SPEED CONTRO OF THREE PHASE INDUCTION MOTOR USING FUZZY … · SPEED CONTRO OF THREE PHASE INDUCTION MOTOR USING FUZZY LOGIC CONTROLLER Juhi Singh1 Ms shweta Chourasia2 1M.Tech Scholar

SPEED CONTRO OF THREE PHASE INDUCTION MOTOR USING FUZZY LOGIC CONTROLLER

Juhi Singh1 Ms shweta Chourasia2

1M.Tech Scholar 2Assistant Professor 1,2Department of Electrical Engineering

1,2RKDF IST, SRK University [email protected] [email protected]

ABSTRACT: Electric drives play a vital role in the field of power electronics; since they are used in a sufficient range of

applications. In current years, the field oriented control of induction motor drive is broadly used in high performance drive

system, because of its benefits such as high efficiency, trouble-free, tremendously rugged, superior power factor. Induction motor

is used in a lot of applications like Industrial drives, automotive control, etc. In the modern years there has been a huge demand

in industry for modifiable speed drives. In this paper a fuzzy logic technique is proposed which is awfully simple and easy to

implement in the real scenario. Fuzzy logic controller based speed control of a three phase induction motor. The system is

modeled in a MATLAB Simulink and the result of proposed method is compared with the conventional PI controller.

KEYWORDS: Three phase induction motor, Speed Control, Fuzzy Logic, Matlab, Simulink

1. INTRODUCTION

In the field of electric drives, Power electronics plays a significant role and it increases the energy

efficiency and controlling characteristics of the drive. It is important to use the correct drive according to

the application. Recently there is tremendous development in the field of power electronics and

microcontrollers[1]. Thus the technology of modern drives has changed dramatically and various studies

are being carried to design the electric drives to make motor usable for certain application with good

efficiency. Many researches are going on to use fuzzy controlling for induction motors as induction

motors are the widely used motors in the industries because of its various advantages like self starting

capability, rugged construction, and maintenance free operation, economical and reliable. As in illustrated

Induction motor possesses many advantages but it also have some disadvantages that its speed controlling

is very much complex. It is best suitable for the constant speed loads but it is not suitable for variable

speed loads. In induction motor speed can be controlled by varying frequency, stator voltage, number of

poles and rotor resistance. Among these the frequency control is the most popular. By using the fuzzy

logic control the frequency of the Induction motor is controlled in real time according to the speed

requirement[3]. There are various methods of speed control such as pole changing method, rotor resistance

control, stator voltage control, slip control, constant V/f control, variable V/f control etc. Three phase

induction motor is the most widely used machine in the Industries. Their characteristics make them

suitable to be used in the tough environment conditions as well.

2. INDUCTION MOTOR The principle of operation of the induction machine is based on the production of a rotating magnetic

field. The power received by the rotor of the induction motor is from stator by the process of induction. A

rotating magnetic field is set up in the air gap when a three phase supply is given to the stator. The

windings are also electrically displaced by 120 degree. According to Faraday‟s law of electromagnetic

induction whenever there is a rate of change of magnetic field there is emf induced in it. The rotor bars

are short circuited by the end ring so heavy current flows which produce starting torque sufficient enough

to start the induction motor.[5] The rotor tends to align itself with the rotating magnetic field by attaining

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same speed but the speed of rotor could not reach the speed of rotating magnetic field as with zero

relative speed torque becomes zero and rotor lags.

Fig 1.1 Rotating Magnetic Field

The rotor rotates in the direction of rotating magnetic field so as to reduce the rate of change of flux as per

the lenz law. The rotor continues to do so till the rate of change of flux is reduced nearly to zero. The

speed at which rotating magnetic field rotates is called synchronous speed and the speed at which the

rotor rotates is called rotor speed. The rotor speed never becomes equal to the synchronous speed as at the

speed near to synchronous speed the relative velocity becomes so less that the induced current becomes

nearly zero and thus torque becomes zero and rotor could not accelerate.[5] The per unit difference

between synchronous speed and the rotor speed with respect to the synchronous speed gives the slip of

the Induction motor. Mathematically, the relation between the speed of an induction motor and the

synchronous speed(speed of rotating flux) can be stated as:

Nr = (1-s) Ns;Ns = 120f/p

Where, Nr is the rotor speed Ns Is the synchronous speed, s is the slip, f is the supply frequency as speed

is a function of frequency and no. of poles , speed can be varied by varying these parameters.

3. FUZZY SET THEORY Fuzzy logic is a superset of Boolean logic which has been extended to handle the concept of partial truth-

truth values between "completely true" and "completely false". It is the logic basic modes of reasoning

which are approximate rather than exact. Fuzzy logic replicates human knowledge in to control logic. The

essential characteristics of fuzzy logic as founded by Zader Lotfi are Any logical system can be fuzzified

and No need of any exact mathematical model.In fuzzy logic, knowledge is interpreted as a collection of

elastic or, equivalently, fuzzy constraint on a collection of variables. Classical logic only permits

conclusion which is either true or false whereas is fuzzy logic degree of truth is analyzed by a probilitic

range from 0 to 1.

4. PROPOSED METHODOLOGY

Fuzzy controller basically contains four essential segments. In the fuzzy logic control first we select the

input to the fuzzy logic control then the proper MFs both for input and output variables are selected and

the input variables are fuzzified then a Fuzzy rule base for the controller is prepared and by Selecting

proper defuzzification technique 6. Output is defuzzified that to obtain control signal for desired

operation.

