Research On Wireless Parallel System For Single-Phase UPS

With the popularization of computer and the rapid development of electronic communication technology, UPS (Uninterruptible Power Supply) have been applied more and more as the power supplies of key equipments in important occasions. Meanwhile, users'demands for the reliability and capacity of power system become higher and higher. Modular N+X parallel redundant technology can greatly improve the reliability, flexibility and capacity of UPS power system. Compared to interconnected parallel system, the PQ droop method controlled UPS parallel system without internal connections have better reliability and redundancy, and the system is more convenient to build and can realize "plug and play",which are the development trend of future UPS.The paper first briefly introduces the research situation of UPS parallel technology without internal connection, and explains in detail the design method for the dual closed loop controller composed of the voltage-loop and current-loop. Then it analyses the contradiction of the output voltage closed-loop control and the current sharing. Next, it introduces the principle of PQ droop control method, shows the current sharing control equations under different line impedance and illustrates the limitations of PQ droop control method. In order to improve the phenomenon that parallel system has poor current sharing under different line impedance, the paper improves PQ droop control from the aspect of line impedance voltage compensation, and the new control strategy are validated by simulations and experiments. Then the paper discusses the parallel technology without internal connections for UPS modules under different power ratings, gives corresponding droop coefficient design methods, discusses the conditions of different line impedances, applies the new control strategy to UPS parallel system without internal connections under different power rating and validates it by simulations and experiments. Finally, this paper uses small signal modeling to analyze the improved droop control method and selects the appropriate droop parameters based on the analysis.Finally, the experimental results verify the theoretical analysis:using the parameters designed, UPS parallel system have preferable current sharing ability under different power ratings, and at the same time, improved current sharing control strategy can effectively improve parallel systems'current sharing performance.