Analysis of Third-Harmonic-Type Modulation Concepts Minimizing the DC-Link Energy Storage Requirement of Star- and Delta-Connected AC/DC Converter Modules of Three-Phase Isolated PFC Rectifier Systems

• Published in: IEEE access 2023-03, p.1-1
• Main Authors: Langbauer, Thomas, Menzi, David, Marugg, Valentin, Vollmaier, Franz, Azurza, Jon, Kasper, Matthias, Kolar, Johann W.
• Format: Article
• Language: English
• Subjects: ac-dc converter; CM current injection; CM voltage injection; DC-DC power converters; Harmonic analysis; harmonic injection; modular; Power system harmonics; Rectifiers; three-phase; Voltage control; Voltage measurement; zero sequence
• ISSN: 2169-3536
• DOI: 10.1109/ACCESS.2023.3261243

A three-phase ac/dc converter with high-frequency isolation can be realized as a monolithic three-phase or as a phase-modular system by combining three single-phase Power Factor Correction (PFC) rectifier modules with individual isolated dc-dc converters. Advantageously, for a phase-modular system the module configuration can be changed depending on the instantaneous input-output voltage ratio (i.e., a star-(Y)- or a delta-(Δ)-arrangement such that wide voltage ranges can be covered without a massive over-dimensioning of the main power components. However, the main disadvantage of a phase-modular converter realization is the fact that the input power of each PFC rectifier module pulsates at twice the mains frequency (which is inherent to single-phase power conversion) such that large dc-link capacitors are required. Recent literature predicts a substantial power pulsation reduction enabled by means of third-(3 rd )-harmonic injection modulation which is applicable for the Y-connection (where a common-mode (CM) / zero-sequence (ZS) voltage is injected), and for the Δ-connection of the three single-phase PFC rectifier modules (where a CM / ZS current is injected). This changes the distribution of the power flow in the three-phase system and the power pulsation is shifted to higher frequencies. This paper experimentally verifies and extends the dc-link energy storage requirement reduction of the 3 rd -harmonic injection modulation concept: In a first step, the derivation of the harmonic injection concept is recapitulated and suitable control methods are discussed for both CM voltage (Y-arrangement) and CM current (Δ-arrangement) injection. Further, an alternative CM voltage injection strategy with simplified reference generation based only on the instantaneous grid voltage measurements is presented and compared to the pure 3 rd -harmonic injection modulation. Measurement results obtained from a 6 kW prototype reveal a dc-link voltage variation and/or energy buffering reduction by up to 38.6 % enabled by the harmonic injection modulation compared to conventional operation without 3 rd -harmonic injection modulation.