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PART 1 VARIABLE SPEED DRIVE IN PUMPING STATIONS: ADVANTAGES PART 2 SPEED CONTROL IN INDUCTION MOTORS.

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Presentation on theme: "PART 1 VARIABLE SPEED DRIVE IN PUMPING STATIONS: ADVANTAGES PART 2 SPEED CONTROL IN INDUCTION MOTORS."— Presentation transcript:

1 PART 1 VARIABLE SPEED DRIVE IN PUMPING STATIONS: ADVANTAGES PART 2 SPEED CONTROL IN INDUCTION MOTORS

2 2 Variable Speed Drive in Pumping Stations ADVANTAGES 1 PART 1

3 3 Variable Speed Drive in Pumping Stations ADVANTAGES 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 SUMMARY – PART 1

4 4 Variable Speed Drives in Pumping Stations INTRODUCTION 1

5 5 1.Power Electronics 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. Variable Speed Drive in Pumping Stations ADVANTAGES 1. INTRODUCTION 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.

6 6 Variable Speed Drives in Pumping Stations CRITERIA FOR THE SELECTION OF A VARIABLE SPEED DRIVE 2

7 7 Variable Speed Drive in Pumping Stations ADVANTAGES A.Input Filters B.Input Chokes C.Protection Degree D.Ambient Temperature E.Constant and Variable Torque VSD? F.VSD Applications G.Technical Assistance 2. CRITERIA FOR THE SELECTION OF A VARIABLE SPEED DRIVE [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ]

8 8 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. A. INPUT FILTERS Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ]

9 9 WHAT PHENOMENA PRODUCE THE RADIOFREQUENCIES IN A VSD? A. INPUT FILTERS Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ]

10 10 RFI EMISSION SOURCES IN A VSD A. INPUT FILTERS Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] » 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.

11 11 CABLE LENGTH A. INPUT FILTERS Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] Vcc = Ve · 1,41= 380 · 1,41 = 534 = 500 · 1,41 = 720 = 690 · 1,41 = 972,9 » 40 meters of screened cable. » 150 meters of screened cable.

12 12 USE OF INPUT CHOKES FOR HARMONIC REDUCTION. B. INPUT CHOKES Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] » Power electronics for SD700 series: 90A – 170A.

13 13 USE OF INPUT CHOKES FOR HARMONIC REDUCTION. B. INPUT CHOKES Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] » Power electronics for SD700 series: 210A – 2200A.

14 14 PROTECTION DEGREE FOR EXTRA PROTECTION C. PROTECTION DEGREE Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] » 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.

15 15 OVER-HEATING CHARACTERISTICS OF THE SD700 SERIES D. AMBIENT TEMPERATURE Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] Operation current at 45º Overload peak for 1 sec. Overload for 30 sec. at 50º Operation current at 40º Operation current at 50º Overload for 60 sec. at 40º

16 16 D. AMBIENT TEMPERATURE Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] ENVIRONMENTAL TEMPERATURE Power Electronics Power Electronics Variable Speed Drives are prepared to resist the hardest environmental working conditions. 50ºC They CAN RESIST TILL 50ºC AMBIENT TEMPERATURE WITHOUT OVER-SIZING THE VARIABLE SPEED DRIVE.

17 17 » Competitors Variable Speed Drive in Pumping Stations ADVANTAGES E. CONSTANT TORQUE AND VARIABLE TORQUE THERMAL SHOT (85ºC) 15 kw 11 kw CONSTANT TORQUE VARIABLE TORQUE OVERLOAD 1.5In (40ºC) OVERLOAD 1.1In (40ºC) Temperature 60ºC THERMAL SHOT (85ºC) 15 kw 11 kw CONSTANT TORQUE VARIABLE TORQUE OVERLOAD 1.5In (50ºC) OVERLOAD 1.25 In (40ºC) Temperature 60ºC Temperature 70ºC Temperature 80ºC Power Electronics » Power Electronics [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ]

18 18 Variable Speed Drive in Pumping Stations ADVANTAGES E. CONSTANT TORQUE AND VARIABLE TORQUE [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] POWER AT CONSTANT TORQUE POWER AT VARIABLE TORQUE P.V.P MODEL A MODEL B 1518,5115

