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International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 –3733, Volume-1, Issue-10, October 2014 Speed Control of Dc Motor Using Chopper Abhishek Soni  arrive at a mathematical description that contains the relevant Abstract— Some devices convert electricity into motion but...

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International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 3733, Volume-1, Issue-10, October 2014

Speed Control of Dc Motor Using Chopper Abhishek Soni Abstract Some devices convert electricity into motion but do not generate usable mechanical power as primary objective and so are not generally referred to as electric motors. Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force. The reverse process, producing electrical energy from mechanical energy, is done by generators such as an alternator or a dynamo; some electric motors can also be used as generators, for example, a traction motor on a vehicle may perform both tasks. Electric motors and generators are commonly referred to as electric machines. Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. They may be powered by direct current, e.g., a battery powered portable device or motor vehicle, or by alternating current from a central electrical distribution grid or inverter. The smallest motors may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses. The very largest electric motors are used for propulsion of ships, pipeline compressors, and water pumps with ratings in the millions of watts. Electric motors may be classified by the source of electric power, by their internal construction, by their application, or by the type of motion they give. The physical principle of production of mechanical force by the interactions of an electric current and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed throughout the 19th century, but commercial exploitation of electric motors on a large scale required efficient electrical generators and electrical distribution networks. The speed of a DC motor can be varied by controlling the field flux, the armature resistance or the terminal voltage applied to the armature circuit. The three most common speed control methods are field resistance control, armature voltage control, and armature resistance control. In this section, modeling procedure of these three methods and feedback control method for DC motor drives for dynamic analysis are presented. Index Terms DC (direct current), PMSM (Permanent Magnet Synchronous Motor).

I. INTRODUCTION

A theory is a general statement of principle abstracted from observation. And a model is a representation of a theory that can be used for control and prediction. For a model to be useful, it must be realistic and yet simple enough to understand and manipulate. These requirements are not easily fulfilled as realistic models are seldom simple and simple models are seldom realistic. The scope of a model is defined by what is considered relevant. Features or behavior that is relevant must be included in the model and those that are not can be ignored. Modeling refers to the process of analysis and synthesis to Manuscript received October 20, 2014 Abhishek Soni, Asst. Prof. Swasthya Kalyan Technical Campus, Jaipur, India

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arrive at a mathematical description that contains the relevant dynamic characteristics of the particular model.

Figure 1: Electromechanical Energy Conversion DC machines may also work as brakes. The brake mode is a generator action but with the electrical power either regenerated or dissipated within the machine system, thus developing a mechanical braking effect. It also converts some electrical or mechanical energy to heat, but this is undesired. The major advantages of DC machines are easy speed and torque regulation. The major parts of any machine are the stationary component, the stator, and the rotating component, the rotor. Types of DC Motor DC Motors are electrically identical to dc generators. In fact, the same dc machine may be driven mechanically to generate a voltage, or it may be driven electrically to move a mechanical load. While this is not normally done, it does point out the similarities between the two machines. There are three types of DC Motors: Series DC Motors. Shunt DC Motors. Compound DC Motors. Emf Equation of DC Motor When the motor armature rotates the conductor also rotates and hence cut the flux. In accordance with the law of electromagnetic induction emf is induced in them, whose direction found by Flemings right hand rule, is in opposition to the applied voltage because of its opposite direction it is referred to as counter emf or back emf Eb. The rotating armature generating the back emf Eb is like a battery of emf Eb put across supply mains of V volt. Obviously V has to drive Ia against the opposition of Eb. The power required to overcome this opposition is EbIa. In DC Motor power is converted into mechanical energy. Ia = Net Voltage/Resistance, Where Ra is the resistance of armature circuit Eb = volt, where N is in rps. Back emf depends upon the other factors of the armature speed if speed is high Eb is large, hence armature current Ia is

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Speed Control of Dc Motor Using Chopper small. If speed is less then Eb is less hence motor current flows which develop motor torque. Starting of DC Motor The counter-emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf is zero and the only factor limiting the armature current is the armature resistance. Usually the armature resistance of a motor is less than 1 ; therefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices. Therefore the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation builds up, the resistance is gradually cut out.

