Research On The Technology Of D-STATCOM For Unbalanced Load

Three-phase voltage source inverter of STATCOM has many functions， such asreactive power compensation, voltage support, improving system stability and harmonicsuppression[8]. This paper studies on the STATCOM under unbalanced load control andcurrent detection.Mathematical model is an effective method to study the three-phase PWM inverter.This paper established a three-phase voltage-type PWM inverter mathematical model in thetwo-phase rotating coordinate system to provide the basis for control system design models.In order to study STATCOM technology under unbalanced load conditions, thetheoretical analysis of unbalanced load appears to have targeted and necessity. Bysymmetrical component method to analyze unbalanced load, this paper proposedcompensation theory through load current and impedance.For load currents, especially unbalanced load current detection is the first key to selectcontrol scheme. Through the current detection research, this paper stressed on real-timedetection method based on three-phase current of the instantaneous power theory analysis.Through understanding of instantaneous reactive power theory and the STATCOM controlstrategy, there are focusing on two methods，p qalgorithms andi p iqalgorithms. In thesecond, it also had a discussion of the effect on the test results when the grid voltagedistortion imbalance.through the direct and indirect current control analysis of STATCOM，it illuminated theSTATCOM f controlling strategy due to closed-loop control based on the synchronousrotating coordinate system and how to get the parameters of indirect current controldesign methods. And this paper also had a research on the direct current control underinstantaneous power theory in the stationary coordinate system and had a compensation forreactive load imbalance and negative sequence current.In conclusion, the methods of three-phase PWM voltage-type inverter on the control ofthe unbalanced load can divide into two categories: one is based on the instantaneous powertheory achieved in the two-phase stationary coordinate system, the second is two-phase rotating coordinate system implementation. The final analysis of unbalanced load isdepended on the compensation current extraction， according to the different extractionways， coordinate systems can have different control strategies. This paper verified thepossibility of the research ideas implemented by MATLAB simulation and achievedreactive load imbalance and negative sequence compensation.