| In our highly computerized world, the demand in power is dramatically increasing. Because of this, the energy suppliers are constantly looking at new ways of providing cleaner, more stable power. Equipment, such as a Static Compensator (StatCom), provides a way to compensate for voltages sags along transmission lines. Being part of the FACTS family, a StatCom has the advantage to be self sufficient, meaning that it does not need any external source to produce the reactive power required to keep constant its terminal voltage. In this research, a five-level Diode-Clamped Converter (DCC) is used as a voltage source within a StatCom. However, the DCC suffers from voltage unbalance amongst its DC-link capacitors. The objective of this thesis is therefore to propose a technique for balancing the capacitor voltages of a five-level DCC based StatCom. This is done by combining two existing techniques. The solution envisages to eliminate this issue by using an auxiliary balancing circuit and by controlling the zero-sequence current of the converter. The state-space model of the converter is presented and thereafter, its controllability is studied. As part of the preliminary work, a linear controller has been fully designed to control the StatCom. However, because the system is nonlinear and its parameters may very well vary, a robust nonlinear controller has also been designed. Finally, simulation results are provided using SimulinkRTM and SimPowerSystemsRTM simulation tools.Keywords. Multilevel DCC, StatCom, zero-sequence current, Proportional-Integral (PI) controller, Backstepping. |
