Ac motor control device

Abstract

To provide an AC motor control device capable of suppressing harmonic components of current flowing through an AC motor and reducing loss generated in the AC motor.SOLUTION: An AC motor control device includes an inverter 3 that performs power conversion from DC power to AC power, and an AC motor control unit 2 that has pulse generating units 22, 23 that generate pulses based on a voltage phase and drives an AC motor 1 using AC power. The pulse generating units 22, 23 generate pulses such that pulse intervals in a voltage phase of a first constant range that includes an inductance smaller than an average value of varying inductance of the AC motor 1 in dq orthogonal coordinates are shorter than pulse intervals in a voltage phase of a second constant range that includes an inductance larger than the average value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control device for driving an AC motor. [Background technology]

[0002] 2. Description of the Related Art In recent years, due to increasing demand for energy saving, AC motor control devices that drive AC motors are being applied to a wide range of applications, such as home appliances, infrastructure, and in-vehicle devices.

[0003] PWM control is generally used as a control device to drive such AC motors. In PWM control, a modulation signal is created based on the voltage command signal applied to the AC motor, and a PWM pulse signal that turns on and off the switching elements of the power conversion device is created by comparing the modulation signal with the carrier. This makes it possible to convert DC power into AC power that drives the AC motor.

[0004] In this way, PWM control makes it possible to convert DC power to AC power, but because the switching elements of the power conversion device repeatedly turn on and off at high speed, the output voltage is applied to the AC motor in pulses, which causes the current flowing through the AC motor to contain harmonic components, which can cause noise and loss.

[0005] A technique for reducing noise and loss caused by the on / off switching of switching elements of such a power conversion device is disclosed in, for example, Patent Document 1.

[0006] The technology described in Patent Document 1 is configured to shorten the carrier period near the current zero crossing. By using this method, it is possible to disperse the harmonic components of the current flowing through the AC motor by dispersing the harmonic components of the voltage applied in a pulsed manner to the AC motor. This is proposed to reduce noise generated in the AC motor and suppress DC voltage fluctuations. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-47688 A Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, PWM control causes harmonic components to be included in the current flowing through the AC motor, which can lead to increased noise and losses.

[0009] However, while the technology described in Patent Document 1 is capable of dispersing the harmonic components of the voltage applied in a pulsed manner to an AC motor, it does not disclose a configuration for actively suppressing the harmonic components of the current flowing through the AC motor, nor does it disclose a configuration for changing the output pulse waveform in accordance with the characteristics of the motor.

[0010] Therefore, the technique described in Patent Document 1 cannot sufficiently reduce noise and loss associated with PWM control.

[0011] An object of the present invention is to provide an AC motor control device capable of suppressing harmonic components of a current flowing through an AC motor and reducing losses occurring in the AC motor. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention is configured as follows.

[0013] The AC motor control device includes an inverter that performs power conversion from DC power to AC power, and an AC motor control unit that has a pulse generating unit that generates pulses based on a voltage phase and drives an AC motor using the AC power, and the pulse generating unit generates the pulses so that the pulse interval in a first constant range of voltage phases that includes inductances smaller than the average value of the varying inductance of the AC motor in dq orthogonal coordinates is shorter than the pulse interval in a second constant range of voltage phases that includes inductances larger than the average value. Effect of the Invention

[0014] According to the present invention, it is possible to provide an AC motor control device that can suppress the harmonic components of the current flowing through an AC motor and reduce losses generated in the AC motor by shortening the pulse interval of the phase where the inductance is small based on the voltage phase without using a carrier wave. [Brief description of the drawings]

