Submodule power losses balancing algorithms for the modular multilevel converter

Abstract

Abstract-Tolerance and component aging can cause significant differences in the capacitance values of the submodules (SMs) in a modular multilevel converter (MMC). Depending on the modulation technique, capacitance mismatches may produce uneven switching transitions of the SMs, hence imbalances in the power losses that can lead to reliability problems. In this paper, a new algorithm that helps to achieve evenly distributed switching and conduction losses within the converter SMs is presented. The proposed algorithm is based on a modification of the common voltage balancing algorithms, balancing a weighted function of voltage and losses. Even distribution of power losses is achieved at the cost of slightly increasing the capacitor voltage ripples. The effectiveness of the strategy has been demonstrated by simulation results of a high-power grid-connected MMC.

Submodule Level Power Loss Balancing Control for Modular Multilevel Converters

“…The method is further extended and validated by experiments [13]. Besides the temperature, regulating power losses is also an alternative for thermal balancing control [14]. However, as revealed in [15], the submodule-level conduction losses among SMs are well balanced regardless of the operation condition, the modulation techniques and the parameter mismatch under the circumstance of balanced SM capacitor voltages.…”

“…It can be readily achieved by various voltage balancing control (VBC) strategies. Therefore, this paper proposes a simplified method with respect to the one presented in [14] by excluding the need for IGBT conduction loss estimation, resulting in reduced computation requirements and less parameters to be adjusted. Moreover, the trade-off between the capacitor voltage balancing and the power loss balancing is studied.…”

Submodule power balancing control of modular multilevel converters under capacitor degradation

“…To attain equal SM loss in the arm, various loss equalisation control techniques for the MMCs are proposed in [32–36]. A power loss distribution scheme based on CCs at dc voltage offset, fundamental frequency, and second‐harmonic components of the output waveform, which maintains equal losses between the upper and lower switches is introduced in [32].…”

Balanced Conduction Loss Distribution among SMs in Modular Multilevel Converters

“…Reliability is one of the major concerns for the MMC because of the large cost investment and the large number of semiconductors, which are the weakest components in power converters [4]. Thus, it is necessary to fulfill the full potential of submodules (SMs) by posing even thermal stress on the devices.…”

“…Various active thermal balancing methods based on the circulating current are explored for component-level power loss balancing, but the effectiveness is limited [8]. [4] focuses on the submodule-level power loss balancing integrated with the capacitor voltage balancing, but the loss model for MMC with a large number of SMs is computationally burdened.…”