Control device for an electric motor

Abstract

A control device (1) is constituted by a control circuit (3). The control circuit (3) obtains voltage command values (Vu*, Vv*, Vw*) in such a way that the d-axis current (Id) and the q-axis current (Iq) approach the d-axis current command value (Id*) and the q-axis current command value (Iq*), and turns on and off switching elements (SW1 to SW6) according to drive signals (S1 to S6) corresponding to the comparison results between the voltage command values (Vu*, Vv*, Vw*) and a carrier wave. The control circuit (3) corrects the voltage command values (Vu*, Vv*, Vw*) according to the polarities of the alternating currents (Iu, Iv, Iw) during the dead time, and makes the d-axis current command value (Id*) during a predetermined period (T1) before and after the alternating currents (Iu, Iv, Iw) become zero greater than the d-axis current command value (Id*) during a period (T2) other than the predetermined period (T1).

Description

Technical Field

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

[0002] As a control device for an electric motor, there is a device that converts an alternating current flowing through the electric motor into a d-axis current and a q-axis current, obtains a voltage command value in such a way 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 turns on and off a plurality of switching elements included in an inverter circuit according to a drive signal corresponding to a comparison result between the voltage command value and a carrier wave, thereby controlling the drive of the electric motor. This device is a device that controls the drive of the electric motor by so-called vector control.

[0003] In addition, as another control device for an electric motor, there is a device that corrects a voltage command value according to the polarity of an alternating current during a dead time in which switching elements that are prohibited from being connected in series to each other are not turned on simultaneously.

[0004] However, in the above-described other control device, when the alternating current is near a zero value, the polarity of the alternating current is frequently switched by a high-frequency current included in the alternating current. Therefore, there is a concern that the correction accuracy of the voltage command value during the dead time is reduced and the controllability of the drive of the electric motor is reduced.

[0005] Therefore, as yet another other control device, there is a device that makes the d-axis current command value relatively large. In this way, by making the d-axis current command value relatively large, the amplitude value of the alternating current becomes large, and the slope of the alternating current near the zero value becomes large. As a result, it is possible to suppress the frequent switching of the polarity of the alternating current due to the high-frequency current. Therefore, it is possible to suppress the reduction in the correction accuracy of the voltage command value during the dead time. As a related technique, there is Patent Document 1.

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-126641

[0007] However, in the control device that makes the d-axis current command value relatively large, the amplitude value of the alternating current becomes large. Therefore, there is a concern about an increase in loss due to an increase in the current flowing through the switching elements and the like. Summary of the Invention

[0008] Therefore, an object of one aspect of the present invention is to provide a control device for an electric motor that suppresses a reduction in the controllability of the drive of the electric motor due to a high-frequency current included in an alternating current flowing through the electric motor and can reduce losses caused by an increase in the current flowing through switching elements and the like.

[0009] A control device for a form of electric motor according to the present invention includes: an inverter circuit that drives the motor by turning on and off a plurality of switching elements; and a control circuit that converts an alternating current flowing through the motor into a d-axis current and a q-axis current, obtains a voltage command value in such a manner 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 turns on and off the plurality of switching elements by a drive signal corresponding to a comparison result between the voltage command value and a carrier wave.

[0010] During a dead time in which switching elements that are prohibited from being connected in series simultaneously are turned on, the control circuit corrects the voltage command value according to the polarity of the alternating current, and makes the d-axis current command value in a predetermined period before and after the alternating current becomes zero greater than the d-axis current command value in a period other than the predetermined period.

[0011] As a result, the slope of the alternating current in the predetermined period is relatively large. Therefore, it is possible to suppress frequent switching of the polarity of the alternating current during the dead time within the predetermined period. Therefore, it is possible to improve the correction accuracy of the voltage command value and suppress a decrease in the controllability of the drive of the motor.

[0012] In addition, it is configured such that the d-axis current command value Id* is relatively large only in a predetermined period within one cycle of the rotor of the motor. Therefore, compared with the case where the d-axis current command value Id* is relatively large throughout one cycle of the rotor, it is possible to suppress the current flowing through the switching elements and the like, and reduce the loss caused by an increase in the current flowing through the switching elements and the like.

[0013] In addition, the control circuit can make the frequency of the carrier wave in the predetermined period greater than the frequency of the carrier wave in a period other than the predetermined period.

