Power Electronics and Industrial Drives PPT

Power electronics

1. Module 2:CONVERTERS Sem: V Year: III R& A Ms.HEMALATHA .G 20RA211 POWER ELECTRONICS AND INDUSTRIAL DRIVES Assistant Professor ( Sr.G )

2. Course Information Semester: V Academic Year 2025-26 (ODD) Regulations: RR2020 Course Code: 20RA211 Activities Planned Quizzes/One minute test paper Periodic MCQ –online Group presentation/Case studies Demonstrations Software Practice / Simulation Internal Assessment Test End Semester Examination Test Weightage Internal Test 1 ( Aug) 12.5 Internal Test 2 (Oct) 12.5 Active Learning Method (ALM) ( Simulation ,Seminar) 05 Surprise Quiz 05 Assignment test 05 SREC/R&A/HG/20RA211 2

3. Syllabus POWER SEMICONDUCTOR DEVICES Review of power semiconductor devices: Switching characteristics of power transistors - MOSFETS - IGBT - SCR – TRIAC-Thyristor commutation techniques CONVERTERS Converters: Principle of phase control - Half wave and full wave - controlled converter - Effect of source impedance on the performance of converters - Dual converters - Types of AC voltage controllers: Single Phase - Three Phase INVERTERS AND CHOPPERS Single Phase Inverter - full bridge inverter and half bridge inverter - Three Phase Inverter - 180 degree and 120- degree mode - Current source inverters - PWM inverters Techniques -Types: Single and multiple and sinusoidal- DC choppers : Buck- Boost - Buck Boost chopper DC DRIVES Introduction to Electric drive - Basic Elements of Drive – Rating of motors - Conventional and Solid state control of DC drives - DC chopper drives. AC DRIVES Induction motor drives - Control of three phase induction motors using stator voltage and frequency control – variable frequency drive - static rotor resistance control - Slip power recovery schemes - Kramer control method - Scherbius control method Drives for special machines: Stepper motor - BLDC motor - PMDC motor - Servo motor SREC/R&A/HG/20RA211 3

4. 20RA211 POWER ELECTRONICS AND IN DUSTRIAL DRIVES COURSE OUTCOMES On successful completion of the course, students will be able to Course Outcome (CO) Description POs CO 1 Summarize the characteristics of real power semiconductor devices. PO1 CO 2 Describe the concept of AC-DC converters and AC voltage controllers. PO1, PO2 CO 3 Analyze the operating principle of single phase and three phase inverter circuits and describe the various PWM techniques. PO1, PO2,PO3,PO5,PO12 CO 4 Interpret the speed control schemes for DC motor drives. PO1, PO2, PO3,PO5, PO12 CO 5 Illustrate the speed control techniques for AC motor and special electrical machines. PO1,PO2, PO3,PO5,PO7, P O12 SREC/R&A/HG/20RA211 4

5. Text Books 1. Muhamed H. Rashid, “Power Electronics Circuits, Devices and Applications”, 3rd Edition, Prentice Hall India Pvt. Ltd., 2014. 2. Bose.B.K . “Power Electronics and Motor Drives - Advances and Trends”, 3rd Edition, Elsevier Academic Press, 2015 Reference Books 1. Bimbhra P.S, “Power Electronics”, 3rd Edition, Khanna Publishers, 2012. 2. G. K. Dubey, “Fundamentals of Electrical Drives”, Alpha Science; 2nd edition, January 30, 2001 WEB REFERNCES: https://nptel.ac.in/courses/108/102/108102145/ https://nptel.ac.in/courses/108/102/108102046/ https://nptel.ac.in/courses/108/104/108104140/ Text Books and Reference Books SREC/R&A/HG/20RA211 5

6. Motion control is required in large number of industrial and domestic applications. Systems employed for getting the required motion and their smooth control are called Drives. Drives require prime movers like Diesel or petrol engines, gas or steam turbines, hydraulic motors or electric motors. These prime movers deliver the required mechanical energy for getting the motion and its control. Drives employing Electric motors as prime movers for motion control are called Electric Drives. Introduction to Electrical Drives SREC/R&A/HG/20RA211 6

