Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Rectifiers
(Line Commutated Rectifiers)
Rectifiers - 1
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Introduction
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Line-Commutated or Naturally Commutating Rectifers
]Un-Controlled (diodes)
]Semi- or Full-Controlled (thyristors)
This Lecture
Force-Commutated Rectifiers
]Switch mode (PWM)
Rectifiers - 2
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
What are used for
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
High Current loads (or multiple
low current ones)
] Conventional Magnets (low time constant)
] SC Magnets (very high time constant)
Elettra – Storage Ring Magnets
High Voltage Loads
] Klystrons for RF plants
Elettra – Storage Ring RF Amplifier klystron in its
trolley with the modulating cavities
Rectifiers - 3
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
The principles of Rectification
Distribution
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Rectification
Conversion of the AC mains in DC
º Fully Controlled Bridge (mostly used)
º Current Regulator & Un-controlled Rectifier
º Rectifier and Linear Output Stage
Harmonics
Filtering
Load
Rectifiers - 4
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Performance Parameters (some)
º
º
Assumptions:
Ideal Devices (instantaneous switching, no losses)
Resistive Load
Vp(t)
DC voltage
on load
T
VDC
1
= ∫ v L(t)dt
T 0
T
1
rms voltage V =
vL2(t)dt
L
∫
on load
T 0
Form
Factor
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
V
FF = L
VDC
Vs(t)
VL(t)
Rectification
Ratio
(a.k.a efficiency)
Ripple
Factor
Load
2
2
PDC
V DC
1
V DC
1
RD = 0
η=
⇒ 2
 → η = 2 =
PL + PD
VL 1 + RD
VL
FF 2
R
2
VL2 − VDC
RF =
= FF 2 − 1
VDC
Transformer
Utilization
Factor
TUF =
PDC
PDC
=
Transformer VA rating VAp + VAs
2
Some Diode/Thyristor Parameters:
Peak Inverse Voltage, Peak Direct Voltage (Thy. Only), Peak Forward Current, Average Current, Rms Current,…
Rectifiers - 5
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Single-Phase topologies - 1
Single–Way
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
(half-wave, just for comparison)
iL(t)
Vs(t)
iL(t)
Vs(t)
R=2Ω
2π
VL(t)
Single–Way
(full-wave, Centre-Tapped)
iL(t)
Vs+(t)
Vs+(t)
VL(t)
iL(t)
2π
Vs-(t)
Rectifiers - 6
R=2Ω
Vs-(t)
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Single-Phase topologies - 2
Double–Way
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
(full-wave, Bridge)
iL(t)
Vs(t)
Vs(t)
iL(t)
VL(t)
º
º
2π
R=2Ω
Applications
Low power loads as stand-alone rectifiers
Output stage of PWM rectifiers
Rectifiers - 7
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Comparison among topologies 1–Ph.
º
º
º
Secondary voltage is sinusoidal: vs(t) = Vs sin (2πfmainst)
Resistive Load
Ideal devices (no device losses)
Vp(t)
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Vs(t)
VL(t)
Load
Half–Wave
Full – Wave
(Center–tapped)
Full – Wave
(Bridge)
Rectified Voltage – VDC
Vs/π = 0.318 ·Vs
2 ·Vs/π = 0.636 ·V s
2 ·Vs/π = 0.636 ·V s
rms Output Voltage – VL
Vs/2 = 0.318 ·Vs
Vs/√ 2 = 0.707 ·Vs
Vs/√ 2 = 0.707 ·Vs
1.57
1.11
1.11
0.405
0.81
0.81
1.21
0.482
0.482
0.286
0.572
0.81
Diode Peak Inverse Voltage (PIV) – VRRM
Vs = π · VDC
2 · Vs = π · VDC
Vs = π/2 · VDC
Peak Direct Voltage (PDV – thyristors only) – VDRM
Vs = π · VDC
2 · Vs = π · VDC
Vs = π/2 · VDC
π · IDC
π/2 · I DC
π/2 · I DC
IDC
0.5 · I DC
0.5 · I DC
π/2 · I DC
π/4 · I DC
π/4 · I DC
fmains
2 · fmains
2 · fmains
Parameter
Form Factor – FF
Rectification Ratio – η
Ripple Factor – RF
Transformer Utilization Factor – TUF
Diode Peak Forward Current – IFRM
Diode Average Current – IF(AV)
Diode Rms Current – IF(RMS)
Fundamental Ripple Frequency – fR
*Extracted from: M.H. Rashid, “Power Electronics Handbook”, Academic Press
Rectifiers - 8
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Mostly Used Configurations Multi-Ph.
