High-Voltage-Gain DC-DC Power Electronic Converters -- New Topologies and Classification

This dissertation proposes two new high-voltage-gain dc-dc converters for integration of renewable energy sources in 380/400V dc distribution systems. The first high-voltage-gain converter is based on a modified Dickson charge pump voltage multiplier circuit. The second high-voltage-gain converter is based on a non-inverting diode-capacitor voltage multiplier cell. Both the proposed converters offer continuous input current and low voltage stress on switches which make them appealing for applications like integration of renewable energy sources. The proposed converters are capable for drawing power from a single source or two sources while having continuous input current in both cases. Theoretical analysis of the operation of the proposed converters and the component stresses are discussed with supporting simulation and hardware results. This dissertation also proposes a family of high-voltage-gain dc-dc converters that are based on a generalized structure. The two stage general structure consists of a two-phase interleaved (TPI) boost stage and a voltage multiplier (VM) stage. The TPI boost stage results in a classification of the family of converters into non-isolated and isolated converters. A few possible VM stages are discussed. The voltage gain derivations of the TPI boost stages and VM stages are presented in detail. An example converter is discussed with supporting hardware results to verify the general structure. The proposed family of converters can be powered using single source or two sources while having continuous input current in both cases. These high voltage gain dc-dc converters are modular and scalable; making them ideal for harnessing energy from various renewable sources offering power at different levels --Abstract, page iv

Analysis and Design of Series LC Resonant-Pulse Assisted Soft-Switching Current-Fed DC/DC Converters

The accelerating pace of electrification via renewable energy sources is shifting focus towards de-carbonization and distributed generation with the potential to combat increasing environmental crisis and to promote sustainable development. Renewable technologies have the potential to fulfil the electricity demand locally which eliminates the unwanted conversion stages, promoting DC microgrid concept, ultimately lowering the energy costs and easy energy access. Alternative energy sources such as solar photovoltaic (PV) and fuel cell along with energy storage systems are promising for DC microgrid applications. However, the effective integration of these alternative energy sources still remains a challenge due to their low voltage output, unregulated and intermittent characteristics issuing a requirement of a dedicated power conditioning unit. To revolutionize the way these alternative sources are interfaced with a high voltage DC microgrid or to the conventional ac grid, dc/dc converters are expected to be power-dense, compact and extremely efficient. Current-fed dc/dc converters have strong application potential owing to their inherent merits. Accomplishing the abovementioned objectives together with distinct merits offered by current-fed circuits, this thesis aims to exploit the quasi-resonance concept for achieving soft-switching and smooth commutation of the semiconductor switching devices. The proposed quasi resonant approach that utilizes the leakage inductance of transformer and a high frequency series resonant capacitor for a short period also termed as ‘resonant-pulse’, has been investigated in various current-fed converter topologies. Proposed converter class emphasize on simple and efficient design, without the use of additional snubber circuits and eliminates device turn-off voltage spike, which is a historical problem with traditional current-fed converters. In this thesis, at first the proposed series resonant-pulse concept is implemented in single-phase current-fed push-pull and half-bridge configuration. The converter operation, control and performance are investigated for low voltage high current specifications. These converter configurations demonstrate good efficiency and compact structure with only two switching devices and simpler gate control requirement because devices having common ground with power supply. The idea has then been extended to modular current-fed full-bridge topology. The proposed series resonant-pulse assisted converter enables wide range ZCS and turn-off spike elimination across the semiconductor switches. Modularity of this converter allows easy scalability for high power and voltage levels with significantly lower current and voltage stress, making it suitable for relatively higher power industrial applications. Lastly, to achieve high power capability with high density, three-phase current sharing current-fed topology utilizing series resonant-pulse feature has been studied and investigated in detail. The proposed three-phase topology combines the benefits of current-sharing primary and load adaptive series resonant-pulse. As a result, these converters demonstrate promising attributes such as wide ZCS operation, reduced filtering requirement, lower component count, lower conduction losses etc