Research On The Technique Of Parallel UPS And Network Control Inverter System Based On PQ Droop

With the developments of information Technology and new energy power generation, the research on inverters in parallel operation becomes more and more important. With the increase of the electric equipment and clients’demands for the quality and capacity of power system, multi-inverters operate in parallel to supply high power becomes a trend.In this paper, the technique of parallel inverter based on PQ droop theory is studied. According to the characteristics of on-line UPS, an improved load sharing controller for parallel UPS systems is proposed, which can realize the current sharing control and phase synchronization regulation between the utility voltage. In order to realize better control effect, network control parallel inverter system is researched based on the summary of power electronics network control theory. Besides, the mathematic model of network control is analyzed.This paper introduces the control of UPS, and the virtual impedance design firstly. By adding virtual impedance, the system output impedance can be changed, and better paralleled inverters system can be realized. The amplitude and voltage control loops are adopted which can realize good steady and dynamic performances under both resistive load and nonlinear load condition. Excellent performance of the UPS unit lays the foundation of wireless parallel operation.Normal P-co, Q-Vdroop method and phase lock loop both adjust the co which has contradiction. In order to solve the parallel operation and phase lock problems, self-adaption virtual impedance is added to change the output impedance so the resistive droop method can be used. In this method, the droop control and phase lock can be decoupled. UPS in parallel operation experimental results show the effectiveness of the control method.The non-signal interconnect parallel inverter system can’t achieve precise current sharing and the intellectual inverter control becomes a trend. It’s a good way by adding networked control to solve these problems. This article describes the concept of networked control for power electronics system, and the mathematics model of network control parallel inverter system is analyzed. Besides, maximum network delay that the system can tolerant is researched. Based on networked control, the parallel system can realize better current sharing than wireless control. Finally the control strategy is validated by experiments.