Download Desing of power sources, converters

Power converters
(not only semiconductor)
Power semiconductor converters
• Equipment for changing quality of electrical energy
(voltage, current, frequency, no. of phases, impedance, etc.)
• Conversion of energy „nearly“ without power losses
• The most often converters:
– rectifiers (diodes, not controlled),
– frequency converters (non-direct, with DC link).
• The most often applications:
– power supply, AC drivers.
History of converters
• electro-mechanical principle
AC vers. DC
– beginning by N. Tesla and T. A. Edison,
– rotating rectifiers, switching of windings, brushes.
• electro-magnetic principle
end of 19th. century
– groups of rotating machines: Ward-Leonardo
History of converters
• Selenium based rectifiers:
– end of 19th. century, low current density
• Mercury based rectifiers:
– current of ions in a steam of Hg,
– Cathode – liquid of Hg, Anode – solid,
Siemens 15 kV / 1A
– range of kA, kV, traction power supply,
– In Prague from 1929 since 1967.
• Thyratrone – units of kV, units of Amperes
Semiconductor converters
• In Czech since the end of 50th. ČKD Elektrotechnika
• In 1964 introduced ČKD Polovodiče – Pankrác
heat sinks,
accessories
discrete devices
silicon wafers
power modules
converters
Converters - overview
rectifiers: AC  DC
inverters: DC  AC
frequency AC  AC converters
(direct/indirect)
DC converter: DC  DC
1 2
RMS (effective) U
u dt
RMS 
voltage:
T

Mean (average) U  1 u.dt
AV
voltage:
T

Most often converter - SMPS
• SMPS – Switch Mode Power
Source,
• all chargers, PC supplies,
household appliances,
U i  4,44 f S B N
N 2 S2
f1


N 1 S1
f2
• basic aim – reducing of mass and
dimension of transformers in
comparison with classic (linear)
power supply,
• product S·B·N stands for a cubic
(volume) of transformer.
Most often converter- DC supply
medium
frequency
transformers
Power supply for industry
• DC sources
• Power Factor Correction
(PFC) – better efficiency
• passive PFC – only
chokes (coils)
Without
PFC
Active
PFC
• active PFC – adapted
DC link with FET, PWM
control, better PF, more
expensive.
Example of high frequency disturbance – influence of SMPS
Basic blocs of SMPS and its frequency
spectrum (bellow). See multiplied PWM
disturbance (x20 kHz)
Disturbance (noise) voltage
of DC brush driver:
M
20
U (mV)
1 kV
15
10
5
f (kHz)
1 ms
0
0
30
60
90
120
150
Detail of voltage on commutator
Noise-suppressing filters for EMC – basic circuit design
• symmetric and asymmetric noise voltage –
more types of L/C necessary,
• impedance matching = for high efficiency,
• reducing of mass and dimensions of coils
• limits for capacitors Cx/Cy = thanks to
leakage currents,
• additional functions = surge protections,
switches, etc.
L
PE
N
L
CY
L1
PE
CX
L1
CY
N
Assembly and mounting of filters
• placing and mounting of filters = big influence on efficiency,
• important is: separating of input/output cables, no loops, minimizing of
lengths/areas,
• filters must be placed directly to input cables,
• good connections between chassis and filters (grounding) is required.
filtr
YES
NO
NO
filtr
filtr
NO
YES
EMC chokes – most simple solutions
• connected in series in powered lines,
• rated for nominal current,
• overdosing of cores (not convenient),
• compensated chokes:
– subtraction of magnetic fluxes,
– not efficient for symmetrical voltage.
I,F
I
F=0
I,F
not-compensated chokes
I
current compensated chokes
Harmonic, inter-harmonic currents
Immediate power
p
V·A
Product of immediate V and I
Apparent power
S
V·A
Product of effective V and I
Active power
P
W
Average value of immediate power p (for
periodical signals)
Non-active power
Q~
V·A, var
Square root of difference between S and P
(just for periodical conditions)
Reactive power
Q
V·A, var
Non active power for linear double-pole
device (R, L, C)
Power factor
l
-
general definitions: P/S
cos 
cos 
-
Just for harmonic signals is P/S equal to cos  !
Phase angle

