Control device and program for three-level inverter

Abstract

A control device (40) is applied to a system including a first power storage unit (21) and a second power storage unit (22) connected in series, a rotating electrical machine (10), and a three-level inverter (30). The control device includes: a selection unit that selects a drive mode, which is a combination of drive states of switches of each phase in one switching period, on the basis of a command voltage for controlling a control amount of the rotating electrical machine to a command value; and a switching control unit that performs switching control of the switch on the basis of the selected driving mode. For two different driving states, the driving states in which the voltages between the three wires of the winding are equal and the directions of the currents flowing through the neutral point are opposite to each other are set as specific driving states. The selection unit selects a driving mode based on the command voltage so as to generate a period for each specific driving state in one switching period.

Description

Priority Application

[0001] This application is based on Japanese Patent Application No. 2023-044830 filed on March 21, 2023, the contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to a control device and program of a three-level inverter. BACKGROUND

[0003] In the past, a control device that turns on and off switches possessed by a three-level inverter is known. The control device turns on and off the switches by space vector modulation control.

[0004] A first power storage unit and a second power storage unit connected in series are connected to a direct current side of a three-level inverter. The control device performs switching control so that a voltage of the first power storage unit and a voltage of the second power storage unit are within a prescribed range. Thereby, it is possible to suppress application of an overvoltage to the switches. As an example of such a control device, a control device disclosed in Patent Literature 1 can be cited. PRIOR ART DOCUMENTS PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. 9-37592 SUMMARY

[0006] Since a variation period of the voltage of the first power storage unit and the voltage of the second power storage unit is long, controllability of the voltage of each power storage unit can be reduced.

[0007] The present disclosure was made in view of the above circumstances, and a main object thereof is to provide a control device and program of a three-level inverter capable of improving controllability of a voltage of a power storage unit.

[0008] The present disclosure is a control device of a three-level inverter, the control device of the three-level inverter being adapted to a system, the system including: a first power storage unit and a second power storage unit connected in series; a rotating electric machine having windings corresponding to three phases; and a three-level inverter having switches corresponding to the three phases that connect the windings of each phase of the rotating electric machine to any one of a positive electrode side of the first power storage unit, a neutral point between a negative electrode side of the first power storage unit and a positive electrode side of the second power storage unit, and a negative electrode side of the second power storage unit, the control device of the three-level inverter including: a selection unit that selects a combination of drive states of the switches of each phase, that is, a drive mode, in one switching period, based on an instruction voltage for controlling a control amount of the rotating electric machine to an instruction value; and a switch control section that performs switching control of the switches based on the selected drive mode, each of the drive states in which the three line-to-line voltages of the winding are equal and the directions of the currents flowing through the neutral point are opposite to each other is set as a specific drive state, the selection section selects the drive mode based on the command voltage to generate the periods that are each of the specific drive states within the one switching cycle.

[0009] According to the present disclosure, a combination of drive states of the switches of each phase in one switching cycle, that is, a drive mode is selected based on a command voltage. Here, the drive mode is selected based on the command voltage to generate the periods that are each of the specific drive states within the one switching cycle. Then, switching control of the switches is performed based on the selected drive mode. In this case, the voltages of each power storage section change in opposite directions to each other in the period within the switching cycle that is the drive state on one side and in the period within the switching cycle that is the drive state on the other side. Therefore, compared to a case where only the period that is the drive state on one side of the specific drive states is generated within the switching cycle, the voltages of each power storage section can be changed at a shorter interval, and the period of change of the voltages of each power storage section can be shortened. As a result, controllability of the voltages of each power storage section can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0010] The above objects, other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: Figure 1 is a configuration diagram of a motor control system of a first embodiment. Figure 2 is a functional block diagram of a process performed by a control device. Figure 3 is a diagram showing a vector space. Figure 4 is a diagram for explaining a voltage vector. Figure 5 is a diagram showing a current path during a period in which a switch is in a drive state HMM. Figure 6 is a diagram showing a current path during a period in which a switch is in a drive state MLL. Figure 7 is a diagram showing an example of a drive mode of a switch. Figure 8 is a flowchart showing a processing step of control performed by a control device. Figure 9 is a diagram for explaining a specific range and a voltage control range. Figure 10 This is a timing diagram illustrating an example of switch control. Figure 11 This is a structural diagram of the motor control system according to the second embodiment. Detailed Implementation

[0011] <First Implementation> Hereinafter, a first embodiment of the control device of the present disclosure will be described with reference to the accompanying drawings. In this embodiment, the control device is installed in an electric vehicle such as an electric car or a hybrid electric vehicle.

[0012] like Figure 1 As shown, the electric motor control system includes a rotary motor 10, a battery 20, an inverter 30, and a control device 40. The rotary motor 10 is the vehicle's main unit, capable of transmitting power to drive wheels (not shown). In this embodiment, the rotary motor 10 is a three-phase synchronous machine, with stator windings including a star-connected U-phase winding 11U, a V-phase winding 11V, and a W-phase winding 11W. The phase windings 11U, 11V, and 11W are arranged with electrical angles staggered by 120°. The rotary motor 10 is, for example, a permanent magnet synchronous machine.

[0013] The battery 20 is electrically connected to the rotary motor 10 via the inverter 30. In this embodiment, the battery 20 is, for example, a battery pack configured as a series connection of individual battery cells. As individual battery cells, for example, a secondary battery such as a lithium-ion battery can be used. The inter-terminal voltage of the battery 20 is, for example, 100V or higher.

[0014] The inverter 30 is a power conversion circuit that converts DC power supplied from the battery 20 into three-phase AC power through switching operation, and supplies the converted AC power to the rotating motor 10. A first capacitor 21 and a second capacitor 22, serving as energy storage units, are provided on the battery 20 side of the inverter 30. The first capacitor 21 and the second capacitor 22 are connected in series. The series connection of the first capacitor 21 and the second capacitor 22 is connected in parallel with the battery 20. In this embodiment, the electrostatic capacitance of the first capacitor 21 and the electrostatic capacitance of the second capacitor 22 are the same value. Furthermore, the first capacitor 21 and the second capacitor 22 can be located outside the inverter 30 or built into the inverter 30.

[0015] The inverter 30 is a T-type three-level inverter, and includes series connection bodies of upper arm switches SUH, SVH, SWH and lower arm switches SUL, SVL, SWL corresponding to three phases. As each switch SUH-SWL, a voltage control type semiconductor switching element is used, specifically, an IGBT. Therefore, the high potential side terminal of each switch SUH-SWL is a collector, and the low potential side terminal is an emitter. Each switch SUH, SVH, SWH, SUL, SVL, SWL is connected in antiparallel with a corresponding freewheeling diode DUH, DVH, DWH, DUL, DVL, DWL.

[0016] The emitter of the U-phase upper arm switch SUH is connected to the collector of the U-phase lower arm switch SUL. The connection point of the U-phase upper arm switch SUH and the U-phase lower arm switch SUL is connected to the first end of the U-phase winding 11U. The emitter of the V-phase upper arm switch SVH is connected to the collector of the V-phase lower arm switch SVL. The connection point of the V-phase upper arm switch SVH and the V-phase lower arm switch SVL is connected to the first end of the V-phase winding 11V. The emitter of the W-phase upper arm switch SWH is connected to the collector of the W-phase lower arm switch SWL. The connection point of the W-phase upper arm switch SWH and the W-phase lower arm switch SWL is connected to the first end of the W-phase winding 11W. The second ends of the respective phase windings 11U, 11V, 11W are connected to each other.

[0017] The collectors of the respective upper arm switches SUH-SWH are connected through a positive side bus 31 or the like. The positive side bus 31 is connected to the positive terminal of the battery 20 and the first end of the first capacitor 21. The second end of the first capacitor 21 is connected to the first end of the second capacitor 22 via a neutral point O. The emitters of the respective lower arm switches SUL-SWL are connected through a negative side bus 32 or the like. The negative side bus 32 is connected to the negative terminal of the battery 20 and the second end of the second capacitor 22.

[0018] The inverter 30 includes clamp switches QU, QV, QW that conduct and cut off a current in both directions. In the present embodiment, as the switches that constitute the respective clamp switches QU-QW, voltage control type semiconductor switching elements are used, specifically, IGBTs. Each switch that constitutes the respective clamp switches QU-QW has a corresponding freewheeling diode DU, DV, DW.

[0019] Specifically, the emitters of the two switches that constitute the U-phase clamp switch QU are connected to each other. The collector of one of the switches that constitute the U-phase clamp switch QU is connected to the connection point of the U-phase upper arm switch SUH and the U-phase lower arm switch SUL, and the collector of the other is connected to the neutral point O. Furthermore, the U-phase clamp switch QU ~ the W-phase clamp switch QW allow bidirectional current to flow when turned on and prevent bidirectional current from flowing when turned off. The U-phase clamp switch QU ~ the W-phase clamp switch QW can also be constituted by connecting the collectors of the switches to each other. As the U-phase clamp switch QU ~ the W-phase clamp switch QW, a reverse blocking IGBT (RB-IGBT) can also be used.

[0020] The motor control system includes a first voltage sensor 41, a second voltage sensor 42, a phase current sensor 43, and a rotation angle sensor 44. The first voltage sensor 41 detects the voltage of the first capacitor 21. The second voltage sensor 42 detects the voltage of the second capacitor 22. The phase current sensor 43 detects the U-phase current, the V-phase current, and the W-phase current that flow through the respective phase windings 11U, 11V, 11W. In addition, the phase current sensor 43 can detect the currents of at least two of the three phases. The rotation angle sensor 44, which is, for example, a resolver, detects the electrical angle of the rotating electric machine 10. The detection values of the respective sensors 41 to 44 are input to a control device 40.

