Research On Control And Main Circuit Of STATCOM In Unbalance System

Three-phase voltage unbalanced degree is the very important index of measuring the quality of network power.In the three-phase system,both unbalanced output voltage of generator and unbalanced load are the main reasons that cause unbanced ouput voltage.When unbanced voltage is very badly,it could cause lots of harms for system.Recently,statcom with fast dynamic respond velocity,little current harmony and small device volume is becoming more and more application.First this paper studied the main circuit of STATCOM based on IGCT.It is necessary to use IGCT in series for getting high output voltage.Differences of characteristics may cause unbalance of transient voltage distribution when devices are used in series,this leads to generating overvoltage of some devices and threating their safety,they can be burnt out when things go seriously.So it's important to use equalizer circuit to make distribution balance of series structure.This paper chiefly studied the design for IGCT series average-voltage and snubber circuit.It analyzed series average-voltage circuit,at the same time,it calculated the value range of absorption capacitor and absorption resistance.Then it made Pspice simulation of snubber circuit,the result of simulation verified the working effect of average-voltage circuit.The results showed that,the values of absorption capacitor and absorption resistance were appropriate to protect series operation of IGCT.It also made design for parameters of 100Kvar/660V STATCOM's main circuit,selected type of IGCT and main components.In this paper,we focus on studying the control strategy of STATCOM in unbalance system.A mathematical model of STATCOM is established based on IGCT. According to the current transient model of STATCOM,We carried out voltage and current sequence decomposition and D-Q coordinate transformation.And then establish the STATCOM mathematical mode of positive and negative sequence under the static coordinate.Based on the established negative sequence model,we study the control strategy of the STATCOM on unbalance condition.This paper applies deadbeat control to the STATCOM imbalance compensator.In addition,we introduce a reference current observer and state observer based on the traditional deadbeat control as the result of the actual problems which we encountered to optimize the deadbeat control method:slow convergence,rely on a fixed load model,robustness margin.This paper introduce how to improve the structure of Deadbeat controller and design the relevant circuit specifically.Analysis and simulation testified the good performance of the unbalance compensation,fast dynamic response and good robustness of this control method...