| The study of the transient performance of an HVDC converter using EMTP requires detailed modelling of the controls and power system elements. Furthermore, due to the complexities associated with EMTP, considerable care has to be exercised during simulation. These requirements take on added importance particularly when the HVDC converter is operated with a weak ac system. In this thesis, modelling aspects of an HVDC system operating with weak ac systems are discussed.; Following a brief introduction to an HVDC system and its control characteristics, a CIGRE benchmark based HVDC system operating with a weak ac system is presented. A converter switch model is described along with the impact of the snubber circuit on the convener performance. Two gate firing units (GFU) are presented and their dynamic performance is assessed under fault conditions. A rectifier current controller, including a Voltage Dependent Current Limit (VDCL) circuit is presented. In addition, an inverter current controller and gamma controller are also presented.; To assess the transient performance achieved with the control schemes presented, results from EMTP based studies for this HVDC system under various ac-dc fault conditions are shown. |
