7. rectifier

8/2/2019 7. Rectifier

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RectifiersRectifiers


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Single-phase, Half Wave Rectifier

Uncontrolled

Controlled Free wheeling diode

Single-phase, Full Wave Rectifier

Uncontrolled Controlled

Three-phase Rectifier

Uncontrolled Controlled

Overview


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Input can be single or multi-phase (e.g. 3-phase). Output can be made fixed or variable

Applications: DC welder, DC motor drive, Battery

charger, DC power supply, HVDC

DEFINITION:DEFINITION:Converting AC (from mains or other AC source) to DC powerby using power diodes or by controlling the firing angles of

thyristors/controllable switches.Basic block diagramBasic block diagram


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Uncontrolled Single Phase

Half Wave Rectifier


Half Wave Rectifier


Half Wave Rectifier


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Single-phase, Half-Wave, R - load


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Given the supply voltage v = 120 Vrms

, 60 Hz.Determines:

a) The average load voltage and currentb) The load voltage in r.m.s.

c) The average power absorbed by the load, RLd) The power factor of the circuit

AnswerAnswer

a) 54 V & 10.8 A,a) 54 V & 10.8 A, b) 84.9 V, c) 1440 W, d) 0.707b) 84.9 V, c) 1440 W, d) 0.707

ExampleExample

Single-phase, Half-Wave, R - load


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SolutionSolution


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Full Wave Rectifier


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Full Wave Rectifier

Center-tapped (CT) rectifier requires center-taptransformer. Full Bridge (FB) does not. CT: 2 diodes FB: 4 diodes. Hence, CT experienced only onediode volt-drop per half-cycle Conduction losses for CT is half.

Diodes ratings for CT is twice the FB.


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Full Wave Rectifier


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Bridge Waveforms


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Center-tappedwaveforms


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Uncontrolled Three Phase

Half Wave Rectifier


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Three-phase half-wave rectifiers


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Uncontrolled Three PhaseFull Wave Rectifier


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In the top group (D1, D3), the cathodes (-) of the two diodes are at acommon potential. Therefore, the diode with its anode (+) at the highestpotential will conduct (carry) id. For example, when vs is ( +), D1 conducts id and D3 reverses (by taking loop

around vs, D1 and D3).When vs is (-), D3 conducts, D1 reverses.

In the bottom group, the anodes of the two diodes are at common potential.Therefore the diode with its cathode at the lowest potential conducts id. For example, when vs (+), D2 carry id. D4 reverses.When vs is (-), D4 carry id. D2 reverses.

Single-phase diode groups


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Three-phase full-wave rectifiers


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vvoo==vvpp --vvnn


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Top group: diode with its anode at the highestpotential will conduct. The other two will be reversed.

Bottom group: diode with the its cathode at thelowest potential will conduct. The other two will bereversed.

For example, if D1 (of the top group) conducts, vp is

connected to van.. If D6 (of the bottom group)conducts, vn connects to vbn . All other diodes are off.

The resulting output waveform is given as:

vo = vp - vn For peak of the output voltage is equal to the peak ofthe line to line voltage vab .



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Three-phase, average voltage

Considers only one of

the six segments.

Obtain its average

over 60 degrees or

/3 radians.

Considers only one of

the six segments.

Note that the output DC

voltage component of a

three - phase rectifier is

much higher than of asingle phase.


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Single Phase Half-WaveControlled Rectifier

Controlled Half Wave


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Controlled Half-Wave

Controlled Half Wave


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Controlled Half-Wave


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Single Phase Full Wave

Controlled Rectifier

Controlled Full


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Controlled FullWave, R load

Controlled Full


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Controlled FullWave, R load


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Three Phase Half Wave


Three Phase Half Wave Controlled Rectifier


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Three Phase Full Wave



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Three-phase full-wave


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pcontrolled rectifier


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7. rectifier

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