Research Of The Design Methods Of 50kVA Three-phase Static Var Generator And Compensator

In this paper,the working principle,control mode and hardware design based on the Static VAR Generator(SVG)are studied.Firstly,the background,main functions and implementation methods of the reactive power compensation device are introduced,and the development history and research status of SVG are implemented.The filtering characteristics,damping methods,introducing resonant branches and splitting capacitance methods of LCL filter used in SVG are summarized.In terms of topology selection of SVG,the difference between two and three levels is discussed,and the diode clamp topology is determined,then its working mode and modulation mode are analyzed.Combined with specific functions,the characteristics and harmonic generation ability of LCL filter are calculated.In terms of control strategy,the outer loop of midpoint voltage and the inner loop of grid current feedback are mainly analyzed,in which the inner loop adopts parallel quasi-PR controller to track the 1/5/7 harmonics.The steps to design a 50 k VA prototype are as follows: Firstly,starting from the power loss of the inverter,several power switching devices are compared.The specific parameters of LCL filter and resonant branch are determined from the control stability,total loss and inductance drop.At the same time,the passive components including filter inductance and DC bus capacitance are designed from the perspective of power and efficiency of the inverter.Then the hardware parameters of the main power part are obtained.Finally,the distribution circuit and the embedded hardware circuit of the system are designed.A new type of LCL filter design method is put forward,which is the split-capacitor LCL filter.By paralleling two capacitor branches,the stability and the damping loss are analyzed.The feasible region is calculated through the linear programming method,and several groups of typical solution are given in different regions.In terms of the control strategy,the quasi-PR controller is selected and the control loop parameters are designed by root locus setting method to ensure the dynamic response and stability margin.According to the above theoretical analysis,the simulation and experiment of SVG prototype are carried out,and a 50 k VA three-phase grid-connected reactive power generation compensation device is designed.In order to further verify the feasibility of the split-capacitor filter,different typical solutions,namely the resistor-capacitance distribution coefficient,are used to conduct experiments.The correctness and effectiveness of the theoretical analysis are verified.