Control device for ac rotary electrical machine, ac rotary electrical machine drive system, and vehicle

Abstract

A control device (1) for an AC rotary electrical machine (5) controls the AC rotary electrical machine (5) that is driven by AC power supplied from an inverter (20) which has a plurality of switching elements (23). The control device (1) comprises: a carrier frequency change unit (34) that determines a driving carrier frequency (fca); and a PWM control unit (33) that performs an on / off control of the plurality of switching elements (23) on the basis of a carrier signal (CA) which has the driving carrier frequency (fca) determined by the carrier frequency change unit (34). The carrier frequency change unit (34) is provided with a carrier frequency determination unit (341) that determines a plurality of carrier frequencies, and a carrier frequency switching unit (342) that determines the driving carrier frequency (fca) by periodically selecting, as the driving carrier frequency (fca), one carrier frequency from the plurality of carrier frequencies at a preset change period (Tc).

Description

Control device for AC rotating electric machine, AC rotating electric machine drive system and vehicle

[0001] The present disclosure relates to a control device for an AC rotating electric machine, an AC rotating electric machine drive system, and a vehicle.

[0002] A control system for an AC rotating electric machine uses an inverter that converts DC power to AC power and performs drive control using PWM (Pulse Width Modulation) control. The inverter compares a sinusoidal modulation signal with a triangular carrier signal to turn on / off semiconductor switching elements (hereinafter simply referred to as switching elements) to output a desired phase voltage. The on / off operation of the inverter's switching elements generates harmonic voltages in the phase voltage due to the carrier frequency. For example, harmonic voltages with frequencies of fc±fs, fc±2fs, and fc±4fs are generated. Here, the frequency of the sinusoidal phase voltage is fs, and the frequency of the carrier signal is fc. This harmonic voltage generates an electromagnetic excitation force with a frequency of fc±3fs. If the frequency of the electromagnetic excitation force overlaps with the resonant frequency band of the stator of the AC rotating electric machine, vibration and noise increase. To suppress the increase in vibration and noise, Patent Document 1 randomly changes the carrier frequency. When the frequency of the harmonic voltage caused by the carrier frequency is within the resonant frequency band of the stator, the increase in vibration and noise caused by the carrier frequency is reduced by changing the carrier frequency at a shorter period than when it is outside the resonant frequency band of the stator.

[0003] Japanese Patent Application Laid-Open No. 2015-33263

[0004] However, in conventional methods, the cycle for driving at that carrier frequency is determined by the carrier frequency, and a judgment process regarding the carrier frequency change cycle is performed each time the carrier frequency is changed randomly to determine the cycle for driving at that carrier frequency, which has the problem of increasing the control load.

[0005] The present disclosure has been made to solve the above-mentioned problems, and provides a control device for an AC rotating electric machine, an AC rotating electric machine drive system, and a vehicle that suppress an increase in vibration and noise caused by the carrier frequency without increasing the control load.

[0006] A control device for an AC rotating electric machine according to the present disclosure is a control device for controlling an AC rotating electric machine driven by AC power supplied from an inverter having a plurality of switching elements, and includes a carrier frequency changer that determines a drive carrier frequency, and a PWM control unit that controls the on / off of the plurality of switching elements based on a carrier signal having the drive carrier frequency determined by the carrier frequency changer. The carrier frequency changer includes a carrier frequency determination unit that determines a plurality of carrier frequencies, and a carrier frequency switching unit that determines the drive carrier frequency by periodically selecting one carrier frequency from the plurality of carrier frequencies at a predetermined change period.

[0007] The AC rotating electric machine drive system according to the present disclosure includes an inverter that converts DC power into AC power, an AC rotating electric machine driven by power supplied from the inverter, and the above-mentioned control device that controls the AC rotating electric machine.

[0008] A vehicle according to the present disclosure includes a main body having drive wheels, and the AC rotating electric machine drive system that rotates the drive wheels.

[0009] In the control device for an AC rotating electric machine according to the present disclosure, a carrier frequency determination unit determines a plurality of carrier frequencies, and a carrier frequency switching unit periodically selects one of the plurality of carrier frequencies as the drive carrier frequency at a predetermined change period, thereby determining the drive carrier frequency. As a result, harmonic voltages caused by the carrier frequencies can be reduced without increasing the control load, and increases in vibration and noise can be suppressed.

[0010] 9 is a schematic configuration diagram of an AC rotating electric machine drive system. It is a schematic block diagram of a control device for an AC rotating electric machine. It is a hardware configuration diagram of the control device for an AC rotating electric machine. It is a diagram showing the configuration of a frequency changing unit. It is a diagram showing the time waveform of a line voltage and a frequency analysis result when the update period of an AC voltage command value is a half period of the drive carrier frequency. It is a diagram showing the time waveform of a line voltage and a frequency analysis result when the update period of an AC voltage command value is the same period as the drive carrier frequency. It is a diagram showing the frequency of an electromagnetic excitation force when the fundamental frequency of an inverter is changed while the drive carrier frequency is constant. It is a diagram showing an example of setting a conventional drive carrier frequency. It is a diagram showing vibration measurement results when an AC rotating electric machine is driven at the drive carrier frequency of FIG. 8. It is a diagram showing time change of a drive carrier frequency determined by the control device for an AC rotating electric machine of the present disclosure. It is a diagram showing the time waveform of a drive carrier frequency and a frequency analysis result of a line voltage when an AC rotating electric machine is driven at a drive carrier frequency determined by a method according to the present disclosure. It is a diagram showing the time waveform of a drive carrier frequency and a frequency analysis result of a line voltage when an AC rotating electric machine is driven at a constant drive carrier frequency. 1 is a diagram showing an example of setting a plurality of carrier frequencies when a modulation rate is changed, and FIG. 2 is a diagram showing an example of setting a plurality of carrier frequencies when a modulation rate is changed, and FIG. 3 is a diagram showing an example of setting a plurality of carrier frequencies when a modulation rate is changed, and FIG.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An AC rotary electric machine drive system according to an embodiment of the present disclosure will now be described with reference to the drawings. Fig. 1 is a schematic diagram of an AC rotary electric machine drive system 100 according to the present embodiment.

