Electric motor driving device and electric motor driving method

Abstract

To provide an electric motor driver capable of suppressing fluctuations in DC voltage or current that occur in conjunction with the LC resonance component of the drive circuit due to harmonic components during asynchronous PWM control of the inverter or suppressing disturbance to a track circuit generated in accordance with an operating frequency component of the track circuit of a route.SOLUTION: The electric motor driver includes an inverter that drives the motor; and a control unit that controls at least by driving the inverter with asynchronous PWM. The control unit is configured to change the preset PWM frequency, during asynchronous PWM drive, in the inverter frequency domain, when the frequency difference between the preset PWM frequency and the harmonic component of the inverter frequency of the inverter is below the resonance frequency of the LC filter that the inverter has or below the operating frequency of the track circuit that detects the position of the rolling stock equipped with the motor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drive device and a drive method for driving an electric motor, and is particularly suitable as a drive device and a drive method for driving an electric motor mounted on a railway vehicle. [Background technology]

[0002] Driving devices that use inverters to control AC motors are widely used in industry, including driving devices for electric motors for railway vehicles. In this type of drive device, the DC voltage is smoothed and high-frequency components are suppressed by installing a smoothing capacitor to suppress DC voltage fluctuations and a reactor for absorbing harmonics, as in DC-powered railway vehicles.

[0003] An LC filter circuit is placed in the drive unit to level the DC voltage and suppress harmonic components. However, while this LC filter circuit reduces high-frequency components in proportion to the square of the frequency above the LC resonant frequency, it has no damping effect below the LC resonant frequency and, conversely, increases vibration at the resonant frequency. For this reason, when high-frequency components including components below the LC resonant frequency are output from the control unit, problems such as control instability and an increase in harmonic components in the DC voltage or current occur.

[0004] In order to suppress such a resonance phenomenon occurring in a drive device, Patent Document 1 discloses a damping control technique that suppresses the resonance phenomenon caused by an LC filter by manipulating the torque based on a DC voltage fluctuation component. Patent Document 2 discloses a technique that increases the PWM frequency when the rotation speed of an electric motor approaches the resonance frequency of an LC filter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4906980 [Patent Document 2] JP 2019-103325 A Summary of the Invention [Problem to be solved by the invention]

[0006] The techniques disclosed in Patent Documents 1 and 2 make it possible to suppress the resonance phenomenon caused by the LC filter. However, the techniques disclosed in Patent Documents 1 and 2 make no mention of high-frequency components that are generated when a drive device is driven by asynchronous PWM control, or harmonic components that are generated in the DC voltage or current as a result.

[0007] Generally, when an electric motor drive device is driven by asynchronous PWM control, harmonic components are generated that are the difference between the PWM frequency and a multiple of the inverter frequency. If such harmonic components match the LC resonance components of the drive device, a problem occurs in that high-frequency components increase in the DC voltage or current. Furthermore, if such harmonic components match the operating frequency components of the track circuit of the line, a problem occurs in that they become a disturbance factor for the track circuit.

[0008] Therefore, an object of the present invention is to provide a drive unit that makes it possible to suppress DC voltage or current fluctuations that occur in agreement with the LC resonance component of the drive unit due to harmonic components during asynchronous PWM control, or to suppress disturbances to the track circuit that occur in agreement with the operating frequency component of the track circuit of the line. [Means for solving the problem]

[0009] In order to solve the above problems, one representative motor drive device of the present invention includes an inverter that drives an electric motor, and a control device that controls the inverter by at least asynchronous PWM drive. During asynchronous PWM drive, the control device determines whether the difference frequency between a set PWM frequency and a harmonic component of the inverter frequency of the inverter is equal to or exceeds a resonant frequency of an LC filter of the inverter. Twice as much or less than the operating frequency of the track circuit that detects the position of the railway vehicle equipped with an electric motor Twice as muchIf the inverter frequency is in the range below, the set PWM frequency is changed. Effect of the Invention

