Design and Characterisation of Optimised Protective Thyristors for VSC Systems

Inhalt:
Voltage Source Converter (VSC) technology provides a number of advantages over traditional HVDC including self commutation, small footprint and black start capability, and is becoming increasingly popular in applications such as offshore wind. One major drawback of VSC systems is their vulnerability to DC faults, which cause a short circuit current to pass through the IGBT diode path. The magnitude of the fault current can be many times the rated current, can last for a number of cycles and can destroy the diode before an AC circuit breaker is able to clear the fault. A common solution is to include a thyristor in parallel with the IGBT diode to divert the majority of the fault current from the diode in such an event. The correct design of such a device can increase fault current handling capability of the VSC and also enable a more compact and cost effective sub-module. This paper discusses the design methodology adopted to produce an optimised protective thyristor and presents a method for characterising and comparing differing thyristor designs for VSC protective applications.