AC-DC Hybrid Electric Power Systems

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For more than a century, the electric power system has evolved into one in which energy is generated and distributed exclusively in the Alternating Current (AC) form; even though High-Voltage Direct Current (HVDC) transmission has been used in specific cases, the transmission system is nonetheless predominantly AC. This is because, despite its merits, Edison's early DC electric power system lost the battle to its AC counterpart, mainly due to the lack of a "DC transformer" and consequent prohibitively large energy losses for long-distance deployment. In recent years, however, advancements in efficient electronic energy conversion have renewed interests in DC electric power systems to supplement the existing AC system. DC power is superior when it comes to sub-sea power transmission, from offshore wind farms for example. Moreover, most energy storage devices and modern electric power generators (such as photovoltaic systems, wind turbines, and fuel cells) can more conveniently and efficiently be interfaced with a DC infrastructure. Furthermore, the consumption of electric energy primarily takes place in the DC form. On the other hand, AC power possesses distinct merits and is the foundation of the existing electric power infrastructure and equipment. Hence, it is believed that the power system of the future will benefit from a combination of both DC and AC powers. The overall objective of the proposed research is thus to study hybrid electric power systems in which AC and DC coexist. More specifically, the research will develop and identify: