Digital Control Method Using Full-Order Observer on Three-Phase Inverter for UPS

Abstract

Uninterruptible power supplies (UPSs) as power sources in computer systems must be offer high quality and high reliable power to their system. To realize such UPSs, inverter controllers in the UPSs must be digitalized with micro processors. And, it is necessary to obtain high sampling frequency and satisfactory compensation for the processor operating time lag and disturbances in the control system. Besides, simple control algorithm is demanded due to application of the digital controllers to low cost UPSs. Then, a control method using full-order observer in the current minor loop is proposed. In this method, to shorten the algorithm, disturbances are assumed as a state valuable, v_D(n) where v_D(n+1)=v_D(n), and the observer is established in the minor loop. To increase the compensation for the time lag and the disturbances, the observer estimates the time-lagahead current and disturbance, and the observer carries out dead beat operation. Experiments demonstrates that this control method provides excellent characteristics of the inverter for the UPSs.