Transcript speed control - Power Electronics

PART 1 VARIABLE SPEED DRIVE IN PUMPING STATIONS: ADVANTAGES
PART 2 SPEED CONTROL IN INDUCTION MOTORS
1
Variable Speed Drive in Pumping Stations
ADVANTAGES
PART 1
2
Variable Speed Drive in Pumping Stations
ADVANTAGES
SUMMARY – PART 1
1.
Introduction
2.
Criteria for the selection of the Variable
Speed Drives
3.
Energy saving in pumps and fans with
Variable Speed Drives
3.1 Typical pump and fan curves
3.2 Movement of the pump curve in accordance
with the speed drop
3.3 Movement of the power and efficiency curves
in accordance with the speed drop
3.4 Basic relationships for the power control
3.5 Efficiency of pumps with VSD
4.
Methods for flow control
5.
Needed information for a correct
consulting in the energy saving field
3
1
Variable Speed Drives in Pumping Stations
INTRODUCTION
4
Variable Speed Drive in Pumping Stations
ADVANTAGES
1. INTRODUCTION
1. Power Electronics offers to its
clients optimization options for the
production process through the
application of variable speed
drives and softstarters in a wide
variety of industrial fields.
2. As a result of the application of
variable speed drives and
softstarters a spectacular raise of
the quality of the product and an
absolute improvement of the
mechanical and electrical
maintenance of the Company.
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2
Variable Speed Drives in Pumping Stations
CRITERIA FOR THE SELECTION OF A
VARIABLE SPEED DRIVE
6
Variable Speed Drive in Pumping Stations
ADVANTAGES
2. CRITERIA FOR THE SELECTION OF A VARIABLE SPEED DRIVE
A. Input Filters
[ SHOW ]
B. Input Chokes
[ SHOW ]
C. Protection Degree
[ SHOW ]
D. Ambient Temperature
[ SHOW ]
E. Constant and Variable Torque VSD?
[ SHOW ]
F. VSD Applications
[ SHOW ]
G. Technical Assistance
[ SHOW ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
A. INPUT FILTERS
WHAT IS ELECTROMAGNETIC COMPATIBILITY?
It is a concept linked to any electronic device.
This concept means the ability of a device to avoid the generation of interferences above
a defined dB level.
It means the measure of its immunity versus a defined dB level.
[ BACK TO THE CRITERIA ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
A. INPUT FILTERS
WHAT PHENOMENA PRODUCE THE RADIOFREQUENCIES IN A VSD?
[ BACK TO THE CRITERIA ]
9
Variable Speed Drive in Pumping Stations
ADVANTAGES
A. INPUT FILTERS
RFI EMISSION SOURCES IN A VSD
» The RFI can be
radiated and
conduced.
» The conduction can
be produced through
the Motor Cables,
through the Power
Supply Cables and
through the Earth
Connections.
[ BACK TO THE CRITERIA ]
10
Variable Speed Drive in Pumping Stations
ADVANTAGES
A. INPUT FILTERS
CABLE LENGTH
» 40 meters of screened cable.
Vcc = Ve · 1,41
= 380 · 1,41 = 534
= 500 · 1,41 = 720
= 690 · 1,41 = 972,9
» 150 meters of screened cable.
[ BACK TO THE CRITERIA ]
11
Variable Speed Drive in Pumping Stations
ADVANTAGES
B. INPUT CHOKES
USE OF INPUT CHOKES FOR HARMONIC REDUCTION.
» Power electronics for SD700 series: 90A – 170A.
[ BACK TO THE CRITERIA ]
12
Variable Speed Drive in Pumping Stations
ADVANTAGES
B. INPUT CHOKES
USE OF INPUT CHOKES FOR HARMONIC REDUCTION.
» Power electronics for SD700 series: 210A – 2200A.
[ BACK TO THE CRITERIA ]
13
Variable Speed Drive in Pumping Stations
ADVANTAGES
C. PROTECTION DEGREE
PROTECTION DEGREE FOR EXTRA PROTECTION
» IP54 protection impedes that dust or any
other particles damage the devices.
» In this case, splashing occurred near the
motor don’t damage our products.