Three point starter The incoming power is indicated as L1 and L2. The components within the broken lines form the three-point starter. As the name implies there are only three connections to the starter. The connections to the armature are indicated as A1 and A2. The ends of the field (excitement) coil are indicated as F1 and F2. In order to control the speed, a field rheostat is connected in series with the shunt field. One side of the line is connected to the arm of the starter (represented by an arrow in the diagram). The arm is spring-loaded so, it will return to the "Off" position when not held at any other position.

chopper involves one stage conversion, these are more efficient Choppers are now being used all over the world for rapid transit systems. These are also used in trolley cars, marine hoist, forklift trucks and mine haulers. The future electric automobiles are likely to use choppers for their speed control and braking. Chopper systems offer smooth control, high efficiency, faster response and regeneration facility. The power semiconductor devices used for a chopper circuit can be force commutated thyristor, power BJT, MOSFET and IGBT.GTO based chopper are also used. These devices are generally represented by a switch. When the switch is off, no current can flow. Current flows through the load when switch is on . The power semiconductor devices have on-state voltage drop of 0.5V to 2.5V across them. For the sake of simplicity, this voltage drop across these devices is generally neglected. As mentioned above, a chopper is dc equivalent to an ac transformer, have continuously variable turn s ratio. Like a transformer, a chopper can be used to step down or step up the fixed dc input voltage. Starting Chopper Circuit The second possibility of controlling the armature current is to use a step-up converter. The step-up converter is usually attributed the name chopper in the literature. The circuitry layout of this mean of control is shown in figure (a). The controlled switch of the chopper circuit is biased by an hysteresis controller. The hysteresis controller is programmed to guaranty an armature current waveform similar to the one shown in figure (b).

Figure 2 Three point Starter of DC Motor

On the first step of the arm, full line voltage is applied across the shunt field. Since the field rheostat is normally set to minimum resistance, the speed of the motor will not be excessive; additionally, the motor will develop a large starting torque. The starter also connects an electromagnet in series with the shunt field. It will hold the arm in position when the arm makes contact with the magnet. Meanwhile that voltage is applied to the shunt field, and the starting resistance limits the current to the armature. As the motor picks up speed counter-emf is built up; the arm is moved slowly to short. III. SPEED CONTROL OF DC MOTOR USING CHOPPER A chopper is a static power electronic device that converts fixed dc input voltage to a variable dc output voltage. A Chopper may be considered as dc equivalent of an ac transformer since they behave in an identical manner. As 6

Figure 3 Using Chopper circuit Mean. a) Circuit Topology b) Hysteresis Controller Function As it can been seen, the chopper circuit did perform its duty as intended but that was at the expense of delaying the motor from reaching its steady state (rated value) in a short time. Themotor reaches its rated speed at time = 8 seconds. The ratio between the maximum and rated values of the armature current is 1.23 but the armature current has a lot of ripples which might be harmful to the armature circuitry. IV. MODELLING AND SIMULATION OF SPEED CONTROL OF DC MOTOR To produce a good design, there needs to be some amount of modeling or simulations done to avoid aimless trial and error techniques with the actual equipment (the DC motor). For this thesis paper, a number of specifications were needed to be obtained and established. The specifications of the DC motor were obtained from the engraving on the metal tag attached www.alliedjournals.com

International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 3733, Volume-1, Issue-10, October 2014 onto the motor casing. It included the motor manufacturer company s name, the size, the model number, power, speed, voltage and current of the armature and field windings. DC Motor: Implements a (wound-field or permanent magnet) DC machine. For the wound-field DC machine, access is provided to the field connections so that the machine can be used as a separately excited, shunt-connected or a series-connected DC machine.

