Sensorless Control Of PMSM Based On High Frequency Pulsating Signal Injection

Permanent magnet synchronous motor (PMSM) has become the main trend of the electrictransmission system drive motor because of its simple structure, high power density and highefficiency. In PMSM control system, the precise information of the rotor position and speed isessential, which can be measured directly by mechanical position sensors. However, some defects arecaused by the installation of mechanical sensors such as increasing the size and cost of the system andlimiting the system’s application area. In order to solve the problem, the sensorless control technologyis proposed. It has been the industrial and academic research focus and becomes one of the mostactive research directions in the field of the electric drive system.In this paper the research about sensorless control of PMSM is reviewed, which shows that toachieve sensorless control at low speed is more difficult. Therefore, focused on estimating the rotorposition and speed of the surface mounted permanent magnet synchronous motor (SPMSM) at lowand zero speed without a position sensor, the pulsating high frequency signal injection method iscarried out in-depth research.First of all, the mathematical model of PMSM and the principle of vector control are analyzed.The static and dynamic performance analysis of the speed and current closed-loop system with theposition sensor is carried out by simulation and experiment. Furthermore, using the sensorless controltechnology instead of the position sensor for zero and low speed control, the basic theory andrealization of three traditional sensorless control methods at are analyzed. These methods are therotating high frequency voltage injection method, the rotating high frequency current injection methodand the pulsating high frequency voltage injection method. Only the last one can be used for SPMSMwithout structural saliency.The most important issue of sensorless control is the initial rotor position detection. A newmethod for the initial rotor position detection of SPMSM without any rotational transducer ispresented. It is based on the nonlinear saturation characteristics of the stator inductance. The methodis realized in two steps. Firstly a high frequency sinusoidal voltage signal is injected into the estimatedsynchronous rotating coordinate system, thus the first estimated value of rotor position can beestimated through closed-loop adjustment. Then pole polarity is determined using different timeconstant characteristics of d-axis equivalent circuit under different poles. Combined with theestimated value, the correct initial position can be obtained. The proposed method can realize fast and accurate initial position detection. Moreover it does not add any hardware circuit.The initial rotor position is detected, and then the sensorless control at zero and low speed isrequired. Based on the depth analysis of the traditional pulsating high frequency voltage signalinjection method, a novel sensorless control method of SPMSM at low speed and a scheme ofestimated position error compensation are presented in this paper. On one hand, considering theimpact of the stator phase winding resistance, the motor high-frequency model is established. Thenthe position and speed estimation system is designed and a form of modulation signal is proposed,which can realize any arbitrary initial rotor position detection at zero speed and steady operation atlow speed. On the other hand, for the reason that the increment of error between the estimatedposition and the real one emerges with the speed increased, leading to uncertainty operation of system,a scheme of estimated position error compensation considering the fundamental frequency back-EMFand cross coupling terms is proposed. Precisely rotor position tracking can be achieved with thescheme.On the basis of the pulsating high frequency voltage injection method, a novel sensorless controlmethod of SPMSM based on high frequency current signal injection is proposed. A high frequencysinusoidal current signal is superimposed into the estimated d-axis, and the rotor position can bedemodulated after q-axis voltage is regulated, which is relative to error angle. Ultimately the rotorposition and speed can be obtained exactly at low and zero speed. Compared to the pulsating highfrequency voltage signal injection method, the proposed method is not only simpler in structurebecause it eliminates the need for two low pass filter in the current feedback loop, but also more stablethe position and speed estimation system because it is not subject to the changes of motor resistanceand inductance parameters.Finally, the hardware platform and the software system of the PMSM control system aredeveloped. Experiments can be carried out to verify the theoretical and simulation analysis of theproposed method in this paper.