PLECS 2.2 Online Help |
The text entries Manufacturer, Part number and Comment are for documentation purposes only. The Type selector serves as a filter for the Thermal description menu entry. It must be set according to the semiconductor type it is intended to be used with.
In order to access the data sheet in a PLECS model it must be saved in a subdirectory on the thermal search path. See section Thermal Library for details of the structure of the thermal library.
Switching losses are defined as a 3D lookup-table in the Turn-on loss and Turn-off loss tabs. The energy for each switching event depends on the blocking voltage, the device current and the device temperature. PLECS uses a linear interpolation technique to calculate the actual losses from the given values.
New interpolation points for temperature, voltage and current are added and removed with the Edit menu or the context menu in the table. Multiple values can be added separated by semicolons or spaces.
To rotate and tilt the 3D view move the mouse within the view while keeping the left mouse button pressed.
Conduction losses are defined by means of the on-state voltage drop as a 2D lookup-table in the Conduction loss tab. The voltage drop depends on the device current and the device temperature. PLECS uses linear interpolation to calculate the actual voltage drop from the given values.
New interpolation points for temperature and current are added and removed with the Edit menu or the context menu in the table. Multiple values can be added separated by semicolons or spaces.
The thermal equivalent circuit of a component describes its physical structure in terms of thermal transitions from the junction to the case. Each transition consists of a thermal resistor and a thermal capacitor. They can be edited in the Therm. impedance tab of the thermal editor. The thermal equivalent circuit is specified either in Cauer or Foster form.
The structure of a Cauer network is shown in the figure below. In the thermal
editor the number of chain elements and the values for
and
for each
chain element need to be entered.
Cauer network
The figure below illustrates the structure of a Foster network. In the thermal
editor the number of chain elements and the values for
and
for each
chain element need to be entered. Foster networks can be converted to Cauer
networks by pressing the button Convert to Cauer.
Foster network
Care must be taken to ensure the polarity of the currents and voltages are correct when specifying conduction and switching loss data for semiconductor switches and diodes. If one or both polarities are in the wrong direction, the losses will be zero or incorrect. The voltage and current polarities of a single semiconductor switch, diode and semiconductor switch with diode are defined in PLECS as shown in the figure below.
Voltage and current polarity of single semiconductor switch, diode and semiconductor
switch with diode
The blocking voltage experienced by a single semiconductor switch is positive; therefore, switching losses are defined in the positive voltage/positive current region. Conduction losses are also defined in the positive voltage/positive current region.
The voltage and current waveforms during a typical diode switching cycle are shown
in the next figure. Turn on losses occur at and turn off losses at
. The
switching energy loss in both cases is calculated by PLECS using the negative
blocking voltage and positive conducting current at the switching instant. These
values are shown in the figure as dots. Therefore, the lookup tables for the turn-on
and turn-off switching losses must be specified in the negative voltage/positive
current region.
Diode voltage and current during switching
Conduction losses occur when . During this time period, the current
and voltage are both positive. Therefore the conduction loss profile must be specified
in the positive voltage/positive current region.
Semiconductor switches with an integrated diode such as the IGBT with Diode model allow losses for both the semiconductor switch and diode to be individually specified using a single set of lookup tables. The conduction and switching loss tables for the semiconductor switch are specified for the same voltage/current regions as for the single semiconductor switch without diode. Due to the polarity reversal of the diode, the diode losses are appended to the loss tables of the semiconductor switch by extending the tables in the negative voltage/negative current direction for the diode conduction losses, and in the positive voltage/negative current direction for the diode switching losses. An example turn-off loss table and conduction loss profile for a semiconductor switch with diode are shown in the next two figures. A summary of the valid voltage and current regions for defining conduction and switching losses for the different types of semiconductors is given below:
Diode | Switch | Switch with Diode | ||||||
Switch | Diode | |||||||
V | I | V | I | V | I | V | I | |
Conduction Loss | + | + | + | + | + | + | - | - |
Switching Loss | - | + | + | + | + | + | + | - |
Turn-off loss lookup table for semiconductor switch with diode
Conduction loss profile for semiconductor switch with diode