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TRANSCRIPT
Hello! In this lesson you will learn how ready-to-use library components can be used
for custom power electronics applications. For this lesson the NPC PV inverter library
component is used to design and test a grid-connected solar PV installation.
This lesson will use the grid-connected NPC PV inverter with ride-through protection functions
example. You can find this example in the example explorer by opening the microgrid folder
and looking for the npc pv inverter example.The model consists of a Photovoltaic Panel, an NPC
PV inverter, and a grid simulator component. The NPC PV inverter component comes as a ready-to-use
component from the microgrid library. The component model contains a controller implementing
MPPT as well as voltage and frequency ride-through according to the UL 1741 SA safety standard.
By double clicking on the mask of the NPC PV inverter component, you will see that you
can specify frequency and voltage. Using this and similar plug-and-play library components,
you can significantly reduce model development time for system-level power electronics and
microgrid applications. In the HIL for Microgrids course, you will learn how
to quickly build microgrid models using libraries of high-fidelity DER models.
Since you are able to unlink and modify this component according to your needs,
let's see what is under the mask. Under the mask, you will see the electrical and
signal processing parts of the component. As a part of the electrical circuit, there is a
three-phase three-level NPC inverter which is directly pulled from the Converters library.
If you double click on the mask, you can see some general properties such as control mode,
operation mode, and carrier frequency. The control property for tis inverter is set to
"internal modulator separated." You can find more details about this component by following
the link in the Materials tab. [JM1] There are also an LC filter and pre-charge circuit.
The signal processing part of the circuit contains a control algorithm and an
implementation of frequency and voltage ride through functionality. The control algorithm
in this model is state feedback control. This inverter implements voltage and frequency
ride-through functionality according to UL 1741 SA with Rule 21 requirements. If you double click on
the voltage ride through subsystem, you can see that you can set nominal voltage on the mask.
If you go inside, you can see three subsystems called Single UL 1741 voltage ride through. These
subsystems implement the timing and behavior for UL 1741 high and low voltage ride-throughs. The
Voltage ride-through subsystem has two outputs. The first output - Enable references - is used for
momentary cessation. The second output - Enable inverter - is used to stop converter energizing.
The start-up procedure is implemented as follows: Once grid voltage and frequency are
in the allowable range, the grid contactor will be closed. After that, if the inverter enable
input is true, the inverter will start switching and the system will track the maximum power point
for the connected PV panel. This inverter will ramp up the references on start-up.
Let's compile the model and see how it behaves in simulation.
This model comes with a pre-built SCADA panel. As you can see, widgets are divided into two
main groups: NPC PV inverter and Grid. As a part of the NPC PV inverter group, there is
a DC link group where you can measure voltage as well as change irradiance and temperature.
The operating point of the selected PV panel is displayed using a PV monitor widget.
Double clicking on the widget will open the properties window. On the basic settings tab, you
can set the name of the widget, add a description, and choose which PV panel you want to monitor.
In the widget settings tab, you can set position and size. The background color can be changed,
if desired, on the advanced settings tab.In the Inverter Controls group there are
widgets for interacting with the inverter, such as LEDs that indicate whether frequency
and voltage ride through are enabled or not. The PCC measurements group
monitors PCC voltages, currents, and power.There is also a Grid control group where you
can change grid settings. The included Fault type combo box allows you to simulate faults.
The Phasor Graph widget can be used to read and display phasors of any complex pair of Analog
signals available in the model. In this example, the phasor graph widget is used to monitor and
display the real-time phase balance and power factor. In this case, the complex power data
is calculated using a Python expression.The Capture/Scope widget allows you to view
and capture signals at the full resolution of the simulation.
Now that you are familiar with the SCADA panel, let's start the simulation.
With the simulation running, you can see that the inverter is working under normal conditions.
If you open the Capture/Scope widget, switch to capture mode,
and click the force trigger button, you can see a snapshot of the inverter's voltages and currents.
Now let's simulate a Low voltage fault. You can find tables summarizing
the UL 1741 specification regarding voltage ride through and frequency
ride through in the NPC PV inverter component documentation linked in the Materials tab.
Three Low voltage cases are implemented in the voltage ride through standard.
Let's check the first one, LV1, which occurs for low voltage faults between 70%
and 88% of nominal voltage. By this standard, the inverter should disconnect from the grid
after a fault duration of 20 seconds. You can manually confirm this fault behavior in SCADA.
Set the low voltage fault level to 0.75 p.u. and change the fault duration to 21 seconds.
Under these conditions, we expect the inverter to disconnect from the grid.
Click the start button to initiate the described fault. As you can see, the voltage is lowered
to the specified 0.75 p.u. and after 20 seconds the inverter is disconnected.
If you, for instance, set the low voltage fault level to 0.75 p.u.
and fault duration to 10 seconds, you can see that the inverter does not disconnect
from the grid since this fault duration is too short to result in a trip by this standard.
You can repeat this process for High Frequency to see how high frequency faults impact the
inverter's operation. Regarding the UL 1741 frequency ride through standard,
for frequencies higher than 62 Hz the inverter will disconnect after 0.16 seconds. To test this,
set the High frequency fault level to 1.1 p.u. and the fault duration to 0.2 seconds, then click the
start button. Since the nominal frequency is 60 Hz and 1.1 p.u. of that frequency is 66 Hz, the
inverter will be disconnected after 0.16 seconds.These manual tests have illustrated two possible
test cases and procedures for this NPC PV inverter example. In practical inverter certification
tests, there could be hundreds of test cases that must be validated. Large test sets like these
require HIL testbed automation. You may remember from the HIL Fundamentals course that in addition
to the Schematic Editor and HIL SCADA, the Typhoon HIL toolchain also contains the Typhoon Test IDE.
This is a tool used to write and run automated tests using the Typhoon Test API.
It also generates easy-to-read test reports.This example model also comes with a test
script for automated testing. To open the test script, first close the HIL SCADA and
then open the Typhoon Test IDE. From here, click the button to open an existing file.
You can see that some examples come with prepared tests. To find the test for this example,
open the folder for npc pv inverter tests.Let's run the test and open the test report.
When you open the report, you can see 7 cases have been tested.
Some test cases have failed and others have passed.
For example, look at test number 3. This test case describes the same low voltage ride through use
case you manually tested earlier. The parameters are the same as in the previous simulation.
With the fault duration greater than the voltage ride through duration, we expect a trip and the
expected behavior is confirmed by the results here. The fault level is 0.75 p.u. while the
fault duration is 21 seconds. With those fault parameters, the inverter should be disconnected
from the grid. This passed test indicates that the inverter is disconnected from the grid,
meaning that UL 1741 is behaving as expected.By looking at the "PV out main contactor" plot,
you can see that the inverter disconnects at the end of the test, as was the case in
the manual simulation in HIL SCADA.With this comparison, you can see that
automated tests in Typhoon Test IDE are truly an extension of manual tests performed in HIL SCADA.
You can learn more about Typhoon Test IDE in the dedicated Test Automation
course that is part of the HIL Specialist 2.0 specialization. Thank you for watching.
