A Simplified Analytical Calculation Model of Average Power Loss for Modular Multilevel Converter

Modular multilevel converters (MMCs) have been widely used in voltage source converter HVdc, and the capacity of MMCs has reached 1000 MW. The accurate calculation and theoretical analysis of the loss has attracted more and more attention, especially in high-power applications. This paper presents a simplified analytical calculation model of average power loss for MMC based on the root mean square (RMS) and absolute values of the arm current. In this model, the analytical expressions of the conduction loss and the switching loss are derived in terms of the whole arm of MMC rather than a single submodule. It avoids the effect of the complexity of its switching pattern on the calculation accuracy of the model. The explicit expressions of the presented model show the relationship between the loss, the voltage balancing methods, and the main variables of MMC directly in comparison with the conventional loss evaluation methods. PSCAD/EMTDC simulation and experimental results of the +/- 350 kV/1000 MW MMC in the Luxi Back-to-Back DC Asynchronous Networking Project verify the correctness and the accuracy of the proposed simplified calculation model.