Control devices for rotating electric machines, control programs for rotating electric machines, rotating electric machine systems, rotating electric machines

Abstract

To suppress an output voltage of an inverter by selectively using excitation-reducing control and weak field control.SOLUTION: According to a rotary electric machine (40), a field current flows by inducing a voltage to a field winding (70), when a high frequency voltage is applied to a stator winding (52). A control device (30) comprises: a switch control part that performs switching control of an inverter (20) so as to apply a composite voltage obtained by the high frequency voltage and a fundamental wave voltage to the stator winding; an excitation-reducing part that performs excitation-reducing control for having an excitation voltage component for making the field current flow through the field winding among voltage components contained in the composite voltage, lower than at present; a weak field part that performs weak field control for adjusting a phase of a fundamental wave current flowing through the stator winding by the fundamental wave voltage so as to generate a magnetic flux in a reverse direction to a magnetic flux generated by the field winding; and a control change part for changing execution / non-execution of the excitation-reducing control and the weak field control according to an operation area of the rotary electric machine in such a manner that an output voltage of the inverter is suppressed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a control device for a rotating electrical machine.

Background Art

[0002] For example, a rotating electrical machine system including a first power converter that passes a current through a stator winding of a synchronous motor and a second power converter that passes an exciting current through a field winding of a rotor is known (see Patent Document 1). In the rotating electrical machine system described in Patent Document 1, when the output voltage of the first power converter exceeds a voltage limit value during high load, the magnetic flux command value of the field winding is decreased. As a result, the exciting current command value decreases, the magnetic flux of the field winding decreases, and the output voltage of the first power converter is suppressed to the voltage limit value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, there is a self-excited field winding type rotating electrical machine in which a voltage is induced in a field winding by applying a high-frequency exciting voltage to a stator winding to cause an exciting current to flow. In a self-excited field winding type rotating electrical machine, the magnetic flux of the field winding can be decreased by decreasing the exciting voltage component of the voltage applied to the stator winding among the voltages applied to the stator winding (hereinafter referred to as "excitation decrease control"). Also, the magnetic flux of the field winding can be substantially decreased by passing a negative d-axis current through the stator winding so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding (hereinafter referred to as "field weakening control").

[0005] Here, the applicant of the present application has noticed that when the rotating electrical machine outputs the same torque under field weakening control and reduced excitation control, the magnitude relationship between the output voltage of the power converter (inverter) during reduced excitation control and the output voltage of the power converter during field weakening control changes depending on the operating region of the rotating electrical machine.

[0006] The present disclosure has been made to solve the above problems, and its main object is to suppress the output voltage of the inverter by properly using reduced excitation control and field weakening control in a control device for a rotating electrical machine capable of performing reduced excitation control and field weakening control.

Means for Solving the Problems

[0007] A first means for solving the above problems is a rotating electrical machine (40) having a stator (50) including a stator winding (52) and a rotor (60) including a field winding (70), an inverter (20) electrically connected to the stator winding, a control device (30) for a rotating electrical machine applied to a rotating electrical machine system (90) including wherein the rotating electrical machine is configured such that a voltage is induced in the field winding and a field current flows when a high-frequency voltage is applied to the stator winding, a switch control unit (109) that performs switching control of the inverter so as to apply a combined voltage of the high-frequency voltage and a fundamental wave voltage having a frequency different from that of the high-frequency voltage to the stator winding, a reduced excitation unit (102, 130, 202) that performs reduced excitation control to reduce an excitation voltage component, which is a component for flowing the field current in the field winding, among the voltage components included in the combined voltage, compared to the present level, a field weakening unit (201) that performs field weakening control to adjust the phase of a fundamental wave current flowing through the stator winding by the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding. A control change unit (209) that changes the execution of the field weakening control by the field weakening unit and the execution of the field reduction control by the field reduction unit according to the operating region of the rotating electrical machine so that the output voltage of the inverter is suppressed; is provided.

[0008] According to the above configuration, the rotating electrical machine is configured such that a voltage is induced in the field winding and a field current flows when a high-frequency voltage is applied to the stator winding. Further, the switch control unit performs switching control of the inverter so that a high-frequency voltage having a higher frequency than the fundamental wave voltage is caused to flow through the stator winding in addition to the fundamental wave voltage for the purpose of generating torque in the rotating electrical machine. As a result, a power converter for flowing a field current through the field winding, other than the above inverter, becomes unnecessary, and the rotating electrical machine system can be simplified.

[0009] The field reduction unit performs field reduction control to reduce a field voltage component, which is a component for flowing the field current through the field winding among the voltage components included in the combined voltage, more than at present. Therefore, when it is necessary to suppress the output voltage of the inverter, the field reduction unit can suppress the output voltage of the inverter by executing the field reduction control. Further, the field weakening unit performs field weakening control to adjust the phase of the fundamental wave current flowing through the stator winding so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding. Therefore, when it is necessary to suppress the output voltage of the inverter, the field weakening unit can suppress the output voltage of the inverter by executing the field weakening control.

[0010] Here, when the rotating electrical machine outputs the same torque under field-weakening control and reduced-excitation control, the present inventors have noted that which of the output voltage of the inverter under reduced-excitation control and the output voltage of the inverter under field-weakening control is higher varies depending on the operating region of the rotating electrical machine. For example, in the high-load region of the rotating electrical machine, when the rotating electrical machine outputs the same torque under reduced-excitation control and field-weakening control, the output voltage of the inverter under field-weakening control becomes lower than the output voltage of the inverter under reduced-excitation control. Then, according to the operating region of the rotating electrical machine so as to suppress the output voltage of the inverter, the control change unit changes whether to execute the reduced-excitation control by the reduced-excitation unit and the field-weakening control by the field-weakening unit. Therefore, reduced-excitation control and field-weakening control can be properly used according to the operating region of the rotating electrical machine, and the output voltage of the inverter can be suppressed.

[0011] The second means is a rotating electrical machine (40) having a stator (50) including a stator winding (52) and a rotor (60) including a field winding (70), an inverter (20) electrically connected to the stator winding, A control program for a rotating electrical machine applied to a rotating electrical machine system (90) including: the rotating electrical machine is configured such that a voltage is induced in the field winding and a field current flows when a high-frequency voltage is applied to the stator winding; a process of performing switching control of the inverter so as to apply a combined voltage of the high-frequency voltage and a fundamental wave voltage having a frequency different from that of the high-frequency voltage to the stator winding; a process of performing reduced-excitation control to reduce an excitation voltage component, which is a component for flowing the field current in the field winding, among the voltage components included in the combined voltage, compared to the present level; a process of performing field-weakening control to adjust the phase of a fundamental wave current flowing through the stator winding by the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding; Processing to change the execution of the field weakening control and the flux weakening control according to the operating region of the rotating electrical machine so that the output voltage of the inverter is suppressed, is executed by a computer (30).

[0012] According to the above configuration, by causing a computer to execute a control program for a rotating electrical machine, the same operational effects as those of the first means can be achieved.

[0013] The third means is A rotating electrical machine system (90) including a rotating electrical machine (40) having a stator (50) including a stator winding (52) and a rotor (60) including a field winding (70), an inverter (20) electrically connected to the stator winding, and a control device (30) for the rotating electrical machine, The rotating electrical machine is configured such that a voltage is induced in the field winding and a field current flows when a high-frequency voltage is applied to the stator winding. The control device is A switch control unit (109) that performs switching control of the inverter so as to apply a combined voltage of the high-frequency voltage and a fundamental wave voltage having a frequency different from that of the high-frequency voltage to the stator winding, An excitation reduction unit (102, 130, 202) that performs excitation reduction control to reduce an excitation voltage component, which is a component that causes the field current to flow through the field winding, among the voltage components included in the combined voltage, A flux weakening unit (201) that performs flux weakening control to adjust the phase of a fundamental wave current flowing through the stator winding by the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding, A control change unit (209) that changes the execution of the excitation reduction control by the excitation reduction unit and the execution of the flux weakening control by the flux weakening unit according to the operating region of the rotating electrical machine so that the output voltage of the inverter is suppressed, is provided.

[0014] According to the above configuration, in a control system for a rotating electrical machine, the same operational effects as those of the first means can be achieved.

Brief Description of the Drawings

[0015]

Figure 1

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Embodiments for Carrying Out the Invention

[0016] While referring to the drawings, a plurality of embodiments will be described. In the plurality of embodiments, functionally and / or structurally corresponding parts and / or associated parts may be assigned the same reference numerals, or reference numerals that differ only in the hundreds place. For corresponding parts and / or associated parts, reference may be made to the description of other embodiments.

[0017] <First Embodiment> Hereinafter, a first embodiment in which a rotating electrical machine system and a control device for a rotating electrical machine according to the present disclosure are embodied will be described with reference to the drawings. The rotating electrical machine system is mounted on, for example, a vehicle. The rotating electrical machine is a driving power source for the vehicle.

