Converter nonintegral harmonics from AC network resonating with DC network

Integral harmonics come from the switching pattern of the modulation method. Nonintegral harmonics, on the other hand, are initiated by random noise that becomes amplified and sustained by the AC network resonating with the DC network. A comprehensive theory of their origins is presented. Its correctness is justified by digital simulations. It is then shown that an efficient method of predicting their potential occurrences is by eigenvalue analysis. The objective of THD compliance can be met by: (i) avoidance by design of network parameters; and (ii) suppression by active filtering. Some directions of parameter design are given. A simulation result is presented showing that an active filtering method is promising.