[ BACK TO THE CRITERIA ]
14
Variable Speed Drive in Pumping Stations
ADVANTAGES
D. AMBIENT TEMPERATURE
OVER-HEATING CHARACTERISTICS OF THE SD700 SERIES
Drive Current (%)
Over-heating Characteristics for SD700 Series
Overload peak for 1 sec.
200
175
Overload for 60 sec. at 40º
Overload for 30 sec. at 50º
150
Operation current at 40º
Operation current at 45º
125
100
Overload peak 1 sec.
Overload 30 sec. at 50º
Operation current at 40º
Operation current at 45º
Operation current at 50º
Operation current at 50º
75
50
25
0
0
25
50
75
400
Hz
[ BACK TO THE CRITERIA ]
15
Variable Speed Drive in Pumping Stations
ADVANTAGES
D. AMBIENT TEMPERATURE
ENVIRONMENTAL TEMPERATURE
Power Electronics Variable Speed Drives are prepared to resist the hardest
environmental working conditions.
They CAN RESIST TILL 50ºC AMBIENT TEMPERATURE WITHOUT OVER-SIZING
THE VARIABLE SPEED DRIVE.
[ BACK TO THE CRITERIA ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
E. CONSTANT TORQUE AND VARIABLE TORQUE
Temperature 80ºC
VARIABLE
TORQUE
15 kw
Temperature 60ºC
THERMAL SHOT (85ºC)
THERMAL SHOT (85ºC)
OVERLOAD 1.1In
(40ºC)
CONSTANT TORQUE
11 kw
» Competitors
Temperature 70ºC
OVERLOAD 1.5In
Temperature 60ºC
(40ºC)
VARIABLE
TORQUE
15 kw
CONSTANT
TORQUE
OVERLOAD 1.25 In
(40ºC)
OVERLOAD 1.5In
(50ºC)
11 kw
» Power Electronics
[ BACK TO THE CRITERIA ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
E. CONSTANT TORQUE AND VARIABLE TORQUE
MODEL A
MODEL B
POWER AT
CONSTANT
TORQUE
POWER AT
VARIABLE
TORQUE
P.V.P
11
15
15
18,5
100
115
[ BACK TO THE CRITERIA ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
F. VARIABLE SPEED DRIVE APPLICATIONS
CONTROL
The Variable Speed Drives extend the regulation field with regard to:
Flow fluctuation
Pressure control
Temperature control
Level control…
APPLICATIONS
Several applications can be considered:
Pumping stations
Pressure groups
Irrigation systems
High concentration of carbonic monoxide, oxygen…
Heating and Air conditioning…
[ BACK TO THE CRITERIA ]
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3
Variable Speed Drives in Pumping Stations
ENERGY SAVING IN PUMPS AND FANS
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Variable Speed Drive in Pumping Stations
ADVANTAGES
3. ENERGY SAVING IN PUMPS AND FANS WITH VSD
3.1 TYPICAL PUMPS AND FANS CURVES.
HEIGHT, POWER AND EFFICIENCY
H (m)
FLOW
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Variable Speed Drive in Pumping Stations
ADVANTAGES
3. ENERGY SAVING IN PUMPS AND FANS WITH VSD
3.2 MOVEMENT OF THE PUMP CURVE IN ACCORDANCE WITH THE SPEED DROP.
H
nnom
16
14
12
10
8
0.9 n nom
0.8 n nom
0.7 n nom
6
4
2
20
40
60
80
100
120
140
Q (l/s)
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Variable Speed Drive in Pumping Stations
ADVANTAGES
3. ENERGY SAVING IN PUMPS AND FANS WITH VSD
3.3 MOVEMENT OF THE POWER AND EFFICIENCY CURVES IN ACCORDANCE WITH
THE SPEED DROP.
p
Power
Efficiency
Q
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Variable Speed Drive in Pumping Stations
ADVANTAGES
3. ENERGY SAVING IN PUMPS AND FANS WITH VSD
3.4 BASIC RELATIONSHIPS FOR THE POWER CONTROL.
POWER (W) = r x g x H x Q x ŋ-1
r = Density (Kg/m³)
g = Gravity (9.81m/s²)
H = Height (m)
Q = Flow (m³/s)
ŋ = Efficiency
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Variable Speed Drive in Pumping Stations
