Abstract:
In this thesis, an imp0l1ant overvIew has been gIven about the need for power factor
improvement, the history of power factor correction by capacitors and the rcview of static power
factor con.ection methods.
A new method is proposed which improves the power factor automatically of varying lagging
loads to unity using one single large shunt capacitor instead of using a bank of switching
capacitors. Basically, this control scheme is a static power factor improvement method by
continuous voltage or current control of a capacitor. In this work, the voltage across the capacitor
is being changed by a bi-directional switch to control the magnitude of compensating capacitor
current and thereby attaining unity power factor. The switching device is turned on-offby a pulse
width modulated signal having moderately high frequency (several times of source frequency) to
produce a current which is equal to the reactive component of load current in magnitude but is
directcd in opposite direction. As a result line current will be in phase with source voltage.
The control scheme is involved in detecting the power factor angle of the load and also the
magnitude of the load current and then making the capacitor voltage is changed automatically
according to the var compensation of the load to improve line power factor..
The scheme is simple in the sense that it uses only one static bi-directional switch controlled by
an electronic control circuit. The electronic control circuit is also simple that uses only analog
ICs and some discrete digital components.
