Transient Waveforms & Simulations

In TRAFOLO, transient simulations require a defined transient waveform. Users can generate basic waveforms parametrically, like square, sine, and triangular waveforms. However, since transformers and inductors are typically part of power converter topologies, their waveforms often differ from these basic shapes. To address this, TRAFOLO provides an option to import waveforms as a file.

For each transient waveform, TRAFOLO performs a Discrete Fourier Transform (DFT) to compute amplitude and phase. This guide will also explain how to convert a transient simulation into a harmonic analysis, transitioning from the time domain to the frequency domain.

To demonstrate the process of importing and analyzing transient waveforms, an existing Flyback transformer template in TRAFOLO is used as an example.

File Format and Importing

To accurately represent the waveform in a flyback transformer, data should be imported in a tabulated format such as CSV, XLS(X).
Make sure that the names in the first row describe the respective dataset, so that it is easier to identify and allot them in TRAFOLO.

Click on Import under Load From File in the Waveform tab. Correct Time, Primary Source, and Secondary Source can be selected from the drop-down list, which contains the names of all the columns in the Spreadsheet file.

Interpolating Waveforms

Primary Original and Secondary Original refer to the imported waveforms. In some cases, the imported waveforms may contain fewer data points in regions with steep amplitude variations. Enabling the Optimize Timesteps option redistributes timesteps and interpolates waveform values accordingly. This improves simulation efficiency while maintaining accuracy in waveform representation.

Algorithm 4 is chosen here. It identifies areas with the highest derivative and adds points there. It also considers steep changes in both primary and secondary waveforms for a balanced distribution. Choose Skip 1st period from averaged losses since the first period usually would have high errors due to mismatched phases between voltage, current, magnetic flux, and inrush currents, when compared with the rest of the periods.

Optimizing Transient waveforms

Fundamental Frequency is set for period identification. Users must also specify the number of Periods and Points per period, however, Points per period is an approximate setting, the actual number of points used in the simulation may vary. For details on these settings, refer to Waveforms under to the Interface Reference Manual.

In TRAFOLO, the initial magnetic flux condition is set to zero. To minimize inrush currents or voltage spikes, users should ensure that the waveform starts at a phase where the magnetic field energy is minimal, if not done then there might be some DC bias for magnetic flux in the simulation. The Move By Points feature enables precise adjustment of the waveform’s starting position, allowing better control over transient behavior.

Analyzing Transient Waveforms in Fourier Domain

When analyzing transient waveforms using the Discrete Fourier Transform (DFT), it is essential to ensure accurate representation of frequency components. Consider the following key aspects:

• DC Bias Verification: The 0 Hz component should be correctly accounted for. If a waveform has no inherent DC bias, it should not appear in the frequency histogram, except for minor numerical errors.
• Transformer Harmonic Analysis: In transformers, the voltage and current ratios at each frequency should align with the expected turn ratio. Any deviation may indicate leakage flux and weak coupling, affecting performance.
• Efficient Harmonic Selection: The software optimizes winding loss calculations based on a selected number of harmonics. The histogram helps identify significant harmonics, while those with negligible impact are disregarded. This reduces computation time and filters out harmonics caused by numerical noise. A smoother, sine-like waveform requires fewer harmonics for accurate representation.

On clicking the Harmonize button, the simulation type changes to harmonic.

Post-Processing Transient Simulation Results

Select the Proper Simulation Results

In the Pipeline Browser, you must differentiate between the two main data sets:

• Electromagnetic results: Contains the transient, time-step data. You must select this to visualize fields that change over time.
• General results: Contains post-processed, time-averaged results (e.g., steady-state temperature distributions).

Visualizing Fields on Specific Geometries

You can control visibility by clicking the eye icons next to items in the Pipeline Browser.

Example – Visualizing Magnetic Flux in the Core:

1. Hide the main Electromagnetic results mesh.
2. Enable the Core geometry filter to isolate the magnetic core.
3. From the active variable dropdown in the top toolbar, select the BT field to visualize magnetic flux density in Teslas.

Changing Visualized Time

To see how the fields behave throughout the simulation:

• Use the Time Toolbar at the top of the screen.
• You can manually select a specific time step from the dropdown menu, or click the Play button to animate the results as a video.

Inspecting Local Values

To quickly check field values at a specific location:

• Click the Hover Cells On icon located in the render view toolbar (above the 3D window).
• Hover your cursor over any element on the 3D model. A tooltip will appear displaying the instantaneous values for all fields calculated at that specific element.

Plotting Values Over Time

To generate a 2D graph of a specific point over the entire transient simulation:

1. Select the specific element or point on your model using the selection tools.
2. Go to the top menu and apply the Plot Selection Over Time filter.
3. Click Apply. ParaView will split the view and display a graph plotting the values of all fields stored in that element across all simulated time steps. (You can then uncheck irrelevant fields in the display properties to isolate a single variable, like BT).