The Speed Control Of Induction Motor

Published Date: 02 Nov 2017

Abstract— This paper gives an overview on Speed control of Induction Motor via Pic Controller using Lab VIEW. For Monitoring and controlling the Induction motor speed we can use the Lab View Simulation software. Lab VIEW Software can be used for continuous monitoring in an Real Time System applications. Most of the Industrial Automation control process are done by Lab VIEW software only. Lab VIEW Software plays major role in Industrial Monitoring and control systems. There are various types of controller used in Drive control systems in order to perform some actions such as Speed control, Run Motor in both forward and reverse direction. Here we have used Pic Controller for speed control process. From Lab VIEW software we can send Signals to Pic Controller to Run Induction Motor in either Forward/Reverse Direction and we can set the Speed of the Motor.

Keywords: Lab VIEW, Induction motor, Speed Control

Introduction

Today's problem in Designing field is usage of many Control Circuits. Increases on Circuit Wiring number increases along with the increase in control circuits. Only way to reduce the wiring and control circuits is to implement the required control task in program level in any simulation Software's. Thus it lead a way to reduce the hardware cost. It is not possible to design distance control of the system as more hardware's and wirings were needed. Hardware Level Implementation of control circuits for Long Distance Control is complicated and controlling process is also inaccurate. we need to add required additional external circuits for modified Process which will increase the cost but it will be implemented with the high signal to noise ratio. Same control circuits cannot be used for different Motor Speed control applications. Rapid Growth of Lab VIEW simulation program have easily made the engineering design with lesser the materials required, it is because the entire design is implemented in software programming paradigm. Lab VIEW along with Pic Controller had been commonly used in the industry for controlling the speed on induction Motors. Thus Designing distance control machinery is now possible in this method along with interfacing with Ethernet mode [1].

Modes Of configurations

Lab VIEW

Lab VIEW meant for Laboratory Virtual Instrumentation Engineering Workbench and is a graphical development environment for generating flexible and scalable design, control, and test applications rapidly at minimal cost. Engineers and scientists are able to interface with real-world signals, analyse data for meaningful information, and share results through intuitive displays, reports, and the Web. Lab VIEW doesn't need any programming Experience from user end so it can be done fast and easy for all users.

The programming method used in Lab VIEW is G programming, which is defined for graphical programming. It is also known as data flow programming as it is depending on the structure of the graphical block diagram to execute the user-designed program. when Comparing with text-based programming, Lab VIEW is user friendly as the user can design the program by simply arrange and wiring the relevant icons together. Lab VIEW programs are also named as virtual instruments, or VI, because their appearance and operation mimic the physical instruments, such as oscilloscope and multi- meters.

Lab VIEW also has an extensive library of math functions similar to MATLAB libraries and also formula nodes that allow text-based programming for certain sections of the code that require complex logical structures. Like other conventional programming, Lab VIEW has standard features such as looping structures, data structures, event handling, object-oriented programming. Lab VIEW has front-end interface applications that allow user to design and then use for controlling systems. In general Lab VIEW has three main elements: the front panel, the block diagram and the connector panel. The front panel allows the user to build the controls and indicators.

Figure 1. Three main elements of Lab VIEW software.

The controls are including Cons, push buttons, dials, and other input mechanism. Indicators are graphs, LEDs, and other output displays. Meanwhile, the block diagram let user to add code using VIs and structures to control the front panel objects. The connector panel allows user to represent a single VI as a sub VI icon that can be called in another VI.

The elements are illustrated in Figure 1.

Levels of Lab View Simulation

1. Virtual Implementation Process

The objective in this paper is to control Induction motor using Lab View simulation Software. To achieve this objectives, the establishment of the communication Lab VIEW and Induction motor has to be done and it should be verified. The implementation used in this Lab VIEW to perform the start and stop operation of the motor, either in forward or reverse direction, and varying the speed by changing the frequency of the motor. Since system is not an SCADA based control so there is no practical data measurement acquire from the actual output of the motor.

The system has three-layer network architecture illustrated in Figure 2.

Figure 2 Three-Layer Network Architecture

2. Implementation of VI Design

The objective of the VI program in this paper is to allow user to make the decision of the start and stop operation of the motor, either in forward or reverse direction, and varying the speed by changing the frequency of the motor, by perform two simple step. This process is implemented in VI's by using some Logics applied. very first step in this simulation is to Press the power Button to Upward Direction to switch on Control circuit and select the Motor turning direction by pressing the selector switch to select Forward/Reverse Direction in the VI Front Panel. Secondly, vary the speed by turning the Frequency knob to the value of the frequency that the user desire. Figure 3 shows the VI Front Panel.

we have created 5 tags and used in the implementation, and the details of the tags have been tabulated in Table 1.

By referring to Figure 3, when the Grey push Forward button is the switch to determine the motor is turning in forward direction. Meanwhile, the Grey Black push button is the switch to determine the motor is turning in reverse direction. Both Forward and Reverse light indicators at the right hand side show whether the push buttons have been switched ON. The knob labelled as "Frequency" is the key program to control the frequency as well as the speed of the motor. The push button labelled as "Stop" function to stop the program execution.

Figure 4 describes about the VI Block Diagram, which the programming part of the VI. By referring to the Figure 4, the following VI components that are visible in both Front Panel and Block Diagram. For Example the push buttons, knob, light indicator. But the Red colour square boxes without dotted lines are the VI component that is visible in Block Diagram but they are not visible in Front Panel, which are essential VI to structure the program. For example, Logics used with in Case Structure and the While loop. The While loop, which is similar concept with the While loop in C Programming, is used in this VI to ensure the program execute continuously until the stop button is triggered.

