Modulation controls for the New Zealand DC hybrid project

The New Zealand HVDC project is being upgraded from a rated 600 MW to 1240 MW. The result is a hybrid system with the addition of thyristor valves in combination with the original mercury arc valves. The additional DC power required developing modulation and control functions for voltage stabilization at the inverter. Other specified requirements are control functions for spinning reserve sharing, frequency stabilization, and constant frequency control. Constant frequency control was defined for those system conditions where the Haywards power converter may be isolated with the load. The modulation function for frequency stabilization was developed to enhance overall AC system response to disturbances. The various modulation functions implemented for this hybrid HVDC system are described.<
>