Sinusoidal PWM has been a very popular technique used in AC motor control. This is a method that employs a triangular carrier wave modulated by a sine wave and the points of intersection determine the switching points of the power devices in the inverter.Though this method is unable to make full use of the inverter’s supply voltage and the asymmetrical nature of the PWM switching characteristics produces relatively high harmonic distortion in the supply it is still popular for its simplicity.This abstract describes the theory of SPWM and the project shall be made using a programmed microcontroller of 8051 family duly interfaced to 3 phase inverter with 6 no’s MOSFET from DC derived from a single phase or 3 phase ,50 Hz supply. The load shall be a three phase 50Hz motor, 440volt, 0.5 to 1 HP motor.
Alternatively a star lamp load can be used to view the waveform only. This project uses an 8051 family microcontroller duly interfaced to the opto-isolators for feeding to the bridge drivers. 3 no’s of dual bridge drivers are used to feed 3 phase bridge inverter with the DC supply developed from single phase AC after rectification.
Powering the circuit is achieved by a pair of control transformers with bridge rectifier and filter capacitors. One set of this power is used for the microcontroller and the other one is used for driving circuits of the three phase bridge.
Further this project can be enhanced by following Space Vector Pulse Width Modulation Technique for higher efficiency and low harmonic distortion for motors.
NOTE: A 3 phase induction motor of 0.5HP or 1HP is required to see the output. Motor is not supplied along with the kit. However, it can be purchased at extra cost.
BLOCK DIAGRAM
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Hardware Requirements
- 8051 series Microcontroller
- MOSFET
- Gate Driver
- Crystal Oscillator
- Toggle Switches
- Resistors
- Capacitors
- Diodes
- Transformer
- Regulator
- Opto-isolators
Software Requirements
- Keil compiler
- Languages:Embedded C or Assembly
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