Research On Improved Voltage Control Strategy Of DC Distribution Network

The DC distribution network has achieved tremendous development in recent years because of many advantages.For the operation of the entire system,which control strategy is one of the key technologies.There is no inductive reactance and capacitive reactance in the DC system.Therefore,the DC system voltage becomes the most important indicator to measure the power balance of the entire network.Different control strategies have different effects on the operating characteristics of the DC distribution network such as voltage and power distribution.Effective control determines the stable operation of the system.Therefore,the voltage control strategy is an indispensable part in the research of DC distribution network.This article takes the two-terminal DC distribution network which under the double-ended power supply operation mode as the object to research the voltage control strategy based on the voltage source converter.Firstly,the article introduces the topological structure and basic components of the DC distribution network,analyzes the basic principles and control strategies of converter control,and explains the advantages and disadvantages of traditional control strategies.Secondly,in order to solve the problem that traditional droop control cannot to stabilize the DC distribution network voltage when under high power fluctuation,an improved droop control is proposed.This strategy corrects the droop coefficient by measuring the system voltage deviation,which not only can stabilize the DC system voltage effectively when subjected to large disturbances,but also maintains the good dynamic response characteristics of traditional droop control when subjected to small disturbances.In order to verify the effectiveness of the improved droop control strategy,a two-terminal DC distribution network model was built on the PSCAD/EMTDC simulation platform,and the strategy was simulated and compared with the traditional droop control.The simulation results shows that compared with the traditional droop control,the improved droop control strategy can stabilize the system voltage more effectively.Finally,in order to solve the problems that slow control mode switching of the converter station and severe voltage fluctuations under the traditional voltage margin control,an improved voltage margin control is proposed.This strategy switches the control mode by outputting the corresponding coefficients,and places the mode switching part before the PI controller.The converter station mode switching does not need to go through the PI controller to speed up the dynamic process.At the same time,the droop characteristics is introduced to alleviate the voltage fluctuations under mode switching.Experiments on the simulation platform show that compared with the traditional voltage margin control,the improved voltage margin control strategy can restore the stable operation of the system more quickly,and reduce voltage fluctuations amplitude.