Three-Phase 17-Level Modular Multilevel Converter (MMC)

The Three-Phase 17-Level Modular Multilevel Converter (MMC) is an advanced power conversion architecture primarily deployed in High-Voltage Direct Current (HVDC) transmission systems. Compared to conventional converters, the MMC topology offers superior efficiency and reliability through its unique modular structure. The fundamental operation involves decomposing the DC bus voltage into multiple discrete voltage levels using series-connected submodules (SMs), which are then synthesized into a high-quality AC waveform through sophisticated modulation techniques. Key implementation aspects include: - Submodule Configuration: Each phase leg utilizes 16 SMs per arm (8 upper + 8 lower) to achieve 17 voltage levels through capacitor voltage stacking - Voltage Balancing Algorithm: Real-time sorting algorithms maintain capacitor voltage equilibrium across SMs using nearest-level modulation (NLM) or phase-shifted PWM - Arm Current Control: Circulating current suppression controllers implemented through inner-loop PR or PI regulators minimize internal energy oscillations The converter's staircase waveform output reduces harmonic distortion by 85% compared to two-level converters, while redundant SM configurations ensure continuous operation during single-module failures. Gate signal generation typically involves FPGA-based controllers executing sorting algorithms at 10-100kHz rates for dynamic voltage balance maintenance. This granular voltage control enables smoother power delivery with total harmonic distortion (THD) below 2%, critical for sensitive high-voltage equipment. The distributed architecture also provides inherent fault tolerance and enables bidirectional power flow control through advanced modulation index manipulation in dq-frame control systems.