| A Multi-Terminal Direct Current (MTDC) system consists of several Voltage-Source Converters (VSCs) whose dc terminals are connected in shunt across the buses of a dc network. The dc voltages are determined by the electric charges stored across the dc capacitor of every Voltage-Source Converter (VSC). As dc over-voltage leads to failure in the solid-state switches and dc under-voltage leads to waveform distortion, the target of safe, economic design is a narrow voltage margin of about 5% around a nominal dc voltage rating. The worst case scenario consists of an accidental loss of a Voltage-Source Converter because the sudden large change in dc power causes the dc capacitors to charge up or down, exceeding the voltage margin before power balance can be re-established by local feedbacks of the Voltage-Source Converters (VSCs).; Part I of the thesis shows how the target can be achieved by: (1) planning the dc voltage reference setting and the power reference settings of the Voltage-Source Converters (VSCs) which satisfy the voltage margins in steady-state for both the pre-fault and post-fault conditions; (2) incorporating an Advanced DC Voltage Control (ADCVC) which enables the dc voltage margins to be satisfied during the transient periods.; Part II of the thesis is concerned with finding innovative applications for Multi-Terminal Direct Current (MTDC) systems. It shows that the high degree of controllability of the Multi-Terminal Direct Current (MTDC) system can be exploited in: (1) optimal acquistion of wind power in offshore wind-farms; (2) providing premium quality power in underground cable in-feeds of city centers; (3) providing simultaneous inter-area decoupling and local area damping in interconnections. |
