Research On Multi-objective Optimal Control Of Grid-connected Inverter Under Unbalanced Power Grid

With China's strong support and investment in power generation such as clean energy such as solar energy and wind energy,people have put forward higher requirements for the adaptability and stability of grid-connected inverters.A reasonable grid-connected inverter control strategy is a prerequisite for sending these clean energy sources to the grid.Ideally,the grid is in equilibrium,but grid imbalances can occur due to load or system parameter settings.When the grid voltage is unbalanced,the traditional grid-connected inverter control strategy will cause the inverter output threephase current imbalance,and the output active power and reactive power will generate twice the grid frequency fluctuation.It can be seen that the traditional control strategy is no longer applicable to the situation of grid imbalance.In the case of grid imbalance,the unbalanced voltage and current can be expressed as the sum of the positive and negative sequence components.In order to realize the separation of positive and negative sequence,the paper analyzes and compares the positive and negative sequence separation methods such as notch method,delay method and second-order generalized integration method.Finally,the second-order generalized integration method is used to measure the unbalanced power.Perform positive and negative sequence separation.Then,the paper takes the grid-connected inverter as the research object,and uses the positive and negative sequence components of the separated grid voltage to obtain the grid voltage imbalance and grid phase,which provides the basis for the subsequent grid-connected inverter control strategy.Through the instantaneous power analysis of the inverter,the reference current expression under the target of achieving inverter three-phase current balance,suppressing active power fluctuation and suppressing reactive power fluctuation is obtained,and then the optimization factor is introduced to obtain a unified reference current expression.Construct a multi-objective function with optimization factors.In order to optimize the multi-objective function,the paper introduces the genetic algorithm and the fruit fly algorithm.Through simulation and comparison analysis,it is concluded that the Drosophila algorithm is superior to the genetic algorithm in accuracy,convergence speed and difficulty in algorithm implementation.In order to prove the effectiveness of the multi-objective optimization control strategy for grid-connected inverters under the condition of grid imbalance,a simulation model is built on MATLAB/Simulink,focusing on the impact of grid imbalance on phase-locked loop and power control.Positive and negative sequence separation scheme,three different control targets for grid-connected inverters,coordinated control between different targets,optimization algorithm for multi-objective optimization function optimization,and multi-target for grid-connected inverter based on fruit fly algorithm Optimize the control strategy to verify.At the same time,a three-phase grid-connected inverter experimental platform was built based on the simulation model.On the experimental platform,the correctness and feasibility of the proposed control strategy are verified.