Research On Control Method And Controller Of Cascaded H-bridge Static Var Generator

In recent years, the increasing presence of inductive load and impact load in the electric power system, the power quality problems, i.e., reactive power, harmonic pollution, voltage drop and three-phase asymmetry. And the power supply reliability and power quality problems have been paid more and more attentions. The cascaded static var generator(static var, generator, SVG) is a new technology in the field of reactive power compensation with the characteristics of modularization and easy extension. And it can be a good way to solve the above problems of power quality. In this paper, we discussed current tracking, the design of controller, DC capacitor voltage balancing of H-bridge cascaded SVG.First, Delta-Connected Cascaded SVG is selected as the main circuit structure of the high voltage SVG, and the basic principle of SVG is described. Then the mathematical models are built. A Finite Control Set model predictive control(FCS-MPC) of mathematical model based on the state of the output level is proposed. Through the optimization of the control set, the difficulty of moving horizon optimization and the amount of computation are effectively reduced; The feedback correction is added to overcome the influence of environment interference and model mismatch, improve the performance of current tracking and enhance the robustness of the control strategy, A simulation platform is constructed, and the effectiveness of the proposed control strategy is validated by the simulation results.Then, the problem of balancing control of capacitors voltage at the DC side is studied from three aspects, including the overall control, the phase balance control and the inter-phase balance control of capacitors voltage at the DC side. The overall control of capacitors voltage at the DC side is realized by PI controller. The phase balance control strategy of capacitors voltage at the DC side is proposed, which is based on predictive sorting algorithm. The proposed strategy can keep the stability of the capacitors voltage at the DC side of H-bridge with permissible range, while ensure the low switching frequency. The reason for imbalance of the inter-phase capacitors voltage at the DC side is analyzed, and the active power imbalance is caused by the interaction between the positive sequence voltage and the negative sequence current, and between the negative sequence voltage and the positive sequence current. According to the imbalance problems under two different working conditions, zero sequence current injection and negative sequence current injection method are presented. And the simulation model is given to verify the balancing strategy of capacitor voltage at the DC side.Finally, this paper designs the controller of high voltage SVG. According to the structural characteristics of high voltage SVG, the control system is divided into three levels. The main controller and H-bridge controller have been designed. The main controller is designed based on DSP+FPGA, and H-bridge controller is designed by selecting the appropriate device, and reasonable circuit design, etc. The experimental prototypes of low and high voltage are constructed, and the effectiveness of the proposed control strategy is validated by experiments results.