Modeling of multi-terminal VSC-based HVDC systems

Improving the efficiency and operation of power transmission is important due to the continual increase in demand for electric power. In addition, many remote areas throughout the world lack sufficient access to electricity. Unfortunately, utilities cannot satisfy the high demand of power by building new power stations because of economic and environmental reasons. However, utilities can increase generation and transmission line efficiencies by controlling the power flow through their systems. One new attractive technology that enables the control of power flow in the system is Voltage-Source-Converter High Voltage Direct Current (VSC-HVDC) transmission. Multi-terminal-HVDC (M-HVDC) can be built using VSC technology. A model of a three-terminal VSC-HVDC system is presented in this thesis. One of the converters is used to regulate the DC voltage while the others converters control the active power independently and bi-directionally. The vector control strategy and pulse width modulation (PWM) technique are described and implemented in PSCAD/EMTDC. In addition, the region of controllability as a function of power flow has been analyzed. Furthermore, the steady-state and dynamic response characteristics as a function of capacitor size has been investigated --Abstract, page iii