The increased demand for electrical power and the concern of environmental pollution drive the development of bulk-power transmission over long distance and renewable energy. The use of multi-terminal (MT) modular multilevel converter (MMC) high-voltage direct current (HVDC) technology to integrate power from the offshore wind farm (OWF) is becoming increasingly popular. However, some technological barriers and potential risks may exist in the new technology, which requires comprehensive research and innovative developments. This thesis investigates several important aspects of an offshore integrated MMC multi-terminal HVDC (MTDC) system, including start-up control, control and protection under AC and DC fault conditions. For the start-up control, a hierarchical start-up scheme is proposed for the terminals with active AC networks and a reduced DC voltage start-up scheme is proposed for the terminal with the OWF. Synthesising both schemes forms a comprehensive start-up control scheme for the start-up control of the MTDC system, which can effectively mitigate the voltage spikes and current surges during the start-up process. For control and protection against AC fault conditions, associated control and protection strategies and detailed control and protection sequences are proposed for the faults occurring at the converter AC-side. In addition, a special control and protection strategy is proposed when the faulted-side MMC experiences blocking failure following the fault. For the DC fault management, a fault isolation strategy is proposed and the system recovery scheme is comprehensively investigated after the fault isolation, with delayed-auto-re-configuration (DARC) schemes being proposed. Combining the DARC scheme and the fault isolation strategy, a complete control and protection sequence is proposed. Effectiveness of the proposed schemes is evaluated on the RTDS simulation platform.