate drive circuits 12a to 12c drive the gates of the upper arm side switching elements 4a to 4c based on the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 from the first fail-safe circuit 8. More specifically, the upper arm gate drive circuit 12a includes an insulating element such as a photocoupler that transmits a signal while being electrically insulated, and converts the gate drive command Gu_LV2 having the reference potential (ground GND_N1) of the auxiliary battery 6 as the reference potential into a gate drive command GuO_HV having the ground GND_U as the reference potential and outputs it to the gate of the upper arm side switching element 4a. The same applies to the upper arm gate drive circuit 12b and the upper arm gate drive circuit 12c.

[0039] The lower arm power supply circuit 10 receives power supply from the auxiliary battery 6 and converts the power supply voltage of the auxiliary battery 6 having the ground GND_N1 as the reference potential into a power supply voltage VHV_1 (for example, the potential of the ground GND_N2 + 12V) having the ground GND_N2 as the reference potential. The lower arm power supply circuit 10 is an example of the first power supply. Here, the power supply voltage VHV_2 output by the power supply circuit 13 as the second power supply is higher than the power supply voltage VHV_1 output by the lower arm power supply circuit 10 as the first power supply. The lower arm power supply circuit 10 may be an isolated DC / DC converter including an isolation transformer. In a mode where power is not supplied from the DC bus capacitor 3 to the motor drive device 220, the lower arm power supply circuit 10 may receive power supply from the auxiliary battery 6 and generate both the power supply voltage VHV_1 and the power supply voltage VHV_2.

[0040] The power supply voltage VHV_1 from the lower arm power supply circuit 10 and the power supply voltage VHV_2 from the power supply circuit 13 are combined through rectifying elements such as rectifying diodes, respectively, to become the power supply voltage VHV. Here, the power supply voltage VHV_2 from the power supply circuit 13 is input to the rectifying element through a semiconductor switch FET1 such as a MOSFET. The semiconductor switch FET1 turns on when the boost signal VHV_2_ON from the second fail-safe circuit 14 indicates the on state of the power supply voltage VHV_2 (for example, logic L), and turns off when the boost signal VHV_2_ON from the second fail-safe circuit 14 indicates the off state of the power supply voltage VHV_2 (for example, logic H).

[0041] The insulation circuit 17 is connected to the first fail-safe circuit 8 and receives the lower arm short-circuit command Short_ON output by the first fail-safe circuit 8. The insulation circuit 17 includes an insulating element such as a photocoupler, and converts the lower arm short-circuit command Short_ON with the reference potential (ground GND_N1) of the auxiliary battery 6 as the reference potential into the lower arm short-circuit command Short_HV with the ground GND_N2 as the reference.

[0042] The second fail-safe circuit 14 is connected to the insulation circuit 17 and is redundant to receive power supply from the power supply voltage merging point of the first power supply and the second power supply. The second fail-safe circuit 14 cooperates with the first fail-safe circuit 8 to perform fail-safe control including at least one of all-on of the plurality of upper arm side switching elements 4a to 4c or all-on of the plurality of lower arm side switching elements 5a to 5c. In the present embodiment, the first fail-safe circuit 8 and the second fail-safe circuit 14 perform fail-safe control to turn off all of the plurality of upper arm side switching elements 4a to 4c and turn on all of the plurality of lower arm side switching elements 5a to 5c.

[0043] In this embodiment, the first fail-safe circuit 8 and the second fail-safe circuit 14 perform fail-safe control when the power supply from the auxiliary battery 6 is lost, when the rotational speed of the motor PM exceeds the upper limit speed, and when a failure or abnormality of the control circuit 7 is detected by the failure detection circuit 15. The second fail-safe circuit 14 performs fail-safe control on the lower arm gate drive circuits 21a to 21c using the power supply voltage VHV_1 from the lower arm power supply circuit 10 and the lower arm short-circuit command Short_HV from the insulation circuit 17.

[0044] In this embodiment, the second fail-safe circuit 14 detects that the power supply from the auxiliary battery 6 is lost in response to the power supply voltage VHV_1 from the lower arm power supply circuit 10 falling below the lower limit voltage. Then, when the power supply from the auxiliary battery 6 is lost, the second fail-safe circuit 14 performs fail-safe control on the lower arm gate drive circuits 21a to 21c that receive power supply from the DC bus capacitor 3 via the power supply circuit 13. In this embodiment, the second fail-safe circuit 14 sets the gate drive command Gxyz_HV to logic L during normal operation. In the fail-safe control when the power supply from the auxiliary battery 6 is lost, the second fail-safe circuit 14 sets the gate drive command Gxyz_HV to logic H to turn on all of the lower arm side switching elements 5a to 5c.

[0045] Also, when the second fail-safe circuit 14 performs fail-safe control in response to the loss of the power supply from the auxiliary battery 6 or receiving the lower arm short-circuit command Short_HV of logic H, it outputs a boost signal VHV_2_ON (for example, logic L) instructing the turn-on of the power supply voltage VHV_2. Thereby, when performing fail-safe control, the second fail-safe circuit 14 changes the power supply voltage VHV supplied to the lower arm gate drive circuits 21a to 21c from the power supply voltage VHV_1 to the power supply voltage VHV_2.

[0046] The lower arm gate drive circuits 21a to 21c are connected to the first fail-safe circuit 8 and the second fail-safe circuit 14, and receive power supply from the auxiliary battery 6 and the power supply voltage VHV. Then, the lower arm gate drive circuits 21a to 21c drive the gates of the lower arm side switching elements 5a to 5c based on the gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2 from the first fail-safe circuit 8 and the second fail-safe circuit 14. When the gate drive command Gxyz_HV from the second fail-safe circuit 14 is logic L, the lower arm gate drive circuit 21a switches the lower arm side switching element 5a on or off based on the gate drive command Gx_LV2 from the first fail-safe circuit 8, and when the gate drive command Gxyz_HV is logic H, outputs a gate drive command GxO_HV for turning on the lower arm side switching element 5a to the lower arm side switching element 5a. Here, the gate drive command GxO_HV is a signal having the reference potential (ground GND_N2) of the main battery 1 and the DC bus capacitor 3 as the reference potential. Note that the lower arm gate drive circuit 21a generates the gate drive voltage of the gate drive command GxO_HV supplied to the gate when turning on the lower arm side switching element 5a using the power supply voltage VHV. The lower arm gate drive circuit 21b and the lower arm gate drive circuit 21c have the same function.

