Adaptive Sliding Mode Observer Design for Three-Phase Grid Voltage Parameters Under Unbalanced Faults

This paper presents an adaptive sliding mode observer (ASMO) to estimate three-phase grid voltage parameters, including both positive and negative sequences of voltage and grid frequency under unbalanced grid faults. First, the dynamic of three-phase voltage is reformulated as the second-order uncertain system, which can transform the traditional phase locked loop problem to the observer design problem. Based on the obtained dynamic system, an ASMO is constructed to estimate three-phase grid voltage parameters, using the adaptive and sliding mode techniques. The stability of the overall system including the observer estimation errors, sliding variable and adaptive estimation errors is rigorously proved by Lyapunov stability theory. The performance of proposed observer is assessed for estimation of three-phase grid voltage parameters by simulation in which two types of faults, i.e., the amplitude of voltage and grid frequency variations. are considered.