A Modified Lyapunov-function based Control Scheme for Three-phase UPS with a Load Estimator in Synchronous Rotating Frame

This paper proposed a modified Lyapunov-function based control scheme for the three-phase UPS without sampling load current by using a real-time load estimator in synchronous rotating frame. The load estimator also inherently built an external voltage control loop with integral action, which contributed to the robustness against load uncertainties, nonlinearities and the other unmodelled dynamics, leading to zero steady-state error and phase delay. Routh-Hurwitz stability criterion was further utilized to prove the small-signal stability of the system. Then, systematic controller parameter selection strategy was given mainly focused on optimization of undamped natural frequency and damping ratio. Finally, control hardware in the loop (HIL) system on a rated 5.5kW prototype validated the effectiveness and efficiency of proposed approach.