Study of System Dynamics of High-Power LEDs

Optical properties of LEDs are sensitive to junction temperature. The understanding of system dynamic behavior is quite important in the controller design of LED. From the principle of solid-state lighting, the luminance of LED is induced from two physical mechanisms: energy effect and optoelectronic effect. The system dynamics model of a high- power LED fixture for energy effect is derived and identified in the present study using step response method. Both theoretical and experimental analyses have shown that the thermal system dynamics model of the LED fixture is 4th- order with 3 zeros and can be further reduced to a first-order biproper system. It is shown that the instantaneous jump of junction temperature dominates the thermal behavior of LED at the beginning of the step input. The optoelectronic effect is induced mainly from the current input and the junction temperature. Combining the two physical effects, an electric- heat-optical system dynamics model of LED luminaire was finally derived which is the basic system dynamics model for LED luminance control.