Abstract: DC transformer (DCT) is the key device of a renewable energy generation DC collection system. The dual active bridge (DAB) has the feature of bidirectional power flow, which is suitable for applications of off-shore windfarm DC collection. For MW DCT, based on DABs, this paper proposes a DC transformer based on IGCT (IGCT-DCT). Firstly, the working frequency of MW DCT is analyzed. And then, considering the turn-off delay, loss limit and the difference of driver delay, the conditions of voltage balancing and current balancing are discussed in detail, therefore, the designs of the voltage-sharing RC circuit and current-sharing magnetic ring are given. Moreover, the calculation methods of voltage equalizing resistor, the voltage equalizing capacitor, and the differential mode inductance are presented. Finally, a 10 kV/1.5 kV 3 MW IGCT-DCT prototype was built to verify the feasibility of the proposed solution and the correctness of the theoretical analysis. The HV side of IGCT-DCT is based on series-connected IGCTs, and the LV side is based on the parallel-connected IGCT bridge arms, thus significantly improving the capacity and power density of the DCT. Moreover, by using the single-phase-shift control, the zero-voltage turn-on of IGCT under high power can be achieved, which reduces the system losses.