A novel auxiliary frequency controller for HVDC transmission links

Since a HVDC transmission line with an auxiliary frequency controller has many advantages in both technical and economic aspects; the paper presents a novel nonlinear PID controller for HVDC systems. The controller consists of a PD controller, a PID controller and a switch with a threshold between two-part controllers. In order to enhance the control flexibility, the dead-zones are also introduced into the controller. With the help of PSCAD/EMTDC, a detailed simulation model of an AC-DC system is created. The simulation results show the controller can satisfy the engineering needs of frequency control for AC-DC systems under different disturbance conditions.