Dissipativity-based adaptive and robust control of UPS in unbalanced operation

In this paper we investigate the output voltage control for three phase uninterruptible power supply (UPS) using controllers based on ideas of dissipativity. To provide balanced sinusoidal output voltages even in the presence of nonlinear and unbalanced loads, we first derive a dissipativity-based controller using a conventional αβ (fixed frame) representation of system dynamics and a frequency-domain representation of system disturbances. Adaptive refinements have been added to the controller to cope with parametric uncertainties. Second, based on the structure of the first adaptive controller and avoiding estimation of one of the parameters, we propose a controller, which leads to an LTI closed loop system and which is directly connected to synchronous frame harmonic voltage control. For the proposed solution, a sufficient condition in terms of the design parameters is presented to guarantee stability of the desired equilibrium and robustness against some parameter uncertainties. Finally, simulation and experimental results on a three-phase prototype show the effectiveness and advantages of the proposed approach