1.0.4 Multi-Level Modeling

Key Concepts

This topic addresses the following key concepts:

• Multi-Level models are configured with a single parameter.
• The schematic-view of the model changes based on the model level parameter.
• The model level is chosen based on the desired simulation objective.

What You Will Learn

In this topic, you will learn the following:

• How models can be configured with different levels of complexity with a single parameter.
• How to choose the appropriate level based on your simulation objective.

Getting Started: Multi-Level MOSFET Model

1. Open the schematic titled 1.1_SelfOscillatingConverter_POP_AC_Tran.sxsch.
2. Double click on the MOSFET Q1.
   Result: The Extract MOSFET Dialog opens. The Model level parameter control is shown below:
   
3. Click on the Help Button in the lower right corner of the dialog.
   Result: The Help system opens to the SIMPLIS MOSFET Models topic.

Discussion: Multi-Level Modeling

At this point, you should have the Extract MOSFET Dialog open in SIMetrix/SIMPLIS and the SIMPLIS MOSFET Models help topic open in a browser window.

MOSFETs, in common with the other semiconductors such as Diodes, Zener Diodes, IGBTs and JFETs have very nonlinear behavior. For example, the drain-to-source capacitance of a MOSFET can radically change as the voltage across the MOSFET changes from the blocking to the conducting state. If you are interested in the switching behavior of this device, it is important to model this capacitance change; However, if you primarily interested in the Bode Plot of the converter, the details of the switching transition are typically not important.

SIMPLIS has the ability to change both the underlying schematic structure and the parameters of a model based on a single parameter value. In the Extract MOSFET Dialog, and indeed, in many SIMPLIS built-in models, the "Level" or "Model Level" parameter controls the schematic view of the model which is used in the simulation.

Multi-Level Model Example #1: The SIMPLIS MOSFET

The MOSFETs used in SIMPLIS have four levels of complexity. Each level is described in detail in the currently open help topic. Below are the schematic views of the level 0 , 1, and 2 models. The level 3 model is intended for user-customized models, and is not supported by the internal model extraction routines.

Level 0 Model	Level 1 Model	Level 2 Model
QQ1: Switch with On and Off Resistance CGS: Linear Capacitance RGS: 10Meg Ω Resistor RG: Internal Gate Resistor !R_BODY: Body diode modeled by PWL Resistor	QQ1: Switch with On and Off Resistance CGS: Linear Capacitance RGS: 10Meg Ω Resistor RG: Internal Gate Resistor !R_BODY: Body diode modeled by PWL Resistor COSS: Lumped linear output capacitance	QQ1: Switch with forward transconductance CGS: PWL Capacitance RGS: 10Meg Ω Resistor RG: Internal Gate Resistor !R_BODY: Body diode modeled by PWL Resistor CDS: PWL capacitance CDG: PWL capacitance

The Level 0 MOSFET is used whenever the detailed switching action of the MOSFET is not important. The Level 2 MOSFET, which models the nonlinear capacitances, is typically used when the switching transitions are important, such as when measuring efficiency. The Level 1 MOSFET is used for power stage development when the converter topology relies on the MOSFET output capacitance.

Multi-Level Model Example #2: The Multi-Level Capacitor

Passive components, such as inductors and capacitors are also available as multi-level models. The model level in this case determines the parasitic elements which are included in the model. In this section the new Multi-Level capacitor is used as an example. This capacitor was introduced with SIMetrix/SIMPLIS version 8.0, and replaces the old electrolytic capacitor.

Exercise #2: Multi-Level Capacitor Model

1. Double click on the output capacitor C1. This is the first capacitor symbol to the right of the transformer output.
   Result: The Edit Multi-Level Capacitor dialog opens:
   

SIMetrix/SIMPLIS has two multi-level capacitor models; the one used here has model levels 0-3, and a second, more detailed model, has levels 4 and 5. The three multi-level capacitors on this schematic all use the new multi-level capacitor model with levels 0-3 and have the model level set to 2. Equivalent schematic images of the level 0-3 models are shown below:

Level 0	Level 1	Level 2	Level 3
CAP Capacitance	CAP Capacitance RLK Leakage Resistance	CAP Capacitance RLK Leakage Resistance RESR Equivalent Series Resistance	CAP Capacitance RLK Leakage Resistance RESR Equivalent Series Resistance ESL Equivalent Series Inductance RESL ESL Shunt Resistance

The Level 4-5 model for the electrolytic capacitor models the low and high frequency components separately. The model is essentially two electrolytic capacitors in parallel. The edit dialog for the Level 4-5 electrolytic capacitor is shown below:

The schematic views of the level 4 and level 5 models are shown below. The Level 5 model adds a Equivalent Series Inductance (ESL) to the Level 4 model.

Level 4	Level 5
CC_LF Low Frequency Capacitance RSH_CC_LF Low Frequency Leakage Resistance RESR_LF Low Frequency Equivalent Series Resistance CC_HF High Frequency Capacitance RSH_CC_HF High Frequency Leakage Resistance RESR_HF High Frequency Equivalent Series Resistance	CC_LF Low Frequency Capacitance RSH_CC_LF Low Frequency Leakage Resistance RESR_LF Low Frequency Equivalent Series Resistance CC_HF High Frequency Capacitance RSH_CC_HF High Frequency Leakage Resistance RESR_HF High Frequency Equivalent Series Resistance L_ESL Equivalent Series Inductance

For future reference, you can place the Multi-Level Capacitors from the SIMPLIS parts selector:

• Commonly Used Parts>Multi-Level Capacitor (Level 0-3 w/Quantity) (Version 8+)
• Commonly Used Parts>Electrolytic Capacitor (w/ HF ESR and ESL) (Level 4 - 5)

Conclusions and Key Points to Remember

• Multi-Level modeling is extremely powerful because:
  1. A multi-level model is a flexible model. The model can range from simple to extremely complex based on the level parameter. The schematic view of the model can change based on the level parameter.
  2. The user can select the minimum complexity which meets the current simulation objective.
  3. By enabling one component symbol to have different underlying models the user can have a single schematic serve multiple simulation objectives. This can save a lot of time and confusion compared with having to manage multiple versions of the same schematic.
• All semiconductors used in SIMPLIS are modeled with PWL devices. To determine what level of model is used, double click on the symbol and note the value of the model level parameter. Using the lowest complexity model level consistent with the required accuracy of the simulation objective will increase simulation speed.
• In Module 6 - Modeling you will learn how to create your own multi-level models. During the training course, think about what kind of models you have used which would benefit from the multi-level modeling concept.
• In SIMPLIS, the parameter name "Level" is used to describe the level of complexity of any given model. There is nothing special about this name, and you can build your own models with any parameter name you would like. For example, an IC model may have a "Process" parameter or a "Corner" Parameter. The Process might have three string values. The model could then have the string value configure the model:
  • 'Slow'
  • 'Typical'
  • 'Fast'
  The model could use the string value to configure the model. Using string values as variables is covered in 6.2 Assembling the Subcircuit Load.