Dc-link current and voltage ripple analysis in single-phase and multiphase voltage source inverters

Vujacic, Marija (2019) Dc-link current and voltage ripple analysis in single-phase and multiphase voltage source inverters, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Ingegneria biomedica, elettrica e dei sistemi, 31 Ciclo.
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Abstract

Dc-link switching and low-frequency current and voltage ripple components in two-level single-phase and multiphase voltage source inverters have been analyzed in this thesis. Voltage ripple components are calculated based on the corresponding dc-link current components and by considering a non-ideal dc voltage source, representing an input filter (such as a dc reactor) or a resistive dc supply (such as a PV system). However, switching ripple analyses are also valid in most of the dc power supplies since the dc source impedance usually becomes much higher than the dc-link capacitor reactance at the inverter switching frequency. The peak-to-peak voltage switching ripple amplitude is derived over a fundamental period as a function of operational conditions: modulation index, the amplitude of phase current and power phase angle. The initial investigation of the dc-link variables has been focused on single-phase H-bridge inverter, considering both, switching and low-frequency dc ripple components. The analysis has been further extended to the case of two-level multiphase inverters with balanced load. The approach has been specifically developed for three-, five- and seven-phase inverters. The cases with different phase numbers are compared and the effect of increasing the number of phases on the dc-link capacitor sizing has been discussed. The final analysis has also included the impact of a slight load unbalance on the dc-link variables in multiphase inverters. Considered unbalance is present in practice in every multiphase ac motor, it is in order of a few percent, and introduces a low frequency instantaneous power oscillation. This reflects in low frequency (i.e. double-fundamental) current and voltage ripple on the dc-link inverter side. Therefore, the amplitudes of both ripple components are calculated and the importance of taking them into consideration for the dc-link capacitor design has been discussed. All analytical developments are validated with detailed simulations and experimental results.

Abstract
Tipologia del documento
Tesi di dottorato
Autore
Vujacic, Marija
Supervisore
Dottorato di ricerca
Ciclo
31
Coordinatore
Settore disciplinare
Settore concorsuale
Parole chiave
Dc-link voltage ripple, single-phase inverter, multiphase inverter, dc-link capacitor, current unbalance, pulse-width modulation
URN:NBN
Data di discussione
3 Aprile 2019
URI

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