New Converter for DC Grids

About

About DC transmission systems have a proven capacity to carry high power over long distances practically without limits under some circumstances (long distances over 500 km, bulk power transmission > 1-2 GW); in these cases they are preferred over more common AC systems. High voltage DC (HVDC) systems that incorporate power electronics can achieve this and are well established in applications that bring offshore wind power to shore. They are therefore of great interest to increase penetration of renewable power. Voltage-source converter (VSC) technology is the most suitable topology for multi-terminal HVDC and DC grids since active power reversal is achieved without DC link voltage polarity change, and because of its resiliency to AC side faults (i.e. there is no risk of commutation failure as with line-commutating HVDC systems). However, vulnerability to short circuits and absence of reliable high voltage DC circuit breakers restrict their application to point-to-point connection. The DC/DC voltage source converter for HVDC power grids transmission developed at the University of Aberdeen offers a universal solution to most of these problems eliminating the drawbacks of similar technologies. In particular, it outperforms thyristor-based converters. The converter is capable of handling short circuits by its built-in open circuit characteristics that naturally brings down current to zero at the non-faulted side without control intervention. This ensures fast fault isolation, protects devices from high transient fault currents, has minimum converter downtime effect and introduces the possibility of replacing an intentionally used DC circuit breaker. Moreover, it is suitable to connect conventional current source HVDC with state-of-the-art VSC HVDC technologies, facilitating active power reversal between both. Key Benefits Suitable for high voltage stepping ratios. Higher efficiency due to zero reactive power control DC fault isolation like DC circuit breakers Safety enhanced by galvanic isolation by magnetic or mutual air-core coupling of the AC inductors Enables DC power flow regulation in meshed DC grid transmission lines Applications Offshore wind renewables High power DC grids  IP Status Drafting priority application