Inverter control device, module provided with inverter control device, program, and inverter control method

Abstract

An inverter control device (80) is applied to a system (10) comprising a rotary electric machine (30) having armature windings (33U-33W) and an inverter (40) that electrically connects the armature windings and an electricity storage unit (20). The system is provided with a capacitor (41) connected in parallel to the electricity storage unit. The inverter control device comprises: a determination unit (100) that determines whether or not there is a request for measuring the impedance of the electricity storage unit; a setting unit (101) that, when it is determined that there is the request for the measurement, sets an AC target current (Iac*) for measuring the impedance of the electricity storage unit, said AC target current being the target value of an AC component of the current flowing through the electricity storage unit; and a switch control unit (105) that performs switching control of the inverter in order to cause the set AC target current to flow to the electricity storage unit.

Description

Inverter control device, module equipped with inverter control device, program, and inverter control method CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-069662, filed on April 23, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to an inverter control device, a module including the inverter control device, a program, and an inverter control method.

[0003] Among control devices applied to circuits having a power storage unit, there is one that obtains a signal for measuring the impedance of the power storage unit by passing an alternating current through the power storage unit. An example of such a control device is the control device disclosed in Patent Document 1.

[0004] Japanese Patent Application Laid-Open No. 2004-028663

[0005] There is still room for improvement in the technology for simplifying the configuration for passing an AC current through the power storage unit to measure the impedance of the power storage unit.

[0006] A main object of the present disclosure is to provide an inverter control device, a program, and an inverter control method that can simplify the configuration for passing an AC current to a power storage unit for impedance measurement.

[0007] The present disclosure relates to an inverter control device that is applied to a system that includes: a rotating electric machine having an armature winding; and an inverter that electrically connects the armature winding and a power storage unit; wherein the system includes a capacitor that is connected in parallel to the power storage unit.

[0008] The present disclosure includes a determination unit that determines whether or not there is a request to measure the impedance of the power storage unit; a setting unit that, when it is determined that there is a measurement request, sets an AC target current for measuring the impedance of the power storage unit, which is a target value of the AC component of the current to be passed through the power storage unit; and a switch control unit that performs switching control of the inverter so that the set AC target current is passed through the power storage unit.

[0009] The processing by the setting unit and the switch control unit generates an AC voltage in the capacitor. As the AC voltage is generated in the capacitor, discharging from the capacitor to the power storage unit and charging from the power storage unit to the capacitor are repeated. This causes an AC current to flow in the power storage unit. In this way, the AC current for measuring the impedance of the power storage unit can be passed by utilizing the inverter and the rotating electric machine. This simplifies the configuration for passing the AC current for measuring the impedance.

[0010] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is an overall configuration diagram of a system according to a first embodiment, Fig. 2 is a block diagram of processing executed by a motor ECU, Fig. 3 is a time chart showing the transitions of d-axis and q-axis currents and three-phase currents in measurement control, Fig. 4 is a time chart showing the transitions of three-phase currents, terminal voltage of a capacitor, and current flowing to a battery in measurement control, Fig. 5 is a flowchart of measurement control, Fig. 6 is a diagram showing the time transition of the frequency of the d-axis current, Fig. 7 is a diagram showing the relationship between the frequency of AC current flowing to a battery and the amplitude of AC current flowing to the battery, Fig. 8 is an overall configuration diagram of a system according to a second embodiment, Fig. 9 is a diagram showing a drive circuit and its peripheral configuration, and Fig. 10 is a diagram showing the three-phase currents, the state of switching control, battery loss, and current flowing to the battery in measurement control. 16 is a time chart schematically showing the transition of torque generated by the rotor according to the third embodiment; FIG. 17 is a diagram showing how gear teeth striking is prevented; FIG. 18 is a time chart showing the transition of rotor rotation angle during measurement control according to the third embodiment and the comparative example; and FIG. 19 is a time chart showing an example of a method for setting a command current.

[0011] Several embodiments will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding and / or associated parts may be designated by the same reference numerals or reference numerals that differ in the hundredth or more digit. For corresponding and / or associated parts, reference may be made to the descriptions of other embodiments.

[0012] A first embodiment of a control device according to the present disclosure will be described below with reference to the drawings. The control device of the present embodiment is applied to a system mounted on an electrically powered vehicle such as an electric vehicle or a hybrid vehicle.

[0013] As shown in FIG. 1 , a system 10 (corresponding to a "module") includes a battery 20 (corresponding to a "power storage unit") that is a DC power source, a rotating electric machine 30, and an inverter 40. The battery 20 is, for example, a battery pack including a series connection of unit cells. A unit cell is a single battery cell or a series connection of multiple battery cells. The battery cell is, for example, a secondary battery such as a lithium-ion battery.

[0014] The rotating electric machine 30 is an on-board main engine that serves as a power source for running the vehicle. The rotating electric machine 30 includes a stator 31 as an armature and a rotor 34. The rotor 34 is capable of transmitting power to drive wheels 51 of the vehicle via a power transmission mechanism 50. Torque generated by the rotating electric machine 30 functioning as an electric motor is transmitted to the drive wheels 51 via the power transmission mechanism 50, causing the drive wheels 51 to rotate. The power transmission mechanism 50 includes a transmission and a shaft. The transmission is, for example, a reduction gear.

[0015] In this embodiment, the rotating electric machine 30 is a permanent magnet field type synchronous machine. The rotor 34 includes a rotor core 35 and permanent magnets 36 (e.g., neodymium magnets) that serve as field poles provided on the rotor core 35.

[0016] The stator 31 includes an armature core 32 and an armature winding wound around the armature core 32. The armature winding includes a U-phase winding 33U, a V-phase winding 33V, and a W-phase winding 33W, and is star-connected. The U-, V-, and W-phase windings 33U, 33V, and 33W are arranged on the armature core 32 with a 120-degree electrical angle offset between them.

[0017] The inverter 40 is a power conversion circuit that converts DC power supplied from the battery 20 into three-phase AC power and supplies it to the armature windings. The inverter 40 includes a series connection of three-phase upper-arm switches SH and lower-arm switches SL. In this embodiment, each of the switches SH and SL is a voltage-controlled semiconductor switching element, more specifically, an N-channel MOSFET. The high-potential terminal of each of the switches SH and SL is the drain, and the low-potential terminal is the source. Each of the switches SH and SL has a body diode. Specifically, the upper-arm switch SH of each phase has an upper-arm diode DH, and the lower-arm switch SL of each phase has a lower-arm diode DL.

