This chapter presents an open-access Matlab/Simulink-based power system simulation toolbox (MatPSST) designed for modeling large-scale wind and photovoltaic power systems. In MatPSST, dynamic modeling is implemented using Simulink, with only the initialization process coded in Matlab. This structure maximizes the capabilities of Simulink, allowing users to leverage its rich solvers and built-in toolboxes, such as small-signal analysis, without the need for additional programming. The integration with real-time platforms like RTLAB and dSPACE is facilitated through the Simulink interface. Additionally, MatPSST offers a uniform interface and flexible framework for user-defined functions, eliminating the need for users to manage interactions between models and dynamic solvers when implementing advanced user-defined models. To streamline the modeling process of detailed wind farms or photovoltaic stations that comprise hundreds of renewable generation units, MatPSST introduces the concept of vector-variable-based modeling. Case studies highlight selected application examples of MatPSST, demonstrating its accuracy through comparisons with Simscape and PSAT. The findings underscore the advantages of MatPSST in modeling large-scale wind and photovoltaic generation systems.