Ac motor control device

Abstract

To provide an AC motor control device that can suppress the harmonic components of a current flowing through an AC motor and reduce losses generated in the AC motor.SOLUTION: An AC motor control device 10 includes a power converter 3 that converts DC power to AC power, and a control unit 2 that controls the AC motor 1 in a synchronous PWM manner. The control unit 2 includes carrier wave generating units 221, 231, and 232 that generate carrier waves, and PWM pulse generating units 22 and 23 that generate PWM pulses on the basis of the carrier waves and a voltage command value 21A. The carrier wave generating units 221, 231, and 232 change the period of the carrier wave such that the harmonic components in the dq orthogonal coordinates of the AC motor 1 contained in the PWM pulses are concentrated on the axis with the larger inductance, either the d axis or the q axis.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an AC motor control device that drives 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 an AC motor 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 PWM 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 into AC power, but because the switching elements of the power conversion device are repeatedly turned on and off at high speed, the output voltage is applied to the AC motor in pulses.

[0005] As a result, the current flowing through the AC motor contains harmonic components, which can cause noise and losses.

[0006] Techniques for reducing noise and loss caused by the on / off switching of switching elements of such a power conversion device are disclosed in, for example, Patent Documents 1 and 2.

[0007] The method described in Patent Document 1 is configured to change the period of the PWM carrier over time, while the method described in Patent Document 2 is configured to shorten the period of the PWM carrier near the current zero crossing.

[0008] This method disperses the harmonic components of the current flowing through the AC motor by dispersing the harmonic components of the voltage applied to the AC motor in a pulsed manner, which has been proposed to reduce noise generated in the AC motor and suppress DC voltage fluctuations. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2010-41877 A [Patent Document 2] JP2019-47688 Public Relations Summary of the Invention [Problem to be solved by the invention]

[0010] 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.

[0011] However, while the methods described in Patent Documents 1 and 2 make it possible to disperse the harmonic components of the voltage applied in a pulsed manner to an AC motor, they do not disclose a configuration for actively suppressing the harmonic components of the current flowing through the AC motor.

[0012] Unless the harmonic components of the current flowing through an AC motor are suppressed, it is difficult to reduce the noise and losses caused by the harmonic components.

[0013] An object of the present invention is to realize 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]

[0014] In order to achieve the above object, the present invention is configured as follows.

[0015] An AC motor control device includes a power converter that converts DC power to AC power, and a control unit that performs synchronous PWM control of an AC motor, the control unit having a carrier wave generation unit that generates a carrier wave, and a PWM pulse generation unit that generates a PWM pulse based on the carrier wave and a voltage command value, and the carrier wave generation unit changes the period of the carrier wave so that harmonic components in a dq orthogonal coordinate of the AC motor contained in the PWM pulse are concentrated on the axis with the larger inductance, either the d axis or the q axis. Effect of the Invention

[0016] According to the present invention, it is possible to realize 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. [Brief description of the drawings]

[0017] [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] 1 is a block diagram showing a PWM pulse generating unit according to a first embodiment of the present invention; [Diagram 3] FIG. 11 is a diagram showing an example of waveforms in a comparative example different from the present invention, in which the period of a carrier wave is constant during synchronous PWM control. [Figure 4] 4 is a diagram showing an example of waveforms when the period of a carrier wave during synchronous PWM control is periodically changed in the first embodiment of the present invention. FIG. [Diagram 5] This is a schematic diagram of the relationship between the orthogonal dq-axis coordinate system and voltage and current in vector control. [Figure 6A] FIG. 11 is a diagram showing harmonic components of an output voltage when the period of a carrier wave is constant. [Figure 6B] 11 is a diagram showing harmonic components of an output voltage when the period of a carrier wave is periodically changed. FIG. [Figure 7A] 6B is a diagram showing current harmonic components that are generated when the voltage harmonic components shown in FIG. 6A are applied to an interior permanent magnet synchronous motor. FIG. [Figure 7B] 6C is a diagram showing current harmonic components that are generated when the voltage harmonic components shown in FIG. 6B are applied to an interior permanent magnet synchronous motor. FIG. [Figure 8] 11 is a graph showing changes in current harmonic components when the amount of period change is changed. [Figure 9] FIG. 11 is a diagram showing an example in which an AC motor control device according to a second embodiment of the present invention is applied to an electric vehicle. [Figure 10] FIG. 11 is a configuration diagram of a PWM pulse generating unit in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. EXAMPLES

[0019] Example 1 A first embodiment of the present invention will be described with reference to FIGS.

