Asymmetric interleaving — a new approach to operating parallel converters

This paper presents asymmetric interleaving as a new method to operate parallel voltage source converters (VSC) in which the carrier phase shifts don´t add to exactly one carrier cycle and may also vary from one pair of modules to another. Double Fourier analysis is applied to develop analytical spectral models for individual module outputs, from which a scaling factor is defined as a measurement of harmonic cancellation effects and is found to be a function of only the carrier phase shifts and independent of the specific PWM method used. Using the scaling factor as a mathematical tool, we investigate practical asymmetric interleaving methods that can achieve different system optimization objectives, including the avoidance of resonance at certain frequencies by selectively eliminating certain carrier harmonics and their sideband components, the minimization of total harmonic voltage or current distortion, and the minimization of EMI filter size. Applications of these methods are illustrated by examples and verified by numerical simulation.