JP2021097436A - Control device of electric motor - Google Patents

Abstract

To prevent the controllability of driving an electric motor from being lowered due to a high-frequency current included in an AC current flowing through the electric motor.SOLUTION: A control device 1 includes an inverter circuit 2 that drives an electric motor M by turning on and off switching elements SW1 to SW6, and a control circuit 3 that turns on and off the switching elements SW1 to SW6 by drive signals S1 to S6 according to the comparison result of voltage command values Vu*, Vv*, and Vw* and a carrier wave, and the control circuit 3 corrects the voltage command values Vu*, Vv*, and Vw* depending on the polarities of AC currents Iu, Iv, and Iw flowing in an electronic motor M during a dead time when the switching elements connected in series with each other are prohibited from being turned on at the same time, and makes a frequency f of the carrier wave in a certain period T1 before and after the AC current flowing through the electronic motor M becomes zero larger than a frequency f of the carrier wave in a period T2 other than the certain period T1.SELECTED DRAWING: Figure 1

Description

The present invention relates to a control device for an electric motor.

As a control device for a motor, the alternating current flowing through the motor is converted into a d-axis current and a q-axis current, and the voltage command value is such that the d-axis current and the q-axis current approach the d-axis current command value and the q-axis current command value. Is obtained, and the drive of the motor is controlled by turning on and off the plurality of switching elements provided in the inverter circuit by the drive signal according to the comparison result between the voltage command value and the carrier, that is, the motor by so-called vector control. There is something that controls the drive of.

Further, as another control device of the electric motor, there is a device that corrects the voltage command value by the polarity of the alternating current in the dead time when the switching elements connected in series with each other are prohibited from being turned on at the same time.

However, in the above other control devices, when the AC current is close to zero, the polarity of the AC current is frequently switched by the high frequency current included in the AC current, so that the correction accuracy of the voltage command value in the dead time is lowered, and the motor There is a risk that the controllability of the drive will be reduced.

Therefore, as another control device, there is a device that relatively increases the d-axis current command value. By making the d-axis current command value relatively large in this way, the amplitude value of the alternating current becomes large, and the slope of the alternating current near zero becomes large. As a result, it is possible to suppress frequent switching of the polarity of the alternating current due to the high-frequency current, and thus it is possible to suppress a decrease in the correction accuracy of the voltage command value during the dead time. Patent Document 1 is a related technique.

Japanese Unexamined Patent Publication No. 2015-126641

However, in a control device in which the d-axis current command value is relatively large, not only the amplitude value of the alternating current but also the amplitude value of the high-frequency current included in the alternating current is large, so that the polarity of the alternating current is prevented from being frequently switched. It may not be possible.

Therefore, an object of the present invention is to provide a motor control device capable of suppressing a decrease in controllability of driving of a motor due to a high frequency current included in an alternating current flowing through the motor. is there.

A plurality of motor control devices according to the present invention are provided by an inverter circuit that drives a motor by turning on and off a plurality of switching elements, and a drive signal according to a comparison result between a voltage command value and a carrier. It is equipped with a control circuit that turns on and off the switching element of.

The control circuit corrects the voltage command value by the polarity of the alternating current flowing through the motor during the dead time when switching elements connected in series with each other are prohibited from turning on at the same time, and at the same time, in a certain period before and after the alternating current becomes zero. The frequency of the carrier wave is made larger than the frequency of the carrier wave in a period other than a certain period.

As a result, the amplitude value of the high-frequency current included in the alternating current can be reduced during the dead time within a certain period of time, so that it is possible to suppress frequent switching of the polarity of the alternating current. Therefore, the correction accuracy of the voltage command value can be improved, and the deterioration of the controllability of the drive of the electric motor can be suppressed.

Further, the control circuit converts the alternating current into d-axis current and q-axis current, obtains the voltage command value so that the d-axis current and q-axis current approach the d-axis current command value and the q-axis current command value, and at the same time, obtains the voltage command value. The d-axis current command value in a fixed period is made larger than the d-axis current command value in a period other than the fixed period.

