Extended Self-Tuning Filter-Based Synchronization Technique for Unbalanced and Distorted Grid

Control of grid-connected converters (GCC) is a challenging task in adverse grid conditions. Due to increasing presence of inverter-interfaced renewable energy sources and nonlinear loads, adverse grid conditions are often can not be avoided. Self-tuning filter (STF) is an widely used technique for the control of GCC in adverse conditions. However, the existing literature only considers balanced grid condition. This paper extends STF for unbalanced grid. Proposed extension is obtained by considering STF in state-space framework together with model of the unbalanced grid. Using open-loop frequency estimation technique, frequency-adaptive STF is proposed that is able to operate in unbalanced and distorted grid. Mathematical analysis are presented to demonstrate the frequency selective property of the extended STF. Comparative numerical simulation results are provided to demonstrate the suitability of the proposed technique.