Electric circuit

Abstract

To warm up a battery.SOLUTION: An electric circuit includes a battery, a motor, an inverter connected between the battery and the motor, and a control device. The inverter includes a smoothing capacitor connected between a high-potential input wiring and a low-potential input wiring, and a plurality of series switch circuits connected between the high-potential input wiring and the low-potential input wiring. When the control device receives a warm-up command while a vehicle is stopped, the control device executes a warm-up operation of controlling one of an upper switching element and a lower switching element in at least one of the series switch circuits to a regular on-state and controlling the other of the upper switching element and the lower switching element to a high-loss on-state in which a loss higher than a loss in the regular on-state occurs.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an electric circuit mounted on a vehicle.

[0002] Patent Document 1 discloses a vehicle that runs on battery power. This vehicle has a motor and an inverter. The inverter converts DC power supplied by the battery into AC power and supplies it to the motor to drive it.

[0003] It is known that a drop in battery temperature leads to a drop in the battery's charge / discharge performance. The vehicle of Patent Document 1 flows a d-axis current through the motor to warm up the battery when the vehicle is stopped and the battery temperature is low. By flowing a d-axis current, the battery can be discharged without rotating the motor. The self-heating caused by battery discharge can increase the battery temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-165526 Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology of Patent Document 1, the q-axis current is controlled to zero when the d-axis current is passed, but an error generates a small q-axis current, which generates a small torque in the motor. As a result, noise occurs during the warm-up operation. This specification proposes a technology for more optimally warming up the battery. [Means for solving the problem]

[0006] The electric circuit disclosed in this specification is mounted on a vehicle. The electric circuit includes a battery, a motor, an inverter connected between the battery and the motor, and a control device. The inverter includes a high-potential input wiring, a low-potential input wiring, multiple output wirings connected to the motor, a smoothing capacitor connected between the high-potential input wiring and the low-potential input wiring, and multiple series switch circuits connected between the high-potential input wiring and the low-potential input wiring. Each of the series switch circuits includes an upper switching element connected between the high-potential input wiring and the corresponding output wiring, and a lower switching element connected between the corresponding output wiring and the low-potential input wiring. When the control device receives a warm-up command while the vehicle is stopped, it executes a warm-up operation in at least one of the series switch circuits, controlling one of the upper switching element and the lower switching element to a normally-on state and controlling the other of the upper switching element and the lower switching element to a high-loss-on state in which a loss is higher than that of the normally-on state.

[0007] In this electrical circuit, when battery warm-up is required, the control device controls one of the upper switching element and the lower switching element in at least one series switch circuit to normally-on and the other to high-loss-on. The normally-on switching element and the high-loss-on switching element connect the high-potential input wiring and the low-potential input wiring, allowing the smoothing capacitor to discharge through these switching elements. At this time, high losses occur in the switching element controlled to high-loss-on, causing it to generate heat. The heat generated by the switching element can raise the temperature of the battery. Furthermore, because the discharge path in this case does not pass through the motor, torque generation in the motor can be suppressed. Therefore, the battery can be warmed up while suppressing noise generation in the motor. [Brief explanation of the drawings]

[0008] [Figure 1] Schematic diagram of an electrical circuit. [Figure 2] 2 is a diagram showing a cooling system for cooling the battery 12 and the inverter 30. FIG. [Figure 3] 6 is a graph showing control signals for switching elements 35UU and 35UL during a warm-up operation in the first embodiment. [Figure 4] 4 is a graph showing the gate potential of each switching element during a warm-up operation in the first embodiment. [Figure 5] 6 is a graph showing a change in gate potential when switching between a first operation and a second operation in Example 1. [Figure 6] 10 is a graph showing a change in gate potential when switching between a first operation and a second operation in a modification of the first embodiment. [Figure 7] FIG. 10 is a circuit diagram of an electric circuit according to a modified example. [Figure 8] 10 is a graph showing the gate potential of each switching element during a warm-up operation in the second embodiment. [Figure 9] 10 is a graph showing a change in gate potential when switching between the first operation and the second operation in Example 2. [Figure 10] FIG. 10 is a circuit diagram of a gate drive circuit according to a third embodiment. [Figure 11] 10 is a graph showing the gate potential of each switching element during a warm-up operation in the third embodiment. [Figure 12] FIG. 10 is a circuit diagram of a gate drive circuit according to a fourth embodiment. [Figure 13] 10 is a graph showing the gate potential of a switching element during a warm-up operation in Example 4. [Figure 14] FIG. 10 is a circuit diagram of a gate drive circuit according to a fifth embodiment. [Figure 15] 10 is a graph showing the gate potential of the switching element during the operation of rotating the motor of Example 5. [Figure 16] 10 is a graph showing the gate potential and drain-source voltage of the switching element during high-loss on-state in Example 5. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0009] The electric circuit 10 shown in FIG. 1 is mounted on a vehicle. The electric circuit 10 has a battery 12, an inverter 30, a motor 80, and a control device 90. The battery 12 is the main battery of the vehicle and outputs DC power. The motor 80 is a three-phase motor that rotates the drive wheels of the vehicle. The inverter 30 converts the DC power supplied from the battery 12 into AC power and supplies it to the motor 80. This causes the motor 80 to rotate the drive wheels and the vehicle to run. The control device 90 controls each part of the electric circuit 10. The control device 90 may be configured by a single circuit board, or may be configured by multiple circuit boards arranged in physically separate locations.

[0010] A battery temperature sensor 14 is attached to the battery 12. The battery temperature sensor 14 detects the temperature Tb of the battery 12. The value of the temperature Tb detected by the battery 12 is input to a comparator 16. When the temperature Tb is lower than a threshold value Tth, the comparator 16 sends a warm-up command to the control device 90.

[0011] The motor 80 has three windings, one end of each winding connected to a neutral point 86. The other end of each winding is connected to a corresponding input terminal of the motor 80.

[0012] The inverter 30 has a high-potential input wiring 31, a low-potential input wiring 32, and three output wirings 33U, 33V, and 33W. The high-potential input wiring 31 is connected to the positive electrode of the battery 12. The low-potential input wiring 32 is connected to the negative electrode of the battery 12. Although the high-potential input wiring 31 and the low-potential input wiring 32 are directly connected to the battery 12 in FIG. 1, the high-potential input wiring 31 and the low-potential input wiring 32 may be connected to the battery 12 via another circuit (e.g., a DC-DC converter). A smoothing capacitor 38 is connected between the high-potential input wiring 31 and the low-potential input wiring 32. Each of the output wirings 33U, 33V, and 33W is connected to a corresponding input terminal of the motor 80. The output wirings 33U, 33V, and 33W are connected to a neutral point 86 via windings inside the motor 80. A current sensor is provided for each of the output wirings 33U, 33V, and 33W. The current sensors detect the currents IU, IV, and IW flowing through the output wirings 33U, 33V, and 33W, respectively. The values ​​of the currents IU, IV, and IW detected by the current sensors are input to the control device 90.

[0013] The inverter 30 has three series switch circuits 34U, 34V, and 34W connected between a high-potential input wiring 31 and a low-potential input wiring 32. Each of the series switch circuits 34U, 34V, and 34W has two switching elements 35 connected in series between the high-potential input wiring 31 and the low-potential input wiring 32. The switching elements 35 are configured with gate-type transistors. Note that while FIG. 1 illustrates each switching element 35 as a metal-oxide-semiconductor field effect transistor (MOSFET), each switching element 35 may also be an insulated gate bipolar transistor (IGBT) or the like. Hereinafter, of the two series-connected switching elements 35, the one connected to the high-potential input wiring 31 is referred to as the upper switching element, and the one connected to the low-potential input wiring 32 is referred to as the lower switching element. In the series switch circuit 34U, the upper switching element 35UU is connected between the high-potential input wiring 31 and the output wiring 33U, and the lower switching element 35UL is connected between the output wiring 33U and the low-potential input wiring 32. In the series switch circuit 34V, the upper switching element 35VU is connected between the high potential input wiring 31 and the output wiring 33V, and the lower switching element 35VL is connected between the output wiring 33V and the low potential input wiring 32. In the series switch circuit 34W, the upper switching element 35WU is connected between the high potential input wiring 31 and the output wiring 33W, and the lower switching element 35WL is connected between the output wiring 33W and the low potential input wiring 32. A freewheeling diode is connected in parallel to each switching element 35. The cathode of the freewheeling diode is connected to the high potential terminal (i.e., drain) of the corresponding switching element 35, and the anode of the freewheeling diode is connected to the low potential terminal (i.e., source) of the corresponding switching element 35.

