AC to DC Converter (Rectifier)

ASNILELEKTRO FT - UNP

Penyerah tiga fasa tak terkendaliTiga fasa setengah gelombang

Penyearah tiga fasa setengah gelombang

Proses penyearahan :

Selama polaritas + dari V1 (dari 0-π): dioda D3 lebih dahulu ONπ): dioda D3 lebih dahulu ONkarena V3 lebih + dari V1 (dari 0-π/6), selanjutnya mulai π/6-5π/6dioda D1 ON, tetapi karena V21 p 2lebih + dari V1 saat 5π/6-π makaD2 ON, dan seterusnya.

the average value of the output can be found as

h l f h l b f dthe rms value of the output voltage can be found as

the rms current in each transformer secondary winding can also be found as

Penyearah gelombang-penuh Tiga Fasa

Proses penyearahan :• D1, D3, dan D5 akan ON jika anoda terhubung dengan tegangan fasa tertinggi saat itu.• Da, D4, atau D6 akan ON jika katoda terhubung dengan tegangan fasa terendah saat itu.• D1 dan D4, D3 dan D6, D2 dan D5 tidak boleh ON secara bersamaan.• Tegangan luaran pada beban dihasilkan dari tegangan line sumber.• Dioda ON secara berpasangan (6,1), (1,2), (2,3), (3,4), (4,5), (5,6), (6,1),…. Jadi, dioda ONdengan urutan 1,2,3,4,5,6,1, …

Tegangan keluaran rata-rata Tegangan keluaran rms adalah

Arus rms pada sekunder trafoArus rms pada sekunder trafo Arus puncak yang melalui dioda

Arus rms yang melalui dioday g

Im adalah arus puncak line sekunder

Vm adalah tegangan fase puncak

AC – DC controlled RectifierAC DC controlled Rectifier

Single-Phase Half-Wave RectifierSingle Phase Half Wave Rectifier

Single thyristor rectifier with resistive load.

The load average voltage is given by:

Vm : puncak tegangan masukan

Gate Signal Generation

Single thyristor rectifier with: (a) resistive-inductive load; and (b) active load.

When the thyristor is turned ON the voltage across the inductance isRectifier for an R - L load.

When the thyristor is turned ON, the voltage across the inductance is

R hid 169The voltage in the resistance R is

h l d i

Rashid, 169

The load current is

Rectifier for inductive-active load

Single-Phase Controlled RectifierThe load is fed via a thyristor in each positive cycle of voltages v1 and v2and the load current returns via the neutral N.With reference in picture bisaides, thyristor T1 can be fired into the ON state at any time provided that voltage vT1 > 0. The firing pulses are delayed by an angle a with respect to the instant

h di d ld d t I b twhere diodes would conduct. In be next waveform also illustrates the current paths for each conduction state. Thyristor T1 remains in the ON stateThyristor T1 remains in the ON state until the load current tries to go to a negative value. Thyristor T2 is fired into the ON state when vT2 > 0, which o e O s e w e v , w ccorresponds in picture below to the condition at which v2 > 0.

The load voltage with resistive load is

Tegangan luaran (output) efektif, Vo,rms dan Arus luaran efektif, Io,rms :

⎤⎡2/1

⎥⎦⎤

⎢⎣⎡ +−

==πα

παπ

42sin

2

2/1

, mrmsrmso VEV

AnalisisAnalisis RangkaianRangkaian dengandengan bebanbeban induktifinduktif (RL)(RL)

απ

cos2,

mDCo

VV =π

Jik di DIODE KOMUTASI dih b k l l d b b RLJika dipasang DIODE KOMUTASI yang dihubungkan paralel dengan beban RL, maka:

( )απ

cos1, +== mdcDCo

VEV

Single-Phase Controlled Rectifier

Single phase bridge rectifier: (a) fully controlled; andSingle-phase bridge rectifier: (a) fully controlled; and (b) half controlled.

This picture shows the voltage and current waveforms of the fully controlled bridge rectifier for acontrolled bridge rectifier for a resistive load. Thyristors T1 and T2 must be fired simultaneously during the positive half wave ofduring the positive half wave of the source voltage vs so as to allow conduction of current. Alternatively, thyristors T3 and T4 must be fired simultaneously during the negative half wave of the source voltage. To ensure simultaneous firing, thyristors T1 and T2 use the same firing signal. The load voltage is similar to the

lt bt i d ith th bi h

Waveforms of a fully controlled

voltage obtained with the biphasehalf-wave rectifier.The input current is given by

Waveforms of a fully controlled bridge rectifier with resistive load.

Waveforms of a fully controlled bridgeWaveforms of a fully controlled bridge rectifier with resistive-inductive load

The high-load inductance generates a perfectly filtered currentand the rectifier behaves like a current source. With continuousload current, thyristors T1 and T2 remain in the on-state beyond the positive half-wave of the source voltage vs . For this reason, the load voltage vd can have a negative instantaneous value Thethe load voltage vd can have a negative instantaneous value. The firing of thyristors T3 and T4 has two effects:i) they turn off thyristors T1 and T2; andii) after the commutation they conduct the load current.This is the main reason why this type of converter is called a‘‘naturally commutated’’ or ‘‘line commutated’’ rectifier Thenaturally commutated or line commutated rectifier. Thesupply current is has the square waveform for continuous conduction.

half controlled with high inductive load

Full controlled with R-L Load (high inductive load)

Full wave controlled with R Load

Three-Phase Half-Wave Rectifier

Three-phase half-wave rectifie

High Inductive load

If

Resistive load and es st ve oad a d

the load average voltage isthe load average voltage is

DC current waveforms with resistive load

AC current waveforms for the half-wave rectifier

The current waveforms shown above are useful for designing the power transformer. Starting from

Then, to establish a relation between ac and dc voltages for

where a is the secondary to primary turn relation of the transformer. On the other hand, a relation between the currents is also obtainable.

and

The meaning of above equation is that the power transformer has to be oversized 21% at the primary side, and 48% at the secondary side. Then, a special transformer has to be built forsecondary side. Then, a special transformer has to be built for this rectifier. In terms of average VA, the transformer needs to be 35% larger that the rating of the dc load. The larger rating of the secondary respect to primary is because therating of the secondary respect to primary is because the secondary carries a dc component inside the windings. Besides, the transformer is oversized because the circulation of current harmonics, which do not generate active power. The core saturation, due to the dc components inside the secondary windings, also needs to be taken in account for y g ,iron oversizing.

Three-Phase Half Control Rectifier

Three-Phase fully Control Rectifier

Three-phase full-wave rectifier

The load average voltage is given by:

Latihan

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