[0021] The control device 40 is constituted by a microcomputer including a CPU or various memories. The functions provided by the microcomputer can be provided by software recorded in a tangible storage device and a computer that executes the software, only software, only hardware, or a combination thereof. For example, in the case where the microcomputer is provided by an electronic circuit as hardware, it can be provided by a digital circuit or an analog circuit including a plurality of logic circuits. For example, the microcomputer executes a program stored in a non-transitory tangible storage medium included as a storage portion in itself. The program contains, for example, a program of the processing shown in FIG. 10. The method corresponding to the program is executed by executing the program. The storage portion is, for example, a nonvolatile memory. In addition, the program stored in the storage portion can be downloaded and updated via a communication network such as the Internet, for example, OTA (Over The Air). Figure 8

[0022] The control device 40 is a control for controlling the control amount of the rotating electric machine 10 to the command value, and performs switching control of turning on / off the respective switches SUH to SWL, QU to QW of the inverter 30. Here, the switching control of the control device 40 is explained using FIG. 10. In FIG. 10, the horizontal axis represents time, and the vertical axis represents the voltage of the first capacitor 21 and the voltage of the second capacitor 22. Figure 2 Figure 2 ​​In the example shown, current feedback control is performed in the switching control. The control quantity is the torque of the rotating electric machine 10, and the command value is the command torque Trq* input from the control device of the upper level.

[0023] The control device 40 has a command current setting section 50. The command current setting section 50 sets the d-axis command current Id* and the q-axis command current Iq* based on the command torque Trq*. For example, the command current setting section 50 can set the d-axis command current Id* and the q-axis command current Iq* based on mapping information or mathematical expression information that associates the command torque Trq* with the d-axis command current Id* and the q-axis command current Iq*.

[0024] The control device 40 has a two-phase conversion section 51. The two-phase conversion section 51 converts the U-phase current, the V-phase current, and the W-phase current in the three-phase fixed coordinate system into the d-axis current Idrand the q-axis current Iqr in the two-phase rotating coordinate system (dq coordinate system) based on the U-phase current, the V-phase current, and the W-phase current flowing through the respective phase windings 11U, 11V, 11W and the electric angle θe of the rotating electric machine 10. The two-phase conversion section 51 can use the detection values of the phase current sensor 43 as the respective phase currents and can use the detection value of the rotational angle sensor 44 as the electric angle θe.

[0025] The control device 40 has a d-axis deviation calculation section 52a and a q-axis deviation calculation section 52b. The d-axis deviation calculation section 52a calculates the d-axis current deviation ΔId by subtracting the d-axis current Idr from the d-axis command current Id*. The q-axis deviation calculation section 52b calculates the q-axis current deviation ΔIq by subtracting the q-axis current Iqr from the q-axis command current Iq*.

[0026] The control device 40 has a d-axis command voltage calculation section 53a and a q-axis command voltage calculation section 53b. The d-axis command voltage calculation section 53a calculates the d-axis command voltage Vd based on the d-axis current deviation ΔId as an operation quantity for feedback-controlling the d-axis current Idr to the d-axis command current Id*. The q-axis command voltage calculation section 53b calculates the q-axis command voltage Vq based on the q-axis current deviation ΔIq as an operation quantity for feedback-controlling the q-axis current Iqr to the q-axis command current Iq*. In addition, the feedback control used in the d-axis command voltage calculation section 53a and the q-axis command voltage calculation section 53b can be, for example, proportional integral control.

[0027] The control device 40 has a fixed coordinate conversion section 54. The fixed coordinate conversion section 54 converts the d-axis command voltage Vd and the q-axis command voltage Vq in the two-phase rotating coordinate system into an α-axis command voltage Vα and a β-axis command voltage Vβ in the two-phase fixed coordinate system, based on the d-axis command voltage Vd and the q-axis command voltage Vq output from the d-axis command voltage calculation section 53a and the q-axis command voltage calculation section 53b, and the electric angle θe. As the electric angle θe, the fixed coordinate conversion section 54 can use the detection value of the rotation angle sensor 44.

[0028] The control device 40 has a modulation section 55. The modulation section 55α sets the voltage vector determined by the α-axis command voltage Vα and the β-axis command voltage Vβ as a command voltage vector Vαβ for controlling the control amount of the rotating electric machine 10 to the command value, and determines the sector in which the command voltage vector Vαβ exists and the existing region within the sector. The sector is a region that divides the vector space in which the command voltage vector Vαβ can exist into six parts in accordance with the angle of deflection of the command voltage vector Vαβ. The angle of deflection of the command voltage vector Vαβ is the angle formed by the command voltage vector Vαβ and the U-phase axis, and specifically, the electric angle θe. The sign of the electric angle θe is positive for left-hand (counterclockwise). Figure 3 The first sector to the sixth sector in which the vector space is divided into six are shown. In the vector space, the axes of the U-phase, the V-phase, and the W-phase are arranged at an electric angle of 120° from each other. Each sector is a region that is sandwiched by the axes of two phases that have an electric angle difference of 60° from each other. In the first sector, the command voltage vector Vαβ exists in the sector in which the U-phase axis and the V-phase axis are sandwiched. Figure 3 In the first sector, the end point on the U-phase axis is indicated by a point shadow.

[0029] The first sector to the sixth sector are further divided into four existing regions. Specifically, the end point of the sector on the axis of the smaller one of the angles of deflection of the axes of the two phases that divide the sector is taken as a first end point, the end point of the sector on the axis of the larger one of the angles of deflection is taken as a second end point, the intermediate point of the origin of the vector space and the first end point is taken as a first intermediate point, the intermediate point of the origin and the second end point is taken as a second intermediate point, and the intermediate point of the first end point and the second end point is taken as an intermediate end point. In this case, the first region R1 is a region surrounded by a triangle having the origin, the first intermediate point, and the second intermediate point as vertices. The second region R2 is a region surrounded by a triangle having the first intermediate point, the second intermediate point, and the intermediate end point as vertices. The third region R3 is a region surrounded by a triangle having the second end point, the second intermediate point, and the intermediate end point as vertices. The fourth region R4 is a region surrounded by a triangle having the first end point, the first intermediate point, and the intermediate end point as vertices. Figure 4The first to fourth regions R1 to R4 as the existence regions are shown with the first sector as an example. In the first sector, the first end point is "HLL", the second end point is "HHL", the first intermediate point is "MLL" and "HMM", the second intermediate point is "MML" and "HHM", and the intermediate end point is "HML".

[0030] The modulation section 55 determines the sector in which the command voltage vector Vαβ exists based on the electrical angle θe. For example, the modulation section 55 determines that the command voltage vector Vαβ exists in the first sector when 0°≤θe<60°. In addition, the modulation section 55 determines the existence region of the command voltage vector Vαβ based on the magnitude of the command voltage vector Vαβ and the angle within the sector. For example, the modulation section 55 determines which of the first to fourth regions R1 to R4 in which the command voltage vector Vαβ exists within each sector using information (specifically, mapping information or mathematical expression information) that associates the magnitude of the command voltage vector Vαβ and the angle within the sector with the first to fourth regions R1 to R4 as the existence regions. The angle within the sector is calculated from the electrical angle θe and the sector number.

[0031] The modulation section 55 determines the drive state of each of the switches SUH to SWL, QU to QW based on the determined sector and existence region of the command voltage vector Vαβ each time. The drive state of each of the switches SUH to SWL, QU to QW that the inverter 30 can realize is determined as shown in Table 1. Figure 3

[0032] The drive state of each of the switches SUH to SWL, QU to QW is represented by a group of phase voltages, each of which is represented by a level H, M, or L of three levels. The phase voltage of the level H is a voltage that is output in the phase that is the object by turning on the upper arm switches SUH, SVH, SWH and turning off the lower arm switches SUL, SVL, SWL and the clamp switches QU, QV, QW. The phase voltage of the level M is a voltage that is output in the phase that is the object by turning on the clamp switches QU, QV, QW and turning off the upper arm switches SUH, SVH, SWH and the lower arm switches SUL, SVL, SWL. The phase voltage of the level L is a voltage that is output in the phase that is the object by turning on the lower arm switches SUL, SVL, SWL and turning off the upper arm switches SUH, SVH, SWH and the clamp switches QU, QV, QW.

[0033] For example, the drive state HML indicates that the U-phase voltage is the level H, the V-phase voltage is the level M, and the W-phase voltage is the level L. In the drive state HML, the U-phase upper arm switch SUH, the V-phase clamp switch QV, and the W-phase lower arm switch SWL are turned on, and the V-phase upper arm switch SVH and the W-phase upper arm switch SWH, the U-phase clamp switch QU and the W-phase clamp switch QW, the U-phase lower arm switch SUL and the V-phase lower arm switch SVL are turned off.​

[0034] In addition, when the voltage of battery 20 is set to VH and the potential of neutral point O is set to the reference potential (0V), the phase voltage of level H is "VH / 2", the phase voltage of level M is "0", and the phase voltage of level L is "-VH / 2".

[0035] At the origin of the vector space, regardless of the sector, each switch SUH~SWL, QU~QW is in a driving state HHH, MMM, or LLL. In other words, at the origin, the driving state of each switch SUH~SWL, QU~QW is the driving state in which the windings 11U~11W of each phase are connected to the first terminal of the first capacitor 21, the neutral point O, or the second terminal of the second capacitor 22. In this embodiment, each driving state HHH, MMM, LLL is referred to as a zero-voltage driving state.