[0014] The inverter 30 has six gate drive circuits 40. Each gate drive circuit 40 is connected to the gate of the switching element 35 to be controlled. Each gate drive circuit 40 changes the gate potential of the switching element 35 to be controlled between a gate-on potential VH and a gate-off potential VL in response to a command value input from the control device 90. The gate-on potential VH is a potential higher than the gate threshold of the switching element 35. The gate-off potential VL is a potential lower than the gate threshold of the switching element 35. Each gate drive circuit 40 controls the gate potential of the switching element 35 to be controlled based on the potential of the low-potential terminal (i.e., source) of the switching element 35 to be controlled. That is, the potentials VH and VL are shown based on the potential of the source of the switching element 35. Therefore, in the upper switching elements 35UU, 35VU, and 35WU, the potentials VH and VL are potentials based on the output wirings 33U, 33V, and 33W. For example, in the upper switching elements 35UU, 35VU, and 35WU, the potential VL may be the same as the output wirings 33U, 33V, and 33W, or the potential VH may be higher than the output wirings 33U, 33V, and 33W. Furthermore, in the lower switching elements 35UL, 35VL, and 35WL, the potentials VH and VL are potentials based on the low-potential input wiring 32. For example, in the lower switching elements 35UL, 35VL, and 35WL, the potential VL may be the same as the low-potential input wiring 32, or the potential VH may be higher than the low-potential input wiring 32. Each gate drive circuit 40 includes a power supply circuit 42 and a gate potential output circuit 44. The power supply circuit 42 outputs a gate-on potential VH. The power supply circuit 42 can change the gate-on potential VH in accordance with a command value input from the control device 90. The gate potential output circuit 44 changes the potential of the gate of the switching element 35 to be controlled between a gate-on potential VH and a gate-off potential VL in accordance with a command value input from the control device 90.

[0015] As shown in FIG. 2, the vehicle is provided with a cooling mechanism that cools the inverter 30 and the battery 12. The cooling mechanism includes a cooler 50, a coolant flow path 52, and a pump 54. A coolant flows through the coolant flow path 52. The pump 54 circulates the coolant through the coolant flow path 52. The cooler 50 is configured as a radiator or a heat exchanger, and cools the coolant through the coolant flow path 52 through heat exchange. The coolant flow path 52 is arranged to pass through the inverter 30 and the battery 12. The coolant flow path 52 is arranged in a position where it can exchange heat with each switching element 35 of the inverter 30. When the vehicle is running, the inverter 30 and each switching element 35 are cooled by the coolant flowing through the coolant flow path 52.

[0016] When the vehicle is running, the gate-on potential VH output from each power supply circuit 42 is fixed to a first gate-on potential VH1 (e.g., 20 V). The first gate-on potential VH1 is a potential sufficiently higher than the gate threshold of the switching element 35. When the first gate-on potential VH1 is applied to the gate of each switching element 35, the switching element 35 is normally on. The normally on state is a state in which the switching element 35 is on with low on-resistance. When the vehicle is running, the control device 90 switches each switching element 35 by switching the gate potential of each switching element 35 between the gate-off potential VL and the first gate-on potential VH1. By switching each switching element 35, the control device 90 converts the DC power output by the battery 12 into three-phase AC power and supplies it to the motor 80. The control device 90 controls the amplitude and frequency of the three-phase AC current supplied to the motor 80, thereby controlling the torque and rotation speed of the motor 80. By supplying power to the motor 80 in this manner, the motor 80 is driven and the vehicle runs.

[0017] While the vehicle is stopped, the battery 12 may be cooled by the outside air, etc. When the temperature Tb of the battery 12 becomes lower than the threshold Tth, the comparator 16 inputs a warm-up command to the control device 90. Upon receiving the warm-up command, the control device 90 executes a warm-up operation.

[0018] During the warm-up operation, the control device 90 operates the pump 54 to circulate the coolant through the coolant flow path 52. Also, during the warm-up operation, the control device 90 does not cause the cooler 50 to cool the coolant.

[0019] Fig. 3 shows control signals for switching elements 35UU and 35UL during warm-up operation. In Fig. 3, the gate drive signal represents a signal input from the control device 90 to the gate potential output circuit 44. When the gate drive signal is ON, the gate potential output circuit 44 applies a gate-on potential VH to the gate of switching element 35. When the gate drive signal is OFF, the gate potential output circuit 44 applies a gate-off potential VL to the gate of switching element 35.

[0020] As shown in FIG. 3, when the warm-up operation starts, the control device 90 turns on both the gate drive signal for the upper switching element 35UU and the gate drive signal for the lower switching element 35UL. Therefore, during the warm-up operation, a gate-on potential VH is applied to the gates of the upper switching element 35UU and the lower switching element 35UL. The control device 90 controls each switching element 35 by controlling the gate-on potential VH during the warm-up operation. The control device 90 alternately and repeatedly executes a first operation and a second operation. In FIG. 3, a period T1 is a period during which the first operation is executed, and a period T2 is a period during which the second operation is executed.

[0021] In the first operation (i.e., period T1), the control device 90 controls the gate-on potential VH for the upper switching element 35UU to a first gate-on potential VH1, and controls the gate-on potential VH for the lower switching element 35UL to a second gate-on potential VH2 (e.g., 5 V). The second gate-on potential VH2 is higher than the gate threshold and lower than the first gate-on potential VH1. Therefore, in the first operation, the gate potential of the upper switching element 35UU becomes the first gate-on potential VH1, and the gate potential of the lower switching element 35UL becomes the second gate-on potential VH2. Because the first gate-on potential VH1 is sufficiently higher than the gate threshold of the switching element 35, the upper switching element 35UU to which the first gate-on potential VH1 is applied becomes in a normally on state. On the other hand, because the difference between the second gate-on potential VH2 and the gate threshold is small, the lower switching element 35UL, to which the second gate-on potential VH2 is applied, is turned on in a state with a higher on-resistance than in the normally-on state. Therefore, high loss occurs in the lower switching element 35UL. This state of being turned on in a state with higher loss than in the normally-on state is referred to as high-loss on. As described above, in the first operation, the upper switching element 35UU is in the normally-on state, and the lower switching element 35UL is in the high-loss on state. This causes the smoothing capacitor 38 to discharge through the upper switching element 35UU and the lower switching element 35UL, and current flows through the series switch circuit 34U. Since the upper switching element 35UU is in the normally-on state, almost no loss occurs in the upper switching element 35UU, and the upper switching element 35UU generates almost no heat. On the other hand, since the lower switching element 35UL is in the high-loss on state, high loss occurs in the lower switching element 35UL, and the lower switching element 35UL generates heat. In this way, in the first action, the low-side switching element 35UL generates heat.

[0022] During the second operation (i.e., during the period T2), the control device 90 controls the gate-on potential VH for the upper switching element 35UU to the second gate-on potential VH2 and the gate-on potential VH for the lower switching element 35UL to the first gate-on potential VH1. Therefore, during the second operation, the gate potential of the upper switching element 35UU becomes the second gate-on potential VH2, and the gate potential of the lower switching element 35UL becomes the first gate-on potential VH1. Therefore, during the second operation, the upper switching element 35UU becomes high-loss on, and the lower switching element 35UL becomes normally on. This causes the smoothing capacitor 38 to discharge via the upper switching element 35UU and the lower switching element 35UL, and current flows through the series switch circuit 34U. Because the lower switching element 35UL is normally on, the lower switching element 35UL generates almost no heat. On the other hand, since the upper switching element 35UU is in a high-loss on state, the upper switching element 35UU generates heat. In this way, in the second operation, the upper switching element 35UU generates heat.

[0023] Since the control device 90 alternately executes the first operation and the second operation, the upper switching element 35UU and the lower switching element 35UL alternately generate heat during the warm-up operation.

[0024] FIG. 4 shows the gate potentials of the six switching elements 35 during a warm-up operation. The gate potentials of the switching elements 35UU and 35UL in FIG. 4 are the same as those in FIG. 3. As shown in FIG. 4, during a warm-up operation, the control device 90 executes first and second operations for the series switch circuit 34V and the series switch circuit 34W in synchronization with the series switch circuit 34U. Therefore, during the first operation (i.e., period T1), the upper switching elements 35UU, 35VU, and 35WU are in a normally-on state, and the lower switching elements 35UL, 35VL, and 35WL are in a high-loss-on state. Therefore, during the first operation, the lower switching elements 35UL, 35VL, and 35WL generate heat. Furthermore, during the second operation (i.e., period T2), the lower switching elements 35UL, 35VL, and 35WL are in a normally-on state, and the upper switching elements 35UU, 35VU, and 35WU are in a high-loss-on state. Therefore, in the second operation, the upper switching elements 35UU, 35VU, and 35WU generate heat. In this manner, during the warm-up operation, the upper switching elements 35UU, 35VU, and 35WU and the lower switching elements 35UL, 35VL, and 35WL alternately generate heat.

