Controlling the input impedance of constant power loads

Power electronic circuits often regulate load power and present a constant power load (CPL) to the utility or other electrical source. Because CPLs exhibit a negative incremental input impedance, they pose stability concerns in both DC and AC systems. This paper presents a power converter for a constant power LED lighting load that mitigates these stability concerns by presenting a controllable input impedance to the electrical source. The use of an energy buffer allows the converter to control input power to resemble a resistive load over short times, while still delivering constant output power. 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.