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
º
º
º
º
Some Considerations:
number of phases → ∞ ⇒ FF → 1 & RF → 0
Max Practical Numbers: 12 or 24
The higher the number of phases the more complicated the transformer is for Star-Connected (single-way)
diode rectifiers
Bridge configurations allow to have 6 or 12 pulses without complex transformer connections
• Single Bridge (6 pulses)
• Double Bridge – Series/Parallel (12 pulses)
3-Phase Star
(single-way, just for comparison)
VR(t)
VR(t)
Vs(t)
VT(t)
iL(t)
iL(t)
2π
VS(t)
R=2Ω
VT(t)
Rectifiers - 9
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
6-p Configuration: Bridge
Bridge:
iL(t)
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
iL(t)
VR(t)
VT(t)
VS(t)
VR(t)
2π
VS(t)
VS(t) -V T(t)
VT(t)
R=1Ω
º
º
º
VS(t) -V T(t)
Comments:
Mostly used configuration
It is the base for structures with a higher number of pulses
• Series (same output current, double output voltage)
• Parallel (double output current, same output voltage)
This configuration (and those derived) are the best for FF, RF and TUF
Rectifiers - 10
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
12-p Configurations (Σ & //)
Series:
R=1Ω
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
iL(t)
iL(t)
2π
iL(t)
Parallel
(with
inter-phase
reactance):
2π
R=1Ω
iL(t)
Rectifiers - 11
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Comparison among topologies 3–Ph.
º
º
º
Secondary voltage is sinusoidal: vs(t) = Vs sin (2πft)
Resistive Load
Ideal devices (no device losses)
Vp(t)
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Vs(t)
VL(t)
Load
3-Phase Star
(Single-Way)
6p Bridge
(Double-Way)
12p Bridge
(Series)
12p Bridge
(Parallel+)
Rectified Voltage – VDC
0.827 · Vs
1.654 · Vs
3.308 · Vs
1.654 · Vs
rms Output Voltage – VL
0.84 · Vs
1.655 · Vs
3.310 · Vs
1.655 · Vs
Form Factor – FF
1.0165
1.0009
1.00005
1.00005
Rectification Ratio – η
0.986
0.998
1.00
1.00
Ripple Factor – RF
0.182
0.042
0.01
0.01
Transformer Utilization Factor – TUF
0.73
0.95
0.97
0.97
Diode Peak Inverse Voltage (PIV) – VRRM
2.092 · VDC
1.05 · VDC
0.524 · VDC
1.05 · VDC
Peak Direct Voltage (PDV – thyristors only) – VDRM
2.092 · VDC
1.05 · VDC
0.524 · VDC
1.05 · VDC
1.21 · I DC
1.05 · I DC
1.01 · I DC
0.524 · I DC
Diode Average Current – IF(AV)
0.333 · I DC
0.333 · I DC
0.333 · I DC
0.167 · I DC
Diode Rms Current – IF(RMS)
0.587 · I DC
0.579 · I DC
0.576 · I DC
0.409 · I DC
3 · fmains
6 · fmains
12 · fmains
12 · fmains
Parameter
DiodePeak Forward Current – IFRM
Fundamental Ripple Frequency – fR
*Extracted from: M.H. Rashid, “Power Electronics Handbook”, Academic Press
Rectifiers - 12
+
With inter-phase transformer
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Three-Phase Controlled Rectifiers
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Goal
º
º
º
To be able to vary the output voltage on the load according to the needs
To be able to recover, if needed, energy from the load to the mains or other energy
storage device
To minimize the losses on some devices when the load requirements are low
Possible Solutions
º
º
º
Use of thyristors in place of diodes
Use thyristors AND diodes
Use diodes or thyristors AND transistors
Applications
º
º
º
º
High Current loads (magnets)
High Voltage loads (klystrons)
Several low current loads supplied from a multi-channel converter (small magnets)
Supply of current to loads of different characteristics
Rectifiers - 13
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Three-Phase Fully Controlled Bridge
]
]
]
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Delay Angle α: the span of period between the instant when the thyristor could start to
conduct and the instant when the trigger pulse is applied
Since in stable conditions also the subsequent couple of thyristors are delayed the conduction
continues until the next trigger pulse
The average value, VDC, is anyway lower and depends on α
Trigger!!!
