JP6905186B2 - Power converter and its control method - Google Patents

Description

The present invention relates to a power conversion device that controls a d-axis current and a q-axis current supplied to a motor.

A power conversion device that controls a d-axis current and a q-axis current supplied to a motor is known. For example, Patent Document 1 discloses a control device for a multi-phase rotating machine that controls a command voltage according to a command current on the q-axis.

In the control device disclosed in Patent Document 1, when the q-axis command current increases, the d-axis command for keeping the arithmetic output voltage value of the inverter determined according to the command voltage within an allowable range. The current is calculated by closed loop control. As a result, in the control device disclosed in Patent Document 1, the amount of change in the d-axis current can be increased immediately after the q-axis command current is increased. Therefore, it is possible to appropriately respond to the demand for increasing the q-axis current such as when the required torque is increased.

Japanese Unexamined Patent Publication No. 2008-109798

By the way, as in the configuration disclosed in Patent Document 1 described above, in the control device (power conversion device) that controls the d-axis current and the q-axis current, the maximum value of the output voltage is determined, so that the q-axis voltage The maximum value of is also determined.

Here, assuming that the resistance of the motor is small and the d-axis current Id is controlled to be constant, the d-axis voltage Vd and the q-axis voltage Vq are expressed by the following equations according to the voltage equation of the motor. Note that w is the rotation speed, Lq is the q-axis inductance of the motor, and Iq is the q-axis current flowing through the motor. Further, φ is the induced voltage constant of the motor, and Ld is the d-axis inductance of the motor.
Vd = -w ・ Lq ・ Iq (1)
Vq = w · (φ + Ld · Id) + Lq · dIq / dt (2)

Further, the maximum value Vmax of the output voltage of the control device is expressed by the following equation.
Vmax = √ (Vd ² + Vq ² ) (3)

As shown in the equations (1) to (3), the maximum value of the q-axis voltage Vq is determined according to the maximum value Vmax of the output voltage. Further, the following equations can be obtained by the equations (1) to (3).
Lq ・ dIq / dt
= ± √ ((Vmax ^2- (w ・ Lq ・ Iq) ² ) -w ・ (φ + Ld ・ Id)) (4)

Since the upper limit value of dIq / dt (time change of q-axis current) is determined by the equation (4), the upper limit value of the torque change amount of the motor is also determined. That is, the upper limit of dIq / dt is determined according to the rotation speed w. For example, as the rotation speed w increases, w · (φ + Ld · Id) increases, so that the margin for increasing dIq / dt decreases.

Therefore, even if it is desired to increase the time change of the q-axis current in response to the torque command when the rotation speed of the motor is high, the time of the q-axis current is limited because the amount of time change of the q-axis current is limited as described above. The amount of change cannot be increased. In other words, if the torque command changes abruptly while the rotation speed of the motor is high, the waveform of the q-axis current may be distorted. Then, there is a possibility that the motor cannot be driven by following the change of the torque command with good responsiveness.

An object of the present invention is to obtain a configuration in which a motor can be driven with good responsiveness to a change in a torque command in a power conversion device that controls a d-axis current and a q-axis current.

The power conversion device according to the embodiment of the present invention is a power conversion device that controls the d-axis current and the q-axis current supplied to the motor. This power conversion device includes a current control unit that controls the d-axis current and the q-axis current supplied to the motor in response to an input q-axis current command. The current control unit refers to the motor when the time change of the input q-axis current command is larger than the upper limit of the time change of the q-axis current when the d-axis current is not flowing through the motor. A power conversion device (first configuration) in which the combined current of the d-axis current and the q-axis current is equal to or less than the maximum rated current of the motor and the d-axis current satisfies the following equation.
-2φ / Ld <Id <0
φ: Motor induced voltage constant Ld: Motor d-axis inductance Id: d-axis current

By passing a negative d-axis current as described above, there is a large margin for changing the q-axis current at the q-axis voltage determined by Vmax. As a result, even if the input torque command changes abruptly when the motor is rotating at high speed, a q-axis current can be passed through the motor in response to the torque command. Therefore, the responsiveness of the motor to a change in the torque command can be improved.

