Voltage stability is a key issue to achieve the uninterrupted operation of wind farms. Shunt Flexible AC Transmission System (FACTS) devices, such as the Static Var Compensator (SVC) and the Static Synchronous Compensator (STATCOM), have been widely used to provide high performance steady state and transient voltage control at the Point of Common Coupling (PCC). The two important parts in a STATCOM are the structure and the controlling method. This dissertation targets on a key component of STATCOM, which is the converter topology, and simulation are carried out for a STATCOM with new type cascaded NPC converter in Matlab/Simulink. Beginning with the study of basic Neutral Clamped Converter (NPC), the cascaded converter analysi and its control method are carried out step by step. The simulation results of the carrier based NPC converter, space vector base NPC converter, cascaded NPC converter, and STATCOM provde the reader a better understanding of the work that has been completed. One problem a Neutral-Point Clamped Converter faced is the capacitor voltage balancing of the tewo capacitors in the converter. The method of controlling the voltage of capacitors are studied and simulated in this dissertation. For verifying their switched output performance, analytical models have been developed in MATLAB / Simulink for simulating the presented capacitor voltage balancing techniques with their obtained results described in detail. An experimental NPC inverter prototype has also been implemented in the laboratory. This hardware inverter has been controlled using both SVM and PWM technique. Master of Science (Power Engineering)