[0020] In the first embodiment, an example in which an AC motor 1 is driven by an AC motor control device 10 of the present invention will be described.

[0021] Fig. 1 is a schematic configuration diagram of an AC motor control device 10 according to a first embodiment. 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. Fig. 2 is an explanatory diagram of the PWM pulse generation unit 22 included in the control unit 2, and the PWM pulse generation unit 22 includes a carrier wave generation unit 221 and a carrier voltage command comparison unit 222.

[0022] The vector control unit 21 of the control unit 2 calculates a modulation factor command value (voltage command value) 21A based on information from a current detection unit 4 that detects the current flowing through the AC motor 1 and information 5A from a position sensor 5 that detects the rotational position of the AC motor 1.

[0023] A PWM pulse generator 22 generates a PWM pulse 22A based on the calculated modulation factor command value 21A, and an inverter 3 converts DC power to AC power based on the generated PWM pulse 22A, and supplies the AC power to an AC motor 1.

[0024] In the PWM pulse generating unit 22, as shown in FIG. 2, a carrier wave such as a triangular wave is generated by a carrier wave generating unit 221, and the generated carrier wave is compared with a modulation factor command value 21A by a comparing unit 222 to generate a PWM pulse 22A.

[0025] A synchronous PWM control method is one of the methods for controlling the AC motor 1 by PWM pulses. The control unit 2 controls the AC motor 1 by synchronous PWM.

[0026] Fig. 3 is a schematic diagram of the carrier wave and modulation factor command value during synchronous PWM control in a comparative example different from the present invention. As shown in Fig. 3, the synchronous PWM control method fixes the number of PWM carrier waves included in one rotation by changing the period of the PWM carrier wave according to the rotation speed of the AC motor.

[0027] For example, in the example shown in Figure 3, one half cycle (0° to 180°) of the AC modulation factor command includes 4.5 cycles each of the rising (peaks) and falling (valleys) of the carrier wave, and one rotation (0° to 360°) of the AC modulation factor command includes 9 cycles each of the rising (peaks) and falling (valleys) of the carrier wave, for a total of 18 cycles.

[0028] In addition, the period of the PWM carrier wave is generally set to a constant interval, and in the example configuration shown in Figure 3, this is called synchronous 9-pulse control.

[0029] In this way, the use of a synchronous PWM control method has the advantage that the symmetry of the waveform is maintained and even-order harmonics are not generated. On the other hand, because the number of PWM carrier waves is fixed, the configuration results in large voltage harmonic components being generated, such as the sideband waves of the first-order component of the carrier wave (6th and 12th order components in the configuration shown in Fig. 3) and the second-order component (18th order component in the configuration shown in Fig. 3).

[0030] Furthermore, when a voltage containing such harmonic components is applied to an AC motor, current harmonic components are also generated in the current due to the influence of these harmonic components.

[0031] In the first embodiment of the present application, in order to suppress harmonic components of a current generated in an AC motor during synchronous PWM control such as the example shown in FIG. 3, the period of a carrier wave during synchronous PWM control is periodically changed.

[0032] Fig. 4 is a schematic diagram showing a synchronous 9-pulse period in which the period of the carrier wave of the synchronous PWM control according to the first embodiment of the present invention is periodically changed. As shown in Fig. 4, the period of the carrier wave is configured to repeat a short period S and a long period L twice. Specifically, the number of peaks and valleys of the synchronous PWM is P (P=9 in Figure 4), the order of the carrier wave period is n, and the period of the carrier wave is set to change in a sixth order cycle as shown in the following equation (1).

[0033]

number

[0034] In the above formula (1), C integrated into the sine wave function is a value corresponding to the amount of period change, and n is the order.

