Research On Three-phase Voltage Unbalance Compensation Stratetegy Of Microgrid Inverter

As wind power,photovoltaics,and other distributed power sources with obvious random,intermittent,and decentralized characteristics have gradually revealed their adverse effects on the operation and control of the power system,microgrids,as a way to maximize the acceptance of distributed power,The electrical network topology that improves the reliability of power supply,and improves the power grid’s disaster resistance and emergency power supply capabilities has received extensive attention.Improving the reliability and stability of the grid-connected system operation has become a key technology in the system.Aiming at the problem of the voltage and current imbalance of the microgrid public connection point(PCC)under the traditional voltage-type gridconnected inverter control strategy,this paper conducts an in-depth study on the threephase voltage imbalance compensation strategy of the inverter.On the basis of reviewing the subject background and research status,this article first analyzes the principle of three-phase unbalanced voltage generation,and then summarizes the existing current source and voltage source three-phase unbalance compensation control strategies.Constructed and analyzed the mathematical model of LC type three-phase grid-connected inverter topology in two-phase rotating and two-phase stationary coordinate systems,and explained the theory of droop control and coordinate transformation required for conversion under different coordinate systems.On this basis,the grid-connected system has been designed with filter design and dual-loop control system design.Aiming at the problem of unbalanced grid connection point under the condition of three-phase unbalance on the grid side,firstly,the method of extracting positive and negative sequence components by the double second-order generalized integrator is analyzed,and then two unbalance compensation control strategies are proposed: Based on traditional droop control,a positive sequence reactive power droop compensation loop and a negative sequence voltage feedforward compensation loop are introduced to superimpose the inverter output voltage compensation reference value,thereby reducing the voltage imbalance at the grid connection point;based on the negative sequence virtual impedance The method of suppressing the negative sequence component of gridconnected current reduces the imbalance of grid-connected current by dynamically changing the equivalent impedance of the negative sequence.According to the proposed improved voltage-type unbalance compensation strategy,the corresponding small-signal model of grid-connection stability is established,the stability of the control strategy is analyzed by the root locus method,and the stable interval of the corresponding control parameters is obtained.Finally,a microgrid simulation model was established through MATLAB/Simulink,and the proposed control method was simulated and verified.