Fractional order sliding mode approach for chattering free direct power control of dc/ac converter

Abstract

A control approach of sliding mode category is applied in this study for direct control of active and reactive power in a grid connected three-phase dc/ac converter. A fractional order sliding mode (FOSM) control is proposed to suppress chattering from power and current signals. The chattering reduction is achieved through fractional order mathematical modelling which has control over the fractional error tolerance and instantaneous error, while all attributes of conventional sliding mode remain intact. FOSM controller drastically reduces signal chattering that is a low order system noise in conventional sliding mode control (CSMC). The controller is designed using active–reactive power errors as input to get reference voltage vector under sliding mode fractional law. The controller uses stationary frame of reference and simplifies the design process in a manner to rule out extra proportional integral (PI)-controlled current loops. The FOSM reduces half of the switching losses as per the fractional reference to switching modulation. Lyapunov candidate function is investigated to prove stability of the proposed controller. Simulation and experiment are carried out to check chattering free response of the proposed controller as compared to CSMC. The transient behaviour and robustness of FOSM controller is investigated and compared to PI-based control.