[0025] The heat generated by each switching element 35 heats the coolant circulating in the coolant flow path 52. The heated coolant is supplied to the battery 12, thereby increasing the temperature of the battery 12. In this way, the warm-up operation can increase the temperature of the battery 12, thereby restoring the charge / discharge performance of the battery.

[0026] As described above, during the warm-up operation, each switching element 35 is alternately switched between normal ON and high-loss ON. This prevents the heat generation period in each switching element 35 from continuing for a long period of time, and prevents the temperature of each switching element 35 from becoming excessively high. Furthermore, since the upper and lower switching elements are alternately made to generate heat, the coolant can be heated efficiently. Furthermore, since the warm-up operation is performed using three series switch circuits 34, the coolant can be heated more efficiently. Therefore, the temperature of the battery 12 can be raised efficiently.

[0027] Furthermore, in the warm-up operation described above, the path through which the discharge current of the smoothing capacitor 38 flows does not pass through the motor 80, thereby preventing noise from being generated by the motor 80. Furthermore, because the three series switch circuits 34 are synchronously controlled, the occurrence of a potential difference among the output wirings 33U, 33V, and 33W can be suppressed. That is, in the first operation, the upper switching elements 35UU, 35VU, and 35WU are normally on, and the output wirings 33U, 33V, and 33W are short-circuited via the high-potential input wiring 31. As a result, the output wirings 33U, 33V, and 33W have the same potential. Furthermore, in the second operation, the lower switching elements 35UL, 35VL, and 35WL are normally on, and the output wirings 33U, 33V, and 33W are short-circuited via the low-potential input wiring 32. As a result, the output wirings 33U, 33V, and 33W have the same potential. In this way, it is possible to suppress the occurrence of a potential difference between the output wirings 33U, 33V, and 33W, thereby preventing a minute current from flowing through the motor 80. Therefore, it is possible to more effectively prevent the occurrence of noise in the motor 80.

[0028] FIG. 5 shows the details of the gate potential changes at timings ta and tb when switching from the first operation to the second operation, as shown in FIG. 3 . At timing ta when switching from the first operation to the second operation, the control device 90 first reduces the gate potential of the upper switching element 35UU from the first gate-on potential VH1 to the second gate-on potential VH2, and then increases the gate potential of the lower switching element 35UL from the second gate-on potential VH2 to the first gate-on potential VH1. That is, a dead time Td1 is provided between the timing when the gate potential of the upper switching element 35UU is reduced and the timing when the gate potential of the lower switching element 35UL is increased. This prevents the upper switching element 35UU and the lower switching element 35UL from being normally on at the same time, thereby preventing an overcurrent from flowing through the series switch circuit 34U. The dead time Td1 also prevents an overcurrent from flowing through the series switch circuits 34V and 34W.

[0029] At timing tb when the second operation is switched to the first operation, the control device 90 reduces the gate potential of the lower switching element 35UL from the first gate-on potential VH1 to the second gate-on potential VH2, and then increases the gate potential of the upper switching element 35UU from the second gate-on potential VH2 to the first gate-on potential VH1. That is, a dead time Td2 is provided between the timing at which the gate potential of the lower switching element 35UL is reduced and the timing at which the gate potential of the upper switching element 35UU is increased. This prevents the upper switching element 35UU and the lower switching element 35UL from being normally on at the same time, thereby preventing an overcurrent from flowing through the series switch circuit 34U. Similarly, the dead time Td2 prevents an overcurrent from flowing in the series switch circuits 34V and 34W.

[0030] Note that during the dead time, the gate potentials may be controlled as shown in FIG. 6. In FIG. 6, at timing ta, the control device 90 reduces the gate potential of the upper switching element 35UU from the first gate-on potential VH1 to the gate-off potential VL. After the dead time Td1 has elapsed, the control device 90 increases the gate potential of the upper switching element 35UU from the gate-off potential VL to the second gate-on potential VH2 and increases the gate potential of the lower switching element 35UL from the second gate-on potential VH2 to the first gate-on potential VH1. Furthermore, at timing tb, the control device 90 reduces the gate potential of the lower switching element 35UL from the first gate-on potential VH1 to the gate-off potential VL. After the dead time Td2 has elapsed, the control device 90 raises the gate potential of the lower switching element 35UL from the gate-off potential VL to the second gate-on potential VH2, and raises the gate potential of the upper switching element 35UU from the second gate-on potential VH2 to the first gate-on potential VH1. This control method also prevents an overcurrent from flowing through the series switch circuit 34U. Note that the dead times Td1 and Td2 similarly prevent an overcurrent from flowing in the series switch circuits 34V and 34W. Note that in other embodiments, both the upper switching element and the lower switching element may be controlled to be off during the dead times Td1 and Td2.

[0031] As described above, the current sensors detect the currents IU, IV, and IW flowing through the output wirings 33U, 33V, and 33W. If a current is detected in any of the output wirings 33U, 33V, and 33W during the warm-up operation, the control device 90 performs an emergency stop of the warm-up operation. In this emergency stop, the control device 90 controls the upper switching elements 35UU, 35VU, and 35WU to be normally on and controls the lower switching elements 35UL, 35VL, and 35WL to be off. Turning off the lower switching elements 35UL, 35VL, and 35WL prevents a short circuit between the high-potential input wiring 31 and the low-potential input wiring 32. Furthermore, by turning on the upper switching elements 35UU, 35VU, and 35WU, the output wirings 33U, 33V, and 33W can be at the same potential, preventing unintended current from occurring. In an emergency stop, the upper switching elements 35UU, 35VU, and 35WU may be controlled to be turned off, and the lower switching elements 35UL, 35VL, and 35WL may be controlled to be normally on.

[0032] 7, each switching element 35 may be provided with a temperature sensor 35a. The temperature sensor 35a detects the temperature of the corresponding switching element 35. Although not shown, the detected value of each temperature sensor 35a is input to a control device 90. The control device 90 changes the second gate-on potential VH2 for a switching element 35 that is the target of high-loss on-state operation in accordance with the temperature of that switching element 35. When the temperature of the switching element 35 is high, the control device 90 lowers the second gate-on potential VH2 for that switching element 35 to reduce the amount of heat generated by the switching element 35. This prevents the temperature of the switching element 35 from rising excessively.

[0033] Instead of the temperature sensor 35a in FIG. 7, a current sensor may be provided for each switching element 35. The current sensor detects the source current flowing through the corresponding switching element. The detected value of each current sensor is input to the control device 90. The control device 90 changes the second gate-on potential VH2 for a switching element 35 that is the target of high-loss on-state operation in accordance with the source current of that switching element 35. When the source current of the switching element 35 is high, the control device 90 lowers the second gate-on potential VH2 for that switching element 35 to reduce the amount of heat generated by the switching element 35. This prevents an excessive increase in the temperature of the switching element 35. Alternatively, a temperature sensor and a current sensor may be provided for each switching element 35, and the second gate-on potential VH2 may be changed in accordance with both the temperature and the current. [Example]

[0034] The electric circuit of the second embodiment has the same circuit configuration as the electric circuit 10 of the first embodiment shown in Fig. 1. However, in the second embodiment, the gate-on potential VH output from each power supply circuit 42 is fixed to a first gate-on potential VH1 (i.e., a value sufficiently higher than the gate threshold). In the second embodiment, unlike the first embodiment, when each switching element is controlled to be in a high-loss on state, the control device 90 inputs a high-frequency pulse signal to the gate of each switching element 35.

[0035] 8 shows the gate potentials of the six switching elements 35 during the warm-up operation in Example 2. When the warm-up operation starts, the control device 90 performs a first operation in a period T1 and a second operation in a period T2. As shown in FIG. 8, the control device 90 alternately and repeatedly performs the first operation and the second operation.

