access icon openaccess Dc-link current computational methods for three-phase inverter with low-order harmonic output current

Both the spectral analysis and the closed-form root-mean-square (RMS) equations are widely used to determine the three-phase inverter dc-link current for capacitor rating proposed. However, the analytical models of the dc-link currents have rarely been reported for applications like the active power filter, where ac currents are mostly low-order harmonics (LOHs). This paper first derived expressions for each dc-link LOH current, in order to compute the capacitor losses for each LOH frequencies. Then, it is shown that the derivation of the dc-link switching harmonic current (SHC) RMS equation is very much complicated when LOHs are present in the ac currents. Hence, new set of generalised RMS equations were successfully derived and simplified into one equation to facilitate the worst case design. The design case of the dc-link current is demonstrated with the proposed equations. A flexible grid-tied inverter lab prototype is developed to inject arbitrary combinations of LOH currents of different orders, sequences, amplitudes and angles into the grid. Good match between the computational and experimental results validates the proposed methods.

Inspec keywords: least mean squares methods; power capacitors; switching convertors; active filters; spectral analysis; invertors; power grids; power harmonic filters

Other keywords: active power filter; ac currents; flexible grid-tied inverter lab prototype; DC-link current computational methods; three-phase inverter dc-link; generalised RMS equations; LOH frequencies; low-order harmonic output; RMS equations; dc-link switching harmonic current; LOH currents; closed-form root-mean-square equations; capacitor rating; harmonic current RMS equation

Subjects: Interpolation and function approximation (numerical analysis); DC-AC power convertors (invertors); Power supply quality and harmonics; Other power apparatus and electric machines

http://iet.metastore.ingenta.com/content/journals/10.1049/iet-pel.2018.5621
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content/journals/10.1049/iet-pel.2018.5621
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