[0012] The AC rotating electric machine drive system 100 includes an AC rotating electric machine 5, an inverter 20, and a control device 1 for the AC rotating electric machine 5. First, the AC rotating electric machine 5 will be described. The AC rotating electric machine 5 has multi-phase windings. The AC rotating electric machine 5 includes a stator and a rotor (not shown), and the multi-phase windings are provided on the stator. In this embodiment, three-phase windings Cu, Cv, and Cw (U-phase, V-phase, and W-phase) are provided. In the example of FIG. 1 , the three-phase windings Cu, Cv, and Cw are star-connected, but the three-phase windings Cu, Cv, and Cw may also be delta-connected. The number of winding phases may be greater than three. The AC rotating electric machine 5 is a permanent magnet synchronous rotating machine with a rotor provided with a permanent magnet. For example, a rare earth magnet with a rare earth element added, such as neodymium or samarium-cobalt, is used as the permanent magnet. Various types of permanent magnets, such as inexpensive ferrite magnets, may also be used. The AC rotating electric machine 5 may be a synchronous rotating machine of a field winding type in which a field winding is provided on a rotor, or may be an induction machine.

[0013] The AC rotating electric machine 5 is provided with a rotation sensor 6 that outputs an electric signal corresponding to the rotation angle of the rotor. The rotation sensor 6 may be a Hall element, an encoder, or a resolver.

[0014] The inverter 20 is a power converter that performs power conversion between the DC power source 10 and the three-phase windings Cu, Cv, and Cw of the AC rotating electric machine 5. The inverter 20 converts DC power from the DC power source 10 into AC power and supplies the AC power to the AC rotating electric machine 5. The AC rotating electric machine 5 is driven by the power supplied from the inverter 20. The inverter 20 has a plurality of switching elements 23H and a plurality of switching elements 23L. The inverter 20 has three series circuits (legs) in total, each of which has a high-potential side switching element 23H (upper arm) connected to the high-potential side of the DC power source 10 and a low-potential side switching element 23L (lower arm) connected to the low-potential side of the DC power source 10 connected in series, corresponding to each phase of the winding of the AC rotating electric machine 5. That is, the inverter 20 has a total of six switching elements, including three high-potential side switching elements 23H and three low-potential side switching elements 23L. The connection point where the high-potential side switching element 23H and the low-potential side switching element 23L are connected in series is connected to the winding of the corresponding phase. The series circuit connected to the U-phase winding of the AC rotating electric machine is referred to as the U-phase series circuit. Similarly, the series circuits connected to the V-phase winding and the W-phase winding are referred to as the V-phase series circuit and the W-phase series circuit, respectively. Hereinafter, the switching elements 23H and 23L will be collectively referred to as switching elements 23.

[0015] Specific connection examples of the U-phase series circuit, V-phase series circuit, and W-phase series circuit will be described below. In each series circuit corresponding to the winding of each phase of the AC rotating electric machine 5, the collector terminal of the high-potential side switching element 23H is connected to the high-potential side electric wire 24, the emitter terminal of the high-potential side switching element 23H is connected to the collector terminal of the low-potential side switching element 23L, and the emitter terminal of the low-potential side switching element 23L is connected to the low-potential side electric wire 25.

[0016] The switching elements 23 may be IGBTs (Insulated Gate Bipolar Transistors) connected in anti-parallel to the diodes 22, or MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) that function as anti-parallel connected diodes. A gate terminal of each switching element 23 is connected to the control device 1. Each switching element 23 is turned on or off by a control signal output from the control device 1.

[0017] A smoothing capacitor 26 is connected between the high-potential side electric wire 24 and the low-potential side electric wire 25. A voltage sensor 27 is provided between the high-potential side terminal and the low-potential side terminal of the smoothing capacitor 26. The voltage sensor 27 outputs an electric signal corresponding to the DC voltage VDC supplied from the DC power supply 10 to the inverter 20. The output signal of the voltage sensor 27 is input to the control device 1. The control device 1 has a voltage detection unit (not shown), which detects the DC voltage VDC supplied from the DC power supply 10 to the inverter 20.

[0018] A current sensor 28 is provided on each electric wire connecting the U-phase series circuit, the V-phase series circuit, and the W-phase series circuit with the three-phase windings Cu, Cv, and Cw, and the current sensor 28 outputs an electric signal corresponding to the value of the current flowing through the windings Cu, Cv, and Cw of each phase. The output signal from the current sensor 28 is input to the control device 1. The control device 1 has a current detection unit (not shown), which detects the detected values ​​Iur, Ivr, and Iwr of the currents flowing through the three-phase windings Cu, Cv, and Cw. Note that the current sensor 28 may be provided in the series circuit of each phase.

[0019] The DC power supply 10 outputs a DC voltage VDC to the inverter 20. The DC power supply 10 may be any device that outputs a DC voltage VDC, such as a battery, a DC-DC converter, a diode rectifier, or a PWM rectifier.

