PHOTOVOLTAIC PUMPING SYSTEMS TECHNOLOGIES TRENDS

Abstract

This paper has reviewed the principle research activity in photovoltaic pumping
systems over the past decades. Prior to the common use of power converters,
the principle problem was the to find the best matching of DC motors connected
directly to the PV array and, naturally such systems were very sub-optimal in
that they were unable to utilise the PV capacity. The use of power converters
has allowed the extra freedom to exploit the maximum energy capture from the
PV arrays. Much of the research focussed on control mechanisms to derive
maximum capture (MPPT algorithms) in the presence of variable insolation and
array temperature. These methods, ranging from simple constant voltage
through to hunting and adaptive techniques have been discussed. Apart from the
requirement of adaptability based on the temperature-dependent array
characteristics, the MPPT algorithms represent an interesting control problem.
This is because the power converter may be viewed as an impedance changer
making possible an optimal (and adaptive) impedance matching between the
array and the motor-pump load. The dynamics for the control design are then
seen to be highly non-linear and represent a good application of fuzzy and
neural network techniques. It is of interest to note that other control techniques,
such as variable structure and model reference adaptive methods have yet to be applied. However, it may also be observed that the plant structural changes are relatively slow and that the low target bandwidths would tend to make the comparative advantages of various methods somewhat marginal.