Research On Control Strategy Of High Voltage Digitized Static Var Generator

Static var generator (SVG) is the most advanced power system for reactive powercompensation equipment. What applied in the field high voltage of SVG is mainly used thechain structure. In this paper, based on SVG as the research object. First, there is a briefintroduction to the development background of SVG. Then it introduces the working principleof SVG. It also depth studies and improve those key technologies,such as tracking anddetection of reactive current, balancing control strategies of DC capacitor voltage, multi-levelPWM control strategies. Last it is verified by MATLAB simulation.Whether or not SVG play a good compensation effect, the key is the ability to achievereal-time monitoring of reactive current. At the present stage, the new SVG is a dynamiccompensation device, It can quickly,flexibly and accurately detect and calculate reactivecurrent. It directly affects the compensation and tracking of SVG, and even the scope ofapplication. Based on the study of harmonic and reactive current detection, this paper proposea reactive current detection method based on instantaneous power balance.This paper studies a variety of PWM modulation. Comparing two of carrier phase shiftmethods, the paper adopt an improved unipolar octave CPS-PWM method. It is controlledPWM waveform and IGBT breaking by comparing the carrier and modulating waves, toachieve reactive power compensation. Its features are a real-time, simple control and so on. Itis most suitable for cascaded H-bridge multi-level structure. For this pape, the structure of12H bridge is used, which output voltage is closer to a sine wave.The problem of DC capacitor voltage balancing has been one of the technical problemsthat trouble the development of SVG. Each H-bridge of SVG consists of Integrated gatecommutated thyristor or IGBT。Each inverter has different switching characteristics, parallelloss, mixing losses, charging and discharging time. Even pulse delay differences. All theselead to distortion of the output voltage. So that the voltage stress of each IGBT is not equal.Thus burn switching devices, and even endanger the safe operation of the device, affecting thequality of output voltage and current. On the basis of the depth study of DC side capacitorvoltage balancing problem, strictly control the fundamental amplitude, phase, and theswitching frequency of the H-bridge. But just the difference of switching time will bring about a large capacitor voltage imbalance. This paper presents an improved unipolar octaveCPS-PWM method, eliminating the DC capacitor voltage imbalance. Matlab system modelbuilt here. It uses a triangular wave for simulation to verify the accuracy, effectiveness andrapidity of the method.