Monopolar Symmetrical DC–DC Converter for All DC Offshore Wind Farms

All dc offshore wind farms are gaining popularity for long-distance and high-power offshore wind energy conversion. It calls for high-power dc–dc converter with high step-up ratio for interconnecting the medium-voltage dc collection and the high-voltage dc transmission systems. This article proposes a monopolar symmetrical dc–dc converter, which is featured with partial-power processing and presents less installed capacity of components, low cost, low power loss, lightweight, and small footprint. Moreover, a modified phase-shifted carrier pulsewidth modulation with variable carrier frequency is developed to further reduce the switching loss and keep the dynamic current tracking performance. The effectiveness of the proposed converter has been verified by a simulation study of a 400 MW, ±25 kV/±250 kV model and experimental results of a 5.4 kW, ±60 V/±320 V scaled-down prototype.