Interior Permanent Magnet Wind Generator Torque Estimation Considering Low-Pass Filter Phase Shift Compensation

Abstract

Nowadays interior permanent magnet generators (IPMGs) are widely used in wind energy conversion systems (WECSs). Since in most WECS applications torque measurement is not available, torque estimation schemes are necessary. Due to simplicity and low computational burden, most common approach to estimate torque is cross product of flux and current. However, such estimation schemes heavily depend on accurate flux estimation. In this paper, torque estimation scheme based on cross product of flux and current in dq reference frame is employed. Flux is obtained by integrating back-EMF which is calculated from the IPMG voltage model. Pure integrator is substituted with low-pass filter (LPF) to avoid drift problems in a digital signal processor (DSP). Phase shift with respect to pure integrator was calculated for both discrete and continuous LPF in order to compute compensation signals. Simulation results show that adding compensation signal calculated for discrete LPF significantly improves flux and consequently torque estimation compared to compensation signal calculated for continuous LPF which is commonly used in literature.