[0035] For example, if C=0 with 9 synchronous pulses and the change between each period is 0, the period of the carrier wave is fixed at (2π / 18)=20[deg] as in the comparative example shown in Fig. 3. If C>0 with 9 synchronous pulses, the following equations (2), (3), and (4) are satisfied, and n=1, 2, and 3 are repeated as in the present invention shown in Fig. 4.

[0036]

number

[0037]

number

[0038]

number

[0039] By changing the number P of peaks and valleys of the synchronous PWM using the above formula (1), it is possible to similarly set the period change at, for example, 15 synchronous pulses.

[0040] FIG. 5 is a diagram showing an outline of the dq orthogonal coordinates and the voltage and current during vector control.

[0041] In Fig. 5, in an AC motor, the dq Cartesian coordinate system is set with the d-axis in the magnet axis direction and the q-axis perpendicular to the magnet axis direction. In vector control, voltage and current are controlled using such dq Cartesian coordinate system.

[0042] 6A and 6B are diagrams showing harmonic components of the output voltage when the period of the carrier wave is constant and when the period of the present application is periodically changed. Fig. 6A shows the case of the constant period, and Fig. 6B shows the case of the embodiment where the period of the carrier wave is periodically changed.

[0043] The horizontal axis of Figures 6A and 6B is the order, and the vertical axis is the amplitude. The solid line components in Figures 6A and 6B are the d-axis (magnet axial direction) components mentioned above, and the dotted lines are the q-axis (direction perpendicular to the magnet axis) components mentioned above.

[0044] In the case of synchronous PWM control with a constant period in Figure 6A, the component with the largest amplitude is the second-order component of the q-axis component (dotted line). Also, the d-axis component (solid line) is generated on the left and right of the second-order component as sideband components of the first- and third-order components.

[0045] Here, as shown in Figure 6B, by periodically changing the period, the harmonic components change. In Figure 6B, it can be seen that the first and third order sideband components of the d-axis component (solid line) are decreasing. It can also be seen that the components before and after the second order component of the q-axis component (dotted line) are increasing. In other words, by periodically changing the period of the carrier wave, a voltage harmonic component configuration is obtained in which the d-axis harmonic component is shifted to the q-axis harmonic component.

[0046] Here, in an AC motor, a voltage containing harmonic components as shown in Fig. 6A or 6B is applied, and current harmonic components are generated due to the voltage harmonic components. The voltage and current related to the harmonic components have the relationship shown in the following formulas (5) and (6) for the d-axis component (magnet axis direction) and q-axis (component perpendicular to the magnet axis).

[0047] 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.

[0048]

number

[0049]

number

[0050] Equations (5) and (6) above indicate that the harmonic current generated in the motor is the value obtained by dividing the frequency corresponding to the order of the harmonic voltage by the inductance.

[0051] Here, in the main motor that is the power source of in-vehicle equipment, an embedded permanent magnet synchronous motor is often used. In such an embedded permanent magnet synchronous motor, the motor has a large salient pole ratio where the q-axis inductance shown in the above equation (6) is larger than the d-axis inductance shown in the above equation (5) (Ldh < Lqh). In other words, when a voltage harmonic of the same amplitude is applied, the motor has the characteristic that the q-axis current harmonic component is smaller than the d-axis current harmonic component.

[0052] Here, FIGS. 7A and 7B show the current harmonic components generated when the voltage harmonic components shown in FIGS. 6A and 6B are applied to such an embedded permanent magnet synchronous motor.

[0053] FIG. 7A is a diagram when the period is constant, and FIG. 7B is a diagram when the period of the carrier wave in one embodiment is periodically changed. In FIGS. 7A and 7B, the horizontal axis represents the order, and the vertical axis represents the amplitude. The solid line component is the d-axis (magnet axis direction) component, and the dotted line indicates the q-axis (direction orthogonal to the magnet axis) component.

