Hierarchal Models for the analysis of a power buss -1- 10/8/2002 A. G. Bell In some cases where the simulation circuit would get to big or cluttered with details it is wise to use a hierarchal approach in a simulation. The hierarchal approach allows the user to bury details into subcircuits and build commonly used elements once. However, there may still a desire to have some control over the subcircuit at the top level of the simulation circuit. This presentation will demonstrate the hierarchal approach by way of a using a twisted pair RLGC model whose electrical characteristics can be modified with a single dimensional parameter (length). Also, the approach to translate a SPICE deck into an AWB simulation will be shown for a new hierarchal subcircuit model.
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Hierarchal Models for theanalysis of a power buss
-1- 10/8/2002A. G. Bell
In some cases where the simulation circuit would get to big or cluttered with details it is wise to use a hierarchal approach in a simulation. The hierarchal approach allows the user to bury details into subcircuits and build commonly used elements once. However, there may still a desire to have some control over the subcircuit at the top level of the simulation circuit.
This presentation will demonstrate the hierarchal approach by way of a using a twisted pair RLGC model whose electrical characteristics can be modified with a single dimensional parameter (length). Also, the approach to translate a SPICE deck into an AWB simulation will be shown for a new hierarchal subcircuit model.
Hierarchal Models for theanalysis of a power buss
-2- 10/8/2002A. G. Bell
We would like to simulate the power buss of a system and include detailed models of the wires and subsystems. To do this it makes sense to build hierarchal models for each wire and subsystem and then interconnect them in a hierarchal simulation.
The wire model will use the RLGC lossy lumped element twisted pair model with a slight modification for grounding and will change electrical characteristics as a function of wire length.
One subsystem model which has been supplied to us as an Intusoft SPICE model will be translated into the proper AWB format and integrated into the hierarchal simulation
Hierarchal Models for theanalysis of a power buss
-3- 10/8/2002A. G. Bell
In our case the temperature coefficient of the wire will be ignored, i.e. temp will be set equal to 20°C.
Using this program the user could determine new R, L and C values based upon otherwire types. Or the model could also be changes to pass these wire parameters.
We have reviewed the literature and found a model for a twisted pair.
This MathCAD program is used to calculate the R, L and C values for the wire we wouldlike to model.
Build our model and compare our electrical characteristic to the calculated values.
Hierarchal Models for theanalysis of a power buss
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A test circuit is built to test the model. In this case the R, L and C will be measured as well as the characteristic impedance Zo
As can be seen there is a good match between the MathCAD program and AWB simulation results. The model is validated and can be used for simulations.
equals 2X for two wires
A subcircuit model is built and shows that for a 1 foot length of wire the simulation results match the expected results.
Hierarchal Models for theanalysis of a power buss
-5- 10/8/2002A. G. Bell
Step 1: Draw the base schematic for the RLGC model and define each value as function of R, L and C.
Now we will build the hierarchal model of the wire.
Hierarchal Models for theanalysis of a power buss
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This is the completed schematic model we will use for the twisted pair RLGC model. We also added 1000MEG resistors to insure that there is a DC path to ground for all nodes.
Next we will need to add the variable table…
Hierarchal Models for theanalysis of a power buss
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Step 2: Add the variable table and define the R, L and C values as functions of wire length.
Other variables are used to define R, L and C but only length will be passed through the body.
Hierarchal Models for theanalysis of a power buss
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Here is the completed schematic model with the variable table.
Next we will need to build the body …
Hierarchal Models for theanalysis of a power buss
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Step 3: Build the body for the part. Step 4: Add dots to the body where you want connections.
Step 5: Add signal names to the dots that match the schematic signal names.
Hierarchal Models for theanalysis of a power buss
-10- 10/8/2002A. G. Bell
Step 6: Add path and length as properties to the body at the origin of the symbol.
of medium between wire in this case the insulation is ETFE (2.5 to 2.6)
S = separation between the wires (in)
and
R, L and C are calculated based upon length…
1000Meg resistors added to model so all nodes would have a dc path to ground.
This is an adaptation of the basic lumped element RLGC model which provides some minimum distributed impedances. G is not included.
R, L and C are all functions of length so the equations for each can be written as expressions where length is a variable attached to the body of the model. Length can then be passed through the body to modify the R, L and C values.
Only the values are shown.
And your done.
Body
Schematic
Hierarchal Models for theanalysis of a power buss
-12- 10/8/2002A. G. Bell
Once the base model is built it can be expanded in a hierarchal fashion to build more complicated models. In this case all the models used here are hierarchal.Now we will expand the base twisted
pair model to mimic the cables used in the system.
Body
Schematic
hierarchal schematic
Imagine how complicated this schematic would be if it was drawn as a flat schematic
Hierarchal Models for theanalysis of a power buss
-13- 10/8/2002A. G. Bell
In this case a SPICE model exists that we want to import into our simulation. The model has a three page schematic.
Also, we have discovered that the “limiter” does not translate into AWB directly because and the model for this stage must be converted into the AWB model.
We will also need to define the inputs and outputs of our model. In this case we will pick VBAT as the input and IDC and I3 to be our outputs. We will also define ground as an I/O in our model. This is an Intusoft SPICE model of
the buss power supply.
We were given a SPICE deck for one of the subsystems that we want to translate into AWB and place in our hierarchal simulations
Hierarchal Models for theanalysis of a power buss
-14- 10/8/2002A. G. Bell
Page two of the Intusoft model.
Hierarchal Models for theanalysis of a power buss
-15- 10/8/2002A. G. Bell
In this case the multiplier also does not convert to AWB so it must bereplace with the AWB multiplier model.
The SPICE deck for the model must be dissected to determine to translate it into the AWB format. With the exception of the two circuit models that don’t translate directly we will also need to remove SPICE options and replace node names with node number which have not been used. A simple text editor can be used for this option.
Step 2: Add the following to the end of the SPICE deck…
"end TEXT PRE-ANALYSIS
start NODESTERM(VA)=1 TERM(ZBUS)=400TERM(GND)=999
end NODES
Term are based on the I/O you have chosen.
Step 3: Move SPICE deck to UNIX side …
Will need to do the DOS2UNIX command to eliminate line feeds
Step 4: Build model body …
Test you new model and your done!
Hierarchal Models for theanalysis of a power buss
-20- 10/8/2002A. G. Bell
Now we can simulate a very large design without having a complicated flat schematic to manage. Plus we have the option to change the wire length on any cable to determine how the performance of the system will change.