For Quadrant Dc Motor Control 5o2q5h

2013 FOUR QUADRANT DC MOTOR CONTROL WITHOUT MICROCONTROLLER

DEFINE PROBLEM

A.V.PAREKH TECHNICAL INSTITUTE RAJKOT

Project Report on

FOUR QUADRANT DCMOTOR CONTROL WITHOUT MICROCONTROLLER PREPARED BY (1) GHEDIYA AKHIL (2) SOLANKI KAPIL (3) GOPANI RAHUL

GUIDED BY V.R.MISTRY

CERTIFICATE This is to certify that Mr.-GOPANI RAHUL. (116020309063)ofDEE6thsemhas satisfactorily completed his term work in PROJECT-ll for the term ending in APRIL-2014

DATE:-

Staff-in-charge

V.R.MISTRY

Head of department

N.M.MEHTA

CERTIFICATE This is to certify that Mr.-GHEDIYA AKHIL. (116020309097)ofDEE6thsem has satisfactorily completed his term work in PROJECT-ll for the term ending in APRIL-2014

DATE:-

Staff-in-charge

V.R.MISTRY

Head of departmen

N.M.MEHTA

CERTIFICTE This is to certify that Mr.-SOLANKI KAPIL. (116020309056ofDEE6thsem has satisfactorily completed his term work in PROJECT-ll for the term ending in APRIL-2014

DATE:-

Staff-in-charge

V.R.MISTRY

Head of department

N.M.MEHTA

CERTIFICATE This is to certify that Mr.-GHEDIYA AKHIL. (116020309097) SOLANKI KAPIL. (116020309056) GOPANI RAHUL.(116020309063) ofDEE 6thsem has satisfactorily completed his term work in PROJECT-ll for the term ending in APRIL-2014.

DATE:-

Staff-in-charge

V.R.MISTRY

Head of department

N.M.MEHTA

INDEX SR.NO.

CONTENTS

PAGE NO.

1

INTRODUCTION

1

2

IGBT BASICS

8

3

THYRISTOR

21

4

DC MOTOR

25

5

OBSERVATION

27

6

CONCLUSION

37

ACKNOWLEDGEMENT We would like to thank professor V.R.MISTRY help of electrical depart for guiding us throughout this project from literature survey he final experiment for our project his constant encouragement and in valuable suggestion has encourage us to finish this project successfully.

ABSTRACT The project is designed to develop a four quadrant control system for a DC motor. The motor is operated in four quadrants i.e. clockwise; counter clock-wise, forward brake and reverse brake. The four quadrant operation of the dc motor is best suited for industries where motors are used and as per requirement as they can rotate in clockwise, counter-clockwise and also apply brakes immediately in both the directions. In case of a specific operation in industrial environment, the motor needs to be stopped immediately. In such scenario, this proposed system is very apt as forward brake and reverse brake are its integral features. Instantaneous brake in both the directions happens as a result of applying a reverse voltage across the running motor for a brief period. Push buttons are provided for the operation of the motor which are interfaced to the circuit that provides an input signal to it and in turn controls the motor through a driver IC. Optionally speed control feature can be achieved (but not provided in this project) by push button operation. This project can be enhanced by using higher power electronic devices to operate high capacity DC motors. Regenerative braking for optimizing the power consumption can also be incorporated.

1.

Introduction 1.1 Introduction 1.2 Circuit Description. 1.3 Switching modes of Four Quadrant Chopper. 1.4 HARDWARE DESCRIPTION

2. IGBT Basics 2.1 Introduction 2.2 IGBT switching characteristics 2.3 Equipment circuit of the IGBT 2.4 Typical opto isolation gate drive 2.5 IGBT safe operating area 2.6 IGBTgatedriverequirement 3. Thyristor 3.1 Silicon Controlled Rectifiers 3.2 Thyristor TURN ON 3.3 Circuit Description 4.DC Motor 4.1 Introduction 4.2 Principle,construction & working 4.3 Application of dc shunt motor