[0015] [Figure 1] 1 is a block diagram showing an overall configuration of an AC motor control device according to a first embodiment of the present invention. [Diagram 2] 1A to 1C are diagrams illustrating example waveforms of a carrier wave, a modulated signal, and a pulse during general PWM control. [Diagram 3] FIG. 1 is a diagram showing an example of a pulse waveform during general PWM control. [Figure 4] 1A and 1B are diagrams illustrating an example of a pulse waveform and a waveform of a change in inductance during general PWM control when an inverse salient pole motor is driven. [Diagram 5] 1A and 1B are diagrams illustrating an example of a current waveform and a waveform of a change in inductance during general PWM control when an inverse salient pole motor is driven. [Figure 6] 5A and 5B are diagrams illustrating examples of pulse waveforms and waveforms of inductance changes when the inverted salient pole motor in the first embodiment is driven. [Figure 7] 5A to 5C are diagrams illustrating examples of waveforms of current and inductance changes in the present invention when the inverse salient pole motor in the first embodiment is driven. [Figure 8] 1A and 1B are diagrams illustrating an example of a pulse waveform and a waveform of a change in inductance during general PWM control when a forward salient pole motor is driven. [Figure 9] 5A to 5C are diagrams illustrating examples of pulse waveforms and waveforms of inductance changes according to the first embodiment of the present invention when a forward salient pole motor is driven. [Figure 10] 1A and 1B are diagrams illustrating an example of a current waveform and a waveform of a change in inductance during general PWM control when a forward salient pole motor is driven. [Figure 11]5A to 5C are diagrams illustrating examples of current waveforms and waveforms of changes in inductance according to the first embodiment of the present invention when a forward salient pole motor is driven. [Figure 12] FIG. 1 is a diagram showing example waveforms of a sine wave voltage at a fundamental rotation frequency and a sine wave voltage at three times the fundamental rotation frequency; [Figure 13] FIG. 11 is a block diagram of a pulse generating unit according to a third embodiment of the present invention. [Figure 14] FIG. 11 is a schematic configuration diagram of a fourth embodiment of the present invention. [Figure 15] FIG. 11 is a schematic configuration diagram of a pulse generating unit according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. EXAMPLES

[0017] Example 1 A first embodiment of the present invention will be described using an example in which an AC motor 1 is driven by an AC motor control unit 2.

[0018] (Overall schematic structure) First, the overall schematic configuration of an AC motor control device according to the first embodiment will be described with reference to FIG.

[0019] In FIG. 1, the AC motor control device includes an inverter 3 that performs power conversion from DC power to AC power, and an AC motor control unit 2 that has a vector control unit 21 and a pulse generating unit 22 that generates a pulse based on a voltage phase and drives an AC motor 1 using AC power.

[0020] In the AC motor control unit 2 according to the first embodiment of the present invention, the vector control unit 21 calculates a modulation factor command value 21A based on the current detection circuit 4 that detects the current flowing through the AC motor 1 and the position sensor information 5A from the position sensor 5 that detects the rotational position of the AC motor 1.

[0021] A pulse generating unit 22 generates a pulse based on the calculated modulation factor command value 21A and a voltage phase, and a pulse 22A is generated by the pulse generating unit 22. An inverter 3 converts DC power to AC power based on the generated pulse 22A and supplies AC power to the AC motor 1.

[0022] (Explanation of the PWM carrier in a typical inverse salient pole motor) Next, a typical PWM carrier in the case of an inverse salient pole motor will be described.

[0023] A PWM control method is one of the general methods for controlling the AC motor 1. Fig. 2 is a diagram showing an example of waveforms of a carrier wave, a modulating signal, and a pulse during general PWM control.

[0024] As shown in Figure 2, in the PWM control method, the modulating signal is compared with the carrier wave, and an on-pulse is output when the modulating signal is large, and an off-pulse is output when the modulating signal is small.

[0025] With this type of PWM control, it is possible to output a pulse waveform such as that shown in Figure 3 by comparing a sinusoidal modulated signal with a carrier wave.

[0026] In the PWM control method, a pulse waveform is generated based on a carrier wave, so it is configured to output an on / off pulse for each carrier period.

[0027] For this reason, in the PWM control method, voltage harmonic components proportional to the carrier period are generated.

[0028] (Relationship between dq-axis inductance and voltage phase angle in a typical inverse salient pole motor) Next, the relationship between the dq-axis inductance and the voltage phase angle will be described.

[0029] Interior permanent magnet synchronous motors (IPMSMs), which are capable of achieving high power density, are often used as the AC motors to be driven in vehicles. In IPMS motors, the inductance is not constant and salient poles occur.