[0018] In each phase, first ends of the U-, V-, and W-phase windings 33U, 33V, and 33W are connected to the source of the upper arm switch SH and the drain of the lower arm switch SL. Second ends of the U-, V-, and W-phase windings 33U, 33V, and 33W are connected to the neutral point.

[0019] In each phase, the drain of the upper arm switch SH is connected to the positive terminal of the battery 20. In each phase, the source of the lower arm switch SL is connected to the negative terminal of the battery 20.

[0020] The system 10 includes a capacitor 41. The capacitor 41 functions as a smoothing capacitor. The capacitor 41 is connected in parallel to a series connection of the upper arm switch SH and the lower arm switch SL of each phase. The capacitor 41 may be built into the inverter 40 or may be provided outside the inverter 40.

[0021] The system 10 includes a main switch SMR for electrically connecting or disconnecting the battery 20 and the capacitor 41. In this embodiment, the main switch SMR is a mechanical relay. When the main switch SMR is turned off, it blocks bidirectional current flow, and when turned on, it allows bidirectional current flow. Note that the main switch SMR is not limited to a mechanical relay, and may be, for example, a semiconductor switching element.

[0022] The system 10 includes a phase current sensor 60, a rotation angle sensor 61, a voltage sensor 62, a battery current sensor 63, and a temperature sensor 64. The phase current sensor 60 detects the phase currents flowing through the U-, V-, and W-phase windings 33U, 33V, and 33W. The rotation angle sensor 61 is, for example, a resolver, and detects the electrical angle of the rotor 34. The voltage sensor 62 detects the voltage between the terminals of each of the unit batteries that make up the battery 20. The battery current sensor 63 detects the current flowing through the battery 20. In this embodiment, the battery current sensor 63 detects the current flowing through a shunt resistor (not shown) that is provided between the source of the lower arm switch SL and the negative terminal of the battery 20. The temperature sensor 64 detects the temperature of each switch SH, SL.

[0023] The system 10 includes a monitoring ECU 70 that monitors the battery 20, a motor ECU 80 (corresponding to an "inverter control device") that controls the inverter 40, and a battery ECU 90 (corresponding to a "measurement control device") that measures the impedance of the battery 20. The monitoring ECU 70 is an electronic control unit (ECU) and includes a processor 71 and a storage unit 72 as hardware. The motor ECU 80 is an electronic control unit and includes a processor 81 and a storage unit 82 as hardware. The battery ECU 90 is an electronic control unit and includes a processor 91 and a storage unit 92 as hardware. In each of the ECUs 70, 80, and 90, the processor 71 and the storage unit 72 are connected to each other via a communication bus 73, the processor 81 and the storage unit 82 are connected to each other via a communication bus 83, and the processor 91 and the storage unit 92 are connected to each other via a communication bus 93.

[0024] The battery ECU 90 is a control device at a higher level than the monitoring ECU 70 and the motor ECU 80. The monitoring ECU 70 and the motor ECU 80 can exchange information via the battery ECU 90.

[0025] The memory units 72, 82, 92 include hardware memory and storage. The memory is a storage device for storing data used in the processing of the monitoring ECU 70, the motor ECU 80, or the battery ECU 90. The memory provides the processors 71, 81, 91 with a working area for temporary use when the processors 71, 81, 91 perform processing, for example. The memory includes, for example, a ROM or a RAM. The storage is a storage device for storing various programs and data to be read and executed by the processors 71, 81, 91, and is a non-transitory tangible storage medium. The storage includes, for example, an HDD or flash memory. The storage stores program information and the like for processing, such as those shown in FIGS. 5 and 11, which will be described later.

[0026] For example, program information stored on a non-transient physical recording medium is installed in the storage units 72, 82, and 92. The recording medium is, for example, a USB memory, a CD-ROM, or a DVD. Also, for example, program information transmitted via a communication network, such as over the air (OTA), is installed in the storage units 72, 82, and 92.

[0027] The monitoring ECU 70 receives the detection value of the voltage sensor 62. The motor ECU 80 receives the detection values ​​of the phase current sensor 60, the rotation angle sensor 61, and the temperature sensor 64. The battery ECU 90 receives the detection value of the battery current sensor 63.

[0028] The main switch SMR may be controlled by any one of the monitoring ECU 70, the motor ECU 80, or the battery ECU 90, or may be controlled by an ECU other than the ECUs 70, 80, and 90. In the present embodiment, the main switch SMR is hereinafter assumed to be controlled by the motor ECU 80.

[0029] Next, a description will be given of measurement control that is executed to obtain a signal (hereinafter, measurement signal) for measuring the impedance of the battery 20. During measurement control, the rotor 34 is maintained in a stopped state. In this embodiment, the measurement signal is a terminal voltage (hereinafter, battery voltage VBr) of the battery 20 (specifically, for example, each unit cell constituting the battery 20) and a current (hereinafter, battery current IBr) flowing through the battery 20, which are obtained by passing AC currents of multiple frequencies through the battery 20. During measurement control, the motor ECU 80 controls the on / off of each switch SH, SL of the inverter 40 to pass AC currents of multiple frequencies through the battery 20.

[0030] FIG. 2 is a block diagram showing the control process of the system 10 executed by the motor ECU 80. As shown in FIG.

[0031] The determination unit 100 determines whether there is a request to measure the impedance of the battery 20. The determination unit 100 determines that there is a measurement request when, for example, it determines that a measurement command has been input from the battery ECU 90. The determination unit 100 inputs the determination result to the setting unit 101.

[0032] When the setting unit 101 determines that a measurement request has been made, it turns on the main switch SMR and executes measurement control. In the measurement control, the setting unit 101 sets an AC command current Iac*, which is a target value of the AC component of the battery current IBr to be supplied to the battery 20. The setting unit 101 calculates d- and q-axis command currents Id* and Iq* to supply the AC command current Iac* to the battery 20 while maintaining the rotor 34 in a rotation-stopped state. The d- and q-axis command currents Id* and Iq* are command values ​​of the d- and q-axis currents to be supplied to the U-, V-, and W-phase windings 33U, 33V, and 33W. Specifically, when supplying the AC command current Iac* of a predetermined measurement frequency to the battery 20, the setting unit 101 sets the AC d-axis command current Id* so that a sinusoidal d-axis current Idr flows through the U-, V-, and W-phase windings 33U, 33V, and 33W, as shown in FIG. 3A . Furthermore, the setting unit 101 sets the q-axis command current Iq* to zero.

