A new method for initial position identification of Interior Permanent Magnet Synchronous Machine
Built in permanent magnet synchronous machine (IPMSM) has the characteristics of high efficiency and high power density. It is widely used in household appliances, electric vehicles, new energy power generation, aerospace and other fields. The sensorless control of permanent magnet synchronous motor starts when the initial position of rotor is unknown, which may lead to large starting current, unable to start, and even reverse rotation. Therefore, accurate identification of rotor initial position is very important to improve the sensorless control performance of permanent magnet synchronous motor.
At present, the common methods for identifying the initial position of motor rotor mainly include voltage pulse injection method and high-frequency signal injection method. The voltage pulse injection method injects a series of positive and negative symmetrical voltage pulse signals into the straight axis to obtain the initial position of the rotor by using the peak value of the current response. However, the voltage pulse signal needs to be injected many times. As the voltage vector direction approaches the real position of the rotor, the peak value difference of the current response decreases and the signal-to-noise ratio of the identified position decreases.
High frequency signal injection method includes high frequency current signal injection method and high frequency voltage signal injection method. The high-frequency current signal injection method is to inject the high-frequency current signal and extract the high-frequency response voltage to identify the rotor position. The performance of this method is greatly affected by the PI parameters of the current loop. High frequency voltage injection methods mainly include high frequency rotating sinusoidal voltage injection method, high frequency pulse voltage injection method and high frequency square wave voltage injection method.
Both high frequency rotating sinusoidal voltage injection method and high frequency pulse voltage injection method are high frequency sinusoidal signal injection. A filter needs to be used to obtain the high frequency response current signal, and then use the signal to identify the rotor position. The use of the filter reduces the dynamic performance of the system.
To solve this problem, a high frequency square wave voltage injection method is proposed. This method injects high-frequency square wave voltage into the direct axis and extracts the high-frequency response current on the quadrature axis to identify the rotor position. By injecting high-frequency square wave signal, the amplitude of high-frequency response current can be obtained directly by making a difference between adjacent sampling currents. Therefore, there is no need to use a filter to extract the rotor position.
However, because the input signal of the observer in this method is the quadrature axis high-frequency response current amplitude, this signal is a sinusoidal function of the position error signal, and there are multiple zeros, the convergence time of the closed-loop regulation of the rotor pole position signal is long; At the same time, this method is based on the convex machine effect of motor, so it can not identify the magnetic polarity; In addition, the quadrature axis high frequency response current signal of this method is related to the motor inductance parameters. The inductance parameters need to be used to normalize the signal to ensure the universality of the observer parameter design.
To solve the above problems, researchers from the school of electrical and information engineering of Hunan University proposed a rotor initial position identification method based on high-frequency orthogonal square wave voltage injection.
Fig.1 Schematic diagram of rotor initial position identification by high frequency orthogonal square wave voltage injection
Figure.2 IPMSM experimental platform
Firstly, the orthogonal high-frequency square wave voltage signal is injected into the static coordinate axis, and the magnetic pole position is identified by the high-frequency response current signal in the static coordinate axis system; Then, while injecting the high-frequency orthogonal square wave voltage signal, inject a low-frequency sinusoidal current signal into the direct axis, the saturation degree of the motor and the inductance of the AC-DC axis will change, resulting in the change of the high-frequency response current. The magnetic polarity (N pole and S pole) is identified by comparing the amplitude of the high-frequency response current near the positive and negative peaks of the low-frequency sinusoidal current.
This method can directly obtain the electrical angle of the rotor magnetic pole position by calculating the arctangent, and does not need to obtain the magnetic pole position signal through closed-loop adjustment. It has fast response speed and easy engineering implementation. In order to make the parameter design of speed observer universal, researchers take the signal obtained by arctangent as the input signal of speed observer, which avoids the dependence of speed observer parameter design on inductance parameters. Finally, the effectiveness and accuracy of the method are verified on the experimental platform of 1.5k wipmsm drive system, and the following conclusions are drawn:
- 1) This method can accurately identify the initial position of the rotor. When the rotor is in different positions, the electrical angle error of the identified initial position of the rotor is less than 4 °; The duration of the whole process of rotor initial position identification can be less than 30ms.
- 2) This method has good starting performance and fast dynamic response such as sudden loading and unloading.
- 3) The amplitude and frequency selection principle of low-frequency sinusoidal current used in magnetic pole polarity identification are analyzed in detail.
Source: China Permanent Magnet Manufacturer – www.rizinia.com
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