[0036] like Figure 3 and Figure 4 As shown, the two different drive states MML and HHM for each switch SUH~SWL and QU~QW are located at the same position in vector space. In these two drive states MML and HHM, the three line-to-line voltages (specifically, UV phase voltage, VW phase voltage, and WU phase voltage) of each winding 11U~11W are equal. Furthermore, the line-to-line voltages applied to each winding 11U~11W under the two drive states MML and HHM may vary with the voltage variations of the first capacitor 21 and the second capacitor 22, but when the voltages of the first capacitor 21 and the second capacitor 22 are within a specified range, the line-to-line voltages applied under the two drive states MML and HHM are equal. The specified range of voltages in the first capacitor 21 and the second capacitor 22 is determined, for example, based on the controllability of the rotating motor 10 and the reliability of each switch SUH~SWL and QU~QW. Similarly, the positions of the two different driving states MLL and HMM of each switch SUH~SWL and QU~QW in the vector space are the same, and the voltage between each line is equal in these two driving states MLL and HMM.

[0037] Figure 5 and Figure 6 An example of the current path during two different drive states HMM and MLL is shown. Here, the current path is shown when the voltage of the first capacitor 21 and the second capacitor 22 is higher than the UV phase voltage and the WU phase voltage. In this case, in each drive state HMM and MLL, the U-phase current flows from the U-phase switches SUH, SUL, QU side toward the U-phase winding 11U, and the V-phase current and W-phase current flow from the V-phase winding 11V and the W-phase winding 11W toward the V-phase and W-phase switches SVH, SVL, QV, SWH, SWL, QW side, respectively. Figure 5As shown, during the period in which each of the switches SUH to SWL and QU to QW is in the drive state HMM, current flows into the neutral point O. As shown in FIG. 6, during the period in which each of the switches SUH to SWL and QU to QW is in the drive state MLL, current flows out of the neutral point O. That is, during each of the periods in which each of the switches SUH to SWL and QU to QW is in the drive state HMM or MLL, the directions of the currents flowing through the neutral point O are opposite to each other. Similarly, during each of the periods in which each of the switches SUH to SWL and QU to QW is in the drive state MML or HHM, the directions of the currents flowing through the neutral point O are opposite to each other. Figure 6 As shown, during the period in which each of the switches SUH to SWL and QU to QW is in the drive state HMM, current flows into the neutral point O. As shown in FIG. 6, during the period in which each of the switches SUH to SWL and QU to QW is in the drive state MLL, current flows out of the neutral point O. That is, during each of the periods in which each of the switches SUH to SWL and QU to QW is in the drive state HMM or MLL, the directions of the currents flowing through the neutral point O are opposite to each other. Similarly, during each of the periods in which each of the switches SUH to SWL and QU to QW is in the drive state MML or HHM, the directions of the currents flowing through the neutral point O are opposite to each other.

[0038] That is, in each of the two different drive states MML and HHM or the drive states MLL and HMM of each of the switches SUH to SWL and QU to QW, the line-to-line voltages are equal, and the directions of the currents flowing through the neutral point O are opposite to each other. In the present embodiment, the drive states MML and HHM of each of the switches SUH to SWL and QU to QW, and the drive states MLL and HMM are referred to as specific drive states. In addition to these, the drive states LML and MHM, the drive states LMM and MHH, the drive states LLM and MMH, and the drive states MLM and HMH also correspond to the specific drive states.

[0039] The modulation section 55 decomposes the command voltage vector Vαβ into a plurality of voltage vectors. At this time, the command voltage vector Vαβ is decomposed into voltage vectors corresponding to the vertices of the existing region of the command voltage vector Vαβ. The modulation section 55 calculates the period in which each of the switches SUH to SWL and QU to QW becomes the drive state corresponding to the voltage vector in one switching cycle of each of the switches SUH to SWL and QU to QW, based on the magnitudes of the decomposed voltage vectors. In addition, one switching cycle here is the period at the time of averaging for each voltage vector outputted at a prescribed time width. The modulation section 55 generates drive commands that turn on and off each of the switches SUH to SWL and QU to QW so that the drive state of each of the switches SUH to SWL and QU to QW becomes the calculated period in one switching cycle. By driving each of the switches SUH to SWL and QU to QW based on the drive commands, an average voltage vector averaged in one switching cycle is outputted.

[0040] For example, as shown in FIG. 7, the modulation section 55 decomposes the command voltage vector Vαβ into voltage vectors corresponding to the vertices of the existing region of the command voltage vector Vαβ. The modulation section 55 calculates the period in which each of the switches SUH to SWL and QU to QW becomes the drive state corresponding to the voltage vector in one switching cycle of each of the switches SUH to SWL and QU to QW, based on the magnitudes of the decomposed voltage vectors. In addition, one switching cycle here is the period at the time of averaging for each voltage vector outputted at a prescribed time width. The modulation section 55 generates drive commands that turn on and off each of the switches SUH to SWL and QU to QW so that the drive state of each of the switches SUH to SWL and QU to QW becomes the calculated period in one switching cycle. By driving each of the switches SUH to SWL and QU to QW based on the drive commands, an average voltage vector averaged in one switching cycle is outputted. Figure 4In the case where it is determined that the command voltage vector Vαβ exists in the first region Rl of the first sector, the command voltage vector Vαβ is decomposed into voltage vectors corresponding to the drive states MLL, HMM and the drive states MML, HHM as shown. Vl is a vector after ta times (0 < ta < 1) of the voltage vector corresponding to the drive states MLL, HMM, and V2 is a vector after tb times (0 < tb < 1) of the voltage vector corresponding to the drive states MML, HHM. In this case, if one switching period is set to TS, the period during which each switch SUH ~ SWL, QU ~ QW is in the drive state MLL or HMM is ta x TS, and the period during which each switch SUH ~ SWL, QU ~ QW is in the drive state MML, HHM is tb x TS. The period other than the periods ta x TS and tb x TS in one switching period is the period during which each switch SUH ~ SWL, QU ~ QW is in the drive state HHH, MMM or LLL.

[0041] In addition, in the case where it is determined that the command voltage vector Vαβ exists in the second region R2 of the first sector, the command voltage vector Vαβ is decomposed into voltage vectors corresponding to the drive states MLL, HMM, the drive states MML, HHM and the drive state HML. In the case where it is determined that the command voltage vector Vαβ exists in the third region R3 of the first sector, the command voltage vector Vαβ is decomposed into voltage vectors corresponding to the drive states MML, HHM, the drive state HML and the drive state HHL. In the case where it is determined that the command voltage vector Vαβ exists in the fourth region R4 of the first sector, the command voltage vector Vαβ is decomposed into voltage vectors corresponding to the drive states MLL, HMM, the drive state HML and the drive state HLL. Then, the periods during which the drive states corresponding to the voltage vectors after the decomposition of the command voltage vector Vαβ become are calculated based on the magnitudes of the voltage vectors.

[0042] In the case where it is determined that the command voltage vector Vαβ exists in the second to sixth sectors, the same processing as in the case of the first sector is performed. For example, in the case where it is determined that the command voltage vector Vαβ exists in the first region Rl of the second sector, the command voltage vector Vαβ is decomposed into voltage vectors corresponding to the drive states HHH, MMM, LLL, the drive states MML, HHM and the drive states LML, MHM. The periods during which the drive states HHH, MMM, LLL, the drive states MML, HHM and the drive states LML, MHM corresponding to the voltage vectors are calculated based on the magnitudes of the voltage vectors after the decomposition.

[0043] The modulation section 55 controls the voltages of the first capacitor 21 and the second capacitor 22 in the switching control so that the voltages of the first capacitor 21 and the second capacitor 22 are within a prescribed range. For example, the modulation section 55 turns on and off the respective switches SUH ~ SWL, QU ~ QW so that the first capacitor 21 and the second capacitor 22 are charged and discharged.

[0044] Since the variation periods of the voltages of the first capacitor 21 and the second capacitor 22 are long, the controllability of the voltages of the first capacitor 21 and the second capacitor 22 can be reduced.

[0045] For example, sometimes the switching control is performed so that the drive states of the respective switches SUH ~ SWL, QU ~ QW are changed in the order of HHH → HHH → HHH in the first half of the switching period and in the order of HHH → HHH → HHH in the second half of the switching period. Assuming a state in which the voltages of the respective capacitors 21, 22 are higher than the respective phase-to-phase voltages, in the drive states HHH, HHH, and HHH, the voltages of the respective capacitors 21, 22 are higher than the respective phase-to-phase voltages. In the drive states HHH, HHH, and HHH, the voltages of the respective capacitors 21, 22 are higher than the respective phase-to-phase voltages. In the drive states HHH, HHH, and HHH, the voltages of the respective capacitors 21, 22 are higher than the respective phase-to-phase voltages. Figure 5 And Figure 6 As explained in the above-described cases, the direction of the current flowing through the neutral point O is opposite. Also, in the drive mode of the above-described switching control, the second capacitor 22 is charged in the first half of the switching period and is discharged in the second half of the switching period. In addition, the first capacitor 21 is discharged in the first half of the switching period and is charged in the second half of the switching period. That is, in the two switching periods, the respective capacitors 21, 22 are charged and discharged only once. In this case, the number of times of variation of the voltages of the respective capacitors 21, 22 at each change of the drive states of the respective switches SUH ~ SWL, QU ~ QW is reduced, and the controllability of the voltages of the first capacitor 21 and the second capacitor 22 can be reduced.

[0046] Therefore, the modulation section 55 selects a drive mode as a combination of the respective drive states in one switching period of the respective switches SUH ~ SWL, QU ~ QW on the basis of the command voltage vector Vαβ. At this time, the modulation section 55 selects a drive mode so that a period in which the respective switches SUH ~ SWL, QU ~ QW become the respective specified drive states is generated within one switching period on the basis of the command voltage vector Vαβ. The modulation section 55 performs the switching control of the respective switches SUH ~ SWL, QU ~ QW on the basis of the selected drive mode.