[0018] As shown in FIG. 1, the rotating electrical machine system 90 includes a DC power supply 10, an inverter 20, a control device 30, and a rotating electrical machine 40. The rotating electrical machine 40 is a self-excited field winding type synchronous machine. For example, an electromechanical integrated drive device is configured including the rotating electrical machine 40, the inverter 20, and the control device 30, or the rotating electrical machine 40, the inverter 20, and the control device 30 are each composed of respective components.

[0019] The rotating electrical machine 40 includes a housing 41, a stator 50, and a rotor 60 housed in the housing 41. The rotating electrical machine 40 of the present embodiment is an inner rotor type rotating electrical machine in which the rotor 60 is disposed radially inside the stator 50.

[0020] The stator 50 includes a stator core 51 and a stator winding 52. The stator winding 52 is composed of, for example, copper wire and includes U, V, W phase windings 52U, 52V, 52W arranged in a state of being shifted from each other by 120° in electrical angle (see FIG. 3).

[0021] The rotor 60 includes a rotor core 61 and a field winding 70. The field winding 70 is composed of, for example, aluminum wire, copper wire, or CNT (carbon nanotube). A rotating shaft 32 is inserted through a central hole of the rotor core 61. The rotating shaft 32 is rotatably supported by the housing 41 via a bearing 42.

[0022] As shown in FIG. 2, the inverter 20 (power converter) includes a series connection of upper arm switches SUp, SVp, SWp for U, V, W phases and lower arm switches SUn, SVn, SWn for U, V, W phases. The first ends (one ends) of the U, V, W phase windings 52U, 52V, 52W are connected to the connection points between the upper arm switches SUp, SVp, SWp for U, V, W phases and the lower arm switches SUn, SVn, SWn for U, V, W phases. The second ends (the other ends) of the U, V, W phase windings 52U, 52V, 52W are connected at the neutral point. That is, in the present embodiment, the U, V, W phase windings 52U, 52V, 52W are star-connected. In the present embodiment, each of the switches SUp to SWn is an IGBT. A freewheel diode is connected in anti-parallel to each of the switches SUp to SWn.

[0023] The positive terminal of the DC power supply 10 is connected to the collectors of the upper arm switches SUp, SVp, SWp for U, V, W phases. The negative terminal of the DC power supply 10 is connected to the emitters of the lower arm switches SUn, SVn, SWn for U, V, W phases. A smoothing capacitor 11 is connected in parallel to the DC power supply 10.

[0024] Subsequently, the stator 50 and the rotor 60 will be described with reference to FIG. 3.

[0025] Both the stator 50 and the rotor 60 are arranged coaxially with the rotation shaft 32 (specifically, with the rotation center axis O as the common axis). In the following description, the direction in which the rotation shaft 32 extends is defined as the axial direction, the direction extending radially from the center of the rotation shaft 32 is defined as the radial direction, and the direction extending circumferentially around the rotation shaft 32 is defined as the circumferential direction.

[0026] The stator 50 is composed of a laminated steel sheet made of a soft magnetic material, and has an annular back yoke 51a and a plurality of teeth 51b protruding radially inward from the back yoke 51a. A plurality of slots 54 arranged in the circumferential direction are formed between adjacent teeth 51b. The stator winding 52 is configured by accommodating the phase windings of each phase in each slot 54 in a predetermined order.

[0027] The rotor 60 is made of a soft magnetic material and is composed of, for example, a laminated steel sheet. The rotor 60 has a cylindrical rotor core 61 and a plurality of main pole portions 62 protruding radially outward from the rotor core 61. In the present embodiment, eight main pole portions 62 are provided at equal intervals in the circumferential direction.

[0028] The field winding 70 includes a first winding portion 71a and a second winding portion 71b. In each main pole portion 62, the first winding portion 71a is wound radially outside, and the second winding portion 71b is wound radially inside of the first winding portion 71a. In each main pole portion 62, the winding directions of the first winding portion 71a and the second winding portion 71b are the same as each other. Also, among the main pole portions 62 adjacent to each other in the circumferential direction, the winding directions of the winding portions 71a, 71b wound on one side are opposite to the winding directions of the winding portions 71a, 71b wound on the other side. For this reason, the magnetization directions of the main pole portions 62 adjacent to each other in the circumferential direction are opposite to each other.

[0029] FIG. 4 shows an electric circuit on the rotor 60 side including the winding portions 71a, 71b wound around the common main pole portion 62. The first winding portion 71a shown in FIG. 4 is a series connection body of the first winding portions 71a wound around each main pole portion 62, and the second winding portion 71b shown in FIG. 4 is a series connection body of the second winding portions 71b wound around each main pole portion 62.

[0030] The rotor 60 is provided with a diode 80 as a rectifying element and a capacitor 81. The diode 80 is electrically connected in parallel to the series connection of the first winding portion 71a and the second winding portion 71b. Specifically, the first end of the first winding portion 71a is connected to the cathode of the diode 80, and the first end of the second winding portion 71b is connected to the second end of the first winding portion 71a. The anode of the diode 80 is connected to the second end of the second winding portion 71b. A capacitor 81 is electrically connected in parallel to the second winding portion 71b. In FIG. 4, L1 represents the inductance of the first winding portion 71a, L2 represents the inductance of the second winding portion 71b, and C represents the capacitance of the capacitor 81.

[0031] In the present embodiment, a series resonance circuit including the first winding portion 71a and the capacitor 81 is configured, and a parallel resonance circuit including the second winding portion 71b and the capacitor 81 is configured. In FIG. 4, f1 represents the first resonance frequency which is the resonance frequency of the series resonance circuit, and f2 represents the second resonance frequency which is the resonance frequency of the parallel resonance circuit.

[0032] Note that the anode of the diode 80 may be connected to the first end of the first winding portion 71a, and the cathode of the diode 80 may be connected to the second end of the second winding portion 71b.

[0033] Returning to the description of FIG. 2, the rotating electrical machine system 90 includes a current sensor 21, an angle sensor 22, and a voltage sensor 23. The current sensor 21 detects at least two-phase currents among the phase currents flowing through the rotating electrical machine 40. The angle sensor 22 detects the rotation angle (electrical angle) of the rotor 60. In the present embodiment, the voltage sensor 23 includes a sensor that detects the voltage of the DC power supply 10 and a sensor that detects the output voltage (phase voltage) of each phase of the inverter 20. The detection values of the respective sensors 21 to 23 are input to the control device 30.

[0034] The control device 30 (control device for a rotating electric machine) is an electronic control unit (Electronic Control Unit) mainly composed of a microcomputer 31. The microcomputer 31 is equipped with a CPU (Central Processing Unit). The functions provided by the microcomputer 31 can be provided by software recorded in a physical memory device and a computer that executes it, software only, hardware only, or a combination thereof. For example, when the microcomputer 31 is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a number of logic circuits or an analog circuit. For example, the microcomputer 31 executes a program stored in a non-transitory tangible storage medium as a storage unit provided therein. The program (control program) includes, for example, programs for the processes shown in FIGS. 5, 7, 8, etc. described later. By executing a set of instructions constituting the program, a method corresponding to the program is executed. The storage unit is, for example, a non-volatile memory. Note that the program stored in the storage unit can be updated via a communication network such as the Internet, for example, OTA (Over The Air).

[0035] The control device 30 generates drive signals for turning on and off each switch SUp to SWn that constitutes the inverter 20. Specifically, the control device 30 generates drive signals for turning on and off each arm switch SUp to SWn so as to convert the DC power output from the DC power source 10 into AC power and supply it to the U, V, W phase windings 52U, 52V, 52W, and supplies the generated drive signals to the gates of each arm switch SUp to SWn. As a result, in each phase, the upper arm switch and the lower arm switch are alternately turned on with a dead time sandwiched therebetween.

[0036] The control device 30 turns on and off each switch SUp to SWn so that a combined current of a fundamental current and a harmonic current (specifically, a harmonic excitation current) higher than the frequency of the fundamental current flows through each phase winding 52U, 52V, and 52W. The fundamental current is mainly a current that generates torque in the rotating electrical machine 40. The harmonic current is mainly a current that excites the field winding 70 to induce a field current in the field winding 70. The phase currents flowing through each phase winding 52U, 52V, and 52W are shifted by 120° in electrical angle from each other.

[0037] Using FIG. 5, torque control of the rotating electrical machine 40 executed by the control device 30 will be described.

[0038] The two-phase conversion unit 100 converts the U, V, and W phase currents in the three-phase fixed coordinate system into a d-axis current Idr and a q-axis current Iqr in the two-phase rotating coordinate system (dq coordinate system) based on the detected value of the current sensor 21 and the electrical angle θe detected by the angle sensor 22.