[0033] Returning to the explanation of Figure 2, the two-phase conversion unit 102 calculates the d-axis current Idr and the q-axis current Iqr based on the phase currents Iur, Ivr, and Iwr detected by the phase current sensor 60 and the electrical angle θr detected by the rotation angle sensor 61.

[0034] The current feedback unit 103 calculates a d-axis command voltage Vd* and a q-axis command voltage Vq* based on the d- and q-axis command currents Id* and Iq* and the d- and q-axis currents Idr and Iqr. Specifically, the current feedback unit 103 calculates a d-axis current deviation, which is the difference between the d-axis command current Id* and the d-axis current Idr, and calculates a d-axis command voltage Vd* as a manipulated variable for feedback-controlling the calculated d-axis current deviation to zero. The current feedback unit 103 calculates a q-axis current deviation, which is the difference between the q-axis command current Iq* and the q-axis current Iqr, and calculates a q-axis command voltage Vq* as a manipulated variable for feedback-controlling the calculated q-axis current deviation to zero. The feedback control is, for example, proportional-plus-integral control.

[0035] The three-phase converter 104 calculates U-, V-, and W-phase command voltages Vu*, Vv*, and Vw* based on the d- and q-axis command voltages Vd* and Vq* and the electrical angle θr. The U-, V-, and W-phase command voltages Vu*, Vv*, and Vw* are command values ​​for the voltages applied to the U-, V-, and W-phase windings 33U, 33V, and 33W.

[0036] The switch control unit 105 calculates U-, V-, and W-phase modulation command values ​​Mu*, Mv*, and Mw* by dividing the U-, V-, and W-phase command voltages Vu*, Vv*, and Vw* input from the three-phase conversion unit 104 by the battery voltage VBr. The switch control unit 105 generates drive signals for the switches SH and SL of the inverter 40 based on the calculated modulation factors Mu*, Mv*, and Mw*. The drive signals include switch on and off commands. Specifically, for example, the switch control unit 105 may generate the drive signals for the switches SH and SL of the inverter 40 by PWM processing based on a magnitude comparison between the modulation factors Mu, Mv, and Mw and a carrier signal (e.g., a triangular wave signal).

[0037] Based on the generated drive signal, the switch control unit 105 controls the charge / discharge current of the gates of the switches SH and SL of the inverter 40. As a result, switching control of the switches SH and SL of the inverter 40 is performed in accordance with the drive signal.

[0038] When a sinusoidal d-axis current Idr flows through the U-, V-, and W-phase windings 33U, 33V, and 33W as shown in Fig. 3(a), an AC current flows through the U-, V-, and W-phase windings 33U, 33V, and 33W as shown in Fig. 3(b). In Fig. 3(b), Iu represents the U-phase current flowing through the U-phase winding 33U, Iv represents the V-phase current flowing through the V-phase winding 33V, and Iw represents the W-phase current flowing through the W-phase winding 33W. The period of the d-axis current Idr is the same as the period of the U-, V-, and W-phase currents Iu, Iv, and Iw.

[0039] In the measurement control, an AC battery current IBr is passed through the battery 20. This will be explained with reference to Fig. 4. Fig. 4(a) shows the transition of the three-phase current, and Fig. 4(b) is an enlarged view of a half cycle Tc of the three-phase current in Fig. 4(a). Fig. 4(c) shows the transition of the capacitor voltage Vcr, which is the voltage between the terminals of the capacitor 41, and Fig. 4(d) shows the transition of the battery current IBr.

[0040] The capacitor voltage Vcr changes periodically as the switches SH and SL of the inverter 40 are switched. As shown by the dashed line in FIG. 4C , one cycle of the sinusoidal envelope Ea of the capacitor voltage Vcr is the same as or equivalent to half a cycle of the d-axis command current Id*. During the period from time t0 to time t1, the capacitor 41 discharges, causing current to flow from the capacitor 41 to the battery 20, thereby charging the battery 20. During the period from time t1 to time t2, the battery 20 discharges, causing current to flow from the battery 20 to the capacitor 41, thereby charging the capacitor 41. Thus, during the period from time t0 to time t2, the battery current IBr changes sinusoidally as the capacitor 41 is charged and discharged.

[0041] The setting unit 101 calculates the d-axis command current Id* so that the AC component of the battery current IBr flowing through the battery 20 crosses zero. As a result, one period of the AC component of the current flowing through the battery 20 includes one period during which a charging current flows through the battery 20 and one period during which a discharging current flows through the battery 20. Note that, for example, due to copper loss in the rotating electric machine 30, the negative amplitude In of the battery current IBr may be smaller than the positive amplitude Ip. In this case, taking into consideration that the negative amplitude In is smaller than the positive amplitude Ip, the d-axis command current Id* may be calculated so that the area S1 of the first region and the area S2 of the second region are equal. The area S1 of the first region is a region surrounded by the positive battery current IBr and the time axis from the first zero-cross timing C1 to the second zero-cross timing C2 of the battery current IBr in one period of the battery current IBr. The area S2 of the second region is an area enclosed by the negative battery current IBr and the time axis from the second zero-crossing timing C2 to the third zero-crossing timing C3 of the battery current IBr in one cycle of the battery current IBr. Note that the zero-crossing timing is the timing at which the value of the battery current IBr changes from a non-zero value to zero.

[0042] In the measurement control of this embodiment, when AC battery current IBr is passed through battery 20, charging and discharging of battery 20 are repeated. When battery 20 is being charged, current flows from capacitor 41 to battery 20. When battery 20 is being discharged, current flows from battery 20 to capacitor 41. Therefore, power stored in battery 20 can be exchanged between capacitor 41 and battery 20. This allows AC battery current IBr to be passed through battery 20 while suppressing consumption of power stored in battery 20.

