Single-loop vs two-loop voltage and frequency control of isolated SEIG based RECS

Present investigation deals with the comparison of performance of a Generalized Impedance Controller (GIC) based 3-phase self excited induction generator (SEIG) terminal voltage and frequency regulator, having single and two-loop control, in an isolated wind/microhydro type renewable energy conversion system (RECS). Where, GIC is a PWM voltage source converter with dc-bus battery, having controlled four-quadrant equivalent impedance. Amplitude and frequency regulation of SEIG terminal voltage under source and load perturbations, are accomplished by controlling modulation index m of the GIC and phase angle δ of fundamental component of GIC terminal voltage with respect to SEIG terminal voltage. These m and δ control are achieved by operating the GIC in closed loop with, (i) only voltage feedback, and (ii) voltage and frequency feedbacks. The PI-controllers in both the schemes are designed for non-fragile system operation with optimized transient response of both amplitude and frequency of SEIG terminal voltage. The integrated SEIG-GIC closed loop system with single and two-loop control schemes are modeled and simulated in MATLAB/Simulink to highlight the superior performance of single-loop control scheme in transient and steady states.