This paper provides a useful tool to investigate and fix resonance phenomena encountered in islanded microgrids with multiple electronically interfaced distributed generators and loads. These systems are usually interfaced with either LC or LCL filters, which provides sufficient switching harmonic attenuation, but brings resonances at various frequencies. In this way, a comprehensive microgrid model is built based on simplified passive circuit models where both Thevenin's and Norton's equivalent representations are considered to describe the dynamic behavior of the interconnected distributed generators and loads, respectively. The proposed model provides the opportunity to investigate the resonance characteristics of islanded microgrids and reveals that these resonances present a frequency-varying behavior resulting in complex resonances at multiple harmonic and sub-harmonic frequencies different from those fixed by filters parameters. The developed model is verified through simulations and experiments for a microgrid composed of two distributed generator and one disturbing load.