Electric motor drive unit

Abstract

In an electric motor drive system that estimates magnetic pole position by superimposing high-frequency signals, the increase in current due to magnetic saturation is suppressed, thereby achieving overcurrent suppression and reduced noise. [Solution] The motor drive device includes an inverter for driving a motor having magnetic salient polarity, a current detector for detecting the current flowing through the motor, a current control unit for calculating a fundamental wave voltage command based on the current command and the current flowing through the motor, a superimposed voltage command generation unit for calculating a superimposed voltage command with a small amplitude when the current command is higher than a predetermined current value and with a frequency higher than the fundamental frequency of the fundamental wave voltage command, a high-frequency voltage superposition unit for calculating a voltage command by superimposing the superimposed voltage command on the fundamental wave voltage command, a rotational phase angle estimation unit for calculating an estimated phase angle based on the current flowing through the motor and the superimposed voltage command, and a gate signal generation unit for generating a gate signal for the inverter based on the voltage command and the estimated phase angle.

Description

Technical Field

[0001] Embodiments of the present invention relate to an electric motor drive device for driving an electric motor.

Background Art

[0002] When driving an electric motor having magnetic salient poles such as a permanent magnet synchronous motor, in order to generate a desired torque, it is necessary to detect the magnetic pole position of the rotor and supply current to the electric motor at an appropriate phase corresponding to the magnetic pole position. Physical sensors such as resolvers and PG sensors are known as sensors for detecting the magnetic pole position of the rotor. In recent years, sensorless control that does not use physical sensors has been used from the viewpoints of cost reduction and reliability improvement.

[0003] As a method for estimating the rotor magnetic pole position of an electric motor having magnetic salient poles, a high frequency higher than the frequency of the fundamental wave is superimposed on the fundamental wave supplied to generate torque in the rotor of the electric motor and applied. Then, there is a method of estimating the magnetic pole position of the rotor by extracting and analyzing the waveform of the component having the same frequency as the applied high frequency obtained as a result. And sensorless control for controlling the speed of the electric motor is performed by supplying current to the electric motor at an appropriate phase corresponding to the estimated result of the rotor magnetic pole position.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in conventional sensorless control, high-frequency currents are superimposed to estimate the magnetic pole position, but the overcurrent flowing through the permanent magnet synchronous motor is not taken into consideration. Even with a constant superimposed high-frequency amplitude, if the current flowing through the permanent magnet synchronous motor increases, the amplitude of the superimposed high-frequency current also increases due to magnetic saturation. Furthermore, there is an upper limit to the current that can be supplied in a typical motor drive system.

[0006] Therefore, in permanent magnet synchronous motor position sensorless drive systems that estimate the magnetic pole position by superimposing high-frequency current, the high-frequency current may exceed the upper limit, potentially damaging the motor drive system. Furthermore, there is still room for improvement in reducing the noise level of permanent magnet synchronous motors in conventional technology. Magnetic saturation increases the amplitude of the superimposed high-frequency current, which in turn increases the noise generated by the high-frequency components of the permanent magnet synchronous motor.

[0007] The present invention has been made in view of the above, and aims to suppress the increase in the amplitude of superimposed high-frequency current due to magnetic saturation, thereby achieving overcurrent suppression and noise reduction. [Means for solving the problem]

[0008] The motor drive device of the embodiment includes an inverter for driving a motor having magnetic salient polarity, a current detector for detecting the current flowing through the motor, a current control unit for calculating a fundamental wave voltage command based on the current command and the current flowing through the motor, a superimposed voltage command generation unit for calculating a superimposed voltage command with a small amplitude and a frequency higher than the fundamental frequency of the fundamental wave voltage command when the current command is higher than a predetermined current value based on the current command, a high-frequency voltage superposition unit for calculating a voltage command by superimposing the superimposed voltage command on the fundamental wave voltage command, a rotational phase angle estimation unit for calculating an estimated phase angle based on the current flowing through the motor and the superimposed voltage command, and a gate signal generation unit for generating a gate signal for the inverter based on the voltage command and the estimated phase angle. [Brief explanation of the drawing]

[0009] [Figure 1]Figure 1 is a block diagram of a permanent magnet synchronous motor sensorless drive system. [Figure 2] Figure 2 is a block diagram of the superimposed amplitude adjustment unit. [Figure 3] Figure 3 shows the relationship between the current command and the superimposed amplitude in the superimposed amplitude adjustment section. [Modes for carrying out the invention]

[0010] The embodiments will be described below with reference to the drawings. Figure 1 is a block diagram of a permanent magnet synchronous motor sensorless drive system. The permanent magnet synchronous motor sensorless drive system includes a permanent magnet synchronous motor 1, an inverter 2, a first current detector 3, a second current detector 4, a first coordinate transformation unit 5, a rotation phase angle estimation unit 6, a current control unit 7, a superimposed voltage command generation unit 8, a high-frequency voltage superimposition unit 9, a second coordinate transformation unit 10, and a PWM modulation unit 11.

