Control device

Abstract

To provide a control device capable of reducing torque ripples in a case where an electric motor is controlled in an overmodulation region of an inverter by vector control.SOLUTION: A control device 3 comprises: a restriction unit 14 that comprises a voltage limiter 19 restricting a d-axis voltage command value and / or a q-axis voltage command value, and a filter 18 whose time constant can be modified; an identification unit 16 that identifies the harmonic component with the largest amplitude, among harmonic components superposed on currents flowing in respective phases of an electric motor M; and a time constant modification unit 17 that modifies the time constant of the filter 18 so as to reduce a harmonic component gain corresponding to the harmonic component identified by the identification unit 16. The filter 18 has such a time constant that a gain of a harmonic component of a sixth order becomes smaller than that of a harmonic component of a predetermined order equal to or lower than fifth order, and such a time constant that the gain of the harmonic component of the predetermined order is smaller than that of the harmonic component of the sixth order.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control device for an inverter of an electric motor.

Background Art

[0002] Non-Patent Document 1 discloses a method of controlling an electric motor by vector control in the overmodulation region of an inverter. In the control device described in Non-Patent Document 1, an alternating current flowing through the electric motor is converted into a d-axis current and a q-axis current, a voltage command value is obtained so that the d-axis current and the q-axis current approach a d-axis current command value and a q-axis current command value, and a plurality of switching elements provided in the inverter are turned on and off by a drive signal according to a comparison result between the voltage command value and a carrier wave, thereby controlling the drive of the electric motor by so-called vector control.

[0003] When using the overmodulation region, which is a non-linear region of the inverter, the inverter has non-linear characteristics. Therefore, in order to use the overmodulation region in vector control, non-linear elements are required. The control device described in Non-Patent Document 1 includes non-linear elements such as a voltage amplitude compensator and a voltage limiter in order to perform vector control using the overmodulation region of the inverter. The voltage limiter is provided to avoid generation of a command voltage exceeding the input voltage of the inverter under driving conditions where the induced voltage is high, such as in a transient state where the current needs to be steeply converted or during high-output driving. The voltage limiter determines the d-axis voltage command value and the q-axis voltage command value so that the command voltage is equal to or lower than the input voltage of the inverter.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the overmodulation region of the inverter, as the voltage command value increases, the output voltage waveform transitions from a sine wave to a rectangular wave. The harmonic components superimposed on the output current increase as the output voltage approaches a rectangular wave. That is, when using the overmodulation region of the inverter, the harmonic components superimposed on the output current become large. In vector control, since current feedback control is performed in the d-q coordinate system, harmonic components appear in the d-q coordinate system when a three-phase rectangular wave voltage is applied. In a control system that utilizes the overmodulation region of the inverter, a 6th-order harmonic component (a harmonic component with a frequency six times that of the electrical angular frequency of the motor) having a large amplitude is superimposed on the d-q coordinate system. Therefore, in the control device described in Non-Patent Document 1, a filter for attenuating (removing) the 6th-order harmonic component superimposed on the d-q coordinate system is provided in the current feedback loop.

[0006] One aspect of the present invention aims to provide a control device capable of reducing torque ripple when controlling an electric motor by vector control in the overmodulation region of an inverter.

Means for Solving the Problems

[0007] While the applicant of the present application was conducting intensive research on the above problems, in a configuration where a voltage limiter is provided to operate the vector control system up to the overmodulation region, it was found that there are two cases for the harmonic components of the sixth order or lower superimposed on the d-q coordinate system: one is the case where the amplitude of the sixth order harmonic component is the highest, and the other is the case where the amplitude of the harmonic components of a predetermined order of the fifth order or lower is the largest. Therefore, the applicant of the present application identified the harmonic component with the largest amplitude among the harmonic components superimposed on the current flowing through each phase of the motor, and obtained the finding that torque ripple can be reduced by attenuating the harmonic component of the identified order, and thus completed the present invention.

[0008] A control device according to one aspect of the present invention includes: a first conversion unit that converts the current flowing through each phase of the motor into a d-axis current and a q-axis current; a current control unit that generates a d-axis voltage command value and a q-axis voltage command value based on the d-axis current and the q-axis current converted by the first conversion unit, the d-axis current command value, and the q-axis current command value; a voltage limiting unit that receives the d-axis voltage command value and the q-axis voltage command value, and limits the d-axis voltage command value and / or the q-axis voltage command value so that they are equal to or lower than the input voltage when the d-axis voltage command value and the q-axis voltage command value exceed the input voltage of the inverter; a variable filter whose time constant can be changed; a second conversion unit that converts the d-axis voltage command value and the q-axis voltage command value output from the limiting unit into voltage command values corresponding to each phase of the motor and outputs the voltage command values; a specifying unit that specifies the harmonic component with the largest amplitude among the harmonic components superimposed on the current flowing through each phase of the motor; and a time constant changing unit that changes the time constant of the variable filter so as to reduce the gain of the harmonic component corresponding to the harmonic component specified by the specifying unit. The control device controls the inverter in overmodulation, and the variable filter has a time constant that makes the gain of the sixth order harmonic component smaller than the gain of the harmonic components of a predetermined order of the fifth order or lower, and a time constant that makes the gain of the harmonic components of the predetermined order smaller than the gain of the sixth order harmonic component.