[0043] Fig. 5 shows a flowchart of the measurement process executed by the motor ECU 80. The process shown in Fig. 5 is repeatedly executed by the processor 81 of the motor ECU 80, for example, at a predetermined control cycle. The determination and setting methods in the following steps are the same as those described with reference to Fig. 2 and the like.

[0044] In step S10, the determining unit 100 determines whether or not there is a request to measure the impedance of the battery 20.

[0045] In step S11, the determination unit 100 checks whether or not the battery 20 is electrically connected to the capacitor 41. In this embodiment, the determination unit 100 determines whether or not the main switch SMR is on.

[0046] If it is determined in step S11 that the main switch SMR is off, the main switch SMR is turned on in step S12.

[0047] In step S13, measurement control is executed. In the measurement control, the setting unit 101 sets the AC command current Iac* so that AC currents of multiple frequencies are passed through the battery 20. Here, the frequency range of the AC command current Iac* is, for example, 1 Hz to 1 kHz. The setting unit 101 sets the frequency fr of the sinusoidal d-axis current Idr to be passed through the U-, V-, and W-phase windings 33U, 33V, and 33W based on the frequency of the AC command current Iac*. Here, when AC currents of multiple frequencies are passed through the battery 20, a measurement signal can be efficiently obtained by performing a frequency sweep in which the frequency fr of the d-axis current Idr is gradually changed (specifically, increased or decreased). Specifically, as shown in FIG. 6 , the frequency fr of the d-axis current Idr is linearly changed during the period from time t1 to time t2.

[0048] When the switch control unit 105 executes measurement control to pass a high-frequency AC current through the battery 20, the switch control unit 105 increases the switching frequency of each switch SH, SL more than in normal control. Here, normal control refers to control that generates and outputs a drive signal for controlling the control amount of the rotating electric machine 30 to a command value in order to run the vehicle.

[0049] When the switching frequency of each switch SH, SL is low, the responsiveness of the AC current flowing through the battery 20 to the d-axis command current Id* is low. Therefore, if the switching frequency of each switch SH, SL when a high-frequency AC current is flowing through the battery 20 in measurement control is equal to the switching frequency of each switch SH, SL in normal control, there is a concern that the AC component of the battery current IBr cannot be controlled to the AC command current Iac*. Therefore, by increasing the switching frequency of each switch SH, SL in measurement control, the AC component of the battery current IBr can be controlled to the AC command current Iac* even if the AC command current Iac* is high frequency.

[0050] The battery ECU 90 calculates the impedance of the battery 20 based on the measurement signals obtained by the measurement control. Specifically, the battery ECU 90 calculates the impedance of each unit battery constituting the battery 20 based on the battery voltage VBr and the battery current IBr. The battery ECU 90 uses the detection value of the voltage sensor 62 as the battery voltage VBr. The battery ECU 90 also uses the detection value of the battery current sensor 63 as the battery current IBr. The battery ECU 90 may, for example, create a complex impedance plane plot (Cole-Cole plot) and calculate the impedance of the battery 20. The battery ECU 90 monitors the state of the battery 20 (e.g., the state of charge (SOC) and the state of health (SOH)) based on the impedance calculation results.

[0051] FIG. 7 shows the relationship between the frequency of the battery current IBr and the amplitude Iar of the battery current IBr. In this embodiment, the higher the frequency of the battery current IBr, the longer the time it takes for the capacitor 41 to charge and discharge, and the larger the amplitude Iar of the battery current IBr. Therefore, the higher the frequency of the battery current IBr, the higher the S / N ratio of the measurement signal of the battery 20. In FIG. 7, Iath represents an amplitude threshold. The amplitude threshold Iath is a value that can obtain a measurement signal with a sufficient S / N ratio to calculate the impedance of the battery 20 when the battery current IBr has an amplitude Iar equal to or greater than the amplitude threshold Iath when the battery current IBr has an amplitude Iar equal to or greater than the amplitude threshold Iath. In this embodiment, when the frequency of the battery current IBr is equal to or greater than the frequency threshold fth, the amplitude Iar of the battery current IBr can be made equal to or greater than the amplitude threshold Iath.

[0052] In this embodiment, the electrical angle of the rotating electrical machine 30 is set to 0 degrees. However, the electrical angle is not limited to this and may be a value other than 0 degrees. In this case, the amplitude Iar of the battery current IBr is larger than when it is 0 degrees, so a measurement signal with a higher S / N ratio can be obtained.

[0053] According to the measurement control of this embodiment described above in detail, AC battery current IBr can be caused to flow through the battery 20 by switching control that utilizes the inverter 40 and the rotating electrical machine 30. Therefore, a signal for measuring the impedance of the battery 20 can be obtained while simplifying the system 10.

[0054] <Modification of First Embodiment> In the measurement control, the motor ECU 80 may control the q-axis current Iqr to a value other than zero (e.g., a value close to zero) instead of setting the q-axis current Iqr to zero. For example, the motor ECU 80 may set the q-axis command current Iq* to a value other than zero that allows the rotor 34 of the rotating electric machine 30 to maintain a stopped state during measurement control. Furthermore, for example, the motor ECU 80 may set the q-axis command current Iq* to a value other than zero and perform a reduction process to reduce the torque transmitted by the power transmission mechanism 50 to the drive wheels 51. The reduction process may be, for example, at least one of a process to reduce the degree of transmission of torque transmitted from the rotor 34 to the drive wheels 51 by a clutch included in the power transmission mechanism 50 and a process to reduce the gear ratio of the transmission. This makes it possible to suppress rotation of the rotor 34 even when the q-axis current Iqr is set to a value other than zero during measurement control.

[0055] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, switching control is performed in addition to measurement control. The switching control is control for changing the switching speed of each switch SH, SL constituting the inverter 40 in order to increase the amplitude of the AC current for impedance measurement.

[0056] 8, the inverter 40 includes a driver 110 provided individually for each of the switches SH and SL. The switch controller 105 outputs a drive signal Gm to the driver 110.

[0057] In this embodiment, the drive units 110 provided for the switches SH and SL have the same configuration. Therefore, the following description will be given using the drive unit 110 provided for the lower arm switch SL as an example.

