Analytical Model of MMC-based Multi-terminal HVDC grid for Normal and DC Fault Operation

This paper proposes a new modeling approach for multi-terminal high voltage direct current (MTdc) grids which use the modular multilevel voltage source converter (MMC-VSC) technology. In this paper, primary focus is given to the mathematical analysis of the MMC operation and control, which coupled with the state-space model that describes the dc grid, can accurately simulate the normal operation and dc fault response of a dc grid with low computational requirements. A 3-terminal MTdc network with half-bridge MMC converter stations in radial configuration is used as a case study for the evaluation of the model and the obtained results are compared to a dynamic switching model implemented in Matlab/Simulink both for normal operation as well as in case of a positive pole-to-ground fault. The study showed that the model can accurately estimate the most important parameters needed for the design of an MTdc grid and can simulate fast dynamics without the need for computationally heavy software implementation.