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. K E Y W O R D Smodular multilevel converter (MMC), sensorless voltage balancing, single-carrier PWM, three-level flying capacitor submodule (3L-FCSM)

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The intrinsic characteristics such as modular structure, filterless operation, and absence of DC-link capacitor have made the modular multilevel converter (MMC) superior to the conventional multilevel converters. However, the submodule (SM) capacitor voltage balancing is crucial. This paper presents a voltage balance control method for MMC. The proposed method generates 2N + 1 levels (where N is the number of SMs per arm) which halves the step size of output voltage and improves the harmonic performance as compared to N + 1 level generation. It requires only one carrier per phase and no voltage and current measurements are needed for the implementation. Therefore, the proposed method makes the system cost-effective and reduces the implementation issues related with carrier-based methods substantially. It also alleviates the non-uniform charge distribution problem with the phase disposition pulse width modulation (PDPWM) technique. Further, a detailed mathematical analysis is presented which enhances the understanding of balancing algorithm. In addition to this, the circulating current with 2N + 1 modulation is analyzed and a control technique is presented. The proposed voltage balancing method is simulated comprehensively in MATLAB/SIMULINK software and validated by the experimental results obtained from a laboratory prototype.

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