In the first configuration, the current control unit calculates the d-axis current from the following equation using the time change of the input q-axis current command (second configuration).
Lq ・ dIq / dt
= ± √ ((Vmax ^2- (w ・ Lq ・ Iq) ² ) -w ・ (φ + Ld ・ Id))

Thereby, the minimum d-axis current that can obtain the action and effect in the first configuration can be obtained. Therefore, it is possible to improve the responsiveness of the motor while suppressing the current consumption.

In the first or second configuration, the current control unit has the d-axis current, the combined current of the d-axis current and the q-axis current is equal to or less than the maximum rated current of the motor, and −φ / Set to Ld (third configuration).

As a result, the margin for changing the q-axis current can be maximized. Therefore, the responsiveness of the motor can be further improved.

The control method of the power conversion device according to the embodiment of the present invention is a control method of the power conversion device that controls the d-axis current and the q-axis current supplied to the motor. In this control method, when the time change of the input q-axis current command is larger than the upper limit of the time change of the q-axis current when the d-axis current is not flowing through the motor, the operation mode of the motor is set. When the operation mode determination step of determining the high response operation mode and the operation mode determination step of the operation mode determine that the operation mode of the motor is the high response operation mode, the d-axis current with respect to the motor. A method for controlling a power conversion device, which comprises a d-axis current adjusting step in which the combined current of the q-axis current is equal to or less than the maximum rated current of the motor and the d-axis current flows so as to satisfy the following equation.
-2φ / Ld <Id <0
φ: Motor induced voltage constant Ld: Motor d-axis inductance Id: d-axis current

According to the power conversion device according to the embodiment of the present invention, when the time change of the input q-axis current command is larger than the upper limit of the time change of the q-axis current when the d-axis current is not flowing through the motor. A d-axis current such that the combined current of the q-axis current and the d-axis current is equal to or less than the maximum rated current and satisfies -2φ / Ld <Id <0 is passed through the motor. As a result, the margin for changing the q-axis current is expanded, so that the responsiveness of the motor to a change in the torque command can be improved.

FIG. 1 is a block diagram showing a schematic configuration of a power conversion device according to an embodiment. FIG. 2 is a circuit diagram showing a schematic configuration of a control unit. FIG. 3 is a vector diagram of the q-axis voltage and the d-axis voltage. FIG. 4 is a diagram showing the relationship between the q-axis current command and the q-axis current flowing through the motor when the d-axis current is set to zero and the motor is rotated at high speed in the conventional configuration. FIG. 5 is a vector diagram of the q-axis voltage and the d-axis voltage when the d-axis current command is Id = −φ / Ld. FIG. 6 is a diagram showing the relationship between the q-axis current command and the q-axis current flowing through the motor when the d-axis current command is Id = −φ / Ld. FIG. 7 is a flow for explaining a method of controlling the d-axis current.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

(overall structure)
FIG. 1 is a diagram showing a schematic configuration of a power conversion device 1 according to an embodiment of the present invention. The power conversion device 1 controls the drive of the motor 2 based on the input signal, the rotation angle of the motor 2, and the current flowing through each phase of the motor 2. Specifically, the power conversion device 1 generates a PWM signal using an input signal, a rotation angle of the motor 2, and a current flowing in each phase of the motor 2, and controls the drive of the motor 2 using the PWM signal. .. The input signal includes a d-axis current input signal (d-axis current command) and a q-axis current input signal (q-axis current command).

In the present embodiment, the motor 2 is a three-phase AC motor having three-phase coils of U-phase, V-phase, and W-phase. Further, in the present embodiment, the motor 2 is an SPM motor (Surface Permanent Magnet Motor) in which a magnet is arranged on the outer surface of the rotor core.

The power conversion device 1 includes an inverter circuit 11 having a plurality of switching elements SW1 to SW6, and a control unit 20 (current control unit) that outputs a gate signal to the switching elements SW1 to SW6 of the inverter circuit 11.

