The Study On Static Synchronous Compensator Of High Voltage Cascaded H-Bridge

Application of cascaded H-bridge STATCOM(Static Synchronous Compensator)will be very popular in the condition of high voltgage and high power,but the balanceproblem of DC side voltage of cascaded H-bridge STATCOM is one of the keytechnical problem for the application of that.In this thesis,an improved H-Bridge DCside voltage control method is presented,it is based on the cause analysis of DC sideunbalance voltage. By adjusting tiny phase angle and tiny modulation index at the sametime, it controls the DC side voltage of H-Bridge, among them,adjusting the tiny phaseangle and the tiny modulation index are based on the method of meandifference.Through the simulation experiment, it shows that this method can find theadjusted range of the tiny phase shift angle quickly and reduce the number of testssignificantly,which reduce the difficult of the former adjustment about the tiny valueand change the basic condition of a long time and a lot of trial and error. The simulationexperiment is carried out under the conditions of parallel loss and mixed loss, ultimatelythe simulation results show that the DC side voltage of H-Bridge is balanced.After the improved control method for DC side of the cascaded H-bridgeSTATCOM, the simulation model of eight H-bridge STATCOM is built in thisthesis,the main structure of the simulation platform is formed by eight cascadedH-bridge,such the output voltage wave of high-voltage H-bridge STATCOM isseventeen level voltage wave.This simulation platform control method is the statedecoupling feedback control based on PARK transformation. By decoupling the loadreactive current feedback value and the load active current feedback value, it cangenerate the initial control parameters which is constituted by modulation index andphase shift angle.Then it integrates the intial control parameters and the tiny modulationindex and the tiny phase shift angle and thus generates the sine modulation wave that isneeded by unipolar dual-frequency CPS-SPWM(Carrier Phase-Shifted SinusoidalPulse-Width Modulation).Finally, the switch devices of each H-bridge is controlled by unipolar dual-frequency CPS-SPWM. When the eight H-bridge STATCOM is operatedin the10kV power system which contain the600kVar reactive power, the simulationexperiment obtains the compensation effect and the compensated simulation parametervalues on each module of compensation device.Above the unipolar dual-frequency CPS-SPWM is the most common controlmethod for the cascaded H-bridge converter,therefore the unipolar dual-frequencyCPS-SPWM method is detailed studied in this thesis. It is that the same sine wave iscompared with the different phase triangular waves,and the compared level and itsinverse contol the same side of each H-bridge arm.After the unipolar dual-frequencyCPS-SPWM is achieved by MATLAB simulation,it is also implemented by VHDLlanguage and tested well.Thus the two H-bridge converter which constitute cascadedH-bridge STATCOM experiment platform is built, this experiment proves thefeasibility of the two H-bridge converter for STATCOM.