AC motor control device

Abstract

Provided is an AC motor control device capable of suppressing a harmonic component of a current flowing through an AC motor and reducing loss generated in the AC motor. An AC motor control device (10) is provided with: a power converter (3) that converts DC power into AC power; and a control unit (2) that performs synchronous PWM control on an AC motor (1). The control unit (2) has a carrier wave generation unit (221, 231, 232) that generates a carrier wave, and a PWM pulse generation unit (22, 23) that generates a PWM pulse on the basis of the carrier wave and the voltage command value (21A). The carrier wave generation units (221, 231, 232) change the period of the carrier wave such that the harmonic components in the dq orthogonal coordinates of the AC motor (1) included in the PWM pulse are concentrated on the axis side of the d axis and the q axis having a large inductance.

Description

Technical Field

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

[0002] In recent years, as the demand for energy saving increases, AC motor control devices that drive AC motors have been used in a wide range of applications such as home appliances, infrastructure, and vehicle-mounted equipment.

[0003] As such an AC motor control device for driving an AC motor, PWM control is generally used. In PWM control, a modulation signal is generated based on a voltage command signal applied to the AC motor, and a PWM pulse signal for turning on / off a switching element of a power conversion device is generated by comparing the modulation signal with a PWM carrier. In this way, DC power can be converted into AC power for driving an AC motor.

[0004] In this way, DC power can be converted into AC power by performing PWM control. However, since the switching element of the power conversion device is repeatedly turned on and off at high speed, the output voltage is applied to the AC motor in a pulsed state.

[0005] Therefore, the current flowing through the AC motor contains harmonic components, which cause noise and loss.

[0006] For example, Patent Documents 1 and 2 disclose technologies for reducing noise and loss caused by turning on and off switching elements of such power conversion devices.

[0007] The method described in Patent Document 1 is a configuration in which the period of the PWM carrier wave is changed with the passage of time. In addition, the method described in Patent Document 2 is a configuration in which the period of the PWM carrier wave is shortened near the current zero crossing.

[0008] According to such a method, by dispersing the harmonic components of the voltage applied to the AC motor in a pulsed state, the harmonic components of the current flowing through the AC motor can be dispersed. Therefore, it is proposed to reduce the noise generated in the AC motor and suppress the DC voltage fluctuation.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2010-41877

[0012] Patent Document 2: Japanese Patent Application Publication No. 2019-47688 Summary of the invention

[0013] Problems to be solved by the invention

[0014] As described above, by performing PWM control, the current flowing through the AC motor contains harmonic components, which causes a problem of increased noise and loss.

[0015] However, the methods described in Patent Documents 1 and 2 can disperse the harmonic components of the voltage applied to the AC motor in a pulsed form, but do not disclose a structure for actively suppressing the harmonic components of the current flowing through the AC motor.

[0016] Unless the harmonic components of the current flowing through the AC motor are suppressed, it will be difficult to reduce the noise and loss caused by the harmonic components.

[0017] An object of the present invention is to realize an AC motor control device that can suppress the higher harmonic components of the current flowing through the AC motor and reduce the loss generated in the AC motor.

[0018] Means for solving problems

[0019] In order to achieve the above-mentioned object, the present invention is constructed as follows.

[0020] An AC motor control device includes: a power converter that performs power conversion from DC power to AC power; and a control unit that performs synchronous PWM control on the AC motor, wherein the control unit has: a carrier generating unit that generates a carrier; and a PWM pulse generating unit that generates a PWM pulse based on the carrier and a voltage command value, wherein the carrier generating unit changes the period of the carrier so that the higher harmonic components in the dq orthogonal coordinates of the AC motor contained in the PWM pulse are concentrated on the axis side with large inductance in the d-axis or q-axis.

[0021] Effects of the Invention

[0022] According to the present invention, it is possible to realize an AC motor control device that can suppress harmonic components of current flowing through the AC motor and reduce losses generated in the AC motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a block diagram showing the overall configuration of an AC motor control device according to the first embodiment of the present invention.

[0024] Figure 2 This is a block diagram showing a PWM pulse generating unit according to the first embodiment of the present invention.

[0025] Figure 3 A waveform example is shown when the period of the carrier wave is made constant during synchronous PWM control in a comparative example different from the present invention.

[0026] Figure 4 A waveform example is shown when the period of the carrier wave is periodically changed during the synchronous PWM control in the first embodiment of the present invention.

[0027] Figure 5 This is a schematic diagram of the relationship between the orthogonal dq axis coordinate system and voltage and current in vector control.

[0028] Fig. 6A This is a diagram showing harmonic components of an output voltage when the period of a carrier wave is constant.