[0014] As a result, during the dead time within the predetermined period, it is possible to make the amplitude value of the high-frequency current contained in the alternating current small. Therefore, it is possible to further suppress frequent switching of the polarity of the alternating current. Therefore, it is possible to further improve the correction accuracy of the voltage command value and further suppress a decrease in the controllability of the drive of the motor.

[0015] In addition, it is configured such that the d-axis current command value Id* and the frequency f of the carrier wave are relatively large only in a predetermined period within one cycle of the rotor of the motor M. Therefore, compared with the case where the d-axis current command value Id* and the frequency f of the carrier wave are relatively large throughout one cycle of the rotor, it is possible to suppress the current flowing through the switching elements and the like and the number of switching operations per unit time of the switching elements, and reduce the loss caused by an increase in the current flowing through the switching elements and the like and the loss caused by an increase in the number of switching operations of the switching elements.

[0016] According to the present invention, it is possible to suppress a situation where the controllability of driving of the motor is reduced due to high-frequency current contained in the alternating current flowing in the motor, and it is possible to reduce losses caused by an increase in the current flowing through the switching element. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. is an example of a control device for a motor according to an embodiment.

[0018] Figure 2 FIG. is a flowchart showing an example of the operation of the control circuit in Embodiment 1.

[0019] Figure 3 FIG. is a diagram showing the relationship between the alternating current, the threshold value, and the carrier wave in Embodiment 1.

[0020] Figure 4 FIG. is a flowchart showing an example of the operation of the control circuit in Embodiment 2.

[0021] Figure 5 FIG. is a diagram showing the relationship between the alternating current, the threshold value, and the carrier wave in Embodiment 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0023] Figure 1 FIG. is an example of a control device for a motor according to an embodiment.

[0024] Figure 1 The control device 1 shown is, for example, a device that controls the driving of a 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 current sensors Se1 to Se3.

[0025] The inverter circuit 2 is a circuit that drives the motor M with the DC power supplied from the DC power source P, and includes a capacitor C and switching elements SW1 to SW6 (for example, IGBT (Insulated Gate Bipolar Transistor)). That is, one end of the capacitor C is connected to the positive terminal of the DC power source P and the collector terminals of the switching elements SW1, SW3, and SW5, and 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 switching elements SW2, SW4, and SW6. 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.

[0026] The capacitor C smoothes the voltage Vin output from the DC power source P and input to the inverter circuit 2.

[0027] 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. The switching elements SW1 to SW6 are turned on or off respectively, so that the DC power output from the DC power source P is converted into three AC powers that are different with a phase interval of 120 degrees from each other, and the above AC powers are input to the input terminals of the U phase, V phase, and W phase of the motor M, so that the rotor of the motor M rotates.

[0028] The current sensors Se1 to Se3 are composed of Hall elements, shunt resistors, 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 circuit 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 circuit 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 circuit 3. In addition, when not particularly distinguishing the AC currents Iu, Iv, and Iw, it is only regarded as the AC current I.

[0029] The control circuit 3 includes a drive circuit 4 and an arithmetic unit 5.

[0030] The drive circuit 4 is composed of an IC (Integrated Circuit) or the like, compares the voltage command values Vu*, Vv*, Vw* output from the arithmetic unit 5 with a carrier wave (such as a triangular wave, a sawtooth wave, or an inverted sawtooth wave), and outputs drive signals S1 to S6 corresponding to the comparison results to the gate terminals of the switching elements SW1 to SW6 respectively. For example, when the voltage command value Vu* is above 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 smaller than the carrier wave, the drive circuit 4 outputs a low-level drive signal S1 and outputs a high-level drive signal S2. In addition, when the voltage command value Vv* is above 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. In addition, when the voltage command value Vw* is above 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 smaller than the carrier wave, the drive circuit 4 outputs a low-level drive signal S5 and outputs a high-level drive signal S6.

[0031] The arithmetic 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, subtraction units 11, 12, a current control unit 13, and a coordinate conversion unit 14. For example, by a microcomputer executing a program stored in a storage unit (not shown), the coordinate conversion unit 6, the estimation unit 7, the subtraction unit 8, the speed control unit 9, the d-axis current command value output unit 10, the subtraction units 11, 12, the current control unit 13, and the coordinate conversion unit 14 are realized.

[0032] The 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.

