Enhancing transient performance of hybrid distribution transformer using event-triggered proportional-integral repetitive controller

A proportional–integral repetitive controller (PIRC) can be employed in hybrid distribution transformers (HDTs) to control voltages and currents across multiple frequencies for the steady-state performance improvement. However, the transient performance of a PIRC under grid faults or step change conditions deteriorates due to the coupling effect between its proportional and repetitive components. Based on the derived transfer function of the PIRC in relation to the HDT, this article reveals that the mismatched dynamic response speeds between the PI and RC loops are the primary cause of the control coupling effect. This mismatch leads to the accumulation of step tracking errors into the next fundamental frequency cycle in the RC loop. To address this issue, a novel event-triggered PIRC (ET-PIRC) scheme is proposed to eliminate the control coupling effect and enhance the HDT’s transient performance. The main contribution of this article is the adoption of an event-triggered control based on the principle of dynamically adjusting the control efforts of the PI and RC loops in response to the step tracking errors, thereby mitigating the inherent coupling between them. During step changes, this approach accelerates the transient response of the PI loop while driving the step tracking error in the RC loop to zero, effectively decoupling the two control loops. The robustness and stability of the ET-PIRC are also examined. Comparative simulation and experimental results validate the feasibility of the proposed control method and its superior transient response performance.