Optimal Common-Mode Voltage Injection for Phase-Modular Three-Phase PFC Rectifiers Minimizing Energy Buffering Requirement
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Date
2023
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Journal Article
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Abstract
Realizing an isolated three-phase Power Factor Correction (PFC) ac-dc converter as a phase-modular system, i.e., by star-connecting three single-phase PFC rectifier front-ends with individual isolated dc-dc converter stages generating a common dc output voltage advantageously facilitates the use of standard single-phase converter modules. Further the low dc-link voltage level of typically 400V (for a grid with 230V_rms line-to-neutral voltage) allows to employ high performance 600V power semiconductors. The main drawback of this concept, however, is the fact that the time-varying single-phase input power only sums to a constant three-phase output power at the isolated dc output, such that large dc-link capacitor values are required in each module (in the range of several 100μF for a 6kW system), thereby limiting the achievable power density. It is known from literature that the dc-link energy buffering requirement ΔE_dc can be reduced by means of a third-harmonic common-mode (CM) voltage injection modulation and this article identifies the optimal CM voltage waveform with respect to minimizing ΔE_dc , i.e., reducing ΔE_dc to the theoretical minimum by combining a brute-force evaluation of the time-domain CM voltage waveform with phase-symmetry considerations. Additionally, converter operation with minimum dc-link voltage and/or dc-link capacitor values is analyzed and a saturable grid current controller allowing operation of the PFC rectifier front-ends with the optimal CM voltage waveform is investigated. Experimental results with a 6kW prototype system yield a reduction in ΔE_dc by up to 42% (compared to conventional sinusoidal modulation), which closely matches the theoretical prediction. Also, PFC rectifier operation with a dc-link voltage level as low as $285 \,{\rm {V}}...
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Volume
4
Pages / Article No.
674 - 686
Publisher
IEEE
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Subject
Ac-dc converter; three-phase; PFC rectifier; modular; harmonic injection; zero sequence; CM voltage injection
Organisational unit
03573 - Kolar, Johann W. (emeritus) / Kolar, Johann W. (emeritus)