[0039] The command current calculation unit 101 calculates a d-axis fundamental command current Idbref and a q-axis command current Iqref based on the command torque Tref. The d-axis fundamental command current Idbref and the q-axis command current Iqref are command values of the DC components corresponding to the fundamental current. The command current calculation unit 101 may calculate the d-axis fundamental command current Idbref and the q-axis command current Iqref based on, for example, the map information in which the command torque Tref, the d-axis fundamental command current Idbref, and the q-axis command current Iqref are related, and the input command torque Tref. Note that the command for field weakening control from the field weakening unit 201 to the command current calculation unit 101 will be described later.

[0040] The exciting current calculation unit 102 calculates the d-axis high-frequency command current Idhref. The d-axis high-frequency command current Idhref is a command value of an AC component corresponding to a harmonic current that excites the field winding 70, and is expressed by the following formula (eq1) in the present embodiment. In the following formula (eq1), Idamp is the amplitude of the d-axis high-frequency command current Idhref, and fh is the fluctuation frequency of the d-axis high-frequency command current Idhref. Note that the exciting current calculation unit 102 may calculate the amplitude Idamp of the d-axis high-frequency command current Idhref so that the amplitude of the harmonic current is, for example, 3% or more of the amplitude of the fundamental wave current.

[0041] [Number] The superposition unit 103 calculates the d-axis command current Idref by adding the d-axis high-frequency command current Idhref to the d-axis fundamental command current Idbref.

[0042] The d-axis deviation calculation unit 104 calculates the d-axis current deviation ΔId by subtracting the d-axis current Idr from the d-axis command current Idref. The q-axis deviation calculation unit 105 calculates the q-axis current deviation ΔIq by subtracting the q-axis current Iqr from the q-axis command current Iqref.

[0043] The d-axis current control unit 106 calculates the d-axis voltage command value Vdref as an operation amount for feedback control of the d-axis current Idr to the d-axis command current Idref based on the d-axis current deviation ΔId. The q-axis current control unit 107 calculates the q-axis voltage command value Vqref as an operation amount for feedback control of the q-axis current Iqr to the q-axis command current Iqref based on the q-axis current deviation ΔIq. Note that in the present embodiment, the feedback control of each current control unit 106, 107 is proportional-integral control.

[0044] The three-phase conversion unit 108 converts the d-axis and q-axis voltage command values Vdref and Vqref in the two-phase rotating coordinate system into the U-phase, V-phase, and W-phase voltage command values VUref, VVref, and VWref in the three-phase fixed coordinate system based on the d-axis and q-axis voltage command values Vdref and Vqref and the electrical angle θe. The U-phase, V-phase, and W-phase voltage command values VUref, VVref, and VWref have waveforms that are shifted by 120 degrees in phase at the electrical angle. The frequencies of the harmonic components included in the U-phase, V-phase, and W-phase voltage command values VUref, VVref, and VWref are set to frequencies near the first resonance frequency f1. Note that the U-phase, V-phase, and W-phase voltage command values VUref, VVref, and VWref are the combined voltages of the fundamental wave voltage corresponding to the fundamental wave current and the harmonic voltage corresponding to the harmonic current.

[0045] Based on the U-phase, V-phase, and W-phase voltage command values VUref, VVref, and VWref, the signal generation unit 109 generates drive signals GUH to GWL for the upper and lower arm switches SUp to SWn in the U-phase, V-phase, and W-phase to cause the combined current to flow through the stator winding 52. The generated drive signals GUH to GWL are input to the gates of the respective switches. Thereby, the switching control of the inverter 20 is executed. Note that in the present embodiment, the signal generation unit 109 corresponds to the "switch control unit".

[0046] When the switching control of the inverter 20 is performed, a combined current in which a harmonic current (see the solid line in FIG. 6(b)) is superimposed on the fundamental wave current (see FIG. 6(a)) flows through each phase winding 52U, 52V, and 52W. The harmonic current flowing through the stator winding 52 causes a field current to flow through the field winding 70. Here, FIG. 6(a) shows the transition of the fundamental wave current in one electrical angle cycle. The dashed-dotted line in FIG. 6(b) shows the envelope of the harmonic current. The envelope of the harmonic current has the same period as the fundamental wave current. The phase of the harmonic current with respect to the fundamental wave current is the phase at which the field current can flow through the field winding 70 with the highest efficiency by the harmonic current (the phase at which the field current becomes maximum when compared with high-frequency currents of the same magnitude). The values on the vertical axis shown in FIG. 6 indicate the relative relationship of the magnitudes of the waves shown in FIGS. 6(a) and 6(b).

[0047] As shown in FIG. 7, the operating region of the rotating electrical machine 40 is represented by the commanded torque Tref and the electrical angular velocity ωe of the rotor 60 (or the rotational speed of the rotor 60). The operating region is divided into a sine wave PWM control region, an overmodulation control region, or a rectangular wave control region. The overmodulation control region is a region adjacent to the high-speed side of the sine wave PWM control region.

[0048] When the control device 30 determines that the electrical angular velocity ωe calculated based on the electrical angle θe is less than the first speed threshold ωth1, the control device 30 performs sine wave PWM control. The sine wave PWM control is switching control of the upper and lower arm switches for making each phase voltage applied to the stator winding 52 into a PWM voltage waveform when the peak value of each phase voltage applied to the stator winding 52 is equal to or less than the terminal voltage of the DC power supply 10. The first speed threshold ωth1 decreases as the commanded torque Tref increases.

[0049] When the control device 30 determines that the electrical angular velocity ωe is equal to or greater than the first speed threshold ωth1 and less than the second speed threshold ωth2, the control device 30 performs overmodulation control. The overmodulation control is switching control of the upper and lower arm switches for making each phase voltage applied to the stator winding 52 into a PWM voltage waveform with a higher modulation ratio than the PWM voltage waveform by the sine wave PWM control when the peak value of each phase voltage applied to the stator winding 52 exceeds the terminal voltage of the DC power supply 10. The second speed threshold ωth2 decreases as the commanded torque Tref increases.

[0050] Note that the control device 30 may determine whether the current operating point is in the overmodulation control region or the rectangular wave control region based on the magnitude of the output voltage vector of the inverter 20 instead of the determination using the first speed threshold ωth1 and the second speed threshold ωth2 as described above.

[0051] When the control device 30 determines that the operating point is in the overmodulation control region or the rectangular wave control region (when the rotational speed of the rotor 60 of the rotating electrical machine 40 is higher than a predetermined rotational speed), the control device 30 performs field reduction control to reduce the field voltage component, which is a component for flowing a field current through the field winding 70. The field reduction control is control for reducing the magnetic flux generated by the field winding 70 of the rotor 60 to be less than the current magnetic flux. Hereinafter, the field reduction control will be described using the block diagram of the field current calculation unit 102 shown in FIG. 8.

[0052] The field current calculation unit 102 functions as a "field reduction unit" and includes a voltage amplitude calculation unit 110, a voltage deviation calculation unit 111, and a feedback control unit 112. The voltage amplitude calculation unit 110 calculates a voltage amplitude Vom, which is the magnitude of the output voltage vector of the inverter 20 in the two-phase rotating coordinate system, based on the d-axis voltage command value Vdref calculated by the d-axis current control unit 106 and the q-axis voltage command value Vqref calculated by the q-axis current control unit 107. Specifically, the voltage amplitude calculation unit 110 calculates the voltage amplitude Vom based on the following equation (eq2).

[0053]

Equation

[0054] The feedback control unit 112 calculates a deviation amount Xh, which is an operation amount for feedback controlling the calculated voltage deviation ΔV to zero. In the present embodiment, the feedback control used by the feedback control unit 112 is proportional-integral control.

[0055] The exciting current calculation unit 102 includes an exciting parameter calculation unit 113. Based on the calculated deviation amount Xh, the exciting parameter calculation unit 113 calculates the amplitude Idamp and the fluctuation frequency fh of the d-axis high-frequency command current Idhref. By decreasing the amplitude Idamp or decreasing the fluctuation frequency fh, the exciting voltage component of the field winding 70 among the voltage components included in the above synthetic voltage is decreased. As a result, the magnetic flux generated by the rotor 60 is decreased and the exciting decrease control is performed. Hereinafter, the reason why the exciting voltage component can be decreased by decreasing the amplitude Idamp or decreasing the fluctuation frequency fh will be described.

[0056] The voltage equations of the motor in the two-phase rotating coordinate system are shown in the following equations (eq3) and (eq4). In the following equations (eq3) and (eq4), R is the resistance value of the stator winding 52, Ld and Lq are the d-axis and q-axis inductances, and φ is the effective value of the magnetic flux linkage of the stator winding 52.

[0057]

Equation

[0058]

Equation

[0059]

Equation

[0060]

Equation

[0061] First, regarding the calculation method of the fluctuation frequency fh, when the deviation amount Xh is 0 or less, the excitation parameter calculation unit 113 sets the fluctuation frequency fh to the first frequency fa. When the deviation amount Xh is greater than 0 and less than the first threshold value Xth1, the excitation parameter calculation unit 113 sets the fluctuation frequency fh to a frequency that is less than the first frequency fa and higher than the second frequency fb (<fa), and the higher the deviation amount Xh is, the lower the frequency is. When the deviation amount Xh is greater than or equal to the first threshold value Xth1, the excitation parameter calculation unit 113 sets the fluctuation frequency fh to the second frequency fb. That is, when the deviation amount Xh increases, the excitation parameter calculation unit 113 decreases the fluctuation frequency fh of the d-axis high-frequency command current Idhref from the current fluctuation frequency fh.

