Tolerances The error tolerances are used to check whether the state vari-
ables are consistent after a switching event. The defaults are
for the rel-
ative tolerance and
for the absolute tolerance.
Synchronize ﬁxed-step sample times This option speciﬁes whether
PLECS should attempt to ﬁnd a common base sample rate for blocks that
specify a discrete sample time.
Use single base sample rate This option speciﬁes whether PLECS should
attempt to ﬁnd a single common base sample rate for all blocks that specify a
discrete sample time.
These options can only be modiﬁed for a variable-step solver; for a ﬁxed-step
solver they are checked by default. For details see section “Multirate Systems”
(on page 40).
Division by zero This option determines the diagnostic action to take if
PLECS encounters a division by zero in a Product block (see page 466) or a
Function block (see page 345). A division by zero yields 1 or
number”, if you divide 0=0). Using these values as inputs for other blocks may
lead to unexpected model behavior. Possible choices are
.In new models, the default is
.In models created with PLECS 3.6
or earlier, the default is
Negative switch loss This option determines the diagnostic action to take
if PLECS encounters negative loss values during the calculation of switch
losses (see “Loss Calculation” on page 107). PLECS can issue an error or a
warning message or can continue silently, In the latter two cases, the losses
that are injected into the thermal model are cropped to zero.
Stiffness detection This parameter only applies to the non-stiff, variable-
step DOPRI solver. The DOPRI solver contains an algorithm to detect when a
model becomes „stiff” during the simulation. Stiff models cannot be solved ef-
ﬁciently with non-stiff solvers, because they constantly need to adjust the step
size at relatively small values to keep the solution from becoming numerically
If the DOPRI solver detects stiffness in model, it will raise a warning or error
message depending on this parameter setting with the recommendation to use
the stiff RADAU solver instead.
Max. number of consecutive zero-crossings This parameter only ap-
plies to variable-step solvers. For a model that contains discontinuities (also
termed „zero-crossings”), a variable-step solver will reduce the step size so as
to make a simulation step precisely at the time when a discontinuity occurs
(see “Event Detection Loop” on page 34). If many discontinuities occur in sub-
sequent steps, the simulation may come to an apparent halt without actually
stopping because the solver is forced to reduce the step size to an excessively
This parameter speciﬁes an upper limit for the number of discontinuities in
consecutive simulation steps before PLECS stops the simulation with an error
message that shows the responsible component(s). To disable this diagnostic,
set this parameter to
Use extended precision When this option is checked, PLECS uses higher-
precision arithmetics for the internal calculation of the state-space matrices
for a physical model. Check this option if PLECS reports that the system ma-
trix is close to singular.
Assertion action Use this option to override the action that is executed
when an assertion fails (see Assertion block on page 274). The default is
,which uses the actions speciﬁed in each individual assertion.
Assertions with the individual setting
are always ignored, even if this
option is different from
use local settings
.Note that during analyses and
simulation scripts, assertions may be partly disabled (see “Assertions” on page
This parameter controls how the system state is initialized at the beginning of
asimulation. The system state comprises
• the values of all physical storage elements (e.g. inductors, capacitors, ther-
• the conduction states of all electrical switching elements (e.g. ideal
switches, diodes), and
• the values of all continuous and discrete state variables in the control block
diagram (e.g. integrators, transfer functions, delays).
Block parameters When this option is selected, the state variables are ini-
tialized with the values speciﬁed in the individual block parameters.
Stored system state When this option is selected, the state variables are
initialized globally from a previously stored system state; the initial values
speciﬁed in the individual block parameters are ignored. This option is dis-
abled if no state has been stored.
Store system state... Pressing this button after a transient simulation
run or an analysis will store the ﬁnal system state along with a time stamp
and an optional comment. When you save the model, this information will be
stored in the model ﬁle so that it can be used in future sessions.
Note Adding or removing blocks that have continuous or discrete state vari-
ables associated with them will invalidate a stored system state.
Model Initialization Commands
The model initialization commands are executed when a simulation is started
in order to populate the base workspace. You can use variables deﬁned in the
base workspace when specifying component parameters (see “Specifying Com-
ponent Parameters” on page 52).
Note The maximum length of variable names is 63 characters. This is due to
the way, inwhich a workspace is stored in PLECS and exchanged withOctave.
Thermal management is an important aspect of power electronic systems and
is becoming more critical with increasing demands for compact packaging and
higher power density. PLECS enables you to include the thermal design with
the electrical design at an early stage in order to provide a cooling solution
suitable for each particular application.
Heat Sink Concept
The core component of the thermal library is an idealized heat sink (see page
353) depicted as a semitransparent box in the ﬁgure below. A heat sink ab-
sorbs the thermal losses dissipated by the components within its boundaries.
At the same time, a heat sink deﬁnes an isotherm environment and propa-
gates its temperature to the components which it encloses.