3⋅ 3
π
⋅ Vm ⋅ cos( α ) = V DC 0 ⋅ cos( α ) 0 ≤ α ≤
π
3
3⋅ 3
π 
π
2 ⋅π

VDC ( α ) =
⋅ Vm ⋅ 1 + cos( α + )
<α ≤
π
3 
3
3

VDC ( α ) =
Rectifiers - 14
º
º
Assumptions:
Ideal Devices (instantaneous switching,
no losses)
Resistive Load
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Conduction vs.
α (Resistive Load)
α = 10°
º
º
º
º
0°= α =60°
Continuous conduction: the output voltage
is always positive
The current flows continuously in the
resistive load
60°< α =120°
Discontinuous conduction: the output
voltage goes to zero for part of each pulse
The current flows as “pulses” in the
resistive load
Rectifiers - 15
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
α = 50°
a = 70°
a = 110°
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
3-Ph.Current Regulator & Diode Br.
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Comments:
º High Voltage Loads (like klystrons) require series connections of switches
º Thyristors in series means a VERY good equalization of their firing pulses,
º
diodes are naturally commutating devices
Pre-regulation of the AC input of the Bridge
Ripple
Factor
2
VL2 − VDC
RF =
= FF 2 − 1
VDC
Elettra – Linac Modulator Klystron
Rectifiers - 16
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
3-Ph.Multi-Channel (unregulated)
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Comments:
º Good solution when there are several low-power loads.
º The common part (transformer, bridge, filter) and the n channels can be
º
housed in a single cabinet.
Using two bridges in series it is possible to supply bipolar channels (e.g. for
corrector magnets)
…
= Ch. Regulation
Ch. 1
Ch. 2
Ch. n
= Load
Elettra – Transfer Line Quadrupole
followed by 2 correctors
Rectifiers - 17
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
3-Ph.Contr. Br. & Linear Output
º
º
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Comments:
Good for load which change their characteristics or for loads which need “fast”
output current changes
Acting on the controlled bridge it is possible to reduce the voltage on the linear
transistor output stage and minimize the power dissipation at low current conditions
= Trans. Regulation
Elettra – Storage Ring Electromagnetic Elliptical Wiggler (EEW):
for a short time in 2001, due to a major fault to its PWM
PS, it was powered by a couple of PS of this type.
Rectifiers - 18
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
The “real” world – DC Side
⇒
The load has a strong inductive component (usually it is a
magnet)
⇒
The current doesn’t follow the output voltage and it is
smoothed by the inductance
⇒
If the inductance is big enough, the current waveform is
continuous even if the voltage one is not
⇒
The output voltage can go negative(when α > 60°) but the
current is still flowing in the same direction (keeping the
thyristor in conduction)
⇒
The load inductance has a strong influence also on the
waveform of the AC line current: the higher the inductance
the less distorted the input current
⇒ The ripple on the output direct current is normally too high for
the applications in accelerators’ field
⇒ There is the need for a Low-Pass Filter
⇒ Cut-off frequency f0 should be much lower than ripple's 1st
harmonic (fripple1 = p x fmains, p = # pulses)
⇒ Dumped passive L-C filters are used
⇒ If additional attenuation is needed, additional Active Filters on
the DC output are also used
Rectifiers - 19
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
i-PES applet:
courtesy of Prof.
J. W. Kolar and
Dr. U. Drofenik ETH Zurich
f0 =
Lf >
1
2 ⋅π ⋅ L f ⋅ ( C1 + C 2 )
Vripple
2 ⋅ π ⋅ f ripple1 ⋅ I DC min
C 2 = 5 ⋅ C1
R f = 0. 4 ⋅
L
( C1 + C 2 )
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Parenthesis: Inversion
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
⇒
With an inductive load, when α > 60°, the output voltage goes temporarily negative while the
current is still flowing in the “positive” direction
⇒
For α > 90°, the average output voltage becomes negative but the current is still positive: the
power is flowing back from the DC side to the AC, the converter is operating in “inverting
mode”
⇒
The inverting mode can be used to recover energy from an inductive load (or a more stable
source of DC like a battery or a solar cell panel) and send it to the AC mains or store in a
capacitor.
⇒
The maximum delay angle is α ≈ 150° (taking into account the commutation angle µ and the
thyristor turn-off time tq)
⇒ In “pure” rectifiers to avoid inversion and keep a
working range up to α = 120°, a free-wheeling diode is
put in parallel to the rectifier output.
⇒ The free-wheeling diode creates a path for the load
current when the output voltage would become
negative.
⇒ The free-wheeling diode has a positive effect in the
ripple reduction and reactive power.