[0030] A state in which the motor inductance is large in the torque axis direction (q axis direction) that is perpendicular to the magnet axis direction (d axis direction) in a Cartesian coordinate system is called an inverse salient pole.

[0031] For an inverse salient pole motor, when the voltage phase and current phase during vector control are sufficiently close to the q-axis direction, an example of the change in inductance with respect to the U-phase pulse waveform of the three-phase AC voltage pulse is shown in Figure 4.

[0032] As shown in Figure 4, inductance increases or decreases depending on the voltage phase, with the inductance being small near 0 degrees, 180 degrees, and 360 degrees and large near 90 degrees and 270 degrees.

[0033] (Explanation of current harmonics in a typical inverse salient pole motor (phase current and inductance)) Fig. 5 shows an example of the U-phase current waveform and inductance changes when the inverter drives an inverse salient pole motor based on the pulses shown in Fig. 4.

[0034] The current harmonic component is proportional to the voltage harmonic component divided by the product of the inductance and the harmonic component frequency.

[0035] In other words, when the inductance is small, the current harmonic components become large for the same voltage harmonic components.

[0036] Therefore, as shown in FIG. 5, the current ripple becomes large in the region where the inductance is small, and the current ripple becomes small in the region where the inductance is large.

[0037] (Summary of typical reverse salient pole motors) As described above, in a typical PWM control method, on-off pulses are generated based on a carrier wave, so voltage harmonic components are concentrated in the frequency components proportional to the carrier period.

[0038] This causes current harmonic components to concentrate at a frequency component proportional to the carrier period.

[0039] Furthermore, as shown in Fig. 5, when an IPMS motor is driven, the current ripple increases in the region where the inductance is small.

[0040] Such current harmonic components increase the torque ripple and harmonic loss of the motor.

[0041] In the first embodiment of the present invention, a method is proposed in which, without using a carrier wave, pulses are generated at unequal intervals based on the voltage phase, and the pulse intervals in the region where the inductance is small in FIG. 4 are shortened to suppress current harmonic components.

[0042] The operation and effects of the first embodiment of the present invention will be described.

[0043] (Explanation of voltage harmonics in Example 1 (pulse and inductance): inverse salient pole) FIG. 6 is a diagram showing an example of a U-phase pulse waveform and an example of a waveform of an inductance change when the inverse salient pole motor in the first embodiment is driven.

[0044] 6, in the first embodiment of the present invention, the pulse generating unit 22 generates pulses at unequal intervals, and generates the pulses so that the pulse interval is shorter in a voltage phase where the inductance is smaller in the dq Cartesian coordinates (region where the inductance is smaller). More specifically, the pulse generating unit 22 generates the pulses so that the pulse interval in a certain range of voltage phases including an inductance smaller than the average value of the varying inductance in the dq Cartesian coordinates is shorter than the pulse interval in a certain range of voltage phases including an inductance larger than the average value.

[0045] In other words, in a region where the inductance is small, the voltage harmonic components are made high frequency and dispersed.

[0046] As a result, if the region where inductance changes is divided into two regions: a region where inductance is small (a first constant range of voltage phases in dq Cartesian coordinates that includes an inductance smaller than the average value of the changing inductance) and a region where inductance is large (a second constant range of voltage phases that includes an inductance larger than the above average value), the number of pulses in the region where the inductance is larger than the average value is smaller than the number of pulses in the region where the inductance is smaller than the average value.

[0047] (Explanation of current harmonics caused by shortening the pulse interval in the region where inductance is small (phase current and inductance): inverse salient pole) FIG. 7 shows an example of the U-phase current waveform and the change in inductance when the inverter 3 drives the inverse salient pole motor based on the pulses shown in FIG.

[0048] As shown in FIG. 7, the effect of suppressing current ripple is obtained in the region where the inductance is small.

[0049] This is because by dispersing the voltage harmonic components at higher frequencies, the product of the inductance for the voltage harmonic components and the frequency of the high-frequency components becomes larger, and the current harmonic components become smaller.

[0050] (Summary of the reverse salient pole motor according to the first embodiment) As described above, in the pulse waveform in Example 1 of the present application, pulses are generated at unequal intervals based on the voltage phase, and the pulse intervals are shortened in areas where the inductance is small, thereby increasing the frequency of the voltage harmonic components and dispersing them.

