This paper aims to analyse the influence of fluctuating renewables on small-signal stability. Most of the research on renewable energy integration assumes that power is provided from a static generation unit and studies how much damping ratio and frequency changes as a result of changing power and inertia. This research is motivated by mode coupling where one oscillatory mode may have an effect on other modes if the mode frequencies are similar. The paper discusses the impact of fluctuating power sources, Type IV wind turbines in our case, on possible coupling between the fluctuating wind power and the existing modes in the system. Since the fluctuating power may combine a large band of frequency components, the power system can react to any specific frequency of a variable generator. In this paper, several influential frequencies were injected through the renewable generator. System identification is used first to obtain the linearized state-space model of the system and the relevant transfer functions, which are then used to identify possible resonant frequencies. DIgSILENT/Power Factory is used next to analyse the system's response to specific frequencies in the time domain.