Frequency Adaption Control Strategy for the Power Electronic Traction Transformer

In this paper, a frequency adaption control strategy for the power electronic traction transformer (PETT) is proposed, where the real-time value of the grid frequency can be estimated by the frequency-locked-loop (FLL), then the center frequencies of the resonant regulators in the current inner loop and the second-order generalized integrators in the phase-locked-loop (PLL) can be adaptive regulated. In order to suppress the dc offset brought in by the sampling process, the dc-offset rejecters are respectively designed and embedded in the current-inner-loop controller and PLL. The discretization form of the proposed control strategy is also derived, by which the corresponding difference equations can be acquired and applied in the digital control chips conveniently. Finally, the effectiveness of the proposed control strategy is verified by the simulation and experiment results.