[0036] In the first operation (i.e., period T1), the control device 90 fixes the gate potential of the upper switching element 35UU to a first gate-on potential VH1 (e.g., 20 V). Therefore, in the first operation, the upper switching element 35UU is normally on. Also, in the first operation, the control device 90 changes the gate potential of the lower switching element 35UL between the first gate-on potential VH1 and the gate-off potential VL at high frequency. That is, the control device 90 controls the gate potential output circuit 44 to input a high-frequency pulse signal that changes between the first gate-on potential VH1 and the gate-off potential VL to the gate of the lower switching element 35UL. By changing the gate potential of the lower switching element 35UL at high frequency in this manner, the lower switching element 35UL is turned on in a state where its on-resistance is higher than in the normally on state. That is, the lower switching element 35UL is turned on in a high-loss on state. As described above, in the first operation, the upper switching element 35UU is normally on and the lower switching element 35UL is high-loss on. Therefore, in the first operation, the lower switching element 35UL generates heat.

[0037] In the second operation (i.e., the period T2), the control device 90 fixes the gate potential of the lower switching element 35UL to the first gate-on potential VH1. Therefore, in the second operation, the lower switching element 35UL is normally on. Also, in the second operation, the control device 90 changes the gate potential of the upper switching element 35UU between the first gate-on potential VH1 and the gate-off potential VL at high frequency. That is, the control device 90 controls the gate potential output circuit 44 to input a high-frequency pulse signal that changes between the first gate-on potential VH1 and the gate-off potential VL to the gate of the upper switching element 35UU. By changing the gate potential of the upper switching element 35UU at high frequency in this manner, the upper switching element 35UU is in a high-loss on state. As described above, in the second operation, the lower switching element 35UL is normally on, and the upper switching element 35UU is in a high-loss on state. Therefore, in the second operation, the upper switching element 35UU generates heat.

[0038] Since the control device 90 alternately executes the first operation and the second operation, the upper switching element 35UU and the lower switching element 35UL alternately generate heat during the warm-up operation.

[0039] 8, during the warm-up operation, the control device 90 executes first and second operations for the series switch circuit 34V and the series switch circuit 34W in synchronization with the series switch circuit 34U. Therefore, in the first operation (i.e., period T1), the upper switching elements 35UU, 35VU, and 35WU are normally on, and the lower switching elements 35UL, 35VL, and 35WL are high-loss on. Therefore, in the first operation, the lower switching elements 35UL, 35VL, and 35WL generate heat. Furthermore, in the second operation (i.e., period T2), the lower switching elements 35UL, 35VL, and 35WL are normally on, and the upper switching elements 35UU, 35VU, and 35WU are high-loss on. Therefore, in the second operation, the upper switching elements 35UU, 35VU, and 35WU generate heat. In this way, during the warm-up operation, the upper switching elements 35UU, 35VU, and 35WU and the lower switching elements 35UL, 35VL, and 35WL alternately generate heat.

[0040] The heat generated in each switching element 35 is transferred to the battery 12 via the coolant circulating in the coolant flow path 52, heating the battery 12. In the second embodiment as well, the temperature of the battery 12 can be increased by the warm-up operation, and the charge / discharge performance of the battery can be restored.

[0041] Furthermore, in the warm-up operation of the second embodiment, each switching element 35 is alternately switched between normal ON and high-loss ON, preventing the temperature of each switching element 35 from becoming excessively high. Also, the upper and lower switching elements are alternately made to generate heat, so the coolant can be heated efficiently. Furthermore, the warm-up operation is performed using three series switch circuits 34, so the coolant can be heated more efficiently. Therefore, the temperature of the battery 12 can be raised efficiently.

[0042] Furthermore, in the warm-up operation of the second embodiment, the path through which the discharge current of the smoothing capacitor 38 flows does not pass through the motor 80, thereby preventing noise from being generated by the motor 80. Furthermore, the three series switch circuits 34 are controlled in synchronization, thereby preventing potential differences from occurring among the output wirings 33U, 33V, and 33W. This prevents minute currents from flowing through the motor 80, thereby more effectively preventing noise from being generated in the motor 80.

[0043] FIG. 9 shows details of the change in gate potential at timings ta and tb when switching from the first operation to the second operation shown in FIG. 8 . At timing ta when switching from the first operation to the second operation, the control device 90 lowers the gate potential of the upper switching element 35UU from the first gate-on potential VH1 to the gate-off potential VL when the high-loss-on state of the lower switching element 35UL ends. After that, after a dead time Td1 has elapsed, the control device 90 raises the gate potential of the lower switching element 35UL from the gate-off potential VL to the first gate-on potential VH1. Then, the upper switching element 35UU is controlled to the high-loss-on state. In this way, the dead time Td1 is provided between the period when the upper switching element 35UU is normally on and the period when the lower switching element 35UL is normally on, and during the dead time Td1, both the upper switching element 35UU and the lower switching element 35UL are controlled to be off. This prevents the upper switching element 35UU and the lower switching element 35UL from being normally on at the same time, and prevents an overcurrent from flowing through the series switch circuit 34U. Similarly, the dead time Td1 prevents an overcurrent from flowing in the series switch circuits 34V and 34W.

[0044] At timing tb when the second operation is switched to the first operation, the control device 90 lowers the gate potential of the lower switching element 35UL from the first gate-on potential VH1 to the gate-off potential VL when the high-loss-on state of the upper switching element 35UU ends. Then, after a dead time Td2 has elapsed, the control device 90 raises the gate potential of the upper switching element 35UU from the gate-off potential VL to the first gate-on potential VH1. Then, the control device 90 controls the lower switching element 35UL to the high-loss-on state. Thus, the dead time Td2 is provided between the normally-on period of the lower switching element 35UL and the normally-on period of the upper switching element 35UU. During the dead time Td2, both the upper switching element 35UU and the lower switching element 35UL are controlled to be off. This prevents the upper switching element 35UU and the lower switching element 35UL from being normally-on at the same time, thereby preventing an overcurrent from flowing through the series switch circuit 34U. Similarly, in the series switch circuits 34V and 34W, an overcurrent is prevented by the dead time Td2.

[0045] Also in the second embodiment, similarly to the first embodiment, the warm-up operation may be stopped urgently when a current is detected in any of the output wirings 33U, 33V, and 33W during execution of the warm-up operation.

[0046] Also, in the second embodiment, as shown in FIG. 7 , each switching element 35 may be provided with a temperature sensor 35a. In this case, the control device 90 changes the duty ratio of the pulse signal input to the gate of the switching element 35 that is the target of high-loss on-state operation, depending on the temperature of the switching element 35. In this specification, the duty ratio refers to the ratio of the period during which the first gate-on potential VH1 is output in the pulse signal. When the temperature of the switching element 35 is high, the control device 90 lowers the duty ratio of the pulse signal. For example, the duty ratio may be lowered by lowering the ratio of the period during which the first gate-on potential VH1 is output without changing the frequency of the pulse signal. Alternatively, the duty ratio may be lowered by shortening the period during which the first gate-on potential VH1 is output without changing the length of the period during which the gate-off potential VL is output. Alternatively, the duty ratio may be lowered by lengthening the period during which the gate-off potential VL is output without changing the length of the period during which the first gate-on potential VH1 is output. By lowering the duty ratio of the pulse signal in this way, the amount of heat generated by the switching element 35 during high-loss on-state operation can be reduced. This prevents the temperature of the switching element 35 from rising excessively.

[0047] In the second embodiment, a current sensor may be provided in each switching element 35 instead of the temperature sensor 35a. The control device 90 changes the duty ratio of the pulse signal input to the gate of the switching element 35 that is the target of high-loss on-state operation, depending on the source current of the switching element 35. When the source current of the switching element 35 is high, the control device 90 lowers the duty ratio of the pulse signal input to the gate of the switching element 35, thereby reducing the amount of heat generated by the switching element 35. This makes it possible to prevent an excessive increase in the temperature of the switching element 35. In addition, a temperature sensor and a current sensor may be provided in each switching element 35, and the duty ratio of the pulse signal may be changed depending on both the temperature and the current. [Example]

[0048] The electric circuit of Example 3, like the electric circuit of Example 2, applies a high-frequency pulse signal that changes between a gate-on potential and a gate-off potential to the gate of each switching element 35 in high-loss ON mode. However, in Example 3, as shown in FIG. 11, the gate-on potential VH2 used in high-loss ON mode is lower than the gate-on potential VH1 used in normal ON mode. Except for this, the configuration of the electric circuit of Example 3 is the same as that of Example 2.

