Choose the Right Block to Model Semiconductor Devices
Simscape™ Electrical™ often provides more than one block that can model the same type of semiconductor device. For example, the MOSFET (Ideal, Switching) and N-Channel MOSFET blocks both model an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET). It is important to use a block that has sufficient modeling detail for the engineering design questions that you plan to answer using your model. It is also important not to use more detail than you need because this slows down simulation and makes the model more complex to parameterize. The right block to use therefore depends on the level of complexity that you need to meet your design goals. This guide shows you how to:
Determine the level of fidelity that you need.
Select the right block to model your semiconductor device at that level of fidelity.
Parameterize the block.
Determine Fidelity Level
Simscape Electrical supports different fidelity levels for modeling semiconductor devices. You can define three levels of model fidelity:
Level 1 — Ideal switching device models with no thermal model
Level 2 — Ideal switching device models with tabulated switching losses and a thermal model
Level 3 — Physics-based electrothermal models
Each successive level requires increasing modeling complexity which restricts the design space that you can practically explore or optimize against. It is important to develop your model with the right level of complexity. You therefore need to use a different fidelity level depending on where you are in the design process. This table lists common design goals and the typical corresponding modeling assumptions at the three levels of fidelity. Use this table to determine the level of fidelity you need.
Fidelity Level | Goals | Modeling Assumptions |
---|---|---|
Level 1 |
|
|
Level 2 |
|
|
Level 3 |
|
|
Choose Right Block
This table shows the blocks that you can use to represent different semiconductor device types at each level of fidelity. Use this table to select the right block to model your semiconductor device and set important parameters values.
Device Type | Blocks | ||
---|---|---|---|
Level 1 | Level 2 | Level 3 | |
Diode |
|
|
|
Bipolar transistor | Not supported | Not supported | |
MOSFET |
|
| |
IGBT |
|
| |
Thyristor |
|
| |
GTO |
|
| Not supported |
JFET | Not supported | Not supported | |
Composite and complete converter circuits |
| Not supported | Not supported |
Note
The Diode block parameterized at Level 1 is equivalent to the Diode block in the Simscape Foundation Library.
You can use a Gate Driver or Half-Bridge Driver block to drive a semiconductor block at any level of fidelity. With some blocks at Level 1 and Level 2, like the MOSFET (Ideal, Switching) block, you can choose to use a physical signal port for the gate terminal which eliminates the need for an electrical model of the gate driver. However, the best practice is to use an electrical port even at lower fidelities. This allows you to easily change between fidelity levels by changing the block that models the semiconductor device that you are driving without having to change the gate driver.
Parameterize Block
Once you have selected the right block, the next step is to parameterize it. Parameterization of semiconductor devices can be challenging, depending on what information the manufacturer provides. Datasheets are a good source for Level 1 and Level 2 modeling but are deficient for Level 3 modeling because they do not provide full charge information. For example, in the case of MOSFETs, you need to tabulate the gate-source charge in terms of gate-source voltage and drain-source voltage but datasheets often give the gate-source charge in terms of the gate-source voltage only.
Some manufacturers provide Level 2 parameterizations stored as an XML file which is
essentially an electronic datasheet. You can import some of these files directly into
Simscape using the ee_importDeviceParameters
function.
SPICE subcircuits usually provide a Level 3 model but Simscape Electrical software cannot use these subcircuits directly. If you have a SPICE subcircuit that you want to simulate in Simscape Electrical software, choose one of these options:
Map the subcircuit to a table-based I-V and charge parameterization using the
ee.spice.semiconductorSubcircuit2lookup
function. This method is numerically more reliable and usually the better choice.Convert the subcircuit to an equivalent Simscape component using the
subcircuit2ssc
function. The devices that you can model using the SPICE-Imported MOSFET block were converted to an equivalent Simscape component using this method. The main drawback of this method is that numerical simulation issues can arise as the original netlist is usually optimized for a specific SPICE simulation engine.