Research On Output Control And Parallel Operation Technology Of UPS Inverters

As a reliable power supply system, UPS has been widely used in communication, finance, power, transportation and other fields. The output voltage and the system reliability are two important aspect when the UPS performance is considered. From these two aspects, the output voltage waveform control scheme and current-sharing control scheme have been studied in this paper.In the aspect of output voltage waveform control, this paper builds the mathematical model of inverter and focus on repetitive control scheme. The main work includes researching its stability, convergence, stable-state error, and introducing two compensator's design methods in detail. In view of repetitive control's poor performance in dynamic property, this paper combined PI control and repetitive control. The improvements of the composite control scheme have been verified through the simulations. In addition, this paper analyses two dual-loop control scheme and proves its feasibility by means of simulations.The parallel redundant UPS can improve the reliability of power supply system. Reducing circulation is the key factor of realizing parallel inverter. In the aspect of current-sharing control, this paper analyzes the causes of paralleling system circulation. Concerning the influence of phase difference on circulation, phase-locked loop is designed to ensure the phase and frequency synchronization between inverters. This paper introduces such two wired control schemes as master-slave control scheme and distributed control scheme. The comparison of the two schemes illustrates the advantages of distributed control scheme in achieving parallel redundant system. The physical implementation methods of the phase synchronization bus and the current-sharing bus have been given. This paper makes a detailed analysis on the theoretical basis of wireless control scheme, and introduces the selection of droop coefficient, the method of power calculation, and the improvement of traditional wireless control scheme. The current-sharing effects of the above-mentioned scheme have been verified.