| Up to now,a great trend in the development of power systems in all countries of the world is the interconnected operation of large power grids in a certain range.As the earliest flexible AC transmission unit characterized by series and parallel converters,UPFC has been the focus of attention from researchers.Because UPFC has strong functional characteristics and flexible characteristics,it can achieve accurate regulation of active and reactive power flow and stability control of AC and DC buses.It is also worth noting that,during the operation of the power system,UPFC can also play an important role in enhancing the stability of the system and optimizing the operation of the system.Therefore,under the background of the increasingly interconnected development of modern power system,strengthening the research of UPFC is a great project for every expert and scholar.In this paper,the mathematical model of the system is built on the basis of UPFC topology,and the working mechanism of its series and shunt side converter is analyzed in detail.On the basis of summarizing the control strategy of UPFC series and shunt side converter,considering on the existing problems,the control scheme of series and shunt side converter and the selection method of main circuit parameters are given.A fuzzy adaptive PI control strategy based on predictive current control is proposed for stability control of shunt side converter to DC bus voltage,so that UPFC has better performance in voltage stability control and reactive power regulation.A variable structure control strategy based on inverse system decoupling is proposed to control the line power flow of series side converter,in order to make UPFC system have good tracking performance and independent control capability for power flow.In order to verify the control performance of the proposed algorithm,UPFC simulation system is built on MATLAB simulation platform separately as STATCOM,SSSC operation and overall operation,and simulation experiments are carried out in this paper.Finally,the simulation waveforms of different control objectives of UPFC under different operation modes are given respectively,and the waveform diagrams of UPFC series and shunt side converters under different control algorithms are compared and analyzed separately.The simulation results show that the control algorithm proposed in this paper can respond to the regulation demand of power system line quickly and accurately,so that the corresponding control objectives can be realized.That is to realize the stability of the DC bus voltage and the effective control of the fast decoupling of the active power flow and the reactive power flow. |