ADVANTAGES
3. ENERGY SAVING IN PUMPS AND FANS WITH VSD
3.5 EFFICIENCY OF PUMPS WITH VARIABLE SPEED DRIVE.
80
N = 1480 RPM
1Xn
30%
50%
60%
70%
70
80%
85%
0.9 X n
87%
60
88%
50
87%
85%
0.8 X n
80%
40
0.7 X n
30
0.6 X n
20
0.5 X n
Efficiency curves
0.4 X n
10
Curves H – Q
System curves
0
10
20
30
40
Q flow
m3/min
25
4
Variable Speed Drives in Pumping Stations
METHODS FOR FLOW CONTROL
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
A. Valve Control
[ SHOW ]
B. By – Pass Control
[ SHOW ]
C. Start – Stop Control (On / Off)
[ SHOW ]
D. Variable Speed Drive
[ SHOW ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
A. VALVE CONTROL. CHARACTERISTICS.
» Pumps always work at maximum speed.
» The transversal section of the conduct or pipe.
» Pressure increases when pipe cross section is reduced.
» Problems with the over-heating of the fluids.
» Cavitation, turbulences.
[ BACK TO THE LIST ]
28
Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
A. VALVE CONTROL. GRAPHIC.
80
Height in m H2O
FLOW
1Xn
STATIC height 20 meters
70
0.9 X n
60
50
40
30
20
0.8 X n
0.7 X n
0.6 X n
0.5 X n
n = 1480 RPM
Efficiency curves
H-Q curves
System curves
0.4 X n
10
0
80%
60%
100%
50%
90%
70%
20
10
50% Flow
30
100% Flow
40
Q Flow m3/min
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
A. VALVE CONTROL. GRAPHIC.
BOTTLENECK INCREASES
H
3
2
OPERATIONAL POINT WITHOUT BOTTLENECK
1
Q
KW
POWER
7
FLOW
Q
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
B. BY - PASS CONTROL.
H
OPERATIONAL POINT
WITHOUT BY-PASS
BY-PASS EFFECT
Q
System curves
Pump H – Q curves
POWER
Efficiency curves
» This is the least
efficient method with
regard to the energy
consumption.
» The pump always
works at maximum
power without taking
into account the flow
level.
KW
Q
FLOW
[ BACK TO THE LIST ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
C. START – STOP CONTROL (On / Off). CHARACTERISTICS.
» It is recommendable for those systems in which the pumping flow is constant.
» It leads to mechanical and electrical stress.
» It does not allow to maintain constant parameters, a small or big variation always
exists.
» Over-pressure during the starting.
» Water hammering during the stop.
[ BACK TO THE LIST ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
D. VARIABLE SPEED DRIVE CONTROL. CHARACTERISTICS.
» It allows to keep constant those parameters to be controlled.
»It provides a reduction of absorbed power by the motor.
» Compensation of reactive power of the motor.
» Reduction of mechanical and electrical failures.
» Reduction of civil construction cost in pumping systems.
[ BACK TO THE LIST ]
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
D. VARIABLE SPEED DRIVE CONTROL. GRAPHIC.
80 Height in m H2O
1Xn
637 kPa
60
490 kPa
STATIC height 20 meters
70
0.9 X n
50 0.8 X n
0.7 X n
40
PID
REFERENCE
30 0.6 X n
20 0.5 X n
10
0
n = 1480 RPM
Efficiency curves
0.4 X n
H – P curves
System curves
0
10
20
30
40
Q Flow
m3/min
1400
RPM
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
D. VARIABLE SPEED DRIVE CONTROL. TABLE.
H
OPERATIONAL POINT AT FULL LOAD
8
SPEED DROP
9
Q
7
KW
POWER
8
9
Q
FLOW
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
D. VARIABLE SPEED DRIVE CONTROL. ENERGY MISUSE.
HEIGHT
VALVES SYSTEM
FREQUENCY
CONVERTER
POWER
LOSSES
MISUSED
POWER
STATIC
HEIGHT
USEFUL
POWER
SET POINT
REDUCED
SPEED
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
D. VARIABLE SPEED DRIVE CONTROL. COMPARATIVE CURVES AND POWER
REQUIREMENTS.
POWER
(%)
A: Control using Variable Speed Drive.
B: Control using valve adjusting.