[0009] In the control device according to one aspect of the present invention, the specifying unit specifies the harmonic component having the largest amplitude among the harmonic components superimposed on the current flowing through each phase of the electric motor. The time constant changing unit changes the time constant of the variable filter so as to reduce the gain of the harmonic component corresponding to the harmonic component specified by the specifying unit. Thereby, in the control device, for example, when the 6th harmonic component is dominant in the d-q coordinate system, the 6th harmonic component can be attenuated by the variable filter, and when the harmonic component of a predetermined order of 5th or lower is dominant in the d-q coordinate system, the harmonic component of a predetermined order of 5th or lower can be attenuated by the variable filter. In this way, the control device can attenuate not only the 6th harmonic component superimposed on the output current of the electric motor but also the harmonic component of a predetermined order of 5th or lower. Therefore, the control device can reduce torque ripple when controlling the electric motor by vector control in the overmodulation region of the inverter.

[0010] In a three-phase AC-driven electric motor (particularly, a PMSM: Permanent Magnet Synchronous Motor), due to its structure, the induced voltage includes harmonic components, so harmonic components of an integer multiple of the electrical angular frequency, mainly the 6th order, occur in the generated torque. In the control device, the harmonic components generated due to the structure of the electric motor can also be attenuated by the variable filter.

[0011] In one embodiment, the specifying unit includes a first filter to which at least one of the d-axis current and the q-axis current is input and which has a time constant that makes the gain of the harmonic component of a predetermined order smaller than the gain of the 6th harmonic component, and a second filter to which at least one of the d-axis current and the q-axis current is input and which has a time constant that makes the gain of the 6th harmonic component smaller than the gain of the harmonic component of a predetermined order. The amplitude of the output current of the first filter and the amplitude of the output current of the second filter may be compared, and the harmonic component having the larger amplitude may be specified. With this configuration, it is possible to specify the harmonic component having the larger amplitude among the harmonic components superimposed on the output current of the electric motor.

[0012] In one embodiment, the specifying unit may identify the harmonic component with the largest amplitude based on the electrical angular frequency of the electric motor and the number of times of the maximum value or the minimum value of the current flowing through at least one phase of the currents flowing through each phase of the electric motor or at least one of the d-axis current and the q-axis current in one period of the electrical angular frequency. Even with this configuration, among the harmonic components of the 6th order or lower superimposed on the output current of the electric motor, the harmonic component with the largest amplitude can be identified.

[0013] In one embodiment, the variable filter may receive a d-axis voltage command value and a q-axis voltage command value. With this configuration, in vector control for performing current feedback control in the d-q coordinate system, the responsiveness can be improved.

Advantages of the Invention

[0014] According to one aspect of the present invention, when controlling an electric motor by vector control in the overmodulation region of an inverter, torque ripple can be reduced.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0017] The control system 1 shown in Fig. 1 controls the drive of an electric motor M mounted on a vehicle such as an electric forklift or a plug-in hybrid vehicle, for example. The control system 1 includes an inverter circuit (inverter) 2, a control device 3, and current sensors Se1, Se2, and Se3.

[0018] The control device 3 of this embodiment controls the electric motor M by vector control in the overmodulation region of the inverter circuit 2, and the harmonic components of the sixth order or less superimposed on the d-q coordinate system are configured such that there are cases where the amplitude of the sixth order harmonic component is the largest and cases where the amplitude of the third order harmonic component is the largest. Note that among the harmonic components of the fifth order or less superimposed on the d-q coordinate system, the order of the harmonic components with an amplitude larger than that of the sixth order harmonic component varies depending on what non-linear elements are provided in the control device 3.

[0019] The inverter circuit 2 drives the electric motor M with the DC power supplied from the DC power source P. The inverter circuit 2 includes a capacitor C and switching elements SW1, SW2, SW3, SW4, SW5, and SW6.

[0020] The capacitor C smoothes the voltage V output from the DC power source P and input to the inverter circuit 2. in to smooth it.