As a result, the slope of the alternating current becomes relatively large in a certain period of time, so that it is possible to further suppress the frequent switching of the polarity of the alternating current during the dead time within a certain period of time. Therefore, the correction accuracy of the voltage command value can be further improved, and the deterioration of the controllability of the drive of the motor can be further suppressed.

According to the present invention, it is possible to suppress a decrease in controllability of driving of an electric motor due to a high frequency current included in an alternating current flowing through the electric motor.

It is a figure which shows an example of the control device of the electric motor of an embodiment. It is a flowchart which shows an example of the operation of the control circuit in Example 1. FIG. It is a figure which shows the relationship between an alternating current, a threshold value, and a carrier wave in Example 1. FIG. It is a flowchart which shows an example of the operation of the control circuit in Example 2. It is a figure which shows the relationship between an alternating current, a threshold value, and a carrier wave in Example 2. FIG.

Hereinafter, embodiments will be described in detail based on the drawings.
FIG. 1 is a diagram showing an example of a control device for an electric motor according to an embodiment.

The control device 1 shown in FIG. 1 controls the drive of the electric motor M mounted on a vehicle such as an electric forklift or a plug-in hybrid vehicle, and includes an inverter circuit 2, a control circuit 3, and a current sensor Se1. ~ Se3 is provided.

The inverter circuit 2 drives the motor M by the DC power supplied from the DC power supply P, and includes a capacitor C and switching elements SW1 to SW6 (for example, an IGBT (Insulated Gate Bipolar Transistor)). That is, one end of the capacitor C is connected to the positive electrode terminal of the DC power supply P and each collector terminal of the switching elements SW1, SW3, SW5, and the other end of the capacitor C is the negative electrode terminal of the DC power supply P and the switching elements SW2, SW4, SW6. It is connected to each emitter terminal of. 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 U-phase input terminal 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 V-phase input terminal 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 W phase input terminal of the motor M via the current sensor Se3.

Capacitor C smoothes the voltage V _in input to the inverter circuit 2 is output from the DC power source P.

The switching element SW1 is turned on or off based on the drive signal S1 output from the control circuit 3. The switching element SW2 is turned on or off based on the drive signal S2 output from the control circuit 3. The switching element SW3 is turned on or off based on the drive signal S3 output from the control circuit 3. The switching element SW4 is turned on or off based on the drive signal S4 output from the control circuit 3. The switching element SW5 is turned on or off based on the drive signal S5 output from the control circuit 3. The switching element SW6 is turned on or off based on the drive signal S6 output from the control circuit 3. When the switching elements SW1 to SW6 are turned on or off, the DC power output from the DC power supply P is converted into three AC powers whose phases are 120 degrees different from each other, and the AC powers are the U phase of the motor M. The rotor of the motor M is rotated by being input to the input terminals of the V phase and the W phase.

The current sensors Se1 to Se3 are composed of a Hall element, a shunt resistor, and the like. The current sensor Se1 detects the alternating current Iu flowing in the U phase of the motor M and outputs it to the control circuit 3, and the current sensor Se2 detects the alternating current Iv flowing in the V phase of the motor M and outputs it to the control circuit 3. The current sensor Se3 detects the alternating current Iw flowing in the W phase of the motor M and outputs it to the control circuit 3. When the alternating currents Iu, Iv, and Iw are not particularly distinguished, they are simply referred to as alternating currents I.