5.Observation 5.1 Graph 5.2 comparisionIGBT and SCR

6.Conclusion 7.Bibiography

Chapter 1

INTRODUCTION 1.1INTRODUCTION The chopper circuit shown in fig.1 can operate in all four quadrants of the Vo-Io plane. That is the output voltage and current can be controlled both in magnitude and direction. Therefore, the power flow can be in any direction. In the first quadrant the power flows from the source to the load and is assumed to be (+ve). In the second quadrant, the voltage is still positive but the current is negative. Therefore, the power is negative. In this case, the power flows from load to source and this can happen if the load is inductive or back emf source such as a dc motor. In the third quadrant both the voltage and current are negative but the power is positive. In the fourth quadrant voltage is negative but current is positive. The power is therefore negative. V

0

II Quadrant Regeneration

-I

I Quadrant Power Positive

I0

0

III Quadrant Power Positive

IV Quadrant Regeneration

-V

0

Fig 1.1: Four quadrant of V0, I0 plane This chopper is widely used in reversible dc motors drives. The reversible dc motor drive requires power flow in either direction in order to achieve fast dynamics response. By employing four-quadrant chopper it is possible to implement regeneration and dynamic braking by means of which fast dynamic response is achieved.

1.2CIRCUIT DESCRIPTION The four quadrant chopper with four switching devices where diodes are connected in anti parallel with the switching devices is also referred to as full bridge converter topology. The input to the full bridge converter is fixed magnitude dc voltage Vdc. The output of the converter can be a variable dc voltage with either polarity. The circuit is therefore called as four quadrant chopper circuit or dc to dc converter. The output of the full bridge converter can also be an ac voltage with variable frequency and amplitude in which case the converter is called as dc- to-ac conversion ( inverter). In a full bridge converter when a gating signal is given to a switching device either the switching device or the diode only will conduct depending on the directions of the output load curret

Fig 1.2: Four quadrant chopper circuit

1.3 SWITCHING MODES OF FOUR QUADRANT CHOPPER The switches in the four quadrant chopper can be switched in two different modes such that: •

The output voltage swings in both direction i.e. from +Vdc to –Vdc. This mode of switching is referred to as PWM with bipolar voltage switching.

•

The output voltage swings either from –zero to +Vdc or zero to- Vdc. This mode of switching is referred to as PWM with unipolar voltage switching.

1.4 HARDWARE DESCRIPTION

The hardware involved in the four quadrant chopper drive is screen printed on the front .it consists of both the power circuitry and the control circuitry. POWER CIRCUIT It consists ofi)single phase diode bridge rectifier ii)four quadrant chopper iii)DC link capacitors iv)Braking circuit v)Field control chopper vi)EMI filter. The diode rectifier rectifies the input ac voltage and provides the dc voltage to the chopper. Large values of dc link capacities maintain a constant dc voltage is also used for the field circuit of the motor through a single quadrant chopper. The chopper consists of four IGBTs rated at 900V, 60A.

Chapter 2

IGBT

IGBT BASICS

2.1INTRODUCTION Recent technology advances in power electronics have arisen primarily from improvements in semiconductor power devices, with insulated gate bipolar transistors (IGBT) leading the market today for medium power applications. IGBTs feature many desirable properties including a MOS input gate, high switching speed, low conduction voltage drop, high current carrying capability, and a high degree of robustness. Devices have drawn closer to the 'ideal switch', with typical voltage ratings of 600 - 1700 volts, on-state voltage of 1.7 - 2.0 volts at currents of up to 1000 amperes, and switching speeds of 200 - 500 ns. The availability of IGBTs has lowered the cost of systems and enhanced the number of economically viable applications. The insulated gate bipolar transistor (IGBT) combines the positive attributes of BJTs and MOSFETs. BJTs have lower conduction losses in the on-state, especially in devices with larger blocking voltages, but have longer switching times, especially at turn-off while MOSFETs can be turned on and off much faster, but their on-state conduction losses are larger, especially in devices rated for higher blocking voltages. Hence, IGBTs have lower on-state voltage drop with high blocking voltage capabilities in addition to fast switching speeds.

IGBTs have a vertical structure as shown in Fig. 2.1. This structure is quite similar to that of the vertical diffused MOSFET except for the presence of the p+ layer that forms the dr drain of the IGBT. This layer forms a p-n n junction (labeled J1 in the figure), which injects minority carriers into what would appear to be the drain drift region of the vertical MOSFET. The gate and source of the IGBT are laid out in an inter-digitated inter geometry etry similar to that used for the vertical MOSFET.

