Variable Speed Pump Storage Based On Cascaded H-Bridge Multilevel Converter

This thesis presents a cascaded H-bridge multilevel converter for application in variable-speed pump storage. The type of pump storage studied and analyzed is the doubly fed adjustable speed pumped storage unit. Most of the results are related to the performance of the inverter voltage, rotor currents and speed when the6kV wound router induction machine is fed by a cascaded H bridge inverter. Multi carrier phase shift modulation is used to obtain the level phase voltage.Power Electronics converters used in doubly fed adjustable speed pumped storage unit are (AC to AC) cyclo-converter, two levels, three levels voltage source converter and cascaded H-bridge converters. The total harmonic distortions of rotor currents of doubly fed asynchronous machine and speed change for each type of converters are analyzed. The results of the study show that cascaded H-bridge eleven levels converter was the best solution than other types. It has lower dv/dt and currents THD and fast response of speed.The mathematical model of indirect field oriented control applied in pump storage to obtain the variable speed was developed. The two identical seven level cascaded H-bridge converters connected in cascade have been used to generate6KV on the rotor side. The input of power cell of cascaded H-bridge multilevel converter fed from a phase-shift transformer to reduce the total harmonic distortion of rotor currents. The slip angle of doubly fed asynchronous induction machine is calculated by using the stator flux of indirect field oriented control. The slip angle calculated is used to control the variable speed of the pump storage based on machine parameters.A wind farm power fluctuation is improved by using the variable-speed pump storage. The variations of the wind power are detected and adjusted through a PI controller to generate the reference speed of variable-speed pump storage. Finally; this model can be applied to improve the wind-power fluctuation in the Dongola station in the north of the Sudan.PSIM software program was used for simulation of the studied system.