[0058] 9, the drive unit 110 includes a drive circuit 111 and a speed change unit 112. The drive signal Gm output from the switch control unit 105 is input to the drive circuit 111. Based on the input drive signal Gm, the drive circuit 111 switches the drive state of the lower arm switch SL from one of an on state and an off state to the other via the speed change unit 112.

[0059] An example of the speed change unit 112 will be described. The speed change unit 112 includes a constant voltage power supply 120, a first charging path 121, a first charging switch 122, and a first charging resistor 123. The constant voltage power supply 120 is connected to the gate of the lower arm switch SL via the first charging path 121. The first charging path 121 is provided with the first charging switch 122 and the first charging resistor 123.

[0060] The speed change unit 112 includes a second charging path 124, a second charging switch 125, and a second charging resistor 126. The gate of the lower arm switch SL is connected to the constant voltage power supply 120 via the second charging path 124. The second charging path 124 is provided with the second charging switch 125 and the second charging resistor 126. The resistance value Ron2 of the second charging resistor 126 is greater than the resistance value Ron1 of the first charging resistor 123.

[0061] The speed change unit 112 includes a first discharge path 131, a first discharge switch 132, and a first discharge resistor 133. The gate of the lower arm switch SL is connected to the source of the lower arm switch SL via the first discharge path 131. The first discharge path 131 is provided with the first discharge switch 132 and the first discharge resistor 133.

[0062] The speed change unit 112 includes a second discharge path 134, a second discharge switch 135, and a second discharge resistor 136. The gate of the lower arm switch SL is connected to the source of the lower arm switch SL via the second discharge path 134. The second discharge path 134 is provided with the second discharge switch 135 and the second discharge resistor 136. Here, the resistance value Roff2 of the second discharge resistor 136 is greater than the resistance value Roff1 of the first discharge resistor 133.

[0063] In this embodiment, the first charging switch 122 and the second charging switch 125 are P-channel MOSFETs, and the first discharging switch 132 and the second discharging switch 135 are N-channel MOSFETs.

[0064] The drive circuit 111 performs switching control to switch the resistor connected to the gate of the lower arm switch SL. In the switching control, the drive circuit 111 controls the first and second charging switches 122 and 125 and the first and second discharging switches 132 and 135 to switch between high-speed control that increases the switching speed and low-speed control that decreases the switching speed.

[0065] In the high-speed control, the drive circuit 111 alternately turns on the first charging switch 122 and the first discharging switch 132, and turns off the second charging switch 125 and the second discharging switch 135.

[0066] In the low-speed control, the drive circuit 111 alternately turns on the second charging switch 125 and the second discharging switch 135, and turns off the first charging switch 122 and the first discharging switch 132.

[0067] When the input drive signal Gm is an ON signal and high-speed control is to be performed, the drive circuit 111 turns on the first charging switch 122 and turns off the second charging switch 125, the first discharging switch 132, and the second discharging switch 135. As a result, a charging current is supplied to the gate of the lower-arm switch SL, the gate voltage of the lower-arm switch SL becomes equal to or greater than the threshold voltage, and the lower-arm switch SL is switched on. On the other hand, when the input drive signal Gm is an OFF signal and high-speed control is to be performed, the drive circuit 111 turns on the first discharging switch 132 and turns off the second discharging switch 135, the first charging switch 122, and the second charging switch 125. As a result, charge is discharged from the gate of the lower-arm switch SL, the gate voltage of the lower-arm switch SL becomes less than the threshold voltage, and the lower-arm switch SL is switched off.

[0068] When the input drive signal Gm is an ON signal and low-speed control is to be performed, the drive circuit 111 turns on the second charging switch 125 and turns off the first charging switch 122, the first discharging switch 132, and the second discharging switch 135. As a result, a charging current is supplied to the gate of the lower-arm switch SL, the gate voltage of the lower-arm switch SL becomes equal to or greater than a threshold voltage, and the lower-arm switch SL is switched on. On the other hand, when the input drive signal Gm is an OFF signal and low-speed control is to be performed, the drive circuit 111 turns on the second discharging switch 135 and turns off the first discharging switch 132, the first charging switch 122, and the second charging switch 125. As a result, charge is discharged from the gate of the lower-arm switch SL, the gate voltage of the lower-arm switch SL becomes less than the threshold voltage, and the lower-arm switch SL is switched off.

[0069] In the high-speed control, a resistor with a relatively low resistance is connected to the gate of the lower-arm switch SL, allowing the charging or discharging rate of the gate charge to be high. On the other hand, in the low-speed control, a resistor with a relatively high resistance is connected to the gate of the lower-arm switch SL, allowing the charging or discharging rate of the gate charge to be low. Here, when the charging or discharging rate of the gate charge is low, the loss of the battery 20 increases due to the switching loss of the lower-arm switch SL compared to when the charging or discharging rate is high. This increases the amplitude of the AC current used for impedance measurement.

[0070] Figure 10(a) shows the change in three-phase current, Figure 10(b) shows the change in the switching state between high-speed control and low-speed control, Figure 10(c) shows the change in loss [W] of battery 20, and Figure 10(d) shows the change in battery current IBr flowing to battery 20.

[0071] The drive circuit 111 executes high-speed control during the period from time t0 to time t1. In this case, the drive circuit 111 turns on the first charging switch 122 or the first discharging switch 132 depending on whether the drive signal Gm is an on command or an off command.

[0072] The drive circuit 111 executes low-speed control during the period from time t1 to time t2. In this case, the drive circuit 111 turns on the second charging switch 125 or the second discharging switch 135 depending on whether the drive signal Gm is an on command or an off command. During the period from time t1 to time t2, the charging or discharging rate of the gate charge becomes low. In this case, the switching loss of the lower arm switch SL increases, and as shown in FIG. 10(c), the loss of the battery 20 increases, and the battery current IBr flowing to the battery 20 increases.

[0073] 10(d), high-speed control and low-speed control are executed in the switching control, thereby causing AC battery current IBr to flow. In this embodiment, measurement / switching control is executed in the measurement control, which switches the switching speed of each of the switches SH and SL that configure the inverter 40.

[0074] 11, after steps S10 and S11 are executed, measurement / switching control is executed in step S20. In the measurement / switching control, the switching loss of each of the switches SH and SL that constitute the inverter 40 is increased. This increases the amplitude Iar of the battery current IBr.

