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Welcome back to the Converter features module.In this lesson, you will learn
about the switching delay feature.The Typhoon HIL modeling approach is based on
ideal switches, which neglect dynamics associated with the transitions between switching states.
However, the transitions between states in actual switching devices are not ideal.
Due to the presence of parasitic elements (such as capacitances) and the need to charge
and discharge the gate, it takes a finite amount of time for those devices to turn on
or turn off. Therefore, there is a delay from the moment the gate drive signal transitions to active
until the start of conduction and vice versa.These turn on and turn off delays affect the
system response as well as the dead time required for the gate drive signals of the converters.
To encompass that in the simulation, Typhoon HIL has a switching delay feature,
which models turn on and turn off delays on IGBTs. A fixed delay is used for IGBT turn on and a
current dependent delay is used for IGBT turn off.The switching delay feature is implemented using
a dedicated variable delay hardware unit. For this reason, it is available
only when using an actual HIL device.The variable switching delay feature is
currently available in the IGBT leg, NPC leg, NPC T Type leg, Three Level Flying Capacitor Inverter
Leg and their corresponding three-phase components, which are shown in this slide.
A block diagram with the relative position of the switching delay is illustrated in this figure.
Notice that the switching delay block is placed before the dead time violation logic.
This allows it to also be used to detect the minimum required dead time period.
More information about this is available in the documentation listed in the materials tab.
The dead time violation detection function will be further discussed in the next lesson.
Let's now go to the Typhoon HIL Schematic Editor to see how to setup the switching delay feature.
In this example, an IGBT leg is connected to a resistive-inductive load and is operating
in open-loop, with a sinusoidal modulating signal. The switching delay can be activated
by opening the converter properties window, going to the Timing tab,
and checking the Enable delays checkbox.In this example, the turn on delay is fixed at a
constant 3 µs. A current dependent turn off delay is defined in a comma-separated variable form.
You can preview the resulting variable delay curve by clicking the Preview button on the Timing tab.
Notice that the variable delay hardware unit allows for switching delay values up to 10 µs.
You can compile the model and run the simulation, which will be done here using a HIL404 device.
Note that when the switching delay is enabled, there is a general warning in the compiler log
informing you that the function is not supported by Virtual HIL Devices, as previously explained.
Let's now open the HIL SCADA panel that was created for this example and run the simulation.
You can use the capture/scope widget to verify the effects of the turn on and turn off delays.
The scope is displaying the load current and the PWM gate drive signals from the top and
bottom switches. A slider widget is included to adjust the amplitude of the modulating signal.
When the switching delay feature is enabled, additional digital signals become available.
You can include them in the scope to verify the switching delays you've implemented.
Let's go to capture mode, import scope settings, and force trigger to capture the results.
Now, you can zoom-in on the signals in a region with current around 1 ampere.
Using the cursors, you can see that the turn on delay is equal to 3 µs,
which is exactly the value that was previously defined.
Regarding the turn off delay, you can see that it is around 1 µs,
following the turn off delay curve that was set in the properties window.
If you zoom in on the signals in the region close to 2 amperes,
you can see that the turn on delay is still fixed at 3 µs. The turn off delay, however,
is now around 2 µs. This matches the current dependent delay set in the converter properties.
That's it for this lesson. Thank you for your attention!
For more information regarding this lesson, don't forget to check the
additional documentation links available in the materials tab.