POWER
Simulation Tools for Precise Power Electronics Design
James Victory, Fellow – Power solutions group TD modelling and simulation solutions, onsemi
T
he use of simulation is commonplace in modern designs as it allows designers to experiment with and validate aspects such as component selection, circuit configurations and other key design elements without the time and expense of a physical prototype. As modern power design briefs are usually demanding in terms of power density and performance, accurate simulation will get you closer to the goal with a first prototype, saving time and reducing risk.
No simulation is, nor can it be, more accurate than the models that underpin the simulation, so ensuring model accuracy under all operating conditions is essential before beginning a simulation. Often, models are derived from datasheet parameters and, while this seems sensible, it is often a source of inaccurate data.
Datasheets are created based upon laboratory configurations and environments within a test facility. Therefore, they do not and cannot represent the infinite variety of real-world conditions encountered in practical use. In all practical designs there has to be a PCB that will contribute parasitic elements that will modify the performance of the components, which needs to be applied to the model in some way.
If these parasitic elements or any other design-specific attributes are not properly modeled, then the simulation can show inaccuracies as high as 30 percent. The “best guess” of an experienced engineer is likely to be better than the prediction of a simulation based upon poor quality modeling. The issue of the significant discrepancies
Figure 1: SSPMG allows customisation of high-density tables
arising from generic models is being understood within the power industry. The industry needs a solution; a means of including real world environmental factors in the simulation to build upon the accuracy of models that are built upon laboratory data. This requires engineers to know how their practical design, especially the PCB, will contribute to overall circuit behavior. Designers are now able to enter parasitic information relating to their specific application environment into onsemi’s Self-Service PLECS Model Generator (SSPMG), building custom PLECS models that have greater accuracy than generic models. SSPMG is a simulation tool for the real world that delivers accurate results. It clearly responds to the needs of the industry and gives designers the ability to create
simulations that show how designs will operate.
Another key source of error in models is interpolation and extrapolation as the information in datasheets is often not dense enough or does not cover the entire operating range. The SSPMG allows customisation to be added to high-density tables based upon electrical bias and temperature conditions, thereby almost eliminating any need for extrapolation or interpolation.
Often, device parameters will vary due to variations in manufacturing process; this can affect behaviour over temperature, efficiency and system losses so that they must be included in any accurate model. The SSPMG tool has a “corner models” capability, allowing shifts due to process variations to be incorporated into simulations. When designing power solutions, losses are calculated differently for soft and hard switching. With hard switching, the double pulse test (DPT) is a commonly used and reliable method for loss calculation. Losses in soft switching designs depend upon the topology and mode of operation, preventing DPT from being used.
Figure 2: Unlike other models, onsemi’s PLECS models are suitable for simulating soft-switching topologies
40 OCTOBER 2024 | ELECTRONICS FOR ENGINEERS
A new transition losses tester built into SSPMG can accurately calculate energy losses in a range of topologies, including phase-shifted full bridge (PSFB), DC-DC LLC and CLLC resonant. This innovative tool ensures that loss calculations are accurate whenever switching schemes are in use, something that many models omit.
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