Presentation Outline Introduction to PFC Discuss Passive PFC method Discuss Active PFC method Conclusion
PFC Definition Power factor is defined as the ratio of the true power dissipated in the load to the apparent power taken by the load PF = (true power)/(apparent power) When the current or voltage is not a true sine wave, it is said to be distorted, then power factor is less than unity
Typical Circuits Have Power Loss Figure 4Figure 5
Passive PFC Power Factor = 48.5% Power Factor = 94%
The circuit functions as following Nmin = (10^6*Vc)/(4.44*f*B*Ac) Where for laminated iron cores, Vc = Vin + 25%Vin F = line frequency, Hz (typically 50Hz or 60Hz) B = maximum flux density, T (typically 1.3T) Ac = effective core area, mm^2 Passive LRC input filter for harmonic reduction f=50Hz f=1MHz
The Valley-Fill Circuit functions as follow Power Factor = 98%
Another Passive PFC Circuits Figure 2 Figure 3 According to Power Factor Correction Testing, (http://www.prodigit.com/e307.htm)http://www.prodigit.com/e307.htm Figure 2 input terminal inductance working frequency is power source frequency (50/60 Hz), due to the fact that inductor can soften the current sudden change, therefore the input current waveform will be smoother. Figure 3 is using partly smoothen circuitry structure, to improve power factor. PF = 98%
Active PFC Method Key Requirements for a Boost PFC Control IC 1.Control switching of Q1 to maintain a good input current waveform 2.For boost to be continuous, Voltage C1 must exceed the input voltage at all time, so IC must control to maintain the output voltage constant 3.If Output voltage maintain constant and load changes, Io and Po change, thus input rms current must change to keep Pin = Po. Hence, IC must adjust the longer term input rms current in response to load changes 4.If Ro and Vo remain constant for a period, then Io and Po remain constant for this period. However, if Vin changes during this period, then to maintain a constant input power, the I(in)rms must again change. Hence, IC must ajust the mean input current to compensate for any longer term input voltage changes.
Conclusion Passive power factor correction method will bring the power factor from less than 60% up to 98%. Passive PFC circuits is used for the low power application. For the high power application, the active power factor correction method will work better. Active PFC method can bring the power factor up to 99%.
Question? Good Luck for your final !!! Merry Christmas and Happy New Year!!!!