An Observer-Based Optimal Voltage Control Scheme for Three-Phase UPS Systems

This paper proposes a simple optimal voltage control method for three-phase uninterruptible-power-supply systems. The proposed voltage controller is composed of a feedback control term and a compensating control term. The former term is designed to make the system errors converge to zero, whereas the latter term is applied to compensate for the system uncertainties. Moreover, the optimal load current observer is used to optimize system cost and reliability. Particularly, the closed-loop stability of an observer-based optimal voltage control law is mathematically proven by showing that the whole states of the augmented observer-based control system errors exponentially converge to zero. Unlike previous algorithms, the proposed method can make a tradeoff between control input magnitude and tracking error by simply choosing proper performance indexes. The effectiveness of the proposed controller is validated through simulations on MATLAB/Simulink and experiments on a prototype 600-VA testbed with a TMS320LF28335 DSP. Finally, the comparative results for the proposed scheme and the conventional feedback linearization control scheme are presented to demonstrate that the proposed algorithm achieves an excellent performance such as fast transient response, small steady-state error, and low total harmonic distortion under load step change, unbalanced load, and nonlinear load with the parameter variations.