[0054] In the case of FIG. 7A with a constant period, in the voltage harmonic component of FIG. 6A, the second-order component of the q-axis component has the maximum voltage amplitude. However, in the embedded permanent magnet synchronous motor, since the q-axis inductance is large, in the current harmonic component of FIG. 7A, the current amplitude of the q-axis second-order component is a small value, and the current harmonic amplitude of the sideband wave of the d-axis first-order component is the maximum value.

[0055] Here, in the configuration where the period of the carrier wave having the configuration of Embodiment 1 is periodically changed, as shown in FIG. 6B, the voltage harmonic component is shifted from the d-axis component to the q-axis component. Therefore, when a voltage according to one embodiment is applied to the embedded permanent magnet synchronous motor, the d-axis current harmonic component decreases as shown in the current harmonic component of FIG. 7B.

[0056] In addition, the increase in the q-axis current harmonic components is small because the q-axis inductance is large, resulting in a slight increase in the current harmonic components. In other words, by combining the dq axes, it is possible to suppress the overall current harmonic components.

[0057] As described above, by periodically changing the PWM carrier wave so that the harmonic components in the dq Cartesian coordinates of the AC motor contained in the PWM pulse are concentrated on the axis side with the large inductance, it is possible to suppress the harmonic components of the current flowing through the AC motor.

[0058] Moreover, by suppressing the current harmonic components, it is possible to reduce losses occurring in the AC motor.

[0059] FIG. 8 shows a schematic diagram in which the horizontal axis represents the period change amount C in the above formula (1) and the vertical axis represents the root mean square (RMS value) of the current harmonic components.

[0060] By increasing the amount of period change 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 in an interior permanent magnet synchronous motor, the current harmonic component can be suppressed.

[0061] This makes it possible to suppress the current harmonic components, as shown in Fig. 8. However, as shown in Fig. 8, it can be seen that as the amount of period change is increased, the distortion of the pulse waveform becomes greater and the current harmonics tend to increase. In other words, the RMS value of the current harmonics versus the amount of period change is a downward convex function with a minimum point (shown by a circle in Fig. 8).

[0062] Therefore, when the period of the carrier wave is changed periodically, the carrier wave generating unit 221 sets the period change amount C, which is changed in the sixth period, to the point where the RMS value of the current harmonics is minimum, making it possible to drive the AC motor with the current harmonic components suppressed.

[0063] 8 represents the loss of the AC motor caused by the current harmonic components, it is possible to set the period change amount C that minimizes the loss. In other words, the carrier wave generating unit 221 sets the period change amount changed in the sixth period to the period change amount that minimizes the loss of the AC motor caused by the current harmonic components.

[0064] This makes it possible to drive the AC motor while suppressing losses that occur in the AC motor due to current harmonic components. In synchronous PWM control, the pulse cannot be changed at or below the period of the carrier wave, so it is common to set the period of the carrier wave as the control period.

[0065] Here, if the period change amount C is set large, the change amount of the carrier wave period becomes large, and a section with a long period occurs. In other words, a region with a long control period occurs, and it becomes necessary to lower the control response. For this reason, when a high-speed control response is required, the carrier wave generating unit 221 can be driven by setting a value smaller than the period change amount C that minimizes the current harmonic components and losses in the AC motor 1, thereby enabling driving while achieving a balance between suppressing the change between periods and the deterioration of the control response and suppressing the current harmonic components and losses.

[0066] As described above, according to the first embodiment of the present invention, the period of the carrier wave is changed at predetermined intervals so that the harmonic components in the dq Cartesian coordinates of the AC motor contained in the PWM pulse are concentrated on the axis side with the large inductance, so that an AC motor control device 10 capable of reducing losses generated in the AC motor can be realized.

[0067] Example 2 Next, a second embodiment of the present invention will be described.

[0068] The second embodiment is an example in which the present invention is applied to an AC motor control device that controls an AC motor of an electric vehicle. In the description of the second embodiment, parts common to the first embodiment will not be illustrated or described.

[0069] As shown in FIG. 9, by applying the AC motor 1 to which the above-mentioned control unit 2 is applied as an on-board main motor 101 to an electric vehicle 100, it is possible to provide a highly efficient electric vehicle 100 that reduces current harmonic components and AC motor.