[0021] The switching elements SW1 to SW6 are, for example, IGBTs (Insulated Gate Bipolar Transistors). One end of the capacitor C is connected to the positive terminal of the DC power source P and the collector terminals of the three upper arm switching elements, which are the switching elements SW1, SW3, and SW5. The other end of the capacitor C is connected to the negative terminal of the DC power source P and the emitter terminals of the three lower arm switching elements, which are the switching elements SW2, SW4, and SW6.

[0022] The connection point between the emitter terminal of the switching element SW1 and the collector terminal of the switching element SW2 is connected to the input terminal of the U-phase of the motor M via the current sensor Se1. The connection point between the emitter terminal of the switching element SW3 and the collector terminal of the switching element SW4 is connected to the input terminal of the V-phase of the motor M via the current sensor Se2. The connection point between the emitter terminal of the switching element SW5 and the collector terminal of the switching element SW6 is connected to the input terminal of the W-phase of the motor M via the current sensor Se3.

[0023] The switching element SW1 turns on or off based on the drive signal S1 output from the control device 3. The switching element SW2 turns on or off based on the drive signal S2 output from the control device 3. The switching element SW3 turns on or off based on the drive signal S3 output from the control device 3. The switching element SW4 turns on or off based on the drive signal S4 output from the control device 3. The switching element SW5 turns on or off based on the drive signal S5 output from the control device 3. The switching element SW6 turns on or off based on the drive signal S6 output from the control device 3.

[0024] By turning on or off the switching elements SW1 to SW6 respectively, the DC power output from the DC power supply P is converted into three AC powers with phases different by 120 degrees from each other, and these AC powers are input to the input terminals of the three phases (U-phase, V-phase, and W-phase) of the motor M, causing the rotor of the motor M to rotate.

[0025] The current sensors Se1 to Se3 are composed of a Hall element, a shunt resistor, etc. The current sensor Se1 detects the AC current Iu flowing through the U-phase of the motor M and outputs it to the control device 3. The current sensor Se2 detects the AC current Iv flowing through the V-phase of the motor M and outputs it to the control device 3. The current sensor Se3 detects the AC current Iw flowing through the W-phase of the motor M and outputs it to the control device 3. When the AC currents Iu, Iv, and Iw are not particularly distinguished, they are simply referred to as the AC current I.

[0026] The control device 3 controls the inverter circuit 2. When the modulation rate is less than a predetermined value, the control device 3 performs PWM control to change the pulse widths of the drive signals S1 to S6 by increasing or decreasing the amplitudes of the voltage command values Vu*, Vv*, and Vw* within a range not exceeding the amplitude of the carrier wave. When the modulation rate is greater than or equal to the predetermined value, the control device 3 performs overmodulation control to make the amplitudes of the voltage command values Vu*, Vv*, and Vw* greater than the amplitude of the carrier wave. Overmodulation control is a control method that utilizes the overmodulation region of the inverter circuit 2. The control device 3 includes a drive circuit 4 and a calculation unit 5.

[0027] The drive circuit 4 is composed of an IC (Integrated Circuit) or the like. The drive circuit 4 compares the voltage command values Vu*, Vv*, and Vw* output from the calculation unit 5 with a carrier wave (such as a triangular wave, a sawtooth wave, or a reverse sawtooth wave), and outputs drive signals S1 to S6 corresponding to the comparison results to the respective gate terminals of the switching elements SW1 to SW6.

[0028] For example, when the voltage command value Vu* is greater than or equal to the carrier wave, the drive circuit 4 outputs a high-level drive signal S1 and outputs a low-level drive signal S2. When the voltage command value Vu* is less than the carrier wave, the drive circuit 4 outputs a low-level drive signal S1 and outputs a high-level drive signal S2. Also, when the voltage command value Vv* is greater than or equal to the carrier wave, the drive circuit 4 outputs a high-level drive signal S3 and outputs a low-level drive signal S4. When the voltage command value Vv* is less than the carrier wave, the drive circuit 4 outputs a low-level drive signal S3 and outputs a high-level drive signal S4. Further, when the voltage command value Vw* is greater than or equal to the carrier wave, the drive circuit 4 outputs a high-level drive signal S5 and outputs a low-level drive signal S6. When the voltage command value Vw* is less than the carrier wave, the drive circuit 4 outputs a low-level drive signal S5 and outputs a high-level drive signal S6.

[0029] The arithmetic unit 5 includes a first coordinate conversion unit (first conversion unit) 6, an estimation unit 7, a subtraction unit 8, a speed control unit 9, a command value output unit 10, subtraction units 11, 12, a current control unit 13, a limit unit 14, a second coordinate conversion unit (second conversion unit) 15, a specification unit 16, and a time constant change unit 17.

