Soft Commutation Isolated DC-DC Converters pp 297-317 | Cite as

# Active Clamp ZVS-PWM Forward Converter

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## Abstract

This chapter studies the Active Clamp ZVS-PWM Forward Converter. After the presentation of the power converter topology, the qualitative analysis is presented, which includes the description of operation, topological states for each time interval and relevant waveforms. Then, quantitative analysis, focusing on static gain and soft-commutation are presented. The necessary equations for the design of the parameters involved in the soft-commutation are obtained. Also included are numerical examples to illustrate the theoretical analysis, proposed exercises with solutions and numerical simulations.

## Keywords

Forward Converter Active Clamp Soft Commutation Relevant Waveforms Current-induced Magnetization## Nomenclature

- V
_{i} Input DC voltage

- V
_{o} Output DC voltage

- P
_{o} Output power

- C
_{o} Output capacitor filter

- L
_{o} Output inductor filter

- R
_{o} Output load resistor

- ZVS
Zero voltage switching

- q
Converter static gain

- D
Duty cycle

- D
_{nom} Nominal duty cycle

- f
_{s} Switching frequency

- T
_{s} Switching period

- t
_{d} Dead time

- n
Transformer turns ratio

- T
Transformer

- N
_{1}, N_{2}and N_{3} Transformer windings

- L
_{c} Commutation inductance (may be the transformer leakage inductance or an additional inductor, if necessary)

- i
_{Lc} Commutation inductor current

- L
_{m} Transformer magnetizing inductance

- i
_{Lm}(I_{Lm}) Transformer magnetizing inductance current and its average value

- \( {{\text{v}}_{\text{o}}^{{\prime }} } \)\( \left({{\text{V}}_{\text{o}}^{{\prime }} } \right)\)
Output voltage referred to the transformer primary side and its average value

- v
_{Lm} Magnetizing inductance voltage

- V
_{C3}\( \left( {\overline{{{\text{V}}_{{{\text{C}}3}} }} } \right) \) Clamping capacitor voltage and its normalized value

- \( {{\text{I}}_{\text{o}}^{{\prime }} } \)\( \left( {\overline{{{\text{I}}_{\text{o}}^{{\prime }} }} } \right) \)
Average output current referred to the primary and its normalized value

- i
_{i}(I_{i}) DC bus current and its average value

- i
_{Lm}(I_{Lm}) Magnetizing inductor current and its average value

- ∆i
_{Lm} Magnetizing inductor current ripple

- I
_{1} Magnetizing inductor current at the end of time interval 4

- I
_{2} Magnetizing inductor current at the end of time interval 8

- S
_{1} Main switch

- S
_{2} Active clamp switch

- D
_{1}, D_{2} Diodes in anti-parallel to the switches (MOSFET—intrinsic diodes)

- D
_{3}, D_{4} Output rectifier diodes

- C
_{1}, C_{2} Capacitors in parallel to the switches (MOSFET—intrinsic capacitors)

- v
_{ab}(V_{ab}) Converter ac voltage, between points “a” and “b” and its average value

- v
_{S1}, v_{S2} Voltage across switches

- i
_{S1}, i_{S2} Switches current

- i
_{C1}, i_{C2}, i_{C3} Capacitors current

- ∆t
_{1} Time interval of the first and second step of operation (t

_{2}–t_{0})- ∆t
_{2} Time interval of the third and fourth step of operation (t

_{4}–t_{2})- ∆t
_{3} Time interval of the fifth, sixth and seventh step of operation (t

_{7}–t_{4})- ∆t
_{32} Time interval of the third step of operation in CCM (t

_{3}–t_{2})- \( {\text{I}}_{{{\text{S1}}\;{\text{RMS}}}} \), \( \left( {\overline{{{\text{I}}_{{{\text{S1}}\;{\text{RMS}}}} }} } \right) \)
Switch S

_{1}RMS current and its normalized value

## References

- 1.Jitaru, I.D., Cocina, G.: High efficiency DC-DC converter. In: IEEE APEC 1994, pp. 638–644 (1994)Google Scholar
- 2.Duarte, C.M.C., Barbi, I.: A family of ZVS-PWM active-clamping DC-to-DC converters: synthesis, analysis, design, and experimentation. IEEE Trans. Circ. Syst.
**44**(8) (1997)Google Scholar - 3.Watson, R., Lee, F.C., Hua, G.C.: Utilization of an active-clamp circuit to achieve soft switching in flyback converters. IEEE Trans. Power Electron., 162–169 (1996)Google Scholar