The carrier-based PWM method for voltage balance of flying capacitor multilevel inverter

This paper proposes a new solution using a carrier-based PWM method to solve the most serious problem of flying capacitor multi-level inverters, that is the unbalance of capacitor voltages. The voltage unbalance occurs due to the difference of each capacitor's charging and discharging time applied to the flying capacitor inverter. The new solution controls the variation of capacitor voltages into the mean '0' during some period by means of new carriers using the leg voltage redundancy in the flying capacitor inverter. The solution can be easily expanded to multi-level inverters. Also, this method can make the switching loss and conduction loss of devices equal by the use of leg voltage redundancy. First, this paper examines the unbalance of capacitor voltage and the conventional theory of self-balance using phase-shifted carriers. Then, a new method that is suitable for flying capacitor inverters is explained. Simulation results verify the proposed method.