[0047] Figure 7 An example of the drive mode selected by the modulation section 55 having the above-described characteristics is shown. Here, the first sector is explained as an example. As shown in FIG. 6, the modulation section 55 selects a drive mode in which the respective switches SUH ~ SWL, QU ~ QW are changed in the order of HHH → HHH → HHH in the first half of the switching period and in the order of HHH → HHH → HHH in the second half of the switching period. Figure 7As shown in the drive pattern of the column of the first region R1, the modulation section 55 can select the drive pattern so that each specific drive state HMM, MLL or HHM, MML appears before the drive state of each switch SUH ~ SWL, QU ~ QW changes three times.

[0048] The modulation section 55 determines that the command voltage vector Vαβ exists in the first region R1 of the first sector, and selects any one of the modes A ~ D shown in the drive pattern of the column of the first region R1. Figure 7 In the modes A, B of the first region R1, the drive states HMM, MMM, MML, MLL are combined. In the modes A, B of the first region R1, although the transition order of the drive state of each switch SUH ~ SWL, QU ~ QW is different from each other, there is a period in which each switch SUH ~ SWL, QU ~ QW is each specific drive state HMM, MLL at the beginning and the end of the switching period. In the modes C, D of the first region R1, the drive states HHM, HMM, MMM, MML are combined. In the modes C, D of the first region R1, although the transition order of the drive state of each switch SUH ~ SWL, QU ~ QW is different from each other, there is a period in which each switch SUH ~ SWL, QU ~ QW is each specific drive state HHM, MML at the beginning and the end of the switching period.

[0049] Each of the modes A ~ D of the drive pattern when the command voltage vector Vαβ exists in the first region R1 of each sector does not include the drive state HHH, LLL, but includes the drive state MMM. That is, the modulation section 55 selects the drive pattern so as to include the drive state MMM in which each winding 11U ~ 11W is connected to the neutral point O among the zero voltage drive states.

[0050] The modulation section 55 determines that the command voltage vector Vαβ exists in the second region R2 of the first sector, and selects any one of the modes A ~ D shown in the drive pattern of the column of the second region R2. Figure 7Any one of the modes A to D in the drive system shown in the column of the second region R2 causes the switches SUH to SWL, QU to QW to turn on and off. In the modes A, B of the second region R2, the drive states HMM, HML, MML, MLL are combined. In the modes A, B of the second region R2, although the transition order of the drive states of the switches SUH to SWL, QU to QW is changed from each other, there are periods in which the switches SUH to SWL, QU to QW are in each specific drive state HMM, MLL at the beginning and end of the switching period. In the modes C, D of the second region R2, the drive states HHM, HMM, HML, MML are combined. In the modes C, D of the second region R2, although the transition order of the drive states of the switches SUH to SWL, QU to QW is changed from each other, there are periods in which the switches SUH to SWL, QU to QW are in each specific drive state HHM, MML at the beginning and end of the switching period.

[0051] The modulation section 55, in the case where it is determined that the command voltage vector Vαβ exists in the third region R3 of the first sector, causes the switches SUH to SWL, QU to QW to turn on and off in any one of the modes A to D in the drive system shown in the column of the third region R3. Figure 7 Any one of the modes A to D in the drive system shown in the column of the third region R3 causes the switches SUH to SWL, QU to QW to turn on and off. In the modes A, B of the third region R3, the drive states HHM, HHL, HML, MML are combined. In the modes A, B of the third region R3, although the transition order of the drive states of the switches SUH to SWL, QU to QW is changed from each other, there are periods in which the switches SUH to SWL, QU to QW are in each specific drive state HHM, MML at the beginning and end of the switching period. In the third region R3, the mode C is the same drive system as the mode A, and the mode D is the same drive system as the mode B.

[0052] The modulation section 55, in the case where it is determined that the command voltage vector Vαβ exists in the fourth region R4 of the first sector, causes the switches SUH to SWL, QU to QW to turn on and off in any one of the modes A to D in the drive system shown in the column of the fourth region R4. Figure 7 Any one of the modes A to D in the drive system shown in the column of the fourth region R4 causes the switches SUH to SWL, QU to QW to turn on and off. In the modes A, B of the fourth region R4, the drive states HMM, HML, HLL, MLL are combined. In the modes A, B of the fourth region R4, although the transition order of the drive states of the switches SUH to SWL, QU to QW is changed from each other, there are periods in which the switches SUH to SWL, QU to QW are in each specific drive state HMM, MLL at the beginning and end of the switching period. In the fourth region R4, the mode C is the same drive system as the mode A, and the mode D is the same drive system as the mode B.

[0053] The modulation section 55 alternately selects the drive modes of the patterns A, B or alternately selects the patterns C, D in the case where the sector in which the command voltage vector Vαβ exists and the existing region are the same as those of the last switching period. In other words, the modulation section 55 selects the drive mode so that the initial drive state and the final drive state in one switching period are each specific drive state, and the specific drive state that initially appears in this one switching period and the specific drive state that finally appears in the last switching period become the same drive state.

[0054] In addition, the above-described selection processing of the drive mode can be applied to the case where the command voltage vector Vαβ exists in the second to sixth sectors. For example, in the case of applying the above-described selection processing of the drive mode to the second sector, the drive mode selected by the modulation section 55 is as follows. In the pattern A of the drive mode in the first region Rl of the second sector, the drive states MML, MMM, MHM, HHM appear in this order, in the pattern B, HHM, MHM, MMM, MML appear in this order, in the pattern C, the drive states LML, MML, MMM, MHM appear in this order, and in the pattern D, the drive states MHM, MMM, MML, LML appear in this order. In the pattern A of the drive mode in the second region R2 of the second sector, the drive states MML, MHL, MHM, HHM appear in this order, in the pattern B, the drive states HHM, MHM, MHL, MML appear in this order, in the pattern C, the drive states LML, MML, MHL, MHM appear in this order, and in the pattern D, the drive states MHM, MHL, MML, LML appear in this order.

[0055] In the pattern A of the drive mode in the third region R3 of the second sector, the drive states LML, LHL, MHL, MHM appear in this order, in the pattern B, the drive states MHM, MHL, LHL, LML appear in this order, the pattern C is the same as the pattern A, and the pattern D is the same as the pattern B. In the pattern A of the drive mode in the fourth region R4 of the second sector, the drive states MML, MHL, HHL, HHM appear in this order, in the pattern B, the drive states HHM, HHL, MHL, MML appear in this order, the pattern C is the same as the pattern A, and the pattern D is the same as the pattern B.

[0056] The modulation section 55 selects the mode in which the variation in the accumulated charge of the first capacitor 21 and the variation in the accumulated charge of the second capacitor 22 caused by a specific phase current that flows through a specific phase during each specific drive state are larger, among the modes included in the selected drive pattern, on the basis of the command voltage vector Vαβ and the current flowing through each winding 11U to 11W. Here, the specific phase is a phase in which the level of the phase voltage during each specific drive state is different from that of the other phases. The specific phase current is the current that flows through the specific phase during a period in which each of the switches SUH to SWL and QU to QW is in each specific drive state. As the current flowing through each winding 11U to 11W, the modulation section 55 can use the detection value of the phase current sensor 43.

[0057] Specifically, a case in which it is determined that the command voltage vector Vαβ exists in the first region R1 of the first sector will be described. The specific phase during each specific drive state HMM and MLL is the U phase, and the specific phase current is the U phase current that flows during each specific drive state HMM and MLL. In addition, the specific phase during each specific drive state HMM and MLL is the W phase, and the specific phase current is the W phase current that flows during each specific drive state HMM and MLL. Each specific drive state HMM and MLL is a drive state used in modes A and B, and each specific drive state HMM and MLL is a drive state used in modes C and D. That is, the drive pattern of the first region R1 of the first sector includes each mode in which the specific phase during each specific drive state is different from each other, as two modes (for example, modes A and C or modes B and D) that can be selected for the same command voltage vector Vαβ. In this case, the modulation section 55 compares the variation in the accumulated charge of each capacitor 21 and 22 due to the U phase current flowing during each specific drive state HMM and MLL with the variation in the accumulated charge of each capacitor 21 and 22 due to the W phase current flowing during each specific drive state HMM and MLL.

[0058] The variation in the accumulated charge of each capacitor 21 and 22 due to the U phase current flowing during each specific drive state HMM and MLL is, for example, |IU| x ta x TS. The variation in the accumulated charge of each capacitor 21 and 22 due to the W phase current flowing during each specific drive state HMM and MLL is, for example, |IW| x tb x TS. Here, |IU| and |IW| represent the magnitude of the U phase current and the W phase current, and TS represents the length of one switching period. As in the previous description, ta and tb represent the ratio of the period in which the U phase current and the W phase current flow, respectively, to one switching period. Figure 4As explained above, the coefficients ta, tb are constant multiples of the voltage vectors V1, V2. In this case, ta x TS corresponds to the total period during which each switch SUH ~ SWL, QU ~ QW is set to each specific drive state MLL, HMM, and tb x TS corresponds to the total period during which each switch SUH ~ SWL, QU ~ QW is set to each specific drive state MML, HHM.

[0059] The modulation section 55 selects either of the modes A, B of the drive system in the case where it is determined that |IU| x ta x TS > |IW| x tb x TS. On the other hand, the modulation section 55 selects either of the modes C, D of the drive system in the case where it is determined that |IU| x ta x TS ≤ |IW| x tb x TS.