[0033] For example, the coordinate conversion unit 6 uses the conversion matrix C1 shown in the following Equation 1 to convert the currents Iu, Iv, Iw into a d-axis current Id and a q-axis current Iq.

[0034] [Mathematical Equation 1]

[0035]

[0036] The estimation unit 7 estimates the rotational speed (rotational velocity) ω^ and the position θ^ of the rotor of the motor M using the d-axis voltage command value Vd* and the q-axis voltage command value Vq* output from the current control unit 13 and the d-axis current Id and the q-axis current Iq output from the coordinate conversion unit 6.

[0037] For example, the estimation unit 7 calculates the back electromotive force ed^ and the back electromotive force eq^ according to the following equations (2) and (3). Further, R represents the resistance included in the motor M, and L represents the inductance of the coil included in the motor M.

[0038] ed^ = Vd* - R × Id + ω^ × L × Id ··· Equation (2)

[0039] eq^ = Vq* - R × Iq - ω^ × L × Iq ··· Equation (3)

[0040] Next, the estimation unit 7 calculates the error θe^ according to the following equation (4).

[0041] θe^ = tan-1(ed^ / eq^) ··· Equation (4)

[0042] Next, the estimation unit 7 obtains the rotational speed ω^ such that the error θe^ becomes zero in the following equation (5). Further, Kp represents the constant of the proportional term of the PI (Proportional Integral) control, and Ki represents the constant of the integral term of the PI control.

[0043] ω^ = Kp × θe^ + Ki × ∫(θe^)dt ··· Equation (5)

[0044] Moreover, the estimation unit 7 calculates the position θ^ by the following equation (6). Further, s represents the Laplace operator.

[0045] θ^ = (1 / s) × ω^ ··· Equation (6)

[0046] 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.

[0047] The speed control unit 9 converts the difference Δω output from the subtraction unit 8 into a q-axis current command value Iq*.

[0048] 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).

[0049] Iq* = Kp × Δω + Ki × ∫(Δω)dt ··· Equation (7)

[0050] The d-axis current command value output unit 10 outputs a predetermined d-axis current command value Id*.

[0051] 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.

[0052] 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.

[0053] 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 a d-axis voltage command value Vd* and a q-axis voltage command value Vq*.

[0054] For example, the current control unit 13 uses the following equation 8 to calculate the d-axis voltage command value Vd*, and uses the following equation 9 to calculate the q-axis voltage command value Vq*. In addition, Lq represents the q-axis inductance of the coil contained in the motor M, Ld represents the d-axis inductance of the coil contained in the motor M, and Ke represents the induced voltage constant.

[0055] Vd* = Kp × ΔId + Ki × ∫(ΔId)dt - ωLqIq ··· Equation 8

[0056] Vq* = Kp × ΔIq + Ki × ∫(ΔIq)dt + ωLdId + ωKe ··· Equation 9

[0057] The coordinate conversion unit 14 uses the position θ^ output from the estimation unit 7 to convert the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into voltage command values Vu*, Vv*, Vw*.

[0058] For example, the coordinate conversion unit 14 uses the conversion matrix C2 shown in the following equation 10 to convert the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into voltage command values Vu*, Vv*, Vw*.

[0059] [Mathematical formula 2]

[0060]

[0061] Alternatively, the coordinate conversion unit 14 uses the calculation result of the following equation 11 as the phase angle δ.

[0062] δ = tan -1 (-Vq* / Vd*) ··· Equation 11

[0063] Next, the coordinate conversion unit 14 uses the sum of the phase angle δ and the position θ^ as the target position θv.

[0064] Then, the coordinate conversion unit 14 refers to the information indicating the correspondence between the target position θv pre-stored in a storage unit (not shown) and the voltage command values Vu*, Vv*, Vw*, and obtains the voltage command values Vu*, Vv*, Vw* corresponding to the target position θv.