The inverter circuit 11 has a plurality of switching elements SW1 to SW6 and diodes connected in parallel to the switching elements SW1 to SW6, respectively. In this embodiment, the inverter circuit 11 has six switching elements SW1 to SW6. The six switching elements SW1 to SW6 form a bridge circuit. A part of each of the six switching elements SW1 to SW6 is electrically connected to the U-phase, V-phase, and W-phase coils of the motor 2.

The current flowing between the inverter circuit 11 and the motor 2 is detected by the current detector 3. That is, the current detector 3 detects the current flowing from the inverter circuit 11 to each phase of the motor 2. The current of each phase detected by the current detector 3 is input to the control unit 20.

In FIG. 1, reference numeral 2a is a rotation angle detection unit that outputs the rotation angle of the rotor of the motor 2 as an angle signal.

The control unit 20 uses the input signal, the rotation angle of the motor 2 (angle signal), and the current flowing in each phase of the motor 2 (output of the current detector 3, Iu, Iv, Iw) to switch elements of the inverter circuit 11. Generates a gate signal to be output to SW1 to SW6. As shown in FIG. 2, the control unit 20 includes a mode determination unit 21, an Id signal generation unit 22, PI calculation units 23 and 24, a two-phase three-phase conversion unit 25, a PWM generation unit 26, and three phases. It has a two-phase conversion unit 27.

The mode determination unit 21 determines the operation mode of the motor 2 based on the q-axis current command input to the control unit 20. Specifically, when the amount of change per time of the q-axis current command (differential value of the q-axis current command) is larger than the threshold value, the mode determination unit 21 determines that the mode is a high-response operation mode, and other than that. In this case, it is determined to be the normal operation mode. The threshold is, for example, the upper limit of the amount of change per time of the q-axis current when no d-axis current flows in the motor 2. The upper limit of this amount of change is, for example, the upper limit of the amount of change such that the distortion of the waveform of the q-axis current does not affect the responsiveness of the motor 2.

When the mode determination unit 21 determines the normal operation mode, the Id signal generation unit 22 generates a d-axis current command that sets the d-axis current Id to zero, while the mode determination unit 21 sets the high response operation mode. If it is determined, a d-axis current command is generated so that the d-axis current becomes a predetermined value. The detailed configuration of the Id signal generation unit 22 will be described later.

The PI calculation unit 23 determines the difference between the q-axis current command input to the control unit 20 and the feedback value of the q-axis current output from the three-phase two-phase conversion unit 27 described later (hereinafter referred to as an Iq feedback signal). Use to perform PI operations.

The PI calculation unit 24 determines the difference between the d-axis current command input to the control unit 20 and the feedback value of the d-axis current output from the three-phase two-phase conversion unit 27 described later (hereinafter referred to as an Id feedback signal). Use to perform PI operations.

The two-phase three-phase conversion unit 25 uses the angle signals output from the rotation angle detection unit 2a to calculate the calculation results of the q-axis current and the d-axis current output from the PI calculation units 23 and 24, and uses the U-phase and V-phase. It is converted into a three-phase signal of phase and W phase.

The PWM generation unit 26 generates a gate signal for performing PWM control using the three-phase signal output from the two-phase three-phase conversion unit 25. The gate signal generated by the PWM generation unit 26 is input to the switching elements SW1 to SW6 of the inverter circuit 11. The switching elements SW1 to SW6 are driven and controlled by the gate signal.

The three-phase two-phase conversion unit 27 uses an angle signal output from the rotation angle detection unit 2a from the three-phase (U-phase, V-phase, and W-phase) currents flowing through the motor 2, and uses an Iq feedback signal and an Id feedback. Generate a signal.

(Limitation of time change of q-axis current)
Next, the limitation of the time change of the q-axis current will be described.

