Design considerations for an HVDC VSC Back-to-Back converter in parallel operation with HVDC LCC Back-to-Back converter

Abstract:
Development of power systems requires, in certain cases, expansion of installations after some years of operation. This paper considers an existing Back-to-Back HVDC system with two LCC converter modules which is planned to be ex-tended to increase the power transfer capability. The third converter module will operate in parallel with the two existing modules. Since VSC technology might offer better performance in weak AC networks, the main purpose of the paper is to investigate in detail the impact of applying VSC technology for the third converter module. To study the system per-formance, a comprehensive EMT model of the system has been developed using the PSCAD simulation tool. This model includes all three HVDC Back-to-Back converters and the HVAC network on both sides. The system response during and following AC faults is presented. The results indicate a benefit by dynamic voltage support through application of the VSC technology.