Rectifiers - 20
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
The “real” world – AC Side
⇒
⇒
⇒
⇒
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
There is a FINITE inductance on the mains side (the inductance of the secondary of the
transformer and the leakage inductance of the line): Ls
The thyristors change their status (on or off) in a FINITE time
During commutation from one phase to another there is an “overlapping time” when two
thyristors on the same side of the bridge are conducting at the same time shorting the phases
through the L s of each phase – it is indicated as the “overlap angle” µ.
For a given ID and α, the duration of the overlapping depends on Vf-f and Ls (LD>>0)
ID =
Vf − f
2 ⋅ω ⋅ Ls
⋅ [cos( α ) − cos( α + µ )]
(Vf-f = peak value of inter-phase voltage)
*Extracted from: M.H. Rashid, “Power Electronics Handbook”, Academic Press
Rectifiers - 21
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
The effects on the mains (current)
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Current:
⇒ The current drawn from AC supply system is not a pure sinusoid
⇒ Fundamental component with superimposed harmonic component
⇒ Harmonic frequency: (n x p ± 1) x fmains with n = 1, 2,… p = # pulses)
⇒ A 12 pulse converter has a lower harmonic impact on the mains than two 6 pulse
units of a comparable size
Line Current
Harm. #
= 250 Hz
7th = 350 Hz
11th = 550 Hz
13th = 650 Hz
…
Fundamental
frequency
component of
Line Current
5th
6 pulse – mains line current (THD=28.45%)
Line Current
Harm. #
= 550 Hz
13th = 650 Hz
23rd = 1150 Hz
25th = 1250 Hz
…
Fundamental
frequency
component of
Line Current
11th
12 pulse – mains line current (THD=9.14%)
*Data extracted from: G.J. Wakileh, “Power Systems Harmonics”, Springer
Rectifiers - 22
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
The effects on the mains (voltage)
º
º
º
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Voltage:
Notches (due to the commutation between phases)
Spikes
Distortion
Notch Width =
2 ⋅ ω ⋅ Ls ⋅ I DC
V f − f ⋅ sin( α )
Phase voltages
Vf-f = peak value of interphase voltage
THDV =
∑ (I
n≥ 2
⋅ n ⋅ ω ⋅ Ls )
2
n
Vphase
Line-line voltage
Vphase = peak value of interphase voltage
In
= n-th harmonic of the AC input current
Ls
= AC source impedance
*Extracted from: N. Mohan-T.M. Undeland-W.P. Robbins, “Power Electronics”, Wiley
Rectifiers - 23
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
The effects on the AC mains (def’s)
⇒
⇒
⇒
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Assuming LD large enough in order that phase R line current iR(t) ~IDC
First assumption: Ls = 0 (instantaneous commutation, µ = 0)
Than considering Ls > 0 (overlapping, µ > 0)
Displacement
Power Factor
DPF = cos( φ 1 ) = cos( α )
vT(t)
vR(t)
iR(t)
i (t)
cos( α + µ ) = cos(R1
α )−
P VRrms ⋅ I Rrms
1 ⋅ cos( φ1 )
PF = =
Power
S
VRrms ⋅ I Rrms
Factor
I Rrms
3
1
PF = rms
⋅ cos( α ) = ⋅ cos( α )
IR
π
IR1 = peak value of fundamental
component of R-Phase line current
Displacement
Power Factor
(Ls >0)
DPF ≅
cos( α ) + cos( α + µ )
2
α
2 ⋅ ω ⋅ Ls
Vf − f
Φ1= α
*Extracted from: N. Mohan-T.M. Undeland-W.P. Robbins, “Power Electronics”, Wiley
vT(t)
vR(t)
iR(t)
iR1(t)
α
µ
*Extracted from: N. Mohan-T.M. Undeland-W.P. Robbins, “Power Electronics”, Wiley
Rectifiers - 24
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Example: existing 12p Magnet PS
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
12-pulses Fully controlled Bridge Rectifier:
⇒ Two 6-p bridges in parallel
⇒ Free-wheeling diodes
⇒ Passive Filter
VBr1
VOut
VBr2
Elettra – Transfer Line Dipole Power Supplies: 2 PS
(200 V / 1080 A, 12p-bridge & 60 V / 1080 A,
6p-bridge) in one cabinet.
Rectifiers - 25
Elettra – Transfer Line Dipole Power Supply
PSB_T2.2: 200 V / 1080 A, 12p fully
controlled bridge – General Scheme.
Elettra – Transfer Line Dipoles: 2 out of 7
dipole magnets. The first one
(arrow) is powered separately
from the others.