[0047] Figure 2 shows an example of the configuration of the second fail-safe circuit 14 according to this embodiment. The second fail-safe circuit 14 includes a reference voltage source 250, a comparator 260, and a logic element 270. The reference voltage source 250 generates a reference voltage. In this embodiment, the reference voltage source 250 generates a threshold voltage Vref that serves as a reference for whether the auxiliary battery 6 is normal or not. The comparator 260 has its negative input terminal (inverting input terminal) receiving the power supply voltage VHV_1 from the lower arm power supply circuit 10, and its positive input terminal (non-inverting input terminal) receiving the threshold voltage Vref of the reference voltage source 250. Thereby, the comparator 260 outputs logic L in response to the power supply voltage VHV_1 being higher than the threshold voltage Vref, and outputs logic H as the gate drive command Gxyz_HV in response to the power supply voltage VHV_1 becoming equal to or lower than the threshold voltage Vref (that is, in response to determining that the auxiliary battery 6 has been lost). Thereby, the second fail-safe circuit 14 can perform fail-safe control in response to the power supply voltage VHV_1 output by the lower arm power supply circuit 10 becoming equal to or lower than the threshold voltage Vref. Note that the comparator 260 may have hysteresis.

[0048] The logic element 270 is a negative OR element as an example. The logic element 270 outputs logic H when the gate drive command Gxyz_HV output by the comparator 260 is logic L and the lower arm short-circuit command Short_HV from the insulation circuit 17 is logic L. The logic element 270 outputs logic L when the gate drive command Gxyz_HV output by the comparator 260 becomes logic H or the lower arm short-circuit command Short_HV from the insulation circuit 17 becomes logic H. Thereby, the logic element 270 turns on FET1 when the power supply from the auxiliary battery 6 is lost or when a failure or abnormality of the control circuit 7 is detected by the failure detection circuit 15, and raises the power supply voltage VHV from the power supply voltage VHV_1 output by the lower arm power supply circuit 10 to the power supply voltage VHV_2 output by the power supply circuit 13.

[0049] As a result, during the period when fail-safe control is performed, the lower-arm gate drive circuits 21a to 21c can supply the gate drive voltage supplied to the gates of the lower-arm side switching elements 5a to 5c using the power supply voltage VHV_2 from the power supply circuit 13. Also, during the period when fail-safe control is not performed, the lower-arm gate drive circuits 21a to 21c can supply the gate drive voltage supplied to the gates of the lower-arm side switching elements 5a to 5c using the power supply voltage VHV_1 from the lower-arm power supply circuit 10.

[0050] FIG. 3 shows an example of the configuration of the lower-arm gate drive circuit 21a according to the present embodiment. The lower-arm gate drive circuit 21a includes an insulation circuit 300, an OR element 310, resistors R31 to R32, transistors 320a to 320b, and a resistor R33. The insulation circuit 300 converts a gate drive command Gx_LV2 referenced to the ground GND_N1 into a gate drive command Gx_HV referenced to the ground GND_N2. The OR element 310 outputs the logical sum of the gate drive command Gx_HV from the insulation circuit 300 and the gate drive command Gxyz_HV from the second fail-safe circuit 14. The resistors R31 to R32 are connected between the output terminal of the OR element 310 and the gates of the transistors 320a to 320b and function as gate resistors of the transistors 320a to 320b.

[0051] The transistors 320a to 320b are connected in series in this order between the node where the power supply voltage VHV_2 from the power supply circuit 13 and the power supply voltage VHV_1 from the lower-arm power supply circuit 10 merge and the ground GND_N2 with their main terminals interposed therebetween. The control terminal of the transistor 320a is connected to the terminal of the resistor R31 opposite to the OR element 310, and the control terminal of the transistor 320b is connected to the terminal of the resistor R32 opposite to the OR element 310.

[0052] When the output of the OR element 310 is logic H, the transistors 320a to 320b drive the intermediate node between the transistors 320a to 320b to the power supply voltage VHV, and when the output of the OR element 310 is logic L, the intermediate node is driven to the voltage of the ground GND_N2. The resistor R33 is provided between the intermediate node between the transistors 320a to 320b and the gate of the lower arm side switching element 5a, and outputs the voltage of the intermediate node driven by the transistors 320a to 320b as the gate drive voltage of the lower arm side switching element 5a.

[0053] Thereby, when the gate drive command Gx_LV2 from the first failsafe circuit 8 and the gate drive command Gxyz_HV from the second failsafe circuit 14 are logic L, the lower arm gate drive circuit 21a sets the gate drive voltage of the lower arm side switching element 5a to the voltage of the ground GND_N2, and in response to at least one of the gate drive command Gx_LV2 or the gate drive command Gxyz_HV becoming logic H, the gate drive voltage of the lower arm side switching element 5a can be raised to the power supply voltage VHV. Note that the lower arm gate drive circuits 21b to 21c may have the same configuration as the lower arm gate drive circuit 21a.

[0054] FIG. 4 shows an example of the waveform of the gate drive signal (gate drive command) according to the present embodiment. More specifically, this figure shows the changes over time of the upper arm gate drive commands GuO_HV, GvO_HV, and GwO_HV output by the plurality of upper arm gate drive circuits 12a to 12c, and the lower arm gate drive commands GxO_HV, GyO_HV, and GzO_HV output by the plurality of lower arm gate drive circuits 21a to 21c.

[0055] While the control circuit 7 is operating normally, it outputs gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 to rotationally drive the motor PM by PWM control. While the failure detection circuit 15 detects that the control circuit 7 is operating normally, the first fail-safe circuit 8 outputs the gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 as they are, as gate drive commands Gu_LV2, Gv_LV2, Gw_LV2, Gx_LV2, Gy_LV2, and Gz_LV2, and sets the lower arm short-circuit command Short_ON to logic L.

