Electric-motor control device

Abstract

An electric-motor control device that controls an electric motor driven by AC power comprises: a pulse control unit that generates a drive pulse on the basis of a voltage phase of the electric motor; and a power converter that converts DC power into AC power on the basis of the drive pulse generated by the pulse control unit and outputs the AC power to the electric motor, in which the pulse control unit generates, as the drive pulse, a primary-component suppression pulse for suppressing a primary component of the voltage higher-harmonic wave and a secondary-component suppression pulse for suppressing a secondary component of the voltage higher-harmonic wave and selectively switches between the primary-component suppression pulse and the secondary-component suppression pulse and outputs the primary-component suppression pulse and the secondary-component suppression pulse. As a result, a loss of the AC electric-motor can be suppressed, and the output can be improved.

Description

Motor control device

[0001] The present invention relates to an electric motor control device.

[0002] BACKGROUND ART In recent years, AC motors have been used in a wide range of applications, such as home appliances, infrastructure, and in-vehicle equipment, and control devices have been applied to meet the increasing demand for energy saving, compact size, and high power density.

[0003] A known drive control method for AC motors is PWM control, which creates a modulation signal based on a voltage command signal corresponding to the voltage applied to the AC motor, compares the modulation signal with a carrier to generate a PWM pulse signal that turns on and off a switching element of a power conversion device, and converts DC power into AC power that drives the AC motor based on the PWM pulse signal, thereby enabling control of the AC motor.

[0004] On the other hand, PWM control generates AC power by repeatedly turning on and off the switching elements of a power converter at high speed, so the voltage applied to the AC motor from the power converter is pulsed, which means that the current flowing through the AC motor contains harmonic components, which can cause noise and loss.

[0005] A technique for reducing losses in an AC motor caused by the on / off switching of switching elements of such a power conversion device is known, for example, from the person described in Patent Document 1. Patent Document 1 discloses a motor drive system including a PWM signal control unit that generates pulse-width-modulated gate pulse signals from voltage command signals for each of three phases, an inverter controlled by the pulse-width-modulated gate signals, and a motor driven by the inverter, wherein the PWM signal control unit generates gate pulse signals for each of the three phases, inserting one or more on-state and one or more off-state operations of a pulse signal in a phase region including and near a zero-cross point of a fundamental wave voltage command based on the voltage command signal, inserting one or more on-state and one or more off-state operations of the pulse signal in a phase region including and near a positive and negative peak point of the fundamental wave voltage command, and maintaining the pulse signal in an on state or an off state in other phase regions.

[0006] JP 2015-053824 Public Relations

[0007] In the above-mentioned conventional technology, the harmonic components of the voltage applied to the AC motor are suppressed by switching between PWM pulses and rectangular wave pulses for a pulse-width modulated gate signal depending on the magnet temperature, thereby reducing losses in the AC motor. However, because the on / off period for the PWM pulse is set based on the pulse-width modulated gate signal, harmonic components are generated in the frequency component of the carrier wave that is the source of the pulse-width modulation. Furthermore, no consideration is given to suppressing magnet losses and magnet temperature rises caused by current harmonics in the magnet direction that occur when the AC motor is a permanent magnet synchronous motor.

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide a motor control device that can suppress losses in an AC motor and improve output.

[0009] The present application includes multiple means for solving the above-mentioned problems. One example is an electric motor control device that controls an electric motor driven by AC power, which includes a pulse control unit that generates drive pulses based on the voltage phase of the electric motor, and a power converter that converts DC power to AC power based on the drive pulses generated by the pulse control unit and outputs the AC power to the electric motor, wherein the pulse control unit generates, as the drive pulses, a primary component suppression pulse that suppresses the primary component of voltage harmonics and a secondary component suppression pulse that suppresses the secondary component of voltage harmonics, and selectively switches between the primary component suppression pulse and the secondary component suppression pulse for output.

[0010] According to the present invention, loss in an AC motor can be suppressed and output can be improved.

