The conventional converter used in an HVDC system requires line voltage to tum off the current flowing through a thyristor or a mercury-arc valve. Hence, the HVDC system cannot supply electric power to the system which has no ac source, such as a generator or a synchronous condenser. Thus, the HVDC system has some difficulties in operating with the weak system.The conventional solution to avoid these problems is to install large-capacity synchronous condensers which require considerable construction costs and maintenance. Another solution is the application of a forced commutation converter.The recent development of high-power and highfrequency semiconductor devices with fast gate turn-off ability (e.g., GTOs and SI thyristors) suggests the application of a voltage-source-type forced commutation converter (VSFC) to an HVDC system. To ensure the promising characteristics of the overall system, further investigation is of course necessary.