Research On Three-Phase Parallel Inverter System Based On Networked Control And Droop Method

With the growing of world energy crisis nowadays, new energy, distributed generation, smart grid and networking technology have developed rapidly. In the new energy power generation systems, the control technology of parallel inverter system is becoming an increasingly important area of research. Based on the summary of the existing inverter parallel control theory and applications, and according to the characteristics of the three-phase inverter, power droop method is added to the three-phase parallel inverter system. And three-phase inverter parallel system with networked control and power droop method is proposed in this dissertation.The control of three-phase inverter is the base of the research on the three-phase parallel inverter system. As the three-phase inverter voltage and current is AC parameters, no-static-error control can not be used directly, but dqO transform can be used to realize it. In the model of the steady and dynamic characteristics of three-phase transformer, three-phase inductance and three-phase inverter, there is phase-coupling existing, which should be omitted in dynamic modeling in order to simplify the analysis. In this paper, the dynamic model of three-phase inverter in dq0coordinate system is derived and the control system is designed.The non-signal-interconnect three-phase parallel inverter system should be analyzed and designed properly. Normally, the PQ droop methed is used to sharing the active and reactivepower.This paper describes the the basic principles of PQ droop method, analyzes the effect of output impedance and wire impedance, and optimizes the output frequency control. A control method of three-phase three-wire non-signal-interconnect parallel inverter system with PQ Droop method is proposed in this paper.The non-signal-interconnect parallel inverter system can not achieve certain targets such as high current sharing precision because of the defects of power droop method. By adopting networked control in three-phase inverter parallel system, the problem can be sovled.This article describes the concept of networked control technology, research and design methods, and gives analysis and communication design of networked control applied for power electronic system.The control principle of three-phase inverter parallel system based on networked control and droop control method is that inverter module sends the module power data to the network, while receives the other module’s power data. The inverter module adds the other module’s power to droop method control to achieve high current sharing precision.Finally, the experimental results verify the principle of the control of three-phase inverter. Through the PQ droop control method, non-signal-interconnect three-phase parallel inverter system is verified. And the networked control improves the current sharing precision.