[0049] FIG. 10 shows each gate drive circuit 40 according to the third embodiment. The gate drive circuit 40 is connected to the gate of the switching element 35 to be controlled (hereinafter, may be referred to as the gate of the controlled element). In the gate drive circuit 40 according to the third embodiment, a gate potential output circuit 44 is connected to power supply circuits 42a and 42b and a gate-off potential output circuit 48. The power supply circuit 42a outputs a gate-on potential VH1. The power supply circuit 42b outputs a gate-on potential VH2. The gate-on potential VH2 is higher than the gate threshold value and lower than the gate-on potential VH1. The gate-off potential output circuit 48 outputs a gate-off potential VL (i.e., the source potential of the switching element 35 to be controlled).

[0050] The gate potential output circuit 44 has a first gate-on switch SWH1, a first gate-on resistor RH1, a second gate-on switch SWH2, a second gate-on resistor RH2, a gate-off switch SWL, and a gate-off resistor RL. The first gate-on switch SWH1, the second gate-on switch SWH2, and the gate-off switch SWL are configured by switching elements and are controlled by the control device 90.

[0051] One terminal of the first gate-on switch SWH1 is connected to the power supply circuit 42a. The other terminal of the first gate-on switch SWH1 is connected to the gate of the controlled object via the first gate-on resistor RH1. When the first gate-on switch SWH1 is turned on, a gate current flows from the power supply circuit 42a to the gate of the controlled object via the first gate-on switch SWH1 and the first gate-on resistor RH1, and the gate of the controlled object is charged.

[0052] One terminal of the second gate-on switch SWH2 is connected to the power supply circuit 42b. The other terminal of the second gate-on switch SWH2 is connected to the gate of the controlled object via the second gate-on resistor RH2. When the second gate-on switch SWH2 is turned on, a gate current flows from the power supply circuit 42b to the gate of the controlled object via the second gate-on switch SWH2 and the second gate-on resistor RH2, and the gate of the controlled object is charged.

[0053] One terminal of the gate-off switch SWL is connected to the gate-off potential output circuit 48. The other terminal of the gate-off switch SWL is connected to the gate of the control target via a gate-off resistance RL. When the gate-off switch SWL is turned on, a gate current flows from the gate of the control target to the gate-off potential output circuit 48 via the gate-off resistance RL and the gate-off switch SWL, and the gate of the control target is discharged.

[0054] FIG. 11 shows the gate potential of each switching element 35 during the warm-up operation of the third embodiment. In the warm-up operation of FIG. 11, a high-frequency pulse signal is input to the gate of the controlled object in high-loss ON mode, similar to the warm-up operation of FIG. 8. However, in FIG. 11, the gate-on potential VH2 applied to the gate of the controlled object in high-loss ON mode is lower than the gate-on potential VH1 applied to the gate of the controlled object in normal ON mode. Except for this, the warm-up operation of FIG. 11 is the same as the warm-up operation of FIG. 8. The operation of the gate drive circuit 40 during the warm-up operation will be described below.

[0055] In the normally-on state, the control device 90 controls the second gate-on switch SWH2 and the gate-off switch SWL to be off, and controls the first gate-on switch SWH1 to be on. As a result, the gate-on potential VH1 output from the power supply circuit 42a is applied to the gate of the controlled device. Therefore, as shown in FIG. 11, in the normally-on state, the gate-on potential VH1 is applied to the gate of the controlled device.

[0056] In the high-loss-on state, the control device 90 controls the first gate-on switch SWH1 to be always off and alternately turns on the second gate-on switch SWH2 and the gate-off switch SWL. When the second gate-on switch SWH2 is on (i.e., the gate-off switch SWL is off), the gate-on potential VH2 output by the power supply circuit 42b is applied to the gate of the controlled device. When the gate-off switch SWL is on (i.e., the second gate-on switch SWH2 is off), the gate-off potential VL output by the gate-off potential output circuit 48 is applied to the gate of the controlled device. Therefore, as shown in FIG. 11, in the high-loss-on state, the potential of the gate of the controlled device changes at high frequency between the gate-on potential VH2 and the gate-off potential VL.

[0057] As described above, in the high-loss ON state of Example 3, the gate potential of the controlled object changes at a high frequency between the gate-ON potential VH2 and the gate-OFF potential VL. That is, the gate-ON potential VH2 used in the high-loss ON state is lower than the gate-ON potential VH1 used in the normal ON state. Therefore, in Example 3 (i.e., FIG. 11), the ON resistance of the switching element 35 in the high-loss ON state is higher than in Example 2 (i.e., FIG. 8). This makes it possible to suppress the current flowing through the switching element 35 in the high-loss ON state.

[0058] Furthermore, in the third embodiment, as described below, the potential difference occurring among the output wirings 33U, 33V, and 33W can be reduced. When the upper switching element 35 is turned on in a high-loss state and the lower switching element 35 is turned on normally, the resistance during the high-loss state is high, so the potentials of the output wirings 33U, 33V, and 33W become closer to the potential of the low-potential input wiring 32, and a potential difference is unlikely to occur among the output wirings 33U, 33V, and 33W. When the upper switching element 35 is turned on normally and the lower switching element 35 is turned on in a high-loss state, the potentials of the output wirings 33U, 33V, and 33W become closer to the potential of the high-potential input wiring 31, and a potential difference is unlikely to occur among the output wirings 33U, 33V, and 33W. In this way, when the three series switch circuits 34U, 34V, and 34W are synchronized, the resistance during the high-loss state is high, so the potential difference occurring among the output wirings 33U, 33V, and 33W can be reduced. As a result, the minute current flowing through the motor 80 during the warm-up operation can be suppressed, and the generation of noise in the motor 80 can be effectively suppressed. [Example]

[0059] The electric circuit of Example 4, like the electric circuit of Example 3, applies a high-frequency pulse signal that changes between a gate-on potential VH2 (i.e., a gate-on potential lower than the gate-on potential VH1) and a gate-off potential VL to the gate of each switching element in high-loss on mode. However, Example 4 differs from Example 3 in the configuration of the gate drive circuit 40. Except for this point, the configuration of the electric circuit of Example 4 is the same as that of Example 3.

[0060] 12 shows each gate drive circuit 40 in Example 4. The gate drive circuit 40 is connected to the gate of the control target. In the gate drive circuit 40 of Example 4, a gate potential output circuit 44 is connected to a power supply circuit 42 and a gate-off potential output circuit 48. The power supply circuit 42 outputs a gate-on potential VH1. The gate-off potential output circuit 48 outputs a gate-off potential VL (i.e., the source potential of the switching element 35 to be controlled).

[0061] The gate potential output circuit 44 has a gate-on switch SWH, a gate-on resistor RH, a gate-off switch SWL, and a gate-off resistor RL. The gate-on switch SWH and the gate-off switch SWL are configured by switching elements and are controlled by the control device 90.

[0062] One terminal of the gate-on switch SWH is connected to the power supply circuit 42. The other terminal of the gate-on switch SWH is connected to the gate of the controlled object via the gate-on resistor RH. When the gate-on switch SWH is turned on, a gate current flows from the power supply circuit 42 to the gate of the controlled object via the gate-on switch SWH and the gate-on resistor RH, and the gate of the controlled object is charged.

[0063] One terminal of the gate-off switch SWL is connected to the gate-off potential output circuit 48. The other terminal of the gate-off switch SWL is connected to the gate of the control target via a gate-off resistance RL. When the gate-off switch SWL is turned on, a gate current flows from the gate of the control target to the gate-off potential output circuit 48 via the gate-off resistance RL and the gate-off switch SWL, and the gate of the control target is discharged.

[0064] The electric circuit of the fourth embodiment performs a warm-up operation similar to that of the third embodiment (i.e., FIG. 11). FIG. 13 shows the gate potential during the warm-up operation of the fourth embodiment in detail. In FIG. 13, the period Tm is the normal ON period, and the period Tn is the high-loss ON period. The operation of the gate drive circuit 40 during the warm-up operation will be described below.

[0065] During the normally-on period (i.e., the period Tm in FIG. 13), the control device 90 controls the gate-on switch SWH to be on and the gate-off switch SWL to be off. As a result, a gate current flows from the power supply circuit 42 to the gate of the controlled object, charging the gate of the controlled object. As a result, the gate potential rises immediately after the start of the period Tm. The current path through which the gate current flows is an RC circuit of the gate-on resistance RH and the gate capacitance, so the gate potential rises at a predetermined slope. Because the normally-on period Tm is long, the gate potential reaches the gate-on potential VH1 (i.e., the output potential of the power supply circuit 42) within the period Tm. In this way, during the normally-on period, the gate-on potential VH1 is applied to the gate of the controlled object.