[0060] In addition, the modulation section 55 can also select the mode A, B or the mode C, D of the drive system according to the comparison of the amounts of change in the accumulated charges of the capacitors 21, 22 caused by the specific phase current in the case where it is determined that the command voltage vector Vαβ exists in the second region R2 of the first sector. The modulation section 55 can not perform the above processing in the case where it is determined that the command voltage vector Vαβ exists in the third region R3 and the fourth region R4 of the first sector, because the modes A, C, the modes B, D of the drive system are the same.

[0061] The mode selection processing of the drive system of each switch SUH ~ SWL, QU ~ QW described above can also be applied to the case where the command voltage vector Vαβ exists in the second sector to the sixth sector.

[0062] Specifically, the mode selection of the drive system is performed in the following manner in the case where the command voltage vector Vαβ exists in the fourth sector. The specific phase in the period during which each specific drive state LMM, MHH is assumed is the U phase, and the specific phase current is the U phase current that flows in the period during which each specific drive state LMM, MHH is assumed. In addition, the specific phase in the period during which each specific drive state LLM, MMH is assumed is the W phase, and the specific phase current is the W phase current that flows in the period during which each specific drive state LLM, MMH is assumed. In this case, the modulation section 55 compares the amount of change in the accumulated charge of each capacitor 21, 22 due to the U phase current that flows in the period during which each specific drive state LMM, MHH is assumed with the amount of change in the accumulated charge of each capacitor 21, 22 due to the W phase current that flows in the period during which each specific drive state LLM, MMH is assumed. The modulation section 55 selects the mode of the drive system according to the comparison result. Specifically, the modulation section 55 selects which one of the specific drive states LMM, MHH on the U phase side and the specific drive states LLM, MMH on the W phase side appears within one switching cycle.

[0063] In a case where the command voltage vector Vαβ exists in the second sector or the fifth sector, the mode selection of the drive pattern is made in the following manner. The specific phase during each of the specific drive states LML, MHM or MLM, HMH is the V phase, and the specific phase current is the V phase current flowing during each of the specific drive states LML, MHM or MLM, HMH. In this case, the modulation section 55 compares the amount of change in the accumulated charge of each capacitor 21, 22 due to the V phase current flowing during each of the specific drive states LML, MHM or MLM, HMH with the amount of change in the accumulated charge of each capacitor 21, 22 due to the W phase current flowing during each of the specific drive states MML, HHM or LLM, MMH. The modulation section 55 selects the mode of the drive pattern in accordance with the comparison result. Specifically, the modulation section 55 selects which of the specific drive states LML, MHM or MLM, HMH on the V phase side and the specific drive states MML, HHM or LLM, MMH on the W phase side occurs within one switching cycle.

[0064] In a case where the command voltage vector Vαβ exists in the third sector or the sixth sector, the mode selection of the drive pattern is made in the following manner. The modulation section 55 compares the amount of change in the accumulated charge of each capacitor 21, 22 due to the U phase current flowing during each of the specific drive states LMM, MHH or MLL, HMM with the amount of change in the accumulated charge of each capacitor 21, 22 due to the V phase current flowing during each of the specific drive states LML, MHM or MLM, HMH. The modulation section 55 selects the mode of the drive pattern in accordance with the comparison result. Specifically, the modulation section 55 selects which of each of the specific drive states LMM, MHH or MLL, HMM on the U phase side and each of the specific drive states LML, MHM or MLM, HMH on the V phase side occurs within one switching cycle.

[0065] The modulation section 55 adjusts the proportion of the occurrence period of each specific drive state with respect to the total of the occurrence periods of two different specific drive states included in the drive pattern in one switching cycle on the basis of the adjustment coefficient k. Here, the modulation section 55 adjusts the value of the adjustment coefficient k on the basis of the command voltage vector Vαβ and the voltages of each capacitor 21, 22. The modulation section 55 can use the detection value of the first voltage sensor 41 as the voltage of the first capacitor 21, and can use the detection value of the second voltage sensor 42 as the voltage of the second capacitor 22.

[0066] Specifically, the case where the first region R1 in which the command voltage vector Vαβ exists in the first sector is determined, and each of the switches SUH ~ SWL, QU ~ QW is driven in the mode A of the drive will be described. In this case, the modulation section 55 sets the period in which each of the switches SUH ~ SWL, QU ~ QW becomes the specific drive state HMM to (1 - k) x ta x TS, and the period in which it becomes the specific drive state MLL to k x ta x TS, and adjusts the value of the adjustment coefficient k (0 ≤ k ≤ 1). Further, ta x TS is the total period of the periods in which each of the switches SUH ~ SWL, QU ~ QW is set to each of the specific drive states MLL, HMM.

[0067] In the present embodiment, the value of the adjustment coefficient k is adjusted so as to reduce the voltage variation amplitude ΔV of each of the capacitors 21, 22 in one switching cycle. For example, the voltage variation amplitude ΔV of each of the capacitors 21, 22 in one switching cycle is represented by the following equation (el).

[0068] [Equation 1]

[0069] For example, the modulation section 55 adjusts the adjustment coefficient k so that the voltage variation amplitude ΔV of each of the capacitors 21, 22 in one switching cycle becomes 0. In addition, in the above equation (el), if ΔV = 0, the adjustment coefficient k is represented by the following equation (e2).

[0070] [Equation 2]

[0071] In addition, the above adjustment processing based on the adjustment coefficient k is not limited to the case where the command voltage vector Vαβ exists in the first region R1 of the first sector, but can also be applied to the case where the command voltage vector Vαβ exists in the first region R1 of the second to sixth sectors. In addition, even in the case where the command voltage vector Vαβ exists in the second to fourth regions R2 to R4 of the first to sixth sectors, the adjustment processing based on the adjustment coefficient k can be applied. In this case, by considering the voltage variation amplitude ΔV in accordance with the sector and the region in which the command voltage vector Vαβ exists, the period in which the two different specific drive states appear in one switching cycle can be adjusted.

[0072] Figure 8 The processing steps of the control performed by the control device 40 are shown. The control is repeatedly performed at a prescribed cycle.

[0073] In step S10, the command torque Trq* input from the higher-level control device, the phase currents flowing through the respective phase windings 11U to 11W, the voltages of the first and second capacitors 21 and 22, and the electric angle of the rotary electric machine 10 are acquired. In the present embodiment, the detection value of the phase current sensor 43 is acquired as the phase current, the detection value of the first voltage sensor 41 is acquired as the voltage of the first capacitor 21, the detection value of the second voltage sensor 42 is acquired as the voltage of the second capacitor 22, and the detection value of the rotational angle sensor 44 is acquired as the electric angle of the rotary electric machine 10.

[0074] Here, the conduction loss due to the current flowing through the respective switches SUH to SWL and QU to QW is sometimes larger in the drive state MMM than in the drive states HHH and LLL. In the present embodiment, in the drive state MMM in which the respective clamping switches QU to QW are on, the current flows through six IGBTs, and in the drive states HHH and LLL in which the respective upper arm switches SUH to SWH or the respective lower arm switches SUL to SWL are on, the current flows through three IGBTs. In this case, if the respective switches SUH to SWL and QU to QW become the drive state MMM in the zero-voltage drive state, the conduction loss in the switch control can possibly become large due to the larger number of switches through which the current flows.

[0075] Therefore, in the present embodiment, the manner of the switch control is switched depending on the operating point of the rotary electric machine 10.

[0076] In step Sll, it is determined whether or not the operating point of the rotary electric machine 10 is within the voltage control range E2. The voltage control range E2 is a range set outside the specific range El in which the conduction loss due to the conduction current of the respective switches SUH to SWL and QU to QW becomes equal to or larger than a prescribed allowable value, and is a range in which the voltage variation amplitude of the respective capacitors 21 and 22 is relatively large. In the case where a negative determination is made in step Sll, the process proceeds to step S17. On the other hand, in the case where a positive determination is made in step Sll, the process proceeds to step S12.

[0077] In detail, as Figure 9As shown, the operating point of the rotary electric machine 10 is determined by the torque and the rotational speed of the rotary electric machine 10. The specific range El and the voltage control range E2 are ranges of the operating point of the rotary electric machine 10. The specific range El is a range in which the torque of the rotary electric machine 10 is a value from a first torque value Tql to a maximum torque value Tqc that the rotary electric machine 10 can output, and the rotational speed of the rotary electric machine 10 is a value from a lower limit value No set on the low rotational speed side to a first rotational speed value Nl higher than the lower limit value No. The lower limit value No is, for example, 0. That is, the specific range El is set on the side where the modulation ratio of the switching control becomes a low modulation ratio. In the specific range El, the conduction loss in the switching control sometimes becomes large, and it is desirable to shorten the period of appearance of the drive state MMM of each switch SUH ~ SWL, QU ~ QW.

[0078] The voltage control range E2 is a range in which the torque of the rotary electric machine 10 is a value from a second torque value Tq2 lower than the first torque value Tql to the maximum torque value Tqc, and the rotational speed of the rotary electric machine 10 is a value from the first rotational speed value Nl to a second rotational speed value N2. The second rotational speed value N2 is a value higher than the first rotational speed value Nl and lower than a prescribed rotational speed value Nc. The prescribed rotational speed value Nc is a value set on the low rotational speed side in a region where the higher the rotational speed of the rotary electric machine 10, the lower the output torque of the rotary electric machine 10. In the voltage control range E2, the voltage variation amplitude of each capacitor 21, 22 is relatively large, and thus it is desirable to improve the controllability of the voltage of each capacitor 21, 22.

