Project Overview

 

 

UVIC ELEC 499

Design Project

Summer 2011

Supervisor: Dr. Bhat

 

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A block diagram has been generated to illustrate the implementation of basic circuitry used in our project:

 
Block Diagram.png

The source voltage is manipulated two ways: it is fed to the switching circuitry for synchronization and

it as also switched by MOSFETs to vary the load voltage. Synchronization is done via a comparator

and the microcontroller's software to ensure no drifting occurs between the 60Hz power signal and

the switching signal. Once synchronized the microcontroller will output two 1 kHz pulse width modulated

square waves, one signal for each MOSFET. Because one MOSFET is in series and the other is in parallel,

one signal must be the complement of the other. Since the microcontroller can not sink or source

enough power to switch the MOSFETs, a MOSFET driver is needed. Opto-isolators are implemented to isolate the control circuit from the power circuit and provide a separate ground/reference voltage

for the source pin of each MOSFET.

 

The switched waveform that will be applied across the load is shown below:

 
Waveforms2.png

The average voltage across the load increases proportionally to the duty cycle of the control signal.

The signal seen by the load remains a recognizable, albeit distorted sinusoid. This waveform can be

corrected by applying a filter inline with the load, which will provide high quality power to the load

while at the same time reducing the line current harmonics that are typical to classic thyristor-based

voltage controllers.