Chopper Fed Dc Motor

INTRODUCTION During the ordinal century, when great magnate fork step up was dc, dc aims were apply extensively to draw occasion train from the dc reservoir book work. The labor amphetamine could be varied by adjusting sphere of influence contemporary by a rheostat. That was an open coil check over. Most of the attempts were eonian whet and the characteristics could not be matched with a job requirement. A vast development in the dc sits frame took place when the ward Leonard catch System was introduced in the 1980s. The system was force-generator system to deliver power to the drive tug.The leave power acquirable was still dc and dc push was employ to drive the dc generator set at a more or less(pre tokenish) eternal quantity luxuriantness. Afterwards when the ac power system came into existence and became popular, ac labors were positive and became attractive owing to their constructional simplicity, ruggedness and deject initial as well as suste ntation cost. Machine requiring inconstant travel rapidly drives use the ward Leonard System employing ac repels capricious dc repels at a constant press forward. In the 1950s electronic came into existence and brought about remarkable amelioration in the revivify take system.The open- twine manual rig system was replaced by close loop feed ski binding take, which resulted in meliorate reply and better accuracy. Initi all toldy, gas diodes and ignitrons were veritable and ac to dc converters were utilise to tick off dc motors. The advent of thyristors capable of handling immense veritable has revolutionized the expanse of voltaic power tick. Thyratrons, ignitrons, mercury arc rectifiers, magnetized amplifiers and motor generator sets have all been replaced by hard bring up circuits employing semi-conductor diodes and thyristors.Thyristor viewled drives employing both(prenominal) ac and dc motors find simple coatings in industry as variable hasten dr ives. In the 1960s ac power was converted into dc power for direct control of drive motors with solid state devices ( proud power atomic number 14 diodes and silicon controlled rectifiers). Initially saturable reactors were employed in concomitant with power silicon rectifiers for dc drives. Of new solid state circuits utilize semi- conductor diodes and thyristors atomic number 18 becoming popular for commanding the hasten of ac and dc otors and ar progressively replacing the tradianitional electric power control circuit establish on thyratrons, ignitrons, mercury arc rectifiers, magnetized amplifiers, motor-generator sets, etc as comp ard to the electric and electro- mechanized systems of despatch control. The electronic system has high uper accuracy, greater reli business leader, and prompt response and also has higher talent as there is no I2R losings and moving parts. Moreover four-quadrant press forward control is possible to have-to doe with precise high stand ards. All electronic circuits control the induce of the motor by controlling either, ?The potential difference employ to the motor armature or ? The land f meek rate or ? Both of the higher up DC motors bottomland be get moody from dc sum up if available or from ac egress, after it has been converted to dc supply with the help of rectifiers which can be either half wave or full wave and either controlled ( by varying the conduction bung of the thyristors use) or anarchical. AC motors can be hold out on the ac supply or from dc supply, after it has been converted into ac supply with the help of inverters (opposite of rectifiers).As state above, the amount takings potentiality of a thyristors controlled rectifiers by changing its conduction angle and hence the armature potential drop can be adjusted to control its travel rapidly. When run on a dc supply, the armature dc voltage can be changed with the help of uncontrolled rectifiers (using only diodes and not thyr istors). The dc voltages so obtained can be thusly(prenominal) chop with the help of a thyristors whirlybird circuit. In this manner of rep bare control of a dc motor, available ac supply is first rectified into dc supply using uncontrolled rectifiers. The supply is then filtered and smooth ended dc output is supplied to the thyristors meat cleaver.It allows dc to flow through for the metre gross ton and then disconnects for the era nob. This unit of ammunition is repeated. During supply-on full stop (i. e. for the time period Ton) the dc motor gets supply and accelerates. During the supply off period Toff (i. e. for the time period Toff) there is no supply to the motor and the motor decelerates till the next on stave begins. If the cycles repeated continuously at a definite frequency and the elements of the cycle are maintained in a fixed relationship, the motor exit then turn tail at a constant voltage across the motor will be,V0 = (V*Ton)/(Ton +Toff) = (V*Ton)/T = f*V*Ton The dc voltage across the motor can be control by varying the clock Ratio govern (TRC) which may be accomplished by, ? vary the duration of the on-time, Ton keeping the full time period, T or frequency, f constant ? Keeping the on- time, Ton constant and varying the frequency, f. ? Varying both. The Variable dc voltage on a lower floor the supply dc voltage is do available to the dc motor and then, the motor promote available is below tail end speed.For automatic control of speed, both genuine feedback and speed feedback is employ. brief DISCUSSION ON eggwhisk A dc cleaver is a noneffervescent device used to obtain variable dc voltage from a source of constant dc voltage. The dc cleaver offers great efficiency, fast-paced response, smooth control, overthrow maintenance, small size, etc. Solid state pearly due to various advantages are widely used in the outpouring operated vehicles, traction motor control, control of a big(p) number of dc motors from a c ommon dc bus with a considerable improvement of power factor. teaching OF CHOPPER OPERATION A chopper is a thyristors on/ off merchandise that connects corrupt to and disconnects it from the supply and produces a chopped file voltage from a constant input voltage. The chopper is represented by a thyristors (SCR). It is triggered periodically and is kept conducting for a period Ton and is blocked for a period Toff. During the period Ton, when the chopper is on, the supply terminals is connected to the load terminals. And during the interval Toff when the chopper is off, load current flows from the freewheel diode Df.So, the load terminals are unretentive circuited by Df and load voltage is whence cypher during Toff. Hence the chopper dc voltage is produced at the load terminals. Now, the average load voltage, Eo is effrontery by Eo = Edc*? ? =duty Cycle=(Ton/Toff) Or, Eo = Edc*(Ton/T) T=Ton + Toff So the voltage can be varied by varying the duty cycle, ? of the chopper. CLAS SIFICATION OF CHOPPER major power semiconductor devices are used in chopper circuits are uni-directional device. A chopper can however operate in any of the four quadrants by an appropriate ar rovement of semiconductor devices.These characteristics of their procedure in any of the four quadrants variety show the innovation of their classification as, 1. Type-A or origin quarter-circle helicopter 2. Type-B or uphold quarter-circle chop shot. 3. Type-C or Two Quadrant Type-A Chopper 4. Type-D or Two Quadrant or Type-B Chopper 5. Type-E or cardinal Quadrant Chopper. PERFORMANCE EQUATION OF DC MOTORS The identical circuit and on its basis the performance equation of a separately-excited dc force and series dc motor are presented below. ? one by one-excited dc motorThe combining weight circuit of a separately-excited dc motor coupled with a load spatestairs steady state condition is shown in the fig 4. 1. The load tortuosity, TL opposes the electro-magnetic contortion, T e. For the field circuit, Vf = If*rf For the armature circuit, Vt = Ia + Ia*ra Motor back electric potential or armature emf, Ea=Ka ? Ia=Km? m &8212&8212&8212&8212 (4. 1) Te=ka ? Ia = KmIa Also, Te = D wm + TL where, rf= playing field circuit opposite in ohm, Ia=Armature current in A, Vt=Motor terminal voltage in V, ra=Armature circuit ohmic resistance in ohm, Km=Ka ?=Torque constant in Nm/A*emf constant in V-sec/rad, m=Angular speed of motor in rad/sec, D= mucilaginous friction constant in Nm-sec/rad. electromagnetic power, P=wmTe watts From equation (1), Ea=Kmwm=Vt-Iara Or wm= (Vt Iara)/Km= (Vt Iara)/Ka ? &8212&8212&8212&8212&8212&8212 (4. 1) So it is seen from equation (4. 2) that speed can be controlled by varying, ? Armature terminal voltage, Vt This method is known as Armature-voltage control. zip below stand speed is obtained by this method. ? dramatics flux, ? This method is known as case flux control. Speed above base speed is obtained by this method. ? DC serie s MotorIn a dc series motor, field winding is in series with the armature circuit. It is designed to carry the rated armature current. The fig. shows the equivalent circuit of a dc series motor driving load with load crookedness, TL. For the armature circuit, Vt = Ea + Ia ( ra+ rs ) .. (4. 3) Te = Ka ? Ia For no fertilization in the magnetic circuit, ? = CIa Hence, Te = KaCIa2 = KIa2 Also, Ea = Ka ? wm = KaCIawm = KIawm From eqn (4. 3), Vt = KIawm + Ia (ra + rs) = Ia Kwm + (ra + rs) Or, speed wm = (Vt/ KIa) (ra +rs)/K . (4. 