[0062] Subsequently, regarding the calculation method of the amplitude Idamp, when the deviation amount Xh is less than or equal to the first threshold value Xth1, the excitation parameter calculation unit 113 sets the amplitude Idamp to the first amplitude Ia. When the deviation amount Xh is greater than the first threshold value Xth1 and less than the second threshold value Xth2 (>Xth1), the excitation parameter calculation unit 113 sets the amplitude Idamp to an amplitude that is less than the first amplitude Ia and greater than the second amplitude Ib (<Ia), and the higher the deviation amount Xh is, the smaller the amplitude is. When the deviation amount Xh is greater than or equal to the second threshold value Xth2, the excitation parameter calculation unit 113 sets the amplitude Idamp to the second amplitude Ib. That is, when the deviation amount Xh increases, the excitation parameter calculation unit 113 decreases the amplitude Idamp of the d-axis high-frequency command current Idhref from the current amplitude Idamp.

[0063] When the amplitude Idamp is decreased, the torque reduction of the rotating electrical machine 40 increases. Therefore, in the present embodiment, the deviation amount Xh at which the fluctuation frequency fh starts to decrease is set to be smaller than the deviation amount Xh at which the amplitude Idamp starts to decrease. As a result, prior to the reduction process of the amplitude Idamp, the magnetic flux of the rotor 60 is reduced by the reduction process of the fluctuation frequency fh. Consequently, it is possible to reduce the field current while suppressing torque reduction.

[0064] Particularly in the present embodiment, when the deviation amount Xh exceeds the first threshold value Xth1 which is the deviation amount Xh at which the reduction of the fluctuation frequency fh is completed, the amplitude Idamp starts to decrease. That is, when the deviation amount Xh does not become 0 or less even by the reduction process of the fluctuation frequency fh, the reduction process of the amplitude Idamp is started. Thereby, it is possible to reduce the field current while preferably suppressing torque reduction.

[0065] In this way, in the field current calculation unit 102, the d-axis high-frequency command current Idhref is adjusted, and as a result, the field voltage component is decreased (adjusted).

[0066] Fig. 9 shows a flowchart of the field reduction control process executed by the control device 30. This process is repeatedly executed, for example, at a predetermined control cycle.

[0067] In step S10, the voltage amplitude calculation unit 110 calculates a voltage amplitude Vom based on the d-axis and q-axis voltage command values Vdref and Vqref.

[0068] In step S11, the voltage deviation calculation unit 111 calculates a voltage deviation ΔV based on the calculated voltage amplitude Vom.

[0069] In step S12, the feedback control unit 112 calculates a deviation amount Xh based on the calculated voltage deviation ΔV.

[0070] In step S13, based on the calculated deviation amount Xh, the excitation parameter calculation unit 113 calculates the fluctuation frequency fh and amplitude Idamp of the d-axis high-frequency command current Idhref.

[0071] In step S14, the d-axis high-frequency command current Idhref determined from the calculated fluctuation frequency fh and amplitude Idamp is calculated, and the calculated d-axis high-frequency command current Idhref is output to the superposition unit 103. Then, this series of processes is temporarily terminated.

[0072] Also, as shown in FIG. 5, the control device 30 includes a field weakening unit 201. When the voltage amplitude Vom is greater than the limit value Vlim (or when the rotational speed of the rotor 60 is higher than a predetermined rotational speed), the field weakening unit 201 executes field weakening control to cause the stator winding 52 to generate a magnetic flux opposite to the magnetic flux generated by the field winding 70 by flowing a negative d-axis current through the stator winding 52. Specifically, the field weakening unit 201 transmits a command for field weakening control to the command current calculation unit 101, and causes the command current calculation unit 101 to calculate the d-axis basic command current Idbref so that a negative d-axis current flows through the stator winding 52. Thereby, the phase of the fundamental wave current flowing through the stator winding 52 due to the fundamental wave voltage is adjusted, and the stator winding 52 generates a magnetic flux opposite to the magnetic flux generated by the field winding 70. The predetermined rotational speed is the rotational speed at which the voltage amplitude Vom becomes greater than the limit value Vlim, and can be obtained in advance based on experiments or the like.

[0073] The control device 30 includes a control change unit 209. The control change unit 209 changes the execution of the field current reduction control by the field current calculation unit 102 and the field weakening control by the field weakening unit 201 according to the operating region of the rotating electrical machine 40 so that the output voltage of the inverter 20 is suppressed. In the present embodiment, the control change unit 209 causes only one of the field current reduction control by the field current calculation unit 102 and the field weakening control by the field weakening unit 201 to be executed.

[0074] FIG. 10 is a diagram showing the voltage difference between the voltage during field-weakening control and the voltage during field-decreasing control. The voltage difference is the voltage difference obtained by subtracting the output voltage (voltage amplitude Vom) of the inverter 20 during field-weakening control from the output voltage (voltage amplitude Vom) of the inverter 20 during field-decreasing control when the rotating electrical machine 40 outputs the same torque at the same rotational speed during field-decreasing control and field-weakening control. The voltage difference between the output voltage during field-decreasing control and the output voltage during field-weakening control is calculated using only the DC component (fundamental wave voltage) of the output voltage. Note that the magnitude of the voltage difference changes slightly depending on the rotational speed of the rotating electrical machine 40, but the influence of the rotational speed is small.

[0075] In the rotating electrical machine 40 of the present embodiment, in the high torque region (high load region), the output voltage during field-weakening control is lower than the output voltage during field-decreasing control, and the voltage difference is a positive value. That is, in the high torque region, when the rotating electrical machine 40 outputs the same torque during field-decreasing control and field-weakening control, it is advantageous that the output voltage can be made lower by executing field-weakening control. On the other hand, in the low torque region (low load region), when the rotating electrical machine 40 outputs the same torque during field-decreasing control and field-weakening control, if the output voltage (fundamental wave voltage) is greater than a predetermined value (threshold value), the output voltage during field-weakening control is lower than the output voltage during field-decreasing control, and if the output voltage is less than the predetermined value, the output voltage during field-decreasing control is lower than the output voltage during field-weakening control. Generally, in the low torque region, the output voltage is often less than the predetermined value. Therefore, when the rotating electrical machine 40 outputs the same torque during field-decreasing control and field-weakening control, it can be said that the output voltage during field-decreasing control is lower than the output voltage during field-weakening control. For this reason, in the low torque region, when the rotating electrical machine 40 outputs the same torque during field-decreasing control and field-weakening control, it can be said that it is advantageous that the output voltage can be made lower by executing field-decreasing control.

[0076] Therefore, when suppressing the output voltage of the inverter 20, the control change unit 209 causes the field weakening unit 201 to execute field weakening control in the high load region of the rotating electrical machine 40 without causing the field current calculation unit 102 to execute field weakening control. When the field current calculation unit 102 does not execute the field weakening control, it keeps the amplitude Idamp, the fluctuation frequency fh, and the phase of the d-axis high-frequency command current Idhref constant. Specifically, as shown in FIG. 8, when the deviation amount Xh is 0 or less, the fluctuation frequency fh of the d-axis high-frequency command current Idhref is set to the first frequency fa, the amplitude Idamp is set to the first amplitude Ia, and the phase is set to the reference phase. Also, when suppressing the output voltage of the inverter 20, the control change unit 209 causes the field current calculation unit 102 to execute field weakening control without causing the field weakening unit 201 to execute field weakening control in the low load region of the rotating electrical machine 40.

[0077] The present embodiment described in detail above has the following advantages.

[0078] · The rotating electrical machine 40 is configured such that a voltage is induced in the field winding 70 and a field current flows when a high-frequency voltage is applied to the stator winding 52. In addition to the fundamental wave voltage for the purpose of generating torque in the rotating electrical machine 40, the signal generation unit 109 performs switching control of the inverter 20 so that a high-frequency voltage having a higher frequency than the fundamental wave voltage flows through the stator winding 52. As a result, an inverter (power converter) for flowing a field current through the field winding 70 other than the inverter 20 becomes unnecessary, and the rotating electrical machine system 90 can be simplified.

[0079] · The exciting current calculation unit 102 performs exciting reduction control to reduce the exciting voltage component, which is the component for flowing the exciting current through the field winding 70 among the voltage components included in the synthesized voltage, compared to the present. For this reason, when it is necessary to suppress the output voltage of the inverter 20, the exciting current calculation unit 102 can suppress the output voltage of the inverter 20 by executing the exciting reduction control. Further, the field weakening unit 201 performs field weakening control to adjust the phase of the fundamental wave current flowing through the stator winding 52 so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding 70. For this reason, when it is necessary to suppress the output voltage of the inverter 20, the field weakening unit 201 can suppress the output voltage of the inverter 20 by executing the field weakening control.