The voltage equation of the motor 2 is expressed by the following equations (1) and (2), assuming that the resistance of the motor 2 is sufficiently small and the d-axis current Id is controlled to be constant. Note that Vd is the d-axis voltage and Vq is the q-axis voltage. Further, w is the rotation speed, Lq is the q-axis inductance of the motor 2, and Iq is the q-axis current flowing through the motor 2. Further, φ is the induced voltage constant of the motor 2, and Ld is the d-axis inductance of the motor 2.
Vd = -w ・ Lq ・ Iq (1)
Vq = w · (φ + Ld · Id) + Lq · dIq / dt (2)

Further, the maximum value Vmax of the output voltage of the control device is expressed by the following equation.
Vmax = √ (Vd ² + Vq ² ) (3)

As shown in the above equations (1) to (3), the maximum value of the q-axis voltage Vq is determined according to the maximum value Vmax of the output voltage. Further, the following equations can be obtained by the equations (1) to (3).
Lq ・ dIq / dt
= ± √ ((Vmax ^2- (w ・ Lq ・ Iq) ² ) -w ・ (φ + Ld ・ Id)) (4)

Since the upper limit value of dIq / dt (time change of q-axis current) is determined by the equation (4), the upper limit value of the torque change amount of the motor is also determined. That is, the upper limit of dIq / dt is determined according to the rotation speed w.

FIG. 3 shows the equation (4) as a vector diagram of Vd and Vq. As shown in FIG. 3, a margin that allows the q-axis voltage Vq to be increased by w · (φ + Ld · Id) with respect to the maximum value of the q-axis voltage Vq determined by the maximum value Vmax of the output voltage (thin arrow in FIG. 3). , Lq · dIq / dt) is determined. That is, the margin that can increase dIq / dt is determined according to the rotation speed w of the motor 2. Further, the margin at which dIq / dt can be reduced (the sum of the thick line arrow and the broken line arrow in FIG. 3, Lq · dIq / dt) is similarly determined according to the rotation speed w of the motor 2.

For example, as the rotation speed w increases, w · (φ + Ld · Id) increases, so that the margin for increasing dIq / dt decreases. On the other hand, as the rotation speed w increases, the margin for reducing dIq / dt increases.

FIG. 4 shows the relationship between the q-axis current command and the q-axis current flowing through the motor 2 when the d-axis current Id is set to zero and the motor 2 is rotated at high speed. As shown in FIG. 4, when the q-axis current command is increased, the q-axis current is limited, so that the q-axis current flowing through the motor 2 has a distorted shape with respect to the sinusoidal q-axis current command. .. Therefore, the responsiveness of the motor 2 to the torque command is not very high.

On the other hand, in the power conversion device 1 of the present embodiment, when a high response of the motor 2 is required, a negative d-axis current Id is passed. Specifically, the Id signal generation unit 22 of the power conversion device 1 generates a d-axis current command in which the d-axis current Id satisfies the following conditions when the operation mode of the motor 2 is the high response operation mode.
√ (Id ² + Iq ² ) ≤ Maximum rated current of motor 2 and -2φ / Ld <Id <0

That is, in the Id signal generation unit 22, the combined current of the d-axis current Id and the q-axis current Iq is equal to or less than the maximum rated current of the motor 2, and the d-axis current Id is -2φ / Ld <Id <0. D-axis current command is generated.

As a result, w · (φ + Ld · Id) can be reduced, so that the margin for increasing dIq / dt can be increased.

FIG. 5 shows a vector diagram when the d-axis current command is Id = −φ / Ld. In this case, since w · (φ + Ld · Id) = 0, the margin for increasing dIq / dt can be increased. FIG. 6 shows the relationship between the q-axis current command and the q-axis current flowing through the motor 2 when the d-axis current command is Id = −φ / Ld. As shown in FIG. 6, the q-axis current command and the q-axis current flowing through the motor 2 are substantially the same.

Therefore, even if the torque command suddenly increases while the motor 2 is rotating at a high rotation speed, it is possible to prevent the waveform of the q-axis current flowing through the motor 2 from being distorted. Therefore, the responsiveness of the motor 2 to the torque command can be improved.

In the present embodiment, the Id signal generation unit 22 obtains the Id from the above equation (4) based on the time change of the q-axis current command input to the control unit 20, and generates the d-axis current command. As a result, the minimum Id obtained from the time change of the input q-axis current command can be set as the d-axis current command. Therefore, the current consumption can be minimized while improving the responsiveness of the motor 2 to the torque command.