[0010] According to the present invention, by changing the PWM frequency so that the harmonic components during asynchronous PWM control do not match the resonance components of the LC filter of the drive device, it is possible to suppress the fluctuation of DC voltage or current due to the resonance phenomenon. Also, by changing the PWM frequency so that the harmonic components do not match the frequency components of the track circuit of the line, it is possible to suppress the disturbance components to the track circuit. Furthermore, since the configuration changes the PWM frequency based on the inverter frequency, it is possible to suppress the harmonic components inexpensively without using additional parts, etc. Problems, configurations and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing an overall configuration of an electric motor drive device according to an embodiment of the present invention; [Diagram 2] FIG. 11 is a diagram showing the relationship between the ninth-order component of the inverter frequency and the resonant frequency of the LC filter. [Diagram 3] FIG. 13 is a diagram showing an overview of a case where the PWM frequency is changed for a combination of a ninth-order component of an inverter frequency and a resonant frequency of an LC filter. [Figure 4] 11 is a diagram showing a manner in which the PWM frequency is increased stepwise when the difference between the PWM frequency and the ninth-order component of the inverter frequency becomes equal to or smaller than twice the resonant frequency. FIG. [Diagram 5] FIG. 13 is a diagram showing a mode in which the PWM frequency is increased in a stepwise manner so that the difference related to the 9th-order component plus the 15th-order component of the inverter frequency is not equal to or less than twice the resonant frequency. [Figure 6] FIG. 11 is a diagram showing the relationship between the ninth-order component of the inverter frequency and the operating frequency of the track circuit. [Figure 7]1 is a diagram showing a schematic configuration of an electric motor drive device according to an embodiment of the present invention when applied to an electric motor for a railway vehicle; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, as a mode for carrying out the present invention, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are indicated by the same reference numerals, and all frequencies are indicated by the lowercase letter f. EXAMPLES

[0013] An embodiment of the present invention will be described with reference to Figures 1 to 7. This embodiment is an example in which an electric motor is driven by a drive device according to the present invention.

[0014] Fig. 1 is a block diagram showing the overall configuration of an electric motor drive device according to this embodiment. As shown in the figure, an inverter 3 is driven by a command signal generated by a control device 2, and an electric motor 1 is operated by receiving the output voltage of the inverter 3. The current flowing through the electric motor 1 is detected by a current detection circuit 4 and input to the control device 2. Here, the inverter 3 receives DC power from a DC power source and includes a smoothing capacitor and reactor (not shown).

[0015] In the control device 2, a vector control unit 21 calculates a voltage command value based on a current detection value from a current detection circuit 4. A PWM pulse generating unit 22 generates a PWM pulse signal based on the voltage command value from the vector control unit 21. The inverter 3 is driven by the PWM pulse signal from the PWM pulse generating unit 22, and generates an output voltage corresponding to the voltage command value.

[0016] The vector control unit 21 drives and controls the electric motor 1 using a general vector control, and does not specify a control method.

[0017] The PWM pulse generating unit 22 generates a PWM pulse signal according to the rotation speed and voltage of the electric motor 1. For electric motors for driving railway vehicles, the electric motor 1 is generally driven in an asynchronous PWM mode in the low speed range and in a synchronous PWM mode in the medium to high speed range.

[0018] When the motor 1 is driven in asynchronous PWM mode, harmonic components as shown in the following equation (1) are generated on the DC voltage side of the inverter 3 due to the PWM frequency Fc output by the PWM pulse generating unit 22 and the inverter frequency Finv, and are superimposed on the DC voltage.

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[0019] In addition, the inverter 3 has a resonant characteristic of a resonant frequency fLC as an LC filter due to a smoothing capacitor and reactor. In general, the resonant frequency fLC of an LC filter is about several tens of Hz. Therefore, when the difference component of the harmonic components superimposed on the DC voltage matches the resonant frequency fLC, a state occurs in which the resonant component becomes large.

[0020] As a specific example, Fig. 2 is a diagram showing the relationship between the ninth-order component of the inverter frequency Finv and the resonant frequency fLC of the LC filter. In Fig. 2, the horizontal axis represents the inverter frequency Finv, and the vertical axis represents the PWM frequency Fc and the harmonic components.

[0021] As shown in Figure 2, the difference component (Fc-Finv*9) between the PWM frequency Fc and the 9th component of the inverter frequency Finv decreases in a downward sloping manner to the right as the inverter frequency Finv increases, and becomes 0 at the inverter frequency Finv where Fc=Finv*9, after which this difference component increases.

[0022] For this reason, the difference component with the ninth-order component described above becomes small from about several hundred Hz, but as the inverter frequency Finv increases, a region occurs where it becomes smaller than the resonance frequency fLC, which is around several tens of Hz (the area enclosed by the dashed line in FIG. 2). In this region, an increase in components below the resonance frequency of the LC filter occurs. The above phenomenon can also occur in the case of higher-order components other than the ninth-order component of the inverter frequency Finv described in FIG. 2.

[0023] As described above, when the inverter 3 is driven in the asynchronous PWM mode, the harmonic components superimposed on the DC component become equal to or lower than the resonant frequency fLC of the LC filter, resulting in a problem that a region in which the harmonic components increase occurs.

[0024] To address this issue, in the asynchronous PWM mode, the increase in harmonic components can be easily suppressed by changing the PWM frequency Fc so that the harmonic components generated on the DC voltage side of the inverter 3 do not fall below the resonant frequency fLC of the LC filter.