[0080] · In the high torque region (high load region) of the rotating electrical machine 40, when the rotating electrical machine 40 outputs the same torque by the exciting reduction control and the field weakening control, the output voltage of the inverter 20 during the field weakening control becomes lower than the output voltage of the inverter 20 during the exciting reduction control. Then, according to the operating region of the rotating electrical machine 40 so that the output voltage of the inverter 20 is suppressed, the control change unit 209 changes the execution presence or absence of the exciting reduction control by the exciting current calculation unit 102 and the field weakening control by the field weakening unit 201. Therefore, the exciting reduction control and the field weakening control can be properly used according to the operating region of the rotating electrical machine 40, and the output voltage of the inverter 20 can be suppressed.

[0081] · The rotating electrical machine 40 has a characteristic that when the rotating electrical machine 40 outputs the same torque by the exciting reduction control and the field weakening control in the high torque region, the output voltage of the inverter 20 during the field weakening control becomes lower than the output voltage of the inverter 20 during the exciting reduction control. Therefore, when suppressing the output voltage of the inverter 20, the control change unit 209 does not execute the exciting reduction control by the exciting current calculation unit 102 in the high torque region of the rotating electrical machine 40, and executes the field weakening control by the field weakening unit 201. Therefore, according to the characteristics of the rotating electrical machine 40, the field weakening control that can make the output voltage of the inverter 20 lower in the high torque region can be executed, and the output voltage of the inverter 20 can be suppressed.

[0082] · In the low torque region, when the rotating electrical machine 40 outputs the same torque under field weakening control and field reduction control, it can be said that the output voltage of the inverter 20 during field reduction control is lower than the output voltage of the inverter 20 during field weakening control. Therefore, when suppressing the output voltage of the inverter 20, the control change unit 209 causes the field reduction control by the field current calculation unit 102 to be executed without executing the field weakening control by the field weakening unit 201 in the low torque region of the rotating electrical machine 40. Therefore, in accordance with the characteristics of the rotating electrical machine 40, it is possible to execute field reduction control that can make the output voltage of the inverter 20 lower in the low torque region, and the output voltage of the inverter 20 can be suppressed.

[0083] · The field voltage component of the synthesized voltage increases as the amplitude Idamp of the d-axis high-frequency current flowing through the stator winding 52 increases. Therefore, the field current calculation unit 102 reduces the field voltage component by reducing the amplitude Idamp of the d-axis high-frequency current flowing through the stator winding 52 in the field reduction control compared to the present. According to such a configuration, the field voltage component can be reduced by utilizing the relationship between the amplitude Idamp of the d-axis high-frequency current flowing through the stator winding 52 and the field voltage component.

[0084] · The field voltage component of the synthesized voltage increases as the fluctuation frequency fh of the d-axis high-frequency current flowing through the stator winding 52 increases. Therefore, the field current calculation unit 102 reduces the field voltage component by reducing the fluctuation frequency fh of the d-axis high-frequency current flowing through the stator winding 52 in the field reduction control compared to the present. According to such a configuration, compared with the case where the field voltage component is reduced by reducing the amplitude Idamp of the d-axis high-frequency current flowing through the stator winding 52 compared to the present, it is possible to suppress the output voltage of the inverter 20 while suppressing a decrease in the output torque of the rotating electrical machine 40.

[0085] · When the field current reduction control is not executed, the excitation current calculation unit 102 keeps the amplitude Idamp, the fluctuation frequency fh, and the phase of the d-axis high-frequency current flowing through the stator winding 52 constant. According to such a configuration, when the field current reduction control is not executed, the field voltage component can be kept constant.

[0086] · When the output voltage of the inverter 20 is higher than the limit value Vlim, the control change unit 209 changes the execution presence or absence of the field current reduction control by the field current calculation unit 102 and the field weakening control by the field weakening unit 201 according to the operating region of the rotating electrical machine 40 so that the output voltage of the inverter 20 is suppressed. According to such a configuration, it is possible to suppress the output voltage of the inverter 20 from becoming higher than the limit value Vlim.

[0087] · Alternatively, when the rotational speed of the rotating electrical machine 40 is higher than a predetermined rotational speed, the control change unit 209 changes the execution presence or absence of the field current reduction control by the field current calculation unit 102 and the field weakening control by the field weakening unit 201 according to the operating region of the rotating electrical machine 40 so that the output voltage of the inverter 20 is suppressed. According to such a configuration, when the rotational speed of the rotating electrical machine 40 is higher than a predetermined rotational speed, the output voltage of the inverter 20 can be suppressed, and the rotational speed of the rotating electrical machine 40 can be increased above the predetermined rotational speed.

[0088] · The field current reduction control for reducing the magnetic flux of the rotor 60 in the high-speed region is performed by the control device 30 that performs torque control of the rotating electrical machine 40. Therefore, the field current reduction control and the torque control can be realized by the switching control of the common inverter 20. This also contributes to the simplification of the rotating electrical machine system 90. Further, since the field voltage component is reduced by the switching control of the inverter 20, the output voltage of the inverter 20 can be quickly reduced.

[0089] <Modification Example of the First Embodiment> · Among the fluctuation frequency fh and the amplitude Idamp, the excitation parameter calculation unit 113 may make only the fluctuation frequency fh variable based on the deviation amount Xh.

[0090] · The excitation parameter calculation unit 113 may make only the amplitude Idamp variable based on the deviation amount Xh among the variable frequency fh and the amplitude Idamp. In this case, the excitation parameter calculation unit 113 may start to decrease the amplitude Idamp when the deviation amount Xh exceeds 0, in the same manner as the decrease mode of the variable frequency fh.

[0091] <Second Embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, centering on the differences from the first embodiment. In this embodiment, for the calculation of the voltage amplitude Vom, the U, V, W phase voltages VUr, VVr, VWr detected by the voltage sensor 23 are used instead of the d, q axis voltage command values Vdref, Vqref.

[0092] FIG. 11 is a block diagram of the excitation current calculation unit 102.

[0093] In the excitation current calculation unit 102, the voltage calculation unit 114 calculates the d, q axis voltages Vdr, Vqr based on the U, V, W phase voltages VUr, VVr, VWr detected by the voltage sensor 23 and the electrical angle θe. Specifically, the voltage calculation unit 114 calculates the d, q axis voltages Vdr, Vqr based on the following equations (eq7), (eq8).

[0094]

Equation

[0095]

Equation

[0096]

Equation

[0097] <Third Embodiment> Hereinafter, the third embodiment will be described with reference to the drawings, centering on the differences from the first embodiment. In the present embodiment, a method of reducing the excitation voltage component of the field winding 70 by increasing the d-axis current flowing through the stator winding 52 is used. The reason why this method can be used will be described.

[0098] When the d-axis current is increased, the d-axis inductance Ld decreases due to the influence of magnetic saturation. In the term enclosed by the square brackets on the right side of the above equation (eq5), the smaller the d-axis inductance Ld, the smaller the excitation voltage component. Therefore, by increasing the d-axis current, the excitation voltage component of the field winding 70 can be decreased.

[0099] FIG. 12 shows a block diagram of torque control processing executed by the control device 30.

[0100] The d-axis command calculation unit 125 calculates a d-axis basic command current Idbref based on the command torque Tref. The d-axis command calculation unit 125 may calculate the d-axis basic command current Idbref based on, for example, map information in which the command torque Tref and the d-axis basic command current Idbref are associated and the input command torque Tref.

[0101] The inductance reduction current calculation unit 130 functions as an "excitation reduction unit" and calculates an inductance reduction current IdL, which is a d-axis current superimposed on the d-axis basic command current Idbref, based on the calculated d-axis and q-axis voltage command values Vdref and Vqref. The inductance reduction current IdL is a value of a direct current component.

[0102] The first adder 122 calculates the added value of the d-axis basic command current Idbref and the inductance reduction current IdL.

[0103] The second adder 123 calculates the d-axis command current Idref by adding the d-axis high-frequency command current Idhref calculated by the excitation current calculation unit 102 to the added value calculated by the first adder 122. The calculated d-axis command current Idref is input to the d-axis deviation calculation unit 104.

[0104] The q-axis command calculation unit 124 calculates the q-axis command current Iqref based on the command torque Tref and the added value "Idbref + IdL" calculated by the first adder 122. The reason why the above added value is used in the calculation of the q-axis command current Iqref is that an appropriate q-axis current corresponding to the command torque Tref changes according to the magnitude of the inductance reduction current IdL. The q-axis command calculation unit 124 may calculate the q-axis command current Iqref based on, for example, the map information in which the command torque Tref, the above added value, and the q-axis command current Iqref are related, and the input command torque Tref and the above added value. The calculated q-axis command current Iqref is input to the q-axis deviation calculation unit 105.

