Research On Voltage Balance Control Strategy Of High Voltage SVG Based On Double Closed-loop PI Regulation

With the continuous improvement of my country’s power quality requirements,various power quality regulation products have emerged.Static var generator(SVG)has been widely used because of its advantages such as good compensation effect,fast response speed and high output performance.However,the compensation performance of SVG is closely related to the voltage stability of the DC side,so the voltage balance control strategy has always been one of the research hotspots of SVG.This article first introduces the background,purpose and significance of reactive power compensation in power systems,sorts out some common methods of high-voltage SVG DC side voltage control at home and abroad,and conducts preliminary induction and comparison.the main circuit structure and working principle of the cascaded SVG are explained,and the mathematical model of the cascaded SVG in the abc and dq coordinate systems is established.The bipolar and unipolar frequency-doubled carrier phase-shifting SPWM modulation strategies are compared and analyzed,and the unipolar frequency-doubled CPS-SPWM modulation is selected as the modulation strategy of the cascaded SVG based on their characteristics.Secondly,analyzing the factors affecting the DC side voltage of the high-voltage SVG,a control strategy based on the combination of double closed-loop control and layered control is proposed for the main circuit topology of the three-phase star SVG.The first level of control is the DC outer loop control.By controlling the fundamental positive-sequence active current,the average voltage on the DC side of all three-phase H-bridge modules is kept stable,and the current inner loop adopts the feed forward decoupling control method.The second layer is the phase-to-phase voltage equalization control.The three-phase power is redistributed by injecting zero sequence voltage to achieve three-phase voltage equalization.The third layer is the balance control of each module in the phase.By fine-tuning the command voltage of each module in each phase along the current direction,the power absorbed by each H-bridge module is redistributed,thereby ensuring the DC side voltage balance of each module in the phase.Finally,a system simulation model was built on MATLAB/SIMULINK,and the simulation experiment verified the reactive power compensation effect of the star-connected cascade SVG on the power grid and the control effect of the designed control strategy on the SVG DC side voltage balance.Designed a 10 k V,± 1Mvar three-phase star-connected cascaded SVG.The actual experiment was carried out through the SVG device,and the results of simulation and high-voltage experimental device were sufficient.This verifies the effectiveness of the control strategy described in this article on the cascaded high-voltage SVG DC side voltage balance control.