[0020] A control device 1 according to this embodiment will be described. FIG. 2 is a schematic configuration diagram of the control device 1. The control device 1 controls an AC rotating electric machine 5 via an inverter 20. The control device 1 includes a rotation detection unit 31, a voltage command calculation unit 32, a PWM control unit 33, and a frequency change unit 34. FIG. 3 shows a hardware configuration diagram of the control device 1 for an AC rotating electric machine according to this embodiment. Each function of the control device 1 is realized by a processing circuit included in the control device 1. Specifically, as shown in FIG. 3, the control device 1 includes, as processing circuits, an arithmetic processing device 90 (computer) such as a CPU (Central Processing Unit), a storage device 91 that exchanges data with the arithmetic processing device 90, an input circuit 92 that inputs external signals to the arithmetic processing device 90, and an output circuit 93 that outputs signals from the arithmetic processing device 90 to the outside.

[0021] The arithmetic processing device 90 may be an application-specific integrated circuit (ASIC), an integrated circuit (IC), a digital signal processor (DSP), a field programmable gate array (FPGA), various logic circuits, various signal processing circuits, or the like. Furthermore, a plurality of the same or different types of arithmetic processing devices 90 may be provided, and each device may share the responsibility of performing various processes. The storage device 91 may include a random access memory (RAM) configured to be able to read and write data from the arithmetic processing device 90, a read-only memory (ROM) configured to be able to read data from the arithmetic processing device 90, and the like. The input circuit 92 is connected to various sensors and switches, such as the voltage sensor 27, the current sensor 28, and the rotation sensor 6, and includes an analog-to-digital (A / D) converter that inputs output signals from these sensors and switches to the arithmetic processing device 90. The output circuit 93 is connected to electrical loads, such as a gate drive circuit that drives switching elements on and off, and includes a drive circuit that outputs control signals from the arithmetic processing device 90 to these electrical loads.

[0022] 2 provided in the control device 1 are realized by an arithmetic processing device 90 executing software (programs) stored in a storage device 91 such as a ROM, and cooperating with other hardware of the control device 1 such as the storage device 91, an input circuit 92, and an output circuit 93. Setting data such as the drive carrier frequency Fca and update period Tup used by the rotation detection device 31, the voltage command calculation device 32, the PWM control device 33, and the frequency change device 34 are stored in the storage device 91 such as a ROM. Each function of the control device 1 will be described in detail below.

[0023] <Rotation Detection Unit 31> In this embodiment, the rotation detection unit 31 detects the magnetic pole position θ (rotor rotation angle θ) and rotational angular velocity ω of the rotor of the AC rotating electric machine 5 based on the output signal of the rotation sensor 6. The magnetic pole position θ and rotational angular velocity ω of the rotor are both electrical angles. The magnetic pole position is set to the direction of the north pole of the rotor. Note that the rotation detection unit 31 may be configured to estimate the rotation angle (magnetic pole position) and rotational angular velocity ω without using a rotation sensor, based on current information obtained by superimposing harmonic components on a current command value (a so-called sensorless method). Note that the rotation period (electrical angle) when the AC rotating electric machine 5 rotates at the rotational angular velocity ω is defined as the AC period TAC.

[0024] <Voltage command calculation unit 32> The voltage command calculation unit 32 calculates and updates three-phase AC voltage command values ​​Vuo, Vvo, and Vwo to be applied to the three-phase windings Cu, Cv, and Cw of the AC rotary electric machine 5. The three-phase AC voltage command values ​​Vuo, Vvo, and Vwo have an AC period TAC. Each process of the voltage command calculation unit 32 is executed at each update period Tup. The update period Tup may be set to the same period as the carrier period, or may be set to a half period of the carrier period or a quarter period of the carrier period if the upper limit of the processing load of the calculation has not been reached.

[0025] The voltage command calculation unit 32 calculates three-phase AC voltage command values ​​Vuo, Vvo, and Vwo using known vector control. The voltage command calculation unit 32 calculates d-axis and q-axis current command values ​​Ido and Iqo based on the torque command value To, the rotor magnetic pole position θ and rotational angular velocity ω detected by the rotation detection unit 31, and the DC voltage VDC detected by a voltage detection unit (not shown). The torque command value To corresponds to the torque value required of the AC rotating electric machine 5 and is determined based on an externally input speed command value or torque command value. The voltage command calculation unit 32 converts detection values ​​Iur, Ivr, and Iwr of currents flowing through the three-phase windings Cu, Cv, and Cw, detected by a current detection unit (not shown) of the control device 1, into d-axis and q-axis current detection values ​​Idr and Iqr based on the magnetic pole position θ. The voltage command calculation unit 32 then changes the d-axis and q-axis voltage command values ​​Vdo, Vqo by PI control or the like so that the d-axis and q-axis current detection values ​​Idr, Iqr approach the d-axis and q-axis current command values ​​Ido, Iqo, respectively. The voltage command calculation unit 32 converts the d-axis and q-axis voltage command values ​​Vdo, Vqo into three-phase AC voltage command values ​​Vuo, Vvo, Vwo based on the magnetic pole position θ. Note that known modulation such as two-phase modulation and third-order harmonic superposition may be applied to suppress the amplitudes of the three-phase AC voltage command values ​​Vuo, Vvo, Vwo.

[0026] <PWM Control Unit 33> The PWM control unit 33 generates a carrier signal CA having a drive carrier frequency fca (described later) and controls the on / off of the multiple switching elements 23 of the inverter 20 based on the generated carrier signal. The carrier signal CA has an amplitude corresponding to the DC voltage VDC supplied to the inverter 20. Specifically, the PWM control unit 33 controls the on / off of the multiple switching elements 23 of the inverter 20 based on a comparison result between the carrier signal CA and each of three-phase AC voltage command values ​​Vuo, Vvo, and Vwo to be output by the inverter 20. For each phase, the PWM control unit 33 outputs an on switching signal when each of the AC voltage command values ​​Vuo, Vvo, and Vwo exceeds the carrier signal CA, and outputs an off switching signal when each of the AC voltage command values ​​Vuo, Vvo, and Vwo falls below the carrier signal. Each switching element is input to a gate drive circuit (not shown). In this case, the switching signal corresponding to the high-potential side switching element 23H is input to the gate drive circuit as is, and the switching signal corresponding to the low-potential side switching element 23L is inverted and input to the gate drive circuit. The gate drive circuit inputs switching signals to the gate terminals of each switching element 23 of the inverter 20, and each switching element 23 is turned on or off based on each switching signal.

