Fractional order PLL based sensorless control of PMSM with sliding mode observer

For an accurate and effective sensorless control of permanent magnet synchronous machine, the position and speed information have to be accurately estimated. Sliding Mode Observer (SMO) is a robust technique used for the estimation of back-EMF. Due to the usage of discontinuous function, SMO has chattering effect on back EMF estimation and a filter is used to limit this. But the usage of filter increases delay in determining the rotor position thereby affecting accuracy. In order to avoid this delay, a new technique based on fractional order is proposed. In the proposed technique, conventional Phase Locked Loop is replaced with the Fractional Order Phase Locked Loop (FO-PLL) for estimation of rotor speed and position. FO-PLL provides an extra degree of freedom and better performance is achieved by proper selection of the fractional order coefficient. The simulation results show the effectiveness of the proposed technique.