[0030] The arithmetic unit 5 is an electronic control unit composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The arithmetic unit 5 can be configured as software in which, for example, a program stored in the ROM is loaded onto the RAM and executed by the CPU. In the arithmetic unit 5, by executing a program, the first coordinate conversion unit 6, the estimation unit 7, the subtraction unit 8, the speed control unit 9, the command value output unit 10, the subtraction units 11, 12, the current control unit 13, the limit unit 14, the second coordinate conversion unit 15, the specification unit 16, and the time constant change unit 17 are realized.

[0031] The first coordinate conversion unit 6 converts the alternating currents Iu, Iv, Iw flowing through the electric motor M into a d-axis current Id and a q-axis current Iq. The first coordinate conversion unit 6 uses the position θ^ output from the estimation unit 7 to convert the alternating currents Iu, Iv, Iw detected by the current sensors Se1 to Se3 into a d-axis current Id and a q-axis current Iq. The first coordinate conversion unit 6 converts the alternating currents Iu, Iv, Iw into a d-axis current Id and a q-axis current Iq using, for example, the conversion matrix C1 shown in the following formula (1). The first coordinate conversion unit 6 outputs the d-axis current Id and the q-axis current Iq to the subtraction units 11, 12 and the specification unit 16.

Equation

[0032] The estimation unit 7 estimates the rotational speed (rotation speed) ω^ and the position θ^ of the rotor of the electric motor M using the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from a filter 18 described later, and the d-axis current Id and the q-axis current Iq output from the first coordinate conversion unit 6. The estimation unit 7 calculates the back electromotive force ed^ and the back electromotive force eq^ according to, for example, the following formulas (2) and (3).

[0033]

Number

Number

[0034] The estimation unit 7 calculates the error θe^ according to the following formula 4.

Number

[0035] The estimation unit 7 obtains the rotational speed ω^ such that the error θe^ becomes zero in the following formula 5.

Number

[0036] The estimation unit 7 calculates the position θ^ according to the following formula (6).

Number

[0037] The subtraction unit 8 calculates the difference Δω between the rotational speed command value ω* input from the outside and the rotational speed ω^ output from the estimation unit 7.

[0038] The speed control unit 9 performs PI control. Specifically, the speed control unit 9 generates the q-axis current command value Iq* from the difference Δω output from the subtraction unit 8. The speed control unit 9 obtains, for example, the q-axis current command value Iq* such that the difference Δω becomes zero in the following formula (7).

Number

[0039] The command value output unit 10 outputs a predetermined d-axis current command value Id* to the subtraction unit 11.

[0040] The subtraction unit 11 calculates the difference ΔId between the d-axis current command value Id* output from the command value output unit 10 and the d-axis current Id output from the first coordinate conversion unit 6. The subtraction unit 11 outputs the difference ΔId to the current control unit 13. The subtraction unit 12 calculates the difference ΔIq between the q-axis current command value Iq* output from the speed control unit 9 and the q-axis current Iq output from the first coordinate conversion unit 6. The subtraction unit 12 outputs the difference ΔIq to the current control unit 13.

[0041] The current control unit 13 performs PI control. Specifically, the current control unit 13 generates a d-axis voltage command value Vd* and a q-axis voltage command value Vq* from the difference ΔId output from the subtraction unit 11 and the difference ΔIq output from the subtraction unit 12. The current control unit 13 calculates the d-axis voltage command value Vd* using, for example, the following formula (8) and calculates the q-axis voltage command value Vq* using the following formula (9). The current control unit 13 outputs the d-axis voltage command value Vd* and the q-axis voltage command value Vq* to the limiting unit 14.

Equation

Equation

[0042] The limiting unit 14 includes a filter 18 and a voltage limiter 19 as a voltage limiting unit. The limiting unit 14 receives the d-axis voltage command value Vd* and the q-axis voltage command value Vq*.

[0043] Filter 18 is a band elimination filter (BEF). Filter 18 is a variable filter capable of changing the cut-off frequency (fc) by changing the time constant (τ). The time constant of filter 18 is changed by the time constant changing unit 17. By changing the time constant of filter 18 by the time constant changing unit 17, the cut-off frequency is changed. Filter 18 can be changed to a time constant that makes the gain of the 6th harmonic component smaller than the gain of the harmonic components of a predetermined order of 5th or lower, and a time constant that makes the gain of the harmonic components of a predetermined order of 5th or lower smaller than the gain of the 6th harmonic component. The variable filter of the present invention only needs to be changeable to a time constant that makes the gain of at least the 6th harmonic component smaller than the gain of the harmonic components of a predetermined order of 5th or lower, and a time constant that makes the gain of at least the harmonic components of a predetermined order of 5th or lower smaller than the gain of the 6th harmonic component.

