Position Estimation in Switched Reluctance Motor Drives Using the First Switching Harmonics Through Fourier Series

Position estimation using only active phase voltage and current is presented to perform high-accuracy position sensorless control of a switched reluctance motor (SRM) drive. By extracting the amplitude of the first switching harmonic terms of phase voltage and current for a pulsewidth modulation period through the Fourier series, flux linkage and position are estimated without external hardware circuitry, such as a modulator and a demodulator, resulting in increasing cost, as well as large position estimation error produced when the motional back electromotive force is ignored near zero speed. Hence, the proposed position estimation scheme covers the entire speed range, including the standstill under various loads, and it has high-resolution information depending on switching frequency. A two-phase SRM drive system, consisting of an asymmetrical converter and a conventional closed-loop proportional-integral current controller, is utilized to validate the performance of the proposed position estimation scheme in comprehensive operating conditions. The estimated values very closely track the actual values in dynamic simulations and experiments. It is shown that the proposed position estimation scheme using the Fourier series is sufficiently accurate and works satisfactorily at various operating points.