Sensorless voltage balancing method for modular multilevel converter

Modular multilevel converters (MMCs) have become prominent for high and medium power applications. The phase-disposition pulse width modulation (PDPWM) technique is a carrier-based method that generates good quality output. However, it has the inherent problem of uneven power distribution. Conventionally, this is solved by expensive voltage and current measurements. In this paper, a capacitor voltage balancing method is presented for MMC, which eliminates the need for voltage and current sensors. It also ensures uniform power distribution among the submodules (SMs). In addition, it needs only one carrier per phase, and one PWM reference, for either upper arm or lower arm to produce N + 1 level with N SMs per arm. The capacitor voltage balancing method is analyzed mathematically and verified for the MMC with two-level half-bridge SMs. The same method is also extended to the MMC with three-level flying capacitor SMs. MATLAB/SIMULINK simulations and experimental results on a laboratory prototype are presented to verify the theoretical concepts.