Principle of Interharmonic Detection in Transformer of AC-DC Converter Based Double Fourier Series

low-frequency interharmonics cause magnetization of transformers of DC-DC and AC-DC converters. One of the causes of interharmonics is the interaction of the rectified voltage ripple and inverter voltage, whose frequencies are not multiples of each other. Detection of interharmonics is quite a challenge since the required time interval of observation depends on the frequencies of processes that are constantly changing. So, the calculation method has to describe the spectrum in a closed analytical form. Fourier series of one variable is inefficient because of the necessity of spectrum recalculation after frequency changing. In the paper Double Fourier series is proposed and adopted for interharmonics calculation. It implementation for AC-DC converter is demonstrated.