Optimizing a Virtual Impedance Droop Controller for Parallel Inverters

This paper explores a previously developed frequency and voltage droop control scheme via virtual impedance emulation. Previously, the control scheme utilized a Kalman observer to extract the fundamental voltage and frequency which increased the complexity of the control loop. This paper investigates the use of a second-order generalized integrator-frequency locked loop (SOGI-FLL) to accomplish the same task in a straightforward fashion. Moreover, a linear quadratic Gaussian (LQG) servo controller was used to implement the control scheme instead of the LQG optimal control approach used formerly. The performance of the modified control algorithm was studied using Matlab/ Simulink simulations under various linear and non-linear load conditions. Furthermore, two inverters were operated in parallel to assess the load-sharing capability of the modified control method. Simulations showed that the optimized control scheme kept output voltage and frequency within acceptable levels. Additionally, simulations exhibited the load sharing capability of the control scheme.