The control circuit 3 includes a drive circuit 4 and a calculation unit 5.
The drive circuit 4 is composed of an IC (Integrated Circuit) or the like, and compares the voltage command values Vu *, Vv *, Vw * output from the arithmetic unit 5 with a carrier wave (triangle wave, sawtooth wave, reverse sawtooth wave, etc.). Then, the drive signals S1 to S6 according to the comparison result are output to the respective gate terminals of the switching elements SW1 to SW6. For example, when the voltage command value Vu * is equal to or higher than the carrier wave, the drive circuit 4 outputs a high-level drive signal S1 and outputs a low-level drive signal S2, and the voltage command value Vu * is smaller than the carrier wave. , The low-level drive signal S1 is output, and the high-level drive signal S2 is output. Further, the drive circuit 4 outputs a high-level drive signal S3 and a low-level drive signal S4 when the voltage command value Vv * is equal to or higher than the carrier wave, and the voltage command value Vv * is smaller than the carrier wave. , The low-level drive signal S3 is output, and the high-level drive signal S4 is output. Further, the drive circuit 4 outputs a high-level drive signal S5 and a low-level drive signal S6 when the voltage command value Vw * is equal to or higher than the carrier wave, and the voltage command value Vw * is smaller than the carrier wave. , The low-level drive signal S5 is output, and the high-level drive signal S6 is output.

The calculation unit 5 is composed of a microcomputer or the like, and includes a coordinate conversion unit 6, an estimation unit 7, a subtraction unit 8, a speed control unit 9, a d-axis current command value output unit 10, and subtraction units 11 and 12. , A current control unit 13 and a coordinate conversion unit 14 are provided. For example, by executing a program stored in a storage unit (not shown), the microcomputer executes a coordinate conversion unit 6, an estimation unit 7, a subtraction unit 8, a speed control unit 9, a d-axis current command value output unit 10, and subtraction. Units 11 and 12, current control unit 13, and coordinate conversion unit 14 are realized.

The coordinate conversion unit 6 converts the alternating currents Iu, Iv, and Iw detected by the current sensors Se1 to Se3 into the d-axis current Id and the q-axis current Iq using the position θ ^ output from the estimation unit 7. ..

For example, the coordinate conversion unit 6 converts the currents Iu, Iv, and Iw into the d-axis current Id and the q-axis current Iq by using the transformation matrix C1 shown in the following equation 1.

The estimation unit 7 uses the d-axis voltage command value Vd * and q-axis voltage command value Vq * output from the current control unit 13 and the d-axis current Id and q-axis current Iq output from the coordinate conversion unit 6. The rotation speed (rotation speed) ω ^ and the position θ ^ of the rotor of the motor M are estimated.

For example, the estimation unit 7 calculates the counter electromotive force ed ^ and the counter electromotive force eq ^ by the following equations 2 and 3. In addition, R shows the resistance included in the electric motor M, and L shows the inductance of the coil included in the electric transmitter M.

ed ^ = Vd * -R × Id + ω ^ × L × Id ・ ・ ・ Equation 2
eq ^ = Vq * -R x Iq-ω ^ x L x Iq ... Equation 3

Next, the estimation unit 7 calculates the error θe ^ by the following equation 4.

θe ^ = tan ^-1 (ed ^ / eq ^) ・ ・ ・ Equation 4

Next, the estimation unit 7 obtains the rotation speed ω ^ such that the error θe ^ becomes zero in the following equation 5. Kp indicates the constant of the proportional term of PI (Proportional Integral) control, and Ki indicates the constant of the integral term of PI control.

ω ^ = Kp × θe ^ + Ki × ∫ (θe ^) dt ・ ・ ・ Equation 5

Then, the estimation unit 7 calculates the position θ ^ by the following equation 6. Note that s indicates a Laplace operator.

θ ^ = (1 / s) × ω ^ ・ ・ ・ Equation 6

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

The speed control unit 9 converts the difference Δω output from the subtraction unit 8 into the q-axis current command value Iq *.

For example, the speed control unit 9 obtains the q-axis current command value Iq * such that the difference Δω becomes zero in the following equation 7.

IQ * = Kp × Δω ＋ Ki × ∫ (Δω) dt ・ ・ ・ Equation 7

The d-axis current command value output unit 10 outputs a predetermined d-axis current command value Id *.

The subtraction unit 11 calculates the difference ΔId between the d-axis current command value Id * output from the d-axis current command value output unit 10 and the d-axis current Id output from the coordinate conversion unit 6.

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 coordinate conversion unit 6.

The current control unit 13 converts the difference ΔId output from the subtraction unit 11 and the difference ΔIq output from the subtraction unit 12 into the d-axis voltage command value Vd * and the q-axis voltage command value Vq *.