(D-axis current control method)
Next, a method of controlling the d-axis current by the power conversion device 1 having the above configuration will be described with reference to FIG. 7. FIG. 7 is a flow showing control of the d-axis current.

When the flow shown in FIG. 7 starts, first, in step S1, the mode determination unit 21 determines whether the operation mode of the motor 2 is a high response operation mode. That is, in step S1, it is determined whether or not the amount of change per time of the q-axis current command input to the control unit 20 is larger than the threshold value.

If it is determined in step S1 that the operation mode of the motor 2 is the high response operation mode (YES), the process proceeds to step S2, and the Id signal generation unit 22 has a predetermined value satisfying the following conditions. Generates a d-axis current command.
√ (Id ² + Iq ² ) ≤ Maximum rated current of motor 2 and -2φ / Ld <Id <0

In the present embodiment, the Id signal generation unit 22 obtains the Id from the above equation (4) based on the time change of the q-axis current command input to the control unit 20, and generates the d-axis current command, for example. do. As a result, the minimum Id obtained from the time change of the input q-axis current command can be set as the d-axis current command.

Therefore, since w · (φ + Ld · Id) can be reduced, the margin for increasing dIq / dt can be increased. Therefore, even if the torque command suddenly increases while the motor 2 is rotating at a high rotation speed, it is possible to prevent the waveform of the q-axis current flowing through the motor 2 from being distorted. Moreover, as described above, the current consumption of the motor 2 can be minimized by setting the minimum Id in the d-axis current command. Therefore, the current consumption can be minimized while improving the responsiveness of the motor 2 to the torque command.

After setting the predetermined value in the d-axis current command in step S2, this flow ends (end).

On the other hand, if it is determined in step S1 that the operation mode of the motor 2 is the normal operation mode (NO), the process proceeds to step S3, and the id signal generation unit 22 causes the d-axis current to become zero. The d-axis current command is generated as described above. After that, this flow ends (end).

Here, step S1 corresponds to the operation mode determination step, and step S2 corresponds to the d-axis current adjustment step.

From the above, when a high response of the motor 2 is required, it is possible to increase the margin in which dIq / dt can be increased by passing a negative d-axis current Id. As a result, even if the torque command suddenly increases while the motor 2 is rotating at a high rotation speed, it is possible to prevent the waveform of the q-axis current flowing through the motor 2 from being distorted. Moreover, by passing the negative d-axis current Id only when a high response of the motor 2 is required, it is possible to prevent a useless d-axis current from constantly flowing. Therefore, the responsiveness of the motor 2 to the torque command can be improved while suppressing the current consumption.

In the present embodiment, the Id signal generation unit 22 of the power conversion device 1 satisfies the following conditions for the d-axis current Id when the operation mode of the motor 2 is the high response operation mode, and the q-axis input to the control unit 20. Based on the time change of the current command, the Id obtained from the above equation (4) is obtained. Then, the Id signal generation unit 22 generates a d-axis current command from the obtained Id.
√ (Id ² + Iq ² ) ≤ Maximum rated current of motor 2 and -2φ / Ld <Id <0

As a result, the current consumption can be minimized while improving the responsiveness of the motor 2 to the torque command.

(Other embodiments)
Although the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the embodiment is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

In the above embodiment, the Id signal generation unit 22 obtains the Id obtained from the above equation (4) based on the time change of the q-axis current command input to the control unit 20, and the d-axis current command is obtained from the Id. To generate. However, the Id signal generation unit 22 may generate a d-axis current command such that Id = −φ / Ld.

In this case, as shown in FIG. 5, since w · (φ + Ld · Id) can be minimized, the margin for increasing dIq / dt and the margin for decreasing dIq / dt can be increased in a well-balanced manner. can do. Therefore, even if the torque command suddenly increases while the motor 2 is rotating at a high rotation speed, it is possible to more reliably prevent the waveform of the q-axis current flowing through the motor 2 from being distorted. Therefore, the responsiveness of the motor 2 to the torque command can be further improved.

