A Repetitive-based Controller for UPS using a Combined Capacitor/load Current Sensing

This paper discusses a repetitive based controller for uninterruptible power supplies (UPS) to compensate for unbalance and harmonic distortion on the load. We propose to use a combined measurement of capacitor and load currents using the same current sensor with the purpose of, on 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 protection purposes. The proposed controller is composed of a proportional term plus a repetitive scheme. The latter is implemented with a simple feedback array of a delay line, thus making the implementation relatively easy. The repetitive scheme acts as a refinement term to reject the harmonic distortion caused by the unbalanced and distorted load current, and thus, allowing the UPS to deliver an almost pure sinusoidal balanced voltage. Experimental results are included to show the performance of the proposed controller