This applet investigates distortion in a current waveform and the affect that it has on the true power factor. The term power factor has been traditionally given as how in phase a fundamental current is to fundamental voltage, and is expressed as cos PHI, where PHI is the angle between the fundamental voltage and current waveforms. But the true power factor is really defined as the ratio of real power to the apparent power (given by Vrms x Irms) and is given by LAMBDA. This definition of power factor now takes into account not only the level of reactive power in the circuit but also the level of distortion in the current caused by the non-fundamental frequencies. Ideally, the power flowing in the circuit should be real power as this is the most efficient and for this case the power factor, LAMBDA, is 1. However in power electronic circuits this is not generally not the case (especially for non-sinusoid looking waveforms), however a designer can strive to obtain a true power factor of one for all our circuits. 

The level of harmonic distortion in the current waveform can be expressed as a percentage and is given as the Total Harmonic Distortion (THD) of a waveform. THD is defined as the ratio of the square root of the sum of all the non fundamental frequency magnitudes squared to the magnitude of the fundamental. If only the fundamental frequency exists in the waveform then the THD will be 0%. It doesn't take much distortion in a waveform to give THD values well over 100% (as can be seen in the applet example). 

This applet assumes that the power being delivered is constant. By changing the duty cycle of the current you can see how the true power factor and the THD change. The rms of the current also changes with the duty cycle. As the duty cycle is reduced the current waveform shape approaches that of an impulse, which contains all frequency components. Therefore for smaller duty cycles there are more harmonics in the waveform and the THD is larger. 

By changing the phase angle of the fundamental component (red dot on the fundamental current), you can see how the true power decreases. As the phase angle approaches 90deg most of the current that is flowing is reactive current so isn't contributing much to the output power. This is why the rms current level must increase dramatically, so as to check the real power constant.

• Adjust the width of the current pulse by dragging the red dot on the edge of the current waveform. By dragging the edge the value of the duty cycle, d, changes. Find the optimum duty cycle in terms of THD and true power factor. Also see how the harmonic spectrum relates to the value of THD.
• Adjust the phase angle of the current waveform by dragging the red dot at the zero amp position on the current sine waveform. Notice how this changes the rms current level and the true power factor value but not the THD.