[0011] The permanent magnet synchronous motor 1 is a synchronous motor that uses permanent magnets in its rotor and has magnetic salient polarity. The inverter 2 converts DC power into AC power to drive the permanent magnet synchronous motor 1. The first current detector 3 and the second current detector 4 detect the output current of the inverter. Here, the first current detector 3 detects the U-phase current, and the second current detector 4 detects the W-phase current. The V-phase current may be detected by providing a current detector, but it can also be calculated from the U-phase and W-phase currents.

[0012] The first coordinate transformation unit 5 performs a coordinate transformation based on the U-phase current and W-phase current detected by the first current detector 3 and the second current detector 4, and the estimated phase angle estimated by the rotation phase angle estimation unit 6 (described later), and outputs the dq-axis current. The rotation phase angle estimation unit 6 estimates the phase angle based on the dq axis current calculated by the first coordinate transformation unit 5 and the superimposed voltage command calculated by the superimposed voltage command generation unit, which will be described later.

[0013] The current control unit 7 compares the dq-axis current command, which is the drive command for the permanent magnet synchronous motor, with the dq-axis current calculated by the first coordinate transformation unit 5. It then performs control calculations to ensure that the dq-axis current command and the dq-axis current match, and outputs a fundamental wave voltage command.

[0014] The superimposed voltage command generation unit 8 generates a superimposed voltage command, which is a voltage signal with a frequency higher than the fundamental frequency of the fundamental voltage command applied to the permanent magnet synchronous motor calculated by the current control unit 7, in order to estimate the rotor pole position. The high-frequency voltage superposition unit 9 superimposes the superimposed voltage command generated by the superimposed voltage command generation unit 8 onto the fundamental wave voltage command calculated by the current control unit 7 and outputs a dq axis voltage command.

[0015] The second coordinate transformation unit 10 performs a coordinate transformation based on the dq axis voltage command calculated by the high-frequency voltage superposition means 9 and the estimated phase angle estimated by the rotation phase angle estimation unit 6, and outputs a three-phase voltage command. The PWM modulation unit 11 is a gate signal generation unit that generates gate signals for the switching elements constituting the inverter, and outputs a gate command for the inverter 2 based on the three-phase voltage command calculated by the second coordinate transformation unit 10.

[0016] Next, the details of the superimposed voltage command generation unit 8 will be explained. Figure 2 is a block diagram of the superimposed amplitude adjustment unit. Figure 3 is a diagram showing the relationship between the current command and the superimposed amplitude in the superimposed amplitude adjustment unit.

[0017] The superimposed voltage generation unit 8 includes a superimposed amplitude adjustment unit 8-1 and a high-frequency voltage command generation unit 8-2. The superimposed amplitude adjustment unit 8-1 has a lookup table 8-11 as shown in Figure 2, and takes the dq axis current command calculated by the current control unit 7 as input, adjusts the superimposed amplitude, and outputs it.

[0018] As shown in Figure 3, the lookup table 8-11 has a relational expression in which, for example, when the input current command exceeds a predetermined value, the superimposed amplitude decreases as the current command value increases, and outputs the adjusted superimposed amplitude.

[0019] The high-frequency voltage command generation unit 8-2 generates a superimposed voltage command based on the superimposed amplitude adjusted by the superimposed amplitude adjustment unit 8-1. That is, when the current command becomes a predetermined value or more, the superimposed voltage command generation unit 8 can output a superimposed voltage command in which the superimposed amplitude decreases according to the current command.

[0020] In the conventional sensorless control, the amplitude of the superimposed voltage command is constant, and a constant superimposed voltage command is superimposed even when the fundamental wave voltage command is high, and a large current flows through the permanent magnet synchronous motor. When a large current flows through the permanent magnet synchronous motor, magnetic saturation occurs and the inductance decreases, which may cause an even larger current to flow and an overcurrent to occur. When an overcurrent occurs, it may cause damage to the devices constituting the permanent magnet synchronous motor sensorless drive system or a decrease in the drivable capacity of the drive system.

