Optimal linear controller design of standalone VSI including emulated output current state

Load type can introduce at least one additional state variable in the state-space representation for dynamic equations of voltage source inverters (VSI) which may make controller design harder to solve. Additionally, the voltage reference term in state space realization demonstrates the VSI control as a tracking problem. This tracking problem can be transformed into a regulation problem using appropriate transformation; consequently, the linear quadratic regulator (LQR) technique, which is originally applicable to regulation problem, can be employed to design a linear controller including load current state for standalone VSIs. The load current is also virtually obtained by an Enhanced Phase Lock Loop (EPLL) in the control structure instead using of a current sensor in hardware. The controller is designed for a VSI unit and then simulation and experimental results are presented to confirm performance of the proposed controller.