[0051] This suppresses current ripples in the region where the inductance is small, as shown in FIG.

[0052] As described above, according to the first embodiment of the present invention, in the case of an inverse salient pole, it is possible to suppress the torque ripple and harmonic loss of the motor by suppressing the current harmonic components.

[0053] (Regarding the forward salient pole motor according to the first embodiment) When the motor inductance in the magnet axis direction (d-axis direction) is greater than the torque axis direction (q-axis direction) in an orthogonal coordinate system, the state is called a forward salient pole.

[0054] In order to clarify the difference between the PWM control method and the method according to the first embodiment of the present invention, the inductance change, pulse waveform, and current waveform in the case of a forward salient pole are shown in the same manner as in the case of a reverse salient pole.

[0055] (Explanation of voltage harmonics, pulses and inductance: forward salient pole) FIG. 8 shows an example of a U-phase pulse waveform and inductance change in a general PWM control method when a forward salient pole motor is used, and FIG. 9 shows an example according to the first embodiment of the present invention. In the case of forward salient poles, the increase or decrease in inductance due to the voltage phase is large near 0 degrees, 180 degrees, and 360 degrees, and small near 90 degrees and 270 degrees. In the method of the present invention, as shown in FIG. 9, the pulse interval is short in the region where the inductance is small, similar to the case of the inverse salient pole.

[0056] (Explanation of current harmonics, U-phase current and inductance: forward salient pole) Fig. 8 is a diagram showing an example of a pulse waveform and a change in inductance during typical PWM control when a forward salient pole motor is driven. Fig. 9 is a diagram showing an example of a pulse waveform and a change in inductance according to the first embodiment of the present invention when a forward salient pole motor is driven. Fig. 10 is a diagram showing an example of a current waveform and a change in inductance during typical PWM control when a forward salient pole motor is driven. Fig. 11 is a diagram showing an example of a current waveform and a change in inductance according to the first embodiment of the present invention when a forward salient pole motor is driven.

[0057] As shown in FIG. 10, with the PWM control method, it can be seen that the current ripple becomes large in the region where the inductance is small.

[0058] As shown in FIG. 11, in the current waveform according to the first embodiment of the present invention, the effect of suppressing current ripples is obtained by shortening the pulse interval in an area where the inductance is small.

[0059] (Summary of forward salient pole motor according to embodiment 1) As described above, even when the motor has forward salient poles, the pulse waveform according to the first embodiment of the present invention makes it possible to suppress current harmonic components.

[0060] Moreover, by suppressing the current harmonic components in this manner, it is possible to suppress the torque ripple and harmonic losses of the motor.

[0061] According to the first embodiment of the present invention, it is possible to provide an AC motor control device capable of suppressing harmonic components of a current flowing through an AC motor and reducing losses occurring in the AC motor.

[0062] Example 2 Next, a second embodiment of the present invention will be described.

[0063] (The third-order component disappears in three-phase AC.) Generally, to drive an AC motor, an inverter outputs a three-phase AC voltage.

[0064] A characteristic of such three-phase AC voltage is that harmonic components with a frequency three times the fundamental rotational frequency of the motor do not appear in Cartesian coordinates.

[0065] Specifically, within the phase range of 0 degrees to 180 degrees of the sinusoidal voltage of the fundamental rotation frequency, the triple frequency component is shown as in FIG.

[0066] As shown in FIG. 12, for the triple frequency component, the voltage increases near 30 degrees and 150 degrees, and is small at 0 degrees, 90 degrees, and 180 degrees.

[0067] In other words, with triple frequency components, there are more on-pulses near 30 degrees and 150 degrees, and more off-pulses near 0 degrees, 90 degrees, and 180 degrees, making triple frequency components more likely to occur.

[0068] Therefore, in the pulse waveform according to the second embodiment of the present invention, a pulse waveform is generated in which the pulse interval is shortened every 90 degrees from 0 degrees in the U-phase pulse waveform, that is, 0 degrees, 90 degrees, and 180 degrees.