[0027] <Frequency Changing Unit 34> Fig. 4 shows the configuration of the frequency changing unit 34. As shown in Fig. 4, the frequency changing unit 34 includes a carrier frequency determination unit 341, a carrier frequency switching unit 342, and an update period generation unit 343. The frequency changing unit 34 determines a base carrier frequency fc0 and a PWM controlled drive carrier frequency fca based on the AC period TAC. The base carrier frequency fc0 is a reference frequency when determining the drive carrier frequency fca.

[0028] In PWM control, if the drive carrier frequency fca is not sufficiently high relative to the inverter's fundamental frequency fs (the reciprocal of the AC period TAC), the on / off intervals of the multiple switching elements 23 become longer. This results in a deterioration in the controllability of the actual phase voltage. Note that a state in which the controllability of the actual phase voltage is deteriorated refers to a state in which the actual phase voltage no longer follows the AC voltage command values ​​Vuo, Vvo, and Vwo, and the deviation between the actual phase voltage and the AC voltage command values ​​Vuo, Vvo, and Vwo becomes greater. Therefore, the higher the drive carrier frequency fca, the better the controllability. However, a high drive carrier frequency fca increases the number of switching operations, resulting in increased switching losses. This increases the temperature of the inverter 20. Each component of the inverter 20 has a set allowable temperature. A state in which the temperatures of all components of the inverter 20 are lower than the allowable temperature is considered to be a thermally established state for the inverter 20, and a state in which the temperature of any component of the inverter 20 is higher than the allowable temperature is considered to be a thermally established state for the inverter 20. If the drive carrier frequency fca is high, the heat generation of the inverter 20 becomes an issue.

[0029] The carrier frequency determination unit 341 determines the base carrier frequency fc0 based on the fundamental frequency fs of the inverter 20 so that the inverter 20 is thermally stable. The base carrier frequency fc0 may be changed according to the fundamental frequency fs of the inverter 20. Alternatively, the storage device 91 may store in advance a table of base carrier frequencies fc0 corresponding to fundamental frequencies fs, and the carrier frequency determination unit 341 may read the base carrier frequency fc0 from the storage device 91 according to the fundamental frequency fs.

[0030] The carrier frequency determiner 341 determines a plurality of carrier frequencies different from the base carrier frequency fc0. Details of a method for generating a plurality of carrier frequencies will be described later. In this embodiment, a case will be described in which the carrier frequency determiner 341 determines four carrier frequencies, which are a first carrier frequency fc1, a second carrier frequency fc2, a third carrier frequency fc3, and a fourth carrier frequency fc4, with the first carrier frequency fc1 being the highest, followed by the second carrier frequency fc2, the third carrier frequency fc3, and the fourth carrier frequency fc4.

[0031] Next, the carrier frequency switching unit 342 determines the drive carrier frequency fca by periodically selecting one frequency from the first to fourth carrier frequencies fc1 to fc4 determined by the carrier frequency determination unit 341 at a predetermined change period Tc as the drive carrier frequency fca. The method for determining the drive carrier frequency fca will be described in detail later. The drive carrier frequency fca is transmitted to the PWM control unit 33. The PWM control unit 33 generates a carrier signal CA having a frequency equal to the drive carrier frequency fca.

[0032] The update period generation unit 343 calculates an update period Tup of the voltage command value based on the drive carrier frequency fca determined by the carrier frequency switching unit 342. The update period Tup is transmitted to the voltage command calculation unit 32 and is reflected in the calculation of the AC voltage command values ​​Vuo, Vvo, and Vwo.

[0033] Here, an increase in noise and vibration due to the carrier frequency will be described. FIG. 5( a) shows the time waveform of the line voltage when the AC rotating electric machine 5 is driven under the condition that the drive carrier frequency fca is constant, and FIG. 5( b) shows the results of frequency analysis of the line voltage in FIG. 5( a). The horizontal and vertical axes in FIG. 5( a) represent time and voltage, respectively, and the horizontal and vertical axes in FIG. 5( b) represent frequency and the amplitude of the harmonic components of the line voltage, respectively. The update period of the AC voltage command values ​​Vuo, Vvo, and Vwo is half the period of the drive carrier frequency fca. From FIG. 5( b), it can be seen that the line voltage has peaks at frequencies fc0±2fs and fc0±4fs. FIG. 6( a) shows the time waveform of the line voltage when the update period of the AC voltage command values ​​Vuo, Vvo, and Vwo is set equal to the period of the drive carrier frequency fca, and FIG. 6( b) shows the results of frequency analysis of the line voltage in FIG. 6( a). The conditions other than the update period of the AC voltage command values ​​Vuo, Vvo, and Vwo are the same as those in Fig. 5. When the update period of the AC voltage command values ​​Vuo, Vvo, and Vwo is the same as the drive carrier frequency fca, the line voltage has peaks at frequencies fc0±fs, fc0±2fs, and fc0±4fs, as shown in Fig. 6. The harmonic voltages with frequencies fc0±fs, fc0±2fs, and fc0±4fs are called sidebands of the carrier frequency. By setting the update period of the AC voltage command values ​​Vuo, Vvo, and Vwo shorter than the drive carrier frequency fca, the waveform of the output voltage approaches a sine wave, the occurrence of the fc0±fs component can be suppressed, and the number of sideband peaks can be reduced, compared to when the update period is the same as the drive carrier frequency fca.