[0029] Figure 6B This is a diagram showing harmonic components of the output voltage when the period of the carrier wave is periodically changed.

[0030] Fig. 7A Indicates the application of embedded permanent magnet synchronous motor Fig. 6A The voltage high harmonic components shown are the current high harmonic components generated.

[0031] Figure 7B Indicates that the embedded permanent magnet synchronous motor is Figure 6B The voltage high harmonic components shown are the current high harmonic components generated.

[0032] Figure 8 This is a graph showing changes in current harmonic components when the period change amount is changed.

[0033] Fig. 9 This is a diagram showing an example in which the AC motor control device according to the second embodiment of the present invention is applied to an electric vehicle.

[0034] Fig.10 This is a structural diagram of the PWM pulse generating unit in the second embodiment. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present invention will be described using the drawings.

[0036] Example

[0037] (Example 1)

[0038] use Figures 1 to 10 Embodiment 1 of the present invention will be described.

[0039] In the first embodiment, an example of driving an AC motor 1 using an AC motor control device 10 of the present invention will be described.

[0040] Figure 11 is a schematic diagram of the AC motor control device 10 according to Embodiment 1. The AC motor control device 10 includes a control unit 2 , an inverter (power converter) 3 , and a current detection unit 4 . The control unit 2 includes a vector control unit 21 and a PWM pulse generation unit 22 . Figure 2 2 is an explanatory diagram of the PWM pulse generating unit 22 included in the control unit 2 . The PWM pulse generating unit 22 includes a carrier generating unit 221 and a carrier voltage command comparing unit 222 .

[0041] Vector control unit 21 of control unit 2 calculates modulation rate command value (voltage command value) 21A based on information from current detection unit 4 for detecting current flowing through AC motor 1 and information 5A from position sensor 5 for detecting the rotational position of AC motor 1 .

[0042] The PWM pulse generator 22 generates PWM pulses 22A based on the calculated modulation rate command value 21A. The inverter 3 converts DC power into AC power based on the generated PWM pulses 22A and supplies AC power to the AC motor 1 .

[0043] In the PWM pulse generating unit 22, as shown in FIG. Figure 2 As shown, a carrier wave such as a triangular wave is generated by a carrier wave generator 221, and the generated carrier wave is compared with a modulation rate command value 21A by a comparison unit 222 to generate a PWM pulse 22A.

[0044] As one method of controlling the AC motor 1 by PWM pulses, a synchronous PWM control method is mentioned. The control unit 2 performs synchronous PWM control on the AC motor 1 .

[0045] Figure 3 A schematic diagram showing carrier and modulation rate command values ​​during synchronous PWM control in a comparative example different from the present invention. Figure 3 As shown, in the synchronous PWM control method, the period of the PWM carrier is changed according to the rotation speed of the AC motor, thereby fixing the number of PWM carriers included in one rotation.

[0046] For example, in Figure 3 In the example shown, the following structure is shown: in a half cycle (0°~180°) of one rotation of the AC modulation rate command, 4.5 cycles of the uplink (peak) and downlink (trough) of the carrier are included, and in a rotation of the AC modulation rate command (0°~360°), 9 cycles of the uplink (peak) and downlink (trough) of the carrier are included, totaling 18 cycles.

[0047] In addition, the period of the PWM carrier is generally set to a certain interval. Figure 3 The structure of the example shown is called synchronous 9-pulse control.

[0048] Thus, by adopting the synchronous PWM control method, the symmetry of the waveform is maintained and even-order harmonics are not generated. On the other hand, since the number of PWM carriers is fixed, a large number of sideband waves of the first-order component of the carrier are generated (in Figure 3 In the example shown, the structure is 6th order, 12th order components), 2nd order components (in Figure 3 The structure of the example shown is a structure of voltage higher harmonic components (18th-order components).

[0049] Furthermore, when a voltage including such harmonic components is applied to the AC motor, current harmonic components are also generated in the current due to the influence of these harmonic components.

[0050] In Example 1 of the present application, Figure 3 In the synchronous PWM control as in the example shown, in order to suppress the harmonic components of the current generated in the AC motor, the period of the carrier during the synchronous PWM control is periodically changed.

[0051] Figure 4 A schematic diagram showing a synchronous 9-pulse case in which the period of the carrier wave of the synchronous PWM control according to the configuration of the first embodiment of the present invention is periodically changed. Figure 4 As shown, the structure is such that the short period S and the long period L are repeated twice with respect to the period of the carrier.

