Research On DSTATCOM In Distribution Network And Its Control Strategy

Today, modern science and technology development has entered a new stage，a lot ofnonlinear, impact of power equipment put into the distribution network，which lead todistribution network voltage unbalance. The unbalance of the distribution network willcause a lot of harmful effects on compensation device,if it only uses the operation of thebalance case control method to DSTATCOM. This thesis focuses on researching under theenvironment of distribution network voltage unbalance of DSTATCOM device should betaken to control strategy is based on the cascade multilevel DSTATCOM as the researchobject. Simulation results show the accuracy and effectiveness of the control strategyproposed in this thesis.First of all, this paper explains the choose of the cascade multilevel DSTATCOMcircuit structure in detail, and analyzes the work principle and mathematical model ofreactive power compensation devices, which laid a foundation for further analysis controlstrategy. After theory analysis this paper carries out on the reactive current detectionmethod, and the two kinds of carrier phases shift PWM modulation method made a detailedcomparison and analysis, under the condition of equilibrium mathematical model,cascading multilevel DSTATCOM device are studied under the condition of the powerbalance control strategy.Secondly,the reason and affect of distribution network voltage imbalance is explainedby the paper. It also introduces the research in the applied to the unbalanced distributionnetwork analysis method and the phase sequence separation technology in the same time.Base on the analysis above, the distribution network voltage unbalance compensationdevice mathematical model of negative sequence is established. The thesis adopted themodified phase locked loop technique to ensure the compensation device can accuratelytrack the fundamental positive sequence component of the phase angle, and do thesimulation of verification.In order to solve the distribution network voltage imbalance, dual sequence currentloop control strategy is adopted in this paper. The positive and negative sequencecomponents detected by this strategy which used a PI regulator and decoupling controlmethod. The reactive power and negative sequence components can be effectivelycompensated and the power factor of distribution network has to be improved. In order tosolve the distribution network voltage sag,this paper take a voltage sag control method.Thisstrategy achieve the voltage sag compensation by controlling the DSTATCOM device toinject reactive power distribution grid.And under the environment of MATLAB/Simulinksimulation results verify the accuracy of the proposed method.