An IGCT-Series-Based DC Transformer With Quasi-Zero Switching Loss Modulation by Minimum Backflow Power Injection

An IGCT-series-based dc transformer (IGCT-series-DCT) and a quasi-zero switching loss modulation technique are proposed together to realize the direct access of single module DCT to medium voltage dc network in dc distribution network and dc pooling. Through IGCTs directly in series, IGCT-series-DCT has a medium voltage port. In order to prevent surge current in buffer capacitors used for voltage balancing, soft commutation modulation (SCM) is used to ensure the zero voltage switching (ZVS) of ICGT under light and no load. Then, the ZVS conditions are analyzed in detail considering buffer capacitor and dead time. The relationship between the system power and the phase shift ratio at the minimum backflow power is derived. Through accurate system parameter design, the voltage balance of IGCT-Series-DCT series in the full power range is realized. Finally, a 10-kV 3-MW IGCT-series-DCT prototype was built to verify the feasibility of the system solution.