Research On Application Of STATCOM In Unbalanced System

Currently,impulsive unbalanced reactive load and unbalanced power system will influence the power quality in power system.In low and medium voltage conditions, STATCOM in unbalanced power system can make the voltage of the DC capacitor fluctuate in two frequency doubling,while with regard to STATCOM under symmetrical control,the negative sequence component of the voltage of power system amount to short circuit,make great negative sequence current and influence the safety of STATCOM seriously.According to the operation characteristics of STATCOM in unbalanced system and the theory of dq reference frame transformation,the dynamic mathematical model of STATCOM in unbalanced system is deduced,and carries on the synthesis compensation aimed at the harmful electric current in electrical power system with unbalanced electrical voltage or unbalanced load.According to the parameters of load and the power system can change momentarily,and the complexity of control theory in STATCOM,the nonlinear dynamic control strategy for reactive power is achieved. And using the control method of two inputs and two outputs linearity,a pseudo linear output variables decoupled system is obtained.The simulink and experimental results demonstrates that nice dynamic performance is achieved using the proposed control method after occurring fault and high power load changing abruptly.Then,using the ip-iq method of instantaneous reactive power theory,a new method of current detection suited to the unbalanced system(especially the unbalanced power net) is expatiated,which is fundamental for the three-phase power fundamental frequency positive sequence voltage synchronous reference coordinates.And then its realization on TMS320F2812 is expounded.The simulink and experimental results demonstrates that the current detection method is better real-time and accurate in unbalanced systems.Lastly,the operation characteristics of cascade STATCOM in medium voltage of unbalanced system are analyzed.Compared and analyzed the method of modulation suited for the cascade STATCOM in unbalanced system,and proposed one new kind of PWM control method——Carrier Overlapping-Switch Frequency Optional PWM (CO-SFO-PWM).The simulink results demonstrate that the system has good performance with CO-SFO-PWM in reactive power compensation and harmonic suppression.