[0069] This makes it possible to shorten the pulse interval without increasing the harmonic components on the orthogonal coordinate system.

[0070] As a specific waveform, a pulse waveform is generated in which the pulse interval is shortened every 90 degrees from 0 degrees, as shown in FIG. 6 and FIG.

[0071] According to the second embodiment of the present invention, it is possible to provide an AC motor control device capable of suppressing harmonic components of current flowing through an AC motor even for a three-phase AC voltage, and reducing losses generated in the AC motor.

[0072] (Variation 1) Next, a first modification of the first and second embodiments will be described.

[0073] The first modification is an example in which the pulse shape is changed according to the voltage amplitude and phase.

[0074] When the vector control unit 21 controls the AC motor 1, it controls the amplitude and phase of the voltage in the Cartesian coordinate system that is supplied to the AC motor 1.

[0075] This changes the waveform of the pulse that suppresses the voltage amplitude and current harmonics, and accordingly, a pulse waveform similar to that of the first or second embodiment is generated in accordance with this change.

[0076] The first modification can also provide the same effects as the first or second embodiment.

[0077] (Variation 2) Next, a second modification of the first and second embodiments will be described.

[0078] Modification 2 is an example in which the pulse shape is changed by the current amplitude and phase.

[0079] The current amplitude and phase in the orthogonal coordinate system change depending on the operating state of the AC motor 1. When the vector control unit 21 controls the AC motor 1, it controls the current amplitude and phase in the orthogonal coordinate system that is supplied to the AC motor 1.

[0080] This causes the inductance characteristics to change due to the effect of magnetic saturation.

[0081] Therefore, the pulse generating unit 22 generates a pulse waveform similar to that in the first or second embodiment in accordance with the change in inductance.

[0082] The second modification can also provide the same effects as the first or second embodiment.

[0083] Example 3 Next, a third embodiment of the present invention will be described.

[0084] The third embodiment of the present invention is an example in which the method of the present invention and the PWM control method are switched depending on the operating conditions.

[0085] In the above-mentioned first and second embodiments, a carrier wave is not used, pulses are generated at irregular intervals, and the pulse intervals in the region where the inductance is small are shortened, thereby suppressing current harmonic components.

[0086] However, in areas where the number of on-off pulses during one rotation of the sinusoidal voltage is sufficiently large, such as in the case of low rotation speeds or when high-speed switching elements are used, the suppression effect of current harmonics using the method compared to PWM control becomes smaller.

[0087] Therefore, as shown in FIG. 13, a pulse control method switching unit 223 is provided which switches between a first pulse generating unit A221 that generates pulses based on a voltage phase and a second pulse generating unit B222 that generates pulses based on a carrier wave, as in the third embodiment of the present invention, depending on an operating condition 1A of the AC motor 1 (an operating condition indicating whether the operating condition is a region with a large number of pulses or a region with a small number of pulses).

[0088] This makes it possible to drive the AC motor 1 using a PWM control method that generates pulses based on a carrier wave in areas with a large number of pulses, and using a method in which the pulse interval in the area where inductance is small is shortened as in the present invention in areas with a small number of pulses.

[0089] Therefore, since the PWM control method can be used in areas with a large number of pulses, it is possible to reduce the amount of memory required to store pulse waveform settings for shortening the pulse interval in areas where inductance is small.

[0090] The operating conditions 1A of the AC motor 1 may be generated by the vector control unit 21 based on the position sensor information 5A from the position sensor 5, or may be supplied from an operating condition setting unit (not shown) provided separately.

[0091] According to the third embodiment of the present invention, in addition to obtaining the same effects as those of the first embodiment, it is possible to obtain an effect of reducing the memory required to store the settings of the pulse waveform for shortening the pulse interval in the region where the inductance is small.

[0092] Example 4 Next, a fourth embodiment of the present invention will be described.

[0093] FIG. 14 is a schematic configuration diagram of a fourth embodiment of the present invention, which is an example in which the AC motor control device 2 of the first to third embodiments is applied to an electric vehicle 100.

[0094] In FIG. 14, an on-vehicle main motor 101 which is an AC motor of an electric vehicle 100 is controlled by the AC motor control device 2 described above.

