An online calibrating method for middle value of current measurement circuit in permanent magnet synchronous motor drives

The measured d/q current signals of vector controlled PMSM in synchronous rotational frame often contain various kinds of noises, which is the main reason for the degradation of a high performance PMSM drive system. In this paper, we investigate a special kind of noise, which has the same frequency with motor's phase current, and come to the conclusion that this noise is induced by the middle value inaccuracy of current measurement circuit. To solve this problem, an online calibrating algorithm based on finite state machine is proposed, which can tightly track the middle value of current measurement circuit, and correct the corresponding parameters used in current sampling and calculating algorithm in time. The calibrating algorithm is calculated incrementally, and therefore it is less time-consuming and suitable for microcontroller. The proposed technique is implemented in a fixed-point DSP based vector controller for PMSM. Experimental results verify the feasibility and effectiveness of the proposed method.