Prepared by: Luis Fernando Montoya Chun-Ju Huang Ashish K. Solanki Speed control of squirrel cage induction machine using V/F control Prepared by: Luis Fernando Montoya Chun-Ju Huang Ashish K. Solanki

Agenda Introduction Applications of AC drives Types of Methods to control the speed of Induction machine V/F control Power Converters Simulation Model Simulation Results Conclusion Reference

Introduction An electric drive system consisting of electric motor, its power controller and energy transmitting shaft consisting of load Types of Drive system DC Drive AC Drive AC Drives are mostly used in Industry.

Advantages and disadvantages of AC Drives compare to DC Drives 1. For the same rating, ac motors are lighter in weight as compared to dc motors. 2. AC motors require low maintenance. 3. AC motors are less expensive. 4. AC motors can work in dangerous areas like chemical, petrochemical etc. Disadvantage of ac drives 1.Power converters for the control of ac motors are more complex. 2.Power converter for ac drives are more expensive. 3.Power converters for ac drives generate harmonics in the supply system and load circuit.

Industrial applications Induction motors with squirrel cage rotors are the workhorse of industry because of their low cost and rugged construction. When Squirrel cage induction machine is operated directly from the line voltages(60 Hz/50 Hz essentially constant voltage) an Induction motor is operated at constant speed. However in the industry we required to vary the speed of an Induction motor. This can be done by Induction motor drives. Main application of Induction Motor drives: Fans, Compressor, Pumps, blowers, machine tools like lathe, drilling machine, lifts, conveyer belts etc.

Methods of Speed Control of Induction motors Stator voltage Control Stator Frequency Control Stator Current Control V/F Control Slip power recovery Control ( Wound Rotor Induction Machine)

Curve of the behavior of the Induction Machine During start up. Normally draws up to seven times the rated current. Normally delivers approximately 1.5 the rated torque, when starting When operating at base speed if the load is increased, the motor will start slowing down and the slip will increase. But if the load is increased beyond the Break down torque, the machine wont be able to recover.

V/Hz Theory Background The induction motor draws the rated current and delivers the rated torque at the base speed. As mentioned before the motor can take up to 2.5 load increase, with 20% drop in the speed.

Description of the principle Assume the voltage applied to the Motor is AC, and the voltage drop across the Armature resistance very small. Then at the steady state we get: (Voltage applied at the stator, and Flux) Since the V/f relation keeps constant, then the flux remains constant and the torque is independent of the supplied frequency.

Description of the Principle Since the flux is maintained constant, the toque developed depends only on the slip speed. Huge starting torque can be obtained without heating-up the machine

V/Hz Open Loop Torque Synchronous frequency

V/Hz control Closed loop

Three Phase Full Bride Uncontrolled Rectifier

DC-DC Boost Converter

DC-DC Boost Converter

3 Phase PWM Inverter

Block Diagram of Simulation Model

Simulation Model

Uncontrolled Rectifier and DC-DC Boost Converter Simulation Model

3 phase inverter with Squirrel Cage Induction Motor

Input Voltage for 3 phase uncontrolled Rectifier Simulation Results Input Voltage for 3 phase uncontrolled Rectifier

Output Voltage of three phase uncontrolled rectifier Simulation Results Output Voltage of three phase uncontrolled rectifier

Output Voltage of DC/DC Boost converter Simulation Results Output Voltage of DC/DC Boost converter

Output Voltage of 3 Phase PWM inverter before filter Simulation Results Output Voltage of 3 Phase PWM inverter before filter

Simulation Results Output Voltage of Inverter after filter ( Controlled Input voltage given to Induction motor)

Simulation Results Stator Current

Rotor Reference speed and Actual Speed Simulation Results Rotor Reference speed and Actual Speed Here the reference speed is 1000 rpm= 104.72 rad/sec

Without Filter after the PWM inverter , rotor speed is fluctuating Simulation Results Without Filter after the PWM inverter , rotor speed is fluctuating

Rotor Reference speed and Actual Speed Simulation Results Rotor Reference speed and Actual Speed Reference speed is 600rpm= 62.83 rad/sec Reference speed is 1300 rpm=136.14 rad/sec Reference speed is 1500rpm= 157.08 rad/sec

Rotor Reference speed and Actual Speed Reference Speed is changed from 104.71 rad/sec to 92.24 rad/sec

Conclusion In Case of Squirrel cage induction motor the slip cannot be increase above certain limit, the operating speed range is very less. By applying the V/F control we can get the large operating range by keeping V/F ratio constant.

THANK YOU QUESTIONS????

Reference [1] Modern Power Electronics and AC drives by Bose, Bimal K. [2] POWER ELECTRONICS Converters, Applications and Design by Ned Mohan [3] Power electronics Lecture Notes by Prof. Nasiri [4] Lecture Notes by Dr. Omar [5] AC Induction Motor Control using Constant V/Hz Principe and Space Vector PWM Technique with TMS320 C240 [6] Speed Control of 3-Phase Induction Motor Using PIC18 Microcontrollers