Research On Compensation Method Of Three-Phase Unbalanced And Nonlinear Load In Distribution Network

With the application of unbalanced load in industrial and civil applications,and more nonlinear loads connected to the power system,the power quality problem of distribution network is becoming more and more serious.Aiming at this situation,based on the compensation principle of passive power filter,a parallel integrated compensation device applied to three-phase three-wire system is designed to compensate the negative sequence,harmonic current and reactive power in the power network.First,the cause,calculation and harm of three-phase imbalance are introduced,as well as the measures to improve three-phase imbalance at home and abroad.Then,the classification,advantages and disadvantages of compensator and its application are summarized.Aiming at the extension structure of parallel compensator,the mathematical models in abc stationary coordinate system and dq rotation coordinate system are derived,and the mathematical model in s domain is obtained by Laplace transform,which provides the theoretical basis for the design of controller.Then the current tracking control method is introduced.The p-q detection method based on instantaneous reactive power theory and the i_p-i_q detection method are the two most representative methods at present.The working principle of p-q detection method and i_p-i_q detection method are deduced in detail in this paper.Finally,the i_p-i_q detection method which is less affected by grid voltage distortion is selected.A constant power factor reactive power compensation method based on ip-iq detection method is proposed.On the basis of compensating negative sequence and harmonic current,some reactive current components are compensated to meet the requirements of system operation,and the cost of energy storage capacitance is reduced at the same time.The economy of the compensator is improved.Finally,a three-phase unbalanced and nonlinear comprehensive compensation simulation model is built based on MATLAB/Simulink,and the feasibility and effectiveness of the compensation strategy are verified by simulation.The simulation results show that the comprehensive compensation device designed in this paper can improve the three-phase imbalance,suppress harmonics and increase the power factor of the system.