Third-Harmonic-Type Modulation Minimizing the DC-Link Energy Storage Requirement of Isolated Phase-Modular Three-Phase PFC Rectifier Systems

Abstract

A three-phase ac-dc converter with high-frequency isolation can be realized as a phase-modular system by using three single-phase Power Factor Correction (PFC) rectifier modules with isolated dc-dc converter output stages, which advantageously allows to cover a wide input voltage range by module reconfiguration from a star-(Y)- to a delta-( $\Delta $ )-arrangement. However, the main limitation of a phase-modular topology is the fact that the input power of each PFC rectifier module pulsates at twice the mains frequency such that large dc-link capacitors are required. Recent literature predicts a substantial single-phase power pulsation reduction enabled by means of third-(3 $^{\mathrm{ rd}}$ )-harmonic common-mode (CM) voltage (Y) or current ( $\Delta $ ) injection modulation. This paper experimentally verifies and extends the dc-link energy storage requirement reduction of the 3 $^{\mathrm{ rd}}$ -harmonic injection modulation concepts: In a first step, the derivation of the harmonic injection concept is recapitulated and suitable control methods are discussed for both CM voltage (Y) and CM current ( $\Delta $ ) 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 $^{\mathrm{ rd}}$ -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 $^{\mathrm{ rd}}$ -harmonic injection modulation.

Keywords

• AC-DC converter
• three-phase
• modular
• harmonic injection
• zero sequence
• CM voltage injection