For example, the current control unit 13 calculates the d-axis voltage command value Vd * using the following formula 8 and calculates the q-axis voltage command value Vq * using the following formula 9. Lq indicates the q-axis inductance of the coil included in the motor M, Ld indicates the d-axis inductance of the coil included in the motor M, and Ke indicates the induced voltage constant.

Vd * = Kp × ΔId + Ki × ∫ (ΔId) dt−ωLqIq ・ ・ ・ Equation 8
Vq * = Kp × ΔIq + Ki × ∫ (ΔIq) dt + ωLdId + ωKe ・ ・ ・ Equation 9

The coordinate conversion unit 14 converts the d-axis voltage command value Vd * and the q-axis voltage command value Vq * into voltage command values Vv *, Vv *, and Vw * using the position θ ^ output from the estimation unit 7. To do.

For example, the coordinate conversion unit 14 converts the d-axis voltage command value Vd * and the q-axis voltage command value Vq * into the voltage command values Vu *, Vv *, and Vw * using the conversion matrix C2 shown in the following equation 10. To do.

Alternatively, the coordinate conversion unit 14 sets the calculation result of the following equation 11 as the phase angle δ.

δ = tan ^-1 (−Vq * / Vd *) ・ ・ ・ Equation 11

Next, the coordinate conversion unit 14 sets the addition result of the phase angle δ and the position θ ^ as the target position θv.

Then, the coordinate conversion unit 14 refers to the information indicating the correspondence between the target position θv and the voltage command values Vu *, Vv *, and Vw * stored in advance in a storage unit (not shown), and refers to the target position. Obtain the voltage command values Vu *, Vv *, and Vw * corresponding to θv.

Further, when the target position θv exists within the dead time, the coordinate conversion unit 14 sets the rotation speed ω ^ to a desired rotation speed, or the q-axis current Iq (torque of the electric motor M) is desired q. The voltage command value Vu * is corrected by the polarity of the AC current Iu so that the shaft current Iq is obtained, the voltage command value Vv * is corrected by the polarity of the AC current Iv, and the voltage command value Vw is corrected by the polarity of the AC current Iw. * Correct. The dead time is the period during which the switching elements SW1 and SW2 connected in series with each other are prohibited from being turned on at the same time, the period during which the switching elements SW3 and SW4 connected in series with each other are prohibited from being turned on at the same time, and the period with which they are prohibited from being turned on at the same time. This is a period during which switching elements SW5 and SW6 connected in series are prohibited from being turned on at the same time. Specifically, the coordinate conversion unit 14 sets the drive signals S1 and S2 to the low level, the drive signals S3 and S4 to the low level, and the drive signals S5 and S6 to the low level in the dead time.

Further, the coordinate conversion unit 14 outputs the frequency f of the carrier wave to the drive circuit 4. The drive circuit 4 has drive signals S1 to S6 according to the comparison result between the voltage command values Vu *, Vv *, Vw * output from the coordinate conversion unit 14 and the carrier wave of the frequency f output from the coordinate conversion unit 14. Is output.

<Example 1>
In the control circuit 3 of the first embodiment, the frequency f of the carrier wave in Tu1 for a certain period before and after the AC current Iu becomes zero is made larger than the frequency f of the carrier wave in Tu2 for a period other than Tu1 for a certain period. Further, the control circuit 3 in the first embodiment makes the frequency f of the carrier wave in Tv1 for a certain period before and after the AC current Iv becomes zero larger than the frequency f of the carrier wave in Tv2 for a period other than Tv1 for a certain period. Further, the control circuit 3 in the first embodiment makes the frequency f of the carrier wave in Tw1 for a certain period before and after the AC current Iw becomes zero larger than the frequency f of the carrier wave in Tw2 for a period other than Tw1 for a certain period. When Tu1, Tv1 and Tw1 are not particularly distinguished for a certain period of time, it is simply referred to as T1 for a certain period of time. Further, when the period Tu2, Tv2, and Tw2 are not particularly distinguished, it is simply referred to as the period T2.