[0070] In the on-board motor 101 applied to an electric vehicle, the rotating parts of the motor may freeze when started at extremely low temperatures, so a warm-up operation is required. During such a warm-up operation, it is desirable for the loss generated by the motor to be large.

[0071] 10, in PWM pulse generating unit 23 (a modified example of PWM pulse generating unit 2), carrier waves generated by carrier wave generating unit 231 (which generates a carrier wave with a constant period) and carrier wave generating unit 232 (which changes the period of the carrier wave) are switched based on AC motor temperature information 1A by carrier wave switching unit 233. AC motor temperature information 1A can be output to carrier wave switching unit 233 from a temperature sensor (not shown) that detects the temperature of AC motor 1.

[0072] With this configuration, when AC motor temperature information 1A is below a certain level, the carrier wave on the fixed cycle carrier wave generating unit 231 side can be selected, and when AC motor temperature information 1A is above a certain level, the carrier wave on the periodically changed 233 side can be selected, making it possible to increase the loss generated by AC motor 1 during warm-up operation. Carrier wave generating unit 231 can be defined as a fixed cycle carrier wave generating unit.

[0073] Even in the case where a heater for increasing the temperature of the AC motor 1 is separately provided, by configuring the PWM pulse generating unit 23 as described above, the warm-up operation can be started earlier.

[0074] According to the second embodiment, in addition to being able to obtain the same effects as those of the first embodiment, there is also an effect that the warm-up operation can be started earlier, as described above.

[0075] In the above example, the q-axis inductance is larger than the d-axis inductance, but the present invention 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 wave is changed at a predetermined interval so that the harmonic components are concentrated on the d-axis side where the inductance is larger. [Explanation of symbols]

[0076] 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 factor command value (voltage command value), 22 PWM pulse generation unit, 23 modified example of PWM pulse generation unit, 100 electric vehicle, 101 vehicle-mounted main motor, 221 carrier wave generation unit, 222 carrier voltage command comparison unit, 231 carrier wave generation unit (constant period carrier wave generation unit), 232 carrier wave generation unit (period), 233 carrier wave switching unit

Claims

1. A power converter that converts DC power into AC power, A control unit that performs synchronous PWM control on an AC motor, Comprising, The control unit, A carrier wave generation unit that generates a carrier wave, and a PWM pulse generation unit that generates a PWM pulse based on the carrier wave and a voltage command value, The carrier wave generation 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 axis side with the larger inductance among the d-axis or the q-axis. An AC motor control device characterized by that.

2. In the AC motor control device according to Claim 1, The carrier wave generation unit changes the period of the carrier wave in a sixth-order period. An AC motor control device characterized by that.

3. In the AC motor control device according to Claim 2, The carrier wave generation unit sets the period change amount for changing the period of the carrier wave in a sixth-order period to a period change amount at which the current harmonic component is minimized. An AC motor control device characterized by that.

4. In the AC motor control device according to Claim 2, The carrier wave generation unit sets the period change amount for changing the period of the carrier wave in a sixth-order period to a period change amount at which the loss of the AC motor generated by the current harmonic component is minimized. An AC motor control device characterized by that.

5. In the AC motor control device according to Claim 3, When a high-speed control response is required, the carrier wave generation unit sets the period change amount for changing the period of the carrier wave in a sixth-order period to a change amount smaller than the period change amount at which the current harmonic component or the loss of the AC motor is minimized, and suppresses a decrease in the control response. An AC motor control device characterized by that.

6. In the AC motor control device according to Claim 1, The carrier wave generation 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 the inductance on the d-axis side. An AC motor control device characterized by that.

7. In the AC motor control device according to any one of Claims 1 to 6, An AC motor control device characterized by being a control device that controls an AC motor of an electric vehicle.

8. In the AC motor control device according to Claim 7, The PWM pulse generation unit further includes a carrier wave generation unit that generates the carrier wave with a constant period, a constant-period carrier wave generation unit that generates the carrier wave whose period is periodically changed, and a carrier wave switching unit that switches between the constant-period carrier wave generation unit and the carrier wave generation unit, and an AC motor control device characterized by this.

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