Research On Control Method Of Hybrid System Based On APF And TSC

With the extensive use of power electronic equipment,the generated harmonic current and reactive power may threaten the safety and stabilization of power system,and cause serious damages such as extra power loss and device fault.Thus,research on harmonic suppression and reactive power compensation is receiving extensive attention.In power systems,devices with the function of both harmonic suppression and reactive power compensation are widely needed.A hybrid compensation system based on small-capacity active power filter(APF)and multi-group thyristor switched capacitor(TSC)was proposed in this paper,to compensate harmonic current and reactive power in grid precisely and continuously,by cooperation of APF and TSC.The hybrid system has both the APF's advantage of fast response and high precision,and the TSC's advantage of large capacity and low cost.And in this paper,the control methods of hybrid system were discussed in depth.Firstly,the mathematic model of hybrid system was established and the selection of TSC's reactance ratio was discussed.On this basis the effect of current compensation factor,reactance ratio and grid inductance on system stabilization was analyzed.Secondly,the basic principle of common current control methods was introduced,and two frequency-dividing current control methods used in hybrid system were designed.Considering the working condition of three-phase symmetry,a frequency-dividing current control method was designed to compensate harmonic and reactive current at high precision,by choosing independent PI or PR controller according to the frequency and property.Considering the working condition of complicated harmonic element in grid current and limited resource of processor,a frequency-dividing current control method based on reduced order generalized integrator(ROGI)was designed,using independent ROGI units to control the active component of fundamental curent,reactive component of fundamental current and harmonic component of different frequencies.So the decreased system overhead,high degree of freedom and better feature of selective harmonic compensation could be achieved.Thirdly,considering the problems in conventional switch method using a fixed time delay such as poor transient response and disordered switch of TSC,a new switch control method based on switch table decision was proposed to execute precise prediction and switch,using switch tables,current rate and zero-cross detection without current sensors of load.So the problems of disordered switch of TSC and overload of APF could be solved effectively,and power quality during transient process of switch could be promoted.Finally,the hardware platform of hybrid system was developed,and the selection of key parameters and hardware device was also discussed.Then the design of control circuit and software process were introduced.Experiments were performed to verify the validity of the suggested current control method and switch control method.