Operation of DC/AC/DC System for HVDC Applications at High Frequency

Abstract

It has been found that the voltage ratings observed mainly for
HVdc point-to-point connections are not as uniform and are
mainly tend to depend on the latest available cable
technology. It is observed that DC/DC conversion at HV is
the main requirement for interconnection of these type of
HVdc schemes. Modular multilevel voltage source converters
(VSCs), such as the modular multilevel converter (MMC) or
the alternate arm converter (AAC), have been shown to incur
knowingly which shows lower switching losses than that of
previous two-level or three-level VSCs. This paper presents
dc/ac/dc system with a transformer coupling two modular
multilevel VSCs. In such a system, the capacitors inhabit a
large numbers volume of the cells but a substantial lessening
in volume which can be achieved by raising the ac frequency.
As we know that using high frequency can also lead in
benefits to other passive components such as the transformer
but also effects in maximizing switching losses due to the
greater number of waveform steps per second. This leads to a
tradeoff between volume and the losses which is explored in
this study, and is verified by simulation results with the help
of transistor level model of 30-MW. The outcome of the
study mainly shows that a frequency of 350 Hz provides a
significant improvement in volume but also a penalty in losses
compared to 50 Hz.