[0065] In addition, the coordinate conversion unit 14 corrects the voltage command value Vu* according to the polarity of the alternating current Iu, corrects the voltage command value Vv* according to the polarity of the alternating current Iv, and corrects the voltage command value Vw* according to the polarity of the alternating current Iw, so that when the target position θv exists within the dead time, the rotational speed ω^ becomes the desired rotational speed, or the q-axis current Iq (the torque of the motor M) becomes the desired q-axis current Iq. In addition, the dead time is the period during which the simultaneously connected switching elements SW1 and SW2 are prohibited from being turned on, the period during which the simultaneously connected switching elements SW3 and SW4 are prohibited from being turned on, and the period during which the simultaneously connected switching elements SW5 and SW6 are prohibited from being turned on. Specifically, during the dead time, the coordinate conversion unit 14 makes the drive signals S1 and S2 low level, makes the drive signals S3 and S4 low level, and makes the drive signals S5 and S6 low level.

[0066] In addition, the coordinate conversion unit 14 outputs the frequency f of the carrier wave to the drive circuit 4. The drive circuit 4 outputs drive signals S1 to S6 corresponding 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.

[0067] <Example 1>

[0068] In Example 1, the d-axis current command value Id* in the predetermined period Tu1 before and after the alternating current Iu becomes zero is greater than the d-axis current command value Id* in the period Tu2 other than the predetermined period Tu1. In addition, in Example 1, the d-axis current command value Id* in the predetermined period Tv1 before and after the alternating current Iv becomes zero is greater than the d-axis current command value Id* in the period Tv2 other than the predetermined period Tv1. In addition, in Example 1, the d-axis current command value Id* in the predetermined period Tw1 before and after the alternating current Iw becomes zero is greater than the d-axis current command value Id* in the period Tw2 other than the predetermined period Tw1. In addition, without particularly distinguishing the predetermined periods Tu1, Tv1, Tw1, they are only regarded as the predetermined period T1. In addition, without particularly distinguishing the periods Tu2, Tv2, Tw2, they are only regarded as the period T2.

[0069] Figure 2 It is a flowchart showing an example of the operation of the control circuit 3 in Example 1.

[0070] On the one hand, when the absolute value of the alternating current I is below the threshold Ith (step S11: Yes), in the d-axis current command value output unit 10, the d-axis current command value Id* is set to the d-axis current command value Id*1 (step S12). In addition, the threshold Ith is preset based on the alternating current I when the period of frequent switching of the polarity of the alternating current I becomes the longest. The period of frequent switching of the polarity of the alternating current I refers to the period during which the number of times of switching the polarity of the alternating current I per unit time is equal to or greater than a predetermined value.

[0071] On the other hand, when the absolute value of the alternating current I is greater than the threshold Ith (step S11: No), in the d-axis current command value output unit 10, the d-axis current command value Id* is set to the d-axis current command value Id*2 (step S13). In addition, the d-axis current command value Id*1 > the d-axis current command value Id*2 is adopted.

[0072] Thereby, it is possible to make the d-axis current command value Id* during the period when the absolute value of the alternating current I is below the threshold Ith greater than the d-axis current command value Id* during the period when the absolute value of the alternating current I is greater than the threshold Ith. That is, it is possible to make the d-axis current command value Id* during the predetermined period T1 before and after the alternating current I becomes zero greater than the d-axis current command value Id* during the period T2 other than the predetermined period T1.

[0073] Figure 3 It is a diagram showing the relationship between the alternating current Iu, the threshold Ith, and the carrier in the first embodiment. In addition, Figure 3 The horizontal axis of the two-dimensional coordinate shown represents the target position θv, and the vertical axis represents the current or voltage.

[0074] The control circuit 3 sets the d-axis current command value Id* during the period (predetermined period Tu1) when the positive alternating current Iu is below the positive threshold Ith or the negative alternating current Iu is below the negative threshold Ith to the d-axis current command value Id*1, and sets the d-axis current command value Id* during the period (period Tu2) when the positive alternating current Iu is greater than the positive threshold Ith or the negative alternating current Iu is greater than the negative threshold Ith to the d-axis current command value Id*2.

[0075] Thereby, it is possible to make the d-axis current command value Id* during the predetermined period Tu1 greater than the d-axis current command value Id* during the period Tu2.

[0076] Similarly, during a period (predetermined period Tv1) in which the positive AC current Iv is below the positive threshold Ith or the negative AC current Iv is below the negative threshold Ith, the control circuit 3 sets the d-axis current command value Id* to the d-axis current command value Id*1, and during a period (period Tv2) in which the positive AC current Iv is greater than the positive threshold Ith or the negative AC current Iv is greater than the negative threshold Ith, the control circuit 3 sets the d-axis current command value Id* to the d-axis current command value Id*2.

