Study On Control Strategy Of Power Conversion System For Microgrid

No matter photo-voltaic or wind power,both of them exit random fluctuation of output power.With the increasing penetration of new energy generation,its large-scale access to the grid has had a great impact on the traditional power system.The emergence of energy storage system provides a solution for the above problems.The energy storage system includes energy storage medium,Power Conversion System(PCS)and corresponding energy management system.PCS is dispatched by micro grid layer management system to reach energy control between grid and energy storage battery.The diversity and quality of its control strategy greatly affect the economy and reliability of micro grid system.This paper takes micro grid as the application background and single-stage two-level PCS as the research object and uses the modeling method of switching converter,power electronics technology and automatic control theory.It has important practical significance to study the control strategy of PCS of micro grid under various working modes.Based on a detailed analysis of the working principle of PCS,the small signal mathematical model was established.According to the application scenario of PCS and the demand of load power quality,the control strategy under the switching working mode of parallel/off-grid and parallel/off-grid was studied.When the grid is connected,the inner loop adopts AC current and the outer loop adopts DC current or voltage to realize the constant current or constant voltage charging of the energy storage battery.The inner loop adopts AC current and the outer loop uses AC power to achieve constant power discharge.The low harmonic current compensation function is realized based on Vector Proportional Integral(VPI)controller.The charging/discharging switching time is guaranteed to be less than 100 ms through the instruction value switching control of the inner loop.When off-grid,V/f control strategy is used to support and adjust AC bus voltage and frequency;Three-phase voltage unbalance and harmonic voltage compensation control are realized based on VPI controller.Aiming at the problem that the output voltage harmonic increases in the resonant circuit formed by inductive load and LC filter,an improved damped V/f control strategy is proposed to effectively reduce the output voltage THD.In parallel/off-grid switching,presynchronization control is adopted to achieve smooth transition.MATLAB/Simulink simulation software was used to verify the feasibility of PCS control strategy in each mode.The simulation waveform showed the feasibility of the control strategy adopted and proposed by the project.Experimental research is carried out on the experimental platform to verify the effectiveness and correctness of the control strategy adopted by the project and proposed.