Introduction
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Operation Features
The GT100 has the following operation features.
Fixed Unity Power Factor Operation
The GT100 maintains unity power factor during operation. The control software
constantly senses utility voltage, and constructs the output current waveform to
match the utility voltage. The GT100 is not capable of operation without the
presence of normal utility voltage, nor is it capable of varying the output power
factor off unity.
Peak Power Tracking
An advanced, field-proven, Maximum Peak Power Tracker (MPPT) algorithm
integrated within the GT100 control software ensures the optimum power
throughput for harvesting energy from the photovoltaic array. The peak power
voltage point of a PV array can vary, primarily depending upon solar irradiance
and surface temperature of the PV panels. This peak power voltage point is
somewhat volatile, and can easily move along the I-V curve of the PV array every
few seconds. The MPPT algorithm allows the GT100 to constantly seek the
optimum voltage and current operating points of the PV array, and maintain the
maximum peak PV output power.
Accessible via the UFCU, there are five user-settable parameters that control the
behavior of the maximum peak power tracker within the GT100. As show in
Figure 1-11 on page 1–15, user settable parameters include:
•
PPT V Ref (ID# 37),
•
I PPT Max (ID#42),
•
PPT Enable (ID# 44),
•
PPT Rate (ID# 45), and
•
PPT V Step (ID# 46).
Upon entering the Power Tracking mode, it takes approximately 20 seconds for
the GT100 to ramp the PV voltage to the “PPT V Ref” setpoint regardless of the
actual PV voltage.
With the “PPT Enable” set to “0” (power tracker disabled), the GT100 will
regulate the DC Bus at the “PPT V Ref” setpoint. Regulating the DC bus means
drawing more or less current out of the PV array to maintain this desired voltage.
With the “PPT Enable” set to “1” (power tracker enabled), followed by the
expiration of the “PPT Rate” (MPPT decision frequency), the MPPT will reduce
the reference voltage by an amount equal to the “PPT V Step” value.
At this point the MPPT will compare the amount of AC output power produced to
the previous amount of AC power produced by the GT100. If the output power
has increased, the next change made (after “PPT Rate” has again expired) to the
reference voltage, will be in the same direction.
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