A wind farm usually consists of a large number of wind turbine generators (WTGs) connected through an internal electrical network and operating simultaneously. In order to study the impact of a wind farm on the dynamics of the power system, a major issue is to develop adequate equivalent models that allow characterizing the dynamics of all individual WTGs. In this sense, with the advance of power electronics, direct-driven permanent magnet synchronous generators (PMSGs) have drawn increased interest to wind turbine manufacturers due to its advantages over other variable-speed WTGs. This paper presents a comprehensive dynamic equivalent model of a wind farm with direct-driven PMSG wind turbines and its control scheme. The proposed simplified modeling is developed using the state-space averaging technique and is implemented in the MATLAB/Simulink environment. The dynamic performance of the wind farm and its impact on the power system operation is fully evaluated using the phasor simulation method.