Designing fuzzy logic controller: The block diagram to control the speed of the induction motor is

shown fig 1.2

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Fig 1.2 Block diagram of fuzzy logic controlled induction motor drive

As shown in the block diagram fig 1.2 the motor speed is taken as the feedback element. The motor speed

is compared with the reference speed and the error signal e(k) is obtained. The difference of error signal

and unit unit change in error signal gives the change in error signal ce(k). The signals e(k) and ce(k) is

given as the input to the fuzzy logic controller. The inputs are fuzzified in the fuzzy logic controller and

proper rules are set. Then according to the rules output is obtained which is then defuzzified to obtain the

control signal. The control signal is then used to modify the output frequency and voltage of the inverter

to obtain the desired speed.

Simulation diagram

The simulation of the proposed scheme is done in the MATLAB simulation fig 1.3 shows the simulation

model of the proposed work. as shown the induction motor is fed through the inverter.

Fig 1.3 Simulation Diagram

The input to the inverter is assumed to be a stiff dc source. The motor output speed is taken as a feedback

it is compared with the reference speed which can be changed accordingly. The error and change in error

input is given to the fuzzy logic controller whose output modifies the control signal according to the

need.[15] According to the control signal a three phase reference current waves are generated which acts as

a reference current waves and that reference current waves are tracked by suitable gate pulse of the

inverter. Here hytersisis current control scheme is utilized to track the reference current. To simulate the

effect of the disturbance in the speed of induction motor the load torque in a motor is varied the fig 1.4

describes the variation of load torque with time. As seen from the figure the load torque is changed at 2

sec.

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Fig 1.4 Variation Of The Load Torque With Time

Fig 1.5, fig 1.6 and fig 1.7 describes the fuzzification of the error signal, change in error signal and output

variable of the fuzzy logic controller respectively. Here ne represents the negative error, ze represents

zero error and pe represents positive error, nce represents negative change in erroe, zce represents zero

change in error and pce represents positive change in error, n represents negative control, z represents

zero control; and p represents positive control.

Fig 1.5 fuzzified error signal Fig 1.6 fuzzified change in error signal

Fig 1.7 fuzzified output variable Fig 1.8 describes the rules that are made to

obtain the output variable

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Fig 1.9 Rules For The Fuzzy Logic Control Fig 1.10 surface rule viewer plot

5. RESULTS AND DISCUSSIONS Fig 1.11, fig 1.12 and fig 1.13 show the variation of rotor speed with time for the reference speed of 1000

rpm, 1200 rpm and 1400 rpm respectively. It is seen that the motor quickly settles to the reference speed

by adjusting the reference current of the inverter. The settling time here is around 2.5 sec. It is also seen in

the intermediate time when there is a load disturbance then there is slight variation in the motor speed but

the motor quickly adjusts itself to the steady state value.

Fig 1.11 Speed Time Curve of the Three Phase Induction Motor For Reference Speed of 1000 Rpm

Fig 1.12 Variation Of Motor Torque With Time For Reference Speed Of 1000 Rpm

Fig 5.2 , fig 1.14 and fig 1.15 describes the variation of motor torque with time for the reference speed of

1000 rpm , 1200 rpm and 1400 rpm respectively. Initially motor torque is less but at the time when load

increases the motor torque increases so as the cope up with the load and maintains stability.

1.13 Speed Time Curve Of The Three Phase Induction Motor For Reference Speed Of 1200 Rpm


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Fig 1.15 Speed Time Curve Of The Three Phase Induction Motor For Reference Speed Of 1400

Rpm


From the various result obtained it is evident that the proposed methodology to control the speed of the

three phase induction motor is highly dynamic and simple in application.

Table 1.1 Comparative analysis with the previous work

Characteristic Previous works Proposed works

Settling time Less Larger

Computations involved Less More

Ripples in torque Less Higher

Circuit complexity Less More

Along with that this control scheme is highly robust that is it is not very much affected by the

disturbances occurring in the system. As the complexity in controlling is not very much as the

mathematical modeling of the system is not required hence it is simple to be applied and the system is

highly adaptable.

6. CONCLUSION The fuzzy conntroller provides a very good result for speed controlling of a three phase induction motor.

From the various results obtained following observations is obtained :By using the fuzzy logic in

controlling there is no need of mathematical modelling of the induction motor.With varying speed the

induction motor adjusts itself very quickly this shows that the dynamic performance of the induction

motor is incresed.When the disturbance is simulated by varying the load it is seen that the induction

motor adjusts its electromagnetic torque very quickly so as to maintain the desired speed this shows that

the robustness of the induction motor is incresed. As far as controlling is considered the controlling

scheme is very much simple and easy to be implemented.

7. FUTURE SCOPE Induction motors are the most widely used motors as it has so much benefits and its maintenance cost is

very less. Generally induction motors are used for constant speed applications. By using the proposed

methodology induction motors can prove to be useful for variable speed drives as well. With the advent of

fast computers and microcontrollers implementing the fuzzy control becomes very much easy and

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economical. So by using this technology in future cheap induction motor drives will be available for

variable speed applications.

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SPEED CONTRO OF THREE PHASE INDUCTION MOTOR USING FUZZY … · SPEED CONTRO OF THREE PHASE INDUCTION MOTOR USING FUZZY LOGIC CONTROLLER Juhi Singh1 Ms shweta Chourasia2 1M.Tech Scholar