[0034] Due to sidebands of the carrier frequency, components with frequencies fc0±3fs are generated in the electromagnetic excitation force. Fig. 7 is a diagram showing the frequency of the electromagnetic excitation force when the drive carrier frequency fca is kept constant at frequency fc0 and the fundamental frequency fs (the reciprocal of the AC period TAC) of the inverter 20 is changed. The horizontal axis represents the fundamental frequency fs of the inverter 20, and the vertical axis represents the frequency of the electromagnetic excitation force. The electromagnetic excitation force has a component whose frequency increases linearly with an increase in fundamental frequency fs and a component whose frequency decreases linearly.

[0035] The AC rotating electric machine 5 has a stator resonant frequency band due to its structure. When the fundamental frequency fs of the inverter 20 is frequency fra, the frequency of the component resulting from the sideband waves of the driving carrier frequency fca of the electromagnetic excitation force matches the resonant frequency band of the stator. When the fundamental frequency fs of the inverter 20 is frequency fra, the stator of the AC rotating electric machine 5 is vibrated by the electromagnetic excitation force, increasing vibration of the stator. This also increases noise. In particular, when the frequency of the component resulting from the sideband waves of the driving carrier frequency fca of the electromagnetic excitation force matches the circular zeroth-order frequency band of the resonant frequency band of the stator, vibration is likely to increase.

[0036] FIG. 8 illustrates an example of setting the drive carrier frequency fca in a conventional control method. In asynchronous PWM, the phase of the carrier signal CA is not synchronized with the rotational phase of the AC rotating electric machine 5 to be controlled. In synchronous PWM, the phase of the carrier signal CA is synchronized with the rotational phase of the AC rotating electric machine 5. Based on the fundamental frequency fs of the inverter 20, the inverter 20 is controlled by asynchronous PWM in a speed range where the fundamental frequency fs is equal to or less than a predetermined value, and the drive carrier frequency fca is set to a constant value. In a speed range where the fundamental frequency fs exceeds the predetermined value, the inverter 20 is controlled by synchronous PWM, and the drive carrier frequency fca is set according to the fundamental frequency fs. In the asynchronous PWM range, the drive carrier frequency fca is preferably set to be 10 times or more the fundamental frequency fs. In the synchronous PWM range, the drive carrier frequency fca is preferably set to be the product of the fundamental frequency fs and a multiple of three.

[0037] 9 is a diagram showing vibration measurement results of the AC rotating electric machine 5 when the AC rotating electric machine 5 is driven by the drive carrier frequency fca set as shown in FIG. 8 . The horizontal axis represents the fundamental frequency fs of the inverter 20, and the vertical axis represents the vibration level of the AC rotating electric machine 5. The vibration level peaks when the fundamental frequency fs of the inverter 20 is equal to the frequency fra. It can be seen that vibration increases when the frequency of a component with a large peak value of the electromagnetic excitation force coincides with the resonant frequency band of the stator. In order to reduce the noise and vibration generated by the AC rotating electric machine 5, it is necessary to reduce the peak value of the electromagnetic excitation force and / or to keep the frequency of the electromagnetic excitation force with a large peak value away from the resonant frequency band of the stator.

[0038] A method for generating the first to fourth carrier frequencies fc1 to fc4 in this embodiment will be described. As described above, the carrier frequency determination unit 341 determines the base carrier frequency fc0 so that the control system is stable and the inverter 20 is thermally stable. The first to fourth carrier frequencies fc1 to fc4 are generated to fall within a predetermined first range. The upper limit value fcu of the first range is determined so that the inverter 20 is thermally stable. The lower limit value fcd of the first range is determined based on the stability of the control system and is preferably determined to be at least 10 times the fundamental frequency fs of the inverter 20. The first range is determined to include the base carrier frequency. The first to fourth carrier frequencies fc1 to fc4 are preferably determined so that there is a large variation within the first range so that the frequencies of the sidebands are dispersed. The first range may be changed depending on the fundamental frequency fs of the inverter 20. In this example, the number of multiple carrier frequencies is four, but the number of determined carrier frequencies may vary depending on the fundamental frequency fs of the inverter 20. Alternatively, the storage device 91 may store a table of multiple carrier frequencies corresponding to the fundamental frequency fs, modulation rate, and torque command value of the inverter 20, and the carrier frequency determination unit 341 may read out the first to fourth carrier frequencies fc1 to fc4 from the table according to the fundamental frequency fs, modulation rate, and torque command value during operation.

[0039] The method of determining the drive carrier frequency fca by the carrier frequency switching unit 342 will now be described. FIG. 10 shows the change in drive carrier frequency fca over time. The horizontal axis represents time, and the vertical axis represents drive carrier frequency fca. As shown in FIG. 10, the carrier frequency switching unit 342 determines the drive carrier frequency fca by periodically selecting one carrier frequency from the first to fourth carrier frequencies fc1 to fc4 as the drive carrier frequency fca at a predetermined change period Tc. In FIG. 10, the first carrier frequency fc1, the fourth carrier frequency fc4, the second carrier frequency fc2, and the third carrier frequency fc3 are selected in this order, but the order in which the carrier frequencies are selected is not important. The order may also be the first carrier frequency fc1, the second carrier frequency fc2, the fourth carrier frequency fc4, and the third carrier frequency fc3. After the third carrier frequency fc3, the process returns to the first carrier frequency fc1, and so on. It is desirable that the change period Tc be a short period in order to reduce vibrations generated from the AC rotating electric machine 5. If the change period Tc is a short period, the processing load of the control device 1 increases. Therefore, it is desirable that the change period Tc be approximately one period of the mechanical angle of the AC rotating electric machine 5.