FLOW (%)
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Variable Speed Drive in Pumping Stations
ADVANTAGES
4. METHODS FOR FLOW CONTROL
D. VARIABLE SPEED DRIVE IN WELLS.
SUMMER
WINTER
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5
Variable Speed Drives in Pumping Stations
NEEDED INFORMATION FOR A CORRECT
CONSULTING IN THE ENERGY SAVING FIELD
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Variable Speed Drive in Pumping Stations
ADVANTAGES
5. NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY
SAVING FIELD
ANALYSIS OF EXISTING SYSTEMS
A. Type of control
B. Height curves and flow of the system
PUMP OR FAN DATA
A. Pump and fans efficiency curves
B. Fan or pump power
C. Motor curves
PROCESS INFORMATION
A. Fluid or gas density
B. Flows and required duty cycles
C. Static and dynamic height values
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Variable Speed Drive in Pumping Stations
ADVANTAGES
5. NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY
SAVING FIELD
IF WE DO NOT HAVE COMPLETE INFORMATION, THE FOLLOWING DATA COULD
BE USEFUL
A.
B.
C.
D.
E.
HEIGHT / FLOW CURVES OR CHARACTERISTICS OF THE SYSTEM
REQUIRED FLOWS AND OPERATION CYCLES
FLUID OR GAS DENSITIES
VALUES OF STATIC AND DYNAMIC HEIGHT
PUMP OR FAN POWER
MINIMUM INFORMATION REQUIRED (GRAPHICS USE)
A. REQUIRED FLOWS AND OPERATION CYCLES
B. PUMP OR FAN POWER (DIFFERENT FLOWS)
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2
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
PART 2
42
1
Speed Control in Induction Motors
INTRODUCTION
43
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
SUMMARY – PART 2
1. Introduction
2. Induction motors Control Outlines
3. Speed control in a Squirrel Cage
Motor
4. Electronic Outlines for A.C. Motor
Control
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
1. INTRODUCTION
1. Induction motor control outlines:
variable speed drive and
softstarters
2. Power Electronics technology
and experience in power
electronics
3. Basic Outlines:
- To know the outlines of the
induction motors
- Variable speed drives
performance
- Softstarters performance
- Harmonics in industrial provisions
- Electromagnetic compatibility of
VSD
- Energy saving in pumps and fans
- Applications and control
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2
Speed Control in Induction Motors
INDUCTION MOTORS CONTROL OUTLINES
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
2. INDUCTION MOTORS CONTROL OUTLINES
INDUCTION MOTORS
The induction motor (asynchronous or squirrel cage), is made up of two main parts:
The ROTOR , fixed along an axis
The STATOR
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
2. INDUCTION MOTORS CONTROL OUTLINES
INDUCTION MOTORS
The rotor is built with electronically
short-circuit bars through rings at
the edges, which form the squirrel
cage
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
2. INDUCTION MOTORS CONTROL OUTLINES
INDUCTION MOTORS
Connecting the motor to a 3-phase
power supply, a rotational magnetic
field it is generated in the stator
(flux).
This is due to:
The physical position of the stator
windings: 3 coils separated
physically 120º.
The current in those windings
diphase 120º electrically.
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
2. INDUCTION MOTORS CONTROL OUTLINES
INDUCTION MOTORS
The flux lines (arrows) induce
currents on the rotor bars.
When a magnetic field acts over a
conductor in which a current flow,
the resultant is a force which
produce the torque and therefore
the motor rotation.
ROTATING FIELD
50
3
Speed Control in Induction Motors
SPEED CONTROL IN A SQUIRREL CAGE
MOTOR
51
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
3. SPEED CONTROL IN A SQUIRREL CAGE MOTOR
SPEED CONTROL
A squirrel cage motor is a constant speed motor.
But speed can be controlled acting on the number of poles of the motor and the
frequency supply.
TORQUE – SPEED RELATIONSHIP
MOTOR
CURRENT
MOTOR
TORQUE
STARTING
CURRENT
MAXIMUM
TORQUE
STARTING
TORQUE
NO LOAD
CURRENT
MOTOR SPEED
MOTOR SPEED
» Torque – Speed curve in a induction motor
» Current – Speed curve
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
3. SPEED CONTROL IN A SQUIRREL CAGE MOTOR
SPEED CONTROL
Method used by electronic speed controllers  To vary the frequency supply of the
motor.
WHY IS VARYING THE FREQUENCY SUPPLY THE BEST METHOD?
