Analysis of the DC-Link current spectrum in voltage source inverters

A general expression for the spectrum of the dc-link current of single- and three-phase voltage source inverters is presented to predict the amplitude and frequency of the harmonic components produced by balanced and unbalanced loads, defining positive, negative and zero sequence components. The computation is developed using the switching functions approach,, relating the output voltage waveform to the absorbed dc-link current; so, the method may be applied also to measured waveforms, when no analytical expression is available. The method is extended also to the general case of non sinusoidal load currents. The spectrum of the dc-link current for several inverter modulations (deterministic and random modulations) is calculated and considerations on the harmonic distortion and dc-link- filter requirements are presented.