Research On Unbalanced Voltage Compensation Oriented Control For Micro-grid Tied Inverters

As the rapid development of distributed new energy grid-tied technology,the increasing in the mixture of single-phase and three-phase load leads to serious unbalance problem of micro-grid voltage,which has to be solved urgently.Inverters are important interfaces between distributed power generation systems,energy storage systems and micro-grids.This thesis proposed to research control strategies of gridtied inverters,and aimed at solving the unbalance problem of micro-grid voltage.The main contents are as follows:A kind of topology of three-phase interconnected and controllable inverter with four-leg was proposed.According to the characteristic that the output voltage and current of the three-phase four-leg inverter can be decoupled and controlled independently,an unbalanced voltage compensation module was designed and a gridtied inverter structure that can achieve both grid connection and the compensation of unbalanced three-phase voltage was presented.Based on the principle of internal model,a dual-mode PI control strategy of the grid-tied inverter with voltage compensation was designed.Conventional PI controller has static error in the control of the AC signal,although it has fast response and good robustness.In order to improve the dynamic performance and steady-state accuracy of the voltage compensated grid-tied inverter and enhance the ability of suppressing the harmonic disturbance,a dual-mode PI controller was designed based on the internal model principle to suppress the odd and even harmonics,respectively.The validity of the method was verified by theoretical analysis and simulation.An adaptive control strategy for unbalanced voltage grading compensation of micro-grid was proposed.According to unbalance degree of micro-grid voltage,the unbalanced voltage state was classified,and the unbalanced voltage state transition model was established,and the adaptive control scheme of output power of the inverter was proposed according to the unbalanced state of the micro-grid voltage.The influence on micro-grid and the compensation strategy and the state switching process in various unbalanced state were analyzed.The experiment platform of the grid-tied inverter with unbalanced voltage compensation was constructed,and the proposed control strategy was experimentally verified.The experimental results showed that the PI controller based on the internal model can realize the static control of the AC signal and effectively suppress the harmonics.In view of the various imbalances that may occur in the micro-grid,the adaptive compensation control strategy proposed in this thesis can compensate the unbalanced voltage rapidly and effectively.