Improving the Light Load Performance of Power Factor Correction Converters Using a Digital Controller
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AC-DC power conversion is the first power stage for all offline electronic devices. To maximize AC power transformer utilization, the power factor of AC-DC converters must be improved. The method that AC-DC converters use to improve the power factor is known as Power Factor Correction (PFC). This improvement of power factor, which can be quantified in terms of the total harmonic distortion (THD) of the converter, almost always is a trade-off for a reduction in overall converter efficiency. With increasing requirements for greater efficiency and lower THD, especially at output power loads much less than the rated output power of the AC-DC converter, new methods have been developed to meet either or both requirements. Many methods, however, can improve light load efficiency, but increase THD. Other methods, can reduce THD, but worsen light load efficiency. Some methods can reduce THD and improve light load efficiency, but at significant complexity and cost. A new method for improving light load efficiency and THD, called Line Cycle Skipping (LCS) is proposed. This method improves the light load efficiency and THD without increasing complexity or cost. LCS can achieve this by conducting higher power over one or one-half line cycle, and then skipping or not conducting power over the next one or more line cycles. This allows the output power to remain constant at light load, while conducting higher input power over one or one-half line cycles. By conducting higher input power over a portion of the entire LCS period, the efficiency and the THD can be improved at lower output power levels, thus improving the light load performance of PFC converters. LCS is implemented in digital control using a low-cost 8-bit microcontroller on a 100W PFC converter operating in critical conduction mode (CRM). Simulation results were verified by the experimental prototype waveforms. Experimental results showed significant improvement in efficiency and THD across the light load power range, proving that LCS has potential to be implemented in existing PFC converters with low cost to improve the light load efficiency and THD performance.
URI for this recordhttp://hdl.handle.net/1974/15455
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