[0044] The filter 18 of the present embodiment can be changed to a time constant that makes the gain of the 6th harmonic component smaller than the gain of the 3rd harmonic component, and a time constant that makes the gain of the 3rd harmonic component smaller than the gain of the 6th harmonic component. Filter 18 outputs the filtered d-axis voltage command value Vd* and q-axis voltage command value Vq* to the voltage limiter 19.

[0045] When the d-axis voltage command value Vd* and the q-axis voltage command value Vq* exceed the input voltage of the inverter circuit 2, the voltage limiter 19 limits the d-axis voltage command value Vd* and / or the q-axis voltage command value Vq* so that they are equal to or lower than the input voltage of the inverter circuit 2. The voltage limiter 19 of the present embodiment limits the filtered d-axis voltage command value Vd* and / or the q-axis voltage command value Vq* so that they are equal to or lower than the input voltage of the inverter circuit 2 when the filtered d-axis voltage command value Vd* and the q-axis voltage command value Vq* exceed the input voltage of the inverter circuit 2.

[0046] Here, since the filtered d-axis voltage command value Vd* and q-axis voltage command value Vq* in the present embodiment are obtained by filtering the d-axis voltage command value Vd* and q-axis voltage command value Vq* output from the current control unit 13, it can be said that they are the d-axis voltage command value Vd* and q-axis voltage command value Vq* output from the current control unit 13.

[0047] In the voltage limiter 19, various known methods can be adopted to limit the d-axis voltage command value Vd* and / or q-axis voltage command value Vq*. Examples of the limiter include a fixed-phase limiter that limits only the voltage amplitude while maintaining the voltage phase, a d-axis priority limiter that limits only the q-axis voltage while maintaining the d-axis voltage, and the like. When limit processing is required (when the filtered d-axis voltage command value Vd* and q-axis voltage command value Vq* exceed the input voltage of the inverter circuit 2), the voltage limiter 19 limits at least one of the d-axis voltage command value Vd* and q-axis voltage command value Vq* and outputs it to the second coordinate conversion unit 15. When limit processing is not required, the voltage limiter 19 outputs the input d-axis voltage command value Vd* and q-axis voltage command value Vq* to the second coordinate conversion unit 15.

[0048] Here, strictly speaking, the d-axis voltage command value Vd* and q-axis voltage command value Vq* output from the current control unit 13, the filtered d-axis voltage command value Vd* and q-axis voltage command value Vq*, and the limited d-axis voltage command value Vd* and q-axis voltage command value Vq* are different values. However, in the present invention, the above three d-axis voltage command values Vd* and q-axis voltage command values Vq* are expressed as the d-axis voltage command value Vd* and q-axis voltage command value Vq*.

[0049] The second coordinate conversion unit 15 receives the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from the limiting unit 14. In the present embodiment, the second coordinate conversion unit 15 receives the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from the voltage limiter 19. The second coordinate conversion unit 15 uses the position θ^ output from the estimation unit 7 to convert the input d-axis voltage command value Vd* and q-axis voltage command value Vq* into voltage command values Vu*, Vv*, Vw* corresponding to the U-phase, V-phase, and W-phase of the motor M. The second coordinate conversion unit 15 outputs the voltage command values Vu*, Vv*, Vw* to the drive circuit 4.

[0050] The second coordinate conversion unit 15 converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into voltage command values Vu*, Vv*, Vw* using, for example, the conversion matrix C2 shown in the following formula (10).

[0051]

Equation

[0052] The second coordinate conversion unit 15 outputs the voltage command values Vu*, Vv*, Vw* to the drive circuit 4.

[0053] The specifying unit 16 compares the amplitude of the 6th harmonic component superimposed on the d-axis current Id and / or the q-axis current Iq with the amplitude of the 3rd harmonic component, and specifies the harmonic component with the larger amplitude. As shown in FIG. 2, the specifying unit 16 includes a first filter 160 and a second filter 161. The first filter 160 receives the d-axis current Id and / or the q-axis current Iq and allows only the 6th harmonic component to pass through. That is, it can be said that the first filter 160 has a time constant that makes the gain of the 3rd harmonic component smaller than the gain of the 6th harmonic component. The second filter 161 receives the d-axis current Id and / or the q-axis current Iq and allows only the 3rd harmonic component to pass through. That is, it can be said that the second filter 161 has a time constant that makes the gain of the 6th harmonic component smaller than the gain of the 3rd harmonic component.

