Control of High-Frequency Isolated Modular Converter

Recently, voltage-source converter (VSC)-based high-voltage dc (HVDC) transmission systems have gained more attention. In this paper, a control method for a modular VSC-based HVDC transmission system with high-frequency isolation referred to as high-frequency isolated modular converter is proposed. In the high-frequency isolated modular converter configuration, several floating dc capacitors in all three phases are connected in series, and voltage balancing control of these floating dc capacitors is required. In this paper, an appropriate control structure with the capacitor voltage balancing controller is proposed. The proposed control scheme consists of three layers to control terminal dc bus voltage and balance dc capacitor voltages of each building block. Detailed PSCAD simulation results are presented to evaluate the performance of high-frequency isolated modular converter. Controller hardware-in-the-loop simulation of the high-frequency isolated modular converter is also performed by real-time digital simulator (RTDS), and RTDS results are presented to verify the control structure. Finally, laboratory-scale experimental results are presented to validate the proposed control method.