On the tuning and performance of Stand-Alone Large-Power PV irrigation systems

Abstract

• A new systematic method of tuning the PID control of frequency converters. • First experimental values of performance for large-power PV irrigation systems. • The average number of abrupt stops per day decreases by more than 80%. • A passing-cloud resistance ratio value greater than 95% can be required. • The expected PR in good quality PV irrigation systems pumping to a water pool is 65%. Stand-alone large-power PV irrigation systems without batteries is a recent innovation. This means that their design has not yet reached maturity and there are no experimental data about their performance available. This paper is a contribution, on the one hand, to the systematic tuning of the control of this type of systems and, on the other hand, to the knowledge of their experimental performance data. A systematic Proportional, Integral and Derivative (PID) control tuning method for frequency converters is proposed, based on the application of the Approximate M−constrained Integral Gain Optimisation (AMIGO) design rules to the frequency response tuning method, and applied to two PV irrigation systems, located respectively in Villena and Aldeanueva de Ebro, Spain, that had a “conservative” tuning by means of an experimental trial and error method. To check the goodness of this systematic tuning, the experimental performance of both systems has been evaluated from 2017 to 2021. New indices have been proposed to assess both the robustness of the system to PV power fluctuations (the “Number of abrupt stops” and the “Passing-cloud resistance ratio”) and the performance (by factoring the traditional Performance Ratio ( PR ) to determine the influence of different factors external to the system). Results show that the percentage of abrupt stops improves from 40% and 39.8% in each PV irrigation system prior to systematic tuning to 7.3% and 1.3% after tuning; the passing cloud ratio increases from 65% and 79% to 97.9% and 99.8% and the PR from 61.4% and 60% to 65.7% and 64.7%.