Fig. 2.1.a:: Physical structure of an IGBT The IGBT structure shown in Fig. 1 has a parasitic thyristor which could latch up in IGBTs if it is turned on. The n + buffer layer between the p + drain and the n + drift layer, with proper doping density and thickness, can significantly improve the operation of the IGBT, in two important respects. It lowers rs the on-state on state voltage drop of the device and, and shortens the turnoff time. On the other hand, the presence of this layer greatly reduces the reverse blocking capability of the IGBT. The circuit symbol for an n-channel n hannel IGBT is shown in Fig. 2.1.b

Fig. 2.1.b IGBT circuit symbol

2.2 IGBTS SWITCHING CHARACTERISTICS One of the main important performance features of any semiconductor switching device is its switching characteristics. Understanding the device switching characteristics greatly improves itss utilization in the various applications.

The main performance switching characteristics of power semiconductor switching devices are the turn-on and turn-off off switching transients in addition to the safe operating area (SOA) of the device.

Since most loads ads are inductive in nature, which subjects devices to higher stresses, the turn turn-on and turn-off off transients of the IGBT are obtained with an inductive load test test circuit as shown in Fig. 2.2.. The load inductance is assumed to be high enough so as to hold th the load current constant during switching transitions. The freewheeling clamp diode is required to maintain current flow in the inductor when the device under test (DUT) is turned off.

Fig. 2.2:: Inductive load test circuit

2.3 equivalent circuit of the IGBT The removal of stored charge can be greatly enhanced with the addition of an n+ buffer layer which acts as a sink for the excess holes and significantly shortens the tail time. This layer has a much shorter excess carrier lifetime fetime that results in a greater recombination rate within this layer. The resultant gradient in hole density in the drift region causes a large flux of diffusing holes towards the buffer region which greatly enhances the removal rate of holes from the dri drift region and shortens the tail time. This device structure is referred to as Punch Punch-Through (PT) IGBT while the structure without the n+ buffer region is referred to as Non Pu Punch-Through (NPT) IGBT (Fig. 2.3).

Fig. 2.3:: (a) Non Punch Through (NPT) IGBT IGB (b) Punch Through (PT) IGBT

2.4 TYPICAL OPTO ISOLATION GATE DRIVE In bipolar applications, separate turn-on turn and turn-off off gate resistors are used to prevent cross conduction ction of an IGBT pair (Fig. 2.4). 2.4 With opto-isolation, isolation, an isolated power supply is required to provide the gate power to the IGBT.

Fig. 2.4: Typical opto-isolation isolation gate drive

Gate drive Layout Considerations 1. Minimize parasitic inductance between the driver output stage and the IGBT (minimizing the loop area) 2. Minimize noise coupling via proper shielding techniques 3. Utilize gate clamp protections (TVS) to minimize over voltage across gate terminals 4. Utilize twisted pairs, preferably shielded, for indirect connection between the driver and the IGBT 5. With OPTO coupling upling isolation, a minimum of 10,000 V/ms transient immunity must be provided (in hard switching applications)

2.5 IGBT SAFE OPERATING AREA The safe operating area (SOA) of a power semiconductor device is a graphical representation of the maximum operational voltage and current limits (i-v) of the device subjected to various constraints. The forward bias safe operating area (FBSOA) and the reverse bias safe operating area (RBSOA) represent the device SOA with the gate emitter junction forward biased or reverse biased, respectively.

The IGBT has robust SOA during both turn-on and turn off. The FBSOA, shown in Fig. 6(a), is square for short switching times, similar to that of power MOSFETs. The IGBT is thermally limited for longer switching times as shown in the FBSOA figure.

The RBSOA of IGBTs, shown in Fig. 2.5(b), is different than the FBSOA. The upper half corner of the RBSOA is progressively cut out which reduces the RBSOA as the rate of change of the collector to emitter voltage across the device, dVce/dt, is increased. The RBSOA is reduced as the dVce/dt is increased to avoid latch up within the device. This condition exists when higher values of dVce/dt are applied may give to the rise to a pulse of forward decaying current in the body region of the device that acts as a pulse of gate current that can turn on the device. Fortunately, the dVce/dt values that would cause latch up in IGBTs are much higher compared to other devices.

