Realization, comparison, and topology investigation of multiple-input converters for distributed generation applications
This dissertation systematically explores multiple-input converters (MICs) configuration and topologies, and then proposes improvements on certain beneficial MICs—time-sharing MICs and soft-switching MICs for distributed generation (DG) applications with high voltage transfer ratio. Compared with other MIC families which are derived from same input and output cells, time-sharing MICs have the fewest circuit components. However, time-sharing MICs lack for bi-directional power flow capability due to their special input switches requirement. In addition, their hard-switching characteristic leads to a low efficiency problem when isolation is necessary. The dissertation investigates into time-sharing MIC input switch selection, which leads to a new driving strategy and new input switch combinations. With the new input switch combinations, bi-directional and high efficiency time-sharing MICs are made possible. Besides isolated time-sharing MIC, Soft-switching MICs might also be a common choice for high voltage transfer ratio DG applications. However, the enormous amount of circuit components makes the soft-switching MICs become less attractive. An input cell reduction method is introduced in this dissertation to greatly reduce the component count of isolated MICs, including soft-switching MICs. In addition to the improvement on existing MIC families, a new push-pull connected MIC family is proposed in this dissertation as another choice of high voltage transfer ratio DG applications. Moreover, a comparison among MIC families is made to provide a sense of topologies selection in certain applications. Prototypes of time-sharing dual-input (DI) SEPICs, a push-pull connected DI-Boost converter, and a DI full-bridge (FB) converter are built to verify aspects discussed in this dissertation. Bi-directional power flow capability of time-sharing MIC is confirmed with a time-sharing DI-SEPIC and a soft-switching time-sharing MIC is realized by an isolated time-sharing DI-SEPIC with an active clamping leg. Maximum power point tracking control feasibility in these converters is evaluated with real photovoltaic modules that are connected to the push-pull connected DI-Boost converter that uses a perturb-and-observe method. Finally, an efficiency comparison is made between time-sharing MIC and push-pull connected MIC.