Research on Low Voltage Ride Through Strategy and Fault Calculation Equivalent Model of Power Electronic Transformer

Abstract

Power Electronic Transformer(PET) can realize flexible control of AC/DC hybrid distribution network and efficient absorption of new energy. During a grid fault, if PET can adopt a superior low-voltage ride-through(LVRT) strategy, the operational safety of PET itself and the stability of AC/DC hybrid grid can be improved significantly. Moreover, PET exhibits obvious controlled characteristics during LVRT operation, which brings difficulties for grid fault analysis and relay protection setting calculation. Therefore, it is urgent to study the LVRT strategy and fault equivalent model of PET, so as to provide guarantee for the safe and stable operation of the system and lay a theoretical foundation for grid fault analysis. In this paper, a LVRT strategy adapted to bidirectional power exchange of PET is proposed for the purposes of maintaining the system stability, assisting the system voltage recovery and protecting PET safety, based on which the fault current analytical expression of PET is obtained by deducing and analyzing the control model in the bidirectional rotating coordinate system. And the corresponding short-circuit current equivalent calculation model of PET is established. Finally, the correctness of the proposed LVRT strategy and the short-circuit calculation equivalent model is verified by simulation.