Sequoia / Tahoe Series User Manual California Instruments
76 M447352-01 REV-A
13. Program the power source to the Constant-Voltage/Constant-Current mode through the display using
the REGULATION menu of the Configuration Screen Top-Level Menu; refer to Section 5.6.2.6 (Source
Mode).
14. Program the output current to 50% of the full-scale output current and verify that the output voltage of
each phase is reduced from the setpoint, while the output current is regulated to its setpoint.
15. Return the current setpoint to 100% of full-scale and verify that the output voltage of each phase
returns to its setpoint.
16. Turn off the OUTPUT switch.
17. Switch on the resistive load to each phase that is set to draw 90% of full-scale current at 333 V(RMS)
for the high-range AC output.
18. Repeat Steps 7 through 11, instead set the AC output of each phase for the following: voltage range =
high, 333 V; output voltage = 333 V(RMS); current setting = full-scale for the model being tested.
19. Repeat Steps 5 through 18 but set the output of each phase for DC mode operation with the voltage
set for 220 VDC in the low range and 440 VDC in the high range, and the load for each phase set
appropriately for the DC range selected.
4.1.2 Grid Simulator Mode
NOTE: This mode applies only to the SEQUOIA series. TAHOE series does not support this mode of
operation.
The Grid simulator mode enables Sequoia AC Sources to sink current from the unit under test. This mode
of operation is particularly useful when testing grid-tied products that feed energy back onto the grid. The
ability of the Sequoia to simulate the grid provides unique opportunities to test the EUT for immunity to
commonly occurring line anomalies like voltage and/or frequency fluctuations. Typical examples of these
types of UUTs are solar and/or wind power inverters.
In this mode of operation, the measured power is negative, indicating energy is being fed back into the
Sequoia amplifiers. The current limit mode will behave differently than it does under source mode
conditions.
When the absolute value of the current exceeds the regenerative current limit set point (current limit is set
in the REGENERATIVE CURRENT SETTINGS screen), the output voltage of the Sequoia will be
increased gradually to reduce the amount of current being fed back. The voltage will continue to be raised
until the user set over-voltage trip point is reached. This trip level can be set in the REGENERATIVE
CONTROL SETTINGS screen located under the CONFIGURATION screen. At this point, and after the
delay set by the “DELAY F” parameter is reached, the AC frequency will be shifted by the amount set in
the dFREQ parameter field. The dFREQ is irrelevant to the DC operation. A consideration in the AC mode
is the fact that most AC inverters will shut down when detecting a sudden change in frequency. If the
frequency shift (dFREQ) is set to zero however, the output voltage will be dropped to the under-voltage
limit setting (UNDER VOLT) set in the REGENERATIVE CONTROL screen instead of the frequency shift.
At this point, the EUT should shut down due to an under-voltage condition. Finally, the output relay is
opened after the user set delay expires and the current still exceeds the regenerative current limit set in
the REGENERATE CONTROL screen.
In grid simulator mode, Sequoia Series AC sources allow positive power operation also, meaning the user
can source from the Sequoia. If the power is positive, then Sequoia will consider the source current limit
instead of the regenerative current limit as the regulation parameter.
For the DC mode, the Sequoia must be set to the DC Voltage mode and voltage range that accepts the
maximum desired set voltage.
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