Modeling and analysis of DC link voltage control for universal power quality controllers

In order to make more effective control of universal power quality controllers (UPQC), an outer loop model for the voltage loop in a three-phase three-wire UPQC is proposed in the paper. The compensation capability of a practical UPQC is then analyzed based on the deduced model. Subsequently, two kinds of methods named feedback control and composite control for DC link voltage control are compared in detail. The covered comparative aspects include the performance in disturbance suppression, stability of the voltage loop with a PI controller and stability of the voltage loop with only a P controller. Computer simulations and hardware prototype experiments are done to verify the validity of the model and analysis in this paper. The corresponding control methods are also proved to be effective.