[0040] FIG. 11(a) shows the time waveform of the drive carrier frequency fca when the drive carrier frequency fca is determined based on the control method according to this embodiment and the AC rotating electric machine 5 is driven at a constant fundamental frequency fs, and FIG. 11(b) shows the results of frequency analysis of the line voltage at this time. For comparison, FIG. 12(a) shows the time waveform of the drive carrier frequency fca when the drive carrier frequency fca is set to a constant frequency fc0 and the AC rotating electric machine 5 is driven at a constant fundamental frequency fs, and FIG. 12(b) shows the results of frequency analysis of the line voltage at this time. The examples of FIGS. 11 and 12 are the same except for the drive carrier frequency fca. The vertical and horizontal axes of FIGS. 11(a) and 12(a) are the same as the vertical and horizontal axes of FIG. 5(a), and the vertical and horizontal axes of FIGS. 11(b) and 12(b) are the same as the vertical and horizontal axes of FIG. 5(b). 12(a) and 12(b), when the AC rotating electric machine 5 is driven at a constant drive carrier frequency fca, the line voltage has large peak values ​​at frequencies fc0±2fs and fc0±4fs. In contrast, as shown in FIGS. 11(a) and 11(b), when the drive carrier frequency fca is determined based on the control method according to this embodiment, the frequencies of the sideband waves are dispersed and the peak values ​​are reduced. This reduces the magnitude of the electromagnetic excitation force, and also reduces vibration and noise.

[0041] When the changed drive carrier frequency fca is smaller than before the change, if the difference between the drive carrier frequency fca before and after the change is large, the actual voltage may not follow the AC voltage command values ​​Vuo, Vvo, and Vwo, resulting in a torque shock. Therefore, when the changed drive carrier frequency fca is smaller than before the change, it is preferable to select the changed drive carrier frequency fca so that the change in the drive carrier frequency fca is smaller than when the changed drive carrier frequency fca is larger than before the change. Specifically, when the maximum change in the drive carrier frequency fca before and after the change when the changed drive carrier frequency fca is larger than before the change is set to Δf_1, and the maximum change in the drive carrier frequency fca before and after the change when the changed drive carrier frequency fca is smaller than before the change is set to Δf_2, the carrier frequency switching unit 342 may select the drive carrier frequency fca so that Δf_1≧Δf_2.

[0042] A state in which the ratio of the amplitude of the AC voltage command values ​​Vuo, Vvo, and Vwo to the amplitude of the carrier signal CA is greater than 1 (modulation factor > 1) is called an overmodulation state, and a state in which the ratio of the amplitude of the AC voltage command values ​​Vuo, Vvo, and Vwo to the amplitude of the carrier signal CA is less than 1 (modulation factor ≦ 1) is called a normal modulation state. FIG. 13 is a diagram showing an overmodulation state and a normal modulation state in the operating range of the AC rotating electric machine 5. The horizontal axis represents the fundamental frequency fs (the reciprocal of the AC period T AC ) of the inverter 20, and the vertical axis represents torque. The AC rotating electric machine 5 is in an overmodulation state in an operating range where the fundamental frequency fs is high and in an operating range where torque is high. In the overmodulation state, the actual voltage has difficulty following the AC voltage command values ​​Vuo, Vvo, and Vwo compared to the normal modulation state, resulting in poor controllability.

[0043] The first range may be determined based on, for example, a modulation factor. For example, the first range may be determined such that the first range when the modulation factor is equal to or less than a predetermined second value is narrower than the first range when the modulation factor is greater than the predetermined second value. Furthermore, the first range may be set to a constant value when the torque command value To is equal to or less than the second value.

[0044] FIG. 14 shows an example of setting the first range when the modulation rate is changed. The horizontal axis of FIG. 14 represents the modulation rate, and the vertical axis represents the frequency. When the modulation rate is equal to or less than a second value, the first range is constant, i.e., the upper and lower limit values ​​fcu and fcd of the first range are constant. When the modulation rate is greater than the second value but equal to or less than the maximum value, the upper limit value fcu of the first range decreases linearly as the modulation rate increases, and the lower limit value fcd of the first range increases linearly as the modulation rate increases. When the modulation rate is at its maximum value, the upper limit value fcu and the lower limit value fcd of the first range each coincide with the base carrier frequency fc0. In the example of FIG. 14, the center value of the upper and lower limit values ​​fcu and fcd of the first range is the base carrier frequency fc0, but the base carrier frequency fc0 may be shifted toward the upper limit value fcu of the first range or toward the lower limit value fcd of the first range.

[0045] The second value is, for example, 1. In this case, the first range is constant within a range of modulation factors in which the AC rotating electric machine 5 is in a normal modulation state, and the first range decreases as the modulation factor increases within a range of modulation factors in which the AC rotating electric machine 5 is in an overmodulation state. The second value may be greater than or less than 1 and is determined depending on whether controllability or reduction of vibration and noise is prioritized at the fundamental frequency fs. When controllability is prioritized, the second value is preferably smaller than 1. When vibration and noise reduction is prioritized, the second value is preferably equal to or greater than 1. Furthermore, when the modulation factor is greater than the second value, the upper and lower limit values ​​fcu and fcd of the first range change linearly. However, the upper limit value fcu of the first range may change as a downward convex function, and the lower limit value fcd of the first range may change as an upward convex function. The upper limit value fcu of the first range may vary according to an upward convex function, and the lower limit value fcd of the first range may vary according to a downward convex function, or one of the upper limit value fcu of the first range or the lower limit value fcd of the first range may vary linearly, and the other may vary according to a downward convex or upward convex function. Furthermore, when the modulation factor is a third value that is greater than the second value and less than the maximum value, the upper limit value fcu of the first range or the lower limit value fcd of the first range may coincide with the base carrier frequency fc0, and when the modulation factor is equal to or greater than the third value, the upper limit value fcu of the first range or the lower limit value fcd of the first range may be constant at the base carrier frequency fc0.