[0056] The upper arm gate drive circuits 12a - c and the lower arm gate drive circuits 21a - c supply a three-phase alternating current to the motor PM according to the gate drive commands Gu_LV2, Gv_LV2, Gw_LV2, Gx_LV2, Gy_LV2, and Gz_LV2 to rotationally drive the motor PM. Here, during normal operation, the power supply voltage VHV_1 of the auxiliary battery 6 exceeds the threshold voltage Vref of the reference voltage source 250, and the lower arm short-circuit command Short_HV is logic L. Therefore, the second fail-safe circuit 14 sets the boost signal VHV_2_ON to logic H and turns off the FET1. As a result, during the period when the fail-safe control of the motor drive device 220 is not performed, the power supply voltage VHV is the power supply voltage VHV_1 from the lower arm power supply circuit 10. Accordingly, when the lower arm gate drive circuits 21a - c turn on the lower arm side switching elements 5a - c, the gate drive voltage VHV of the lower arm gate drive commands GxO_HV, GyO_HV, and GzO_HV during the period when the fail-safe control is not performed is the power supply voltage VHV_1.

[0057] When the rotational speed of the motor PM exceeds the upper limit speed, or when the failure detection circuit 15 detects an abnormality or failure in the control circuit 7, the first failsafe circuit 8 performs failsafe control to short-circuit the windings of the motor PM. In the failsafe control, the first failsafe circuit 8 sets the upper arm gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 to logic L (low). Accordingly, the upper arm gate drive circuits 12a to 12c turn off all the upper arm side switching elements 4a to 4c.

[0058] Also, in the failsafe control, the first failsafe circuit 8 sets the lower arm gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2 to logic H. Accordingly, the lower arm gate drive circuits 21a to 21c turn on all the lower arm side switching elements 5a to 5c. Here, in such failsafe control, the first failsafe circuit 8 sets the lower arm short-circuit command Short_ON to logic H. In response to this, the second failsafe circuit 14 receives the lower arm short-circuit command Short_HV of logic H and turns on FET1 by setting the boost signal VHV_2_ON to logic L. Therefore, the power supply voltage VHV is boosted from the power supply voltage VHV_1 to the power supply voltage VHV_2. As a result, during the period when the failsafe control is being performed, the lower arm gate drive circuits 21a to 21c supply the gate drive voltage VHV to the gates of the lower arm side switching elements 5a to 5c, which is higher than the gate drive voltage VHV_1 during the period when the failsafe control is not being performed, i.e., VHV_2.

[0059] Here, when the power supply from the auxiliary battery 6 is lost, the power supply voltage VLV supplied to the control circuit 7 and the first fail-safe circuit 8 is lost, and the control circuit 7 and the first fail-safe circuit 8 stop operating. In this case, the second fail-safe circuit 14 detects that the power supply voltage VHV_1 has become equal to or lower than the threshold voltage Vref, sets the gate drive command Gxyz_HV to logic H, sets the boost signal VHV_2_ON to logic L, and turns on the FET1. Accordingly, the power supply voltage VHV is boosted from the power supply voltage VHV_1 to the power supply voltage VHV_2. As a result, the lower arm gate drive circuits 21a to 21c turn on all the lower arm side switching elements 5a to 5c even when the power supply from the auxiliary battery 6 is lost. Then, during the period in which the fail-safe control is performed, the lower arm gate drive circuits 21a to 21c set the gate drive voltage VHV supplied to the gates of the lower arm side switching elements 5a to 5c to a gate drive voltage VHV_2 higher than the gate drive voltage VHV_1 during the period in which the fail-safe control is not performed.

[0060] FIG. 5 shows an example of drain-source voltage characteristics according to the gate voltage of a switching element. This figure shows the relationship between the current (drain current) flowing through the MOSFET and the voltage (drain-source voltage) generated between the main terminals of the MOSFET when the gate voltage (gate-source voltage) is changed to 10V, 12V, …, 20V in a certain MOSFET.

[0061] Switching elements such as n-type IGBTs and MOSFETs that turn on in response to the gate voltage exceeding the threshold have a smaller voltage generated between the main terminals when the same current flows as the gate voltage increases. Since the power consumed by the switching element is the product of the current flowing through the switching element and the voltage between the main terminals, in the case of an n-type switching element, the higher the gate voltage, the lower the power consumption (i.e., the lower the loss) and the lower the heat generation amount.

[0062] As one of the characteristics, the maximum value of the gate-source voltage (or gate-emitter voltage) that can be applied to an n-type switching element is defined in the specifications (for example, the maximum rating of the gate-source voltage). Generally, in order to reduce the failure rate and extend the lifespan of the switching element, the drive circuit of the switching element does not drive the switching element at the maximum-rated gate-source voltage, but provides a certain sufficient margin.

[0063] For example, assume that the maximum rating of the gate-source voltage of a switching element having the characteristics shown in this figure is 20V. When the drive circuit drives the gate-source voltage at 12V to turn on this switching element, when a current of 50A flows through the switching element, a potential difference of approximately 4.7 to 4.8V is generated between the main terminals. In this case, the on-resistance of the switching element is 4.7 to 4.8V / 50A = 0.094 to 0.096Ω, and the power consumption of the switching element is 50A × 4.7 to 4.8V = 235 to 240W.

[0064] On the other hand, when the drive circuit drives the gate-source voltage at 16V to turn on this switching element, when a current of 50A flows through the switching element, a potential difference of approximately 1.4 to 1.5V is generated between the main terminals. In this case, the on-resistance of the switching element is 1.4 to 1.5V / 50A = 0.028 to 0.03Ω, and the power consumption of the switching element is 50A × 1.4 to 1.5V = 70 to 75W.

[0065] As described in relation to FIG. 4, in the lower arm gate drive circuits 21a to 21c according to the present embodiment, during the period when fail-safe control is performed, the gate drive voltage supplied to the gates of the lower arm side switching elements 5a to 5c to be turned on is made higher than the gate drive voltage during the period when fail-safe control is not performed. As a result, during the period when fail-safe control is performed, the lower arm gate drive circuits 21a to 21c reduce the on-resistance of the plurality of lower arm side switching elements 5a to 5c to be turned on compared to the on-resistance during the period when fail-safe control is not performed, and can reduce the power consumption (on-loss) to protect the lower arm side switching elements 5a to 5c from failures due to heat generation and the like.

