Multiple feedback loop control strategy for single-phase voltage-source UPS inverter

This paper investigates the performance of multiple feedback loop control strategy for single-phase voltage-source UPS inverter with an L-C filter. In order to select appropriate feedback variables and assess the stability of the closed loop operation of the overall system, the power circuit (inverter and filter plus load) incremental dynamics is investigated using the state-space averaging technique and root locus method. The results of the stability analysis show that a control scheme which employs the filter capacitor current in an inner feedback loop and the load voltage in an outer voltage control loop results in successful operation of the UPS system. Computer simulation results of a single-phase voltage-source half-bridge UPS inverter with a second order filter and R-L load is presented to demonstrate the performance of the proposed control scheme. Experimental verification of a laboratory model of the UPS system is also provided for both linear and nonlinear loads so as to verify the predicted performance of the system. It is shown that the control scheme offers improved performance measures over existing schemes. It is simple to implement and capable of producing nearly perfect sinusoidal load voltage waveform at moderate switching frequency and reasonable size of filter parameters. Furthermore, the scheme has fast dynamic response and high voltage utilization of the DC source