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

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-(?)-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-(3rd)-harmonic common-mode (CM) voltage (Y) or current (?) injection modulation. This paper experimentally verifies and extends the dc-link energy storage requirement reduction of the 3rd-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 (?) 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 3rd-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 3rd-harmonic injection modulation.