Research Simulation Of SVG System Based On Cascaded Multilevel Inverter Technology

With the development of economy and society, as a commodity, power quality isgetting more and more national attention. When power system is running at rated voltage,the balance of reactive power is one of the most important symbols of measurements topower quality. Real-time and fast compensation of reactive power is of extremely vitalsignificance to power quality. Traditional reactive power compensation equipment isbackward, slow and difficult to meet system requirements. So, this paper designs anadvanced Static Var Generator (SVG). It is of fast response, low power consumption, longlife, and becomes one of the most important members of Flexible Alternative CurrentTransmission Systems(FACT).Firstly, two common reactive current detection methods: Ip-Iq method and dq0methodare introduced. Both of the mathematical models of these methods were built. By analyzingthe advantages, disadvantages and application range of the two methods, it can be knownthat when three-phase voltages are asymmetric, only dq0method can accurately detect thereactive power current, which can be used as the reactive reference current of SVG.Secondly, several kinds of main circuit topology of SVG system are analyzed. Aimproved multi-level chain of three-phase cascaded H-bridge inverter circuit is designed.Then, According to the characteristics of the structure of this inverter circuit, twomodulation methods of the circuit structure: bipolar and unipolar dual-frequencyCPS-SPWM. Through detailed mathematical analysis and simulation studies, it can beknown that single-stage multiplier CPS-SPWM can greatly increase the switchingfrequency of the power of the device, reduce the output harmonic and filter costs.Three-phase star chain seven-level H-bridge inverter circuit, based on single-stagemultiplier CPS-SPWM, is designed as main circuit of SVG system.Thirdly, this paper analyzes SVG control system，including: DC capacitor voltagecontrol and AC current control. A feedback decoupling PI controller is designed withreactive current which is detected by dq0method and main circuit structure.Finally, a simulation model of SVG system is built using MATLAB/SIMULINK.Simulation study of reactive power compensation of stable load and mutation load is down.The results show that SVG system is of fast response, good compensation effect, simplecontrol, when reactive power compensation is needed, especially mutation load.