Customization of Simulations

Here we explain how to change the components and values, as well as conditions etc., in a simulation circuit that has been provided, and then run the simulation.

Those persons who have not read any introductory articles prior to this one should consult “Starting a Simulation Circuit in the ROHM Solution Simulator” to start up the example simulation circuit. The following link can also be used to start the simulation directly. https://www.rohm.com/solution-simulator/buck_converter_vo250v_io20a
For a quick introduction to methods of operation, please refer to the ”Hands-On User’s Manual（PDF）”.

Customization of Simulations

Here an example problem is used to explain methods of customization and related matters.

Example problem: Change a PWM frequency from 50 kHz to 25 kHz and execute a simulation, then compare the waveform frequencies at net75 (the source of the SiC MOSFET xQ1) before and after the change of frequency.

The procedure is as follows.

• ▶ Change the switching frequency setting (FSW) of xPWM1H1 from 50 kHz to 25 kHz
• ▶ Execute the simulation
• ▶ Use Waveform Viewer to display and compare the net75 waveforms before and after changing FSW

Changing the Properties of Components

In the ROHM Solution Simulator, component properties can be changed before running simulations. Fig. 1 is the simulation circuit for the example problem. The components with properties that can be changed are displayed in light blue.

Fig. 1. Simulation circuit for the example problem

In the example problem, the PWM frequency is to be changed, and so the Property Editor for xPWM1H1 is opened. To open the Property Editor, either double-click on the component, or right-click on the component and select “Properties”, as shown in Fig. 2. At this time the component color changes to yellow-green.

Fig. 2. Opening the Property Editor for a component to change a property

Here it should be noted that the component properties that can be changed in the ROHM Solution Simulator are only properties of a component displayed in light blue, and which moreover are properties with a white background in the Property Editor (in Fig. 2-②, only FSW). Properties in gray cannot be changed, and upon mouseover (with the cursor above a property) a symbol indicating that operations are forbidden appears. Components not displayed in light blue can likewise be opened, but all properties are grayed out and cannot be changed.

In this way, there are limits to what can be changed in the ROHM Solution Simulator. However, if a simulation circuit is exported to the PartQuest™ Explorer, editing can be performed freely, including addition of components and detailed parameter changes. Exporting to the PartQuest™ Explorer will be explained in the next article.

Well then, let’s open the Property Editor for xPWM1H1 and overwrite the 50k value for the switching frequency FSW to 25k.

When the cursor hovers over FSW (mouseover), a message should have been displayed (Fig. 3, left). The message said “the value should be between 10k and 300k (inclusive)”; thus the value of FSW is limited. As indicated in Fig. 3, there are a number of types of property changes; changes are as indicated by the message displayed on mouseover.

Fig. 3. Methods for changing/setting properties

When changing properties, the model can be changed in the case of power devices such as transistors and diodes. One example is shown in Fig. 3, “Selection type”; an SiC Schottky barrier diode can be selected from among the options in the pulldown menu.

We have digressed a bit here. In any case, after overwriting FSW to 25k, click the “Run” icon on the toolbar to execute the simulation.

Displaying the Simulation Results for the Changed Conditions and Comparing Them with Results Before the Change

The simulation results are used to display and compare, using Waveform Viewer, the waveforms for net75 (the source of the SiC MOSFET xQ1) before and after changing FSW.

First, the Waveform Viewer open/close icon, which is at the bottom of the circuit diagram display area, is clicked to open Waveform Viewer. On the left side is the “Simulation Results” folder; at the bottom of this folder are a “C6 Buck Converter Vo=250V Io=20A” folder and a “Copy of C6 Buck Converter Vo=250V Io=20A – (date) – (time)_(serial #)” folder (Fig. 4).

Fig. 4. Waveform Viewer and saved simulation results

Default simulation results are stored in the “C6 Buck Converter…” folder. The simulation results after changing FSW are stored in the “Copy of C6 Buck Converter…” folder. From Fig. 4, we see, with the “Copy of C6 Buck Converter…” folder opened, that there is “net75” data in the folder.

The waveforms are displayed simply by double-clicking on each of the “net75” items. In Fig. 5, the waveforms are displayed in the order of FSW=50k (before the change) and FSW=25k (after the change), with the time axis enlarged for easy comparison of frequencies. Moreover, the figure shows how the frequency analysis functions of the Waveform Analyzer can be used to display frequencies. Visit this link for the methods of use of Waveform Viewer and Waveform Analyzer.

Fig. 5. Displaying and comparing in the Waveform Viewer

It should also be noted that a “Copy of…” folder is created each time the simulation is run even when component properties are not changed; the serial number at the end of the filename is incremented (#1, #2, …) each time a file is created.