Project Title: AC Voltage Controller

Project Group #4



Scott Warren:

Brent Sutherland:

Tim Bodell:

Justin Saukarookoff:


Faculty Supervisor:

Supervisor: Dr. Bhat


1. Problem Definition

The commonly used thyristor-based voltage controllers generated line harmonics and

poor power factor. This can reduce the efficiency, performance and life-expectancy

of any down-stream loads.


2. Proposed Solution

To design, build and test a more improved AC voltage controller by the way of

pulse-width modulation.


3. Milestones and Assigned Tasks (tentative deadlines)

- Design voltage controller circuit. (May 27) Brent, Tim

- Acquire components. (May 27) Scott

- Build Circuit. (June 3) Justin, Scott, Brent

- Interface the micro-controller with a PC for programming. (June 3) Tim

- Design and implement pulse-width modulation algorithm. (June 10) Tim, Scott

- Confirm operation of pulse-width modulation algorithm. (June 10) Tim, Scott

- Interface micro-controller with voltage controller transistors (Design some

- I/O circuitry for A/D and possibly D/A conversion. Also, we will probably

require some amplification and isolation between the voltage controller and

the micro-controller. (June 17) Brent, Justin

- Invent a user-interface to control the system. (June 20) TBD

- Test Circuit, Modify and Debug. (July 8) All

- Poster presentation. (July 22)

- Write report. (July 29)


4. Progress

We have started the circuit design and acquired most of the components. Assigned

tentative tasks to group members to stay on schedule and force accountability.


5. Project Summary


The use of phase controlled AC choppers are well known to get a variable AC voltage

from a fixed AC voltage source. The phase control method encounters certain

disadvantages that are listed below:

(i) The phase control method presents a lagging power factor at the input. The

input power factor (PF) angle is always greater than the load PF angle.

(ii) The load voltage contains harmonics (multiples of the supply frequency).

Filtering these harmonics to achieve the correct sine-wave can be difficult.

(iii) There is a dead time-lag that produces a slow response.


Our project is aimed to design a transistor based AC voltage controller in order to

overcome all of these problems. The use of a multiple pulse width modulation (MPWM)

is our substitute instead of an AC chopper. The AC chopper switches the sine-wave

signal only twice in one cycle, where as MPWM is used to turn-on and turn-off the

sine-wave multiple times. This achieves a smother sine-wave and as a result, less

lagging power factor, harmonics, and dead time lag. By varying the width of the

pulse, we can vary the amount of power sent to the load.