[0079] Therefore, in the present embodiment, in a case where it is determined in step Sll that the operating point of the rotary electric machine 10 is within the voltage control range E2, the processing of the following steps S12 to S16 is performed. In addition, as the torque that determines the operating point of the rotary electric machine 10, the command torque can be used, and as the rotational speed, the rotational speed calculated based on the detection value of the rotational angle sensor 44 can be used. The processing of step Sll corresponds to a "determination section".

[0080] In step S12, the command voltage vector Vαβ is calculated. In step S13, the sector in which the command voltage vector Vαβ exists and the existing region within the sector are determined. In steps S12, S13, the control device 40 functions as the command current setting section 50, the two-phase conversion section 51, the d-axis deviation calculation section 52a, the q-axis deviation calculation section 52b, the d-axis command voltage calculation section 53a, and the q-axis command voltage calculation section 53b, the fixed coordinate conversion section 54, and the modulation section 55 described in the foregoing. Figure 2

[0081] ​In step S14, the drive pattern is selected based on the command voltage vector Vαβ and the phase current. Based on the command voltage vector Vαβ, the drive pattern is selected so as to generate a period in which two different specific drive states appear within one switching cycle. Further, in the present embodiment, the drive pattern is selected so that the initial drive state and the final drive state in one switching cycle are each the specific drive state, and the specific drive state that initially appears in the present one switching cycle and the specific drive state that finally appears in the previous one switching cycle become the same drive state. In addition, the drive state MMM is selected in a period in which the drive state of each switch SUH to SWL, QU to QW is the zero voltage drive state. Based on the command voltage vector Vαβ and the phase current, the mode in which the amount of change in the accumulated charge of the first capacitor 21 and the second capacitor 22 caused by the specific phase current is larger is selected from among the two modes included in the selected drive pattern. Further, the process of step S14 corresponds to the "selection section".

[0082] In step S15, the adjustment coefficient k is calculated. In the present embodiment, the adjustment coefficient k is adjusted so that the voltage variation amplitude ΔV of each capacitor 21, 22 in one switching cycle becomes 0 or minimum. Further, the process of step S15 corresponds to the "adjustment section".

[0083] In step S16, switching control is performed based on the drive pattern and the mode of each switch SUH to SWL, QU to QW decided by the processes of steps S12 to S15.

[0084] In step S17, normal control is performed. In the normal control, unlike the selection process of the drive pattern in step S14, the drive pattern can be selected without being in a manner in which a period in which two different specific drive states appear within one switching cycle is generated. Further, in the normal control, even when it is determined that the command voltage vector Vαβ exists in the first region R1 of each sector, the drive pattern can be selected without being in a manner in which the drive state of each switch SUH to SWL, QU to QW is limited to the drive state MMM that is one of the zero voltage drive states. In this case, in the normal control, switching control is performed in a manner in which the period in which each switch SUH to SWL, QU to QW becomes the drive state MMM in a period in which the zero voltage drive state is generated is shortened compared to when the affirmative determination is made in step S11. For example, in the normal control, the drive state of each switch SUH to SWL, QU to QW changes in the order of HHH→HHM→HMM→MMM or MMM→MML→MLL→LLL during one switching cycle. Further, the processes of steps S16, S17 correspond to the "switching control section".

[0085] Figure 10One example of comparing the switching control of the present embodiment with that of the comparative example is shown. In Figure 10 (a) shows the progress of the phase current, and (b) shows the progress of the voltage of each capacitor 21, 22. In Figure 10 (b), the solid line shows the progress of the voltage of the first capacitor 21, and the broken line shows the progress of the voltage of the second capacitor 22. Here, the normal control is performed as the comparative example. In addition, in Figure 10 (a), (b), the scales of the vertical and horizontal axes in each graph of the present embodiment and the comparative example are made consistent.

[0086] In the present embodiment, by performing the processes of steps S12 to S16, the charge and discharge period (i.e., the variation period) of each capacitor 21, 22 is shortened compared with the comparative example. Thus, in the present embodiment, the variation amplitude V0-p of the voltage of each capacitor 21, 22 is reduced compared with the comparative example. Figure 10 SC1 shown in (b) shows the charge and discharge period of each capacitor 21, 22 in the comparative example, and SC2 shows the charge and discharge period of each capacitor 21, 22 in the present embodiment. In Figure 10 In one of the examples shown in (b), by performing the switching control of the present embodiment, the charge and discharge period of each capacitor 21, 22 can be shortened to half that of the comparative example, and the variation amplitude V0-p of the voltage of each capacitor 21, 22 can be reduced to 40% of that of the comparative example.

[0087] According to the present embodiment described in detail above, the following effects can be obtained.

[0088] Based on the command voltage vector Vαβ, a drive mode is selected as a combination of drive states of each switch SUH to SWL, QU to QW. Here, based on the command voltage vector Vαβ, the drive mode is selected so as to generate a period that is two different specific drive states within one switching period. Then, based on the selected drive mode, the switching control of each switch SUH to SWL, QU to QW is performed. In this case, in the period within one switching period in which each switch SUH to SWL, QU to QW becomes one of the drive states of the specific drive states and the period within one switching period in which it becomes the other drive state, the voltages of each capacitor 21, 22 change in opposite directions to each other. Thus, compared with the case in which only a period that is either one of the two different specific drive states is generated within one switching period, the voltages of each capacitor 21, 22 can be caused to vary at a shorter interval, and the variation period of the voltages of each capacitor 21, 22 can be shortened. As a result, the controllability of the voltages of each capacitor 21, 22 can be improved.

[0089] The proportion of the period during which each specific drive state appears with respect to the total of the periods during which each specific drive state appears in the drive pattern included in one switching cycle is adjusted based on the adjustment coefficient k. Thus, the amount of change in the voltages of the capacitors 21, 22 when the voltages of the capacitors 21, 22 change in opposite directions to each other can be adjusted. Therefore, the voltages of the capacitors 21, 22 can be reliably controlled. As a result, the controllability of the voltages of the capacitors 21, 22 can be reliably improved.

[0090] The mode in which the amount of change in the accumulated charge of the first capacitor 21 and the second capacitor 22 caused by a specific phase current is larger is selected from among the modes included in the selected drive pattern based on the command voltage vector Vαβ and the phase current. Then, switching control is performed based on the selected drive pattern and the mode. In this case, compared to the case in which the mode in which the amount of change in the accumulated charge of the first capacitor 21 and the second capacitor 22 caused by a specific phase current is smaller is selected from among the modes included in the selected drive pattern, the amount of variation in the voltages of the capacitors 21, 22 within one switching cycle can be reduced.

[0091] The drive pattern is selected so that two different specific drive states within one switching cycle appear before the drive states of the switches SUH to SWL, QU to QW change three times. In this case, compared to the case in which the drive states of the switches SUH to SWL, QU to QW change four or more times before two different specific drive states appear, the number of times the voltages of the capacitors 21, 22 vary each time the drive states of the switches SUH to SWL, QU to QW change can be increased. Therefore, the period of variation in the voltages of the capacitors 21, 22 can be reliably shortened.

[0092] The drive pattern is selected so that the first and last drive states in one switching cycle are two different specific drive states, and the specific drive state of each switch SUH to SWL, QU to QW that first appears in the present switching cycle and the specific drive state of each switch SUH to SWL, QU to QW that last appeared in the previous switching cycle become the same drive state. Thus, unnecessary switching in consecutive switching cycles can be suppressed. As a result, switching control that is suitable for reducing switching loss can be implemented.

[0093] In the first region R1 of the first to sixth sectors, the drive states of the switches SUH to SWL, QU to QW are sometimes set to zero voltage drive states. In this case, during the period from the first specific drive state to the last specific drive state in one switching cycle, the switches SUH to SWL, QU to QW become zero voltage drive states. At this time, it is desirable to suppress unnecessary switching.

[0094] To address this, the driving mode in the first region R1 of sectors 1 to 6 is set to include the driving state MMM in the zero-voltage driving state. In this case, compared to the case where the driving states of switches SUH to SWL and QU to QW are the driving states HHH and LLL in the zero-voltage driving state, unnecessary switching within a single switching cycle can be suppressed. As a result, switching control suitable for reducing switching losses can be achieved.

[0095] The system determines whether the operating point of the rotary motor 10 is within the voltage control range E2. If it is determined that the operating point of the rotary motor 10 is within the voltage control range E2, switching control is performed, which improves the controllability of the voltage in each capacitor 21 and 22, and sets the drive state of each switch SUH~SWL and QU~QW to the zero-voltage drive state MMM. On the other hand, if it is determined that the operating point of the rotary motor 10 is outside the voltage control range E2, normal control is performed.

[0096] In normal control, the zero-voltage drive state is not limited to the drive state MMM; switches SUH~SWL and QU~QW can also be in the drive states HHH and LLL. In this case, compared to when the operating point of the rotating motor 10 is within the voltage control range E2, the period during which switches SUH~SWL and QU~QW are in the drive state MMM can be shortened. Therefore, even when conduction losses in switch control may increase, conduction losses can be reduced during the period when switches SUH~SWL and QU~QW are in the zero-voltage drive state. Thus, it is possible to suppress the increase in conduction losses in switch control and improve the controllability of the voltages of capacitors 21 and 22.

[0097] <Second Implementation> Hereinafter, with reference to the accompanying drawings, the second embodiment will be described focusing on the differences from the first embodiment. In this embodiment, the structure of the inverter is changed.

