Simulations of deflagration propagation through initially quiescent stoichiometric hydrogen/air mixture inside a large-scale 2.3-m-diameter spherical vessel are performed. A large-eddy simulation (LES) model of premixed combustion is suggested, which is based on a subgrid-scale turbulence model of renormalization group theory, a gradient method for combustion modeling and the dependence of burning velocity on transient pressure and temperature. An unstructured grid with one level of refinement/de-refinement around the flame front area is used. Wrinkled by hydrodynamic instability, the flame front structure has been resolved for the first time in LES of large-scale explosions. The growth of cell sizes with flame radius is reproduced numerically in agreement with theoretical and experimental results. The minimum resolved size of the flame cells is of the order of the simulated flame front thickness, which is about three control volume edges. The fractal dimension of the wrinkled flame front surface grows and reaches a value of 2.15, close to observed in experiments.