 A high performance in the whole range of speeds is obtained
 This method disposes of a continuous variation of the speed, that might be electrically
through control signals such as 0-10VDC o 4-20mA. This makes VSD for A.C. motors to
be the best option for process automation.
 The available motor torque is constant even at low speeds. This offers the possibility
to work with any load.
 It is possible to work with frequencies above 50Hz.
53
4
Speed Control in Induction Motors
ELECTRONIC OUTLINES FOR A.C. MOTOR
CONTROL
54
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
FREQUENCY SUPPLY VARIATION
Torque – speed curve evolution when the frequency supply varies.
% OF NOMINAL
TORQUE
MOTOR SPEED
» Torque – Speed curve
55
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
WHY V/Hz CONSTANT?
Equivalent circuit per phase can be represented according to:
IR: Component of load. “Real” component that flows
through the rotor. This current generates the torque and
therefore increases as the load of the motor increases.
IM: “Imaginary” component, 90º diphased regarding to the
“real” component. Magnetizing current responsible of the
motor flux. It is convenient to keep it constant as the load
varies.
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
WHY V/Hz CONSTANT?
Real current (Torque)
Real current (Torque)
Vector diagram of the motor current.
Imaginary current
(Magnetizing)
» At full load
cos  = Power factor
Imaginary current
(Magnetizing)
» At medium load
Magnetizing current IM is constant regardless of the load.
It is this current which generates the magnetic field in the stator, affecting to the motor
capacity of producing torque.
57
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
WHY V/Hz CONSTANT?
Controlling the voltage applied to the stator (E1) it is possible to control the magnetizing
current (IM) and therefore the flux.
IM 
E1 =
f =
LS =
E1
2 · · f ·L S
Supply voltage
Supply frequency
Magnetizing inductance of the stator
In a electronic speed controller, the motor voltage supply must be adjusted proportionally
to the frequency, so that the magnetization current remains constant.
Increasing the motor speed, the slip (S) decreases and the relative frequency decreases
too. Then the cosR improves, the losses inductance is reduced and e Ir decreases.
E 2 .S
Ir 
R
2
r
 ( X 2 ·S )
2
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
RELATIONSHIP VOLTAGE – FREQUENCY IN A VSD. VOLTAGE COMPENSATION AT
REDUCED SPEEDS
Voltage increase. It is necessary when the load requires a high starting torque (transport
bands, high inertia load, …).
100%
OUTPUT VOLTAGE
AREA WHERE THE MAGNETIC FIELD
MAKES WEAKER
OUTPUT VOLTAGE
100%
STARTING
VOLTAGE
50Hz
OUTPUT FREQUENCY
» Voltage – Frequency relationship in the drive
50Hz
OUTPUT FREQUENCY
» Voltage compensation at reduced speeds
59
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
DIAGRAM BLOCK FOR A VARIABLE SPEED DRIVE
60
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
INVERTER CIRCUIT
Output waveforms of
the inverter bridge
61
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
CURRENT IN THE MOTOR WITH SEMI-SQUARED VOLTAGE
» Output voltage (quasi-rectangular wave)
Transistor Free flow
current
current
» Output motor current
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
MODULATION AND WAVE SHAPES. OUTPUT VOLTAGE
CARRIER WAVE
SINUSOIDAL WAVE
REFERENCE SIGNAL
SUPERIOR TRANSISTOR ON
INVERTER OUTPUT VOLTAGE
(REGARDING TO THE MIDDLE POINT IN THE DC BUS)
INFERIOR TRANSISTOR ON
OUTPUT VOLTAGE BETWEEN
PHASES PWM
» Modulation and waveforms of the output voltage
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
OUTPUT WAVES MODULATION
NOMINAL FREQUENCY – NOMINAL VOLTAGE
A triangular signal is
compared to a senoidal one
in the sinusoidal modulation.
The wave shape of the
current produced in the
motor is very similar to the
senoidal one, with a very
long distortion.
MEDIUM LEVEL FREQUENCY – MEDIUM LEVEL VOLTAGE
» Output voltage modulation
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
OUTPUT WAVES MODULATION
The width and the number of
hollows are electronically
adjusted in order to reduce
the output voltage as long as
the frequency diminishes.
NOMINAL FREQUENCY – NOMINAL VOLTAGE
New technology: vector
space modulation  better
wave shapes and less
commutations.
