Investigation of the use of inverter control strategy instead of synchronous condensers at inverter terminal of an HVDC system

This paper presents a comparison of performance of traditionally used synchronous condensers (SCs) at inverter side HVDC terminal and a novel inverter control method. The novel controller has earlier demonstrated good responses with very weak inverter AC systems and widely changing AC system parameters. The aim of this research is to study if it is possible to offer adequate replacement for SC at weak HVDC-HVAC interconnection point. The simulation results on an actual HVDC system show excellent small signal responses, but the main obstacle for the application of the new control method could be increased probability of commutation failure. Subsequent tests show that in order to keep the same commutation failure probability, half of the SC must be maintained in normal operation. Further SC can also be disconnected, when the new control method is employed, however the nominal operating angle has to be somewhat increased. The cost benefit study is performed to analyze the financial benefits of the proposed project. It is concluded that, although the benefits are evident for the new HVDC links, the proposed replacement of SC may not be justifiable for the existing links.