[0075] Specifically, the drive circuit 111 performs measurement / switching control so that the frequency of the AC command current Iac* and the frequency at which the switching speed of each switch SH, SL are switched are equivalent. The drive circuit 111 also performs measurement / switching control so that the period during which the low-speed control is performed includes the timing at which the magnitude of the discharge current of the battery current IBr is maximized in each cycle of the AC battery current IBr. As a result, as shown in FIG. 12 , compared to when only measurement control is performed, the amplitude Iar of the battery current IBr is higher even when the frequency of the battery current IBr flowing through the battery 20 is low.

[0076] 12, the frequency threshold value fth in FIG. 7 is referred to as a first frequency threshold value fth1. In this embodiment, when the frequency of the battery current IBr is equal to or higher than a second frequency threshold value fth2 that is lower than the first frequency threshold value fth1, the battery current IBr having an amplitude Iar equal to or higher than the amplitude threshold value Iath can be made to flow through the battery 20.

[0077] According to the measurement / switching control of this embodiment described above in detail, the S / N ratio of the measurement signal can be increased over a wide range of frequencies.

[0078] As shown in FIG. 10 , of the total period (= Tf + Ts) of the high-speed period Tf in which high-speed control is executed and the low-speed period Ts in which low-speed control is executed, the ratio D (= Ts / (Tf + Ts) × 100) of the low-speed period is set based on the temperature Tr of each switch SH, SL that constitutes the inverter 40. The temperature Tr of each switch SH, SL that constitutes the inverter 40 is, for example, a detection value of the temperature sensor 64. The switch temperature Tr is, for example, the highest temperature among the temperatures of each switch SH, SL that constitutes the inverter 40.

[0079] An example of a control method based on temperature will now be described.

[0080] In the first example, the drive circuit 111 calculates a temperature difference ΔT, which is the difference between the switch temperature Tr and a target temperature T* (e.g., 140°C), and sets a ratio D of the low-speed period as a manipulated variable for feedback control of the calculated temperature difference ΔT to 0. The ratio D of the low-speed period is, for example, "10%≦D≦20%."

[0081] In the second example, the drive circuit 111 reduces the ratio D of the slow period as the switch temperature Tr increases.

[0082] This allows measurement / switching control to be performed while protecting the switches of the inverter 40 from overheating.

[0083] <Variation of the second embodiment> When performing low-speed control, the drive circuit 111 may slow down only one of the switching speeds of the switches SH and SL when switching them to the on state and when switching them to the off state, instead of slowing down the switching speeds of both of them.

[0084] When changing the switching speed of each switch SH, SL, instead of changing the resistance value of the resistor connected to the gate of each switch SH, SL, the power supply connected to the gate may be a variable voltage source, and the voltage applied to the gate may be changed. In this case, as shown in FIG. 13 , the speed changer 112 includes first and second variable voltage sources 220, 221. The positive terminal of the first variable voltage source 220 is connected to the gate of the lower arm switch SL via a second charging path 124. The negative terminal of the first variable voltage source 220 is connected to the source of the lower arm switch SL. The negative terminal of the second variable voltage source 221 is connected to the gate of the lower arm switch SL via a second discharging path 134. The positive terminal of the second variable voltage source 221 is connected to the source of the lower arm switch SL.

[0085] When the drive circuit 111 switches the lower arm switch SL to the on state using the low-speed control, the drive circuit 111 lowers the voltage of the first variable voltage source 220 compared to when the high-speed control is executed. When the drive circuit 111 switches the lower arm switch SL to the off state using the low-speed control, the drive circuit 111 lowers the voltage of the second variable voltage source 221 compared to when the high-speed control is executed.

[0086] Third Embodiment A third embodiment will now be described with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, the setting unit 101 calculates the q-axis command current Iq* so that the time average value of the torque Trqr generated by the rotor 34 is always offset from 0 by an offset value Toffset in order to reduce noise and vibration (NV) generated by measurement control.

[0087] 14 and 17, the transmission included in the power transmission mechanism 50 includes a first gear 52 and a second gear 53. The first gear 52 and the second gear 53 are meshed with each other and are rotatable about a central axis of rotation extending in a predetermined direction.

[0088] As shown in FIG. 14 , backlash is provided in the first gear 52 and the second gear 53 that constitute the power transmission mechanism 50. FIG. 14 illustrates an example in which the gears 52, 53 are external gears. In a configuration in which backlash is provided, when the polarity of the torque Trqr generated by the rotor 34 alternates between positive and negative as shown in FIG. 15 due to switching control of the inverter 40 in the measurement control, the rotation directions of the first gear 52 and the second gear 53 alternate, which may result in tooth strike, in which the teeth 52 a of the first gear 52 and the teeth 53 a of the second gear 53 collide with each other. Trqmax in FIG. 15 is a torque threshold value. The torque threshold value Trqmax is the torque at which the drive wheels 51 begin to rotate, and is set, for example, to the upper limit of an expected range of torque at which the drive wheels 51 begin to rotate. TrH and TrL in FIG. 15 are upper and lower limit values ​​that define the torque width ΔTr that keeps NV characteristic values ​​(for example, noise and vibration) generated by measurement control below an allowable value.

[0089] In measurement control, if the generated torque Trqr of the rotor 34 becomes equal to or less than the torque threshold value Trqmax and the rotor 34 is maintained in a stopped state, and the gear rattle noise increases, the noise and vibration of the system 10 deteriorates.

[0090] Even when measurement control is performed to set the generated torque Trqr to 0, there is a concern that the polarity of the generated torque may alternate between positive and negative due to detection errors of the phase current sensor 60, even though the amount of fluctuation in the actual generated torque is small, and tooth strike may occur.

[0091] Therefore, in this embodiment, as shown in Fig. 16, switching control of the inverter 40 is performed so as to satisfy the condition that the time average value of the generated torque Trqr in one cycle or multiple cycles of the AC current flowing through the armature winding is offset from 0 by an offset value Toffset. As a result, as shown in Fig. 17 and Fig. 18, the teeth 52a of the first gear 52 and the teeth 53a of the second gear 53 are maintained in a pressed state against each other, suppressing the occurrence of rattle noise and improving NV.

