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Electrical engineering, Ecole Polytechnique Voltage Source Converter (VSC) technologies present a bright opportunity in a variety of fields within the power system industry. New Modular Multilevel Converters (MMCs) are expected to supersede two-and three-level VSC-based technologies for HVDC applications due to their recognized advantages in terms of scalability, performance and efficiency. Computational burden introduced by detailed modeling of MMC-HVDC systems in EMT-type programs complicates the study of transients especially when such systems are integrated into a large network. This paper presents a novel average-value model (AVM) for efficient and accurate representation of a detailed MMC-HVDC system. It also develops a detailed 401-level MMC-HVDC model for validating the AVM and studies the performance of both models when integrated into a large 400 kV transmission system in Europe. The results show that the AVM is significantly more efficient while maintaining its accuracy for the dynamic response of the overall system.

Electrical engineering, Polytechnique Modular multilevel converters (MMCs) may contain numerous IGBTs. The modeling of such converters for electromagnetic transient type (EMT-type) simulations is complex. Detailed models used in MMC-HVDC simulations may require very large computing times. Simplified and averaged models have been proposed in the past to overcome this problem. In this paper existing averaged and simplified models are improved in order to increase their range of applications. The models are compared and analyzed for different transient events on a MMC-HVDC system.

Design and operation of FB (full bridge) MMC that meets HVDC specifications are studied in this paper. Three new design parameters: the over-modulation index (k MMC), the DC modulation index (M dc), the minimal DC voltage (V minpu) are introduced to specify the operation of a FB MMC. Power increase and semiconductor count increase with the increase of k MMC is analyzed to understand benefits of over-modulation. The required number of submodules and the number of more-costly FB submodules for specified rated dc voltage, V minpu and k MMC are calculated. The relationship of the submodule inserting logic and dynamics of an arm is analyzed. The submodule voltage balancing is studied and the constraints on the required number of FB submodules are deduced. The capability of over-modulation and the operation under low DC voltage with optimal submodule count are verified using EMTP simulation.