[0077] Thereby, the d-axis current command value Id* during the predetermined period Tv1 can be made greater than the d-axis current command value Id* during the period Tv2.

[0078] In addition, during a period (predetermined period Tw1) in which the positive AC current Iw is below the positive threshold Ith or the negative AC current Iw is below the negative threshold Ith, the control circuit 3 sets the d-axis current command value Id* to the d-axis current command value Id*1, and during a period (period Tw2) in which the positive AC current Iw is greater than the positive threshold Ith or the negative AC current Iw is greater than the negative threshold Ith, the control circuit 3 sets the d-axis current command value Id* to the d-axis current command value Id*2.

[0079] Thereby, the d-axis current command value Id* during the predetermined period Tw1 can be made greater than the d-axis current command value Id* during the period Tw2.

[0080] Generally, the larger the d-axis current command value Id*, the larger the amplitude value of the AC current I.

[0081] Thereby, the slope of the AC current I during a predetermined period T1 before and after the AC current I becomes zero is relatively large. Therefore, it is possible to suppress the frequent switching of the polarity of the AC current I due to high-frequency current.

[0082] In this way, in the control device 1 of the first embodiment, it is configured such that the d-axis current command value Id* during a predetermined period T1 before and after the AC current I becomes zero is greater than the d-axis current command value Id* during a period T2 other than the predetermined period T1. Therefore, it is possible to make the slope of the AC current I relatively large during the dead time within the predetermined period T1, and it is possible to suppress the frequent switching of the polarity of the AC current I due to high-frequency current. Therefore, it is possible to improve the correction accuracy of the voltage command values Vu*, Vv*, and Vw* during the dead time, and it is possible to suppress the deterioration of the controllability of the drive of the motor M.

[0083] In addition, the control device 1 of Embodiment 1 is configured to make the d-axis current command value Id* relatively large only during a predetermined period T1 in one cycle of the rotor of the motor M. Therefore, compared with the case where the d-axis current command value Id* is made relatively large during the entire period of one cycle of the rotor, it is possible to suppress the current flowing through the switching elements SW1 to SW6, etc., and reduce the loss caused by the increase in the current flowing through the switching elements SW1 to SW6, etc.

[0084] <Embodiment 2>

[0085] In Embodiment 2, the control circuit 3 can make the d-axis current command value Id* during a predetermined period Tu1' before and after the AC current Iu becomes zero greater than the d-axis current command value Id* during a period Tu2' other than the predetermined period Tu1'. In addition, the control circuit 3 in Embodiment 2 makes the d-axis current command value Id* during a predetermined period Tv1' before and after the AC current Iv becomes zero greater than the d-axis current command value Id* during a period Tv2' other than the predetermined period Tv1'. In addition, the control circuit 3 in Embodiment 2 makes the d-axis current command value Id* during a predetermined period Tw1' before and after the AC current Iw becomes zero greater than the d-axis current command value Id* during a period Tw2' other than the predetermined period Tw1'. In addition, without particularly distinguishing the predetermined periods Tu1', Tv1', Tw1', they are simply referred to as a predetermined period T1'. In addition, without particularly distinguishing the periods Tu2', Tv2', Tw2', they are simply referred to as a period T2'.

[0086] In addition, the control circuit 3 in Embodiment 2 makes the frequency f of the carrier during the predetermined period Tu1' greater than the frequency f of the carrier during the period Tu2'. In addition, the control circuit 3 in Embodiment 2 makes the frequency f of the carrier during the predetermined period Tv1' greater than the frequency f of the carrier during the period Tv2'. In addition, the control circuit 3 in Embodiment 2 makes the frequency f of the carrier during the predetermined period Tw1' greater than the frequency f of the carrier during the period Tw2'.

[0087] Figure 4 is a flowchart showing an example of the operation of the control circuit 3 in Embodiment 2.

[0088] When the absolute value of the AC current I is equal to or less than the threshold Ith (step S21: Yes), the control circuit 3 sets the d-axis current command value Id* to the d-axis current command value Id*1 in the d-axis current command value output unit 10 (step S22), and sets the frequency f of the carrier to the frequency f1 in the coordinate conversion unit 14 (step S23).