[0098] like Figure 11 As shown, inverter 30 is a neutral-point clamped three-level inverter. Inverter 30 includes U-phase first switches Su1 to fourth switches Su4, V-phase first switches Sv1 to fourth switches Sv4, W-phase first switches Sw1 to fourth switches Sw4, and first clamping diodes Dc1 to sixth clamping diodes Dc6. In this embodiment, voltage-controlled semiconductor switching elements, more specifically IGBTs, are used as each of the switches Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4. In this case, the high-potential side terminals of switches Su1 to Su4, Sv1 to Sv4, and Sw1 to Sw4 are collectors, and the low-potential side terminals are emitters. Furthermore, in... Figure 11In the drawings, the same or similar components are designated by the same reference numerals, and the description will be provided below. Figure 1

[0099] The U-phase first switch Su1 to the U-phase fourth switch Su4 are connected in series in a form in which the emitter and the collector are connected. The positive terminal of the battery 20 is connected to the collector of the U-phase first switch Su1 via the positive-side bus bar 31, and the negative terminal of the battery 20 is connected to the emitter of the U-phase fourth switch Su4 via the negative-side bus bar 32. The input terminal of the U-phase of the rotating electrical machine 10 is connected at the connection point of the U-phase second switch Su2 and the U-phase third switch Su3. In addition, the connection point of the U-phase first switch Su1 and the U-phase second switch Su2 is connected to the cathode of the first clamp diode Dcl, and the anode of the first clamp diode Dcl is connected to the cathode of the second clamp diode Dc2. The anode of the second clamp diode Dc2 is connected to the connection point of the U-phase third switch Su3 and the U-phase fourth switch Su4. In addition, the freewheeling diodes Du1, Du2, Du3, Du4 are connected in reverse parallel to each of the switches Su1, Su2, Su3, Su4 of the U-phase.

[0100] The V-phase first switch Sv1 to the V-phase fourth switch Sv4 are connected in series in a form in which the emitter and the collector are connected. The positive terminal of the battery 20 is connected to the collector of the V-phase first switch Sv1 via the positive-side bus bar 31, and the negative terminal of the battery 20 is connected to the emitter of the V-phase fourth switch Sv4 via the negative-side bus bar 32. The input terminal of the V-phase of the rotating electrical machine 10 is connected at the connection point of the V-phase second switch Sv2 and the V-phase third switch Sv3. In addition, the connection point of the V-phase first switch Sv1 and the V-phase second switch Sv2 is connected to the cathode of the third clamp diode Dc3, and the anode of the third clamp diode Dc3 is connected to the cathode of the fourth clamp diode Dc4. The anode of the fourth clamp diode Dc4 is connected to the connection point of the V-phase third switch Sv3 and the V-phase fourth switch Sv4. In addition, the freewheeling diodes Dv1, Dv2, Dv3, Dv4 are connected in reverse parallel to each of the switches Sv1, Sv2, Sv3, Sv4 of the V-phase.

[0101] ​The W-phase first switch Swl to the W-phase fourth switch Sw4 are connected in series in a form connecting the emitter and the collector. The positive terminal of the battery 20 is connected to the collector of the W-phase first switch Swl via the positive side bus bar 31, and the negative terminal of the battery 20 is connected to the emitter of the W-phase fourth switch Sw4 via the negative side bus bar 32. The input terminal of the W-phase of the rotating electric machine 10 is connected at the connection point of the W-phase second switch Sw2 and the W-phase third switch Sw3. Further, the connection point of the W-phase first switch Swl and the W-phase second switch Sw2 is connected to the cathode of the fifth clamping diode Dc5, and the anode of the fifth clamping diode Dc5 is connected to the cathode of the sixth clamping diode Dc6. The anode of the sixth clamping diode Dc6 is connected to the connection point of the W-phase third switch Sw3 and the W-phase fourth switch Sw4. Further, the freewheeling diodes Dwl, Dw2, Dw3, Dw4 are connected in antiparallel to each of the switches Swl, Sw2, Sw3, Sw4 of the W-phase.

[0102] The neutral point O is connected at the connection point of the first clamping diode Dcl and the second clamping diode Dc2, the connection point of the third clamping diode Dc3 and the fourth clamping diode Dc4, and the connection point of the fifth clamping diode Dc5 and the sixth clamping diode Dc6.

[0103] In the neutral-point-clamped inverter 30, the drive state of each of the switches Su 1 to Sw4 is determined as described below. The phase voltage of the level H is output by turning on the first switch and the second switch Su 1, Su2, Sv 1, Sv2, Swl, Sw2 and turning off the third switch and the fourth switch Su3, Su4, Sv3, Sv4, Sw3, Sw4 in the phase that is the object. The phase voltage of the level M is output by turning on the second switch and the third switch Su2, Su3, Sv2, Sv3, Sw2, Sw3 and turning off the first switch and the fourth switch Su 1, Su4, Sv 1, Sv4, Swl, Sw4 in the phase that is the object. The phase voltage of the level L is output by turning on the third switch and the fourth switch Su3, Su4, Sv3, Sv4, Sw3, Sw4 and turning off the first switch and the second switch Su 1, Su2, Sv 1, Sv2, Swl, Sw2 in the phase that is the object.

[0104] For example, during the period in which the switches Su 1 to Sw4 are in the drive state HML, the U-phase first switch Su 1 and the U-phase second switch Su2, the V-phase second switch Sv2 and the V-phase third switch Sv3, the W-phase third switch Sw3 and the W-phase fourth switch Sw4 are turned on, and the U-phase third switch Su3 and the U-phase fourth switch Su4, the V-phase first switch Sv 1 and the V-phase fourth switch Sv4, the W-phase first switch Swl and the W-phase second switch Sw2 are turned off.

[0105] Even the neutral-point-clamped inverter 30 described above can perform the previous Figure 8 the processes of the steps S10 to S17 shown.

[0106] In the neutral-point-clamped inverter 30, in a case where the switches Su1 to Sw4 become the drive state MMM, the six IGBTs become the on state, and the six clamping diodes become the on state. In a case where the switches Su1 to Sw4 become the drive state HHH, LLL, the six IGBTs become the on state. In this case, according to the on loss of the clamping diodes, even in the present embodiment, since the switches Su1 to Sw4 become the drive state MMM during the period of the zero-voltage drive state, there is a possibility that the on loss in the switch control becomes large. Therefore, in the previous Figure 8 In the step S11 of the previous embodiment, by switching the mode of the switch control based on the drive state of the rotating electric machine 10, it is possible to suppress the on loss in the switch control from becoming large, and it is possible to improve the controllability of the voltage of each capacitor 21, 22.

[0107] <OTHER EMBODIMENTS> In addition, the above-described embodiment can be implemented with the following changes.

[0108] • The modulation section 55 can adjust the proportion of the period during which each specific drive state appears with respect to the total of the periods during which each specific drive state included in the drive mode appears, based on at least either the voltage of the first capacitor 21 or the voltage of the second capacitor 22, instead of the adjustment coefficient k. For example, in a case where it is determined that the command voltage vector Vαβ exists in the first region R1 of the first sector, and each switch SUH to SWL, QU to QW is driven in the mode A of the drive mode, the higher the detected voltage of the first capacitor 21, the longer the modulation section 55 preferably makes the period during which each switch SUH to SWL, QU to QW becomes the drive state HMM, and the shorter the period during which it becomes the drive state MLL. Also, for example, the higher the detected voltage of the second capacitor 22, the longer the modulation section 55 makes the period during which each switch SUH to SWL, QU to QW becomes the drive state MLL, and the shorter the period during which it becomes the drive state HMM.

[0109] In the present embodiment, it is also possible to adjust the proportion of the period during which each switch SUH to SWL, QU to QW is driven in two different specific drive states, and it is possible to reliably control the voltage of each capacitor 21, 22.

[0110] • In the previous Figure 8In step S17 of the embodiment, instead of the drive mode of the normal control, the drive mode explained in step S14 can be selected. However, in step S17 of the embodiment, the drive mode is selected so that the drive state of each switch SUH to SWL, QU to QW is set to the drive state HHH or LLL in the period in which the zero voltage drive state is attained. Thus, compared with the case where the drive mode explained in step S14 is used, the period in which each switch SUH to SWL, QU to QW attains the drive state MMM can be shortened.

[0111] • In the previous Figure 8 In step S11, instead of determining whether the operation point of the rotating electric machine 10 is within the voltage control range E2, it can be determined whether it is within the specific range El. In this case, in the case where the negative determination is made in step S11, the process proceeds to step S12. On the other hand, in the case where the positive determination is made in step S11, the process proceeds to step S17.

[0112] • The previous Figure 8 The processes of steps S11 and S17 can not be performed. That is, instead of switching the mode of the switch control depending on the operation point of the rotating electric machine 10, the processes of steps S12 to S16 can be performed.

[0113] • As the semiconductor switch constituting the inverter, it is not limited to the IGBT, but can be, for example, an N-channel MOSFET. In this case, the high potential side terminal of the switch is the drain, and the low potential side terminal is the source. Further, each switch has a corresponding body diode.

[0114] • The power storage section connected to the inverter is not limited to the capacitor, but can be a secondary battery that can charge and discharge.

[0115] • As the rotating electric machine, it is not limited to the rotating electric machine whose windings of each phase are star-connected, but can be a rotating electric machine whose windings of each phase are delta-connected.

[0116] • As the installation object of the inverter, the rotating electric machine, and the control device, it is not limited to the vehicle, but can be, for example, a mobile body such as an airplane or a ship. In the case where the mobile body is the airplane, the rotating electric machine becomes a flight power source of the airplane, and in the case where the mobile body is the ship, the rotating electric machine becomes a propulsion power source of the ship. Further, as the installation object of the inverter, the rotating electric machine, and the control device, it is not limited to the mobile body.