[0021] On the other hand, when the current command becomes a predetermined value or more, the superimposed voltage command generation unit 8 of the present embodiment outputs a superimposed voltage command in which the superimposed amplitude decreases according to the current command, so that in the region where the fundamental wave voltage command is large and the current flowing through the permanent magnet synchronous motor is large, the superimposed voltage command to be superimposed can be made small, and sensorless control can be realized without flowing an excessive current. In addition, the superimposed voltage to be superimposed is a high frequency in the audible range, which is a cause of noise in the permanent magnet synchronous motor, but by reducing the amplitude, it is possible to realize low noise.

[0022] In the above embodiments, lookup tables 8-11 are used, making it possible to set the superimposed amplitude to any value, and to set an appropriate superimposed amplitude that does not affect the control system. For example, it is easy to set the superimposed amplitude so that the amplitude of the current flowing due to the dq-axis voltage command, which is the sum of the fundamental wave voltage command and the superimposed voltage command in a steady state, is approximately the same as the amplitude of the current flowing due to the dq-axis voltage command, which is the sum of the fundamental wave voltage command and the superimposed voltage command in a state where a large current is flowing. Furthermore, if the superimposed amplitude is reduced, the high-frequency components included in the output will also be reduced, which may reduce the accuracy of magnetic pole position estimation in sensorless control. Therefore, the superimposed amplitude is adjusted within a range that maintains the accuracy of magnetic pole position estimation.

[0023] Next, a modified example of the present invention will be described. The superimposed voltage generation unit 8 may, instead of adjusting the superimposed amplitude using the dq-axis current command calculated by the current control unit 7 as input, adjust the superimposed amplitude using the dq-axis current calculated by the first coordinate transformation unit 5 as input.

[0024] When the control time constant of the current control unit 7 is large, precise control can be achieved by using the dq-axis current instead of the dq-axis current command. Furthermore, the superimposed voltage generation unit 8 may determine the superimposed amplitude by calculation rather than using a lookup table.

[0025] For example, this can be achieved by having an arithmetic unit that performs operations on linear expressions such as the one shown in equation (1) below. vhRef=a·x+b···Formula (1) vhRef: Superimposed Amplitude a: Slope of a linear equation x:q-axis current command b: Intercept of a linear equation

[0026] In equation (1), the intercept b of the linear equation is the superimposed amplitude vhRef when the q-axis current command is zero, and a small value is set within the range in which the rotation phase angle estimation control is stable. The slope a of the linear equation is determined using the following equation (2), with respect to the maximum value iqRefMax of the q-axis current command that the permanent magnet synchronous motor sensorless drive system can take, a small superimposed amplitude vhRefMax within the range in which the rotational phase angle estimation control is stable when iqRefMax is the maximum value of the q-axis current command, and the intercept b. a=(vhRefMax-b) / iqRefMax...Equation (2)

[0027] Thus, it is possible to achieve overcurrent suppression control and noise reduction by determining the superimposed amplitude through calculations performed by the calculation unit, without using a lookup table. Furthermore, while using a lookup table requires a large amount of memory from the control processor, calculating the value requires less memory compared to using a lookup table. Therefore, even when sufficient memory capacity is not available, motor overcurrent suppression and noise reduction can be achieved.

[0028] Although embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0029] 1. Permanent magnet synchronous motor 2. Inverter 3. First current detector 4. Second current detector 5. First Coordinate Transformation Unit 6. Rotation Phase Angle Estimation Unit 7. Current control unit 8. Superimposed Voltage Command Generation Unit 9. High-frequency voltage superposition section 10...Second Coordinate Transformation Section 11. PWM Modulation Section

Claims

1. An inverter that drives an electric motor having magnetic salient polarity, A current detector for detecting the current flowing through the aforementioned electric motor, A current control unit that calculates a fundamental wave voltage command based on a current command and the current flowing through the motor, A superimposed voltage command generation unit calculates a superimposed voltage command with a small amplitude and a frequency higher than the fundamental frequency of the fundamental wave voltage command when the current command is higher than a predetermined current value based on the aforementioned current command, A high-frequency voltage superposition unit calculates a voltage command by superimposing the superimposed voltage command onto the fundamental wave voltage command, A rotation phase angle estimation unit calculates an estimated phase angle based on the current flowing through the motor and the superimposed voltage command, An electric motor drive device comprising: a gate signal generation unit that generates a gate signal for the inverter based on the voltage command and the estimated phase angle.

2. The motor drive device according to claim 1, wherein the superimposed voltage generation unit determines the amplitude of the superimposed voltage command using a lookup table that stores the relationship between the current command and the amplitude of the superimposed voltage command.

3. The motor drive device according to claim 1, wherein the superimposed voltage generation unit determines the amplitude of the superimposed voltage command using a relationship formula between the current command and the amplitude of the superimposed voltage command.

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