Optimal Hybrid Multiplexed AC-DC-AC converters

Abstract: The flexibility of multi-terminal AC-DC-AC converters connected in distribution networks can be increased by changing the sizes of the individual AC-DC converter stages and connecting the AC side of those converters to electromechanical switches (multiplexers) to allow reconfiguration within the network. The combinations of real powers that can be transferred by such a design can be described using a capability chart. In this work, it is proposed that the area of these capability charts is a meaningful metric for describing the flexibility of such a device. These capability chart areas are calculated in closed form for a three-terminal AC-DC-AC device consisting of three AC-DC converters of arbitrary sizes, allowing the optimal AC-DC converter sizing to be determined to maximise this area. It is shown that this optimal design yields a capability chart area that is 64% larger than the equivalent area from a conventional equally-sized AC-DC-AC converter. Converters which are optimal in other senses are discussed, such as a design with 10% increased per-feeder real power transfer, albeit with an 8% area reduction. It is concluded that the capability chart area is an intuitive and informative approach for describing the increased flexibility of multiplexed AC-DC-AC converters.