Stability assessment and optimal state-feedback system design for PQ-Vf coordination in a PV/DFIG/DSG based microgrid

In this paper an improved comprehensive stability region is presented towards optimal feedback solution for multiple distributed generators (DGs) based microgrid. Overall optimal control design challenges for DGs undergoing grid integrated/islanded operation (i.e. variable stability regions) are addressed for photovoltaic (PV), wind generation system (WGS) as these are considered for multi-DGs dynamics in the present microgrid. Second order phase locked loop (PLL) based PV side voltage source converter (VSC) control, and doubly fed induction generator's (DFIG's), grid side converter (GSC) control are considered for proposed overall gain optimization. To enhance the stability margin global/overall optimal feedback path is targeted here instead of local optimal solutions (individual DG consideration). To achieve optimal stability margin out of multiple individual optimality an Improved Firefly Algorithm (IFA) with increased diversity of population and enhanced population density (by harmony search algorithm) is proposed in this paper. The efficacy for global solution is achieved with incorporation of linear incremental pitch adjustment rate (PAR) and exponential decaying bandwidth to obtain fast convergence and to incorporate less randomization for proposed IFA. The overall DG optimization enhances the dynamic stability limits of respective controllers by minimizing low frequency network behavior. The efficacy of proposed stability assessment in terms of power oscillation damping and improved stability limits are verified in MATLAB script, Simulink platforms and validated in TMS320 C6713 DSP test-bench simulation.