Analysis of Innovative HVDC Control

HVDC control has much faster inherent capability of the response than the dynamic response of the AC system. The valve firing angle control has a transient response time of only few milliseconds with the accuracy of a fraction of an electrical degree for firing the converter valves. Consequently, the control can have a significant influence on the improvements of system stability e.g. fast power recovery after faults and quick response against the disturbances around the operating points. This paper introduces a new practical control concept to increase the performance of HVDC transmission. The studies are performed by the use of a back-to-back HVDC to compare the benefits of the new control concept with the conventional one during fault recovery. Furthermore, the comparisons of AC voltage transients between the use of the new and conventional control concept are investigated when fixed capacitor (FC) and fixed reactor (FR) are switched.