[0011] 13 is a functional block diagram schematically showing an electric motor control device according to a first embodiment together with related configuration. FIG. 14 is a functional block diagram schematically showing the processing function of a pulse control unit. FIG. 15 is a diagram showing an example of a pulse waveform of a primary component suppression pulse. FIG. 16 is a diagram showing a phase current waveform when an AC motor is driven by a primary component suppression pulse. FIG. 17 is a diagram showing the order analysis result of the current waveform of FIG. 4. FIG. 18 is a diagram showing an example of a pulse waveform of a secondary component suppression pulse. FIG. 19 is a diagram showing a phase current waveform when an AC motor is driven by a secondary component suppression pulse. FIG. 19 is a diagram showing the order analysis result of the current waveform of FIG. 7. FIG. 19 is a functional block diagram schematically showing an electric motor control device according to a second embodiment together with related configuration. FIG. 19 is a diagram showing a case where the electric motor control device is applied to an electric vehicle. FIG. 19 is a diagram showing an example of waveforms of a carrier wave, a modulation signal, and a pulse in PWM control shown as a comparative example. FIG. 20 is a diagram showing an example of a pulse waveform of a PWM pulse shown as a comparative example. FIG. 21 is a diagram showing a phase current waveform when an AC motor is driven by a PWM pulse shown as a comparative example. FIG. 22 is a diagram showing the order analysis result of the current waveform of FIG.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

[0014] Fig. 1 is a functional block diagram showing a motor control device according to the present embodiment together with related components, and Fig. 2 is a functional block diagram showing a processing function of a pulse control unit.

[0015] In FIG. 1 , the motor control device 100 controls an AC motor 1, such as a permanent magnet synchronous motor (PMSM), that is driven by AC power, and includes a pulse control unit 2 that generates drive pulses 22 a based on the voltage phase of the AC motor 1, and an inverter 3 as a power converter that converts DC power supplied from a DC power supply 7 into AC power based on the drive pulses 22 a generated by the pulse control unit 2 and outputs the AC power to the AC motor 1.

[0016] The pulse control unit 2 has a vector control unit 21 that generates and outputs a modulation factor command value 21 a based on the detection result from a current detection circuit 4 that detects the current supplied from the inverter 3 to the AC motor 1 and the detection result from a position sensor 5 that detects the position of the rotor of the AC motor 1, and a pulse generation unit 22 that outputs a drive pulse 22 a based on the modulation factor command value 21 a output from the vector control unit 21 and a selection signal 6 a from a pulse selection device 6.

[0017] As shown in FIG. 2, the pulse generating unit 22 includes a primary component suppression pulse generating unit 221 that generates a drive pulse (primary component suppression pulse) that suppresses the primary component of the voltage harmonics, a secondary component suppression pulse generating unit 222 that generates a drive pulse (secondary component suppression pulse) that suppresses the secondary component of the voltage harmonics, and a pulse switching unit 223 that selectively switches between the primary component suppression pulse generated by the primary component suppression pulse generating unit 221 and the secondary component suppression pulse generated by the secondary component suppression pulse generating unit 222 based on a selection signal 6 a from the pulse selecting device 6, and outputs the selected drive pulse 22 a.

[0018] In this embodiment, the case where the pulse selection device 6 is arranged outside the pulse control unit 2 is described as an example, but the present invention is not limited to this. For example, the function of the pulse selection device 6 may be arranged as a pulse selection unit inside the pulse control unit 2, and the drive pulse 22a output from the pulse generation unit 22 may be selectively switched by a selection signal output from the pulse selection unit in accordance with the drive conditions of the AC motor 1.

[0019] Fig. 3 is a diagram showing an example of the pulse waveform of a primary component suppression pulse, showing a U-phase pulse as an example of the pulse waveform. Fig. 4 is a diagram showing the phase current waveform when an AC motor is driven by the drive pulse (primary component suppression pulse) shown in Fig. 3 under continuous rated maximum output conditions, and Fig. 5 is a diagram showing the order analysis results of the current waveform. Note that in a permanent magnet motor, a dq fixed coordinate system is generally set with the magnet magnetic flux direction as the d-axis and the direction perpendicular to the d-axis as the q-axis. Therefore, Fig. 5 shows the order analysis results of the dq-axis current waveforms obtained by dq-transforming the phase current waveforms in Fig. 4.

[0020] As shown in FIG. 3, the drive pulse (first-order component suppression pulse) for suppressing the first-order component of the voltage harmonics is generated so that the pulses are spaced at irregular intervals. For example, the pulses are generated so that the pulse intervals are short in the voltage phase regions of 0 degrees, 90 degrees, 180 degrees, and 270 degrees.

[0021] Fig. 6 is a diagram showing an example of a pulse waveform of a second-order component suppression pulse, illustrating a U-phase pulse as an example of the pulse waveform. Fig. 7 is a diagram showing a phase current waveform when an AC motor is driven by the drive pulse (second-order component suppression pulse) shown in Fig. 6 under continuous rated maximum output conditions, and Fig. 8 is a diagram showing the results of order analysis of the current waveform. Fig. 8 also shows the results of order analysis of dq-axis current waveforms obtained by dq-transforming the phase current waveforms in Fig. 7.