[0066] During the high-loss on period (i.e., the period Tn in FIG. 13), the control device 90 alternately turns on the gate-on switch SWH and the gate-off switch SWL. In FIG. 13, the period Tx is the period during which the gate-on switch SWH is on (i.e., the period during which the gate-off switch SWL is off), and the period Ty is the period during which the gate-off switch SWL is on (i.e., the period during which the gate-on switch SWH is off). During the period Ty, a gate current flows from the gate of the controlled object to the gate-off potential output circuit 48 via the gate-off resistance RL and the gate-off switch SWL, discharging the gate of the controlled object. During the period Ty, the gate potential drops to the gate-off potential VL. During the period Tx, a gate current flows from the power supply circuit 42 to the gate of the controlled object via the gate-on switch SWH and the gate-on resistance RH, charging the gate of the controlled object. As a result, the gate potential rises immediately after the start of the period Tx. The gate potential rises at a predetermined slope. The period Tx is set to be short, and ends before the gate potential reaches the gate-on potential VH1. In the period Ty following the period Tx, the gate of the controlled device is discharged as described above, and the gate potential drops to the gate-off potential VL. Therefore, at the end of the period Tx, the gate potential reaches a peak value Vp. The length of the period Tx is set so that the peak value Vp reaches the gate-on potential VH2 (i.e., a potential lower than the gate-on potential VH1 and higher than the gate threshold value Vth). In this way, during the high-loss on period Tn, the gate potential changes at high frequency between the gate-on potential VH2 and the gate-off potential VL.

[0067] As described above, in the high-loss ON state, the gate potential of the controlled device changes at high frequency between the gate-ON potential VH2 and the gate-OFF potential VL. Therefore, in the fourth embodiment, as in the third embodiment, the ON resistance of the switching element 35 in the high-loss ON state can be increased. This reduces the current flowing through the switching element 35 in the high-loss ON state. Furthermore, the generation of a potential difference between the output wirings 33U, 33V, and 33W is reduced, thereby preventing minute currents from flowing through the motor 80. Furthermore, according to the configuration of the fourth embodiment, the potential VH2 can be generated based on the potential VH1, eliminating the need for a dedicated power supply circuit for generating the potential VH2. This allows the electrical circuit to be miniaturized. [Example]

[0068] The electric circuit of Example 5, like the electric circuit of Example 2, applies a high-frequency pulse signal that changes between a gate-on potential VH1 and a gate-off potential VL to the gate of each switching element 35 in high-loss on mode. However, the electric circuit of Example 5 can change the discharge speed when discharging the gate of each switching element 35. Except for this, the electric circuit of Example 5 is the same as the electric circuit of Example 2.

[0069] 14 shows each gate drive circuit 40 in the fifth embodiment. The gate drive circuit 40 is connected to the gate of the control target. In the gate drive circuit 40 of the fifth embodiment, a gate potential output circuit 44 is connected to a power supply circuit 42 and a gate-off potential output circuit 48. The power supply circuit 42 outputs a gate-on potential VH1. The gate-off potential output circuit 48 outputs a gate-off potential VL (i.e., the source potential of the switching element 35 to be controlled).

[0070] The gate potential output circuit 44 has a gate-on switch SWH, a gate-on resistor RH, a first gate-off switch SWL1, a first gate-off resistor RL1, a second gate-off switch SWL2, and a second gate-off resistor RL2. The gate-on switch SWH, the first gate-off switch SWL1, and the second gate-off switch SWL2 are configured with switching elements and are controlled by the control device 90.

[0071] One terminal of the gate-on switch SWH is connected to the power supply circuit 42. The other terminal of the gate-on switch SWH is connected to the gate of the controlled object via the gate-on resistor RH. When the gate-on switch SWH is turned on, a gate current flows from the power supply circuit 42 to the gate of the controlled object via the gate-on switch SWH and the gate-on resistor RH, and the gate of the controlled object is charged.

[0072] One terminal of the first gate-off switch SWL1 is connected to the gate-off potential output circuit 48. The other terminal of the first gate-off switch SWL1 is connected to the gate of the controlled object via the first gate-off resistor RL1. When the first gate-off switch SWL1 is turned on, a gate current flows from the gate of the controlled object to the gate-off potential output circuit 48 via the first gate-off resistor RL1 and the first gate-off switch SWL1, and the gate of the controlled object is discharged.

[0073] One terminal of the second gate-off switch SWL2 is connected to the gate-off potential output circuit 48. The other terminal of the second gate-off switch SWL2 is connected to the gate of the controlled object via the second gate-off resistor RL2. The electrical resistance of the second gate-off resistor RL2 is higher than the electrical resistance of the first gate-off resistor RL1. When the second gate-off switch SWL2 is turned on, a gate current flows from the gate of the controlled object to the gate-off potential output circuit 48 via the second gate-off resistor RL2 and the second gate-off switch SWL2, and the gate of the controlled object is discharged. Because the electrical resistance of the second gate-off resistor RL2 is higher than the electrical resistance of the first gate-off resistor RL1, when the second gate-off switch SWL2 is turned on, the discharge speed of the gate (i.e., the rate at which the gate potential decreases) is slower than when the first gate-off switch SWL1 is turned on.

[0074] First, the operation of rotating the motor 80 of the fifth embodiment (i.e., the operation of supplying three-phase AC power to the motor 80 by the inverter 30) will be described. FIG. 15 shows the gate potentials of the switching elements 35 during the operation of rotating the motor 80. During the operation of rotating the motor 80, the control device 90 controls the second gate-off switch SWL2 to always be off and alternately turns on the gate-on switch SWH and the first gate-off switch SWL1. During the period To when the gate-on switch SWH is on (i.e., the period To when the first gate-off switch SWL1 is off), the gate-on potential VH1 is applied to the gate of the controlled object. During the period Tp when the first gate-off switch SWL1 is on (i.e., the period Tp when the gate-on switch SWL1 is off), the gate-off potential VL is applied to the gate of the controlled object. Therefore, as shown in FIG. 15, during the operation of rotating the motor 80, the potential of the gate of the controlled object changes between the gate-on potential VH1 and the gate-off potential VL.

[0075] Furthermore, when the period To switches to the period Tp, a gate current flows from the gate of the controlled object to the gate-off potential output circuit 48 via the first gate-off resistor RL1 and the first gate-off switch SWL1, discharging the gate of the controlled object. Because the electrical resistance of the first gate-off resistor RL1 is low, the gate is rapidly discharged, and the gate potential drops rapidly from the gate-on potential VH1 to the gate-off potential VL. Therefore, the drain-source current flowing through the switching element 35 drops rapidly, causing a surge voltage to occur between the drain and source of the switching element. However, when rotating the motor 80, the motor 80 (i.e., the load) is present in the current path of the drain-source current, so a very high surge voltage is not generated.

[0076] Next, the warm-up operation of the fifth embodiment will be described. In the fifth embodiment, the warm-up operation is performed in the same manner as in the second embodiment (i.e., FIG. 8). That is, each switching element 35 is controlled to alternately repeat normal-on and high-loss-on states. In the normal-on state, the control device 90 controls the gate-on switch SWH to be on and the first gate-off switch SWL1 and the second gate-off switch SWL2 to be off. Therefore, the gate-on potential VH1 output by the power supply circuit 42 is applied to the gate to be controlled.

[0077] FIG. 16 shows the gate potential in the high-loss-ON state of Example 5. Note that in FIG. 16, the solid line graph shows the values ​​of Example 5, and the dashed line graph shows the values ​​of the comparative example. In the high-loss-ON state, the control device 90 controls the first gate-off switch SWL1 to always be OFF, and alternately turns on the gate-on switch SWH and the second gate-off switch SWL2 at a high frequency. During the period Tx when the gate-on switch SWH is ON (i.e., the period Tx when the second gate-off switch SWL2 is OFF), the gate-on potential VH1 is applied to the gate of the controlled object. During the period Ty when the second gate-off switch SWL2 is ON (i.e., the period Ty when the gate-on switch SWH is OFF), the gate-off potential VL is applied to the gate of the controlled object. Therefore, as shown in FIG. 16, in the high-loss-ON state, the potential of the gate of the controlled object changes at a high frequency between the gate-on potential VH1 and the gate-off potential VL.

