# Active Clamp ZVS-PWM Forward Converter

Chapter
Part of the Power Systems book series (POWSYS)

## 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.

## Nomenclature

Vi

Input DC voltage

Vo

Output DC voltage

Po

Output power

Co

Output capacitor filter

Lo

Output inductor filter

Ro

ZVS

Zero voltage switching

q

Converter static gain

D

Duty cycle

Dnom

Nominal duty cycle

fs

Switching frequency

Ts

Switching period

td

n

Transformer turns ratio

T

Transformer

N1, N2 and N3

Transformer windings

Lc

Commutation inductance (may be the transformer leakage inductance or an additional inductor, if necessary)

iLc

Commutation inductor current

Lm

Transformer magnetizing inductance

iLm (ILm)

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

vLm

Magnetizing inductance voltage

VC3$$\left( {\overline{{{\text{V}}_{{{\text{C}}3}} }} } \right)$$

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

ii (Ii)

DC bus current and its average value

iLm (ILm)

Magnetizing inductor current and its average value

∆iLm

Magnetizing inductor current ripple

I1

Magnetizing inductor current at the end of time interval 4

I2

Magnetizing inductor current at the end of time interval 8

S1

Main switch

S2

Active clamp switch

D1, D2

Diodes in anti-parallel to the switches (MOSFET—intrinsic diodes)

D3, D4

Output rectifier diodes

C1, C2

Capacitors in parallel to the switches (MOSFET—intrinsic capacitors)

vab (Vab)

Converter ac voltage, between points “a” and “b” and its average value

vS1, vS2

Voltage across switches

iS1, iS2

Switches current

iC1, iC2, iC3

Capacitors current

∆t1

Time interval of the first and second step of operation (t2–t0)

∆t2

Time interval of the third and fourth step of operation (t4–t2)

∆t3

Time interval of the fifth, sixth and seventh step of operation (t7–t4)

∆t32

Time interval of the third step of operation in CCM (t3–t2)

$${\text{I}}_{{{\text{S1}}\;{\text{RMS}}}}$$, $$\left( {\overline{{{\text{I}}_{{{\text{S1}}\;{\text{RMS}}}} }} } \right)$$

Switch S1 RMS current and its normalized value

## References

1. 1.
Jitaru, I.D., Cocina, G.: High efficiency DC-DC converter. In: IEEE APEC 1994, pp. 638–644 (1994)Google Scholar
2. 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. 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 