Modulation and Voltage Balance Control of a Four-Level ANPC H-Bridge Converter for Ship Medium-Voltage Propulsion Systems

Aiming at a new generation of medium voltage DC (MVDC) power propulsion system for new ship integrated power system (IPS), this paper proposes an active neutral-point-clamped (ANPC) H-bridge structure, which directly connects two four-level ANPC topologies. Without any flying capacitors, this topology has high power density, and can be used in 6 kV voltage level. To address the problem of unbalanced neutral-point (NP) voltage, this paper derives a mathematical model of NP voltage and uses a combination of COPWM modulation strategy and fine-tuned duty cycle to achieve balanced control of the NP voltage by software. Simulation and experimental results prove the rationality and validity of the proposed method.