Examiner

In this Master’s project, a simplified control model for HVDC classic has been built in the EMTDC simulation program with PSCAD v.4.2 interface. The control functions in the simplified control are based on functions from ABB Power Systems. A number of cases have been simulated to evaluate the simplified control model, which demand correct function during earth fault and load disturbances. The main functions in the simplified control are the Voltage Dependent Current Order Limiter (VDCOL), Current Order Amplifier (CCA), as well as functions that are acting on the upper and lower limits of the CCA. The VDCOL will reduce the current order at direct voltage reduction. This will avoid voltage instabilities during and after AC disturbances. It will also ease the stresses on the valves and speed up the recovery after disconnection of the earth fault. The CCA is principally a proportional-integral controller, which give the current control loop proper dynamics. For an inverter, it will decrease the firing angle and for a rectifier it will increase the firing angle. Furthermore, the CC