Research On Improved Droop Control Method In Parallel UPS System

As users have higher and higher requirements for power supply quality,the market scale of Uninterruptible Power Supply(UPS)is gradually expanding.Due to the limitation of equipment capacity and parameters,in order to improve the safety and reliability of power supply,multiple equipments are often required to run in parallel.As an important part of the UPS system,the inverter’s control performance directly affects the normal operation of the electrical equipment.Parallel inverter control methods mainly include interconnection and non-interconnection control methods.Among them,interconnection control includes centralized control method,master-slave control method and decentralized logic control method.The non-interconnection control method mainly refers to Sag control method.In recent years,the droop control method has been widely used because of its advantages of no communication,high reliability,and low design cost.However,in the working conditions of the UPS system,the resistance and inductance environment of the low-voltage feeder will cause the traditional droop control to fail,and the load distribution accuracy is not high.Moreover,under complex working conditions,such as when there are a large number of nonlinear loads,it is difficult to guarantee the output voltage accuracy,which will cause great harm to electrical equipment.Therefore,it is of great significance to study the improvement method of traditional sag control.Aiming at the problems of traditional P-V droop control in low-voltage microgrid environment,inaccurate power distribution in the case of mismatched line impedance parameters,and low output voltage accuracy under complex operating conditions,this thesis focuses on two aspects: droop coefficient adjustment and adaptive parameter control.The main research contents are as follows:1.Based on the typical topology of the parallel inverter system,the power characteristics of the inverter are analyzed,the traditional droop control method is analyzed,and its shortcomings are analyzed from three perspectives: power distribution accuracy,power response speed,and output voltage control accuracy,and analyze the related improvement ideas.2.The traditional P-V droop control coefficient adjustment process is improved,the principle of adjusting the droop coefficient through the PI link is analyzed,and the PI parameter is adjusted in real time during the coefficient adjustment process through the fuzzy control method to improve the dynamic response.Finally,the simulation and experiments are used to verify the results proposed method.3.In the improved droop control method,the state space model of the parallel inverter is established,and the adaptive parameter control method is derived based on the Lyapunov function,so that the output voltage is within a certain constraint range;in order to further improve the output voltage control accuracy,the adaptive parameter control method is adopted.Equation,the parameter optimization strategy was deduced,and the steady-state and dynamic control performances were significantly improved.The simulation and experiment were used to compare and verify.4.An experimental platform is built based on DSP TMS320F28379 D dual-core microcontroller.The hardware design and software design are introduced in detail,and a large number of experiments are used to verify the effectiveness of the improved droop control method.