[0092] The torque Trq generated by the rotary electric machine 30 is expressed by the following equation (eq1): In the following equation (eq1), P represents the number of pole pairs of the rotary electric machine 30, and φ represents the armature flux linkage.

[0093] Trq = P (φ + (Ld - Lq)) Id Iq ... (eq1) In measurement control, the motor ECU 80 controls the switching of the inverter 40 so that a sinusoidal d-axis current Idr flows through the U-, V-, and W-phase windings 33U, 33V, and 33W.

[0094] Here, in order to satisfy the condition that the time average value of the generated torque Trqr in one cycle of the AC current flowing through the armature winding is always offset from 0 by the offset value Toffset, the left side of the above equation (eq1) is replaced with the offset value Toffset, thereby deriving the following equation (eq2): The offset value Toffset is set to a value such that the generated torque of the rotor 34 is equal to or less than the torque threshold value Trqmax.

[0095] Toffset=P・(φ+(Ld−Lq))・Id・Iq…(eq2)

[0096] When the above equation (eq2) is solved for the q-axis current Iq, the following equation (eq3) is derived.

[0097] The setting unit 101 calculates the q-axis command current Iq* based on the offset value Toffset, the d-axis command current Id*, and the above equation (eq3).

[0098] The motor ECU 80 may gradually change the q-axis current Iqr when switching from one of the cases where the time average value of the generated torque Trqr is set to 0 and the case where the generated torque Trqr is offset by the offset value Toffset to the other. Specifically, for example, when switching from one to the other, the motor ECU 80 may gradually change the q-axis command current Iq*. Figure 19 shows an example in which the command value is gradually increased. This makes it possible to suppress current overshoot during measurement control and maintain the rotor 34 in a rotation-stopped state.

[0099] According to the measurement control of this embodiment described above in detail, it is possible to obtain a measurement signal while suppressing deterioration of the noise and vibration of the system 10.

[0100] Other Embodiments The above-described embodiments may be modified as follows.

[0101] The setting unit 101 may calculate the d-axis command current Id* so that the AC component of the battery current IBr flowing through the battery 20 does not cross 0. In this case, a positive or negative battery current IBr always flows through the battery 20 in one cycle of the battery current IBr.

[0102] The carrier signal is not limited to a triangular wave signal, but may be, for example, a sawtooth wave signal.

[0103] In each of the above embodiments, the motor ECU 80 may generate the drive signal by PWM processing based on space vector modulation, instead of PWM processing based on a magnitude comparison between the command value and the carrier signal. Furthermore, the motor ECU 80 may generate the drive signal based on a pulse pattern that is information that associates switch on and off commands with electrical angles, without using a carrier signal.

[0104] The DC power source is not limited to a battery, and may be, for example, a fuel cell.

[0105] The rotating electric machine is not limited to a permanent magnet field type synchronous machine, but may be, for example, a wound field type synchronous machine having a field winding on a rotor.Furthermore, the rotating electric machine is not limited to a synchronous machine, but may be, for example, an induction machine.

[0106] The semiconductor switches that make up the inverter are not limited to N-channel MOSFETs, but may also be IGBTs, for example. In this case, the high-potential terminal of the switch is the collector, and the low-potential terminal is the emitter. Also, a freewheeling diode is connected in reverse parallel to each switch.

[0107] The inverter, rotating electric machine, and control device may be installed in a mobile body other than a vehicle, such as an aircraft or a ship. If the mobile body is an aircraft, the rotating electric machine serves as a power source for the aircraft's flight, and if the mobile body is a ship, the rotating electric machine serves as a power source for the ship's navigation. Furthermore, the inverter, rotating electric machine, and control device may be installed in a mobile body other than a vehicle.

[0108] The control device and method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control device and method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control device and method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer.

[0109] Characteristic configurations extracted from the above-described embodiments are described below. [Configuration 1] An inverter control device (80) applied to a system (10) including: a rotating electric machine (30) having armature windings (33U to 33W); and an inverter (40) electrically connecting the armature windings and a power storage unit (20), wherein the system includes a capacitor (41) connected in parallel to the power storage unit, and the inverter control device includes: a determination unit (100) that determines whether or not there is a request to measure the impedance of the power storage unit, a setting unit (101) that sets an AC target current (Iac*) for measuring the impedance of the power storage unit when it is determined that there is the measurement request, which is a target value of an AC component of a current to be passed through the power storage unit, and a switch control unit (105) that performs switching control of the inverter so that the set AC target current passes through the power storage unit. [Configuration 2] The inverter control device according to Configuration 1, wherein the setting unit sets the AC target current so that one period of an AC component of the current passed through the power storage unit includes a period during which a discharging current flows through the power storage unit and a period during which a charging current flows through the power storage unit. [Configuration 3] The inverter control device according to Configuration 1 or 2, wherein the rotating electric machine has a rotor (34), the setting unit calculates d- and q-axis command currents (Id*, Iq*) to be passed through the armature winding so as to pass the set AC target current through the power storage unit, the switch control unit controls a d-axis current (Idr) flowing through the armature winding using the calculated d-axis command current, and performs the switching control so as to control a q-axis current (Iqr) flowing through the armature winding using the calculated q-axis command current, and the setting unit calculates the d- and q-axis command currents so as to satisfy a condition that a torque generated by the rotor is set to a torque that can maintain a stopped state of the rotor. [Configuration 4] The inverter control device according to any one of configurations 1 to 3, wherein the inverter has upper and lower arm switches (SH, SL) of multiple phases, and a drive unit (110) that switches the switching speed of the upper and lower arm switches, and the drive unit performs switching control to alternately switch the switching speed of the upper and lower arm switches between a low speed and a high speed in the switching control.[Configuration 5] The inverter control device according to Configuration 4, wherein the drive unit, in the switching control, equalizes the frequency of the AC target current and the frequency at which the switching speed of the upper and lower arm switches is switched. [Configuration 6] The inverter control device according to Configuration 5, wherein the drive unit performs the switching control so that a period during which the switching speed of the upper and lower arm switches is set to the low speed includes a timing at which the magnitude of the discharge current flowing through the power storage unit is maximized in each cycle of the current flowing through the power storage unit. [Configuration 7] The inverter control device according to Configuration 4, wherein the drive unit, in the switching control, switches the switching speed of the upper and lower arm switches based on temperatures of the upper and lower arm switches. [Configuration 8] The inverter control device according to any one of Configurations 1 to 7, wherein the setting unit sweeps the frequency of the AC target current. [Configuration 9] The inverter control device according to any one of Configurations 1 to 8, wherein the switch control unit, when it is determined that there is a request to measure the impedance of the power storage unit, increases the switching frequency of the inverter more than when it is determined that there is no request to measure the impedance of the power storage unit. [Configuration 10] The system comprises at least one pair of gears (52, 53) that constitute a power transmission mechanism (50) from the rotor to a rotationally driven object (51), and that rotate by rotational power from the rotor and mesh with each other, wherein the setting unit calculates the d- and q-axis command currents so as to satisfy a first condition that a torque generated by the rotor is set to a torque that can maintain a stopped state of the rotor, and a second condition that a time average value of the generated torque in one cycle or multiple cycles of an AC current flowing through the armature winding is offset from zero. [Configuration 11] The inverter control device according to any one of configurations 1 to 10, a module comprising: a measurement control device (90) that measures the impedance of the power storage unit; a voltage detection unit (62) that detects the voltage of the power storage unit; and a current detection unit (63) that detects the current flowing in the power storage unit, wherein the measurement control device measures the impedance of the power storage unit based on a voltage detection value of the voltage detection unit and a current detection value of the current detection unit.

