In this paper, a novel method for modeling and simulation of large-scale energy storage systems (ESS) is provided. Specifically, the model is developed for large-scale series connected supercapacitors (SCs) intended for power electronic applications. This method is especially useful for high voltage applications where a large number of series connected energy storage units (ESUs) are required. The proposed solution reduces a multi-node string of series connected SCs-together with their corresponding voltage balancing circuit-to a single unit with two electrical nodes. The proposed model is connected to the dc link of a three phase grid-connected modular multilevel converter (MMC). In this system, the effectiveness of the proposed model and the proposed voltage balancing scheme is demonstrated for a string comprising ten thousand series connected ESUs. The efficacy of the proposed model and the balancing algorithm is proven by simulations in the MATLAB/Simulink environment.