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A Unified Model for the ZVS DC-DC Converters With Active Clamp

A Unified Model for the ZVS DC-DC Converters With Active Clamp. by N.Lakshminarasamma, B. Swaminathan, Prof V. Ramanarayanan, IISC. Department of Electrical Engineering Indian Institute of Science Bangalore. (1-K)Vg. R. Vg. +. KVg. -. Series Regulator Efficiency = K.

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A Unified Model for the ZVS DC-DC Converters With Active Clamp

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  1. A Unified Model for the ZVS DC-DC Converters With Active Clamp by N.Lakshminarasamma, B. Swaminathan, Prof V. Ramanarayanan, IISC Department of Electrical Engineering Indian Institute of Science Bangalore

  2. (1-K)Vg R Vg + KVg - Series Regulator Efficiency = K Linear Regulator • Best dynamic performance • Very good regulation • Poor efficiency and bulky

  3. + - Switching Regulator • Ideal losses zero • Output discontinuous • Smoothing filter needed TON TOFF Vg R Switching Voltage Regulator

  4. L C Vg S Vo Typical Converter • Switches control power flow • Reactive elements smoothen power flow • Both are non-dissipative elements

  5. Classification of SMPS

  6. Hard Switching Converter P T1 T2 V I t I V t

  7. V I OFF/ON Transient ZCS V t I I ZVS ON/OFF Transient t V Soft Switching Converter

  8. C R CR C CR R DC LR S Throw1 1 Pole LR CC + I S1 V D Clamp Capacitor s D S2 2 Clamp Switch Active Clamp ZVS Buck Converter

  9. CR CR D2 D1 i(t) VC LR i(0) = -I* I S1 V S2 Vo i(T1) = I D Interval T1 - Zero-voltage Turn-on IN - Normalized current

  10. v(t) v(0) = V v(T2) = 0 CR CR D2 D1 VC LR i(t) I S1 i(0) = I V S2 Vo D Interval T2 - Resonant Commutation

  11. CR CR D2 D1 VC LR i(t) I S1 V S2 Vo D Interval T3 - Power-on Duration S1 turned off at end of T3and CR almost instantly charges to V+VC.

  12. i(T4) = I CR CR D2 D1 VC LR i(t) I S1 V S2 Vo D Interval T4 – Assisted Turn-off

  13. v(0) = 0 CR CR D2 D1 VC LR i(t) I S1 V S2 v(T5) = V Vo D Interval T5 – Resonant Commutation V ( T5 ) = V

  14. CR CR D2 D1 VC LR i(t) I S1 V S2 Vo D Interval T6 – Power Freewheeling Duration At the end of T6 interval current i(t) has reversed and Flows through MOSFET of S2. CR almost instantly discharges to zero. Now S1 may be switched on with zero voltage across the same.

  15. Resonant Inductor LR Current I I(T5) t kI(T5) I* T1 T3 T6 T2 T5 T4 I Active Switch S1 I Freewheel Diode t Vg Pole Voltage Vo t Theoretical Waveforms

  16. Resonant Inductor LR Current I I(T5) t kI(T5) I* T1 T3 T6 T2 T5 T4 I Clamp Capacitor Current t kI(T5) Clamp Ratio and Clamp Voltage

  17. Steady State Equivalent Circuit for Active Clamp Buck converter (1+k)LR/Ts 1: D Steady State Equivalent Circuit Model

  18. Rd 1-D: 1 Equivalent Circuit Models of Other Converters Rd 1-D: 1 1:D Rd1 Rd2 1-D: 1 1: D Equivalent circuits of the active clamped ZVS boost, buck-boost and cuk converters

  19. Spread Sheet Design..\pesc04\work\spreadsheetdesign.xls

  20. Steady State Definitions Of Base Voltages And Currents Buck Boost Cuk Buckboost v Vg Vo Vg+Vo Vg+Vo Ig+ IL Ig Io I IL Rd M

  21. L C + + + - - Rc 1:D L C - + R Rc - + + - 1:D Small signal ac model of active clamp buck converter Dynamic Model Of Active Clamp Buck Converter Perturbation of the nonlinear circuit averaged model about a quiescent operating point.

  22. Simulated Active Clamp Buck Converter Output power = 60 watts Input voltage = 50 volts Output voltage = 20 volts Switching frequency = 250 KHz

  23. Resonant Inductor Current Waveform

  24. Clamp Capacitor Current Waveform

  25. Steady State Performance Of Active Clamp Buck Converter

  26. Vgs and Vds of S1 showing ZVS; Vgs and Vds of S2 showing ZVS Experimental Waveforms Of Active Clamp Buck Converter

  27. Pole voltage and Inductor current waveforms; Pole voltage and Clamp capacitor current waveforms Experimental Waveforms Of Active Clamp Buck Converter

  28. Measured output impedance of Hard-switched buck converter and Active clamp buck converter Dynamic Performance Of Active Clamp Buck Converter

  29. Conclusions – Active Clamp Converters • Derived from Hard-Switched Converters by the addition of few Resonant elements following the simple rule. • Circuit equations governing these sub-intervals are identical when expressed in terms of pole current; throw voltage and freewheeling resonant circuit voltage (I, V, and VC). • Steady state and Dynamic equivalent circuits are obtained from this idealized analysis. • The resonant sub-interval introduces lossless damping in the converter dynamics.

  30. Advantages – Active Clamp Converter • High Efficiency - ZVS • Simple Dynamic Model • Wide Variety of Topologies

  31. Thanks

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