Xantrex Technology PV100S-208 manual Peak Power Tracking

Operation Features

Peak Power Tracking

An advanced, field-proven, Maximum Peak Power Tracker (MPPT) algorithm integrated within the PV100S 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 PV100S 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 PV100S. As show in Figure 1-1 on page 1–4,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 PV100S to ramp the PV voltage to the “PPT V Ref” set point regardless of the actual PV voltage.

With the “PPT Enable” set to “0” (power tracker disabled), the PV100S will regulate the DC Bus at the “PPT V Ref” set point. 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 PV100S. 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.

Conversely, if the power comparison proves undesirable, the power tracker will reverse the direction of the change to the “PPT_V Step”. The MPPT algorithm within the PV100S will then continue this ongoing process of “stepping and comparing” in order to seek the maximum power throughput from the PV array.

The changes made by the MPPT to the reference voltage are restricted to ± 20% of “PPT V Ref” and by the maximum and minimum PV input voltage (600 and

300 volts respectively). Also, the MPPT will not attempt to produce power greater than that allowed by the “I PPT Max” set point. If available PV power is above the maximum allowable power level of the PV100S, the MPPT will increase voltage as needed to maintain output power below rated maximum.

152379 Rev C 1–3