[0052] Specifically, the number of peaks and valleys of synchronous PWM is set to P( Figure 4 In the case of P=9), the order of the carrier period is set to n, and the carrier period is set to change with a 6-order period as shown in the following formula (1).

[0053] [Mathematical formula 1]

[0054]

[0055] In the above formula (1), C multiplied by the sine wave function is a value corresponding to the period change amount. In addition, n is the order.

[0056] For example, when C=0 is set in the sync 9 pulse and the change between each cycle is set to 0, Figure 3 As shown in the comparative example, the period of the carrier is fixed to (2π / 18) = 20 [deg]. In addition, when C>0 in the synchronization 9 pulse, as shown in the following equations (2), (3), and (4), Figure 4 As in the present invention shown in FIG. 1 , n=1, 2, and 3 are repeated.

[0057] [Mathematical formula 2]

[0058]

[0059] [Mathematical formula 3]

[0060]

[0061] [Formula 4]

[0062]

[0063] By changing the number P of peaks and valleys of the synchronous PWM using the above-mentioned equation (1), it is also possible to set the period variation in the case of, for example, 15 synchronous pulses in a similar manner.

[0064] Figure 5 This figure shows the outline of dq orthogonal coordinates, voltage, and current during vector control.

[0065] exist Figure 5 In the AC motor, the dq orthogonal coordinates are set to coordinates in which the d-axis is in the magnet axis direction and the q-axis is orthogonal to the magnet axis direction. In vector control, such dq orthogonal coordinates are used to control voltage and current.

[0066] Fig. 6A and Figure 6B It shows the harmonic components of the output voltage when the period of the carrier wave is constant and when the period is periodically changed according to the present invention. Fig. 6A is the graph for the case where the period is constant, Figure 6B This is a diagram showing a case where the period of a carrier wave is periodically changed according to an embodiment.

[0067] Fig. 6A and Figure 6B The horizontal axis is the order and the vertical axis is the amplitude. Fig. 6A and Figure 6B The solid line component is the above-mentioned d-axis (magnet axis direction) component, and the dotted line represents the above-mentioned q-axis (magnet axis orthogonal direction) component.

[0068] exist Fig. 6A In the case of synchronous PWM control with a constant cycle, the component with the largest amplitude is the second-order component of the q-axis component (dashed line). In addition, the d-axis component (solid line) is generated on the left and right of the second-order component as a sideband wave component of the first-order component and the third-order component.

[0069] Here, if Figure 6B As shown in FIG. 1 , by periodically changing the period, the result of the change of the high-order harmonic components can be obtained. Figure 6BIn the figure, it can be confirmed that the sideband wave components of the 1st-order component and the 3rd-order component of the d-axis component (solid line) are reduced. In addition, it can be confirmed that the components before and after the 2nd-order component of the q-axis component (dashed line) are increased. In other words, by periodically changing the period of the carrier, a voltage harmonic component structure is formed in which the d-axis harmonic component is shifted to the q-axis harmonic component.

[0070] Here, a method including Fig. 6A or Figure 6B The voltage of the harmonic component shown generates the current harmonic component caused by the voltage harmonic component. With respect to the d-axis component (magnet axis direction) and the q-axis (magnet axis orthogonal component), the voltage and current related to the harmonic component become the relationship as shown in the following equations (5) and (6).

[0071] In equation (5), idh(n) is the d-axis current, vdh(n) is the d-axis voltage, and Ldh is the d-axis inductance. In equation (6), iqh(n) is the q-axis current, vqh(n) is the q-axis voltage, and Lqh is the q-axis inductance.

[0072] [Formula 5]

[0073]

[0074] [Mathematical formula 6]

[0075]

[0076] The above-mentioned equations (5) and (6) indicate that the harmonic current generated in the motor is a value obtained by dividing the frequency corresponding to the order of the harmonic voltage and the inductance.

[0077] Here, embedded permanent magnet synchronous motors are often used in the main motors that serve as the power source of the vehicle-mounted equipment. In such embedded permanent magnet synchronous motors, the q-axis inductance shown in the above equation (6) is large compared to the d-axis inductance shown in the above equation (5), and the salient pole ratio is large (Ldh<Lqh). In other words, it is a motor with the characteristic that the q-axis current harmonic component is smaller than the d-axis current harmonic component when voltage harmonics of the same amplitude are applied.

[0078] Here, in Fig. 7A as well as Figure 7B The following figure shows the effect of applying Fig. 6A as well as Figure 6B The voltage high harmonic components shown are the current high harmonic components generated.