°, rad
Angle from voltage to current vector
Definitions according ČSN IEC 60050-131: Basic circuit theory
Typical currents - consumption
Non-harmonic conditions (rectifier):
Harmonic conditions (inductive load):
400
400
napětí
voltage
U (V)
I (m A)
proud
current
U (V)
I (m A)
200
200
current
proud
(m s)
0
0
0
5
10
15 (m s)
0
20
-200
-200
-400
-400
5
10
voltage
napětí
15
20
Power triangle, power factor
Harmonic conditions:
• linear devices (R, L, C),
• sinusoidal current.
General non-harmonic conditions:
• nonlinear devices (etc. rectifiers),
• general consumption of current.
S = UI
S
Q = UI sin f
Q~
f
P = UI cos f
P

l  P S  cos
P
l 
S
l
U I
h 1
h h
cos h
UI
P UI1 cos 1 I1

 cos 1
S
UI
I
Deformation and displacing of current/voltage waveforms
400
400
current
proud
U (V)
I (m A)
U (V)
I (m A)
200
200
proud
current
(m s)
0
0
0
-200
(m s)
5
10
15
20
napětí
voltage
-400
Deformation only of current waveform
(low impedance of distribution network)
0
-200
5
10
15
20
napětí
voltage
-400
Deformities of voltage and current
waveforms (simultaneously, distribution
network with higher impedance)
Influence of higher harmonics components
• creation of non-active power, increase of apparent power,
• it makes power factor (l) worse,
• it makes bigger power losses,
• increase of loading for compensation capacitors,
• increase of pulsing moments (AC drivers),
• higher harmonics currents are not compensated (neutral conductor!),
• overloading of neutral conductor.
Reducing of harmonics currents (components of current)
• PFC – Power Factor Correction (removing of root cause)
• compensations (passive/active filters) – removing of consequences
• principle of PFC – prolongation of current consumption (chokes)
pasivní PFC
passive
PFC
aktivní
PFC
active
PFC
Passive PFC
400
100
voltage
napětí
U (V)
I (m A)
200
50
proud
current
(m s)
0
0
5
10
15
20
0
1
11
21
31
-200
Spectrum of harmonics
-400
Consumption of current – time dependence
41
Active PFC
400
100
napětí
voltage
U (V)
I (m A)
200
proud
50
current
(m s)
0
0
5
10
15
20
0
1
-200
-400
Consumption of current – time dependence
11
21
31
Spectrum of harmonics
41
Filters for compensation
Passive filters:
• resonance LC circuits for actual
harmonics,
• short circuit for undesired harmonics,
• disadvantage – accumulation of
harmonics from the nearest networks.
Active filters:
• transistor based PWM converters,
• active filter are producing (by means
of PWM) higher harmonics (IH) and
reactive components (IJ) of the load
current (IZ),
• more complicated circuit.
Main parts of frequency converters
•
backplane board,
•
power modules,
•
aluminum body (heat
sink),
•
cooling fan (at the
bottom),
•
cooling from bottom to
the top,
•
control circuits,
keyboard at front side.
• aluminum body and plastics cover
• control panel, keyboard – on the top.
Cooling of modules
Vertical channels for cooling
Standard channels and temperature
distribution on the heat-sink.
Big power module with water/liquid
cooling
Cooling cells with meander channels
Six independent modules on cooling
board
Typical devices for converters
•
•
•
•
modules – integrated semiconductor devices,
cooling – passive/active = forced air-flow,
inductance-less housing,
potential-free
copper bases.
•
•
•
•
DC link (circuit) – battery of electrolytic capacitors,
electrolytic cap. – up to 450/500 V,
102 mF / 500 V, endurance up 600 V,
outlets – screws or SNAP-IN for
soldering into PCB.
Unconventional converters (I)
Up/down DC converters:
• for cars/automotive …12/24 VDC
• for power supply… 12VDC / 230 VAC
• massive outlets (terminals)
• heat transfer through whole body
• compact design
Unconventional converters (II)
Traction converter for Czech
Railways (CZ train type 560)
• supply voltage 2x 465 V
• output voltage 730 V
• output current 630 A (permanently)
• output current 1200 A (1 min)
• nominal power 420 kW permanently
• 465 kW per hour
• IGCT thyristors
• operating frequency 600 Hz
• active air cooling 4000 m3 / hour
• dimensions 1015 × 930 × 1250 mm
• weight 460 kg
Unconventional converters (III)
Extensible rectifier for underground in
Prague
• installed at line C
• three-phase bridge, all diodes made as
pairs
• input voltage 660 V AC / 50 Hz
• output voltage 884 V DC
• max. input voltage 2000 V
• output current IDC = 3000 A (permanently)
• IDC = 4500 A (2 hour)
• IDC = 9000 A (1 min.)