[0066] Note that the lower arm gate drive circuits 21a to 21c may increase the gate drive voltage supplied to the gates of the lower arm side switching elements 5a to 5c to be turned on only during a part of the period when fail-safe control is performed, compared to the gate drive voltage during the period when fail-safe control is not performed, so as to further reduce the on-resistance. For example, the motor drive device 220 may boost the power supply voltage VHV to the power supply voltage VHV_2 for a predetermined period from the start of fail-safe control, and return to the power supply voltage VHV_1 even during fail-safe control after the elapse of the predetermined period. According to this method, the lower arm gate drive circuits 21a to 21c can reduce the on-resistance of the lower arm side switching elements 5a to 5c while the rotational speed of the motor PM is high immediately after the start of fail-safe control, and can protect the lower arm side switching elements 5a to 5c from failures due to heat generation and the like.

[0067] Conversely, the motor drive device 220 may maintain the power supply voltage VHV at the power supply voltage VHV_1 for a predetermined period from the start of the fail-safe control, and may boost the power supply voltage VHV to VHV_2 if the fail-safe control is still in progress after the elapse of the predetermined period. According to this method, when the fail-safe control continues beyond the predetermined period after starting the fail-safe control, the lower arm gate drive circuits 21a to 21c can reduce the on-resistance of the lower arm side switching elements 5a to 5c at that time, and can suppress further heat generation of the lower arm side switching elements 5a to 5c to some extent.

[0068] Further, the motor drive device 220 may increase the power supply voltage VHV to the power supply voltage VHV_2 on the condition that the current flowing through at least one of the lower arm side switching elements 5 exceeds the threshold current, or the rotational speed of the motor PM exceeds the threshold, etc. during at least a part of the period in which the fail-safe control is performed. As a result, during at least a part of the period in which the fail-safe control is performed, the lower arm gate drive circuits 21a to 21c reduce the on-resistance of the lower arm side switching elements 5a to 5c in response to such a condition being satisfied, compared to the on-resistance during the period in which the fail-safe control is not performed. According to such a method, the motor drive device 220 increases the gate drive voltage on the condition that the current flowing through the lower arm side switching element 5 is excessive due to, for example, a high rotational speed of the motor PM, and can suppress heat generation of the lower arm side switching element 5.

[0069] Further, the lower arm gate drive circuits 21a to 21c may reduce the on-resistance of the lower arm side switching elements 5a to 5c to be turned on during at least a part of the period in which the fail-safe control is performed, as compared with the on-resistance during at least a part of the period in which the fail-safe control is not performed. For example, the lower arm gate drive circuits 21a to 21c may further have a function of reducing the on-resistance of the switching elements to be turned on among the lower arm side switching elements 5a to 5c even during a part of the period in which the fail-safe control is not performed. In such a configuration, the resistance value of the on-resistance of the lower arm side switching element 5 to be turned on during a part of the period in which the fail-safe control is not performed by the lower arm gate drive circuits 21a to 21c may be equal to or less than the resistance value of the on-resistance of the lower arm side switching elements 5a to 5c during the period in which the fail-safe control is performed.

[0070] Further, the motor drive device 220 does not necessarily reduce the on-resistance of all of the lower arm side switching elements 5a to 5c during the period in which the fail-safe control is performed, and may reduce the on-resistance of at least one of the lower arm side switching elements 5. For example, the motor drive device 220 may measure the temperature of each lower arm side switching element 5, and reduce the on-resistance of only the lower arm side switching element 5 whose temperature exceeds the threshold value.

[0071] Note that the electric machine system 200 may use, as the lower arm side switching elements 5a to 5c, a p-type MOSFET or the like that turns on in response to a gate drive voltage less than the threshold voltage being supplied to the gate. In this case, the motor drive device 220 may reduce the on-resistance of the lower arm side switching elements 5a to 5c by making the gate drive voltage supplied to the gates of the lower arm side switching elements 5a to 5c to be turned on lower than the gate drive voltage during at least a part of the period in which the fail-safe control is not performed, during at least a part of the period in which the fail-safe control is performed.

[0072] FIG. 6 shows the configuration of an electric machine system 600 according to a modified example of the present embodiment. The electric machine system 600 includes a main battery 1, a switch 2, a DC bus capacitor 3, an auxiliary battery 6, a motor PM, one or more current sensors 100, an angle sensor 101, an inverter 210, and a motor drive device 220. Here, for each component other than the motor drive device 220, it has the same function and configuration as the component with the same reference numeral in the electric machine system 200 shown in FIG. 1, so the description is omitted except for the differences.

[0073] The motor drive device 220 includes a control circuit 7, a first fail-safe circuit 8, a fault detection circuit 15, a plurality of upper arm power supply circuits 9a to 9c, a plurality of upper arm gate drive circuits 12a to 12c, a gate drive power supply circuit 617, and a plurality of lower arm gate drive circuits 21a to 21c. Each of these components has the same or similar function and configuration as the component with the same reference numeral in the electric machine system 200 shown in FIG. 1, so the description is omitted except for the following differences.

[0074] The first fail-safe circuit 8 performs fail-safe control on the upper arm gate drive circuits 12a to 12c and the lower arm gate drive circuits 21a to 21c using at least one of the detection signal from the angle sensor 101 and the signal from the fault detection circuit 15. In fail-safe control, the first fail-safe circuit 8 alternately performs an operation of turning on all of the plurality of upper arm side switching elements 4a to 4c with the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 being logic H and the gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2 being logic L, and an operation of turning on all of the plurality of lower arm side switching elements 5a to 5c with the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 being logic L and the gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2 being logic H. Also, when not performing fail-safe control, the first fail-safe circuit 8 sets the upper arm short-circuit command Short_U and the lower arm short-circuit command Short_L to logic L, and sets the upper arm short-circuit command Short_U and the lower arm short-circuit command Short_L to logic H in fail-safe control.

