Soft-Switched Multi-Input Converter for Renewable Energy Systems

In a renewable energy system, multiple energy sources (such as combining renewable energy and energy storage) are utilized together to enhance the overall energy conversion reliability since renewable energy, such as wind and solar, are intermittent in nature. In conventional power architecture, each energy source requires a dedicated individual power converter to perform specific control or power management function. To reduce the overall number of circuit components, multi-input converter (MIC) configuration provides a cost effective power architecture when multiple energy sources are utilized, as they can use fewer filter circuit components and utilize smaller system space. To maximize the features offered by MICs, a truly power efficient and compact MIC should utilize minimal number of active switching components with soft-switching features, while at the same time, assist each energy power interface to achieve all the required control functions.
In the first part of this thesis, a class of several soft-switched DC-DC MICs is proposed, where each input module of the devised MICs utilizes only a single switch. Each of the presented MIC circuits can also be integrated with a front-end (either single phase or three phase) AC-DC stage without adding additional switches to interface with renewable energy generation unit that outputs an AC voltage. In addition, input power factor correction is also provided. The second part of this thesis investigates the use of the devised DC-DC MIC circuit to improve the double power conversion steps typically seen in a solar-battery energy conversion system with a common DC grid that utilizes a bi-directional energy storage power converter. This chapter focuses on the development of a soft-switched MIC circuit that consists of integrated unidirectional energy storage (i.e. battery) power interface, for use in module-connected solar energy power optimizer system with distributed energy storage. In the proposed circuit, the storage charging (storage absorbs power) circuit is integrated with the input stage of the main converter via high frequency AC link, whereas the storage discharging (storage delivers power) circuit is connected to the output stage of MIC. As a result, energy is directed from the input to the battery and from the battery to the load through a single power conversion step.
The third part of this thesis utilizes the circuit concepts devised previously to develop a new soft-switched MIC configuration that consists of an integrated unidirectional energy storage power interface, as well as to provide output voltage regulation. Hence, the proposed MIC is applicable for both regulated and unregulated grids. The control mechanism of the proposed system is presented. The operating principles and characteristics of each proposed converter topology are provided in detail. Simulation and experimental results on proof-of-concept prototypes are provided to demonstrate the functionalities of each devised MIC topology.