Control of a modular multilevel cascade BTB system using bidirectional isolated DC/DC converters

This paper discusses the 6.6-kV BTB (back-to-back) system combining bidirectional isolated dc/dc converters with modular multilevel cascade PWM converters. The system consists of multiple converter cells connected in cascade per phase at both front ends. Each converter cell consists of a bidirectional isolated high-frequency dc/dc converter and two voltage-source H-bridge PWM converters. Extremely low voltage steps bring a significant reduction in harmonic voltage and current to the supply (line) current. This paper designs, constructs and tests a single-phase downscaled model rated at 120 V and 3.3 kW to verify the viability and effectiveness leading to the 6.6-kV actual system.