The maximum value of ICM is set to avoid latch up which is determined based on the dynamic latch up condition. In addition, a maximum VGE voltage is specified in order to limit the current during a fault condition to ICM by forcing the device out of the on-state into the active region where the current becomes constant regardless of the drain to source voltage. The IGBT must be turned off under these conditions as quickly as possible to avoid excessive dissipation. The avoidance of latch up and the continuous gate control over the collector current are very desirable features.

(a)

(b)

Fig. 2.5:: (a) FBSOA (b) RBSOA of an IGBT

2.6 IGBT GATE DRIVE REQUIREMENTS IGBTs are voltage controlled devices and require gate voltage to establish collector collector-toemitter conduction. Recommended gate drive circuitry includes substantial ion and off biasing as shown in Fig. 2.6.

Fig. 2.6:: Typical gate drive circuitry

Due to the large input gate-to-emitter emitter capacitance of IGBTs, MOSFET drive techniques can be used. However, the off biasing needs to be stronger. A +15 V positive gate drive is normally recommended to o guarantee full saturation and limit short circuit current. A negative voltage bias is used to improve the IGBT immunity to collector-to-emitter collector emitter dv/dt injected noise and reduce turn-off off losses as shown in Fig. 2.8. 2.8

Chapter 3

THYRISTOR THYRISTORS

3.1 SILICON CONTROLLED RECTIFIERS Thyristor is a four layer, three junction p-n-p-n semiconductor switching device. It has three terminals; anode, cathode and gate. The four layers of alternate p-type and n-type semiconductors forming three junctions J1, J2, and J3. The terminal connected to outer p region is called Anode (A), the terminal connected to outer n region is called cathode (C) and that connected to inner p region is called gate (G).For large current applications, thyristors need better cooling which is achieved to a great extent by mounting them onto heat sinks.

3.2 THYRISTOR TURN ON The thyristor is turned on by increasing the anode current. This can be accomplished in the following ways.

Thermals If the temperature of a thyristor is high, there is an increase in the number of electron-hole pairs, which increases the leakage currents. This increase in currents causes α1 and α2 to increase. Due to regenerative action (α1 + α2 ) may tend to unity and thyristor may be turned on.

Light If light is allowed to strike the junctions of a thyristor, the electron-hole pairs increase; and the thyristor may be turned on. The light-activated thyristors are turned on by allowing light to strike silicon wafers. High voltage If the forward anode –to-cathode voltage is greater than the forward breakdown voltage VBO , sufficient leakage current flows to initiate regenerative turn on. This type of turn-on may be destructive and should be avoided. Gate current If a thyristor is forward biased, the injection of gate current by applying a positive gate voltage between the gate and the cathode terminals turns on the thyristor. As the gate current is increased, the forward blocking voltage is decreased.

3.3 CIRCUIT DESCRIPTION

A IN4007 T1

T

50Ω, 5A 0-5 A MC

2 0-300V MC

Supply

D1

V

M

D2

To Oscilloscope Fig 3.3: Half Controlled Bridge rectifier

The general arrangement for the speed control of the shunt motor is shown above. The firing angle control of converter regulates the armature voltage applied to the dc motor. Thus the variation of the delay angle of converter gives speed control below the base speed as we are dealing with armature circuit only. Similarly if we deal with field circuit it will give speed above the base speed only. This converter is commonly used in applications up to 15kW. During the positive half cycle T1 is forward biased. When T1 is fires at wt= ,the load is connected to the input supply through T1 and D2.During the negative half cycle of input voltage, T2 is forward biased and the firing of T2 occurs and the load is connected to the supply through T2 and D1. In the following experiment the armature current (Ia) is assumed constant. The firing angle was varied in small steps and the armature voltage current and speed were measured and corresponding graphs were plotted.

Chapter 4

DC MOTOR DC MOTOR

4.1 INTRODUCTION DC motors are used extensively in adjustable-speed drives and position control applications. Their speeds below the base speed can be controlled by armature-voltage control. Speeds above the base speed are obtained by field-flux control. As speed control methods for DC motors are simpler and less expensive than those for the AC motors, DC motors are preferred where widespeed range control is required. Phase controlled converters provide an adjustable dc voltage from a fixed ac input voltage. DC choppers also provide dc output voltage from a fixed dc input voltage. The use of phase controlled rectifiers and dc choppers for the speed control of dc motors have revolutionized the modern industrial controlled applications.