[0105] Subsequently, with reference to FIG. 13, the processing of the inductance reduction current calculation unit 130 will be described.

[0106] The inductance reduction current calculation unit 130 includes a voltage amplitude calculation unit 131, a voltage deviation calculation unit 132, and a feedback control unit 133. Similar to the voltage amplitude calculation unit 110 in FIG. 8 above, the voltage amplitude calculation unit 131 calculates the voltage amplitude Vom based on the d-axis and q-axis voltage command values Vdref and Vqref.

[0107] The voltage deviation calculation unit 132 calculates the voltage deviation ΔV by subtracting the limit value Vlim from the calculated voltage amplitude Vom.

[0108] The feedback control unit 133 calculates a deviation amount Xh, which is an operation amount for feedback - controlling the calculated voltage deviation ΔV to 0. In the present embodiment, the feedback control used by the feedback control unit 133 is proportional - integral control.

[0109] The inductance - decreasing current calculation unit 130 includes a current value calculation unit 134. The current value calculation unit 134 calculates an inductance - decreasing current IdL based on the calculated deviation amount Xh. Specifically, when the deviation amount Xh is 0 or less, the inductance - decreasing current calculation unit 130 sets the inductance - decreasing current IdL to 0.

[0110] When the deviation amount Xh is greater than 0 and less than the threshold value Xth, the current value calculation unit 134 sets the inductance - decreasing current IdL to a value greater than 0 and less than a predetermined current IK (>0), and the greater the deviation amount Xh, the greater the value. When the deviation amount Xh is greater than or equal to the threshold value Xth, the current value calculation unit 134 sets the inductance - decreasing current IdL to the predetermined current IK. In this way, in the inductance - decreasing current calculation unit 130, the inductance - decreasing current IdL is increased (adjusted), and as a result, the excitation voltage component is decreased (adjusted). That is, when the deviation amount Xh increases, the inductance - decreasing current calculation unit 130 decreases the d - axis inductance Ld from the current d - axis inductance Ld.

[0111] FIG. 14 shows a flowchart of the excitation - decreasing control process executed by the control device 30. This process is repeatedly executed, for example, at a predetermined control cycle.

[0112] In step S30, the voltage amplitude calculation unit 131 calculates a voltage amplitude Vom based on the d - axis and q - axis voltage command values Vdref and Vqref.

[0113] In step S31, the voltage deviation calculation unit 132 calculates a voltage deviation ΔV based on the calculated voltage amplitude Vom.

[0114] In step S32, the feedback control unit 133 calculates a deviation amount Xh based on the calculated voltage deviation ΔV.

[0115] In step S33, the current value calculation unit 134 calculates an inductance decrease current IdL based on the calculated deviation amount Xh.

[0116] In step S34, the calculated inductance decrease current IdL is output to the first adder 122. Then, this series of processes is temporarily terminated.

[0117] In the present embodiment, when suppressing the output voltage of the inverter 20, the control change unit 209 causes the excitation decrease control by the inductance decrease current calculation unit 130 to be executed instead of the excitation decrease control by the excitation current calculation unit 102. That is, when suppressing the output voltage of the inverter 20, in the high load region of the rotating electrical machine 40, the control change unit 209 does not execute the excitation decrease control by the inductance decrease current calculation unit 130, but executes the field weakening control by the field weakening unit 201. When the inductance decrease current calculation unit 130 does not execute the excitation decrease control, the inductance decrease current IdL is made constant. Specifically, as shown in FIG. 13, when the deviation amount Xh is 0 or less, the inductance decrease current IdL is set to 0. Further, when suppressing the output voltage of the inverter 20, in the low load region of the rotating electrical machine 40, the control change unit 209 does not execute the field weakening control by the field weakening unit 201, but executes the excitation decrease control by the inductance decrease current calculation unit 130.

[0118] The excitation voltage component increases as the d-axis inductance Ld of the field winding 70 becomes larger. Therefore, in the excitation decrease control, the inductance decrease current calculation unit 130 increases the d-axis current flowing through the stator winding 52 more than the current value at present, and decreases the d-axis inductance Ld of the field winding 70 more than the current value at present due to magnetic saturation, thereby decreasing the excitation voltage component. According to such a configuration, the excitation voltage component can be decreased by utilizing magnetic saturation.

[0119] Incidentally, each of the above embodiments can also be implemented with the following modifications. For parts identical to those of the above embodiments, the description is incorporated by attaching the same reference numerals.

[0120] · As shown in FIG. 15, when the rotating electrical machine 40 outputs the same torque at the same rotational speed by field weakening control and field reduction control from the low torque region to the high torque region, the output voltage of the inverter 20 during field weakening control may be lower than the output voltage of the inverter 20 during field reduction control. In this case, when suppressing the output voltage of the inverter 20, the control change unit 209 does not execute the field reduction control by the field current calculation unit 102 (or the inductance reduction current calculation unit 130) in the low torque region of the rotating electrical machine 40, but executes the field weakening control by the field weakening unit 201. Therefore, in accordance with the characteristics of the rotating electrical machine 40, field weakening control that can make the output voltage of the inverter 20 lower in the low torque region can be executed, and the output voltage of the inverter 20 can be suppressed.

[0121] · As shown in FIG. 16, before reducing the excitation voltage component, the phase of the harmonic current determined from the amplitudes of the d-axis component and q-axis component of the harmonic current with respect to the phase of the fundamental wave current is the phase at which the harmonic current can flow the field current through the field winding 70 with the highest efficiency (the phase at which the field current becomes maximum when compared with high-frequency currents of the same magnitude). Therefore, by changing the phase of the harmonic current with respect to the fundamental wave current, the field current can be reduced. That is, the magnitude of the excitation voltage component changes according to the phase of the high-frequency current that flows through the stator winding 52 and causes the field current to flow through the field winding 70. Therefore, the field current calculation unit 102 reduces the excitation voltage component by adjusting the phase of the high-frequency current in the field reduction control. According to such a configuration, the excitation voltage component can be reduced by utilizing the relationship between the phase of the high-frequency current that causes the field current to flow through the field winding 70 and the excitation voltage component.

[0122] · As shown in Fig. 17, the output voltage vector of the inverter 20 includes a fundamental voltage and an excitation voltage required for excitation. The output voltage vector is limited by a limit value Vlim. The magnitude of the excitation voltage in the d-axis direction is larger than that in the q-axis direction of the excitation voltage. Therefore, when the output voltage vector is limited by the limit value Vlim, the closer the phase of the output voltage vector is to the d-axis, the larger the excitation voltage becomes. Thus, as shown by the dashed line in Fig. 5, the phase calculation unit 202 (excitation reduction unit) may reduce the excitation voltage component by making the phase of the output voltage vector of the inverter 20 closer to the q-axis than it is currently in the excitation reduction control. According to such a configuration, the excitation voltage component can be reduced by utilizing the relationship between the phase of the output voltage vector of the inverter 20 and the excitation voltage.

[0123] · In the low torque region of the rotating electrical machine 40 of the first to third embodiments, when the rotating electrical machine 40 outputs the same torque under the excitation reduction control and the field weakening control, if the fundamental wave current is larger than the threshold value, the output voltage of the inverter 20 during the field weakening control is lower than the output voltage of the inverter 20 during the excitation reduction control, and if the fundamental wave current is smaller than the threshold value, the output voltage of the inverter 20 during the excitation reduction control is lower than the output voltage of the inverter 20 during the field weakening control. Therefore, when suppressing the output voltage of the inverter 20, the control change unit 209 may execute the excitation reduction control by the excitation current calculation unit 102 and the field weakening control by the field weakening unit 201 in the low torque region of the rotating electrical machine 40. According to such a configuration, even when the control for making the output voltage of the inverter 20 lower changes according to the magnitude of the fundamental wave current, the output voltage of the inverter 20 can be stably suppressed. Note that the control change unit 209 may execute the excitation reduction control by the inductance reduction current calculation unit 130 instead of the excitation reduction control by the excitation current calculation unit 102.

[0124] · The high-frequency current (specifically, the high-frequency excitation current) flowing through the stator winding 52 is not limited to the harmonic current whose fluctuation frequency is N times (N is an integer of 2 or more) the frequency of the fundamental wave current, and may be one whose fluctuation frequency deviates from N times the frequency of the fundamental wave current.

[0125] · The second winding portion 71b may be arranged closer to the stator 50 than the first winding portion 71a in the radial direction.

[0126] · The capacitor 81 that constitutes the resonance circuit of the rotor 60 may be electrically connected in parallel to the first winding portion 71a instead of the second winding portion 71b.

[0127] · In the resonance circuit of the rotor 60, the capacitor 81 may not be provided.

[0128] · The rotating electrical machine is not limited to an inner rotor type rotating electrical machine, and may be an outer rotor type rotating electrical machine. In this case, the main pole portion protrudes radially inward from the rotor core.

[0129] · The rotating electrical machine is not limited to a star-connected rotating electrical machine, and may be a Δ-connected rotating electrical machine.