The Id signal generation unit 22 ^{considers the current consumption if √ (Id 2} + Iq ² ) ≤ the maximum rated current of the motor 2 and the id is within the range satisfying -2φ / Ld <Id <0. Id may be appropriately selected.

In the above embodiment, the range of the d-axis current Id that the motor 2 flows in the high response operation mode is -2φ / Ld <Id <0. However, Id may be in the range 0 to −φ / Ld. Further, Id may be in the range of -2φ / Ld <Id <−φ / Ld.

In the embodiment, the motor 2 is an SPM motor in which magnets are arranged on the outer surface of the rotor core. However, the motor 2 may be an IPM motor (Interior Personal Magnet Motor) in which a magnet is arranged inside a rotor core. When the motor 2 is an IPM motor, a d-axis current flows through the motor 2 even in the normal operation mode of the motor 2. Therefore, when the motor 2 is in the high response operation mode, the d-axis current may be controlled so that the d-axis current on the negative side of the d-axis current flowing in the normal operation mode flows in the motor 2. As a result, as in the above embodiment, the margin for increasing dIq / dt can be increased, so that the responsiveness of the motor 2 to the torque command can be improved.

In the above embodiment, the configuration of the power conversion device 1 for driving the three-phase AC motor 2 has been described, but the present invention is not limited to this, and the present invention may be applied to a power conversion device for driving a multi-phase AC motor other than the three-phase AC motor. ..

The present invention can be used in a power conversion device that controls a d-axis current and a q-axis current supplied to a motor.

1 Power converter 2 Motor 2a Rotation angle detector 3 Current detector 11 Inverter circuit 20 Control unit (current control unit)
21 Mode determination unit 22 Id signal generation unit 23, 24 PI calculation unit 25 2-phase 3-phase conversion unit 26 PWM generation unit 27 3-phase 2-phase conversion unit SW1 to SW6 Switching element

Claims (4)

A power conversion device that controls the d-axis current and q-axis current supplied to the motor.
A current control unit that controls the d-axis current and the q-axis current supplied to the motor in response to an input q-axis current command is provided.
The current control unit refers to the motor when the time change of the input q-axis current command is larger than the upper limit of the time change of the q-axis current when the d-axis current is not flowing through the motor. A power conversion device for passing the d-axis current such that the combined current of the d-axis current and the q-axis current is equal to or less than the maximum rated current of the motor and satisfies the following equation.
-2φ / Ld <Id <0
φ: Motor induced voltage constant Ld: Motor d-axis inductance Id: d-axis current In the power conversion device according to claim 1,
The current control unit is a power conversion device that calculates the d-axis current from the following equation using the time change of the input q-axis current command.
Lq ・ dIq / dt
= ± √ ((Vmax ^2- (w ・ Lq ・ Iq) ² ) -w ・ (φ + Ld ・ Id))
Lq: Motor q-axis inductance
Iq: q-axis current
Vmax: Maximum value of output voltage of power converter
w: Motor rotation speed In the power conversion device according to claim 1 or 2.
The current control unit sends the d-axis current having a combined current of the d-axis current and the q-axis current equal to or less than the maximum rated current of the motor and −φ / Ld to the motor. Power converter. It is a control method of a power conversion device that controls the d-axis current and the q-axis current supplied to the motor.
When the time change of the input q-axis current command is larger than the upper limit of the time change of the q-axis current when the d-axis current is not flowing through the motor, the operation mode of the motor is the high response operation mode. The operation mode determination process for determining that
When the operation mode of the motor is determined to be the high response operation mode in the operation mode determination step, the combined current of the d-axis current and the q-axis current is the maximum rated current of the motor with respect to the motor. A control method for a power conversion device, which comprises the following and a d-axis current adjusting step for passing the d-axis current so as to satisfy the following equation.
-2φ / Ld <Id <0
φ: Motor induced voltage constant Ld: Motor d-axis inductance Id: d-axis current

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