Parallel operation of electronic power transformer and conventional transformer

The idea that the secondary voltage of the conventional transformer is selected as the reference voltage of electronic power transformer - EPT´s output voltage is proposed on the base of the analysis of parallel principle of EPT and conventional transformer in this paper, in order to eliminate the circulation current and the power unbalance resulted from the parallel operation of EPT and conventional transformer. A novel parallel control scheme based on the proposed idea is proposed and its control performance is also analyzed in detail. The proposed scheme includes three control loops, one is the reference voltage feedforward loop and the other two are the instantaneous output voltage feedback loop and the instantaneous inductance current feedback loop. The theory analysis indicates the proposed scheme has good steady- state accuracy and a fast dynamic response compared with the conventional PI control scheme. Detailed computer simulations based on MATLAB/SIMULINK for one EPT and one conventional transformer parallel operation is conducted, and this parallel system is also implemented in laboratory based on DSP TMS320F2812. Simulation results and experimental results show that the proposed control scheme has excellent power sharing and current-sharing regulation characteristic, a fast dynamic response.