slides topic

Topic 3
Multi-pulse Diode Rectifiers

Lecture Topics
Six-pulse Diode Rectifier (Building Block)
Series-type 12-, 18- and 24-pulse rectifiers
Separate-type 12-, and 18-pulse rectifiers
Multi-pulse Diode Rectifiers

Why Use Multipulse Diode Rectifiers?
To reduce line current THD;
To improve input power factor; and
To avoid semiconductor devices in series.
Multi-pulse Diode Rectifiers

Resistive Load
Supply Voltages:
Six-pulse Diode Rectifier

Waveforms
Six-pulse Diode Rectifier

Capacitive Load
Assumption:
Six-pulse Diode Rectifier

Waveforms
Six-pulse Diode Rectifier

Discontinuous Current Operation
Six-pulse Diode Rectifier

Discontinuous Current Operation
Differential Equation:
Solution:
Six-pulse Diode Rectifier

Discontinuous Current Operation
Peak dc current:
Average dc current:
Voltage – theta relation:
Six-pulse Diode Rectifier

Continuous Current Operation
Note:
- With the increase of the load current, the rectifier will
enter into continuous current operation.
- During commutation interval, three diodes are on.
Six-pulse Diode Rectifier

Definition of Total Harmonic Distortion (THD)
Phase voltage (pure sine):
Line current (distorted):
RMS line current:
Line current THD:
Six-pulse Diode Rectifier

Definition of Power Factor (PF)
Per-phase average (real) power:
Per-phase apparent power:
Total power factor (PF):
Distortion factor (DF) :
Displacement power factor (DPF) :
PF = f (THD) :
Six-pulse Diode Rectifier

Per Unit System
Rated power, rated lint-to-line voltage:
Base voltage and frequency:
Base current and impedance:
Base inductance and capacitance:
Example
Rectifier ratings: 4160V, 60Hz, 2MVA.
Base current = 277.6A, Base inductance = 22.9mH.
Line inductance = 2.29mH = 0.1pu
Line current = 138.8A = 0.5pu
and
Six-pulse Diode Rectifier

Typical Waveforms / Harmonic Content
Six-pulse Diode Rectifier

THD and PF
Six-pulse Diode Rectifier

Rectifier Topology
Series type:
Two six-pulse rectifiers
are in series at the output.
Phase shifting transformer:
Secondary line-to-line voltage:
Turns ratio:
and
12-pulse Series-type Diode Rectifier

Simplified Block Diagram
12-pulse Series-type Diode Rectifier

Waveforms and FFT
No 5th or 7th harmonics in the line current.
Primary line current THD: 8.38%
12-pulse Series-type Diode Rectifier

Comparison with six-pulse rectifier:
THD is reduced; and
PF is improved.
THD and PF
12-pulse Series-type Diode Rectifier

Phase-Shifting
(Zigzag) Transformer
Converter Topology
18-pulse Series-type Diode Rectifier

Simulated Waveforms
No 5th, 7th, 11th, or 13th harmonics in the line current.
Lowest harmonic: 17th
Line current THD: 3.06%
18-pulse Series-type Diode Rectifier

Measured Waveforms
18-pulse Series-type Diode Rectifier

THD and PF
Comparison with 12-pulse:
Improved THD
18-pulse Series-type Diode Rectifier

Converter Topology
Phase-Shifting
(Zigzag) Transformer
24-pulse Series-type Diode Rectifier

Typical Waveforms
Lowest line current harmonic: 23th
THD: 1.49%
24-pulse Series-type Diode Rectifier

THD and PF
24-pulse Series-type Diode Rectifier

Rectifier Topology
Separate Type
Each six-pulse rectifier feeds a separate dc load.
12-pulse Separate-type Diode Rectifier

Application Example
Multilevel Cascade
H-bridge Inverter Fed Drive
Phase Shifting
Transformer
12-pulse Separate-type Diode Rectifier

Typical Waveforms
Comparison with series-type:
- DC current ripple: higher
- Line current THD: close
12-pulse Separate-type Diode Rectifier

Measured Waveforms
12-pulse Separate-type Diode Rectifier

Line Current THD and Input PF
12-pulse Separate-type Diode Rectifier

Rectifier Topology
18-pulse Separate-type Diode Rectifier

Simulated Waveforms
18-pulse Separate-type Diode Rectifier

Line Current THD and Input PF
18-pulse Separate-type Diode Rectifier

Line Current THD and Input PF
24-pulse Separate-type Diode Rectifier