7. modern variable speed electrical drive system has the following components • Electrical machines and loads • Power Modulator • Sources • Control unit • Sensing unit Electrical Machines: Most commonly used electrical machines for speed control applications are the following DC Machines Shunt, series, compound, separately excited DC motors and switched reluctance machines. AC Machines Induction, wound rotor, synchronous, PM synchronous and synchronous reluctance machines. Special Machines Brush less DC motors, stepper motors, switched reluctance motors are used. Basic Elements SREC/R&A/HG/20RA211 7

8. Basic Elements Power Modulators Modulates flow of power from the source to the motor in such a manner that motor is imparted speed-torque characteristics required by the load During transient operation, such as starting, braking and speed reversal, it restricts source and motor currents with in permissible limits. It converts electrical energy of the source in the form of suitable to the motor Selects the mode of operation of the motor (i.e.) Motoring and Braking. Types of Power Modulators In the electric drive system, the power modulators can be any one of the following • Controlled rectifiers (ac to dc converters) • Inverters (dc to ac converters) • AC voltage controllers (AC to AC converters) • DC choppers (DC to DC converters) • Cyclo converters (Frequency conversion) SREC/R&A/HG/20RA211 8

9. Electrical Sources Very low power drives are generally fed from single phase sources. Rest of the drives is powered from a 3 phase source. Low and medium power motors are fed from a 400v supply. For higher ratings, motors may be rated at 3.3KV, 6.6KV and 11 KV. Some drives are powered from battery. Sensing Unit: Speed Sensing Torque Sensing Position Sensing Current sensing and Voltage Sensing from Lines or from motor terminals Torque sensing Temperature Sensing Control Unit: Control unit for a power modulator are provided in the control unit. It matches the motor and power converter to meet the load requirements Basic Elements SREC/R&A/HG/20RA211 9

10. TYPES OF ELECTRIC DRIVES According to Means of Control • Manual • Semi automatic • Automatic According to Dynamics and Transients • Uncontrolled transient period • Controlled transient period According to Mode of Operation • Continuous duty drives • Short time duty drives • Intermittent duty drives According to Number of machines • Individual drive • Group drive • Multi-motor drive Another main classification: • DC drive • AC drive SREC/R&A/HG/20RA211 10

11. The choice of the electric drives There are three classification namely  G roup drive  Individual drive  M ultimotor drive CLASSIFICATION OF ELECTRIC DRIVES WITH FACTOR SREC/R&A/HG/20RA211 11

12. One motor is used as a drive for two or more than machines. The motor is connected to a long shaft. All the other machines are connected to this shaft through belt and pulleys Group drive SREC/R&A/HG/20RA211 12

13. In this drive, there will be a separate driving motor for each process equipment. One motor is used for transmitting motion to various parts or mechanisms belonging to signal equipment. Ex: Lathe One motor used in lathe which rotates the spindle, moves feed with the help of gears and imparts motion to the lubricating and cooling pumps ). Individual drive SREC/R&A/HG/20RA211 13

14. In this type of drive, separate motors are provided for actuating different parts of the driven mechanism. Ex: cranes, drives used in paper mills, rolling mills etc., In cranes, separate motors are used for hoisting, long travel motion and cross travel motion. Multimotor drive SREC/R&A/HG/20RA211 14

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16. ( i) Nature of electric supply Whether AC or DC supply is to be used for supply (ii) Nature of the drive Whether the particular motor is going to drive individual machine or a group of machines (iii)Capital and running cost (iv) Maintenance requirement (v) Space ad weight restrictions (vi) Environment and location (vii) Nature of load Whether the load requires light or heavy starting torque Whether load torque increases with speed remain constant Whether the load has heavy inertia which may require longer straight time FACTORS INFLUENCING THE CHOICE OF ELECTRICAL DRIVES SREC/R&A/HG/20RA211 16

