A Single DC Source Multilevel Inverter for Drives With Increasing Linear Modulation Range and Fault Tolerant Capability

The proposed seven-level hybrid multilevel inverter integrates a three-level flying capacitor with a cascaded H-bridge inverter. The main goal is to develop a seven-level topology that operates efficiently in both linear and extended linear modulation ranges using sinusoidal control. This design expands the linear modulation range with sinusoidal pulse width modulation (PWM) while preserving the multilevel structure. By linearizing the over-modulation region with sinusoidal PWM, the system improves performance during flux weakening, where conventional six-step inverters generate lower-order harmonics. In this topology, the maximum phase peak fundamental remains 0.637 times the dc-link voltage, even in the extended linear modulation range. The inverter is fault-tolerant, ensuring the motor drive continues to operate smoothly and without interruption if an H-bridge switch fails, with the flying capacitor inverter still providing sinusoidal currents. The proposed design uses a single dc source, a reduced switch count, and low-rated voltage semiconductor switches, making it more efficient than other seven-level topologies. It is particularly well-suited for electric vehicles and general ac motor drives. Capacitors remain balanced under all dynamic conditions through space vector redundancies, maintaining proper voltage levels in the output phase voltages. The effectiveness of the proposed method has been experimentally validated in both steady and transient states.