FIG. 2 is a flowchart showing an example of the operation of the control circuit 3 in the first embodiment.
When the absolute value of the alternating current I is equal to or less than the threshold value Is (step S11: Yes), the control circuit 3 sets the frequency f of the carrier wave to the frequency f1 in the coordinate conversion unit 14 (step S12). It is assumed that the threshold value Is is set in advance based on the alternating current I when the period in which the polarity of the alternating current I is frequently switched is the longest. The period in which the polarity of the alternating current I is frequently switched is defined as a period in which the number of times the polarity of the alternating current I is switched per unit time continues to be equal to or greater than a predetermined value.

On the other hand, when the absolute value of the alternating current I is larger than the threshold value Is (step S11: No), the control circuit 3 sets the frequency f of the carrier wave to the frequency f2 in the coordinate conversion unit 14 (step S13). It should be noted that frequency f1> frequency f2, and for example, frequency f1: frequency f2 = 2: 1 or frequency f1: frequency f2 = 4: 1.

Thereby, the frequency f of the carrier wave in the period when the absolute value of the AC current I is equal to or less than the threshold value Is can be made larger than the frequency f of the carrier wave in the period when the absolute value of the AC current I is larger than the threshold value Is. That is, the frequency f of the carrier wave in T1 for a certain period before and after the AC current I becomes zero can be made larger than the frequency f of the carrier wave in T2 for a period other than T1 for a certain period.

FIG. 3 is a diagram showing the relationship between the alternating current Iu, the threshold value Is, and the carrier wave in the first embodiment. The horizontal axis of the two-dimensional coordinates shown in FIG. 3 indicates the target position θv, and the horizontal axis indicates the current or voltage.

The control circuit 3 sets the frequency f of the carrier to the frequency f1 during the period when the positive alternating current Iu is equal to or less than the positive threshold Is or the negative alternating current Iu is equal to or less than the negative threshold Is (Tu1 for a certain period). Then, the frequency f of the carrier during the period (period Tu2) in which the positive alternating current Iu is larger than the positive threshold Is or the negative alternating current Iu is larger than the negative threshold Is is set to the frequency f2.

As a result, the frequency f of the carrier wave in the period Tu1 can be made larger than the frequency f of the carrier wave in the period Tu2.

Similarly, the control circuit 3 sets the frequency f of the carrier during the period (constant period Tv1) in which the positive alternating current Iv is equal to or less than the positive threshold Is or the negative alternating current Iv is equal to or less than the negative threshold Is. It is set to f1, and the frequency f of the carrier during the period (period Tv2) in which the positive AC current Iv is larger than the positive threshold Is or the negative AC current Iv is larger than the negative threshold Is is set to the frequency f2.

Thereby, the frequency f of the carrier wave in the period Tv1 can be made larger than the frequency f of the carrier wave in the period Tv2.

Further, the control circuit 3 sets the frequency f of the carrier during the period (constant period Tw1) in which the positive alternating current Iw is equal to or less than the positive threshold Is or the negative alternating current Iw is equal to or less than the negative threshold Is. Is set to, and the frequency f of the carrier during the period (period Tw2) in which the positive alternating current Iw is larger than the positive threshold value Is or the negative alternating current Iw is larger than the negative threshold value Is is set to the frequency f2.

As a result, the frequency f of the carrier wave in the period Tw1 can be made larger than the frequency f of the carrier wave in the period Tw2.

Generally, the larger the frequency f of the carrier wave, the smaller the amplitude value of the high frequency current included in the alternating current I.

Therefore, in the fixed period T1 before and after the AC current I becomes zero, the amplitude value of the high frequency current included in the AC current I can be made smaller than that in the period T2 other than the fixed period T1.

