Investigation of a practical approach for rotor position estimation of PM machines without rotor saliency

Based on conventional PWM modulation techniques and low inductance characteristics of PM machines, this paper presents a novel and practical approach of rotor position estimation for a PM machine without rotor saliency. In conventional PWM modulations such as sin-Δ and space vector PWM techniques, there are three voltage vectors in action during each sampling period. For each different voltage vector, the phase current change will be different. By measuring the current changes under different voltage vectors, the back-EMF can be obtained and therefore the rotor position estimated. In this method, no prior knowledge of the machine parameters is needed. Further, at low speed, the back-EMF detection technique works well because the current ripples at very low speed are effectively utilized and no integration is needed. The proposed approach has been investigated by comprehensive computer simulation and the preliminary experimental testing results illustrate the effectiveness of the proposed approach