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
“Real” 3-Ph.12p Contr. Br. Output
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
⇒ Output voltages of both bridges and PS output voltage (Vf-n = 166 V; Iout = 1000 A)
⇒ Delay angle is α ≈ 22.5°
⇒ Overlapping angle is µ ≈ 3.4° (overlapping time ~190 µs)
⇒ Ls = 23 µH (as calculated from the formula shown before)
Elettra – Transfer Line Dipole Power Supply PSB_T2.2: 200 V / 1080 A, 12p fully controlled bridge (without inter-phase reactor) – Output Voltage waveforms.
Rectifiers - 26
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Protection & Interlock - Switches
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Protection of Thyristors (Diodes):
º
Overcurrent (preventing the junction
temperature to exceed the limit)
• Fuses
• Proper choice of components (ratings 30 to 50%
•
º
higher than specified)
Anode current monitoring acting on the trigger
delay angle
Overvoltage (avoid the reverse break
down and the unwanted turn-on)
• Proper choice of components (ratings 30 to 50%
higher than specified) both VRRM and VDRM
º
Voltage Transients or Surges
Golden Rule: store quickly the surge energy (in C)
and dissipate it slowly (in R)
•
•
Rectifiers - 27
AC Input side surges (e.g. due to opening of the
main contactor) ⇒ “Bucket Circuit”
Reverse Recovery charge of Thyristor (at turnoff) ⇒ “Snubber Circuit”
Note
Sometimes a diode is placed in
parallel to R1 to charge C1 more
efficiently
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Protection & Interlock - Converter
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Main Items:
º Circuit Breaker & Contactor (with “Soft Start”)
º Transformer (overcurrent, over-temperature)
º Thyristor Bridge (over-temperature)
º Passive Filter (excessive ripple, over-temperature)
º Load (overvoltage, over-temperature)
º Personnel (interlock on doors, emergency off button, …)
“Soft Start”
Circuit
Breaker
Rectifiers - 28
Main
Switch
Transformer
Thyristor
Bridge
F-W
Diode
Passive Filter
F-W
Diode
Load
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Example: Elettra’s SR Dipoles’ PS
1.
2.
3.
4.
5.
6.
Circuit Breaker
Transformer
Bridge (a) & Thyristor (b)
Passive Filter
PS cabinet
Magnets
2
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
3
6
1
4
3b
1
Rectifiers - 29
2
3a
4
5
5
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Example: Elettra’s SR quads’ PS
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
º 6-p and 12-p
Elettra – Storage Ring QD and S1Power Supplies Cabinet.
Converters
º Single and
Multiple
converters in
each cabinet
Elettra – Storage Ring QF Power Supply Cabinet.
Elettra – Storage Ring Quadrupoles.
Rectifiers - 30
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Example: Elettra’s SR Steerers’ PS
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Elettra – Storage Ring Combined
H+V corrector.
Elettra – Storage Ring Corrector Power Supply.
Elettra – Storage Ring Correctors Power Supplies Cabinet.
Rectifiers - 31
Linear Multichannel:
º Thyristor PreRegulator
º 12-p Diode Bridge (in
series, “zero” is
common point)
º 14 Channels + 2 spares
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Line Comm. Rectifiers – Pros & Cons
º
º
º
º
º
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Pros
Very well known and established technology with simple structures
The effect of “parasitic” parameters (inductance and capacitance) is low
High Efficiency
High Voltage and High Power Capability
Used as “building blocks” inside Switched Mode converters with “Unity Power
Factor”
Cons
º
º
º
º
º
º
Bandwidth limited (not really important for DC applications)
Power factor depending on firing angle, in any case below 0.75
Strong Harmonic content on input current
Thyristors notches in mains and noise spikes
Large and heavy magnetic elements (transformers, chokes)
Residual ripple at low frequency (300 Hz up) which require large passive
filters and, often, active filters to meet specifications
Rectifiers - 32
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004
Emerging Topologies…
Line Commutated Rectifiers
Roberto Visintini
Sincrotrone Trieste
Goals:
Ø
Ø
Ø
Ø
Ø
Reduce alternating current harmonic content
Improve Power Factor
Better filtering of output current ripple
Higher dynamic response
More flexible control…
ð PWM Techniques
On the other hand:
Ø High Switching Frequency ⇒ parasitic elements ARE important
Ø Sometimes quite complicated structures
Ø EM noise
Rectifiers - 33
CAS – “Power Converters” – Warrington, UK – 12 to 18 May 2004