[0075] Each of the upper arm power circuits 9a to 9c receives power supply from the auxiliary battery 6, and converts the power supply voltage from the auxiliary battery 6 into power supply voltages (VHV_u, VHV_v, and VHV_w) for controlling each of the upper arm side switching elements 4a to 4c. In this modification, each of the upper arm power circuits 9a to 9c outputs the power supply voltage VHV_1 as the power supply voltage for controlling each of the upper arm side switching elements 4a to 4c when the upper arm short-circuit command Short_U is logic L, and outputs the power supply voltage VHV_2 when the upper arm short-circuit command Short_U is logic H.

[0076] The upper arm gate drive circuits 12a to 12c are connected to the first fail-safe circuit 8 and receive power supply from the auxiliary battery 6 and the upper arm power circuits 9a to 9c. Then, the upper arm gate drive circuits 12a to 12c drive the gates of the upper arm side switching elements 4a to 4c based on the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 from the first fail-safe circuit 8 and the upper arm short-circuit command Short_U. In this modification, the upper arm gate drive circuits 12a to 12c reduce the switching speed of the upper arm side switching elements 4a to 4c during at least a part of the period when fail-safe control is performed, compared to the switching speed during at least a part of the period when fail-safe control is not performed, based on the upper arm short-circuit command Short_U.

[0077] The gate drive power circuit 617 receives power supply from the auxiliary battery 6, and converts the power supply voltage of the auxiliary battery 6 with the ground GND_N1 as the reference potential into a power supply voltage VHV_xyz with the ground GND_N2 as the reference potential. Here, the gate drive power circuit 617 sets the power supply voltage VHV_xyz as the power supply voltage VHV_1 when the upper arm short-circuit command Short_U from the first fail-safe circuit 8 is logic L, and sets the power supply voltage VHV_xyz as the power supply voltage VHV_2 when the upper arm short-circuit command Short_U from the first fail-safe circuit 8 is logic H.

[0078] The lower arm gate drive circuits 21a to 21c are connected to the first fail-safe circuit 8 and receive power supplies from the auxiliary battery 6 and the gate drive power supply circuit 617. Then, the lower arm gate drive circuits 21a to 21c drive the gates of the lower arm side switching elements 5a to 5c based on the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 from the first fail-safe circuit 8. In this modified example, the lower arm gate drive circuits 21a to 21c lower the switching speed of the lower arm side switching elements 5a to 5c during at least a part of the period when fail-safe control is performed, compared to the switching speed during at least a part of the period when fail-safe control is not performed, based on the lower arm short circuit command Short_L.

[0079] FIG. 7 shows an example of the configuration of the upper arm gate drive circuit 12a according to a modified example of the present embodiment. The upper arm gate drive circuit 12a includes a gate driver 700, an insulating element 710, a logical negation element 720, a plurality of switches 730a to 730b, and a plurality of resistors 740a to 740b.

[0080] The gate driver 700 receives the supply of the power supply voltage VLV from the auxiliary battery 6 and the power supply voltage VHV_u from the upper arm power supply circuit 9a. The gate driver 700 is connected to the first fail-safe circuit 8 and receives the gate drive command Gu_LV2 output by the first fail-safe circuit 8. The gate driver 700 includes an insulating circuit such as the insulating circuit 300 shown in FIG. 3 as an example, and converts the gate drive command Gu_LV2 having the reference potential (ground GND_N1) of the auxiliary battery 6 as the reference potential into a gate drive command having the ground GND_U as the reference. Further, the gate driver 700 includes a drive circuit such as the transistors 320a to 320b shown in FIG. 3 as an example, and outputs a gate drive command GuO_HV for driving the gate of the upper arm side switching element 4a based on the gate drive command converted with the ground GND_U as the reference.

[0081] The insulating element 710 is connected to the first fail-safe circuit 8 and receives the upper arm short-circuit command Short_U output by the first fail-safe circuit 8. The insulating element 710 includes an insulating element such as a photocoupler, and converts the upper arm short-circuit command Short_U with the reference potential of the auxiliary battery 6 (ground GND_N1) as the reference potential into an upper arm short-circuit command with ground GND_U as the reference. The logical negation element 720 inverts the logical value of the upper arm short-circuit command Short_U converted by the insulating element 710.

[0082] The switch 730a is connected between the gate driver 700 and the resistor 740a, and switches whether to output the gate drive command GuO_HV output by the gate driver 700 to the upper arm side switching element 4a via the resistor 740a. Here, the switch 730a turns on when the output of the logical negation element 720 is logical H, that is, when the upper arm short-circuit command Short_U is logical L, and turns off when the upper arm short-circuit command Short_U is logical H.

[0083] The switch 730b is connected between the gate driver 700 and the resistor 740b, and switches whether to output the gate drive command GuO_HV output by the gate driver 700 to the upper arm side switching element 4a via the resistor 740b. Here, the switch 730b turns on when the output of the insulating element 710 is logical H, that is, when the upper arm short-circuit command Short_U is logical H, and turns off when the upper arm short-circuit command Short_U is logical L.

[0084] Each of the plurality of resistors 740a~b is connected between the corresponding switch 730 among the plurality of switches 730a~b and the upper arm side switching element 4a. Each of the plurality of resistors 740a~b is connected between the gate driver 700 and the upper arm side switching element 4a in response to the corresponding switch 730 being turned on, and functions as the gate resistor of the upper arm side switching element 4a.

[0085] The resistor 740a functions as the gate resistor of the upper-arm side switching element 4a as the switch 730a turns on during the period when fail-safe control is not performed (the period when the upper-arm short-circuit command Short_U is at logic L). The resistor 740b functions as the gate resistor of the upper-arm side switching element 4a as the switch 730b turns on during the period when fail-safe control is performed (the period when the upper-arm short-circuit command Short_U is at logic H).

[0086] The resistor 740b used during the period when fail-safe control is performed has a larger resistance value than the resistor 740a used during the period when fail-safe control is not performed. Therefore, the upper-arm gate drive circuit 12a can make the gate resistor (i.e., the resistor 740b) connected to the gate of the upper-arm side switching element 4a larger than the gate resistor (i.e., the resistor 740a) during the period when fail-safe control is not performed during the period when fail-safe control is performed.