[0025] As an example, FIG. 3 is a diagram showing an outline of a case where the PWM frequency Fc is changed with respect to a combination of the ninth-order component of the inverter frequency Finv and the resonant frequency fLC of the LC filter.

[0026] As shown in Figure 3, the harmonic component due to the difference component (Fc-9·Finv) between the PWM frequency Fc and the 9th component of the inverter frequency Finv decreases downward to the right as the inverter frequency Finv increases, and the PWM frequency Fc is changed when it becomes equal to or less than twice the resonant frequency fLC. In other words, by preventing this harmonic component from becoming equal to or less than twice the resonant frequency fLC, it is possible to suppress the increase in the harmonic component.

[0027] Specifically, as shown in FIG. 3 and below, when the harmonic component (Fc-9·Finv), which is the difference between the PWM frequency Fc and the ninth-order component of the inverter frequency Finv, is smaller than twice the resonant frequency fLC, the PWM frequency Fc is set (Equation 3) so that this harmonic component (Fc-9·Finv) is twice the resonant frequency fLC (Equation 2).

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[0028] As described above, by setting the PWM frequency Fc shown in (Equation 3), the harmonic components due to the difference between the PWM frequency Fc and the ninth-order component of the inverter frequency Finv (Fc-9·Finv) will not become smaller than twice the resonant frequency fLC, making it possible to suppress an increase in the harmonic components.

[0029] FIG. 3 explains the harmonic components due to the difference related to the ninth-order component described above. However, for other components, by applying the target harmonic component to the left side of (Equation 2), it is possible to derive (Equation 3) and set the PWM frequency Fc in a similar manner.

[0030] In addition, the method of changing the PWM frequency Fc so that the harmonic components generated due to the PWM frequency Fc and the higher-order components of the inverter frequency Finv do not match the components twice the resonant frequency fLC is not limited to the manner shown in Figure 3, and variations of this manner are also possible.

[0031] As one modified example, FIG. 4 shows a manner in which the PWM frequency Fc is increased in a stepwise manner when the difference (Fc-9·Finv) between the PWM frequency Fc and the ninth-order component of the inverter frequency Finv becomes equal to or smaller than twice the resonant frequency fLC.

[0032] In this modification, the harmonic components due to the difference related to the ninth order component can be set so as not to be less than twice the resonant frequency fLC. In this modification, the PWM frequency Fc is increased in a stepped manner compared to the embodiment shown in Fig. 3, so that it is possible to avoid matching with the mechanical resonant frequency and to reduce the harshness of the generated sound due to continuous changes. Also, although Fig. 4 shows the harmonic components due to the difference related to the ninth order component, it is possible to modify other harmonic components in the same way.

[0033] On the other hand, the PWM frequency Fc that can be set in the inverter 3 has an upper limit frequency that can be set due to the characteristics of the elements and gate drive circuit used in the inverter 3. Therefore, in the aspect of increasing the frequency in a stepwise manner shown in Fig. 4, when the frequency is changed, a region will be generated where the set value will be higher than the upper limit frequency that can be set.

[0034] To avoid such a situation, the case of a difference related to the 15th order component in addition to the difference related to the 9th order component is shown. Fig. 5 is a diagram showing a mode in which the PWM frequency Fc is increased in a stepwise manner so that the difference related to the 15th order component in addition to the difference related to the 9th order component is not less than twice the resonance frequency fLC.

[0035] As shown in Fig. 5, when 2*fLC+15*finv corresponding to the difference related to the 15th order component reaches the upper limit frequency that can be set, the PWM frequency Fc is temporarily set to a value less than 2*fLC+15*finv and greater than 2*fLC+9*finv. After that, the PWM frequency Fc is changed in a step-like manner so that the difference related to the 9th order component does not become less than twice the resonant frequency fLC.

[0036] As described above, by changing the PWM frequency Fc in a stepped manner and configuring it so that the difference related to the low order components does not become equal to or less than twice the resonance frequency fLC when the settable upper limit frequency is reached, it is possible to suppress the increase of the components equal to or less than the resonance frequency fLC at or below the settable upper limit frequency. Also, although Fig. 5 shows the case of the difference between the 15th order component and the 9th order component, other harmonic components can also be combined in a similar manner.

[0037] In addition, in a configuration in which the PWM frequency Fc is changed in a stepped manner, in order to prevent the harmonic components due to the asynchronous PWM mode from falling below the resonant frequency fLC of the LC filter, the PWM frequency Fc may be set to any value as long as it is below the settable upper limit value.

[0038] However, when the inverter 3 is driven with an asynchronous PWM frequency, a sound caused by the set PWM frequency Fc is generated by the inverter 3 and the electric motor 1. For this reason, when changing in a stepped manner, by setting a frequency defined by a musical scale, it is possible to set the sound caused by the PWM frequency Fc so that it is not unpleasant to a person (for example, musical scale names such as C 6: 1046 Hz, D 6: 1174 Hz, E 6: 1318 Hz, etc.).