4) where, rs = Series field resistance in ohm,K = KaC = constant in Nm/A2 or in V-sec/ A- rad. unopen LOOP CONTROL OF CHOPPER cater DC MOTOR For practical purposes motors are unavoidable to operate at in demand(p) speed with low losses to equal the desired load tortuousness characteristics which depends on the armature current. Suppose a motor is operate at a particular speed an suddenly a load is applied, the speed falls and the motors takes time to come up to the desired speed . moreover a speed feed back with an national current loop provides faster response to any disturbance in speed command ,load crookedness and supply voltage.another(prenominal) reason for the requirement of feedback loop in dc drives is that, the armature of a large motor represents very small impedance which when supplied with nominal voltage would result in an luxuriant current of up to 10 propagation the nominal protect. Under normal conditions, this is prevented by the induced armature voltage, E which cancels most of the applied voltage, Va so that only the difference is driving the armature current, Ia. But under transient conditions or steady state over load of the motor, there is always a danger of excessive currents due to sudden tortuosity demand and rapidly changing armature voltage or speed . t is therefore important to provide a fast current or crookedness bourn to protect the motor, the power supply and the load. This is crush rea lized by feedback control establishing an hard-hitting safe guard against electrical and mechanical stresses. In it the output of the speed ascendency, Ec is applied to the current limiter which sets the reference current, Ia (reference) for the current loop. the armature current is sensed by a current sensor, after being filtered by an active filter to take out ripples which is then compared with the reference current, Ia (ref. the fault current is processed through a current controller whose output, Vc adjusts the firing angle of the chopper and brings the motor speed to the desired value. whatsoever positive speed error caused by an increased in either speed command or load torsion demand can produce a high reference current, Ia (ref) the motor accelerates to compensate the speed error and finally settles down at any reference current, Ia(ref) which makes the motor torque equal to the load torque resultant in a speed error closed to zero.For any large positive speed erro r, current limiter saturates and limits the reference currents, Ia (ref) to a level best value, Ia (max) the speed error is then corrected at the maximum allowable armature current ,Ia(max)until the speed error becomes small and the current limiters comes out of the saturation . normally ,the speed error is corrected with the Ia less than the maximum permissible armature current, Ia max. For speeds below the base speeds, the field error, Ef is large and the field controller saturates thereby applying the maximum ield voltage and current. The speed control from zero to base speed is normally make at the maximum field by armature voltage control. When the speed is closed to the base speed, Va is almost near the rated value and field controller comes out of saturation. The speed control above base speed is by and large done by field enfeebling at the rated armature voltage. In the field control loop, the back emf Eb is compared with a reference voltage , Eb (ref) the value of which is slackly amidst 0. 85 to 0. 95 of the rated armature voltage.For a speed command above the base speed, the speed error causes a higher value of Va then motor accelerates, back emf , Eb increases and field error, Ef decreases. The field current when decreases and the motor speed continue to increase until it reaches the desired speed. In this mode of operation, the drive responds late due to large field time constant. A full converter is generally used in the field because it has the ability to reverse the voltage thereby cut back the field current much faster as compared to the semi converter.MODELING AND OBSERVATIONS ? mildew using Matlab ? DC Motor with consign Parameter given emf = 220v genuine = 6. 2A Ra = 4 ohm La = 0. 072H Speed = 1470 rpm J = 0. 0607 kg-m2 Kb= 1. 26v/rad/sec Bt =0. 0869N-m/rad/sec Parameters figure Ta=La/Ra= 0. 02sec Tm=j/Bt =0. 7sec K1 = Bt/KB2 + Ra Bt =0. 0449 -1/T1 1/T2 =-1/2Bt/J +Ra/La + sqre1/4(Bi/J + Ra/La)2-(Kb2 + Ra Bt ) /JLa T1 = 0. 1077 sec T2 = 0. 0208sec Tm = J/Bt = 0. 7sec DC Motor enrapture decease I(s)/V(s) =k1(1+sTm)/ (1+sT1)(1+sT2)= 0. 032s+0. 045/0. 002s2+0. 4s+1 wm(s)/I(s)= Kb/Bt(1+sTm) =14. 5/(1+0. 75) Converter Transfer process Kr =1. 35V/Vcm =1. 35*230/10 =31. 05V/v Tr = 1/12*Fs = 1/12*50 =0. 00166sec T. F = kr/(1+sTr) =31. 05/(1+0. 00166s) Design of online Controller Tc=T2=0. 0208sec K = T1/2Tr = 0. 1077/2*0. 00166 = 32. 43 Kc = KTc/k1HCKrTm =32. 43 *0. 0208/0. 0449*1*31. 05*0. 7 =0. 69 Transfer function Gc(s) = Kc(1+sTc)/sTc = 0. 69(1+0. 0208s)/0. 0208s = 0. 69 + 0. 0143s/0. 0208s new Loop I(s)/I*(s) = Ki/(1+sTi) Ti = T3/1+ kfi Ki = kfi/Hc(1+ kfi) Kfi = KcKrKiTmHc/Tc Kfi = 0. 9*31. 05*0. 0449*0. 7*1/0. 0208 Kfi = 32. 44 Ki = Kfi/HC(1+ Kfi) Kfi = 32. 44/1*(1+32. 44) Kfi = 0. 97 Ti = T3/(1+ Kfi) = T1+Tr/(1+ Kfi) = 0. 1077+0. 00166/1+32. 44 = 0. 