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This paper discusses the control and design of the 6.6-kV back-to-back (BTB) system combining bidirectional isolated dc/dc converters and modular multilevel cascade pulsewidth modulation (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 medium-frequency dc/dc converter and two voltage-source H-bridge (single-phase full-bridge) PWM converters. Extremely low-voltage steps bring a significant reduction in harmonics and electromagnetic interference emissions to the BTB system. This paper designs, constructs, and tests a single-phase downscaled BTB system rated at 120 V and 3.3 kW to verify the viability and effectiveness, leading to the actual system.