[0130] · In the first embodiment, the stator core may be a stator core without teeth.

[0131] · The rotating electrical machine is not limited to a rotating electrical machine used as an in-vehicle main machine, and may be, for example, a rotating electrical machine used as an ISG (Integrated Starter Generator) that is both a motor and a generator.

[0132] · The moving body on which the rotating electrical machine system 90 is mounted is not limited to a vehicle, and may be, for example, an aircraft or a ship. Further, the rotating electrical machine system 90 is not limited to a system mounted on a moving body, and may be a stationary system.

[0133] · The control device 30 and its method described in the present disclosure may be implemented by a dedicated computer configured by a processor and a memory programmed to execute one or more functions (instructions) embodied by a computer program. Alternatively, the control device 30 and its method described in the present disclosure may be implemented by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Or, the control device 30 and its method described in the present disclosure may be implemented by one or more dedicated computers configured by a combination of a processor programmed to execute one or more functions and a memory and a processor configured by one or more hardware logic circuits. Further, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer.

[0134] Note that each of the above embodiments and each modification example can also be executed in combination within a combinable range.

[0135] Hereinafter, characteristic configurations extracted from each of the above-described embodiments and each modification example will be described. [Configuration 1] A rotating electrical machine (40) having a stator (50) including a stator winding (52) and a rotor (60) including a field winding (70), and An inverter (20) electrically connected to the stator winding, and A control device (30) for a rotating electrical machine applied to a rotating electrical machine system (90) including: The rotating electrical machine is configured such that a voltage is induced in the field winding and a field current flows when a high-frequency voltage is applied to the stator winding, A switch control unit (109) that performs switching control of the inverter so as to apply a combined voltage of the high-frequency voltage and a fundamental wave voltage having a frequency different from that of the high-frequency voltage to the stator winding, An exciting reduction unit (102, 130, 202) that performs exciting reduction control to reduce an exciting voltage component, which is a component for flowing the exciting current through the field winding, among the voltage components included in the synthesized voltage, compared to the present; A field weakening unit (201) that performs field weakening control to adjust the phase of a fundamental wave current flowing through the stator winding by the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding; A control change unit (209) that changes the execution presence or absence of the exciting reduction control by the exciting reduction unit and the field weakening control by the field weakening unit according to the operating region of the rotating electrical machine so that the output voltage of the inverter is suppressed; A control device for a rotating electrical machine, comprising: [Configuration 2] In the high load region of the rotating electrical machine, when the rotating electrical machine outputs the same torque by the exciting reduction control and the field weakening control, the output voltage of the inverter during the field weakening control is lower than the output voltage of the inverter during the exciting reduction control; The control change unit, when suppressing the output voltage of the inverter, does not execute the exciting reduction control by the exciting reduction unit and executes the field weakening control by the field weakening unit in the high load region of the rotating electrical machine. The control device for a rotating electrical machine according to Configuration 1. [Configuration 3] In the low load region of the rotating electrical machine, when the rotating electrical machine outputs the same torque by the exciting reduction control and the field weakening control, the output voltage of the inverter during the exciting reduction control is lower than the output voltage of the inverter during the field weakening control; The control change unit, when suppressing the output voltage of the inverter, does not execute the field weakening control by the field weakening unit and executes the exciting reduction control by the exciting reduction unit in the low load region of the rotating electrical machine. The control device for a rotating electrical machine according to Configuration 1 or 2. [Configuration 4] When the rotating electrical machine outputs the same torque by the field weakening control and the field reduction control from a low load region to a high load region, the output voltage of the inverter during the field weakening control is lower than the output voltage of the inverter during the field reduction control, When suppressing the output voltage of the inverter, the control change unit causes the field weakening unit to execute the field weakening control and does not cause the field reduction unit to execute the field reduction control in a low load region of the rotating electrical machine, for the control device of the rotating electrical machine according to Configuration 1 or 2. [Configuration 5] In a low load region of the rotating electrical machine, when the rotating electrical machine outputs the same torque by the field reduction control and the field weakening control, when the fundamental wave current is greater than a threshold value, the output voltage of the inverter during the field weakening control is lower than the output voltage of the inverter during the field reduction control, and when the fundamental wave current is less than the threshold value, the output voltage of the inverter during the field reduction control is lower than the output voltage of the inverter during the field weakening control, When suppressing the output voltage of the inverter, the control change unit causes the field reduction unit to execute the field reduction control and the field weakening unit to execute the field weakening control in a low load region of the rotating electrical machine, for the control device of the rotating electrical machine according to Configuration 1 or 2. [Configuration 6] The field reduction unit (102) reduces the field voltage component by reducing the amplitude of the d-axis high-frequency current flowing through the stator winding compared to the present in the field reduction control, for the control device of the rotating electrical machine according to any one of Configurations 1 to 5. [Configuration 7] The field reduction unit (102) reduces the field voltage component by reducing the frequency of the d-axis high-frequency current flowing through the stator winding compared to the present in the field reduction control, for the control device of the rotating electrical machine according to any one of Configurations 1 to 5. [Configuration 8] In the above-described field-weakening control, the field-weakening unit (130) increases the d-axis current flowing through the stator winding to decrease the inductance of the field winding due to magnetic saturation, thereby decreasing the field voltage component, and the control device for a rotating electrical machine according to any one of Configurations 1 to 5. [Configuration 9] In the above-described field-weakening control, the field-weakening unit (102) adjusts the phase of the high-frequency current flowing through the stator winding to flow the field current through the field winding so that the d-axis current component of the amplitude of the high-frequency current decreases, thereby decreasing the field voltage component, and the control device for a rotating electrical machine according to any one of Configurations 1 to 5. [Configuration 10] In the above-described field-weakening control, the field-weakening unit (202) decreases the field voltage component by bringing the phase of the output voltage vector of the inverter closer to the q-axis than at present, and the control device for a rotating electrical machine according to any one of Configurations 1 to 5. [Configuration 11] When the field-weakening control is not executed, the field-weakening unit keeps the amplitude, frequency, and phase of the d-axis high-frequency current flowing through the stator winding constant, and the control device for a rotating electrical machine according to Configuration 2 or 4. [Configuration 12] When the output voltage of the inverter is higher than the voltage limit value, the control change unit changes whether to execute the field-weakening control by the field-weakening unit and the field-weakening control by the field-weakening unit according to the operating region of the rotating electrical machine so that the output voltage of the inverter is suppressed, and the control device for a rotating electrical machine according to any one of Configurations 1 to 11. [Configuration 13] When the rotational speed of the rotating electrical machine is higher than a predetermined rotational speed, the control change unit changes whether to execute the field-weakening control by the field-weakening unit and the field-weakening control by the field-weakening unit according to the operating region of the rotating electrical machine so that the output voltage of the inverter is suppressed, and the control device for a rotating electrical machine according to any one of Configurations 1 to 11.

Description of Reference Numerals

[0136] 20... Inverter, 30... Control device, 40... Rotating electrical machine, 50... Stator, 52... Stator winding, 60... Rotor, 70... Field winding, 90... Rotating electrical machine system, 102... Excitation current calculation unit, 130... Inductance reduction current calculation unit, 201... Field weakening unit, 202... Phase calculation unit, 209... Control change unit.

Claims

1. A rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), An inverter (20) electrically connected to the stator winding, A control device (30) for a rotating electric machine, which is applied to a rotating electric machine system (90) comprising: The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. A switch control unit (109) performs switching control of the inverter so as to apply the combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding, An excitation reduction unit (102, 130, 202) performs excitation reduction control to reduce the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the composite voltage, A field weakening unit (201) performs field weakening control by adjusting the phase of the fundamental wave current flowing through the stator winding using the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding, A control modification unit (209) that changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit according to the operating range of the rotating electric machine so as to suppress the output voltage of the inverter, Equipped with, The control modification unit is, During the period when the rotating electric machine is operating in a high-load region, the excitation reduction control by the excitation reduction unit is not performed, and the field weakening control by the field weakening unit is performed. A control device for a rotating electric machine, wherein, during periods when the rotating electric machine operates in a lower load region than the high load region, the field weakening control by the field weakening unit is not performed, and the excitation reduction control by the excitation reduction unit is performed.

2. A rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), An inverter (20) electrically connected to the stator winding, A control device (30) for a rotating electric machine, which is applied to a rotating electric machine system (90) comprising: The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. A switch control unit (109) performs switching control of the inverter so as to apply the combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding, An excitation reduction unit (102, 130, 202) performs excitation reduction control to reduce the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the composite voltage, A field weakening unit (201) performs field weakening control by adjusting the phase of the fundamental wave current flowing through the stator winding using the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding, A control modification unit (209) that changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit according to the operating range of the rotating electric machine so as to suppress the output voltage of the inverter, Equipped with, The excitation reduction unit (202) is a control device for a rotating electric machine that reduces the excitation voltage component in the excitation reduction control by bringing the phase of the output voltage vector of the inverter closer to the q-axis than it is currently.