[0078] Furthermore, when the period Tx switches to the period Ty, a gate current flows from the gate of the controlled device to the gate-off potential output circuit 48 via the second gate-off resistor RL2 and the second gate-off switch SWL2, discharging the gate of the controlled device. Therefore, the drain-source current flowing through the switching element 35 decreases, generating a surge voltage between the drain and source of the switching element. During the period Tx, a current flows through the series circuit of the upper switching element 35 and the lower switching element 35. Therefore, the motor 80 (i.e., the load) is not present in this current path, and the drain-source current flowing through the switching element 35 during the period Tx is high. Therefore, if the gate potential is rapidly reduced as shown by the dashed line in FIG. 16 when switching from the period Tx to the period Ty, the drain-source current rapidly decreases, generating an extremely high surge voltage. In contrast, in the fifth embodiment, the gate is discharged by the second gate-off resistor RL2, which has a high electrical resistance, when switching from the period Tx to the period Ty. Therefore, the rate at which the gate potential drops is slow, and the occurrence of a high surge voltage is suppressed.

[0079] The configuration capable of changing the rate at which the gate potential decreases as in the fifth embodiment may be applied to the third and fourth embodiments. That is, in the gate drive circuits of the third and fourth embodiments, two types of gate-off resistors for discharging the gate may be provided, and in the high-loss-on state, the gate may be discharged at a speed slower than the speed at which the motor is rotated.

[0080] In the above embodiment, the comparator 16 determines whether the temperature Tb is lower than the threshold value Tth. However, the detected value of the temperature Tb may be directly input to the control device 90, which then determines whether the temperature Tb is lower than the threshold value Tth. In this case, the data on the temperature Tb input to the control device 90 (i.e., data indicating a low temperature) corresponds to the warm-up command.

[0081] In the above embodiment, the heat generated in each switching element 35 is transferred to the battery 12 via the coolant flow path 52. However, as long as the heat generated in each switching element 35 is transferred to the battery 12, the heat may be transferred via any route.

[0082] The configurations of the technology disclosed in this specification are listed below. (Configuration 1) An electrical circuit mounted on a vehicle, a battery (12); a motor (80); an inverter (30) connected between the battery and the motor; A control device (90), and The inverter A high potential input wiring (31); A low potential input wiring (32); A plurality of output wirings (33U, 33V, 33W) connected to the motor; a smoothing capacitor (38) connected between the high potential input wiring and the low potential input wiring; a plurality of series switch circuits (34U, 34V, 34W) connected between the high potential input wiring and the low potential input wiring; and Each of the series switch circuits is an upper switching element connected between the high potential input wiring and the corresponding output wiring; a lower switching element connected between the corresponding output wiring and the low potential input wiring; and When the control device receives a warm-up command while the vehicle is stopped, the control device executes a warm-up operation in at least one of the series switch circuits, controlling one of the upper switching element and the lower switching element to a normally-on state and controlling the other of the upper switching element and the lower switching element to a high-loss-on state in which a loss higher than that in the normally-on state occurs. Electrical circuit. (Configuration 2) 2. The electric circuit according to claim 1, wherein the control device alternately performs, in the series switch circuit during the warm-up operation, a first operation of controlling the upper switching element to the normally-on state and the lower switching element to the high-loss-on state, and a second operation of controlling the upper switching element to the high-loss-on state and the lower switching element to the normally-on state. (Configuration 3) The electric circuit according to configuration 2, wherein when the control device receives the warm-up command while the vehicle is stopped, the control device executes the warm-up operation in each of the series switch circuits such that the first operation and the second operation are executed synchronously in each of the series switch circuits. (Configuration 4) The normally-on state is a state in which a first gate-on potential higher than a gate threshold is applied to the gate; The high-loss on state is a state in which a second gate-on potential higher than the gate threshold and lower than the first gate-on potential is applied to the gate. 4. The electric circuit according to any one of configurations 1 to 3. (Configuration 5) in at least one of the series switch circuits, at a timing when a first switching element, which is one of the upper side switching element and the lower side switching element, is switched from the normally-on state to the high-loss-on state and a second switching element, which is the other of the upper side switching element and the lower side switching element, is switched from the high-loss-on state to the normally-on state, a dead time is provided between a normally-on period of the first switching element and a normally-on period of the second switching element, During the dead time, the first switching element is controlled to be in the high-loss on or off state, and the second switching element is controlled to be in the high-loss on or off state. 5. The electrical circuit of claim 4. (Configuration 6) The electric circuit of configuration 4 or 5, wherein the control device changes the second gate-on potential applied to the gate of the switching element to be turned on with high loss, depending on at least one of the temperature and the current of the switching element to be turned on with high loss. (Configuration 7) The normally-on state is a state in which a gate-on potential higher than a gate threshold is applied to the gate; The high-loss on state is a state in which a fluctuating voltage fluctuating between the gate on potential and a gate off potential lower than the gate threshold is applied to the gate. 4. The electric circuit according to any one of configurations 1 to 3. (Configuration 8) the gate-on potential applied to the gate in the normally-on state is a first gate-on potential; the gate-on potential applied to the gate in the high-loss-on state is a second gate-on potential lower than the first gate-on potential; 8. The electrical circuit of claim 7. (Configuration 9) further comprising a plurality of gate drive circuits; each of the gate drive circuits is connected to a gate of a corresponding one of the upper switching element and the lower switching element; Each of the gate drive circuits is a power supply circuit that outputs the first gate-on potential; a gate-off potential output circuit that outputs the gate-off potential; a switching circuit that switches between a first state in which the power supply circuit is connected to a corresponding gate and a second state in which the gate-off potential output circuit is connected to the corresponding gate, the switching circuit being in the first state when the gate-on potential is applied to the corresponding gate and in the second state when the gate-off potential is applied to the corresponding gate; and In the normally-on state, the length of the period of the first state is set so that the potential of the corresponding gate rises to the first gate-on potential within the period of the first state, In the high-loss ON state, the length of the period of the first state is set so that the potential of the corresponding gate at the end of the period of the first state becomes the second gate-ON potential. 9. The electrical circuit of claim 8. (Configuration 10) further comprising a plurality of gate drive circuits; each of the gate drive circuits is connected to a gate of a corresponding one of the upper switching element and the lower switching element; The gate drive circuit a first power supply circuit that outputs the first gate-on potential; a second power supply circuit that outputs the second gate-on potential; a gate-off potential output circuit that outputs the gate-off potential; a switching circuit that switches among a state in which the first power supply circuit is connected to the corresponding gate, a state in which the second power supply circuit is connected to the corresponding gate, and a state in which the gate-off potential output circuit is connected to the corresponding gate; and When applying the gate-off potential to the corresponding gate, the switching circuit connects the gate-off potential output circuit to the corresponding gate; When the first gate-on potential is applied to the corresponding gate in the normally-on state, the switching circuit connects the first power supply circuit to the corresponding gate; When the second gate-on potential is applied to the corresponding gate in the high-loss-on state, the switching circuit connects the second power supply circuit to the corresponding gate. 9. The electrical circuit of claim 8. (Configuration 11) in at least one of the series switch circuits, at a timing when a first switching element, which is one of the upper side switching element and the lower side switching element, is switched from the normally-on state to the high-loss-on state and a second switching element, which is the other of the upper side switching element and the lower side switching element, is switched from the high-loss-on state to the normally-on state, a dead time is provided between a normally-on period of the first switching element and a normally-on period of the second switching element, During the dead time, the first switching element is controlled to be turned off and the second switching element is controlled to be turned off. 11. The electric circuit according to any one of configurations 7 to 10. (Configuration 12) 12. The electric circuit according to any one of configurations 7 to 11, wherein the control device changes the duty ratio of the variable voltage applied to the gate of the switching element to be turned on with high loss, depending on at least one of the temperature and current of the switching element to be turned on with high loss. (Configuration 13) further comprising a plurality of gate drive circuits; each of the gate drive circuits controls a potential of a gate of a corresponding one of the upper switching element and the lower switching element; each gate drive circuit controls the gate potential of the corresponding switching element so that the rate of decrease in gate potential when the corresponding switching element is switched from the high-loss on state to the off state during the warm-up operation is slower than the rate of decrease in gate potential when the corresponding switching element is switched from on state to off state during the operation of rotating the motor; 13. The electric circuit according to any one of aspects 7 to 12. (Configuration 14) The electric circuit according to any one of configurations 1 to 13, wherein, when a current is detected in any of the output wirings during execution of the warm-up operation, the upper switching element in each of the series switch circuits is controlled to be normally on and the lower switching element is controlled to be off, or the upper switching element in each of the series switch circuits is controlled to be off and the lower switching element is controlled to be normally on. (Configuration 15) 15. The electric circuit according to any one of configurations 1 to 14, further comprising a coolant flow path (52) for cooling the battery and the inverter.