[0054] Note that the time constant of the first filter of the present invention only needs to be a time constant that makes the gain of a harmonic component of a predetermined order, which is larger than the amplitude of the 6th harmonic component among the harmonic components of the 5th order or lower superimposed on the d-q coordinate system, smaller than the gain of the 6th harmonic component. Further, the time constant of the second filter of the present invention only needs to be a time constant that makes the gain of the 6th harmonic component smaller than the gain of a harmonic component of a predetermined order, which is larger than the amplitude of the 6th harmonic component among the harmonic components of the 5th order or lower superimposed on the d-q coordinate system.

[0055] The specifying unit 16 specifies which of the 3rd harmonic component and the 6th harmonic component is larger based on the amplitude of the output signal from the first filter 160 and the amplitude of the output signal from the second filter 161. That is, the specifying unit 16 is provided in the control device 3 where there are cases where the amplitude of the 6th harmonic component is the largest and the amplitude of the 3rd harmonic component is the largest among the harmonic components of the 6th order or lower superimposed on the d-q coordinate system, and specifies the harmonic component with the largest amplitude among the harmonic components superimposed on the d-axis current Id and the q-axis current Iq obtained by converting the alternating currents Iu, Iv, and Iw flowing through each phase of the electric motor M. Therefore, it can be said that the specifying unit 16 specifies the harmonic component with the largest amplitude among the harmonic components superimposed on the current flowing through each phase of the electric motor M.

[0056] As a result of comparing the amplitude of the output signal from the first filter 160 and the amplitude of the output signal from the second filter 161, when the amplitude of the output signal from the first filter 160 is larger, the specifying unit 16 sends an instruction signal to the time constant changing unit 17 described later so that the time constant of the filter 18 becomes a time constant that makes the gain of the 6th harmonic component smaller than the gain of the 3rd harmonic component. Further, as a result of comparing the amplitude of the output signal from the first filter 160 and the amplitude of the output signal from the second filter 161, when the amplitude of the output signal from the second filter 161 is larger, the specifying unit 16 sends an instruction signal to the time constant changing unit 17 described later so that the time constant of the filter 18 becomes a time constant that makes the gain of the 3rd harmonic component smaller than the gain of the 6th harmonic component.

[0057] Based on the instruction signal from the specifying unit 16, the time constant changing unit 17 changes the time constant of the filter 18.

[0058] As described above, in the control device 3 of the control system 1 according to the present embodiment, the specifying unit 16 compares the amplitude of the sixth-order harmonic component and the amplitude of the third-order harmonic component superimposed on the d-q coordinate system, and specifies the harmonic component with the larger amplitude. Based on the instruction signal from the specifying unit 16, the time constant changing unit 17 changes the time constant of the filter 18. Thereby, in the control device 3, for example, when the sixth-order harmonic component is dominant in the harmonic components superimposed on the d-q coordinate system, the sixth-order harmonic component can be attenuated by the filter 18, and when the harmonic components of a predetermined order of the fifth order or lower are dominant in the harmonic components superimposed on the d-q coordinate system, the harmonic components of a predetermined order of the fifth order or lower can be attenuated by the filter 18. In this way, in the control device 3, not only the sixth-order harmonic component superimposed on the d-q coordinate system but also the harmonic components of a predetermined order of the fifth order or lower superimposed on the d-q coordinate system can be attenuated. Therefore, in the control device 3, when controlling the electric motor M by vector control in the overmodulation region of the inverter circuit 2, torque ripple can be reduced.

[0059] In the control system 1 according to the present embodiment, the specifying unit 16 of the control device 3 includes a first filter 160 that allows only the sixth-order harmonic component to pass through and a second filter 161 that allows only the third-order harmonic component to pass through. The specifying unit 16 compares the amplitude of the output current of the first filter 160 and the amplitude of the output current of the second filter 161, and specifies the harmonic component with the larger amplitude. With this configuration, among the harmonic components superimposed on the current flowing through each phase of the electric motor M, the harmonic component with the largest amplitude can be specified.

[0060] In the control system 1 according to this embodiment, the filter 18 of the control device 3 receives the d-axis voltage command value Vd* and the q-axis voltage command value Vq*. With this configuration, in vector control that performs current feedback control in the d-q coordinate system, it is possible to improve responsiveness.

[0061] As described above, the embodiments of the present invention have been described. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the gist thereof.

[0062] In the above embodiment, in the specific unit 16, as an example, the amplitude of the output current of the first filter 160 and the amplitude of the output current of the second filter 161 are compared, and the harmonic component with the larger amplitude among the 6th harmonic component and the 3rd harmonic component is specified. However, the specific unit may specify the harmonic component with the largest amplitude by other methods.