[0117] • The control section and the method thereof according to the present disclosure can also be implemented by a special-purpose computer provided by a processor programmed to execute one or more functions embodied by a computer program, or by a special-purpose computer provided by a processor composed of one or more special-purpose hardware logic circuits. Alternatively, the control section and the method thereof according to the present disclosure can be implemented by one or more special-purpose computers composed of a processor programmed to execute one or more functions and a processor composed of one or more hardware logic circuits. Furthermore, the computer program can be stored in a non-transitory tangible recording medium readable by a computer as instructions to be executed by the computer.

[0118] • Hereinafter, characteristic structures extracted from the above-described embodiments are described. [Structure 1] A control device of a three-level inverter, the control device of a three-level inverter (40) is adapted to a system, the system includes: a first power storage unit (21) and a second power storage unit (22) connected in series; and a rotating electric machine (10) having windings (11U-11W) corresponding to three phases; and a three-level inverter (30) having switches (SUH-SWL, QU-QW, Su1-Sw4) corresponding to the three phases that connect the windings of each phase of the rotating electric machine to any one of a positive electrode side of the first power storage unit, a neutral point between a negative electrode side of the first power storage unit and a positive electrode side of the second power storage unit, and a negative electrode side of the second power storage unit, wherein the control device of a three-level inverter includes: a selection unit that selects a combination of drive states of the switches of each phase in one switching period, i.e., a drive mode, based on an instruction voltage for controlling a control amount of the rotating electric machine to an instruction value; and a switch control unit that performs switching control of the switches based on the selected drive mode, each of the drive states that equalizes three line-to-line voltages of the windings and reverses directions of currents flowing through the neutral point is set as a specific drive state, the selection unit selects the drive mode based on the instruction voltage to generate a period that is each of the specific drive states within the one switching period. [Structure 2] The control device of a three-level inverter according to Structure 1, wherein The adjustment section adjusts a ratio of a period during which each of the specific drive states occurs with respect to a total of periods during which each of the specific drive states in the drive pattern included in the one switching cycle occurs, based on at least one of a voltage of the first power storage section and a voltage of the second power storage section. [Structure 3] The control device of the three-level inverter according to Structure 1 or Structure 2, The connection section connects the winding in each of the specific drive states in each phase to any one of the positive side of the first power storage section, the neutral point, and the negative side of the second power storage section, and the specific phase is set to a phase different from the other phases, The drive pattern includes each mode in which the specific phase in each of the specific drive states is different from each other, as two modes selectable for the same command voltage, The current flowing through the specific phase during the period in which each of the specific drive states is the specific phase current, The selection section selects the mode in which the amount of change in the accumulated charge of the first power storage section and the amount of change in the accumulated charge of the second power storage section caused by the specific phase current are larger among the specific modes included in the selected drive pattern, based on the command voltage and the current flowing through the winding in each phase. [Structure 4] The control device of the three-level inverter according to any one of Structures 1 to 3, The selection section selects the drive pattern so that each of the specific drive states occurs before the drive state changes three times. [Structure 5] The control device of the three-level inverter according to any one of Structures 1 to 4, The selection section selects the drive pattern so that the first drive state and the last drive state in the one switching cycle are each of the specific drive states, and the specific drive state that occurs first in the one switching cycle and the specific drive state that occurs last in the one switching cycle become the same drive state. [Structure 6] The control device of the three-level inverter according to Structure 5, The drive state in which the winding in each phase is connected to the positive side of the first power storage section, the neutral point, or the negative side of the second power storage section is set to a zero voltage drive state, The selection section selects the drive pattern to include the drive state in which the winding in each phase is connected to the neutral point in the zero voltage drive state. [Structure 7] According to the control device of the three-level inverter according to Structure 6, in a case where the winding of each phase and the neutral point are connected through the switch, the conduction loss due to current flowing through the switch is greater than in a case where the positive electrode side of the first power storage unit or the negative electrode side of the second power storage unit and the winding of each phase are connected through the switch, According to the control device of the three-level inverter according to Structure 6, in a case where the winding of each phase and the neutral point are connected through the switch, the conduction loss due to current flowing through the switch is greater than in a case where the positive electrode side of the first power storage unit or the negative electrode side of the second power storage unit and the winding of each phase are connected through the switch, The control device of the three-level inverter according to Structure 6 includes a determination unit that determines whether or not the operation point of the rotating electric machine is within a specific range in which the conduction loss due to current flowing through the switch is greater than or equal to an allowable value, The switch control unit shortens the period in which the winding of each phase and the neutral point are connected, compared to a case where it is determined that the operation point is outside the specific range, during a period in which the switch is in the zero-voltage drive state.

[0119] Although the present disclosure is described based on the embodiments, it should be understood that the present disclosure is not limited to the above-described embodiments, structures. The present disclosure also includes various modifications, modifications within the equivalent scope. In addition, various combinations, modes, and further, only one element, more than or less than that, other combinations, modes, are also within the scope of the present disclosure, the range of ideas.

Claims

1. A control device for a three-level inverter, the control device (40) for the three-level inverter being applicable to a system comprising: The first energy storage unit (21) and the second energy storage unit (22) are connected in series; Rotary electric motor (10), the rotary electric motor having windings (11U~11W) corresponding to three; and A three-level inverter (30) having three corresponding switches (SUH~SWL, QU~QW, Su1~Sw4) for connecting the windings of each phase of the rotating motor to the positive side of the first energy storage unit, the neutral point between the negative side of the first energy storage unit and the positive side of the second energy storage unit, and the negative side of the second energy storage unit. The control device for the three-level inverter includes: The selection unit selects a combination of drive states of the switches in each phase of a switching cycle, i.e., a drive mode, based on the command voltage used to control the control quantity of the rotating motor to the command value. as well as A switch control unit, which controls the switching of the switch based on the selected driving method. Each of the driving states, which are two different driving states, in which the three line-to-line voltages of the winding are equal and the directions of the current flowing through the neutral point are opposite to each other, is designated as a specific driving state. The selection unit selects the driving mode based on the command voltage to generate a period that becomes each of the specific driving states within the one switching cycle.

2. The control device for the three-level inverter as described in claim 1, characterized in that, The system includes an adjustment unit that, based on at least one of the voltages of the first energy storage unit and the second energy storage unit, adjusts the ratio of the occurrence period of each of the specific driving states to the total occurrence period of each of the specific driving states in the driving mode included in the one switching cycle.

3. The control device for the three-level inverter as described in claim 1, characterized in that, A phase in which the connection point between the winding of each phase and any one of the following—the positive terminal side of the first energy storage unit, the neutral point, and the negative terminal side of the second energy storage unit—is different from that of the other phases is designated as a specific phase. The driving method includes modes that are different from each other during the specific phase in each specific driving state, and which are two modes selectable for the same command voltage. The current flowing through the specific phase during the period of each of the specific drive states will be referred to as the specific phase current. The selection unit selects, based on the command voltage and the current flowing through the windings of each phase, the mode that has the larger change in the stored charge of the first energy storage unit and the change in the stored charge of the second energy storage unit caused by the specific phase current, from among the modes included in the selected driving mode.

4. The control device for the three-level inverter as described in claim 1, characterized in that, The selection unit selects the driving mode so that each specific driving state appears before the driving state changes three times.

5. The control device for the three-level inverter as described in claim 1, characterized in that, The selection unit selects the driving mode so that the initial driving state and the last driving state in the switching cycle are each of the specific driving states, and the specific driving state that first appears in the current switching cycle is the same as the specific driving state that last appeared in the previous switching cycle.

6. The control device for a three-level inverter as described in claim 5, characterized in that, The driving state in which the windings of each phase are connected to the positive terminal side of the first energy storage unit, the neutral point, or the negative terminal side of the second energy storage unit is set to a zero-voltage driving state. The selection unit selects the driving mode to include the driving state in which the windings of each phase are connected to the neutral point in the zero-voltage driving state.

7. The control device for the three-level inverter as described in claim 6, characterized in that, For the three-level inverter, compared to the case where the positive side of the first energy storage unit or the negative side of the second energy storage unit is connected to the windings of each phase via the switch, the conduction losses caused by the current flowing through each switch are greater when the windings of each phase are connected to the neutral point via the switch. The system includes a determination unit that determines whether the operating point of the rotating motor is within a specific range where the conduction loss caused by the current flowing through the switch is above an allowable value. When the switch control unit determines that the circuit is within the specified range, compared to when it determines that the circuit is outside the specified range, it performs switch control in a manner that shortens the period during which the windings of each phase are connected to the neutral point during the period when the switch is in the zero-voltage drive state.

8. A program applicable to a system and executed by a computer (40), the system comprising: The first energy storage unit (21) and the second energy storage unit (22) are connected in series; as well as Rotary electric motor (10), the rotary electric motor having windings (11U~11W) corresponding to three; and A three-level inverter (30) having three corresponding switches (SUH~SWL, QU~QW, Su1~Sw4) for connecting the windings of each phase of the rotating motor to the positive side of the first energy storage unit, the neutral point between the negative side of the first energy storage unit and the positive side of the second energy storage unit, and the negative side of the second energy storage unit. The program causes the computer to perform a process that includes selection and control steps. The selection step, based on the command voltage used to control the control quantity of the rotating motor to the command value, selects a combination of the drive states of the switches in each phase of a switching cycle, i.e., the drive mode. The control steps involve controlling the switching of the switch based on the selected driving method. Each of the driving states, which are two different driving states, in which the three line-to-line voltages of the winding are equal and the directions of the current flowing through the neutral point are opposite to each other, is designated as a specific driving state. In the selection step, the following process is performed: based on the command voltage, the driving mode is selected to generate a period that becomes each of the specific driving states within the one switching cycle.

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