The VI block diagram consists of two parts of the program. First part of the program is to allow user to switch on either Forward or Reverse direction of the squirrel cage induction motor. The second part of the program is to vary the frequency of the motor by changing the Frequency knob value.

Table 1

THE DETAILS OF TAGS AND ITS CONNECTION TO INVERTER.

TAG NAME

CONNECTED TERMINAL

TERMINAL NAME

OUTPUT BIT 1

S1

Multi Function

input1

(Forward/Stop)

OUTPUT BIT 2

S2

Multi Function

Input2

(Reverse/Stop)

OUTPUT BIT 5

S5

Multi Function

Input5

(Multispeed reference 1)

OUTPUT BIT 6

S6

Multi Function

Input5

(Multispeed reference 2)

OUTPUT BIT 7

S7

Multi Function

Input5

(Multispeed reference 3)

By referring to Figure 3, if the user has switched on the Forward button, the signal will be transmitted to the "outputbit1, i.e. the signal will be Generated from the Reference Frequency.

Then once the signal has been successfully triggers the light indicator of the output address, and the "Forward" direction indicator in the LabVIEW’s Front Panel will light. The same process is identical to the reverse direction as well.

Figure 3. VI front panel of the project.

By referring to the Figure 4, the square boxes indicate the Frequency calculations. After the user set the value of the frequency by turning the "Frequency Variable" knob, the value will be sent to the Case Structure where Logics used. The output of the Case structure has been divided into Multispeed Reference 1,2,and 3, in which the number is either 0 or 1.

Table 2 below describes the relationship between the multi-step speed references 1 through 3 and frequency references 1 through 8.The value of each frequency reference can be set in the function parameters of the variable frequency drive. In this paper, the value of each frequency reference has been tabulated in Table 3.

Figure 4. VI Block Diagram of the project.

Figure 5. VI block diagram program (motor orientation switching part).

By referring to Table 3, as long as the user has set the input frequency according to any of the condition, the number will be converting into Boolean in which it will arrange according to the relevant Multi-step speed reference. Then this Boolean number will trigger the variable frequency drive and determine the frequency and as well as the speed of the squirrel cage induction motor according to the output condition listed in Table 3.

For example, if the user set the input as 8 Hz, in which the input range of this value is within 7 <= x < 14. Therefore, the Boolean number of Multi-step speed reference 1 is 1, and the rest are 0. Then, this signal triggers the variable frequency drive to deliver the frequency of 7 Hz.

Table 2

Logics Applied Between multi-step speed references and frequency reference.

Frequency reference

Multi-step speed reference 1 (Set value: 6)

Multi-step speed reference 2 (Set value: 7)

Multi-step speed reference 3 (Set value: 8)

Frequency ref.1

OFF

OFF

OFF

Frequency ref.2

ON

OFF

OFF

Frequency ref3

OFF

ON

OFF

Frequency ref4

ON

ON

OFF

Frequency ref5

OFF

OFF

ON

Frequency ref6

ON

OFF

ON

Frequency ref7

OFF

ON

ON

Frequency ref8

ON

ON

ON

Table 3

Data Conversion of input frequency in LabVIEW for varying frequency reference

Frequency reference

Multi-step speed reference 1 (output bit 5)

Multi-step speed reference 2 (output bit 6)

Multi-step speed reference 3 (output bit 7)

Output frequency of squirrel cage induction motor (Hz)

x < 7

0

0

0

0

7 ≤ x < 14

1

0

0

7

14 ≤ x < 21

0

1

0

14

21 ≤ x < 28

1

1

0

21

28 ≤ x < 35

0

0

1

28

35 ≤ x < 42

1

0

1

35

42 ≤ x < 48

0

1

1

42

x > 48

1

1

1

49

VARIABLE FREQUENCY DRIVE

In starting a motor, a VFD initially applies a low frequency and voltage, thus avoiding high inrush current associated with direct on line starting. After the start of the VFD, the applied frequency and voltage are increased by using the KNOB CONTROL.

This starting method typically allows a motor to develop 150% of its rated torque while the VFD is drawing less than 50% of its rated current from the mains in the low speed range. A VFD can be adjusted to produce a steady 150% starting torque from standstill right up to full speed.

With a VFD, the stopping sequence is just the opposite as the starting sequence. The frequency and voltage applied to the motor are ramped down at a controlled rate. When the frequency approaches zero, the motor is shut off. 

3. Testing and Verification

Testing the created Simulation is the final stage of this project. We have tested the simulation by step by step process in both Forward and in Reverse Directions. We found good results from this simulation. Thus Speed Control on Induction Motor has been implemented with the Lab VIEW Software.

CONCLUSIONS

Thus we came to conclude, that from this the objective, scope and fundamental requirements of the project had been achieved. Every decision made by the user is done through Lab VIEW Simulation only. There is limitation in the speed control as there are only 3 multi-step references in the VFD. The frequency changes in this project cannot perform in smaller steps unless there are additional multi-step references provided.

In overall, choosing Lab VIEW as the human machine interface for the implementation is a proper decision as it has various types of applications and functions that are easy to understand and use. Additionally, this approach is more economical as the objectives of the system implementation have been achieved with only basic functionality of the Lab VIEW toolkits used.