The mechanisms of broadband oscillations in renewable energy power systems and their suppression technologies are discussed. Starting from the dilemma faced in analyzing AC grid resonance stability based on impedance models, it is demonstrated that the "negative resistance" mechanism of broadband oscillations is untenable. A general method is proposed to describe power electronic devices using broadband voltage source converter models and broadband current source converter models, thereby representing the nonlinear characteristics of power electronic devices with harmonic voltage sources and harmonic current sources. This enables renewable energy power systems to still be described as linear systems, and interprets the mechanism of broadband oscillations as a "harmonic amplification" phenomenon caused by network resonance, thus establishing a new framework for explaining the mechanisms of broadband oscillations in renewable energy power systems. Through analysis of two basic resonant circuits, the relationship between resonant mode damping ratio and harmonic amplification factor is derived, laying the theoretical foundation for analyzing and suppressing broadband oscillations based on the s-domain nodal admittance matrix method and C-type damping filters. Based on the maximum damping criterion, a design method for C-type damping filters is proposed, and the designed C-type damping filters exhibit strong broadband damping effects.