[0110] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. An inverter control device (80) applied to a system (10) including: a rotating electric machine (30) having an armature winding (33U to 33W); and an inverter (40) electrically connecting the armature winding and a power storage unit (20), wherein the system is provided with a capacitor (41) connected in parallel to the power storage unit, and the inverter control device includes: a determination unit (100) that determines whether or not there is a request to measure the impedance of the power storage unit; a setting unit (101) that sets an AC target current (Iac*) for measuring the impedance of the power storage unit, which is a target value of the AC component of the current to be passed through the power storage unit when it is determined that there is the measurement request; and a switch control unit (105) that performs switching control of the inverter so that the set AC target current passes through the power storage unit.

2. The inverter control device according to claim 1, wherein the setting unit sets the AC target current so that, in one cycle of the AC component of the current flowing to the storage unit, there is a period in which a discharging current flows to the storage unit and a period in which a charging current flows to the storage unit.

3. The inverter control device according to claim 1, wherein the rotating electric machine has a rotor (34), the setting unit calculates d- and q-axis command currents (Id*, Iq*) to be passed through the armature winding so as to pass the set AC target current through the power storage unit, the switch control unit controls the d-axis current (Idr) flowing through the armature winding to the calculated d-axis command current, and performs the switching control to control the q-axis current (Iqr) flowing through the armature winding to the calculated q-axis command current, and the setting unit calculates the d- and q-axis command currents so as to satisfy the condition that the torque generated by the rotor is torque capable of maintaining the rotor in a stopped state.

4. The inverter control device according to claim 1, wherein the inverter has upper and lower arm switches (SH, SL) of multiple phases, and a drive unit (110) that switches the switching speed of the upper and lower arm switches, and the drive unit performs switching control to alternately switch the switching speed of the upper and lower arm switches between low speed and high speed in the switching control.

5. The inverter control device according to claim 4, wherein the drive unit, in the switching control, equalizes the frequency of the AC target current with the frequency at which the switching speed of the upper and lower arm switches is changed.

6. The inverter control device according to claim 5, wherein the drive unit performs the switching control so that the period during which the switching speed of the upper and lower arm switches is set to the low speed includes the timing at which the magnitude of the discharge current flowing to the storage unit is maximum in each cycle of the current flowing to the storage unit.

7. The inverter control device according to claim 4, wherein the drive unit switches the switching speed of the upper and lower arm switches based on the temperatures of the upper and lower arm switches during the switching control.

8. The inverter control device according to claim 1, wherein the setting unit sweeps the frequency of the AC target current.

9. The inverter control device according to claim 1, wherein the switch control unit increases the switching frequency of the inverter when it is determined that there is a request to measure the impedance of the storage unit, more than when it is determined that there is no request to measure the impedance of the storage unit.

10. The inverter control device according to claim 3, wherein the system comprises a power transmission mechanism (50) from the rotor to a rotationally driven object (51), and includes at least one pair of gears (52, 53) that rotate by rotational power from the rotor and mesh with each other, and the setting unit calculates the d- and q-axis command currents so as to satisfy a first condition that the torque generated by the rotor is a torque that can maintain the rotor in a stopped state, and a second condition that the time average value of the generated torque in one cycle or multiple cycles of the AC current flowing through the armature winding is offset from zero.

11. A module comprising: an inverter control device according to any one of claims 1 to 10; a measurement control device (90) that measures the impedance of the power storage unit; a voltage detection unit (62) that detects the voltage of the power storage unit; and a current detection unit (63) that detects the current flowing through the power storage unit, wherein the measurement control device measures the impedance of the power storage unit based on the voltage detection value of the voltage detection unit and the current detection value of the current detection unit.

12. A program applicable to a system (10) comprising: a rotating electric machine (30) having an armature winding (33U-33W); and an inverter (40) electrically connecting the armature winding and a power storage unit (20), wherein the system comprises a capacitor (41) connected in parallel to the power storage unit, and the program causes a processor (81) to execute the following processes: a determination process for determining whether or not there is a request to measure the impedance of the power storage unit; a setting process for setting an AC target current (Iac*) for measuring the impedance of the power storage unit, which is a target value of the AC component of the current to be passed through the power storage unit, when it is determined that there is a measurement request; and a control process for controlling the switching of the inverter so that the set AC target current passes through the power storage unit.

13. A method of controlling an inverter applied to a system (10) comprising: a rotating electric machine (30) having an armature winding (33U to 33W); and an inverter (40) electrically connecting the armature winding and a power storage unit (20), wherein the system is provided with a capacitor (41) connected in parallel to the power storage unit, the method comprising: a determination step of determining whether or not there is a request to measure the impedance of the power storage unit; a setting step of setting an AC target current (Iac*) for measuring the impedance of the power storage unit, which is a target value of the AC component of the current to be passed through the power storage unit, when it is determined that there is a measurement request; and a control step of performing switching control of the inverter so that the set AC target current passes through the power storage unit.

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