Parameters and States Estimation with Linear Quadratic Regulator Applied to Uninterruptible Power Supplies (UPS)

Abstract

This paper presents a control strategy applied for UPS with a low commutation frequency. An adaptive linear quadratic controller (LQR) for a DC/AC converter is presented. The controller gains are determined by minimizing a cost function. A recursive least square (RLS) estimator is used to identify the parameters model at different load conditions. The inductor current is estimated by a Kalman filter. The capacitor voltage and the inductor current are used as state variables. Simulation results show that the proposed strategy offers good performances for either linear and non-linear loads with low total harmonic distortions even at low frequencies making it very useful for high power applications.