[0046] Instead of determining the first range based on the modulation rate, the first range may be determined based on the torque command value To. For example, the first range may be determined such that the first range when the torque command value To is equal to or less than a predetermined third value is narrower than the first range when the torque command value To is greater than the predetermined third value. Furthermore, when the torque command value To is equal to or less than the third value, the first range may be set to a constant value.

[0047] When the drive carrier frequency fca changes, the switching loss generated by turning on / off the multiple switching elements 23 of the inverter 20 also changes. Because the switching loss is proportional to the drive carrier frequency fca, the average value of the switching loss is proportional to the average value of the drive carrier frequency fca. The first to fourth carrier frequencies fc1 to fc4 may be determined so that their average values ​​are equal to the base carrier frequency fc0. This makes it possible to evaluate the loss at each operating point of the AC rotating electric machine 5 using the base carrier frequency fc0, facilitating verification of the operating characteristics.

[0048] The frequency of the component of the electromagnetic excitation force resulting from the sideband waves of the drive carrier frequency fca is determined by the drive carrier frequency fca and the fundamental frequency fs of the inverter 20. If the resonant frequency band of the stator is known in advance, the first to fourth carrier frequencies fc1 to fc4 may be determined so that the frequency of the component of the electromagnetic excitation force resulting from the sideband waves of each carrier frequency does not match the resonant frequency band of the stator (the resonant frequency band of the AC rotating electric machine 5). As a result, the frequency of the electromagnetic excitation force does not match the resonant frequency band of the stator of the AC rotating electric machine 5, thereby suppressing noise and vibration.

[0049] <Effects> The control device 1 according to this embodiment is a control device for controlling an AC rotating electric machine 5 driven by AC power supplied from an inverter having a plurality of switching elements 23. The control device 1 includes a carrier frequency changer 34 that determines a drive carrier frequency fca and a PWM control unit 33 that controls the on / off of the plurality of switching elements 23 based on a carrier signal CA having the drive carrier frequency fca determined by the carrier frequency changer 34. The frequency changer 34 includes a carrier frequency determiner 341 that determines a plurality of carrier frequencies and a carrier frequency switcher 342 that periodically selects one carrier frequency from the plurality of carrier frequencies at a predetermined change period Tc to determine the drive carrier frequency fca. This configuration eliminates the need for a determination process when changing the drive carrier frequency fca, thereby reducing sidebands of the carrier frequency of the line voltage, which can cause electromagnetic excitation forces, without increasing the control load. This reduces noise and vibration.

[0050] Furthermore, in the control device according to this embodiment, the frequency changer 34 generates multiple carrier frequencies based on the modulation factor or the torque command value so that the multiple carrier frequencies fall within a first range that is preset to include the base carrier frequency fc0. This reduces the change in drive carrier frequency fca before and after the periodic change, resulting in stable controllability.

[0051] Furthermore, in the control device according to this embodiment, the first range when the modulation factor is greater than the second value is set to be narrower than the first range when the modulation factor is equal to or less than the second value. Alternatively, the first range when the torque command value is greater than the third value is set to be narrower than the first range when the torque command value is equal to or less than the third value. As a result, when the modulation factor or torque command value is large, the actual voltage value tends to not follow the command value, making control unstable. However, narrowing the first range improves the stability of control.

[0052] Furthermore, in the control device according to this embodiment, the PWM control unit 33 updates the voltage command value for the AC rotary electric machine 5 at a cycle shorter than the drive carrier frequency fca. This reduces the frequency at which the sideband wave peaks occur, and also reduces the frequency at which the electromagnetic excitation force peaks occur, thereby reducing noise and vibration.

[0053] <Vehicle> Figure 15 shows an example in which the drive system 100 is mounted on a vehicle 200. As shown in Figure 15, the vehicle 200 includes a main body 202 having multiple (four in this example) drive wheels 201, and the drive system 100 according to this embodiment. The drive system 100 is provided in the main body 202 and generates a drive force that rotates at least one of the multiple drive wheels 201. As described above, in the drive system 100, the frequency of the sideband waves is dispersed and the peak value is reduced, thereby reducing the magnitude of the electromagnetic excitation force and reducing vibration and noise. This makes it possible to suppress vibration and noise when the vehicle 200 is running.

[0054] The AC rotating electric machine 5 may be selectively driven in a plurality of operation modes determined by a combination of a rotation direction and an operation state. For example, the rotation direction may include a forward direction and a reverse direction, and the operation state may include a powering operation and a regenerative operation. In this case, the AC rotating electric machine 5 is selectively driven in the plurality of operation modes, including a first operation mode in which powering operation is performed for forward rotation, a second operation mode in which regenerative operation is performed for forward rotation, a third operation mode in which powering operation is performed for reverse rotation, and a fourth operation mode in which regenerative operation is performed for reverse rotation. When the fundamental frequency fs of the inverter 20 is the same but the operation mode is different, the first range may be different. By changing the first range depending on the operation mode, the AC rotating electric machine 5 can be appropriately controlled depending on the situation, whether prioritizing controllability or noise and vibration.

[0055] For example, when the drive system 100 is used as a drive source for the vehicle 200, the AC rotating electric machine 5 is driven in a first operating mode when the vehicle 200 is moving forward and not braking. The AC rotating electric machine 5 is driven in a second operating mode when the vehicle 200 is moving forward and not braking. The AC rotating electric machine 5 is driven in a third operating mode when the vehicle 200 is moving backward and not braking, and the AC rotating electric machine 5 is driven in a fourth operating mode when the vehicle 200 is moving backward and braking. The frequency of use when the vehicle 200 is moving forward is higher than the frequency of use when the vehicle is moving backward, and it is desirable to reduce noise and vibration when the vehicle 200 is moving forward. Therefore, in order to reduce sidebands, the first range when the vehicle is moving forward may be wider than the first range when the vehicle is moving backward. In this case, noise and vibration when the vehicle is moving forward can be reduced and controllability when the vehicle is moving backward can be improved.