17. viii) Electrical characteristics of motor  Starting characteristics,  running characteristics,  speed control and Braking characteristics (ix) Size, rating and duty cycle of motors Whether the motor is going to the operator for a short time or whether it has to run continuously intermittently or on a variable load cycle (x) Mechanical considerations Type of enclosures, type of bearings, transmission of drive and Noise level. Due to practical difficulties, it may not possible to satisfy all the above considerations. In such circumstances, it is the experience and knowledge background which plays a vital role in the selection of the suitable drive. The following points must be given utmost important for the selection of motor. The factors are Nature of the mechanical load driven Matching of the speed torque characteristics of the motor with that of the load Starting conditions of the load. FACTORS INFLUENCING THE CHOICE OF ELECTRICAL DRIVES SREC/R&A/HG/20RA211 17

18. • Continuous or Constant loads: In this type load occurs for a long time under the same conditions. Eg. Fan, Paper making machine • Continuous variable loads: The load is variable over a period of time but occurs repetitively for a long duration. Eg. Metal cutting lathes, conveyors. • Pulsating loads: The load is continuously variable. Eg. Reciprocating pumps, compressors • Impact loads: These are peak loads occur at regular intervals of time. Eg. Rolling mils, Presses, Shearing machine, Forging hammers • Short time intermittent loads: The load appears periodically identical duty cycles, each consisting of a period of applications of load. Eg. Cranes, Hoists, Elevators • Short time loads: A constant load appears on the drive and the system rests for the remaining period of cycle. Eg. Motor – generator sets for charging batteries, house hold equipments . LOADING CONDITIONS SREC/R&A/HG/20RA211 18

19. • Continuous duty • Continuous duty, variable load • Short time duty • Intermittent periodic duty • Intermittent periodic duty with starting • Intermittent periodic duty with starting and braking Continuous duty • Operation at constant load for a long duration of time • N indicates duration of operation. CLASSES OF DUTY SREC/R&A/HG/20RA211 19

20. Continuous duty, variable load • It denotes a sequence of identical duty cycles each consisting of a period of operation at load and period of no load Short time duty It denotes operation at constant load during a given time, then followed by rest of sufficient duration . CLASSES OF DUTY SREC/R&A/HG/20RA211 20

21. Intermittent periodic duty: Sequence of identical duty cycles each consisting of a period of operation at a constant load and then a period of rest. Intermittent periodic duty with starting: This consists of a load at start, then constant load and then a period of rest CLASSES OF DUTY SREC/R&A/HG/20RA211 21

22. Intermittent periodic duty with starting and braking: This indicates a load as “Intermittent periodic duty with starting” along with a period of braking and then a rest period. CLASSES OF DUTY SREC/R&A/HG/20RA211 22

23. The heating and Electric Motor Cooling calculation are based on the following The machine is considered to be a homogeneous body having a uniform temperature gradient. All the points at which the heat is generated have the same temperature. All the points at which the heat is dissipated to the cooling medium are also at the same temperature. Heat dissipation taking place is proportional to the difference of temperatures of the body and surrounding medium. No heat is radiated. The rate of dissipation of heat is constant at all temperatures Electric Motor Cooling and Heating 23

24. Under these assumptions a machine develops heat internally at a uniform rate and gives it to the surroundings proportional to the temperature rise. It can be shown that the temperature rise of a body follows an exponential law. Assuming the heat developed is proportional to the losses, we have the heat balance equation. SREC/R&A/HG/20RA211 24

25. W – is the power loss on the motor responsible for heat, Watts. G – weight of active parts of the motor in kg s – specific heat of the material of the body in J/degree/kg A – cooling surface in m2 λ – specific heat dissipation or emissivity in J/s/m2/degree difference in temperature θ – is temperature rise of the body dθ – temperature rise in a small interval dt SREC/R&A/HG/20RA211 25

26. The total heat generated in the body (W dt ) is equal to the sum of the heat dissipated to the surrounding medium ( Aλθ dt ) and the heat stored in the body causing a temperature rise θ above the ambient ( Gs dθ ). Then the temperature rise reaches a constant value, the body is said to have reached maximum temperature rise θm . When this condition is reached dθ = 0. The heat developed in the body is completely dissipated to the surroundings. No more heat is stored in the body and the body attains thermal equilibrium. Therefore, SREC/R&A/HG/20RA211 26

