8.2 Measuring Control Loop Parameters

The DVM Bode Plot test objective measures the gain crossover, gain margin, and phase margin for a single line voltage and load current. Executing multiple Bode plot tests and aggregating the results can generate a visual picture of the control loop behavior over all line and load conditions. DVM automates the process of executing the tests and generating the summary curves.

Since a SIMPLIS AC analysis can be run only after a successful periodic operating point (POP) analysis, each Bode plot test first runs a POP analysis and then the AC analysis. With the data for both analyses available, DVM makes steady-state measurements, including efficiency, on the POP data, and then makes AC measurements on the AC analysis data. The Bode plot tests can, therefore, generate both AC data and steady-state data.

This example demonstrates  how to gather the usual AC scalar measurements and make measurements on the steady-state data, in particular, the efficiency and switching frequency of the converter.

The schematic design for this example is an LLC converter operating from a PFC converter output of 380V. The output voltage is 24V and the output power level is 120W. The schematic for this example is shown below and from   SIMPLIS_dvm_tutorial_examples.zip at this path: LLC/8.2_LLC Closed Loop.sxsch

Features of the above schematic:

• To generate the scalar measurement of the converter switching frequency, the DVM CLK probe was placed on the schematic and connected to the POP trigger output.
• The fixed probe measurement Frequency is applied to the DVM CLK probe to generate the scalar named Frequency(CLK) with the value measured from the simulation.
• The testplan Alias() function is used to create three scalar measurement aliases for each scalar (Nominal, Minimum, and Maximum) with one for each line voltage.
• After all simulations complete, the summary curves are generated with the CreateXYScalarPlot() function. As with the example in 8.1 Adding Power Losses to a Testplan, a post-process script runs using the SIMetrix script version of the CreateXYScalarPlot() function, which is SimplisDVMAdvancedUtilMeasurementCreateXYScalarPlot().

The testplan for this example, as shown below, contains Bode plot tests at load levels from 5% to 100% of full load at three input voltages, Minimum, Nominal, and Maximum. As with the example in 8.1 Adding Power Losses to a Testplan, this testplan uses 5% load steps from 5% to 40% of full load and 10% load steps from 40% to 100% of full load. The final summary curves are generated from five different tests to allow for easy report customization.

After running the entire testplan on the test schematic LLC/8.2_LLC Closed Loop.sxsch, the overview test report contains the five summary graphs followed by the individual test reports.