By using the Monte Carlo method, numerical modeling of the vortex system of a Bi-2212 superconductor in a ramping external magnetic field has been carried out for different ramp-rates. The influence of concentration and distribution of pinning centers on the magnetic flux penetration has been studied. Features of flux penetration have been observed and described in terms of the vortex system dynamics, the conditions for their occurrence have been determined. Ascending dependences of the saturation field on defect concentration have been obtained for homogeneous and inhomogeneous samples.