[0083] According to the second configuration, the amount of heat generated by the inverter can be increased while preventing the switching elements from rising excessively in temperature.

[0084] According to the third configuration, the amount of heat generated by the inverter can be increased.

[0085] By applying the second gate-on potential to the gate of the switching element as in configuration 4, the switching element can be turned on in a state where high loss occurs.

[0086] According to the fifth configuration, it is possible to prevent an overcurrent from flowing through the series switch circuit.

[0087] According to the sixth configuration, the temperature of the switching element that turns on with high loss can be appropriately controlled.

[0088] By applying a fluctuating voltage to the gate of the switching element as in configuration 7, the switching element can be turned on in a state where high loss occurs.

[0089] According to the eighth configuration, the on-resistance of the switching element in the high-loss on state can be increased.

[0090] According to the ninth configuration, the first gate-on potential and the second gate-on potential can be generated by one power supply circuit.

[0091] According to the tenth configuration, the first gate-on potential and the second gate-on potential can be stabilized.

[0092] According to the eleventh configuration, it is possible to prevent an overcurrent from flowing through the series switch circuit.

[0093] According to the twelfth aspect, the temperature of the switching element that turns on with high loss can be appropriately controlled.

[0094] According to the configuration 13, it is possible to reduce the surge voltage that occurs when switching from high-loss on to off.

[0095] According to the fourteenth aspect, the warm-up operation can be stopped appropriately when an abnormal current occurs.

[0096] According to the fifteenth aspect, the temperature of the battery can be increased more effectively by using the heat generated by the inverter.

[0097] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0098] 12: Battery, 30: Inverter, 31: High-potential input wiring, 32: Low-potential input wiring, 35UU, 35VU, 35WU: Upper switching elements, 35VL, 35VL, 35Wl: Lower switching elements, 38: Smoothing capacitor

Claims

1. An electrical circuit mounted on a vehicle, a battery (12); a motor (80); an inverter (30) connected between the battery and the motor; a control device (90); and The inverter A high potential input wiring (31); A low potential input wiring (32); A plurality of output wirings (33U, 33V, 33W) connected to the motor; a smoothing capacitor (38) connected between the high potential input wiring and the low potential input wiring; a plurality of series switch circuits (34U, 34V, 34W) connected between the high potential input wiring and the low potential input wiring; and Each of the series switch circuits is an upper switching element connected between the high potential input wiring and the corresponding output wiring; a lower switching element connected between the corresponding output wiring and the low potential input wiring; and When the control device receives a warm-up command while the vehicle is stopped, the control device executes a warm-up operation in at least one of the series switch circuits, controlling one of the upper switching element and the lower switching element to a normally-on state and controlling the other of the upper switching element and the lower switching element to a high-loss-on state in which a loss higher than that in the normally-on state occurs. Electrical circuit.

2. 2. The electric circuit according to claim 1, wherein the control device alternately executes, in the series switch circuit during the warm-up operation, a first operation of controlling the upper switching element to the normally-on state and the lower switching element to the high-loss-on state, and a second operation of controlling the upper switching element to the high-loss-on state and the lower switching element to the normally-on state.

3. 3. The electric circuit according to claim 2, wherein when the control device receives the warm-up command while the vehicle is stopped, the control device executes the warm-up operation in each of the series switch circuits such that the first operation and the second operation are executed synchronously in each of the series switch circuits.

4. The normally-on state is a state in which a first gate-on potential higher than a gate threshold is applied to the gate, the high-loss-ON state is a state in which a second gate-ON potential higher than the gate threshold and lower than the first gate-ON potential is applied to the gate; An electric circuit according to any one of claims 1 to 3.

5. in at least one of the series switch circuits, at a timing when a first switching element, which is one of the upper side switching element and the lower side switching element, is switched from the normally-on state to the high-loss-on state and a second switching element, which is the other of the upper side switching element and the lower side switching element, is switched from the high-loss-on state to the normally-on state, a dead time is provided between a normally-on period of the first switching element and a normally-on period of the second switching element, During the dead time, the first switching element is controlled to be in the high-loss on or off state, and the second switching element is controlled to be in the high-loss on or off state.

5. The electrical circuit of claim 4.

6. 5. The electric circuit according to claim 4, wherein the control device changes the second gate-on potential applied to the gate of the switching element to be turned on with high loss, depending on at least one of a temperature and a current of the switching element to be turned on with high loss.

7. The normally-on state is a state in which a gate-on potential higher than a gate threshold is applied to the gate; The high-loss on state is a state in which a fluctuating voltage fluctuating between the gate on potential and a gate off potential lower than the gate threshold is applied to the gate. The electric circuit according to any one of claims 1 to 3.

8. the gate-on potential applied to the gate in the normally-on state is a first gate-on potential; the gate-on potential applied to the gate in the high-loss-on state is a second gate-on potential lower than the first gate-on potential; 8. The electrical circuit of claim 7.

9. further comprising a plurality of gate drive circuits; each of the gate drive circuits is connected to a gate of a corresponding one of the upper switching element and the lower switching element; Each of the gate drive circuits is a power supply circuit that outputs the first gate-on potential; a gate-off potential output circuit that outputs the gate-off potential; a switching circuit that switches between a first state in which the power supply circuit is connected to a corresponding gate and a second state in which the gate-off potential output circuit is connected to the corresponding gate, the switching circuit being in the first state when the gate-on potential is applied to the corresponding gate and being in the second state when the gate-off potential is applied to the corresponding gate; and In the normally-on state, the length of the period of the first state is set so that the potential of the corresponding gate rises to the first gate-on potential within the period of the first state, In the high-loss on state, the length of the period of the first state is set so that the potential of the corresponding gate at the end of the period of the first state becomes the second gate-on potential.

9. The electrical circuit of claim 8.

10. further comprising a plurality of gate drive circuits; each of the gate drive circuits is connected to a gate of a corresponding one of the upper switching element and the lower switching element; The gate drive circuit a first power supply circuit that outputs the first gate-on potential; a second power supply circuit that outputs the second gate-on potential; a gate-off potential output circuit that outputs the gate-off potential; a switching circuit that switches among a state in which the first power supply circuit is connected to the corresponding gate, a state in which the second power supply circuit is connected to the corresponding gate, and a state in which the gate-off potential output circuit is connected to the corresponding gate; and When applying the gate-off potential to the corresponding gate, the switching circuit connects the gate-off potential output circuit to the corresponding gate; When the first gate-on potential is applied to the corresponding gate in the normally-on state, the switching circuit connects the first power supply circuit to the corresponding gate; the switching circuit connects the second power supply circuit to the corresponding gate when the second gate-on potential is applied to the corresponding gate in the high-loss-on state; 9. The electrical circuit of claim 8.

11. in at least one of the series switch circuits, at a timing when a first switching element, which is one of the upper side switching element and the lower side switching element, is switched from the normally-on state to the high-loss-on state and a second switching element, which is the other of the upper side switching element and the lower side switching element, is switched from the high-loss-on state to the normally-on state, a dead time is provided between a normally-on period of the first switching element and a normally-on period of the second switching element, During the dead time, the first switching element is controlled to be turned off and the second switching element is controlled to be turned off.

8. The electrical circuit of claim 7.

12. 8. The electric circuit according to claim 7, wherein the control device changes a duty ratio of the varying voltage applied to the gate of the switching element to be turned on with high loss, depending on at least one of a temperature and a current of the switching element to be turned on with high loss.

13. further comprising a plurality of gate drive circuits; each of the gate drive circuits controls a potential of a gate of a corresponding one of the upper switching element and the lower switching element; each gate drive circuit controls the gate potential of the corresponding switching element so that the rate of decrease in gate potential when the corresponding switching element is switched from the high-loss on state to the off state during the warm-up operation is slower than the rate of decrease in gate potential when the corresponding switching element is switched from on state to off state during the operation of rotating the motor; 8. The electrical circuit of claim 7.

14. 4. The electric circuit according to claim 1, wherein, when a current is detected in any of the output wirings during execution of the warm-up operation, the upper switching element in each of the series switch circuits is controlled to be normally on and the lower switching element is controlled to be off, or the upper switching element in each of the series switch circuits is controlled to be off and the lower switching element is controlled to be normally on.

15. The electric circuit of any one of claims 1 to 3, further comprising a coolant flow path (52) for cooling the battery and the inverter.

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