| In recent years,due to the adjustment of national economic and industrial structure,the application of distributed generation in power production and life is increasing.When the distributed generation is connected to the power grid,it always needs to convert the power through the converter,which leads to the increasing penetration of the converter in the power network.The converter,especially the three-phase PWM converter,is a strong nonlinear element.Its strong nonlinearity mainly comes from its internal switching elements.The on and off action of switch element is discontinuous action.Therefore,the switching elements will produce harmonics and introduce them into the power grid with the access of the converter,which will lead to the fluctuation of the voltage amplitude and frequency of the power grid,and then threaten the stability and security of the whole power grid operation.Therefore,it is necessary to carry out efficient and accurate modeling and Simulation of the converter system,so as to study the impact of converter access on the power network.At present,there are many excellent literature works about converter simulation model and related issues at home and abroad.However,most of the research on converter simulation model focuses on DC-DC converter,and the research on DC-AC converter is relatively rare.Therefore,in order to analyze the impact of converter access on power grid operation in detail,and provide convenience for subsequent converter structure optimization design and converter access system control strategy design,it is particularly necessary to carry out modeling and Simulation of converter,especially DC-AC converter three-phase PWM converter in electromagnetic transient time scale.In this paper,based on the existing theory,an adaptive three-phase PWM converter simulation model based on ripple precision control is proposed.The model can speed up the simulation speed and improve the simulation efficiency under the condition that the converter system simulation has a certain accuracy.The specific work of this paper is as follows:1.This paper describes the background of electromagnetic transient modeling and Simulation of converter system and the current situation of related research at home and abroad;introduces the basic principle,topology and basic state equation of three-phase PWM converter operation;introduces several basic integration methods for electromagnetic transient simulation of converter system.It lays the foundation for the new three-phase PWM converter simulation model.2.The main modeling ideas applied in electromagnetic transient simulation of converter system are described.The average modeling theory and several typical average modeling methods(including KBM averaging method,zero order state space averaging method,generalized state space averaging method,piecewise average method,piecewise generalized state space averaging method,etc.)are introduced emphatically.The applicability of these typical simulation methods in electromagnetic transient simulation of three-phase PWM converter system is evaluated.3.Based on KBM average theory and subsection theory,an adaptive three-phase PWM converter model based on ripple precision control is proposed.The model can adapt to different operation conditions of converter system by switching between the two modes,and the accuracy of model simulation is controlled by setting the ripple accuracy limit value.Compared with the traditional model,the proposed model can be better applied to the electromagnetic transient simulation of three-phase PWM converter system.It provides a new idea for the future research of converter system simulation model. |
