Implementation of speed controlled Permanent-Magnet Synchronous Motor drive using low-resolution encoder for low-cost applications

The high-resolution encoder is typically used to detect the rotor position in Permanent-Magnet Synchronous Motor (PMSM) drive (AC servo drive) in many high performance applications where the high-precision position and extremely low speed controls are required. Therefore, the overall cost of such drive system is generally very expensive. This drive is absolutely not be attractive for low-cost applications where the speed control may be operating in the middle or high speed range. To reduce the cost, the high-resolution encoder may be replaced by the low-resolution encoder. In this paper, the implementation of speed controlled PMSM drive using low-resolution encoder down to 12 and 24 pulses/rev (or 3 and 6 pulses/electrical period for 8-pole PMSM respectively) for low-cost applications is thus proposed. The extrapolation technique is primarily adopted to increase the position resolution in both rotational directions and under the step load condition. The details of the overall drive system are given. Both simulation and experimental results are finally provided to validate the implementing system on a fixed-point TMS320F2812 DSP controller.