[0089] On the other hand, when the absolute value of the alternating current I is greater than the threshold Ith (step S21: No), in the d-axis current command value output unit 10, the d-axis current command value Id* is set to the d-axis current command value Id*2 (step S24), and in the coordinate conversion unit 14, the frequency f of the carrier wave is set to the frequency f2 (step S25). In addition, the d-axis current command value Id*1 > the d-axis current command value Id*2. Also, the frequency f1 > the frequency f2. For example, the frequency f1: the frequency f2 = 2:1 or the frequency f1: the frequency f2 = 4:1.

[0090] Thereby, during the period when the absolute value of the alternating current I is below the threshold Ith, the d-axis current command value Id* can be made greater than the d-axis current command value Id* during the period when the absolute value of the alternating current I is greater than the threshold Ith, and during the period when the absolute value of the alternating current I is below the threshold Ith, the frequency f of the carrier wave can be made greater than the frequency f of the carrier wave during the period when the absolute value of the alternating current I is greater than the threshold Ith. That is, the d-axis current command value Id* during a predetermined period T1' before and after the alternating current I becomes zero can be made greater than the d-axis current command value Id* during a period T2' other than the predetermined period T1', and the frequency f of the carrier wave during the predetermined period T1' can be made greater than the frequency f of the carrier wave during a period T2' other than the predetermined period T1'.

[0091] Figure 5 It is a diagram showing the relationship among the alternating current Iu, the threshold Ith, and the carrier wave in Embodiment 2. In addition, Figure 5 The horizontal axis of the two-dimensional coordinate shown represents the target position θv, and the vertical axis represents the current or voltage.

[0092] In the control circuit 3 in Embodiment 2, the d-axis current command value Id* during the period (predetermined period Tu1') when the positive alternating current Iu is below the positive threshold Ith or the negative alternating current Iu is below the negative threshold Ith is set to the d-axis current command value Id*1, and the d-axis current command value Id* during the period (period Tu2') when the positive alternating current Iu is greater than the positive threshold Ith or the negative alternating current Iu is greater than the negative threshold Ith is set to the d-axis current command value Id*2.

[0093] In addition, in the control circuit 3 in Embodiment 2, the frequency f of the carrier wave during the period (predetermined period Tu1') when the positive alternating current Iu is below the positive threshold Ith or the negative alternating current Iu is below the negative threshold Ith is set to the frequency f1, and the frequency f of the carrier wave during the period (period Tu2') when the positive alternating current Iu is greater than the positive threshold Ith or the negative alternating current Iu is greater than the negative threshold Ith is set to the frequency f2.

[0094] Thus, it is possible to make the d-axis current command value Id* in a given period Tu1' greater than the d-axis current command value Id* in a period Tu2', and it is possible to make the frequency f of the carrier wave in the given period Tu1' greater than the frequency f of the carrier wave in the period Tu2'.

[0095] Similarly, the control circuit 3 in Embodiment 2 sets the d-axis current command value Id* in a period (a given period Tv1') when the positive alternating current Iv is less than or equal to the positive threshold Ith or the negative alternating current Iv is less than or equal to the negative threshold Ith to the d-axis current command value Id*1, and sets the d-axis current command value Id* in a period (a period Tv2') when the positive alternating current Iv is greater than the positive threshold Ith or the negative alternating current Iv is greater than the negative threshold Ith to the d-axis current command value Id*2.

[0096] In addition, the control circuit 3 in Embodiment 2 sets the frequency f of the carrier wave in a period (a given period Tv1') when the positive alternating current Iv is less than or equal to the positive threshold Ith or the negative alternating current Iv is less than or equal to the negative threshold Ith to the frequency f1, and sets the frequency f of the carrier wave in a period (a period Tv2') when the positive alternating current Iv is greater than the positive threshold Ith or the negative alternating current Iv is greater than the negative threshold Ith to the frequency f2.

[0097] Thus, it is possible to make the d-axis current command value Id* in the given period Tv1' greater than the d-axis current command value Id* in the period Tv2', and it is possible to make the frequency f of the carrier wave in the given period Tv1' greater than the frequency f of the carrier wave in the period Tv2'.

[0098] In addition, the control circuit 3 in Embodiment 2 sets the d-axis current command value Id* in a period (a given period Tw1') when the positive alternating current Iw is less than or equal to the positive threshold Ith or the negative alternating current Iw is less than or equal to the negative threshold Ith to the d-axis current command value Id*1, and sets the d-axis current command value Id* in a period (a period Tw2') when the positive alternating current Iw is greater than the positive threshold Ith or the negative alternating current Iw is greater than the negative threshold Ith to the d-axis current command value Id*2.

