slides topic

Topic 4
Multi-pulse SCR Rectifiers

Lecture Topics
Six-pulse SCR Rectifier (Building Block)
12-, 18- and 24-pulse SCR Rectifiers
THD and PF
Multi-pulse SCR Rectifiers

Why Use Multi-pulse SCR Rectifiers?
To reduce line THD
To improve input power factor
To avoid semiconductor devices in series.
Multi-pulse SCR Rectifiers

Converter Configuration
Assumption: 1) Ideal SCRs - no power loss
2) dc current ripple free
Use constant current source Id as a load
Six-pulse SCR Rectifier

Waveforms
Average dc voltage
Six-pulse SCR Rectifier

Fourier Analysis
RMS current
THD
Six-pulse SCR Rectifier

Power Factor (PF)
Displacement Power Factor
Overall Power Factor
Six-pulse SCR Rectifier

Waveforms at Various Firing Angles
Six-pulse SCR Rectifier

Effect of Line Inductance Ls
Six-pulse SCR Rectifier

Waveform During SCR Commutation
Six-pulse SCR Rectifier

DC Voltage Reduction (caused by commutation)
S1 and S5 on (during commutation)
from which
Since ia + ic = Id, and id is constant
from which
Six-pulse SCR Rectifier

DC Voltage Reduction
Since
Shaded Area Aγ
Average dc voltage loss Average dc output voltage
Six-pulse SCR Rectifier

Commutation Interval
Aγ can be rearranged as
where
Substitute
from which
Six-pulse SCR Rectifier
into the above equation

Line Current Waveforms
Ls = 0.05pu
Six-pulse SCR Rectifier

Line Current THD
Six-pulse SCR Rectifier

Power Factor
Six-pulse SCR Rectifier

Topology
Main Benefits
- Low line current THD
- No SCRs in series
12-pulse SCR Rectifier

Application Example
Used for current source inverter (CSI) fed drive
12-pulse SCR Rectifier

Waveforms of Idealized Rectifier (Ls = Llk = 0)
12-pulse SCR Rectifier

Fourier Analysis
Secondary currents
12-pulse SCR Rectifier

Fourier Analysis (continued)
Secondary currents referred to the primary side
Primary line current
12-pulse SCR Rectifier

Line Current THD
Secondary side
Primary side
12-pulse SCR Rectifier

Line Current Waveform (Ls ≠ 0 )
12-pulse SCR Rectifier

THD and PF
12-pulse SCR Rectifier

Rectifier Configuration
18-pulse SCR Rectifier

Waveforms
18-pulse SCR Rectifier

Line Current THD
18-pulse SCR Rectifier

Rectifier Configuration
24-pulse SCR Rectifier

Line Current THD
24-pulse SCR Rectifier