[0087] Here, the larger the gate resistor, the smaller the gate current and the lower the rising and falling speeds of the gate voltage of the upper-arm side switching element 4a. Therefore, the upper-arm gate drive circuit 12a can reduce the switching speed of the upper-arm side switching element 4a during the period when fail-safe control is performed compared to the switching speed during the period when fail-safe control is not performed.

[0088] In this modification, the upper-arm gate drive circuits 12b to c may have the same functions and configurations as the upper-arm gate drive circuit 12a. Also, the lower-arm gate drive circuits 21a to c may also reduce the switching speed of the lower-arm side switching elements 5a to c during the period when fail-safe control is performed compared to the switching speed during the period when fail-safe control is not performed, in the same manner as the upper-arm gate drive circuit 12a.

[0089] As described above, according to the motor drive device 220 according to this modification example, in the fail-safe control, the on-resistances of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c are reduced as compared with the on-resistances when the fail-safe control is not performed. Thereby, the motor drive device 220 can suppress the heat generation of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c during the fail-safe control.

[0090] Also, according to the motor drive device 220 according to this modification example, when the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c are alternately turned on completely in the fail-safe control, the gate resistances connected to the respective ones of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c are made larger as compared with the gate resistances when the fail-safe control is not performed. Thereby, even when a current exceeding the current flowing during normal motor drive flows through the motor PM, the motor drive device 220 reduces the switching speed of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c when switching the full-phase short circuit of the upper and lower arms, and can prevent a large surge voltage from occurring.

[0091] FIG. 8 shows an example of the waveform of the gate drive signal according to the modification example of the present embodiment. More specifically, this figure shows the changes over time of the upper-arm gate drive commands GuO_HV, GvO_HV, and GwO_HV output by the plurality of upper-arm gate drive circuits 12a to 12c and the lower-arm gate drive commands GxO_HV, GyO_HV, and GzO_HV output by the plurality of lower-arm gate drive circuits 21a to 21c in the electric machine system 600.

[0092] While the control circuit 7 is operating normally, it outputs gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 for rotationally driving the motor PM by PWM control. While the failure detection circuit 15 detects that the control circuit 7 is operating normally, the first fail-safe circuit 8 outputs the gate drive commands Gu_LV1, Gv_LV1, Gw_LV1, Gx_LV1, Gy_LV1, and Gz_LV1 as they are, as gate drive commands Gu_LV2, Gv_LV2, Gw_LV2, Gx_LV2, Gy_LV2, and Gz_LV2, and sets the upper arm short-circuit command Short_U and the lower arm short-circuit command Short_L to logic L.

[0093] The upper arm gate drive circuits 12a - c and the lower arm gate drive circuits 21a - c supply a three-phase alternating current to the motor PM according to the gate drive commands Gu_LV2, Gv_LV2, Gw_LV2, Gx_LV2, Gy_LV2, and Gz_LV2 to rotationally drive the motor PM. Here, during normal operation, the upper arm power supply circuits 9a - c supply the power supply voltage VHV_1 with respect to the reference potentials GND_U, GND_V, and GND_W for each phase to the upper arm gate drive circuits 12a - c according to the upper arm short-circuit command Short_U being logic L. Also, during normal operation, the gate drive power supply circuit 617 supplies the power supply voltage VHV_1 with respect to the reference potential GND_N2 to the lower arm gate drive circuits 21a - c according to the lower arm short-circuit command Short_L being logic L. Therefore, when the plurality of upper arm gate drive circuits 12a - c and the plurality of lower arm gate drive circuits 21a - c turn on the plurality of upper arm side switching elements 4a - c and the plurality of lower arm side switching elements 5a - c, the gate drive voltages of the upper arm gate drive commands GuO_HV, GvO_HV, and GwO_HV and the gate drive voltages of the lower arm gate drive commands GxO_HV, GyO_HV, and GzO_HV during the period when fail-safe control is not performed are set to the power supply voltage VHV_1.

[0094] Here, when the upper-arm short-circuit command Short_U is logic L, the upper-arm gate drive circuit 12a selects the resistor 740a with a smaller resistance value among the plurality of resistors 740a to b as the gate resistor of the upper-arm side switching element 4a. Similarly, the upper-arm gate drive circuits 12b to c and the lower-arm gate drive circuits 21a to c also select the resistor with a smaller resistance value among the plurality of resistors as the gate resistors of the upper-arm side switching elements 4b to c and the lower-arm side switching elements 5a to c.

[0095] When the rotational speed of the motor PM exceeds the upper limit speed, or when the failure detection circuit 15 detects an abnormality or failure of the control circuit 7, the first fail-safe circuit 8 performs fail-safe control to short-circuit the windings of the motor PM. In the fail-safe control, the first fail-safe circuit 8 alternately performs an operation of turning on all of the plurality of upper-arm side switching elements 4a to c with the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 being logic H and the gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2 being logic L, and an operation of turning on all of the plurality of lower-arm side switching elements 5a to c with the gate drive commands Gu_LV2, Gv_LV2, and Gw_LV2 being logic L and the gate drive commands Gx_LV2, Gy_LV2, and Gz_LV2 being logic H.

[0096] The first fail-safe circuit 8 sets the upper arm short-circuit command Short_U and the lower arm short-circuit command Short_L to logic H in fail-safe control. The upper arm power supply circuits 9a to 9c supply the power supply voltage VHV_2 based on the respective phase reference potentials GND_U, GND_V, and GND_W to the upper arm gate drive circuits 12a to 12c in response to the upper arm short-circuit command Short_U being logic H. Also, the gate drive power supply circuit 617 supplies the power supply voltage VHV_2 based on the reference potential GND_N2 to the lower arm gate drive circuits 21a to 21c in response to the lower arm short-circuit command Short_L being logic H. Therefore, when all of the plurality of upper arm side switching elements 4a to 4c are turned on and when all of the plurality of lower arm side switching elements 5a to 5c are turned on during the period when fail-safe control is performed, the plurality of upper arm gate drive circuits 12a to 12c and the plurality of lower arm gate drive circuits 21a to 21c boost the gate drive voltages of the upper arm gate drive commands GuO_HV, GvO_HV, and GwO_HV and the gate drive voltages of the lower arm gate drive commands GxO_HV, GyO_HV, and GzO_HV to the power supply voltage VHV_2.

