an improved zct-pwm dc–dc converter for

8/21/2019 An Improved ZCT-PWM DCDC Converter For

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An Improved ZCT-PWM DCDC

Converter for

High-Power and FrequencyApplications

Presented by Awais Ahmad


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zero-current-transition PWM

converters

This family of converters implements zero-currentturn-off for power transistor(s) withoutincreasing voltage/current stresses and operates

at a fixed frequency. zero-voltage transition (ZVT)zero-current

transition (ZCT) quasi-resonant buck converter,which ensures zero crossings at any time required

for soft switching (SS) and provides ZVT turn-onand ZCT turn-off together for the main switch ofactive snubber cell in buck converter


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Hard and Soft Switching

Hard Switching. Hard Switching occurs when there is an overlap between

voltage and current when switching the transistor on and off.

. This overlap causes energy loss which can be minimized by

increasing the di/dt and dv/dt.

. However, fast changing di/dt or dv/dt causes EMI to begenerated. Therefore the di/dt and dv/dt should be optimized

to avoid EMI issues.


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Soft Switching Soft switchingis a possible way of reducing losses in power electronic switches.

The expression "soft switching" actually refers to the operation of power

electronic switchesas zero voltage switches(ZVS) or zero current switches(ZCS).

Soft Switching brings

to zero (currentor voltage) before th

off. This has benefits

in terms of losses.

. The smooth resona

also minimize EMI.

. Common topologiesand LLC are soft


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Implementation

Improved ZCT-PWM buck converter with IGBT.

Both the main switch S1 and the auxiliary

switch S2 consist of an IGBT


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Operation Stages

Seven stages occur within one switching cycle

in the steady state operation of the proposed

converter. The equivalent circuit schemes of

these operation stages are shown in further

slides


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Stage 1

When t1< t


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Stage 2

When t1< t


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Stage 3

When t2< t


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Stage 4

When t3< t


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Stage 5

When t4< t


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Stage 6

When t5< t


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Stage 7

When t6< t


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waveforms concerning the operation

stages in the converter.


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Design procedure

The following design procedure considering is

mainly based on the soft switching turn off

requirements of the main switch with the

maximum load current.

1. Resonant inductor Lr and resonant capacitor

Cr are selected to allow the peak value of the

resonant current to be approximately twicethe maximum load current.


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Lr and Crare selected to allow one half resonant

cycle to be approximately twice the fall time of

the main transistor.

the sum of the transient intervals, and the

minimum and maximum time durations of the

turn on signal of the main transistor can be

defined, respectively, as follows:


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The sum of the transient periods is permitted

to be equal to at most 20% of the switching

cycle as given, for possible maximum

switching frequency

for the minimum and maximum values of the

duty ratio of the converter


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EXPERIMENT

Theoretical analysis is verified with a

prototype of a 5-kW and 50-kHz IGBT-PWM

buck converter.

Experimental circuit of a 5-kW and 50-kHz IGBT-PWM buck converter.


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EXPERIMENTAL RESULTS

A prototype of a 5-kW and 50-kHz IGBT-PWM

buck converter given in previous Figure has

been realized to verify the predicted operation

principles and analysis of the improved ZCT-PWM buck converter.


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CONCLUSION

an improved active resonant snubber cell thatovercomes most of the drawbacks of the normal ZCT-PWM dcdc converter is proposed. It is particularlysuitable for an IGBT-PWM converter at high power and

high frequency levels. Also, the proposed snubber cellhas a simple structure, low cost, and ease of control.The converter with the proposed snubber cell canoperate successfully with soft switching under light-load conditions and at considerably high frequencies.

The predicted operation principles and theoreticalanalysis of this converter have been exactly verifiedwith a prototype of a 5-kW and 50-kHz IGBT-PWMbuck converter.


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The End

an improved zct-pwm dc–dc converter for

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