An adaptive Linear Quadratic Regulator for Three-phase UPS system Powering Nonlinear Loads

Abstract

This paper presents a control strategy applied to three-phase unintemrptible power supplies with a low switching frequency (1500 IIz). In The controller design, the gains are determined by minimizing a cost function, which rcduces the hacking error and smoothes the control signal. A recursive least square estimator identifies the parameters model at diflèrent load conditions. Then the linear quadratic controller gains are adapted periodically. The output voltage is the only state variable measured. The other state variables are obtained by estimation process. Simulation rcsults show that the proposed control strategy otlèrs good performances for either linear and non-linear loads rvith low total harmonic distortions (TIID) even at low frequencies making it very useful for high power applications.