19 19 F. VARIABLE SPEED DRIVE APPLICATIONS Variable Speed Drive in Pumping Stations ADVANTAGES [ BACK TO THE CRITERIA ][ BACK TO THE CRITERIA ] 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…

20 20 Variable Speed Drives in Pumping Stations ENERGY SAVING IN PUMPS AND FANS 3

21 TYPICAL PUMPS AND FANS CURVES. 3. ENERGY SAVING IN PUMPS AND FANS WITH VSD Variable Speed Drive in Pumping Stations ADVANTAGES HEIGHT, POWER AND EFFICIENCY H (m) FLOW

22 MOVEMENT OF THE PUMP CURVE IN ACCORDANCE WITH THE SPEED DROP. 3. ENERGY SAVING IN PUMPS AND FANS WITH VSD Variable Speed Drive in Pumping Stations ADVANTAGES H n nom 0.8 n nom 0.7 n nom 0.9 n nom Q (l/s)

23 MOVEMENT OF THE POWER AND EFFICIENCY CURVES IN ACCORDANCE WITH THE SPEED DROP. 3. ENERGY SAVING IN PUMPS AND FANS WITH VSD Variable Speed Drive in Pumping Stations ADVANTAGES p Q Power Efficiency

24 BASIC RELATIONSHIPS FOR THE POWER CONTROL. 3. ENERGY SAVING IN PUMPS AND FANS WITH VSD Variable Speed Drive in Pumping Stations ADVANTAGES 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

25 EFFICIENCY OF PUMPS WITH VARIABLE SPEED DRIVE. 3. ENERGY SAVING IN PUMPS AND FANS WITH VSD Variable Speed Drive in Pumping Stations ADVANTAGES 50% 60% 70% 80% 85% 80% 88% 87% 85% 87% 30% 1 X n 0.9 X n 0.8 X n 0.7 X n 0.6 X n 0.5 X n 0.4 X n N = 1480 RPM Efficiency curves Curves H – Q System curves Q flow m 3 /min

26 26 Variable Speed Drives in Pumping Stations METHODS FOR FLOW CONTROL 4

27 27 Variable Speed Drive in Pumping Stations ADVANTAGES A.Valve Control B.By – Pass Control C.Start – Stop Control (On / Off) D.Variable Speed Drive 4. METHODS FOR FLOW CONTROL [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ][ SHOW ] [ SHOW ][ SHOW ]

28 28 A. VALVE CONTROL. CHARACTERISTICS. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES » 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 ][ BACK TO THE LIST ]

29 29 A. VALVE CONTROL. GRAPHIC. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES STATIC height 20 meters Height in m H 2 O n = 1480 RPM Efficiency curves H-Q curves System curves Q Flow m 3 /min 100% Flow50% Flow 100%90% 80% 70%60%50% 80 FLOW 1 X n 0.9 X n 0.8 X n 0.7 X n 0.6 X n 0.5 X n 0.4 X n

30 30 A. VALVE CONTROL. GRAPHIC. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES Q FLOW BOTTLENECK INCREASES 1 Q HEIGHT H OPERATIONAL POINT WITHOUT BOTTLENECK 7 POWER KW 2 3

31 31 B. BY - PASS CONTROL. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES » 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. Q FLOW BY-PASS EFFECT Q HEIGHT H OPERATIONAL POINT WITHOUT BY-PASS POWER KW System curves Pump H – Q curves Efficiency curves [ BACK TO THE LIST ][ BACK TO THE LIST ]

32 32 C. START – STOP CONTROL (On / Off). CHARACTERISTICS. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES » 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 ][ BACK TO THE LIST ]

33 33 D. VARIABLE SPEED DRIVE CONTROL. CHARACTERISTICS. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES » 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 ][ BACK TO THE LIST ]

34 34 D. VARIABLE SPEED DRIVE CONTROL. GRAPHIC. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES STATIC height 20 meters Height in m H 2 O n = 1480 RPM Efficiency curves H – P curves System curves Q Flow m 3 /min kPa 637 kPa REFERENCE 1 X n 0.9 X n 0.8 X n 0.7 X n 0.6 X n 0.5 X n 0.4 X n 1400 RPM PID 0

35 35 D. VARIABLE SPEED DRIVE CONTROL. TABLE. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES SPEED DROP 9 8 Q HEIGHT H OPERATIONAL POINT AT FULL LOAD Q FLOW POWER KW

36 36 D. VARIABLE SPEED DRIVE CONTROL. ENERGY MISUSE. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES POWER LOSSES HEIGHT VALVES SYSTEM FREQUENCY CONVERTER REDUCED SPEED MISUSED POWER USEFUL POWER STATIC HEIGHT SET POINT

37 37 D. VARIABLE SPEED DRIVE CONTROL. COMPARATIVE CURVES AND POWER REQUIREMENTS. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES FLOW (%) POWER (%) A: Control using Variable Speed Drive. B: Control using valve adjusting.