0032sec Speed controller Design T4 = Ti + Tw K2 = Ki Kb Hw /Bt Tm K2 = 0. 97*1. 26*1/0. 0869*0. 7 K2 = 20. 092 KS = 1/(2 Kt T4) KS = 1/2*20. 092*0. 0032 KS = 7. 77 Ts = 4T4 =4*0. 0032 Ts = 0. 0128 Transfer function T. F = KS (1+sTS)/sTS = 7. 77(1+0. 0128s)/0. 0128s = (7. 77 + 0. 0994)/0. 0128s ? Modeling using PSIM Parameters Given Source (Vdc) = 800V Transistor (npn) color electric potential = 0 Initial purview = 0 Current Flag = 1 Gating Block (G) Frequency = 50Hz Number of Points = 2 Switching Points = 0 180 Diode (D) Diode Voltage Drop = 0 Initial go under = 0 Current Flag = 0 Inductor (L) Inductance = 0. 01 Initial Current = 0A Current Flag = 0 capacitor (C) Capacitance = 0. 00005F Initial Capacitive Voltage = 0V Current Flag = 0 DC MOTOR (DCM) Ra = 0. 055 ohm La = 0. 01H Rf = 55 ohm Lf = 0. 02H MI = 0. 2 Vt = 440V Ia = 80A If = 4A n = 1 vitamin Drpm Torque Flag = 0 cut across/Slave Flag = 1 Field Source = 400VSpeed Sensor (Ws) wee-wee = 1 Simulation Control Time beat = 1e-005 Total Time = 0. 02 publish Time = 0 Print Step = 1 Load Flag = 0 Slave Flag = 0 industrial APPLICATIONS DC drives are highly several(a) energy conve rsion devices. It can meet the demand of loads requiring high starting time, accelerating and decelerating torques. At the same time dc drives are easily adaptable for wide range of speed control and quick reversal. So, in industrial application where accurate control of speed and / or torque is required chopper controlled dc drives are unrivalled.Therefore, chopper controlled dc motors are universally employed in steel and aluminum mills, power shovels, electric elevators, railway locomotives and large land moving equipments. Uses o Various Chopper Controlled DC drives with reasons Types of DC drives Applications Advantages Accurate speed control can be done. Separately Excited dc drives use in paper mills, steel rolling regeneration of speed from very high to low value can be mills, diesel-electric propulsion of done ships, etc. head start torque is very high upto 500%. Maximum momentary operating torque is upto 400%. Speed formula is widely variable. It is very high Series dc drive Used in hoists, cranes, conveyors, at no load. trolley-cars, electric locomotives, Speed control by series field. etc. Used in lathes, centrifugal pumps, Starting torque is medium, commonly limited to 250% by unvaried speed dc shunt drive reciprocating pumps, fans, blowers, a starting resistance but may be increased. conveyors, spinning and distort Maximum momentary operating torque is usually limited machines, etc. to about two hundred% by commutation. Speed regulation is about 5-10 %. Speed increases about 200% by field control and decreases by armature voltage control. Starting torque is medium, usually limited to 250% by a starting resistance but may be increased. Maximum momentary operating torque is usually limited Adjustable speed dc shunt drives Used for application requiring to about 200% by commutation. adjustable speed control, either constant torque or constant output. SCOPE OF MODIFICATIONS Chopper cont rolled dc drives are widely used in hoists, cranes, elevators, shears, crushers, conveyor, blending mills, punch presses, air compressors, ice making machines, tractions, etc.So these drives should be modified in the future(a) ways to make them more expeditious and accurate, 1. The chopper controlled dc motors should be made with large diameter armatures and large celestial pole size of subdued height. 2. The yoke as well as the main and commutating poles should be well laminated to slash the eddy current raise and to improve the commutation. 3. Large number of commutator bars should be used to reduce the voltage between the commutator segments and to improve the commutation. 4.The commutator should be made larger in recount to provide extra insulation to detain large and rapid voltage fluctuations. 5. Compensating windings should be used in large motors to reduce the armature reactions effects. 6. The current densities used for the armature and Interpol windings should be cut as compared to the conventional dc motors of the same frame size and rating in order to reduce the effect of passion of armature and Interpol. 7. Low inertia armature should be employed for improving the response. 8.Split brushes of good commutating timber should be used for reducing the effect of transformer voltage in the coil undergoing commutations. 9. give away class of insulation should be used to allow higher temperature rise and wasteland of more losses from a given frame. 10. Now a days chopper controlled dc drives are widely used in the automobile industries. So, it should have high efficiency and accuracy, light weight, low maintenance cost. BIBLIOGRAPHY 1. Electric Drives Ramakrishnan, Prentice Hall India. 2. Power Electronics P. S. Bimbhra, Khanna Publishers. 3. Software MATLAB 6. 5 and PSIM.