I. Introduction
In recent years, DC power supply technology has been regarded again. High Voltage Direct Current (HVDC) technology has proved to be an efficient, cost effective and reliable way of transmitting electrical power over long distances as compared to the classic and traditional AC transmission [1]. Especially the use of Voltage Source Converter (VSC) based HVDC, which draws on pulse width modulation (PWM) control strategies, has provided a number of benefits compared to the classical HVDC, in terms of enhanced flexibility in independent control of active and reactive power [2]. Hence, VSC-HVDC provides a new choice for grid inter-connection, city centre infeed and offshore installation, which is a major breakthrough in the field of power transmission and distribution technology [3]–[5].