38 38 D. VARIABLE SPEED DRIVE IN WELLS. 4. METHODS FOR FLOW CONTROL Variable Speed Drive in Pumping Stations ADVANTAGES WINTER SUMMER

39 39 Variable Speed Drives in Pumping Stations NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY SAVING FIELD 5

40 40 ANALYSIS OF EXISTING SYSTEMS A. Type of control B. Height curves and flow of the system 5. NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY SAVING FIELD Variable Speed Drive in Pumping Stations ADVANTAGES 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

41 41 IF WE DO NOT HAVE COMPLETE INFORMATION, THE FOLLOWING DATA COULD BE USEFUL 5. NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY SAVING FIELD Variable Speed Drive in Pumping Stations ADVANTAGES A.HEIGHT / FLOW CURVES OR CHARACTERISTICS OF THE SYSTEM B.REQUIRED FLOWS AND OPERATION CYCLES C.FLUID OR GAS DENSITIES D.VALUES OF STATIC AND DYNAMIC HEIGHT E.PUMP OR FAN POWER MINIMUM INFORMATION REQUIRED (GRAPHICS USE) A.REQUIRED FLOWS AND OPERATION CYCLES B.PUMP OR FAN POWER (DIFFERENT FLOWS)

42 42 Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 2 PART 2

43 43 Speed Control in Induction Motors INTRODUCTION 1

44 44 Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 1.Introduction 2.Induction motors Control Outlines 3.Speed control in a Squirrel Cage Motor 4.Electronic Outlines for A.C. Motor Control SUMMARY – PART 2

45 45 1.Induction motor control outlines: variable speed drive and softstarters 2.Power Electronics 2.Power Electronics technology and experience in power electronics Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 1. INTRODUCTION 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

46 46 Speed Control in Induction Motors INDUCTION MOTORS CONTROL OUTLINES 2

47 47 INDUCTION MOTORS The induction motor (asynchronous or squirrel cage), is made up of two main parts: The ROTOR, fixed along an axis The STATOR 2. INDUCTION MOTORS CONTROL OUTLINES Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS

48 48 INDUCTION MOTORS The rotor is built with electronically short-circuit bars through rings at the edges, which form the squirrel cage 2. INDUCTION MOTORS CONTROL OUTLINES Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS

49 49 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. 2. INDUCTION MOTORS CONTROL OUTLINES Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS

50 50 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. 2. INDUCTION MOTORS CONTROL OUTLINES Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS ROTATING FIELD

51 51 Speed Control in Induction Motors SPEED CONTROL IN A SQUIRREL CAGE MOTOR 3

52 52 SPEED CONTROL A squirrel cage motor is a constant speed motor. poles frequency supply But speed can be controlled acting on the number of poles of the motor and the frequency supply. 3. SPEED CONTROL IN A SQUIRREL CAGE MOTOR Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS TORQUE – SPEED RELATIONSHIP MOTOR TORQUE MAXIMUM TORQUE STARTING TORQUE MOTOR SPEED » Torque – Speed curve in a induction motor MOTOR CURRENT MOTOR SPEED STARTING CURRENT NO LOAD CURRENT » Current – Speed curve

53 53 SPEED CONTROL Method used by electronic speed controllers  To vary the frequency supply of the motor. 3. SPEED CONTROL IN A SQUIRREL CAGE MOTOR Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 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.

54 54 Speed Control in Induction Motors ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL 4

55 55 FREQUENCY SUPPLY VARIATION Torque – speed curve evolution when the frequency supply varies. 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS » Torque – Speed curve % OF NOMINAL TORQUE MOTOR SPEED

56 56 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS WHY V/Hz CONSTANT? Equivalent circuit per phase can be represented according to: I R : 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. I M : “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.