As described above, the control device 1 of the first embodiment has a configuration in which the frequency f of the carrier wave in the fixed period T1 before and after the alternating current I becomes zero is made larger than the frequency f of the carrier wave in the period T2 other than the fixed period T1. Therefore, the amplitude value of the high-frequency current included in the alternating current I can be made relatively small in T1 for a certain period of time. As a result, the amplitude value of the high-frequency current included in the alternating current I can be made relatively small during the dead time within T1 for a certain period of time, so that it is possible to suppress frequent switching of the polarity of the alternating current I. Therefore, the correction accuracy of the voltage command values Vu *, Vv *, and Vw * in the dead time can be improved, and the deterioration of the controllability of the drive of the motor M can be suppressed.

Further, since the control device 1 of the first embodiment has a configuration in which the frequency f of the carrier wave is relatively increased only in T1 for a certain period of one cycle of the rotor of the motor M, it is included in one cycle of the rotor. In all periods, the number of switchings of the switching elements SW1 to SW6 per unit time can be suppressed as compared with the case where the frequency f of the carrier wave is relatively increased, and the loss due to the increase in the number of switchings of the switching elements SW1 to SW6 is reduced. can do.

<Example 2>
The control circuit 3 in the second embodiment sets the d-axis current command value Id * in Tu1'for a certain period before and after the AC current Iu becomes zero from the d-axis current command value Id * in Tu2' for a period other than Tu1' for a certain period. Enlarge. Further, the control circuit 3 in the second embodiment sets the d-axis current command value Id * in Tv1'for a certain period before and after the AC current Iv becomes zero, and the d-axis current command value Id in Tv2'for a period other than Tv1' for a certain period. * Make it larger. Further, the control circuit 3 in the second embodiment sets the d-axis current command value Id * in the fixed period Tw1'before and after the AC current Iw becomes zero, and the d-axis current command value Id in the period Tw2'other than the fixed period Tw1'. * Make it larger. When Tu1', Tv1', and Tw1'for a certain period are not particularly distinguished, it is simply referred to as T1'for a certain period. Further, when the period Tu2', Tv2', and Tw2'are not particularly distinguished, it is simply referred to as the period T2'.

Further, in the control circuit 3 in the second embodiment, the frequency f of the carrier wave in the period Tu1'is made larger than the frequency f of the carrier wave in the period Tu2'. Further, in the control circuit 3 in the second embodiment, the frequency f of the carrier wave in the period Tv1'is made larger than the frequency f of the carrier wave in the period Tv2'. Further, in the control circuit 3 in the second embodiment, the frequency f of the carrier wave in the period Tw1'is made larger than the frequency f of the carrier wave in the period Tw2'.

FIG. 4 is a flowchart showing an example of the operation of the control circuit 3 in the second embodiment.
When the absolute value of the alternating current I is equal to or less than the threshold value Is (step S21: Yes), the control circuit 3 sets the d-axis current command value Id * to the d-axis current command value Id * in the d-axis current command value output unit 10. It is set to 1 (step S22), and the frequency f of the carrier wave is set to the frequency f1 in the coordinate conversion unit 14 (step S23).

On the other hand, when the absolute value of the AC current I is larger than the threshold value Is (step S21: No), the control circuit 3 sets the d-axis current command value Id * to the d-axis current command value Id in the d-axis current command value output unit 10. It is set to * 2 (step S24), and the frequency f of the carrier wave is set to the frequency f2 in the coordinate conversion unit 14 (step S25). The d-axis current command value Id * 1> d-axis current command value Id * 2. Further, frequency f1> frequency f2, and for example, frequency f1: frequency f2 = 2: 1 or frequency f1: frequency f2 = 4: 1.

As a result, the d-axis current command value Id * during the period when the absolute value of the AC current I is equal to or less than the threshold Is is made larger than the d-axis current command value Id * during the period when the absolute value of the AC current I is larger than the threshold Is. At the same time, the frequency f of the carrier during the period when the absolute value of the AC current I is equal to or less than the threshold Is can be made larger than the frequency f of the carrier during the period when the absolute value of the AC current I is larger than the threshold Is. That is, the d-axis current command value Id * in the fixed period T1'before and after the AC current I becomes zero can be made larger than the d-axis current command value Id * in the period T2'other than the fixed period T1'. The frequency f of the carrier wave in the fixed period T1'can be made larger than the frequency f of the carrier wave in the period T2'other than the fixed period T1'.

