Accounting for Switching and Conduction Losses
Thermal management is an important aspect of power electronic systems and becomes more critical with increasing demands for compact packaging and higher power density. PLECS enables the user to include the thermal design with the electrical design at an early stage, providing a cooling solution suitable for each particular application. In addition, switching and conduction loss calculations are easily done. Simulation speed is not adversely affected during loss calculations since ideal switching is maintained.
Instead of determining semiconductor switching losses from current and voltage transients, PLECS records the semiconductor's operating condition (forward current, blocking voltage, junction temperature) before and after each switch operation. It then uses these parameters to read the resulting dissipated energy from a 3D look-up table. During the on-state, the dissipated power is computed from the device current and temperature.
This combination of ideal switch models with detailed loss data provides an efficient and accurate alternative to detailed device simulations. The required data tables are entered via PLECS' integrated visual editor.
Heat Sink Concept
The core component of the thermal library is an idealized heat sink depicted as a semi-transparent box. A heat sink absorbs the thermal losses dissipated by the components within its boundaries. At the same time, a heat sink defines an isotherm environment and propagates its temperature to the components it encloses.
Thermal Equivalent Network
Heat conduction from one heat sink to another or to an ambient temperature is modeled with lumped thermal resistances and capacitances connected to the heat sinks. This approach allows the user to control the level of detail of the thermal structural model.
Thermal Semiconductor Models
Several manufacturers of power semiconductors provide ready-to-use thermal models for PLECS.