57 57 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS WHY V/Hz CONSTANT? Vector diagram of the motor current. Magnetizing current I M 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. Real current (Torque) IT Total Current Imaginary current (Magnetizing) Real current (Torque) IT Total Current Imaginary current (Magnetizing) cos  = Power factor » At full load » At medium load

58 58 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS WHY V/Hz CONSTANT? Controlling the voltage applied to the stator (E 1 ) it is possible to control the magnetizing current (I M ) and therefore the flux. 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 1 =Supply voltage f = Supply frequency L S =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.

59 59 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 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 50Hz OUTPUT FREQUENCY AREA WHERE THE MAGNETIC FIELD MAKES WEAKER 100% OUTPUT VOLTAGE 50Hz OUTPUT FREQUENCY STARTING VOLTAGE » Voltage – Frequency relationship in the drive» Voltage compensation at reduced speeds

60 60 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS DIAGRAM BLOCK FOR A VARIABLE SPEED DRIVE

61 61 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS INVERTER CIRCUIT Output waveforms of the inverter bridge

62 62 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS CURRENT IN THE MOTOR WITH SEMI-SQUARED VOLTAGE » Output voltage (quasi-rectangular wave) Transistor current Free flow current » Output motor current

63 63 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS MODULATION AND WAVE SHAPES. OUTPUT VOLTAGE » Modulation and waveforms of the output voltage CARRIER WAVE SINUSOIDAL WAVE REFERENCE SIGNAL SUPERIOR TRANSISTOR ON INFERIOR TRANSISTOR ON INVERTER OUTPUT VOLTAGE (REGARDING TO THE MIDDLE POINT IN THE DC BUS) OUTPUT VOLTAGE BETWEEN PHASES PWM

64 64 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS OUTPUT WAVES MODULATION » Output voltage modulation 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.

65 65 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS OUTPUT WAVES MODULATION » Output voltage modulation The width and the number of hollows are electronically adjusted in order to reduce the output voltage as long as the frequency diminishes. vector space modulation New technology: vector space modulation  better wave shapes and less commutations.

66 66 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS VECTOR SPACE MODULATION » 3-Phase vector A system of 3-phasic senoidal waves can be represented through three rotating vectors (phasors). VCVC N VAVA VEVE Frequency Rotation speed (rev/sec)  Frequency Status in a cycle Instantaneous position  Status in a cycle Voltage amplitude Vector length  Voltage amplitude

67 67 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 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

68 68 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 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 Advantages of the IGBT : Less voltage saturation Higher commutation frequencies Higher overload capability Less power demand in the motor circuit

69 69 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS 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.

70 70 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS MONOPHASIC DEVICES » Wiring connections for 230/400V motors 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. Drive with single- phase input of 230Vac.

71 71 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS REGENERATION Current operation Motor operation Generator operation Generator torque Motor Torque 0 N2 N1 speed slip +ve -ve torque +ve

72 72 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS LOADS TYPES. CONSIDERATIONS Before choosing the size of the motor and VSD, it is necessary to understand the torque- speed characteristics for every single load. 100% Motor speed Constant Torque Constant Power TORQUE POWER POWER TORQUE 100% 200% 50% Magnetic field makes weaker Available TORQUE peak POWER TORQUE Motor speed 50Hz 100Hz 100% 200% 63% Continuous Torque (limited due to the motor cooling) » Relation (%) between torque and power » Torque loss due to motor cooling

73 73 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS BASIC LOADS TYPES Constant power load  Constant power load  The torque required by the load increases as the speed decreases. Constant power (mills, winding machines) Constant load torque  Constant load torque  Constant torque at any speed (transport bands, presses of printers, crane and hoist, …etc) » Load at constant power» Load at constant torque TORQUE Area for intermittent operation Area for continuous operation Continuous torque Required resistant torque Area for intermittent operation Available torque peak

74 74 4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS TORQUE – SPEED RELATIONSHIP » Torque proportional to the Speed» Torque proportional to the Square of the Speed

75 Thanks for your attention Presentation Variable Speed Drives in Pumping Systems: Advantages Speed Control in Induction Motors Realization Pilar Navarro Organization Marketing Department ©2006 Power Electronics España, S.L.


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