FIG. 5 is a diagram showing the relationship between the alternating current Iu, the threshold value Is, and the carrier wave in the second embodiment. The horizontal axis of the two-dimensional coordinates shown in FIG. 5 indicates the target position θv, and the horizontal axis indicates the current or voltage.

The control circuit 3 in the second embodiment is a d-axis current command during a period in which the positive alternating current Iu is equal to or less than the positive threshold Is or the negative alternating current Iu is equal to or less than the negative threshold Is (Tu1'for a certain period). In a period (period Tu2') in which the value Id * is set to the d-axis current command value Id * 1 and the positive alternating current Iu is greater than the positive threshold Is or the negative alternating current Iu is greater than the negative threshold Is. The d-axis current command value Id * is set to the d-axis current command value Id * 2.

Further, the control circuit 3 in the second embodiment is a carrier of a carrier during a period (a certain period of time Tu1') in which the positive alternating current Iu is equal to or less than the positive threshold Is or the negative alternating current Iu is equal to or less than the negative threshold Is. The frequency f is set to the frequency f1, and the frequency f of the carrier during the period (period Tu2') in which the positive AC current Iu is larger than the positive threshold Is or the negative AC current Iu is larger than the negative threshold Is is set to the frequency f2. Set to.

As a result, the d-axis current command value Id * in the fixed period Tu1'can be made larger than the d-axis current command value Id * in the period Tu2', and the frequency f of the carrier wave in the fixed period Tu1' can be set to the period Tu2'. It can be made larger than the frequency f of the carrier wave in.

Similarly, the control circuit 3 in the second embodiment d in a period (constant period Tv1') in which the positive alternating current Iv is equal to or less than the positive threshold Is or the negative alternating current Iv is equal to or less than the negative threshold Is. The axis current command value Id * is set to the d-axis current command value Id * 1, and the period during which the positive AC current Iv is larger than the positive threshold Is or the negative AC current Iv is larger than the negative threshold Is (period Tv2). The d-axis current command value Id * in ´) is set to the d-axis current command value Id * 2.

Further, the control circuit 3 in the second embodiment is a carrier of a carrier during a period (constant period Tv1') in which the positive alternating current Iv is equal to or less than the positive threshold Is or the negative alternating current Iv is equal to or less than the negative threshold Is. The frequency f is set to the frequency f1, and the frequency f of the carrier during the period (period Tv2') in which the positive AC current Iv is larger than the positive threshold Is or the negative AC current Iv is larger than the negative threshold Is is set to the frequency f2. Set to.

As a result, the d-axis current command value Id * in the fixed period Tv1'can be made larger than the d-axis current command value Id * in the period Tv2', and the frequency f of the carrier wave in the fixed period Tv1' can be set to the period Tv2'. It can be made larger than the frequency f of the carrier wave in.

Further, the control circuit 3 in the second embodiment has a d-axis during a period (constant period Tw1') in which the positive alternating current Iw is equal to or less than the positive threshold Is or the negative alternating current Iw is equal to or less than the negative threshold Is. A period in which the current command value Id * is set to the d-axis current command value Id * 1 and the positive AC current Iw is larger than the positive threshold Is or the negative AC current Iw is larger than the negative threshold Is (period Tw2'. ) Is set to the d-axis current command value Id * 2.

Further, the control circuit 3 in the second embodiment is a carrier of a carrier during a period (constant period Tw1') in which the positive alternating current Iw is equal to or less than the positive threshold Is or the negative alternating current Iw is equal to or less than the negative threshold Is. The frequency f is set to the frequency f1, and the frequency f of the carrier during the period (period Tw2') in which the positive alternating current Iw is larger than the positive threshold Is or the negative alternating current Iw is larger than the negative threshold Is is set to the frequency f2. Set to.

