An adaptive control for UPS to compensate unbalance and harmonic distortion using a combined capacitor/load current approach

An adaptive controller for UPS to compensate for unbalance and harmonic distortion on the load is proposed. We propose to use a combined measurement of capacitor and load currents using the same current sensor for the purpose of, on the one hand, reaching a similar performance as that obtained in a capacitor current based controller, and on the other hand, to obtain an estimate of the load current for security purposes. Adaptation is included to cope with uncertainties in the system parameters. The controller is based on a frequency domain description of the periodic disturbances, which include both symmetric components, namely, the negative and positive sequence. And thus, allowing the treatment under unbalance operation, as well. As a consequence, the controller compensates only for a selected group of harmonic components, and thus, belonging to the family of selective control algorithms. Simulations are presented to assess the performance of the proposed algorithm.