[0063] As shown in FIG. 3, in the control system 1A, the specific unit 16A of the control device 3A receives a signal from the estimation unit 7. The specific unit 16A acquires the electrical angular frequency of the electric motor M using the position θ^ output from the estimation unit 7. The specific unit 16A specifies the harmonic component with the largest amplitude based on the number of maximum or minimum values of the d-axis current Id and / or the q-axis current Iq in one cycle of the electrical angular frequency. For example, when the number of maximum values of the d-axis current Id and / or the q-axis current Iq in one cycle of the electrical angular frequency is 6, the specific unit 16A specifies that the harmonic component with the largest amplitude is the 6th order. For example, when the number of maximum values of the d-axis current Id and / or the q-axis current Iq in one cycle of the electrical angular frequency is 3, the specific unit 16A specifies that the harmonic component with the largest amplitude is the 3rd order. Even in this case, the harmonic component with the largest amplitude can be specified.

[0064] Further, the specific unit 16A may specify the harmonic component with the largest amplitude based on the slope of the d-axis current Id and / or the q-axis current Iq in one cycle of the electrical angular frequency. Even in this case, the harmonic component with the largest amplitude can be specified.

[0065] In the above embodiment, the form in which the position θ^ is calculated in the estimation unit 7 has been described as an example. However, as shown in FIG. 4, the control system 1B may include a position detection unit Sp. The position detection unit Sp detects the position θ of the rotor of the electric motor M and outputs the position θ to the control device 3. The position detection unit Sp is, for example, a resolver or the like.

[0066] In the control system 1B, the first coordinate conversion unit 6B of the control device 3B uses the position θ detected by the position detection unit Sp for each control cycle to convert the alternating current Iu, Iv, Iw detected by the current sensors Se1 to Se3 into the d-axis current Id and the q-axis current Iq. The first coordinate conversion unit 6B converts the alternating current Iu, Iv, Iw into the d-axis current Id and the q-axis current Iq using the conversion matrix C1 shown in the above formula (1). In the above formula (1), replace the position θ^ with the position θ.

[0067] The estimation unit 7B estimates the rotational speed ω^ of the rotor of the electric motor M using the position θ detected by the position detection unit Sp for each control cycle. For example, the estimation unit 7B estimates the rotational speed ω^ by dividing the position θ by the control cycle of the control device 3.

[0068] The second coordinate conversion unit 15B uses the position θ detected by the position detection unit Sp for each control cycle to convert the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into the voltage command value Vu*, the voltage command value Vu*, and the voltage command value Vw*. The second coordinate conversion unit 15B converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into the voltage command value Vu*, the voltage command value Vv*, and the voltage command value Vw* using the conversion matrix C2 shown in the above formula (10). In the above formula (10), replace the position θ^ with the position θ.

[0069] In the above embodiment, the specifying units 16, 16A have been described as an example of a form in which the harmonic component having the largest amplitude is specified using the d-axis current Id and the q-axis current Iq. However, the specifying units 16, 16A may specify the harmonic component having the largest amplitude using at least one of the alternating currents Iu, Iv, Iw flowing through each phase of the electric motor M.

[0070] Among the harmonic components superimposed on the alternating current Iu, Iv, Iw flowing through each phase of the electric motor M, there are cases where the amplitude of the fifth harmonic component is the largest among the harmonic components of the seventh order or lower, cases where the amplitude of the seventh harmonic component is the largest, and cases where the amplitude of the harmonic components of the fourth order or lower is the largest. In the alternating current Iu, Iv, Iw, when the amplitude of at least one of the fifth harmonic component and the seventh harmonic component is the highest among the harmonic components of the seventh order or lower, the amplitude of the sixth harmonic component becomes the largest among the harmonic components superimposed on the d-q coordinate system. Therefore, when the specific parts 16, 16A identify the harmonic component with the largest amplitude among the harmonic components of the seventh order or lower superimposed on the alternating current Iu, Iv, Iw using the alternating current Iu, Iv, Iw, they may be provided with a filter that allows only the fifth harmonic component to pass through, a filter that allows only the seventh harmonic component to pass through, and a filter that allows at least one harmonic component among the harmonic components of the fourth order or lower to pass through. Even in this case, it is possible to identify the harmonic component with the largest amplitude among the harmonic components superimposed on the current flowing through each phase of the electric motor M.

[0071] In the above embodiment, an example has been described in which the d-axis voltage command value Vd* and the q-axis voltage command value Vq* filtered by the filter 18 are input to the voltage limiter 19, but the present invention is not limited to this. For example, a form in which the d-axis voltage command value Vd* and the q-axis voltage command value Vq* generated by the current control unit 13 are input to the voltage limiter 19 may be used. In this case, the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from the voltage limiter 19 are output to the filter 18.

