Assessment of the error in the average current sensed by the unidirectional current pulse transformer

Neville McNeill, Naren Gupta

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Advantages of using a current transformer (CT) for current sensing in switched mode power converters are that galvanic isolation is inherent, losses are low, the bandwidth is high and a high-amplitude output signal may be obtained. However, 'droop' occurs as a result of the magnetising current drawn. Peak current droop is defined as the instantaneous per-unit shortfall in sensed current at the end of a rectangular pulse. Average current droop is defined as the per-unit shortfall in the average current sensed. The CT inherently operates in a resonant mode when sensing a unidirectional current pulse. This is advantageous as some of the current-time product lost to the magnetising branch may be recovered thereby alleviating the average current droop. Average current droop is investigated when diode rectification is used. Three operating modes are identified and described. These are designated the discontinuous magnetising current, continuous magnetising current and discontinuous secondary current modes (DSCM). It is shown that the CT's core losses may predominately influence the average current droop. Provided the DSCM is avoided, simple correction factors are shown to be appropriate for substantially correcting the sensed current to allow for these losses.
LanguageEnglish
Pages265-276
Number of pages12
JournalIET Circuits, Devices & Systems
Volume2
Issue number2
DOIs
Publication statusPublished - 18 Apr 2008

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Pulse transformers
Electric instrument transformers
Power converters
Diodes
Bandwidth

Keywords

  • switched mode power supplies
  • current transformers
  • power converters
  • pulse transformers

Cite this

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abstract = "Advantages of using a current transformer (CT) for current sensing in switched mode power converters are that galvanic isolation is inherent, losses are low, the bandwidth is high and a high-amplitude output signal may be obtained. However, 'droop' occurs as a result of the magnetising current drawn. Peak current droop is defined as the instantaneous per-unit shortfall in sensed current at the end of a rectangular pulse. Average current droop is defined as the per-unit shortfall in the average current sensed. The CT inherently operates in a resonant mode when sensing a unidirectional current pulse. This is advantageous as some of the current-time product lost to the magnetising branch may be recovered thereby alleviating the average current droop. Average current droop is investigated when diode rectification is used. Three operating modes are identified and described. These are designated the discontinuous magnetising current, continuous magnetising current and discontinuous secondary current modes (DSCM). It is shown that the CT's core losses may predominately influence the average current droop. Provided the DSCM is avoided, simple correction factors are shown to be appropriate for substantially correcting the sensed current to allow for these losses.",
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Assessment of the error in the average current sensed by the unidirectional current pulse transformer. / McNeill, Neville; Gupta, Naren.

In: IET Circuits, Devices & Systems, Vol. 2, No. 2, 18.04.2008, p. 265-276.

Research output: Contribution to journalArticle

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AU - McNeill, Neville

AU - Gupta, Naren

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N2 - Advantages of using a current transformer (CT) for current sensing in switched mode power converters are that galvanic isolation is inherent, losses are low, the bandwidth is high and a high-amplitude output signal may be obtained. However, 'droop' occurs as a result of the magnetising current drawn. Peak current droop is defined as the instantaneous per-unit shortfall in sensed current at the end of a rectangular pulse. Average current droop is defined as the per-unit shortfall in the average current sensed. The CT inherently operates in a resonant mode when sensing a unidirectional current pulse. This is advantageous as some of the current-time product lost to the magnetising branch may be recovered thereby alleviating the average current droop. Average current droop is investigated when diode rectification is used. Three operating modes are identified and described. These are designated the discontinuous magnetising current, continuous magnetising current and discontinuous secondary current modes (DSCM). It is shown that the CT's core losses may predominately influence the average current droop. Provided the DSCM is avoided, simple correction factors are shown to be appropriate for substantially correcting the sensed current to allow for these losses.

AB - Advantages of using a current transformer (CT) for current sensing in switched mode power converters are that galvanic isolation is inherent, losses are low, the bandwidth is high and a high-amplitude output signal may be obtained. However, 'droop' occurs as a result of the magnetising current drawn. Peak current droop is defined as the instantaneous per-unit shortfall in sensed current at the end of a rectangular pulse. Average current droop is defined as the per-unit shortfall in the average current sensed. The CT inherently operates in a resonant mode when sensing a unidirectional current pulse. This is advantageous as some of the current-time product lost to the magnetising branch may be recovered thereby alleviating the average current droop. Average current droop is investigated when diode rectification is used. Three operating modes are identified and described. These are designated the discontinuous magnetising current, continuous magnetising current and discontinuous secondary current modes (DSCM). It is shown that the CT's core losses may predominately influence the average current droop. Provided the DSCM is avoided, simple correction factors are shown to be appropriate for substantially correcting the sensed current to allow for these losses.

KW - switched mode power supplies

KW - current transformers

KW - power converters

KW - pulse transformers

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