[0022] As shown in FIG. 6, the drive pulse (first-order component suppression pulse) for suppressing the first-order component of the voltage harmonics is generated so that the pulses are spaced at irregular intervals. For example, the pulses are generated so that the pulse intervals are short in the 180° and 270° voltage phase regions.

[0023] The effects of the present embodiment configured as above will be described.

[0024] First, as a comparative example of this embodiment, a PWM control method, which is one of the general methods for controlling an AC motor, will be described.

[0025] FIG. 11 shows an example of the waveforms of a carrier wave, a modulation signal, and a pulse in PWM control. As shown in FIG. 11, the PWM control method compares the modulation signal with the carrier wave, outputting an on pulse when the modulation signal is large and an off pulse when the modulation signal is small. In this way, PWM control generates a pulse waveform (drive pulse) for controlling a power converter by comparing a sinusoidal modulation signal with the carrier wave. That is, the PWM control method generates a pulse waveform based on the carrier wave, so it outputs an on / off pulse for each carrier period. The example shown in FIG. 11 shows an example of a synchronous 15-pulse waveform, in which 15 on / off pulses occur per period. Therefore, the PWM control method generates voltage harmonics with components proportional to the number of synchronization pulses.

[0026] For example, a permanent magnet synchronous motor (PMSM) capable of achieving high power density may be used as an in-vehicle AC motor. When PWM control of such a PMSM is performed, applying a drive pulse (PWM pulse) as shown in FIG. 12 under the continuous rated maximum output condition results in a phase current waveform as shown in FIG. 13. With 15 synchronous pulses, the on-off cycle is repeated 15 times per voltage cycle. The 15th-order component of the number of synchronous pulses per voltage cycle is called the first-order component of the voltage harmonic, and the 30th-order component per voltage cycle is called the second-order component of the voltage harmonic. In this case, as shown in the order analysis results in FIG. 14, a q-axis current component (dashed line) is generated as the first-order sideband of the 15th-order ±3rd-order voltage harmonics. Furthermore, a d-axis current component (solid line) is generated as the second-order component of the 30th-order voltage harmonic.

[0027] In this way, in the PWM control system, on / off pulses are generated based on a carrier wave, so voltage harmonic components are concentrated at a frequency component proportional to the number of synchronous pulses. The current harmonic components are the cause of increased torque ripple in AC motors and increased harmonic losses in the motor.

[0028] In contrast to this, in the present embodiment, a motor control device 100 that controls an AC motor 1 (e.g., a PMSM) driven by AC power includes a pulse control unit 2 that generates a drive pulse 22 a based on the voltage phase of the AC motor 1, and a power converter (e.g., an inverter 3) that converts DC power to AC power based on the drive pulse 22 a generated by the pulse control unit 2 and outputs the AC power to the AC motor 1. The pulse control unit 2 generates, as the drive pulse 22 a, a primary component suppression pulse that suppresses the primary component of the voltage harmonics and a secondary component suppression pulse that suppresses the secondary component of the voltage harmonics, and selectively switches between the primary component suppression pulse and the secondary component suppression pulse to output the drive pulse to the power converter.

[0029] For example, under continuous rated maximum output conditions, when the AC motor 1 is driven by the drive pulse (primary component suppression pulse) shown in Fig. 3 as the drive pulse 22a, the phase current waveform is as shown in Fig. 4. Comparing the phase current waveform in PWM control (Fig. 12) exemplified as the prior art with the phase current waveform in control using the primary component suppression pulse of this embodiment (Fig. 4), it can be seen that the current ripple near the current zero crossing is finer in control using the primary component suppression pulse.

[0030] Comparing the order analysis results for PWM control (FIG. 13) with the order analysis results for control using the first-order component suppression pulse in this embodiment (FIG. 5), it can be seen that the control using the first-order component suppression pulse suppresses the q-axis current harmonics of the first-order component sidebands (15th order ±3rd order) of the voltage harmonics. On the other hand, the d-axis current harmonics of the second-order component (30th order) of the voltage harmonics have a lower frequency and a larger peak value.

[0031] In other words, when the first-order component suppression pulse of this embodiment is applied as a drive pulse under the continuous rated maximum output condition, it is possible to suppress the total dq-axis current harmonics, which is the sum of the dq-axis current harmonic components. Furthermore, with regard to the dq-axis components, the q-axis current harmonic component is significantly reduced, while the d-axis current harmonic component is increased.