Figure 4 Simulink model of DC Motor Starter: As DC motor never self-starts. So Starter is used to give the starting torque to DC motor. And here weare using the 3-point starter.

Figure 7 Scope of Speed Control Using Chopper

Figure 5 Starter of DC Motor Simulink Model of DC motor speed control :Here is the Simulink model of the DC motor speed control.It consists of speed controller, current controller filters choppers and a motor.The proposed model has a flexible structure and enablesusers to change motor parameters easily.

Figure 8 Graph for reference speed 100-125. For the set reference speed to any rpm the voltage will set automatically. As here we are using speed controller. Thus the motor can be controlled. We can control DC motor by varying supply voltage also where motor ratings are 5 HP/240 volt.

Figure 6 Simulink Model of Speed Control of Dc Motor Using Chopper V. SIMULATION RESULTS The result from the simulation of the motor model in SIMULINK is shown in Figure 4.4

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Speed Control of Dc Motor Using Chopper the user to observe the effect on the speed response of the DC motor speed response by varying the field current REFERENCES

Figure 9 Speed Control Using Chopper for Ref Speed 100 and 135

[1] MathWorks. (2001). Introduction to MATLAB. The MathWorks, Inc.Available:http://www.mathworks.com/access/helpdesk/help/ techdoc/learn_MATLAB/ch1intro.shtml#12671 [2] MathWorks. (2001). SIMULINK. The MathWorks, Inc.Available: http://www.mathworks.com/access/helpdesk/help/toolbox/SIM ULINK SIMULINK.shtml [3] MathWorks. (2001). what is SIMULINK. The MathWorks, Inc. Available:http://www.mathworks.com/access/helpdesk/help/tool box/SIMULINK/ug/ug.s html [4] MathWorks. (2000). Using MATLAB Version 6. The MathWorks, Inc.Available:http://www.mathworks.com/access/helpdesk/help/ pdf_doc/MATLAB/ using_ml.pdf [5] The MathWorks. MATLAB Student Version Learning MATLAB 6 (Release 12), 2nd printing, January 2001. [6] P.C. Sen, Principles of Electric Machines and Power Electronics (2nd Edition), John Wiley and Sons Inc., 1989 [7] G.R. Slemon and A. Straughen, Electric Machines, Addison-Wesley publishing company, 1982 [8] D. M. Etter, Engineering Problem Solving with MATLAB, Prentice Hall, 1993. [9] Chee-Mun Ong, Dynamic Simulation of Electric Machinery, Prentice Hall PTR, 1998. [10] Peter F.Ryff, David Platnick and Joseph A.Karnas, Electrical Machines and Transformers, Principles and Applications, Prentice Hall, Inc., 1987. [11] The Starting Block. All about DC motors. (2001) [12] http://www.solarbotics.net/starting/200111_dcmotor/200111_d cmotor.html [13] Theodore Wildi, Electrical Machines, Drives, and Power Systems, Fourth [14] Edition, Prentice Hall International, Inc., 2000.

VI. FUTURE SCOPE Actual experimentation on bulky power components can be expensive and time consuming. But simulation offers a fast and inexpensive means to learn more about these components. In this paper, the block diagram of a DC motor was developed by using SIMULINK, a toolbox extension of the MATLAB program, the block diagram was simulated with expected waveforms output. Furthermore, by varying certain parameters of the DC motor block diagram, the output waveform of the simulation would change accordingly. These parameters include the field current, armature circuit resistance and armature voltage. The simulation and modeling of the DC motor in chapter 4 also gave an inside look of the expected output when testing the actual DC motor. The results from the simulation were never likely to occur in real-life condition due to the response time and condition of the actual motor. There are a number of topics for future work and development related with the simulation model designed in this thesis. These may include: Inserting external resistors into the armature circuit during start up of the simulation to reduce the large starting current. These resistors can either be manually or automatically shorted out as the motor accelerates. Modifying the block diagram to control the speed of the DC motor by varying the current (If) of the field circuit. This can be achieved by using a field circuit rheostat. This would allow

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