27. and the maximum temperature rise If the Electric Motor Cooling were not there the machine would heat up enormously and the temperature rise would attain very high values. But θ must be limited to θm . The time taken by the machine to reach this temperature rise in the absence of dissipation can be determined using SREC/R&A/HG/20RA211 27

28. which gives a linear relation between θ and t if r 1  is the time taken to reach θ m SREC/R&A/HG/20RA211 28

29.    the value of r1, the time taken by the body to reach the maximum temperature rise r 1  is called the  thermal (heating) time constant . In other words this happens to be the time taken by the motor to reach the final steady-state temperature rise if the initial rate of rise of temperature continues. SREC/R&A/HG/20RA211 29

30. Heat balance equation must be solved to obtain a relationship between the temperature rise and time.  Integrating both sides  SREC/R&A/HG/20RA211 30

31. where log C 1  is a constant of integration. It is evaluated using the initial conditions at the start of heating. This equation can be written as substituting for C 1  and rearranging the terms  For simplicity, it is assumed that the machine is started from cold. There­fore θ = 0, at t = 0. SREC/R&A/HG/20RA211 31

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33. However while considering the heating and Electric Motor Cooling, in many cases the initial temperature rise is not zero, i.e., at t = 0, θ = θ SREC/R&A/HG/20RA211 33

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35. The heating curve can be looked upon as the sum of two curves: heating curve when the machine has a load to give a maximum temper­ature rise of θ m . cooling curve when the machine is disconnected from supply with an initial temperature rise of θ . Heating time constant r 1  : r 1   is called the  heating time constant . It can be seen from equation that it would have been the time taken by the ineffective or had the initial rate of rise of temperature been continued, SREC/R&A/HG/20RA211 35

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37. B ut the machine has cooling, machine takes longer time to reach the max­imum temperature rise and the time is greater than r1 Substituting t = r1 in equation we see that the temperature rise of the body is 63.2% of θm . There­fore it can be defined as the time taken by the machine to reach a temperature rise of 63.2% of maximum temperature rise. The value of r1 gives an an idea of the effectiveness of cooling. Well ventilated machines have smaller time constants. The time constants of open machines are of the order of 25 minutes. The totally enclosed machines have poor ventilation . Heating time constant can be determined from the experimental curve using the definition that it is the time taken to reach the 63.2% of θm . The The time constant SREC/R&A/HG/20RA211 37

38. When a machine is switched off from the mains or when the load on the motor is reduced, the machine cools. In the first case it cools to the ambient temperature and in the second case it cools to a temperature determined by the power losses at reduced load. The cooling curve is also an exponential curve. When the machine is switched off there is no heat generation in the motor and all the heat stored in the machine is now dissipated to the surroundings. In this Eq reduces to Cooling curve SREC/R&A/HG/20RA211 38

39. Where r2 is the time constant during cooling. The machine sometimes is not switched off but load on it is reduced in which case it cools to a temperature SREC/R&A/HG/20RA211 39

40. There W 1  is the total loss at  reduced load . The cooling curve in this case determined as which can also be written as SREC/R&A/HG/20RA211 40

41. The cooling curve is shown in Fig. 5.4. This may also be looked upon as the sum of two curves 1.heating curve as if the machine is loaded to give a maximum temperature rise of θ f . 2.cooling curve as if the machine is disconnected from the supply when it had a temperature rise of θ m . SREC/R&A/HG/20RA211 41

42. r 2  in the cooling curve is the cooling time constant. The heating time constant r 1  and cooling time constant r 2  are not equal in self cooled machines. r 2  is two to three times greater than r 1 . All other conditions being equal, the time taken by the motor to cool to  ambient temperature  is longer than the time taken by the motor for heating. If forced cooling is employed r 2  = r 1.  In such cases the heating curve and cooling curve are mirror images of each other. The power rating of a motor for a particular operating condition is selected based on the thermal rating of the motor, so that it meets the specification regarding the final steady-state temperature rise, i.e., it must be equal to or slightly less than the  permissible temperature  rise. As has already been pointed out, an Electric Motor Cooling has a very good overload capacity. The Duration of overload is normally till the motor reaches the permissible temperature rise. This overload must be within pull-out torque capability of the motor. SREC/R&A/HG/20RA211 42