Advantages of Flux-based Position Sensorless Drive for Surface Permanent Magnet Machine

This paper improves a flux-based position sensorless drive for surface permanent magnet (PM) machines. On the basis, the rotor position is obtained from the spatial information in the magnet flux. The flux estimation is realized based on the integration of EMF voltage. In this paper, several implementation issues on the flux estimation are considered to improve the position sensorless drive. First, the machine phase voltage is measured for the flux estimation. By obtaining the actual inverter voltage outputs, the inverter deaditme effect is negligible on the flux and position estimation. Second, a modified integration is proposed to remove the flux estimation drift due to the voltage offset. Because the flux linkage is theoretically independent to the rotor speed, the signal-to-noise (SNR) ratio of postion estimation greatly increases at low speed. According to experimental results, the PM machine sensorless drive is improved at ~6% rated speed among the spaital signal SNR and drive dynamic response. More importantly, the overall current regulation bandwidth can be increased to 1kHz which is compatible to standard encoder-based drives.