[0056] The drive system 100 is not limited to vehicles, and may also be applied to railway vehicles, industrial equipment, or air conditioners.

[0057] REFERENCE SIGNS LIST 1 control device, 5 AC rotating electric machine, 6 rotation sensor, 10 DC power supply, 20 inverter, 22 diode, 23 switching element, 24 high potential side electric wire, 25 low potential side electric wire, 26 smoothing capacitor 27 voltage sensor, 28 current sensor, 29 31 rotation detection unit, 32 voltage command calculation unit, 33 PWM control unit, 34 carrier frequency change unit, 341 carrier frequency determination unit, 342 carrier frequency switching unit, 343 update period generation unit, 90 arithmetic processing device, 91 storage device, 92 input circuit, 93 output circuit, 100 drive system of AC rotating electric machine, 200 vehicle, TAC AC period, Tuc update period, Tc change period, fs fundamental frequency, fc0 base carrier frequency, CA carrier signal, fca: drive carrier frequency; fc1, fc2, fc3, fc4: carrier frequency; fcu: upper limit of the first range; fcd: lower limit of the first range

Claims

1. A control device for controlling an AC rotating electric machine driven by AC power supplied from an inverter having a plurality of switching elements, comprising: a carrier frequency changing unit that determines a drive carrier frequency; and a PWM control unit that controls the on / off of the plurality of switching elements based on a carrier signal having the drive carrier frequency determined by the carrier frequency changing unit, wherein the carrier frequency changing unit includes: a carrier frequency determination unit that determines a plurality of carrier frequencies; and a carrier frequency switching unit that determines the drive carrier frequency by periodically selecting one carrier frequency from the plurality of carrier frequencies at a predetermined change period.

2. The control device for an AC rotating electric machine according to claim 1, wherein the carrier frequency determination unit determines a base carrier frequency based on the fundamental frequency of the inverter so that the inverter is thermally stable, and determines the plurality of carrier frequencies so that they are each different from the base carrier frequency.

3. The control device for an AC rotating electric machine according to claim 2, wherein the average value of the plurality of carrier frequencies is the base carrier frequency.

4. A control device for an AC rotating electric machine according to claim 2, wherein the PWM control unit controls the on / off of the plurality of switching elements based on an AC voltage command value corresponding to the AC voltage to be output by the inverter, and the carrier frequency determination unit determines a first range to include the base carrier frequency based on a modulation factor which is the ratio of the amplitude of the AC voltage command value to the amplitude of the carrier signal, or a torque command value corresponding to a torque value required for the AC rotating electric machine, and determines the plurality of carrier frequencies to be each within the first range.

5. The control device for an AC rotating electric machine according to claim 4, wherein the first range when the modulation factor is greater than a predetermined second value is narrower than the first range when the modulation factor is equal to or less than the second value.

6. The control device for an AC rotating electric machine according to claim 4, wherein the first range when the torque command value is greater than a predetermined third value is narrower than the first range when the torque command value is equal to or less than the third value.

7. The control device for an AC rotating electric machine according to claim 5, wherein the second value is the modulation factor when the amplitude of the AC voltage command value and the amplitude of the carrier signal are equal to each other.

8. The control device for an AC rotating electric machine according to claim 6, wherein the third value is the torque command value when the amplitude of the AC voltage command value and the amplitude of the carrier signal are equal to each other.

9. A control device for an AC rotating electric machine as described in claim 4, wherein the AC rotating electric machine is selectively driven in a plurality of operating modes including a first operating mode in which powering operation is performed for rotation in the forward direction, a second operating mode in which regenerative operation is performed for rotation in the forward direction, a third operating mode in which powering operation is performed for rotation in the reverse direction, and a fourth operating mode in which regenerative operation is performed for rotation in the reverse direction, and the first range is different when the fundamental frequency of the inverter is the same but the operating modes are different.

10. A control device for an AC rotating electric machine as described in any one of claims 1 to 9, wherein the carrier frequency switching unit determines the driving carrier frequency so that Δf_i > Δf_d, and Δf_i is the maximum value of the change range of the driving carrier frequency before and after the driving carrier frequency is periodically changed at the change period when the changed driving carrier frequency is larger than the driving carrier frequency before the change, and Δf_d is the maximum value of the change range of the driving carrier frequency before and after the driving carrier frequency is periodically changed at the change period when the changed driving carrier frequency is smaller than the driving carrier frequency before the change.

11. The control device for an AC rotating electric machine according to any one of claims 1 to 10, further comprising a voltage command calculation unit that calculates the AC voltage command value, wherein the voltage command calculation unit updates the AC voltage command value at a cycle shorter than the drive carrier frequency.

12. A control device for an AC rotating electric machine according to any one of claims 1 to 11, wherein the carrier frequency determination unit generates the plurality of carrier frequencies so that the frequency of the electromagnetic excitation force resulting from sideband waves of the drive carrier frequency does not match the resonant frequency band of the AC rotating electric machine.

13. An AC rotating electric machine drive system comprising: an inverter that converts DC power into AC power; an AC rotating electric machine that is driven by power supplied from the inverter; and a control device according to any one of claims 1 to 12 that controls the AC rotating electric machine.

14. A vehicle comprising: a main body having drive wheels; and an AC rotating electric machine drive system according to claim 13 that rotates the drive wheels.

Images