Abstract
The classical method to suppress resonances in power systems is by installing passive dampers in parallel to the loads. However, observations indicate significant power losses due to harmonic currents flowing over passive dampers. Certainly, passive dampers absorb harmonic active power and dissipate this power as heat on their resistive elements leading to energy waste. On the other hand, the passive damper counterpart is the active damper. The latter is also known in technical literature as Voltage driven shunt active power filter (VSAPF). The active damper is a power-electronics-based system that emulates a virtual resistance at harmonic frequencies. Truly, very little was known about the harmonic power absorption on active dampers. Therefore, this dissertation delves into a profound analysis of the capability of an ultra-low losses active damper based on SiC semiconductor technology to process the harmonic power intake and perform harmonic power recovery. Harmonic power recovery in this context is understood as the process of transforming the harmonic active power absorbed into fundamental power that is injected back into the power system. The next topic that is addressed is the reduction in the fundamental power demanded by an industrial facility due to the recovery of harmonic active power. To this end, this dissertation analyzes the power balance flow of a distribution power system (e.g., industrial grid) that includes an ultra-low losses active damper. Arising out of the power balance flow analysis, it was found that the active damper with harmonic recovery function achieves a 1.4% reduction on the fundamental power demanded compared to a passive damper. Naturally, the lower the active damper´s power losses, the higher will be the amount of harmonic active power that can be recovered from the power system. Therefore, during this research work, various power electronics converters topologies are analysed to find the best possible design for the active damper with harmonic power recovery functionality. Arising out of this investigation, it was found that the conventional three-level neutral point piloted converter (3L-TNPC) and the asymmetrical three-level converter (3L-ASYM) are the most suitable power circuit topologies for the ultra-low losses active damper. The former topology, the 3L-TNPC, exhibits the lowest power losses for switching frequencies up to 60 kHz. And then, the 3L-ASYM topology presents the lowest losses among all the studied power circuits for switching frequencies beyond 70 kHz. Furthermore, as an active damper forms a closed loop between harmonic voltages and compensating currents, its stability must be ensured. Thus, a careful design of the VSAPF control system and its inner current controllers is essential. On account of this, this dissertation proposes using the Ragazzini method to design the VSAPF’s inner current controllers.
Furthermore, the direct design of the inner current controllers on the discrete domain using the Ragazzini method increases the current controllers’ bandwidth by a factor of three compared to the controllers’ design with conventional methods. Consequently, the increased current controller’s bandwidth achieved through the Ragazzini method pushes the stability limit of the active damper forward compared with traditional current controller designs.