An adaptive linear quadratic regulator with repetitive controller applied to uninterruptible power supplies

This paper proposes a discrete time adaptive linear quadratic regulator (LQR) with a repetitive controller (RP) for uninterruptible power supplies (UPS). In the controller design, the gains are determined by minimizing a cost function which reduces the tracking error and the control signal. A recursive least squares (RLS) estimator identifies the plant parameters at different load conditions. Then, the LQR gains are adapted periodically. The output voltage is the only state variable measured in this scheme. The other state variables are obtained by filtering. It was verified through simulation and experimental results that the proposed strategy has good performance to linear and nonlinear loads providing fast transient response and accurate tracking with a low control effort even at low switching frequency.