Sliding Mode Observer for Wide Speed Range Sensorless Induction Machine Drives: Considerations for Digital Implementation

The paper discusses the issues and provides solutions to digital implementation of sliding mode observer (SMO), especially for sensorless controlled induction machine (IM) operating over a wide speed range. An adaptive low pass filter (LPF) is proposed with variable cut-off frequency for a wide speed range, including a programming technique of using over-sampling to increase the sampling rate seen by the SMO. The sampling rate is made much higher than the system PWM frequency. Methods of designing proper gain are given for a specific SMO. Simulation and experimental results based on the fixed-point DSP TMS320F2812 are provided to verify the effectiveness of the proposed methods