A Novel High-Voltage DC Transformer Based on Diode-Clamped Modular Multilevel Converters with Voltage Self-Balancing Capability

DC transformers are essential for dc grids to interconnect different dc networks. This article proposed a high-voltage dc transformer, which consists of two diode-clamped modular multilevel converters (DCM2Cs) front-to-front connected with a medium-frequency transformer. The DCM2C is prominent for its simplified voltage balancing control using clamping circuits. However, a voltage controller and corresponding measuring circuits are still needed for each converter arm. With the existing quasi two-level modulation technology, this article proposed a voltage self-balancing method of the DCM2C when applied to the dc transformer. This approach is beneficial for reducing the overall cost of the system with no voltage sensor requirements. Meanwhile, the power loss of the clamping circuit is kept low with the clamping inductor. Both mathematical analysis and experimental results are conducted to verify the effectiveness of the proposed converter.