As a result, the d-axis current command value Id * in the fixed period Tw1'can be made larger than the d-axis current command value Id * in the period Tw2', and the frequency f of the carrier wave in the fixed period Tw1' can be set to the period Tw2'. It can be made larger than the frequency f of the carrier wave in.

In general, the larger the d-axis current command value Id *, the larger the amplitude value of the alternating current I.
Therefore, in the second embodiment, as compared with the first embodiment, the inclination of the alternating current I in a certain period before and after the alternating current I becomes zero becomes large, and it is further suppressed that the polarity of the alternating current I is frequently switched. Can be done.

As described above, in the control device 1 of the second embodiment, since not only the frequency f of the carrier wave but also the d-axis current command value Id * is relatively large in T1'for a certain period of time, the polarity of the alternating current I is frequently switched. Can be further suppressed. As a result, the correction accuracy of the voltage command values Vu *, Vv *, and Vw * can be further improved, and the deterioration of the controllability of the drive of the motor M can be further suppressed.

Further, the control device 1 of the second embodiment has a configuration in which the d-axis current command value Id * and the frequency f of the carrier are relatively large only in a certain period T1'of one cycle of the rotor of the motor M. In all periods of one cycle of the rotor, the current flowing through the switching elements SW1 to SW6 and the switching elements SW1 to SW1 are compared to the case where the d-axis current command value Id * and the frequency f of the carrier are relatively large. The number of switching times per unit time of the SW6 can be suppressed, and the loss due to the increase in the current flowing through the switching elements SW1 to SW6 and the loss due to the increase in the number of switching times of the switching elements SW1 to SW6 can be reduced.

Further, the present invention is not limited to the above embodiments, and various improvements and changes can be made without departing from the gist of the present invention.

The control device 1 of the above embodiment is configured to control the drive of the motor M by vector control, but may be configured to control the drive of the motor M by a control method other than vector control. For example, as a control method other than vector control, the control device 1 has voltage command values Vu *, Vv *, Vw * according to at least one of a rotation speed command value (target rotation speed) and a current command value (target torque). Is obtained, and the switching elements SW1 to SW6 are turned on and off by the drive signals S1 to S6 according to the comparison result between the voltage command values Vu *, Vv *, Vw * and the carrier.

Further, the control device 1 of the above embodiment has a configuration in which the position θ ^ estimated by the estimation unit 6 is output to the coordinate conversion units 6 and 14, but the electric motor M is detected by a detector such as an encoder or a resolver. The position θ of the rotor of the above may be output to the coordinate conversion units 6 and 14 instead of the position θ ^.

Further, although the control device 1 of the above embodiment is configured to include current sensors Se1 to Se3, it may be configured to include two current sensors of the current sensors Se1 to Se3. In this configuration, the control device 1 obtains the remaining alternating current using the two alternating currents detected by the two current sensors.

1 Control device 2 Inverter circuit 3 Control circuit 4 Drive circuit 5 Calculation unit 6 Coordinate conversion unit 7 Estimate unit 8 Subtraction unit 9 Speed control unit 10 d-axis current command value output unit 11 Subtraction unit 12 Subtraction unit 13 Current control unit 14 Coordinate conversion Department

Claims (2)

An inverter circuit that drives an electric motor by turning multiple switching elements on and off,
A control circuit that turns on and off the plurality of switching elements by a drive signal according to the comparison result between the voltage command value and the carrier wave, and
With
The control circuit corrects the voltage command value by the polarity of the alternating current flowing through the motor during the dead time when the switching elements connected in series with each other are prohibited from being turned on at the same time, and the alternating current becomes zero. A control device for an electric motor, wherein the frequency of the carrier wave in a certain period before and after is made larger than the frequency of the carrier wave in a period other than the fixed period. The motor control device according to claim 1.
The control circuit converts the alternating current into a d-axis current and a q-axis current, and obtains the voltage command value so that the d-axis current and the q-axis current approach the d-axis current command value and the q-axis current command value. At the same time, the control device for the electric motor is characterized in that the d-axis current command value in the fixed period is made larger than the d-axis current command value in a period other than the fixed period.

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