Researchers of the University of Aberdeen have developed a new DC/DC converter for high power DC grids that eliminates most of the drawbacks of alternative technologies (e.g. short circuits or commutation failures). It can help address bulk power transmission, integration of renewable energy sources more economically and efficiently.

About the technology

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.

Applications and benefits

The new DC/DC voltage source converter for HVDC power grids transmission 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.

  • Suitable to inter-connect conventional current source HVDC with state-of-the-art VSC HVDC technologies.
  • High efficiency of operation thanks to zero reactive power operation at rated active power.
  • Safety enhanced by the use of galvanic isolation by magnetic or mutual air-core coupling of the AC inductors.
  • Enables DC power flow regulation in meshed DC grid transmission lines.
  • Self-commutated IGBT technology enables fixed frequency square wave control, faster operation than thyristors (smaller passive elements footprint), reduced lower harmonic generation (lower reactive power consumption and higher efficiency), and does not suffer from commutation failure problems.

It is expected to be of interest for the advance of high power DC grids and offshore renewable energy companies.

IP status

A patent application is currently under consideration.