An energy buffer for constant power loads

Abstract

Constant power loads (CPLs) are a class of loads steadily increasing in use. They are present whenever a load is regulated to maintain constant output power, such as with LED drivers in high quality lighting that is impervious to input fluctuations. Because CPLs exhibit a negative incremental input impedance, they pose stability concerns in DC and AC systems. This thesis presents a power converter for a constant power LED bulb that presents a favorable input impedance to the grid. The use of an energy buffer allows the converter to draw variable power in order to resemble a resistive load, while the output consumes constant power. A switched-mode power supply consisting of a cascaded boost and buck converter accomplishes this by storing energy in the boost stage output capacitor. Experimental results demonstrate that the converter exhibits a resistive input impedance at frequencies over 0.5 Hz while maintaining constant power to the LED load.