[0099] In addition, the control circuit 3 in Embodiment 2 sets the frequency f of the carrier wave in a period (a given period Tw1') when the positive alternating current Iw is less than or equal to the positive threshold Ith or the negative alternating current Iw is less than or equal to the negative threshold Ith to the frequency f1, and sets the frequency f of the carrier wave in a period (a period Tw2') when the positive alternating current Iw is greater than the positive threshold Ith or the negative alternating current Iw is greater than the negative threshold Ith to the frequency f2.

[0100] Thus, it is possible to make the d-axis current command value Id* in the predetermined period Tw1' greater than the d-axis current command value Id* in the period Tw2', and make the frequency f of the carrier wave in the predetermined period Tw1' greater than the frequency f of the carrier wave in the period Tw2'.

[0101] Generally, the larger the frequency f of the carrier wave, the smaller the amplitude value of the high-frequency current contained in the alternating current I.

[0102] Therefore, in the predetermined period T1' before and after the alternating current I becomes zero, compared with the period T2' other than the predetermined period T1', it is possible to make the amplitude value of the high-frequency current contained in the alternating current I smaller. Therefore, it is possible to suppress the frequent switching of the polarity of the alternating current I in the predetermined period T1'.

[0103] In this way, in the control device 1 of the second embodiment, in the predetermined period T1', not only is the d-axis current command value Id* relatively large, but also the frequency f of the carrier wave is relatively large. Therefore, it is possible to further suppress the frequent switching of the polarity of the alternating current I. As a result, it is possible to further improve the correction accuracy of the voltage command values Vu*, Vv*, Vw*, and it is possible to further suppress the reduction in the controllability of the drive of the motor M.

[0104] In addition, the control device 1 of the second embodiment is configured to make the d-axis current command value Id* and the frequency f of the carrier wave relatively large only in the predetermined period T1' in one cycle of the rotor of the motor M. Therefore, compared with the case where the d-axis current command value Id* and the frequency f of the carrier wave are relatively large in the entire period of one cycle of the rotor, it is possible to suppress the current flowing through the switching elements SW1 to SW6, etc., and the number of switching operations per unit time of the switching elements SW1 to SW6, and it is possible to reduce the loss caused by the increase in the current flowing through the switching elements SW1 to SW6 and the loss caused by the increase in the number of switching operations of the switching elements SW1 to SW6.

[0105] In addition, 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.

[0106] The control device 1 of the above embodiment is configured to output the position θ^ estimated by the estimation unit 7 to the coordinate conversion units 6 and 14, but it may be configured to output the position θ of the rotor of the motor M detected by a detector such as an encoder or a resolver to the coordinate conversion units 6 and 14 instead of the position θ^.

[0107] In addition, the control device 1 of the above embodiment is configured to include the current sensors Se1 to Se3, but it may be configured to include two of the current sensors Se1 to Se3. In this case, the control device 1 uses the two alternating currents detected by the two current sensors to calculate the remaining alternating current.

[0108] Description of Reference Numerals

[0109] 1... Control device; 2... Inverter circuit; 3... Control circuit; 4... Drive circuit; 5... Arithmetic unit; 6... Coordinate conversion unit; 7... Estimation 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 unit.

Claims

1. A control device for an electric motor, characterized in that, Comprising: An inverter circuit that drives a motor by turning on and off a plurality of switching elements; And A control circuit that converts an alternating current flowing through the motor into a d-axis current and a q-axis current, obtains a voltage command value in such a manner 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 turns on and off the plurality of switching elements by a drive signal corresponding to a comparison result between the voltage command value and a carrier wave. During a dead time in which the switching elements prohibited from being connected in series are not turned on simultaneously, the control circuit corrects the voltage command value according to the polarity of the alternating current, and makes the d-axis current command value during a predetermined period before and after the alternating current becomes zero greater than the d-axis current command value during a period other than the predetermined period.

2. The control device for a motor according to claim 1, wherein The control circuit makes the frequency of the carrier wave during the predetermined period greater than the frequency of the carrier wave during a period other than the predetermined period.

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