Heat conduction from one heat sink to another or to an ambient temperature
is modeled with lumped thermal resistances and capacitances that are con-
VB.NET PDF - View PDF with WPF PDF Viewer for VB.NET
Tools Tab. Item. Name. Description. Ⅰ. Hand. Pan around the PDF document. Ⅱ. Select. Select text and image to copy and paste using Ctrl+C and Ctrl+V. how to search pdf files for text; find and replace text in pdf file
nected to the heat sinks. This approach allows you to control the level of de-
tail of the thermal model.
Each heat sink has an intrinsic thermal capacitance versus the thermal refer-
ence node. All thermal losses absorbed by the heat sink ﬂow into this capaci-
tance and therefore raise the heat sink temperature. Heat exchange with the
environment occurs via the external connectors.
You may set the intrinsic capacitance to zero, but then you must connect the
heat sink either to an external thermal capacitance or to a ﬁxed temperature,
i.e. the Constant Temperature block (see page 300) or the Controlled Tempera-
ture block (see page 302).
Thermal Loss Dissipation
There are two classes of intrinsic components that dissipate thermal losses:
semiconductor switches and ohmic resistors.
Power semiconductors dissipate losses due to their non-ideal nature. These
losses can be classiﬁed as conduction losses and switching losses. For com-
pleteness the blocking losses due to leakage currents need to be mentioned,
but they can usually be neglected.
Semiconductor losses are speciﬁed by referencing a thermal data sheet in the
component parameter Thermal description. See section “Thermal Descrip-
tion Parameter” (on page 109) and “Thermal Library” (on page 113) for more
The conduction losses can be computed in a straightforward manner as the
product of the device current and the device voltage. By default the on-state
voltage is calculated from the electrical device parameters as v = V
However, PLECS also allows you to specify the on-state voltage used for the
loss calculation as an arbitrary function of the device current and the device
temperature: v = v
(i;T). You may also specify additional custom function
arguments. This function is deﬁned in the Conduction loss tab of the ther-
mal description as a 2D look-up table or a functional expression (see “Thermal
Editor” on page 115).
for a single temperature and current value means no conduc-
tion losses. If you do not specify a thermal description in the device parame-
ters, the default will be used, i.e. the losses are calculated from the electrical
Note If youspecify the Thermal description parameter, the dissipated ther-
mal power does not correspond to the electrical power that is consumed by the
device. This must be takeninto account when you use the thermal losses for
estimating the efﬁciency of a circuit.
Switching losses occur because the transitions from on-state to off-state and
vice versa do not occur instantaneously. During the transition interval both
the current through and the voltage across the device are substantially larger
than zero which leads to large instantaneous power losses. This is illustrated
in the ﬁgure below. The curves show the simpliﬁed current and voltage wave-
forms and the dissipated power during one switching cycle of an IGBT in an
In other simulation programs the computation of switching losses is usually
challenging because it requires very detailed and accurate semiconductor mod-
els. Furthermore, very small simulation time-steps are needed since the du-
ration of an individual switching transition is in the order of a few hundred
In PLECS this problem is bypassed by using the fact that for a given circuit
the current and voltage waveforms during the transition and therefore the to-
tal loss energy are principally a function of the pre- and post-switching condi-
tions and the device temperature: E = E
;T), E = E
You may also specify additional custom function arguments. These functions
are deﬁned in the tabs Turn-on loss and Turn-off loss of the thermal editor
as 3D look-up tables or functional expressions (see “Thermal Editor” on page
Asetting of 0 J for a single voltage, current and temperature value means no
Semiconductor components that implement this loss model are
• the Diode (see page 311),
• the Thyristor (see page 563),
• the GTO (see page 348),
• the GTO with Diode (see page 350),
• the IGBT (see page 361),
• the IGBT with Diode (see page 377),
• the Reverse Blocking IGCT (see page 383),
• the Reverse Conducting IGCT (see page 385),
• the MOSFET (see page 435),
• the MOSFET with Diode (see page 438) and
• the TRIAC (see page 608).
In addition, the Set/Reset Switch (see page 507) is also included in this group
to enable you to build your own semiconductor models.
Ohmic losses are calculated as i2 R resp. u2=R. They are dissipated by the
• the Resistor (see page 477),
• the Variable Resistor with Variable Series Inductor (see page 629),
• the Variable Resistor with Constant Series Inductor (see page 626),
• the Variable Resistor with Variable Parallel Capacitor (see page 627) and
• the Variable Resistor with Constant Parallel Capacitor (see page 625).
Heat Sinks and Subsystems
By default, if you place a subsystem on a heat sink, the heat sink temperature
is propagated recursively into all subschematics of the subsystem. All thermal
losses dissipated in all subschematics ﬂow into the heat sink. In some cases
this is not desirable.
The implicit propagation mechanism is disabled if a subschematic contains
one or more heat sinks or the Ambient Temperature block (see page 267). This
Documents you may be interested
Documents you may be interested