Hybrid four-quadrant DC-DC converter for DC wind farm collection systems

This paper proposes a hybrid four-quadrant isolated DC-DC converter that enables bidirectional energy transfer and is suitable for DC wind farm collection systems. The proposed converter consists of a fully controlled DC-AC converter on the low-voltage (LV) side, a medium-frequency transformer, a resonant tank, and a four-quadrant converter composed of anti-parallel thyristors connected in series on the high-voltage (HV) side. The transformer leakage inductance is incorporated in the resonant tank, which reduces the design difficulty of the transformer and helps reduce losses. Moreover, the use of thyristors as switching devices on the HV side makes it easier to meet HV and large-capacity demands and also reduces the cost of the converter. First, the converter topology and operation principle are described. Then, based on a time domain analysis, the DC voltage gain, a thyristor turn-off study, and soft-switching characteristics are detailed. Furthermore, a pulse frequency modulation-phase shift modulation (PFM-PSM) hybrid control for forward operation is proposed and the resonant tank parameters are designed. Finally, the feasibility of the converter is analyzed and validated through simulation and experimental results.