4.2 PRINCIPLE ,CONTRUCTION & WORKING

When a rectangular coil carrying current is placed in a magnetic field, a torque acts on the coil which rotates it continuously. When the coil rotates, the shaft attached to it also rotates and thus it is able to do mechanical work.

contruction and working

Parts of a DC Motor

Armature A D.C. motor consists of a rectangular coil made of insulated copper wire wound on a soft iron core. This coil wound on the soft iron core forms the armature. The coil is mounted on an axle and is placed between the cylindrical concave poles of a magnet.

Commutator A commutator is used to reverse the direction of flow of current. Commutator is a copper ring split into two parts C1 and C2. The split rings are insulated form each other and mounted on the axle of the motor. The two ends of the coil are soldered to these rings. They rotate along with the coil. Commutator rings are connected to a battery. The wires from the battery are not connected to the rings but to the brushes which are in with the rings.

Brushes Two small strips of carbon, known as brushes press slightly against the two split rings, and the split rings rotate between the brushes. The carbon brushes are connected to a D.C. source.

Working of a DC Motor When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn towards the right, causing rotation.

When the coil turns through 900, the brushes lose with the commutator and the current stops flowing through the coil. However the coil keeps turning because of its own momentum.

Now when the coil turns through 1800, the sides get interchanged. As a result the commutator ring C1 is now in with brush B2 and commutator ring C2 is in with brush B1. Therefore, the current continues to flow in the same direction.

RESISTOR

A resistor is an electric element that limits the flow of the electric current into an electric circuit. A current that is ed through the resistor is always directly proportional to the voltage across the terminals of the resistors. This is clearly defined in Ohm’s law. Which states I=V divided by R. Almost every electric circuit and electric network consists of resistors. Resistors can be integrated into both hybrid and printed circuits. Without a resistor an electric circuit cannot work properly. Thus resistors play an important role in running circuits.

Resistor Color Code: For the purpose of calculating the value of the resistor of a particular resistor you require color codes. There are different colors of resistors and each color of resistor represents specific number. Below mentioned are the number and the color of resistors: 0 black, 1 brown, 2 red, 3 orange, 4 yellow, 5 green, 6 blue, 7 violet, 8 grey, 9 white. In this, the gold is of 5% and the silver is of 10%. By using these colors you can calculate the value of the resistor with the help of ohm’s law. Most of the time on electronic repairs the five band resistor colors are used. The reason behind using these 5 color bands is that, it provides accurate values as compared to the four color band. Most of the resistors inside a multimeter use these five color bands because you will get a precise voltage and measure of the current. Overall the five color band resistor makes the circuit precise and the output received too is that desired by the engineers.

4.3 APPLICATION OF DC SHUNT MOTOR 1. For a given field current in a shunt motor, the speed drop from no-load to full load is invariably less than 6% to 8%. In view of this, the shunt motor is termed as a constant speed motor. Therefore, for constant speed drives in industry DC shunt motors are employed. 2. When constant speed service at low speeds is required, DC shunt motors are preferred over synchronous motors. 3. When the driven load requires a wide range of speed control, both below and above the base speed, a DC shunt motor is employed. Eg: Lathes 4. DC shunt motor can be used as a separately excited motor, if the field disconnected from armature and connected to a external voltage source.

winding is

Chapter 5

OBSERVATIONS 5.1 GRAPH GRAPH .1

Field Voltage Vs Speed 2500 2000 1500 Speed

Speed 1000 (rpm) 500 0 75 100 125 150 175 200 Field Voltage(V)

Table .1 FIELD CONTROL at Va=200V S.No

Vf(Volts)

N (rpm)

1

75

2070

2

100

1860

3

125

1700

4

150

1600

5

175

1550

6

200

1480

OBSERVATION .1 FIELD VOLTAGE VS SPEED DESCRIPTION: Here armature voltage Va was kept constant at 200V. The field voltage was varied and the corresponding speed was noted down.

CONCLUSION: The graph was plotted and it was observed that the speed of motor is decreasing as the field voltage increases. We also observed that using field flux method the speed greater than base speed was achieved.

