The Rotor Position Detection Technology For Synchronous Motor Based On Signal Injection

With the development of production technology, all the requirements of theelectrical drives industry gradually increased. Electrically excited synchronousmotors (ESM) with its high power factor, large flux weakening ratio and highcontrol accuracy are used in many applications. For the realization of ESMs’ precisecontrol, the rotor position is needed all the time. However, the traditionalmechanical sensors in practical applications may have many negative effects, whichmakes sensorless rotor position detection has an important practical significance.By comparing various existing detection methods, the paper adopts the highfrequency signal injection method, combined with the phase-locked loop (PLL)technology to detect the synchronous motor’s rotor position. While thyristors arecommon used in ESM applications, the subject taken to inject high-frequencycurrent in the excitation circuit to detect the rotor position.Firstly, this paper develops mathematical models of ESM in the stationary androtating coordinate system, and derives the rotor position detection method whichbased on the high-frequency signal injection, and then analyzes the excitationdamper winding on the impact of this detection method. Secondly it describes thebasic principles of PLL, and builds PLL’s mathematical model. Then it proposes thetheory of PLL which based on d-q conversion in the ESM’s rotor position detection,and analyzes the stability and steady-state error of this PLL, then carries out on thePLL design parameters. Thirdly it analyzes signal injection method, and parameters’selection method for different motors. And then it theoretically analyzes theinfluence of the motor’s torque caused by the injection signal. Finally, this paperdesigns and builds an experimental platform based on self-controlled synchronousmotor soft-start system to check the effectiveness of the rotor position detectionmethod, which includes the designs of the main circuit, signal conditioning circuit,auxiliary circuit, drive and filtering circuit, etc.In experimental section, this paper firstly simulates the method in MATLAB,the results show that the detections at stationary and low speed are good, and can beapplied to the soft-start system, in which the motor can be drove smoothly andreliably. Secondly, it does the experimental verification in the built platform, thesame result as the simulation, which shows that this method can effectively detectthe synchronous motor’s rotor position.