Research On Power Quality Improvement Of Micro-grid With Nonlinear Load

As an important link and bridge between large-scale grid and distributed generation can effectively reduce the impact of DG on the grid and improve the reliability of power supply.However,due to the fragility of the microgrid network grid,with the large number of nonlinear loads,harmonics and voltage imbalances in the power grid affect the power quality of the microgrid more and more significantly.In view of the influence of grid harmonics and three-phase voltage imbalance,the impact of grid harmonics and unbalanced three-phase voltages.This article adopts Unified Power Quality Regulator(UPQC)to comprehensively manage power quality of microgrid.Focusing on the detection and control strategies of UPQC in improving microgrid power quality,the following research was conducted:First of all,the mathematical model of distributed power and nonlinear load such as wind,light and storage are analyzed.Through the analysis,the factors that affect the power quality problems are proposed,including the influence of power grid harmonics and voltage unbalance on the micro-grid.Secondly,the current prediction method is improved.A new algorithm combining with Least Mean Square(LMS)algorithm and a Newton's interpolation algorithm into the adaptive module based on the adaptive prediction method and a new matrix transformation C is used.A current detection method of fractional compensated distortion command is proposed which can be applied to any harmonic component,and made an analysis of the accuracy and the response speed of the direct prediction method and the indirect prediction method of full compensation distortion command current.At the same time,in order to prevent the drastic change of voltage and influence the effective compensation of UPQC and improve the detection accuracy,two methods of command voltage detection based on Park transform and resonance control are studied in this paper respectively,which make the detection result not disturbed by voltage unbalance and distortion.In the research of UPQC multi-objective control strategy,suppression of voltage problems through series unit suppression in the micro-grid transfer and joint control of parallel units and energy storage units eliminates power quality problems generated within the micro-grid.Series and parallel unit by obtaining voltage,current command detection information,the parallel unit adopts current command value compensation strategy and the strategy of grid-connected phase pre-synchronization to reduce transient voltage and current surge in the switching process,to improve the transient power quality of the micro-grid,Smooth and network.When the distribution network has a great voltage distortion,the series unit uses adaptive triangular carrier tracking strategy to improve the triangular carrier modulation performance and improve the voltage waveform quality.Finally,the simulation model of UPQC is built under the Matlab simulation platform,and the simulations are carried out under different conditions to improve the voltage quality and the current quality.The simulation results show that the multi-objective control Strategy is highly effective and feasible.