I. Introduction
For the past decade, high power semiconductor devices have been undergoing massive developments. As a result, the utilization of pulse-width modulated (PWM) voltage source converter (VSC) technology is feasible nowadays. Such a technology offers nearly sinusoidal input current, good power factor and compactness compared to phase-controlled rectifiers. Additionally, given the rapid technological revolution in power electronics, fast switching devices are becoming cheaper [1]–[2]. Major applications of VSC technology include connection with low voltage electric drives, uninterruptable power supply (UPS) systems and AC/DC interconnection in HVDC [3]–[4]. Self-commutated VSC-HVDC transmission system technology, commonly referred to as HVDC Light™, was developed in the late 1990's to overcome the drawbacks of the conventional HVDC system. HVDC Light uses IGBT switching valves with PWM technique, switching at relatively high frequencies, which allows generation of output voltage at any desired phase angle or amplitude instantly, thus, giving full control over the device [3]. In this paper, the control of the front-end converter of an HVDC Light system is studied, while considering the receiving-end converter along with its AC power supply as a load model as shown in Fig. 1.
Schematic diagram of the grid-connected VSC station.