Extraction of Boundary Condition Independent Dynamic Compact Thermal Models of LEDs—A Delphi4LED Methodology

Abstract

Multi-domain electro-thermal-optical models of LEDs are required so that their thermal and optical behavior may be predicted during a luminaire design process. Today, no standardized approach exists for the extraction of such models. Therefore, models are not readily provided by LED suppliers to end-users. This results in designers of LED-based luminaires wasting time on LED characterization and ad hoc model extraction themselves. The Delphi4LED project aims to address these deficiencies by identifying standardizable methodologies to extract both electro-optical and thermal compact models of LEDs that together can be used in a multi-domain simulation context. This article describes a methodology to extract compact thermal models of LEDs that are dynamic, in that they accommodate transient thermal effects, and are boundary condition-independent, in that their accuracy is independent of their thermal operating environment. Such models are achieved by first proposing an equivalent thermal nodal network topology. The thermal resistances and capacitances of that network are identified by means of optimization so that the transient thermal response of the network matches that of either an equivalent calibrated 3D thermal model or a transient thermal measurement of a physical sample. The accuracy of the thermal network is then verified by comparing the thermal compact model with a 3D detailed model, which predicts thermal responses within a 3D system-level model.

Luminaire Digital Design Flow with Multi-Domain Digital Twins of LEDs

“…At the chip level, a physics-based model is created by using characteristics derived from measurements while at the package level a dynamic thermal compact model is created in two steps. First a detailed thermal model of the LED package structure is set up and "calibrated" with the help of structure functions derived from the measured thermal impedance, ( ) of the package and then, in a subsequent step, thermal capacitance and thermal resistance values of a thermal RC network model of the package are optimized to best represent the thermal properties of the LED package under any boundary conditions at the package footprints and the LED's dome (lens) [8]. (1) a boundary condition-independent compact thermal model of the physical LED package and (2) a multi-domain, so called Spice-like, model that describes the LED operation at the chip level [7].…”

“…A LED digital twin, also called multi-domain compact model [7,[14][15][16][17], is created. This includes a dynamic compact thermal model of the mechanical structure of the LED package [8]. 4.…”

Multi-Domain Modelling of LEDs for Supporting Virtual Prototyping of Luminaires

“…In the bottom-up modular approach, the modelling starts from a multi-domain model of LED chips [5][6][7], followed by compact thermal models of the LED packages, modules (orange framed items in Figure 1), and finally, luminaires [8,9]. Details of the compact modelling of the 3D thermal environment of LED chips (package, substrate, luminaire with optics) are provided in other publications, such as [8,10,11]. In the "Industry 4.0" language, these simulation models are called "digital twins" to represent the relevant aspects of the physical samples of LED chips, LED packages, modules, etc.…”

“…A further stage in the evolution of our model is that the I dis component is no longer calculated, since through the use of Equations (2) and (3), an LED as a "diode" is described and Equations (10) and (11) yield the radiant flux. From this, and using Equation (9), the total dissipated power heating the LED is calculated.…”

Modified Modelling for Heat Like Equations within Caputo Operator

“…The problem of fractal heat conduction describes heat transport in inhomogeneous materials as fibrous materials, coal deposits, textiles and other discontinuous media where homogenization is not acceptable because this approach neglects the important physical characteristics of transport processes. Non-smoothness raises problems and avoids the implementation of classical calculus a fractional and integer-order [5][6][7].…”