Encoderless servo drive with adequately designed IPMSM for pulse voltage injection based position detection

This paper presents a technology fusion of encoderless control technique and encoderless-specialized motor aiming for servo drive applications. First, a high speed encoderless control technique which employs a high frequency pulsating signal injection method with square-wave pulse voltage at d-axis is proposed. The estimation principle is almost the same as that of resolver, and the control technique includes a high speed initial position estimation algorithm based on magnetic hysteresis phenomenon as well. Next, a prototype interior permanent magnet synchronous motor (IPMSM) is designed to act like resolver for the proposed control technique. Then, evaluation results of a prototype encoderless drive system are reported. Finally, the prototype system is confirmed to fulfill major servo specifications, such as, about 10bits net-resolution of the position detection at standstill, and, more than 60Hz speed control bandwidth in operation speed from 0 min^-1 up to 1000 min^-1. In conclusion, the proposed encoderless drive system is verified to achieve major control performances almost comparable to those of encoder-assisted servo drive systems.