Investigations into LCC-HVDC Converter connecting to weak ac systems using various compensator configurations
Line-commutated Converters (LCC) have been used for over half a century, are robust, and can handle much higher power than the other alternatives. The impact of voltage and frequency disturbances can be onerous on an LCC-HVDC link terminating in a very weak ac network. Such systems use synchronous condensers (SCs) to provide voltage and frequency support at the receiving end. A promising new topology for connecting SCs into an ac network has been developed at TGS (the industry partner). In this approach, the SC is interfaced with the network through an asynchronous by-passable back-to-back VSC link. This removes the requirement for the SC to operate at network frequency, thereby allowing much larger energy transfer to the SC's rotating mass during under/over frequency events. Closing the bypass circuit breaker during normal operation allows the SC to perform its usual voltage control function in parallel with two converters which work as two STATCOMS. This provides the system with much more reactive power during voltage disturbances. The project aims to investigate the applicability of this approach in LCC-HVDC converters considering the range of operating contingencies.