[0039] On the other hand, even at the operating frequency fTC of the track circuit, when the inverter 3 is driven in asynchronous PWM mode, harmonic components generated in the DC component coincide with the operating frequency fTC of the track circuit and become disturbance elements, which is an issue.

[0040] To address this issue, the increase in disturbance elements can be easily suppressed by changing the PWM frequency Fc so that the harmonic components generated on the DC voltage side of the inverter 3 in asynchronous PWM mode do not fall below the operating frequency fTC of the track circuit.

[0041] Fig. 6 is a diagram showing the relationship between the ninth-order component of the inverter frequency Finv and the operating frequency fTC of the track circuit. In Fig. 6, as in Fig. 2, the horizontal axis is the inverter frequency Finv, and the vertical axis is the PWM frequency Fc and the harmonic components.

[0042] As shown in Figure 6, the harmonic component due to the difference between the PWM frequency Fc and the 9th component of the inverter frequency Finv decreases downward to the right as the inverter frequency Finv increases, and when it becomes equal to or less than twice the track circuit operating frequency fTC, the PWM frequency Fc is changed. This makes it possible to prevent this harmonic component from becoming equal to or less than twice the track circuit operating frequency fTC, thereby suppressing the increase in disturbance elements.

[0043] Specifically, similarly to the case of suppressing the LC resonance component, the PWM frequency Fc is set so that the harmonic component due to the difference between the track circuit operating frequency fTC and the ninth-order component of the inverter frequency Finv, as shown in (Equation 4), is twice the track circuit operating frequency fTC (Equation 5).

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[0044] This makes it possible to suppress the increase in disturbance factors for the track circuit operating frequency fTC by changing the PWM frequency Fc during asynchronous PWM drive.

[0045] In addition, in the configurations of the other modified examples shown in FIG. 4 and FIG. 5, by replacing the LC resonant frequency fLC with the operating frequency fTC of the track circuit, it is possible to suppress an increase in disturbance factors for the track circuit.

[0046] FIG. 7 is a diagram showing a schematic configuration in which the electric motor drive device according to this embodiment is applied to an electric motor for a railway vehicle.

[0047] A railway vehicle 100 equipped with an electric motor drive device (control device 2, inverter 3 and current detection circuit 4) according to this embodiment receives DC power from an overhead line 101 and runs on rails 102 with wheels driven by electric motors (e.g., induction motors 1a to 1d).

[0048] By applying the motor drive device of this embodiment, the harmonic components caused by the asynchronous PWM drive of the inverter 3 become lower than the resonant frequency of the LC filter (not shown) provided in the drive device, making it possible to suppress an increase in the harmonic components.

[0049] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0050] 1, 1a to 1d ... electric motor, 2 ... control device, 3 ... inverter, 4 ... current detection circuit, 21 ... vector control unit, 22 ... PWM pulse generation unit, 100 ... railway vehicles, 101 ... overhead lines, 102 ... rails

Claims

1. an inverter that drives an electric motor; A control device that controls the inverter at least by asynchronous PWM drive; Equipped with During the asynchronous PWM drive, the control device changes the set PWM frequency in the inverter frequency range where a frequency difference between the set PWM frequency and a harmonic component of the inverter frequency of the inverter is equal to or less than twice the resonant frequency of an LC filter of the inverter or equal to or less than twice the operating frequency of a track circuit that detects the position of a railway vehicle equipped with the electric motor. An electric motor drive device comprising:

2. 2. The electric motor drive device according to claim 1, The control device increases the change in the set PWM frequency in a stepwise manner in accordance with an increase in the inverter frequency. An electric motor drive device comprising:

3. 3. The electric motor drive device according to claim 2, When an upper limit frequency exists for the PWM frequency, the control device suppresses the changed PWM frequency to be equal to or lower than the upper limit frequency by combining the manner of changing the set PWM frequency based on a difference frequency between the set PWM frequency and a different harmonic component of the inverter frequency. An electric motor drive device comprising:

4. 4. The electric motor drive device according to claim 2 or 3, The control device changes the PWM frequency that is increased stepwise to a frequency that corresponds to a musical scale. An electric motor drive device comprising:

5. A method for driving an electric motor by an inverter controlled by at least asynchronous PWM drive, comprising: When the difference frequency between the set PWM frequency and the harmonic components of the inverter frequency of the inverter during the asynchronous PWM drive is equal to or less than twice the resonant frequency of the LC filter of the inverter or equal to or less than twice the operating frequency of a track circuit that detects the position of a railway vehicle equipped with the electric motor, the set PWM frequency is changed in the inverter frequency range. A method for driving an electric motor comprising the steps of:

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