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Buck Converter with Thermal Model

Overview

This demonstration shows a simple unregulated buck converter including a basic thermal model. It serves as an example for using thermal descriptions, heat sinks and the thermal chain.

Electrical model

This schematic shows a simple buck converter using an IGBT. The circuit is clocked with a fixed frequency of 10 kHz.

Thermal model

A thermal description is assigned to both the IGBT and the free wheeling diode. You can view and edit the thermal description by selecting "Edit..." from the drop-down menu of the "Thermal description" parameter. The thermal parameters were obtained from measurements of commonly available semiconducters.

A Thermal Chain component is used to model the thermal transitions of the cases of the semiconductor to the heat sink and from the heat sink to the ambient temperature of the environment.

The thermal descriptions are stored in a private thermal library in the directory /demos/Thermal_plecs/.

The instantaneous switching and conduction losses of semiconductors can be calculated easily. In order to obtain averaged loss values, filtering blocks should be used to condition the instantaneous loss signals, which are accessed by probing any semiconductor. The Periodic Average component can calculate the the average conduction losses while the Periodic Impulse Average component can calculate the average switching losses. The total losses of all semiconductors can also be summed together.

Simulation

The first Scope shows the output voltage, the source current and the heat sink temperature. The electrical values reach equilibrium very early on in the simulation while the temperature takes much longer to approach steady-state conditions.

Steady-state operation

The final temperature of the heat sink can be calculated with the Steady-State Analysis that is pre-configured in the model. To access the analysis, go to the Simulation menu and choose Analysis tools.... To start the analysis, click on the Start analysis button. You can display the progress of the analysis by clicking on the Show log button.

Loss calculation

The total average losses of the diode and IGBT are calculated and compared with the heat flow in the thermal circuit. Note that it takes several seconds for the heat sink to warm up, while the loss probes are connected directly to the source components.