[0032] More specifically, control using this type of primary component suppression pulse is effective in reducing motor loss throughout the PSMS when the magnet temperature is low, output is small, or other conditions where there is little possibility of demagnetization due to a rise in magnet temperature. Therefore, depending on these drive conditions, the primary component suppression pulse is selected as a drive pulse that reduces the dq-axis total current harmonic components under continuous rated maximum output conditions. This makes it possible to suppress harmonic losses such as motor iron loss due to dq-axis current harmonics, thereby suppressing loss and temperature rise throughout the motor.

[0033] Furthermore, control using the primary component suppression pulse is effective in suppressing loss and temperature rise in the entire motor, even when there is no need to consider magnet loss and magnet temperature rise due to eddy current loss. PMSMs that use magnets that do not generate eddy current loss are known. Drive systems that drive AC motors without magnets are also known. With such PMSMs and AC motors, there is no need to consider magnet loss and magnet temperature rise due to eddy current loss. Therefore, the primary component suppression pulse is selected as a drive pulse that reduces the dq-axis total current harmonic components under continuous rated maximum output conditions. This allows harmonic losses, such as motor iron loss due to dq-axis current harmonics, to be suppressed, even in the case of PMSMs that do not generate eddy current loss or AC motors that do not use magnets, thereby suppressing loss and temperature rise in the entire motor.

[0034] Furthermore, when the AC motor 1 is driven by the drive pulse (secondary component suppression pulse) shown in Fig. 6 as the drive pulse 22a under continuous rated maximum output conditions, the phase current waveform is as shown in Fig. 7. Comparing the phase current waveform in PWM control (Fig. 12) exemplified as the prior art with the phase current waveform in control using the secondary component suppression pulse of this embodiment (Fig. 7), it can be seen that the current ripple near the current peak is finer in control using the secondary component suppression pulse.

[0035] At this time, comparing the order analysis results for PWM control (FIG. 13) with the order analysis results for control using second-order component suppression pulses in this embodiment (FIG. 8), it is found that in control using second-order component suppression pulses, in addition to the q-axis current harmonics of the first-order component sidebands (15th±3rd) of the voltage harmonics, 6th-, 24th-, etc. components are generated. On the other hand, the d-axis current harmonic of the second-order component (30th) of the voltage harmonics becomes higher in frequency and its peak value becomes smaller.

[0036] That is, when the second-order component suppression pulse of this embodiment is applied as a drive pulse under the continuous rated maximum output condition, it is possible to suppress the dq-axis total current harmonic components. Furthermore, with regard to the dq-axis components, the q-axis current harmonic increases and the d-axis current harmonic decreases.

[0037] More specifically, control using such a secondary component suppression pulse is effective in suppressing eddy current loss caused by d-axis current harmonic components, which are in the direction of the magnet magnetic flux, in the magnets used in PMSMs. It is also effective in suppressing magnet demagnetization due to magnet temperature rise when increasing the power density of a PMSM. Therefore, depending on these drive conditions, a secondary component suppression pulse is selected as a drive pulse that reduces the d-axis current harmonic components under continuous rated maximum output conditions. This makes it possible to suppress eddy current loss caused by d-axis current harmonics, and to suppress magnet loss and magnet temperature rise.

[0038] As described above, in this embodiment, the drive pulse 22a is configured to generate a primary component suppression pulse that suppresses the primary component of voltage harmonics and a secondary component suppression pulse that suppresses the secondary component of voltage harmonics, and to selectively switch between the primary component suppression pulse and the secondary component suppression pulse. This allows the AC motor 1 to be controlled by the primary component suppression pulse or the secondary component suppression pulse, and allows the dq-axis total current harmonic components to be suppressed. Furthermore, since the AC motor 1 can be controlled by switching between the primary component suppression pulse and the secondary component suppression pulse, the current harmonic components to be suppressed can be changed. In other words, loss in the AC motor can be suppressed, and output can be improved.

[0039] Second Embodiment A second embodiment of the present invention will be described with reference to FIG.

[0040] This embodiment shows a case where a PWM pulse can be selected as a drive pulse in addition to a primary component suppression pulse and a secondary component suppression pulse.

[0041] In this embodiment, only the differences from the first embodiment will be described, and the same members as those in the first embodiment will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0042] FIG. 9 is a functional block diagram schematically showing the processing functions of the pulse control unit according to this embodiment.