MEDIUM LEVEL FREQUENCY – MEDIUM LEVEL VOLTAGE
» Output voltage modulation
65
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
VECTOR SPACE MODULATION
A system of 3-phasic
senoidal waves can be
represented through three
rotating vectors (phasors).
VA
Rotation speed (rev/sec)  Frequency
Instantaneous position  Status in a cycle
Vector length  Voltage amplitude
N
V
C
VE
» 3-Phase vector
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
ADVANTAGES OF VECTOR SPACE MODULATION VERSUS SINUSOIDAL
MODULATION

Small content of harmonics in the motor

Small pulsate pairs

Constant frequency modulation

Better use of voltage supply

Adapted to the wave generation using microprocessor
67
Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
ELECTRONIC DEVICES BASED ON COMMUTATION
THYRISTORS  Power semiconductor with PNPN structure. Currently not used.
BIPOLAR TRANSISTORS  Based on NPN or PNP structure.
ISOLATED GATE BIPOLAR TRANSISTORS (IGBT)  the latest generation; control
realized by mean of voltage, the commutation is done by the application of voltage to the
gate.
Advantages of the IGBT:
• Less voltage saturation
• Higher commutation frequencies
• Higher overload capability
• Less power demand in the motor circuit
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
ELECTRONIC CONTROL  THE BRAIN OF THE DRIVE
Functioning:
It receives the required speed signal.
It receives user commands: stop, start…etc.
It generates waveforms modulated in vector space technology.
It commutates the switches.
It controls the current in the motor to protect the drive and the motor from
overloads.
It allows to do the necessary adjustments for one application: acceleration
and deceleration ramps, maximum and minimum speed…etc.
It offers output information: motor current, frequency, start, stop, failure
indication…etc.
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
MONOPHASIC DEVICES
Small motors are designed
with windings of 230Vac.
Drive with 3-phasic
input of 400V 
Control configured with
the voltage and the
frequency of the motor.
WIRING FOR 230V MOTOR CONNECTION
DELTA CONNECTION OF THE TERMINALS
WIRING FOR 400V MOTOR CONNECTION
STAR CONNECTION OF THE TERMINALS
Drive with singlephase input of 230Vac.
» Wiring connections for 230/400V motors
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
REGENERATION
Motor operation
Current operation
Generator operation
torque
Motor Torque
-ve
N2
N1
speed
+ve
0
Generator torque
slip
2
1
0
-1
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
LOADS TYPES. CONSIDERATIONS
Before choosing the size of the motor and VSD, it is necessary to understand the torquespeed characteristics for every single load.
Constant Torque
100%
Constant Power
TORQUE
Magnetic field
makes weaker
POWER
200%
Available TORQUE peak
50%
100%
Continuous Torque
(limited due to the motor
cooling)
63%
100%
200%
Motor speed
» Relation (%) between torque
and power
50Hz
100Hz
Motor speed
» Torque loss due to motor cooling
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
BASIC LOADS TYPES
Constant power load  The torque required by the load increases as the speed
decreases. Constant power (mills, winding machines)
Area for
intermittent Area for
continuous
operation
operation
Available torque
peak
TORQUE
TORQUE
Constant load torque  Constant torque at any speed (transport bands, presses of
printers, crane and hoist, …etc)
Area for
intermittent
operation
Area for
continuous
operation
Available torque
peak
Area for
intermittent
operation
Continuous torque
Required
resistant torque
» Load at constant power
Required resistant torque
Continuous torque
» Load at constant torque
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Speed Control in Induction Motors
VARIABLE SPEED DRIVE & SOFTSTARTERS
4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
TORQUE – SPEED RELATIONSHIP
Area of continuous
operation
Available torque peak
Area of
intermittent
operation
TORQUE
TORQUE
Available torque peak
Area of continuous
operation
Area of
intermittent
operation
Continuous torque
Continuous torque
Speed
» Torque proportional to the Speed
Speed
» Torque proportional to the
Square of the Speed
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Thanks for your attention
Presentation
Variable Speed Drives in Pumping Systems: Advantages
Speed Control in Induction Motors
Realization
Pilar Navarro
Organization
Marketing Department
www.power-electronics.com
©2006 Power Electronics España, S.L.