[0072] In the above embodiment, an example of a form in which the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from the current control unit 13 are input to the filter 18, and the d-axis voltage command value Vd* and the q-axis voltage command value Vq* subjected to filter processing are output to the voltage limiter 19 has been described, but the present invention is not limited to this. The filter 18 may be provided anywhere in the control device 3 as long as the amplitude of the sixth-order harmonic component superimposed on the d-q coordinate system is smaller than the amplitude of the harmonic components of a predetermined order of the fifth order or lower superimposed on the d-q coordinate system, and the amplitude of the harmonic components of a predetermined order of the fifth order or lower superimposed on the d-q coordinate system can be made smaller than the amplitude of the sixth-order harmonic component.

[0073] In the above embodiment, an example of a form in which the estimation unit 7 estimates the rotational speed (rotation speed) ω^ and the position θ^ of the rotor of the electric motor M using the d-axis voltage command value Vd* and the q-axis voltage command value Vq* processed by the filter 18 has been described, but the present invention is not limited to this. For example, the rotational speed (rotation speed) ω^ and the position θ^ of the rotor of the electric motor M may be estimated using the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from the voltage limiter 19.

[0074] The position estimation accuracy in the estimation unit 7 is improved when the position is estimated using a value closer to the voltage applied to the inverter circuit 2 finally. It is preferable that the estimation unit 7 estimates the rotational speed (rotation speed) ω^ and the position θ^ of the rotor of the electric motor M using the d-axis voltage command value Vd* and the q-axis voltage command value Vq* processed by the filter 18.

[0075] In the above embodiment, an example of a form in which the filter 18 is a band elimination filter (BEF) has been described. However, the filter 18 may be composed of a low-pass filter and a high-pass filter.

Explanation of Reference Numerals

[0076] 2... Inverter circuit (inverter), 3, 3A, 3B... Control device, 6... First coordinate conversion unit (first conversion unit), 13... Current control unit, 14... Limiting unit, 15... Second coordinate conversion unit (second conversion unit), 16, 16A... Specifying unit, 17... Time constant change unit, 18... Filter (variable filter), 19... Voltage limiter (voltage limiting unit), 160... First filter, 161... Second filter, Id... d-axis current, Id*... d-axis current command value, Iq... q-axis current, Iq*... q-axis current command value, Iu, Iv, Iw... Currents, M... Motor, Vd*... d-axis voltage command value, Vq*... q-axis voltage command value, Vu, Vv, Vw... Voltage command values.

Claims

1. A first conversion unit that converts the current flowing through each phase of the motor into a d-axis current and a q-axis current; A current control unit that generates a d-axis voltage command value and a q-axis voltage command value based on the d-axis current and the q-axis current converted by the first conversion unit, and a d-axis current command value and a q-axis current command value; A voltage limiting unit that receives the d-axis voltage command value and the q-axis voltage command value, and limits the d-axis voltage command value and / or the q-axis voltage command value so that they are equal to or less than the input voltage when the d-axis voltage command value and the q-axis voltage command value exceed the input voltage of the inverter, and a variable filter whose time constant can be changed; A second conversion unit that converts the d-axis voltage command value and the q-axis voltage command value output from the limiting unit into voltage command values corresponding to each phase of the motor, and outputs the voltage command values; A specifying unit that specifies the harmonic component with the largest amplitude among the harmonic components superimposed on the current flowing through each phase of the motor; A time constant changing unit that changes the time constant of the variable filter so as to reduce the gain of the harmonic component corresponding to the harmonic component specified by the specifying unit, and a control device that performs overmodulation control on the inverter, The variable filter has a time constant that makes the gain of the 6th harmonic component smaller than the gain of the harmonic components of a predetermined order of 5th or lower, and a time constant that makes the gain of the harmonic components of the predetermined order smaller than the gain of the 6th harmonic component, the control device.

2. The specifying unit A first filter that receives at least one of the d-axis current and the q-axis current and has a time constant that makes the gain of the harmonic components of the predetermined order smaller than the gain of the 6th harmonic component, and a first filter that receives at least one of the d-axis current and the q-axis current and has a time constant that makes the gain of the 6th harmonic component smaller than the gain of the harmonic components of the predetermined order, and The control device according to claim 1, wherein the amplitude of the output current of the first filter is compared with the amplitude of the output current of the second filter, and the harmonic component with the larger amplitude is specified.

3. The control device according to claim 1, wherein the specific unit acquires an electrical angular frequency of the electric motor, and based on a number of maximum values or minimum values of currents flowing in at least one of currents flowing in each phase of the electric motor in one period of the electrical angular frequency or at least one of the d-axis current and the q-axis current, identifies a harmonic component having the largest amplitude.

4. The control device according to any one of claims 1 to 3, wherein the variable filter receives the d-axis voltage command value and the q-axis voltage command value.

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