Reliability of industrial automation software, which is usually ensured with testing and simulation, can be improved using formal analysis and, in particular, the technique of model checking. In model checking, considering the closed loop composition of the plant model and the controller model allows checking a larger class of properties than in the more traditional open-loop case, where the model of the controller is verified alone. Constructing the formal model of the plant automatically may significantly reduce human workload and mitigate the human factor issue. Commonly, complex industrial plants and controllers have modular structure, and thus the problem of automatic construction of a modular plant model is important. This paper proposes two techniques which extend an earlier proposed method of monolithic plant model construction to the modular case.