[0043] As shown in FIG. 9, the pulse generating unit 22A has a primary component suppression pulse generating unit 221 that generates a drive pulse (primary component suppression pulse) that suppresses the primary component of the voltage harmonics, a secondary component suppression pulse generating unit 222 that generates a drive pulse (secondary component suppression pulse) that suppresses the secondary component of the voltage harmonics, a PWM pulse generating unit 224 that generates a drive pulse (PWM pulse) that performs PWM control, and a pulse switching unit 223A that selectively switches between the primary component suppression pulse generated by the primary component suppression pulse generating unit 221, the secondary component suppression pulse generated by the secondary component suppression pulse generating unit 222, and the PWM pulse generated by the PWM pulse generating unit based on a selection signal 6a from the pulse selecting device 6, and outputs the selected drive pulse 22a.

[0044] The other configurations are the same as those of the first embodiment.

[0045] The present embodiment configured as above can also achieve the same effects as the first embodiment.

[0046] Furthermore, in cases where motor current harmonics can be sufficiently reduced by increasing the carrier frequency, such as when using an inverter capable of low rotation speed conditions or high-speed switching operation, the computational load on the pulse generation unit 22A can be reduced by making it possible to select a PWM pulse based on the carrier wave.

[0047] <Other Embodiments> FIG. 10 is a diagram showing a case where the motor control device shown in the first embodiment or the second embodiment is applied to an electric vehicle.

[0048] As shown in FIG. 10, an electric vehicle 1000 according to this embodiment includes an AC motor 1 as a prime mover that supplies driving force to the wheels, and a motor control device 100 that controls the AC motor 1.

[0049] In this way, by applying the motor control device 100 to an electric vehicle 1000 that uses an AC motor 1 as the main on-board motor, it is possible to provide a highly efficient electric vehicle with reduced current harmonic components and harmonic losses.

[0050] <Notes> The present invention is not limited to the above-described embodiments, and includes various modifications and combinations within the scope of the gist thereof. Furthermore, the present invention is not limited to those including all of the configurations described in the above-described embodiments, and also includes those in which some of the configurations are omitted. Furthermore, the above-described configurations, functions, etc. may be realized in part or in whole by designing them as, for example, integrated circuits. Furthermore, the above-described configurations, functions, etc. may be realized in software by a processor interpreting and executing a program that realizes each function.

[0051] 1...AC motor, 2...pulse control unit, 3...inverter, 4...current detection circuit, 5...position sensor, 6...pulse selection device, 6a...selection signal, 7...DC power supply, 21...vector control unit, 21a...modulation factor command value, 22, 22A...pulse generation unit, 22a...drive pulse, 100...motor control device, 221...primary component suppression pulse generation unit, 222...secondary component suppression pulse generation unit, 223, 223A...pulse switching unit, 224...PWM pulse generation unit, 1000...electric vehicle

Claims

1. An electric motor control device that controls an electric motor driven by AC power, comprising: a pulse control unit that generates drive pulses based on the voltage phase of the electric motor; and a power converter that converts DC power to AC power based on the drive pulses generated by the pulse control unit and outputs the AC power to the electric motor, wherein the pulse control unit generates, as the drive pulses, a primary component suppression pulse that suppresses the primary component of voltage harmonics and a secondary component suppression pulse that suppresses the secondary component of voltage harmonics, and selectively switches between the primary component suppression pulse and the secondary component suppression pulse for output.

2. An electric motor control device according to claim 1, characterized in that the pulse control unit selects and outputs a drive pulse that suppresses d-axis current harmonics from the primary component suppression pulse and the secondary component suppression pulse according to the drive conditions of the electric motor.

3. An electric motor control device according to claim 1, characterized in that the pulse control unit selects and outputs a drive pulse that suppresses dq-axis total current harmonics from the primary component suppression pulse and the secondary component suppression pulse according to the drive conditions of the electric motor.

4. An electric motor control device according to claim 1, characterized in that the pulse control unit selects and outputs drive pulses that suppress dq-axis total current harmonics when the magnet of the electric motor does not generate eddy current loss or when no magnet is used in the electric motor.

5. An electric motor control device according to claim 1, wherein the pulse control unit generates, in addition to the primary component suppression pulse and the secondary component suppression pulse, a PWM pulse for performing PWM control based on a carrier wave as the drive pulse, based on the carrier wave, and selectively switches and outputs the primary component suppression pulse, the secondary component suppression pulse, and the PWM pulse.

6. An electric vehicle comprising: an electric motor as a prime mover for supplying driving force to wheels; and the electric motor control device according to claim 1 for controlling said electric motor.

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