Role of type-2 fuzzy algorithm to improve response of rectifier in HVDC-model

Nowdays high voltage direct current (HVDC) link is an effective way to deliver power for long distance transmission or under-ground/sea cable. The HVDC main component is thyristor that serves as rectifier on sending-end and as inverter on receiving-end. Heart of HVDC operation is to control rectifier/inverter by regulating their firing angles. High peak transient response appears especially for too high value of up-ramp signal at start-up time. Interval type-2 fuzzy (IT2F) is proposed to help PI controller. This combines controller is named supplementary controller (SC) and applied to reduce high peak transient response in rectifier. The IT2F is designed by 3 Gauss type-2 membership functions (MFs) for respective inputs and 5 constant MFs on output. To evaluate performance of SC controller, increasing of up-ramp current reference is used to test the SC controller. At up-ramp 15 pu/s, maximum overshoot (
$M_{p}$
) are 2.96 and 2.98% for the SC and PI controllers. When up-ramp increases to 19 pu/s, the
$M_{p}$
and
$T_{st}$
are obtained 7.13 and 7.6%. Settling time of the SC control is shorter than the PI control. By applying uncertainty or random disturbance, it is obtained that the SC controller gives smaller value than the PI controller on ITAE/ITSE criteria.