[0095] According to the fourth embodiment of the present invention, it is possible to provide an electric vehicle having an AC motor control device capable of suppressing harmonic components of a current flowing through an AC motor and reducing losses occurring in the AC motor.

[0096] Example 5 Next, a fifth embodiment of the present invention will be described.

[0097] In the on-board main motor 101 applied to the electric vehicle 100, a warm-up operation may be required because the rotating parts of the on-board main motor 101 may freeze when started at an extremely low temperature. During such a warm-up operation, it is desirable for the loss generated by the on-board main motor 101 to be large.

[0098] 13, the motor operating condition 1A is replaced with a temperature sensor 24 that supplies AC motor temperature information to the pulse control method switching unit 223. The pulse control method switching unit 223 switches between the first pulse generating unit 221 and the second pulse generating unit 222 according to the temperature detected by the temperature sensor 24.

[0099] With this configuration, when the temperature of the AC motor 1 is above a certain level, the pulse control method switching unit 223 is set to the first pulse generating unit A221 (a pulse generating unit to which embodiment 1, 2 or 3 of the present invention is applied), and when the temperature of the AC motor 1 is below a certain level, the pulse control method switching unit 223 is set to the second pulse generating unit B222 (a pulse generating unit to which the present invention is not applied), making it possible to increase the loss generated by the AC motor 1 and perform warm-up operation.

[0100] According to the fifth embodiment, in addition to obtaining the same effects as those of the first embodiment, it is possible to provide an electric vehicle having an AC motor control device that can perform warm-up operation by increasing the loss generated by the AC motor 1 when the temperature of the AC motor 1 is below a certain level. [Explanation of symbols]

[0101] 1 AC motor, 1A operating conditions, 2 AC motor control unit, 3 inverter, 4 current detection circuit, 5 position sensor, 5A position sensor information, 21 vector control unit, 21A modulation factor command value, 22, 23 pulse generation unit, 24 temperature sensor, 100 electric vehicle, 101 vehicle-mounted main motor, 221 first pulse generation unit A, 222 second pulse generation unit B, 223 pulse control method switching unit

Claims

1. An inverter that converts DC power into AC power; an AC motor control unit that has a pulse generating unit that generates a pulse based on a voltage phase and drives an AC motor using the AC power; Equipped with The AC motor control device is characterized in that the pulse generating unit generates the pulses so that a pulse interval in a first constant range of voltage phases including an inductance smaller than an average value of the varying inductance of the AC motor in dq orthogonal coordinates is shorter than a pulse interval in a second constant range of voltage phases including an inductance larger than the average value.

2. 2. The AC motor control device according to claim 1, The AC motor control device, wherein the pulse generating unit generates the pulses so that the pulse intervals become shorter every 90 degrees from 0 degrees of the voltage phase.

3. 3. The AC motor control device according to claim 1, The AC motor control device is characterized in that the AC motor control unit has a vector control unit, and the vector control unit changes the waveform of the pulse depending on the voltage amplitude and phase supplied to the AC motor.

4. 3. The AC motor control device according to claim 1, The AC motor control device is characterized in that the AC motor control unit has a vector control unit, and the vector control unit changes a pulse waveform according to the amplitude and phase of a current supplied to the AC motor.

5. 3. The AC motor control device according to claim 1, The pulse generating unit is a pulse control method switching unit that switches between a first pulse generating unit that generates a pulse based on a voltage phase and a second pulse generating unit that generates a pulse based on a carrier wave according to an operating state of the AC motor; An AC motor control device comprising:

6. 3. The AC motor control device according to claim 1, An AC motor control device that controls an on-board main motor of an electric vehicle.

7. 7. The AC motor control device according to claim 6, A temperature sensor; A pulse control method switching unit; Equipped with The pulse generating unit is A first pulse generating unit generates a pulse based on a voltage phase, and a second pulse generating unit generates a pulse based on a carrier wave, 2. An AC motor control device, comprising: a pulse control method switching unit that switches between the first pulse generating unit and the second pulse generating unit in response to a temperature detected by the temperature sensor.

Images