Low-voltage Micro-grid Master-slave Control Study Based On Improved VF Droop Control

Conventional VF droop control was unable to provide a stable frequency and voltage in the low-voltage micro-grid of the main line was resistive,and most of our micro-grids are low-voltage micro-grid,so it is important to study low-voltage micro-grid VF droop control strategy.This article has established a master-slave control low-voltage micro-grid with the VF droop control strategy based on analysis of inverter control method of low-voltage micro-grid and the distributed power model to verify the effectiveness of the control strategy.The main work is as follows:First,to design inner current loop of power control by analyzing the relationship between micro-grid inverters and power control model is to control output power,and then to design VQ and PQ control strategy according to the outer for different distributed power inverter control as a building slave control strategy of low-voltage micro-grid.Secondly,the frequency with active power and reactive power with voltage is linear operation when analysis the principles of conventional VF droop control strategy building in the grid line approximation inductive of high-voltage micro-grid which to stabilize frequency and voltage by an appropriate droop factor.However,the power and frequency and voltage is no longer a linear relationship between the low-voltage micro-grid which line is mainly characterized by resistance,so output frequency and voltage cannot be stable by adjusting droop factor.Then to deduce the presence of coupling relationship between the frequency and voltage with active power and reactive power when adding the ratio of the resistance and inductor which to stabilize voltage and frequency by adjusting the droop factor and the ratio of the resistance and inductor,and then adding feedback compensation of frequency and voltage for secondary regulation,and to stabilize the load voltage by controlling the load output voltage and capacitive current.So it has finished the design of improved VF droop Control Strategy containing ratio of the resistance and inductor.Finally,to set up low-voltage micro-grid with micro gas turbine power generation unit by the PQ control and permanent magnet direct drive wind turbine unit by the VQ control and the battery unit which using improved VF droop control in isolated networks and PQ control in networks is to verify the validity of improved VF droop control in low-voltage micro-grid operation under different conditions.The work can solve unstable problem of voltage and frequency of the isolated operation low-voltage micro-grid when using improved VF droop control,it is useful for the further development of low-voltage micro-grid control strategies.