Applications; Maximum Power Point Tracking - Alpha Group OutBack Power FLEXmax Series Owner's Manual

Applications

Maximum Power Point Tracking

Maximum Power Point Tracking (MPPT) is the technology used by FLEXmax controllers to optimize the
harvest of power from PV arrays.
PV modules do not have a defined operating voltage. Their voltage is defined strictly by the load
connected to them. With no load (disconnected), a module displays "open-circuit" voltage (Voc), and
delivers no current. At full load (shorted), a module has no voltage, although it delivers the maximum
"short-circuit" current (Isc). In neither case does it produce usable wattage.
When partially loaded, a PV module delivers partial current and voltage. These numbers can be
multiplied to see the available wattage. However, the delivery of wattage is not linear. The current
and voltage delivered at a given load will change with the load, along a curve such as that shown in
the drawing to the left in Figure 99. This is known as the V-I curve. The wattage is different at every
point along the curve. (The V-I curve also varies with module type and manufacturer.) Only one point
on the V-I curve represents the delivery of the module's maximum (rated) wattage. This is known as
the maximum power point , or MPP. The current at this point, Imp, is the highest that can be drawn
while still maintaining the highest voltage, Vmp.
The FLEXmax controller places a variable load on the PV array and tracks the result to determine the
maximum power point. This process, MPPT, is maintained so that the FLEXmax can deliver the
maximum PV power regardless of any change in conditions. The drawing to the right in Figure 99
shows the MPP and compares the V-I curve against the available wattage.
Isc Isc
MPP
Imp
VOLTAGE
Voc VOLTAGE Vmp Voc
V-I curve Available wattage
Figure 99 Maximum Power Point Tracking
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