[0097] Also, the upper arm gate drive circuit 12a selects the resistor 740b with a larger resistance value among the plurality of resistors 740a to 740b as the gate resistor of the upper arm side switching element 4a in response to the upper arm short-circuit command Short_U being logic H. Similarly, the upper arm gate drive circuits 12b to 12c and the lower arm gate drive circuits 21a to 21c also select the resistor with a larger resistance value among the plurality of resistors as the gate resistors of the upper arm side switching elements 4b to 4c and the lower arm side switching elements 5a to 5c.

[0098] In this way, in the fail-safe control, the motor drive device 220 according to this modification example can reduce the on-resistances of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c as compared with the on-resistances when fail-safe control is not performed. Further, the motor drive device 220 can increase the gate resistances connected to the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c as compared with the gate resistances when fail-safe control is not performed.

[0099] In this modification example, the first fail-safe circuit 8 sets the upper-arm short-circuit command Short_U and the lower-arm short-circuit command Short_L to logic H during fail-safe control. Alternatively, the first fail-safe circuit 8 may set the upper-arm short-circuit command Short_U to logic H from the start of turn-on to the end of turn-off of the plurality of upper-arm side switching elements 4a to 4c, and set the upper-arm short-circuit command Short_U to logic L from the end of turn-off of the plurality of upper-arm side switching elements 4a to 4c to the start of the next turn-on. Similarly, the first fail-safe circuit 8 may set the lower-arm short-circuit command Short_L to logic H from the start of turn-on to the end of turn-off of the plurality of lower-arm side switching elements 5a to 5c, and set the upper-arm short-circuit command Short_L to logic L from the end of turn-off of the plurality of lower-arm side switching elements 5a to 5c to the start of the next turn-on.

[0100] Further, the motor drive device 220 may have only one of the function of further reducing the on-resistance of the switching element in fail-safe control and the function of further increasing the gate resistance of the switching element in fail-safe control. For example, the motor drive device 220 may have only the function of further increasing the gate resistance of the switching element in fail-safe control among these functions.

[0101] Further, the motor drive device 220 may adopt various alternatives described in relation to FIG. 4 with respect to the function of further reducing the on-resistance of the switching element in the fail-safe control. Also, the motor drive device 220 may adopt the same or similar alternatives as the various alternatives described in relation to FIG. 4 with respect to the function of increasing the gate resistance of the switching element in the fail-safe control.

[0102] For example, the upper arm gate drive circuits 12a to 12c and the lower arm gate drive circuits 21a to 21c may reduce the switching speed of the switching elements to be turned on among the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c during at least a part of the period in which the fail-safe control is performed, as compared with the switching speed during the period in which the fail-safe control is not performed. For example, the motor drive device 220 sets the upper arm short-circuit command Short_U and the lower arm short-circuit command Short_L to logic H for a predetermined period from the start of the fail-safe control, and increases the gate resistance of the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c, for example, by using the switch 730b. After the elapse of the predetermined period, even during the fail-safe control, the upper arm short-circuit command Short_U and the lower arm short-circuit command Short_L are set to logic L, and the gate resistance of the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c may be returned to, for example, the switch 730a. According to this method, the lower arm gate drive circuits 21a to 21c can reduce the switching speed of the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c while the rotational speed of the motor PM is high and a large surge voltage may be generated immediately after the start of the fail-safe control, and can prevent an overvoltage from being applied to the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c.

[0103] Also, during the period when fail-safe control is performed, the motor drive device 220 increases the gate resistances of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c during the turn-on period or turn-off period for switching the on / off states of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c. During the steady period when the on / off states of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c are not switched, even during fail-safe control, the gate resistances of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c may be restored to their original values.

[0104] Also, the motor drive device 220 may increase the gate resistances of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c on the condition that, for example, the current flowing through at least one lower-arm side switching element 5 exceeds a threshold current or the rotational speed of the motor PM exceeds a threshold during at least a part of the period when fail-safe control is performed. As a result, the upper-arm gate drive circuits 12a to 12c and the lower-arm gate drive circuits 21a to 21c reduce the switching speed of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c during at least a part of the period when fail-safe control is performed in response to such conditions being satisfied, compared to the switching speed during the period when fail-safe control is not performed. According to such a method, the motor drive device 220 reduces the switching speed of the plurality of upper-arm side switching elements 4a to 4c and the plurality of lower-arm side switching elements 5a to 5c on the condition that the current flowing through the lower-arm side switching element 5 is excessive due to, for example, a high rotational speed of the motor PM, and can suppress the surge voltage.

[0105] Further, the upper arm gate drive circuits 12a to 12c and the lower arm gate drive circuits 21a to 21c may increase the gate resistances of the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c during at least a part of the period in which the fail-safe control is performed, as described above, compared to the gate resistances during at least a part of the period in which the fail-safe control is not performed. For example, the upper arm gate drive circuits 12a to 12c and the lower arm gate drive circuits 21a to 21c may further have a function of increasing the gate resistance of the switching element even in another part of the period in which the fail-safe control is not performed. In such a configuration, the resistance values of the gate resistances of the switching elements in another part of the period in which the fail-safe control is not performed by the upper arm gate drive circuits 12a to 12c and the lower arm gate drive circuits 21a to 21c may be equal to or greater than the resistance values of the gate resistances of the switching elements increased during the period in which the fail-safe control is performed.

[0106] Also, the motor drive device 220 does not necessarily increase the gate resistances of all of the plurality of upper arm side switching elements 4a to 4c and the plurality of lower arm side switching elements 5a to 5c during the period in which the fail-safe control is performed, and may increase only the gate resistance of at least one switching element. For example, the motor drive device 220 may measure the current flowing through each switching element, and turn off the switching element after increasing the gate resistance only for the switching element through which a current exceeding the threshold value is flowing.

