VARIABLE FREQUENCY DRIVE (VFD) FOR SINGLE PHASE INDUCTION MOTOR GROUP # 42405GROUP MEMBERS:RASHID NABI (12036) SALAHUDDIN (12037)DEEPAK KUMAR (12008) MUHAMMAD SAAD (12029)

PROJECT SUPERVISORSENGR. SHAHID AHMEDB.E.(ELECTRONICS); DCET, NEDUET, KARACHIM.ENGG. (INDUSTRIALELECTRONICS), NEDUET, KARACHI

ENGR. ASGHAR DAUDANIB.E.(ELECTRICAL), MUET, JAMSHOROM.ENGG. (ELECTRONICS), NEDUET, KARACHI

PROJECT WORK IN CHARGEENGR. DR. FARAH HAROONIN-CHARGE ACADEMICSB.E. INDUSTRIAL ELECTRONICS, IIEE/NEDUET, KARACHIM.ENGG. (ELECTRICAL) NEDUET, KARACHIPH.D. (TELECOM), ASIAN INSTITUTE OF TECH, THAILAND

INTRODUCTION TO VFD•VFD is a type of adjustable speed drive used in electro mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.•VFD is the combination of Embedded System, Control System & Power Electronics.

FUNCTIONS & FEATURES OF VFD

• Soft Start• Wide speed controlling (20Hz to 50Hz).• Acceleration or Accel-Ramp Rate• Motor Protection• Fault Diagnostics• Bidirectional

INDUCTION MOTOR• An asynchronous type of an induction motor is an AC electric motor in which

the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.

• An induction motor can therefore be made without electrical connections to the rotor as are found in universal, DC and synchronous motors.

• Induction motors are used worldwide in many residential, commercial, utility and popularly for industrial applications.

• Induction Motors transform electrical energy into mechanical energy

WHY INDUCTION MOTOR (IM)?

•Robust; No brushes. No contacts on rotor shaft •High Power/Weight ratio compared to Dc motor • Lower Cost/Power •Easy to manufacture •Almost maintenance-free, except for bearing and other mechanical parts

DISADVANTAGES

•Essentially a “fixed-speed” machine

•Speed is determined by the input frequency

•To vary its speed need a variable frequency and variable voltage ratio (v/f)

SYNCHRONOUS SPEED• The synchronous speed of an induction motor is determined

by the following equation:

• An AC motor's synchronous speed, ns, is the rotation rate of the stator's magnetic field,• f = power grid frequency

• p = number of poles

• The only way to change the speed, for the given poles is to vary the frequency.

BASIC DESIGN OF VFD• Its basic design consists of four elements:1)Rectifier2)DC Bus or Intermediate Circuitry3)Invertor4)Control Unit

RECTIFIER• The working principle of rectifier is changing the incoming

alternating current (AC) supply to direct current (DC).• The rectifier design will influence the extent to which

electrical harmonics are induced on the incoming supply.• It can also control the direction of power flow.

DC BUS OR INTERMEDIATE CIRCUITRY• The rectified DC supply is then conditioned in the

intermediate circuit, normally by the combination of inductors and capacitors.• The DC bus is the true link between the converter and

inverter sections of the drive. Any ripple must be smoothed out before any transistor switches “on”. If not, this distortion will show up in the output to the motor. • The DC bus voltage and current can be viewed through the

bus terminals.

INVERTER• The inverter converts the rectified and

conditioned DC back into an AC supply of variable frequency and voltage. • This is normally achieved by generating a

high frequency pulse width modulated signal of variable frequency and effective voltage. • Semiconductor switches are used to create

the output; different types are available, the most common being the Insulated Gate Bipolar Transistor (IGBT).

CONTROL UNIT• The control unit controls the whole operation of the variable

frequency drive• It monitors and controls the inverter to deliver the correct

output in response to an external control signal.• In control unit we have a microcontroller Atmega 328p which

performs the logical operation for the switching to generate the sine pulse width modulation (SPWM) according to given signal.

V/F RATIO OPERATION• All Variable Frequency Drives maintain the output

voltage – to – frequency (V/f) ratio.• The voltage has to vary with frequency to keep the

magnetic flux constant.

Where,N = number of stator turns per phase.Φm = magnetic flux

• If you didn't reduce the voltage, the flux would increase, This would cause magnetic saturation resulting in very high currents.

V/F TABLEf (Hz) V (volts) v/f (volts/Hz)

50 110 2.245 99 2.240 88 2.235 77 2.230 66 2.225 55 2.220 44 2.2

CONTROL SYSTEM DIAGRAM OF VFD BY V/F METHOD

SIMULATION & DESIGN OF VFD

THE WAVEFORM OF LOAD OUTPUT & CONTROLLER OUTPUT

PROBLEMS FACED• Circuitry didn't uphold 220 volts, and caused to burn out circuitry.• Previously we were using MOSFET IRF840 (8A,600v) and

IRFP460 (13A,500v) which couldn't provide the enough initial current for the motor to rotate the shaft.• We faced difficulties while setting bootstrap capacitor value

because we can’t get the real value of capacitor from given formula.• Faced trouble when we use same controller for the PWM sine wave

generation and rpm calculation through encoder.• Faced trouble in serial communication.

SOLUTIONS• We replaced MOSFET’s with IGBT’s G25N120 (25A,1200V).• We used step down transformer to reduce voltage from 220v

to 110v.• We used trial and error method to find suitable value for

bootstrap capacitor value.• We replace our ½ Hp motor with ¼ Hp because our circuitry

can’t provide enough current for ½ Hp motor.

CONCLUSION

• Significant energy savings• Retrofits (add to something that did not have it when

manufactured)• Occupy less space• Better design• Competitive edge

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