AC to DC Converter (Rectifier)
ASNIL ELEKTRO FT - UNP
Penyerah tiga fasa tak terkendali Tiga fasa setengah gelombang
Penyearah tiga fasa setengah gelombang
Proses penyearahan : Selama polaritas + dari V1 (dari 0π): dioda D3 lebih dahulu ON karena V3 lebih + dari V1 (dari 0π/6), selanjutnya mulai π/6-5π/6 dioda D1 ON, tetapi p karena V2 lebih + dari V1 saat 5π/6-π maka D2 ON, dan seterusnya.
the average value of the output can be found as
the h rms value l off the h output voltage l can be b found f d 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 ON dengan urutan 1,2,3,4,5,6,1, …
Tegangan keluaran rata-rata
Arus rms pada sekunder trafo
Tegangan keluaran rms adalah
Arus puncak yang melalui dioda
Arus rms y yang g melalui dioda
Im adalah arus puncak line sekunder Vm adalah tegangan fase puncak
AC – DC controlled Rectifier Single-Phase Single Phase Half Half-Wave 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.
Rectifier for an R - L load. When the thyristor is turned ON ON, the voltage across the inductance is
The voltage in the resistance R is
The h load l d current is i
Rectifier for inductive-active load
R hid 169 Rashid,
Single-Phase Controlled Rectifier The load is fed via a thyristor in each positive cycle of voltages v1 and v2 and 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 where h diodes di d would ld conduct. d t In I be b nextt waveform also illustrates the current paths for each conduction state. Thyristor T1 remains in the ON state until the load current tries to go to a negative value. Thyristor T2 is fired into o thee ON O sstatee w when e v vT2 > 0,, which w c corresponds 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 :
V o , rms = E rms = V m
⎡ π −α sin 2α ⎤ ⎢⎣ 2π + 4π ⎥⎦
1/ 2
Analisis Rangkaian dengan beban induktif (RL) Vo , DC =
2Vm
π
cos α
Jika dipasang Jik di DIODE KOMUTASI yang dihubungkan dih b k paralel l l dengan d beban b b RL, RL maka:
Vo , DC = Edc =
Vm
π
(1 + cos α )
Single-Phase Controlled Rectifier
Single phase bridge rectifier: (a) fully controlled; and Single-phase (b) half controlled.
This picture shows the voltage and current waveforms of the fully controlled bridge rectifier for a resistive load. Thyristors T1 and T2 must be fired simultaneously during 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 voltage lt obtained bt i d with ith th the biphase bi h half-wave rectifier. Waveforms of a fully controlled bridge rectifier with resistive load.
The input current is given by
Waveforms of a fully controlled bridge rectifier with resistive-inductive load
The high-load inductance generates a perfectly filtered current and the rectifier behaves like a current source. With continuous load 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. value The firing of thyristors T3 and T4 has two effects: i) they turn off thyristors T1 and T2; and ii) after the commutation they conduct the load current. This is the main reason why this type of converter is called a ‘‘naturally naturally commutated’’ commutated or ‘‘line line commutated commutated’’ rectifier. rectifier The supply 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 es st ve load oad aand d
the 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 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 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 secondaryy windings, g , also needs to be taken in account for 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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