[0107] Various embodiments of the present invention may be described with reference to flowcharts and block diagrams, where the blocks may represent (1) stages of a process in which operations are performed or (2) sections of an apparatus having a role of performing operations. Specific stages and sections may be implemented by dedicated circuits, programmable circuits supplied with computer-readable instructions stored on a computer-readable medium, and / or processors supplied with computer-readable instructions stored on a computer-readable medium. The dedicated circuits may include digital and / or analog hardware circuits, and may include integrated circuits (ICs) and / or discrete circuits. The programmable circuits may include reconfigurable hardware circuits including memory elements such as logical AND, logical OR, logical XOR, logical NAND, logical NOR, and other logical operations, flip-flops, registers, field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), etc.

[0108] The computer-readable medium may include any tangible device capable of storing instructions executable by an appropriate device, such that a computer-readable medium having instructions stored therein will comprise a product including instructions executable to create means for performing the operations specified in the flowchart or block diagram. Examples of computer-readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, etc. More specific examples of computer-readable media may include floppy (registered trademark) disks, diskettes, hard disks, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM or flash memory), electrically erasable programmable read only memory (EEPROM), static random access memory (SRAM), compact disk read only memory (CD-ROM), digital versatile disk (DVD), Blu-ray (registered trademark) disk, memory stick, integrated circuit card, etc.

[0109] Computer-readable instructions may include any combination of one or more programming languages, including assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state-setting data, or source code or object code written in object-oriented programming languages such as Smalltalk®, JAVA®, C++, and conventional procedural programming languages such as the "C" programming language or similar programming languages.

[0110] Computer-readable instructions may be provided locally or via a wide area network (WAN) such as a local area network (LAN), the Internet, etc. to a processor or programmable circuit of a programmable data processing apparatus such as a general-purpose computer, a special-purpose computer, or other computer, and the computer-readable instructions may be executed to create means for performing the operations specified in a flowchart or block diagram. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, etc.

[0111] As described above, the present invention has been described using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that forms with such changes or improvements may also be included in the technical scope of the present invention.

[0112] In the claims, the specification, and the drawings, the execution order of each process such as operations, procedures, steps, and stages in the apparatus, system, program, and method shown is not explicitly stated as "before" or "preceding" etc., and it should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if it is described for convenience using "first," "next," etc., it does not mean that it is essential to be implemented in this order.

Explanation of Reference Signs

[0113] 1 Main battery 2 Switch 3 DC bus capacitor 4a - c Upper arm side switching element 5a - c Lower arm side switching element 6 Auxiliary battery 7 Control circuit 8 First fail - safe circuit 9a - c Upper arm power circuit 10 Lower arm power circuit 12a - c Upper arm gate drive circuit 13 Power circuit 14 Second fail - safe circuit 15 Fault detection circuit 17 Insulation circuit 21a - c Lower arm gate drive circuit 100 Current sensor 101 Angle sensor 200 Electric machine system 210 Inverter 220 Motor drive device 250 Reference voltage source 260 Comparator 270 Logic element 300 Insulation circuit 310 OR element 320a - b Transistor 600 Electric machine system 617 Gate drive power circuit 700 Gate Driver 710 Insulating Element 720 Logical Negation Element 730a~b Switch 740a~b Resistor

Claims

1. A gate drive unit that drives a plurality of upper-arm side switching elements and a plurality of lower-arm side switching elements included in an inverter for driving a motor, A fail-safe unit that performs fail-safe control including at least one of all-on of the plurality of upper-arm side switching elements or all-on of the plurality of lower-arm side switching elements, A first power source, A second power source that outputs a power supply voltage higher than that of the first power source are provided, During at least a part of the period in which the fail-safe control is performed, the gate drive unit reduces the on-resistance of at least one switching element among the plurality of upper-arm side switching elements or the plurality of lower-arm side switching elements to be all-on, compared with the on-resistance during at least a part of the period in which the fail-safe control is not performed, The gate drive unit, During at least a part of the period in which the fail-safe control is performed, supplies a gate drive voltage supplied to the gate of the at least one switching element using the power supply voltage from the second power source, During at least a part of the period in which the fail-safe control is not performed, supplies a gate drive voltage supplied to the gate of the at least one switching element using the power supply voltage from the first power source, The fail-safe unit performs the fail-safe control in response to the power supply voltage output by the first power source becoming equal to or lower than a threshold voltage Motor drive device.

2. Each of the plurality of upper-arm side switching elements and the plurality of lower-arm side switching elements turns on in response to a gate drive voltage exceeding a threshold voltage being supplied to the gate, During at least a part of the period in which the fail-safe control is performed, the gate drive unit makes the gate drive voltage supplied to the gate of the at least one switching element higher than the gate drive voltage during at least a part of the period in which the fail-safe control is not performed The motor drive device according to Claim 1.

3. The motor drive device according to Claim 1, wherein the second power source is connected to a DC bus of the inverter.

4. The gate drive unit reduces the on-resistance of the at least one switching element during at least a part of the period in which the fail-safe control is performed, as compared with the on-resistance during the period in which the fail-safe control is not performed. The motor drive device according to any one of claims 1 to 3.

5. The gate drive unit reduces the on-resistance of the at least one switching element during at least a part of the period in which the fail-safe control is performed, on the condition that the current flowing through the at least one switching element exceeds a threshold current, as compared with the on-resistance during at least a part of the period in which the fail-safe control is not performed. The motor drive device according to any one of claims 1 to 4.

6. In the fail-safe control, the fail-safe unit turns on all of the plurality of upper-arm side switching elements and the plurality of lower-arm side switching elements alternately. The motor drive device according to any one of claims 1 to 5.

7. The gate drive unit reduces the on-resistance of each switching element that is turned on all at once among the plurality of upper-arm side switching elements and the plurality of lower-arm side switching elements during at least a part of the period in which the fail-safe control is performed, as compared with the on-resistance during at least a part of the period in which the fail-safe control is not performed. The motor drive device according to claim 6.

8. The gate drive unit reduces the switching speed of the at least one switching element during at least a part of the period in which the fail-safe control is performed, as compared with the switching speed during at least a part of the period in which the fail-safe control is not performed. The motor drive device according to any one of claims 1 to 6.

9. The gate drive unit increases the gate resistance connected to the gate of the at least one switching element during at least a part of the period in which the fail-safe control is performed, as compared with the gate resistance during at least a part of the period in which the fail-safe control is not performed. The motor drive device according to claim 8.

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