Incremental fuzzy PI control of a HVDC plant

This paper investigates a fuzzy logic (FL) based current controller for a high voltage direct current (HVDC) plant connected to a weak AC system under the EMTP RV simulation environment. A typical HVDC system is modeled with a detailed representation of the converter, converter controls and AC system. An incremental fuzzy gain scheduling proportional and integral controller (IFGSPIC) is used for the rectifier current control. The current error and its derivative are taken as two parameters necessary to adapt the proportional (P) and integral (I) gains of the controller based on fuzzy reasoning. Two different fuzzy rule bases are designed to tune the PK gains independently. The fuzzy control rules and analysis of IFGSPIC are presented. To improve performance, the IFGSPIC is designed like a hybrid controller that combines the advantages of a FL and conventional PI controllers. During transient states, the PI gains are adapted by the IFGSPIC to damp out undesirable oscillations around the set point and reduce settling time. During the steady state, the controller is automatically switched to the conventional PI controller to maintain the control stability and accuracy. Performance evaluation under AC fault and set-point step change is studied. A performance comparison between the conventional PI controller and hybrid IFGSPIC is made. Results from the various tests show that the proposed controller outperforms its conventional counterpart in each case