3. The rotating electric machine has the following characteristics: in a low-load region, when the rotating electric machine outputs the same torque with the excitation reduction control and the field weakening control, the output voltage of the inverter during field weakening control becomes lower than the output voltage of the inverter during excitation reduction control when the fundamental wave current is greater than a threshold, and the output voltage of the inverter during excitation reduction control becomes lower than the output voltage of the inverter during field weakening control when the fundamental wave current is less than a threshold. The control device for a rotating electric machine according to claim 2, wherein the control modification unit causes the excitation reduction unit to perform the excitation reduction control and the field weakening unit to perform the field weakening control in the low-load region of the rotating electric machine when suppressing the output voltage of the inverter.

4. The control device for a rotating electric machine according to claim 1, wherein the excitation reduction unit (102) reduces the excitation voltage component by reducing the amplitude of the d-axis high-frequency current flowing through the stator winding compared to the current value in the excitation reduction control.

5. The control device for a rotating electric machine according to claim 1, wherein the excitation reduction unit (102) reduces the excitation voltage component by lowering the frequency of the d-axis high-frequency current flowing through the stator winding compared to the current frequency in the excitation reduction control.

6. The control device for a rotating electric machine according to claim 1, wherein the excitation reduction unit (130) reduces the excitation voltage component in the excitation reduction control by increasing the d-axis current flowing through the stator winding to reduce the inductance of the field winding to the current level due to magnetic saturation.

7. The control device for a rotating electric machine according to claim 1, wherein the excitation reduction unit (102) reduces the excitation voltage component in the excitation reduction control by adjusting the phase of the high-frequency current that flows through the stator winding and causes the field current to flow through the field winding such that the d-axis current component of the amplitude of the high-frequency current is reduced.

8. The control device for a rotating electric machine according to claim 1, wherein the excitation reduction unit (202) reduces the excitation voltage component in the excitation reduction control by bringing the phase of the output voltage vector of the inverter closer to the q-axis than it is currently.

9. The control device for a rotating electric machine according to claim 1, wherein the excitation reduction unit keeps the amplitude, frequency, and phase of the d-axis high-frequency current flowing through the stator winding constant when the excitation reduction control is not performed.

10. The control device for a rotating electric machine according to claim 1 or 2, wherein the control modification unit changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit according to the operating range of the rotating electric machine, so as to suppress the output voltage of the inverter when the output voltage of the inverter is higher than a voltage limit value.

11. The control device for a rotating electric machine according to claim 1 or 2, wherein the control modification unit changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit according to the operating range of the rotating electric machine, so as to suppress the output voltage of the inverter when the rotational speed of the rotating electric machine is higher than a predetermined rotational speed.

12. A rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), An inverter (20) electrically connected to the stator winding, A control program for a rotating electric machine applied to a rotating electric machine system (90) comprising: The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. A process of controlling the switching of the inverter so as to apply the combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding, A process to reduce the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the composite voltage, is performed to reduce the excitation voltage component from its current value. A process of weakening the field by adjusting the phase of the fundamental wave current flowing through the stator winding using the fundamental wave voltage so as to generate a magnetic flux in the opposite direction to the magnetic flux generated by the field winding, A process to change whether or not to perform the excitation reduction control and the field weakening control according to the operating range of the rotating electric machine so as to suppress the output voltage of the inverter, The computer (30) will execute this, In the process of changing whether or not to perform the excitation reduction control and the field weakening control, During the period when the rotating electric machine is operating in the high-load region, the excitation reduction control is not performed, and the field weakening control is performed. A control program for a rotating electric machine that, during periods when the rotating electric machine is operating in a lower load region than the high load region, does not execute the field weakening control and instead executes the excitation reduction control.

13. A rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), An inverter (20) electrically connected to the stator winding, A control program for a rotating electric machine applied to a rotating electric machine system (90) comprising: The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. A process of controlling the switching of the inverter so as to apply the combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding, A process to reduce the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the composite voltage, is performed to reduce the excitation voltage component from its current value. A process of weakening the field by adjusting the phase of the fundamental wave current flowing through the stator winding using the fundamental wave voltage so as to generate a magnetic flux in the opposite direction to the magnetic flux generated by the field winding, A process to change whether or not to perform the excitation reduction control and the field weakening control according to the operating range of the rotating electric machine so as to suppress the output voltage of the inverter, The computer (30) will execute this, A control program for a rotating electric machine, which reduces the excitation voltage component by bringing the phase of the output voltage vector of the inverter closer to the q-axis than it is currently.

14. A rotating electric machine system (90) comprising a rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), an inverter (20) electrically connected to the stator windings, and a control device (30) for the rotating electric machine, The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. The control device is A switch control unit (109) performs switching control of the inverter so as to apply the combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding, An excitation reduction unit (102, 130, 202) performs excitation reduction control to reduce the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the composite voltage, A field weakening unit (201) performs field weakening control by adjusting the phase of the fundamental wave current flowing through the stator winding using the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding, A control modification unit (209) that changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit according to the operating range of the rotating electric machine so as to suppress the output voltage of the inverter, Equipped with, The control modification unit is, During the period when the rotating electric machine is operating in a high-load region, the excitation reduction control by the excitation reduction unit is not performed, and the field weakening control by the field weakening unit is performed. A rotating electric machine system in which, during periods when the rotating electric machine is operating in a lower load region than the high load region, the field weakening control by the field weakening unit is not performed, and the excitation reduction control by the excitation reduction unit is performed.

15. A rotating electric machine system (90) comprising a rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), an inverter (20) electrically connected to the stator windings, and a control device (30) for the rotating electric machine, The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. The control device is A switch control unit (109) performs switching control of the inverter so as to apply the combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding, An excitation reduction unit (102, 130, 202) performs excitation reduction control to reduce the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the composite voltage, A field weakening unit (201) performs field weakening control by adjusting the phase of the fundamental wave current flowing through the stator winding using the fundamental wave voltage so as to generate a magnetic flux opposite to the magnetic flux generated by the field winding, A control modification unit (209) that changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit according to the operating range of the rotating electric machine so as to suppress the output voltage of the inverter, Equipped with, The excitation reduction unit (202) is a rotating electric machine system that reduces the excitation voltage component in the excitation reduction control by bringing the phase of the output voltage vector of the inverter closer to the q-axis than it is currently.

16. A rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), An inverter (20) electrically connected to the stator winding, The control device (30) for the rotating electric machine, A rotating electric machine applied to a rotating electric machine system (90) comprising, The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. The switch control unit (109) of the control device performs switching control of the inverter, thereby applying a combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding. The excitation reduction control performed by the excitation reduction unit (102, 130, 202) of the control device reduces the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the combined voltage, to a decrease from the current level. The field weakening unit (201) of the control device performs field weakening control, thereby adjusting the phase of the fundamental wave current flowing through the stator winding with the fundamental wave voltage so that a magnetic flux opposite to the magnetic flux generated in the field winding is generated. The control modification unit (209) of the control device changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit, according to the operating range of the rotating electric machine, so that the output voltage of the inverter is suppressed. The control modification unit is, During the period when the rotating electric machine is operating in a high-load region, the excitation reduction control by the excitation reduction unit is not performed, and the field weakening control by the field weakening unit is performed. A rotating electric machine that, during periods when the rotating electric machine operates in a lower load region than the high load region, does not perform field weakening control by the field weakening unit, but instead performs excitation reduction control by the excitation reduction unit.

17. A rotating electric machine (40) having a stator (50) including stator windings (52) and a rotor (60) including field windings (70), An inverter (20) electrically connected to the stator winding, The control device (30) for the rotating electric machine, A rotating electric machine applied to a rotating electric machine system (90) comprising, The aforementioned rotating electric machine is configured such that a high-frequency voltage is applied to the stator winding, which induces a voltage in the field winding and causes a field current to flow. The switch control unit (109) of the control device performs switching control of the inverter, thereby applying a combined voltage of the high-frequency voltage and a fundamental wave voltage of a different frequency to the stator winding. The excitation reduction control performed by the excitation reduction unit (102, 130, 202) of the control device reduces the excitation voltage component, which is the component that causes the field current to flow through the field winding, among the voltage components included in the combined voltage, to a decrease from the current level. The field weakening unit (201) of the control device performs field weakening control, thereby adjusting the phase of the fundamental wave current flowing through the stator winding with the fundamental wave voltage so that a magnetic flux opposite to the magnetic flux generated in the field winding is generated. The control modification unit (209) of the control device changes whether or not to perform the excitation reduction control by the excitation reduction unit and the field weakening control by the field weakening unit, according to the operating range of the rotating electric machine, so that the output voltage of the inverter is suppressed. The excitation reduction unit reduces the excitation voltage component in the excitation reduction control by bringing the phase of the output voltage vector of the inverter closer to the q-axis than it is currently.

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