[0079] Fig. 7A is the graph when the period is constant, Figure 7BThis is a diagram of an embodiment in which the period of the carrier wave is periodically changed. Fig. 7A and Figure 7B In the graph, the horizontal axis is the order and the vertical axis is the amplitude. The solid line component is the d-axis (magnet axis direction) component, and the dotted line represents the q-axis (magnet axis orthogonal direction) component.

[0080] In a constant cycle Fig. 7A In the case of Fig. 6A The 2nd order component of the q-axis component in the voltage high harmonic components has the largest voltage amplitude, but the q-axis inductance is large in the embedded permanent magnet synchronous motor, so Fig. 7A Among the current higher harmonic components, the current amplitude of the q-axis second-order component becomes a small value, and the current higher harmonic amplitude of the sideband wave of the d-axis first-order component becomes a maximum value.

[0081] Here, in the structure of the first embodiment, that is, the structure of periodically changing the period of the carrier wave, as shown in FIG. Figure 6B As shown in FIG. 1 , the voltage harmonic component is shifted from the d-axis component to the q-axis component. Therefore, when a voltage of an embodiment is applied to the embedded permanent magnet synchronous motor, as shown in FIG. Figure 7B As shown in FIG. 2 , the d-axis current higher harmonic components are reduced.

[0082] In addition, regarding the q-axis current harmonic component, the increase is small due to the large q-axis inductance, resulting in a slight increase in the current harmonic component. In other words, when the dq axes are combined, the overall current harmonic component can be suppressed.

[0083] As described above, by periodically changing the PWM carrier, the harmonic components of the AC motor in the dq orthogonal coordinates contained in the PWM pulse are concentrated on the axis side with large inductance, thereby suppressing the harmonic components of the current flowing through the AC motor.

[0084] In addition, by suppressing the current harmonic components, the loss generated in the AC motor can be reduced.

[0085] Here, Figure 8 The figure shows a schematic diagram in which the period change amount C of the above-mentioned equation (1) is plotted on the horizontal axis and the root mean square (RMS value) of the current harmonic component is plotted on the vertical axis.

[0086] By increasing the period change amount C in the above equation (1), the d-axis voltage harmonic component can be shifted to the q-axis voltage harmonic component as described above, and the current harmonic component can be suppressed in the interior-type permanent magnet synchronous motor.

[0087] Therefore, if Figure 8 As shown in , the current high harmonic components can be suppressed. Figure 8As shown in FIG. 1 , when the period change amount is increased, the distortion of the pulse waveform increases, and the trend of increasing current harmonics can be confirmed. In other words, the RMS value of the current harmonics becomes the minimum point ( Figure 8 The circle shows a downward convex function.

[0088] Therefore, when the period of the carrier wave is periodically changed, the carrier wave generator 221 sets the period change amount C that changes with the sixth-order period to the point where the RMS value of the current harmonics is minimum, so that the AC motor can be driven with the current harmonic components suppressed.

[0089] In addition, by Figure 8 The vertical axis of is set as the loss of the AC motor caused by the current harmonic component, and the period change amount C with the minimum loss can be set. That is, the carrier generator 221 sets the period change amount that changes with the sixth order period as the period change amount with the minimum loss of the AC motor caused by the current harmonic component.

[0090] This allows the AC motor to be driven while the loss caused by the current harmonic components is suppressed.

[0091] In synchronous PWM control, since the pulse cannot be changed below the period of the carrier wave, the period of the carrier wave is generally set as the control period.

[0092] Here, when the period change amount C is set large, the change amount of the carrier period becomes large, and a long period section is generated. In other words, since a long control period area is generated, it is necessary to reduce the control response.

[0093] Therefore, in cases where a high-speed control response is required, the carrier generating unit 221 is driven by setting a value smaller than the period change amount C that minimizes the current harmonic components or the losses of the AC motor 1, so that the suppression of the inter-cycle variation and the reduction of the control response can be balanced with the suppression of the current harmonic components or losses.

[0094] As described above, according to the first embodiment of the present invention, the period of the carrier is changed at predetermined intervals so that the higher harmonic components in the dq orthogonal coordinates of the AC motor contained in the PWM pulse are concentrated on the axis side with large inductance, thereby realizing an AC motor control device 10 that can reduce the loss generated in the AC motor.

[0095] (Example 2)

[0096] Next, Example 2 of the present invention will be described.

[0097] Embodiment 2 is an example in which the present invention is applied to an AC motor control device for controlling an AC motor of an electric vehicle.

[0098] In the description of the second embodiment, illustration and description of the parts common to the first embodiment are omitted.

[0099] like Fig. 9 As shown, by applying the AC motor 1 to which the control unit 2 is applied as the vehicle-mounted motor main unit 101 to the electric vehicle 100, a high-efficiency electric vehicle 100 with reduced current harmonic components and AC motor loss can be provided.

