MT5 Multi-Tracer Operating Manual
page 79
Appendix B - Peak-Power Tracking
The MT5 Load Unit peak-power, tracks using a walking algorithm. The nature of peak-
power tracking a PV module is that there is no way to detect that any given operating
point is actually the peak-power point. All that can be done is to continually compare the
operating point to near-by operating points by making small step changes. This can only
be done by continually moving the operating point voltage.
The technique used by the Multi-Tracer is to increase or decrease the operating voltage
and note the change in power. If the power increases, then the next step is taken in the
same direction. I.E, the voltage is increased or decreased again. The operating voltage
is continually changed in the same direction until the power drops relative to the last
measurement. By do
ing this, the system “knows” that it has just crossed the peak-power
point.
At this time, the unit reverses direction and steps back toward the peak-power point.
After initially crossing the point, it will take a smaller step every time it changes direction.
In this way, the system is said to be walking back and forth across the peak-power
point. Ultimately the step size is reduced to very small values, with the ideal to make the
changes in power so small as to be insignificant.
Unfortunately, there are several real-world issues that complicate this process. The first
is signal measurement noise. Every measurement system has some level of noise.
Given the resolution of the Multi-tracer measurements, noise is easily measured. As a
result, when making small step variations in operating voltage, power may appear to
change simply due to signal noise. Therefore the Multi-Tracer requires that the power
change by an amount large enough to reject signal noise. Currently the limit is 1/1000
(0.1%) of the measured power. There is also a minimum limit defined by the power
rating of the channel to prevent absurdly small fractions of power when the measured
power is very small.