GRAPH .2

Armature Voltage Vs Speed 1600 1400 1200 1000 800 600 Speed (rpm)

400 200 0 0

50

100

Armature Voltage(V)

150

200

Table .2ARMATURE CONTROL VF=200V S.No

Armature Voltage(V)

Speed(rpm)

1

0

0

2

50

390

3

100

790

4

150

1180

5

200

1480

OBSERVATION .2 ARMATURE VOLTAGE VS SPEED DESCRIPTION: Here field voltage Vf was kept constant at 200V. The armature voltage was varied and the corresponding speed was noted down.

CONCLUSION: The graph was plotted and its was observed that the speed of the motor was varies directly with increase in armature voltage. We also observed that using armature control method the speed control was obtained for speed below the base speed.

GRAPH .3

Armature Current Vs Speed 1400 1200 1000 800 Speed 600 Speed 400 (rpm) 200 0 0.11

0.12

0.13

0.14

Armature Current (A)

0.15

Table .3ARMATURE CURRENT VS SPEED S.No

Armature Current (A)

Speed (rpm)

1

0.11

1200

2

0.12

1190

3

0.13

1150

4

0.14

1103

5

0.15

990

OBSERVATION .3 ARMATURE CURRENT VS SPEED DESCRIPTION: Here armature current Ia was varied and the corresponding speeds were noted down.

CONCLUSION: It was found that speed decreases with increase in armature current Ia. It shows drooping characteristics

GRAPH .4

Armature voltage VS Speed

Armature voltage(volts)

Table .4 ARMATURE VOLTAGE VS SPEED

S.No

Armature Voltage (V)

Speed (rpm) IGBT

Thyristor

1

0

0

0

2

50

360

430

3

75

550

630

4

100

734

850

5

120

910

1070

6

150

1130

1330

7

170

1300

1520

8

200

1490

1598

OBSERVATION .4 ARMATURE VOLTAGE VS SPEED( COMPARISON BETWEEN IGBT AND SCR) DESCRIPTION: Here the field voltage Vf was kept constant the armature voltage Va was varied and the speed was noted accordingly for IGBT and SCR.

CONCLUSION: It was observed that the slop of the graph for IGBT is less in comparison to that of SCR.The base speed is attained at comparatively lower armature voltage for SCR as compared to IGBT. Hence IGBT gives better control over speed.

5.2 COMPARISON BETWEEN IGBT AND SCR IGBT

SCR

1.Gate- Drive Requirements Lower

Higher

2.Switching Losses

Less

More

3. Snubber Circuit Requirements

Small

Large

4. Efficiency

More efficient being smaller , lighter and generate fewer harmonics

Less efficient being bulky and generate more harmonics

5. Switching Speed

Faster than BJT but lesser than MOSFET

Slower than IGBT & MOSFET

6. Input Impedance

High

Low

7. Second Breakdown Voltage

Absent

Present

8. Control Parameter

Voltage Controlled device

Current Controlled device

9. Cost

Costly

Cheap

Gujarat Technological University, GujaratPage42

CONCLUSION

Speed control of dc motor motor using IGBT based Four Quadrant Chopper drive was carried out and following conclusions were made

1. Speed varies directly with armature voltage by keeping field voltage constant. 2. Speed varies inversely with field voltage by keeping armature voltage constant. 3. Armature voltage control gives the speed below the base speed whereas field control gives the speed control above the base speed. 4. Armature current vs Speed at constant flux gives a drooping characteristic. Though it should have been a straight line parallel to x-axis but due to saturation effect there is slight decrease in speed and shows a drooping characteristics. 5. The IGBT based circuit gives smoother control over the entire speed range as compared with the SCR based circuit. 6. IGBTs feature many desirable properties including a MOS input gate, high switching speed, low conduction voltage drop, high current carrying capability, and a high degree of robustness. 7. Devices have drawn closer to the 'ideal switch', with typical voltage ratings of 600 1700 volts, on-state voltage of 1.7 - 2.0 volts at currents of up to 1000 amperes, and switching speeds of 200 - 500 ns. 8. The availability of IGBTs has lowered the cost of systems and enhanced the number of economically viable applications.

Gujarat Technological University, GujaratPage43