A decoupled converter topology for active compensation of power systems

In recent years, the requirements on the reliability and quality of electric power supply have become more stringent due to increased use of sensitive electronic equipment. At the same time, deregulatory changes are transforming the electricity industry into a competitive market in many parts of the world. In response to these forces, utilities are focusing on retaining large customers by providing premium-quality power and enhancing the operating flexibility and utilization of their transmission and distribution networks by incorporating advanced technologies.;Power electronic converter-based controllers offer a promising approach for operating the transmission network in a more efficient and flexible manner and for solving power quality problems at the distribution level. However, present power converter topologies are not optimal for utility applications. The converter switches have to withstand system-level voltages and currents and operate at high switching frequencies for good waveform synthesis. The resulting high cost and low efficiency reduces the practical viability of present active compensators.;This dissertation introduces a novel converter topology which decouples the fundamental-frequency and harmonic-frequency compensation functions. A slow-switching converter is assigned the task of compensating fundamental frequency components, while a fast-switching converter handles compensation of harmonics. The decoupled arrangement results in a significant reduction of ratings required for the fast semiconductor switches in the harmonic compensation converter. This offers the potential for active compensation at lower costs and higher efficiencies. Circuit implementations, control strategies and design guidelines are developed for shunt and series controllers based on the decoupled topology. Simulated and experimental results are presented to demonstrate the performance of the proposed compensators.;The dissertation also introduces a new control scheme for unbalance compensation in three-phase systems using a multi-pulse converter. Multi-pulse converters have been hitherto gated symmetrically and hence not capable of unbalanced control. The new approach can be applied for compensation of loads such as arc furnaces and electric traction which typically lead to large unbalances in the three-phase system. Simulation results are presented to show the performance of the proposed unbalanced triggering technique.