[0100] In the vehicle-mounted motor main unit 101 applied to electric vehicles, when starting at extremely low temperatures, a warm-up operation may be performed due to freezing of the rotating parts of the motor. In such a warm-up operation, it is preferable that the loss generated by the motor is large.

[0101] Therefore, if Fig.10 As shown, in the PWM pulse generator 23 (a modified example of the PWM pulse generator 2), the carrier generated by the carrier generator 231 (generating a carrier with a constant period) and the carrier generator 232 (changing the period of the carrier) is switched by the carrier switch 233 according to the AC motor temperature information 1A. The AC motor temperature information 1A can be output to the carrier switch 233 from a temperature sensor (not shown) that detects the temperature of the AC motor 1.

[0102] By setting such a structure, when the AC motor temperature information 1A is below a certain value, the carrier wave of the carrier wave generator 231 with a constant period can be selected, and when the AC motor temperature information 1A is above a certain value, the carrier wave of the periodically changed 233 side can be selected, and the loss generated by the AC motor 1 during the warm-up operation can be increased. The carrier wave generator 231 can be defined as a carrier wave generator with a constant period.

[0103] Even when a heater for raising the temperature of the AC motor 1 is separately provided, the warm-up operation can be started earlier by configuring the PWM pulse generating unit 23 as described above.

[0104] According to the second embodiment, in addition to obtaining the same effects as those of the first embodiment, there is also an effect of being able to start the warm-up operation earlier as described above.

[0105] In addition, the above example describes an example where the q-axis inductance is larger than the d-axis inductance, but it can also be applied to an example where the d-axis inductance is larger than the q-axis inductance. In this case, the period of the PWM carrier is changed at predetermined intervals so that the harmonic components are concentrated on the d-axis side where the inductance is larger.

[0106] Description of Reference Numerals

[0107] 1···AC motor, 2···control unit, 3···inverter, 4···current detection unit, 5···position sensor, 10···AC motor control device, 21···vector control unit, 21A…modulation rate command value (voltage command value), 22···PWM pulse generating unit, 23···variation example of PWM pulse generating unit, 100···electric vehicle, 101···on-vehicle motor main unit, 221···carrier generating unit, 222···carrier voltage command comparing unit, 231…carrier generating unit (constant period carrier generating unit), 232···carrier generating unit (period), 233···carrier switching unit.

Claims

1. An AC motor control device, characterized in that: have: a power converter that performs power conversion from DC power to AC power; and A control unit that performs synchronous PWM control on the AC motor, The control unit has: a carrier wave generating unit that generates a carrier wave; and a PWM pulse generating unit, which generates a PWM pulse according to the carrier and the voltage command value, The carrier wave generating unit changes the period of the carrier wave so that the harmonic components of the AC motor in the dq orthogonal coordinates contained in the PWM pulse are concentrated on the axis side having a larger inductance between the d-axis and the q-axis.

2. The AC motor control device according to claim 1, characterized in that: The carrier wave generating unit changes the period of the carrier wave in a 6th order period.

3. The AC motor control device according to claim 2, characterized in that: The carrier wave generating unit sets a period change amount for changing the period of the carrier wave in a sixth-order period to a period change amount that minimizes a current harmonic component.

4. The AC motor control device according to claim 2, characterized in that: The carrier wave generating unit sets a period change amount for changing the period of the carrier wave in a sixth-order period as a period change amount that minimizes a loss of the AC motor due to a current harmonic component.

5. The AC motor control device according to claim 3, characterized in that: When a high-speed control response is required, the carrier generating unit sets the period change amount of the carrier wave with a 6th-order periodic change to a change amount smaller than the period change amount at which the loss of the current higher harmonic component or the AC motor is minimized, thereby suppressing a reduction in control response.

6. The AC motor control device according to claim 1, characterized in that: The carrier wave generating unit changes the period of the carrier wave so that the harmonic components in the dq orthogonal coordinates of the AC motor included in the PWM pulse are concentrated on the q-axis side where the inductance is larger than that on the d-axis side.

7. The AC motor control device according to any one of claims 1 to 6, characterized in that: The AC motor control device is a control device for controlling the AC motor of the electric vehicle.

8. The AC motor control device according to claim 7, characterized in that: The PWM pulse generating unit further comprises: A carrier wave generating unit that generates a carrier wave with a constant period; a periodic constant carrier generation unit that generates a periodically changing carrier; and A carrier switching unit switches between the constant-period carrier generating unit and the carrier generating unit.

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