This paper presents a simple and efficient method for detecting harmonics, interharmonics, and subharmonics in voltage and current waveforms. The proposed technique is based on a series RLC resonant circuit and is characterized by its simplicity, relatively fast response, and ease of implementation. The performance of the proposed method is validated using both mathematically generated signals with severe waveform distortion and signals measured in real distribution networks with high penetration of renewable energy sources. The maximum relative errors in the frequency of detected harmonic components were 1.33% for the mathematically generated strongly distorted signals and 0.60% for the mea... More >