Pablo Sanchis solves the detection of the “island effect”

The “island effect” is one of the main problems in photovoltaic compound solar systems.

The doctoral thesis of Pablo Sanchis, presented in the Public University of Navarre (Basque Country), proposes three main contributions: the first one is a new control strategy of a booster inverter for autonomous systems; the second one is a new implementation of impedance measurement method, and the third one, a new methodology for the design of drift method in frequency, which guarantees with total reliability the detection of operation in the island.

Growing interest in photovoltaic energy

This research arises from the information in power electronics of Pablo Sanchis and his interest for renewable energies. In this field, it was noticed that there was still a lot to research in the conversion phase of two types of existing photovoltaic systems, autonomous ones and compound ones.

During the phase of conversion energy coming from photovoltaic panels is transformed. At the output of this panel direct voltage of low level is produced. This voltage must be transformed through electronic power converters so that it can be used, usually in an alternate current voltage of 220 V and 50 Hz.

The thesis proposes solutions for both photovoltaic systems, autonomous and compounds. For the autonomous systems, the use of booster inverter is proposed as an alternative to conventional power converters. Actually, the innovation does not lie so much in the structure self as in the control strategy of the converter proposed in the thesis. The advantages of this converter are its validity to work with variable references, its high level to reject external disturbances and its high reliability. That is, it rejects efficiently disturbances and allows exceeding the provisional short circuits. Furthermore, the dynamic of operation is faster and more precise.

This converter has drawn the attention of Laboratoire d’Electrotechnique et Electronique Industrielle de Toulouse (France). In fact, they have signed a partnership agreement with this University to use it in hydrogen fuel cell systems.

Compound photovoltaic systems

In the second part, the thesis studies the compound photovoltaic systems and, in particular, two problems that appear within those structures: the island effect and the filtering in single-phase inverters.

As for the first one, the “island effect”, it constitutes one of the main reasons for reluctance of power supply companies to accept the connection to its mains of distributed generation systems. For example, in case of a house with photovoltaic panels on the ceiling connected to the electric power supply. In a given moment, due to maintenance reasons or for any other reason, the electric power supply is turned off. However, the photovoltaic system can still keep the voltage in the mains sector that has been switched off. That is known as the island effect and is very dangerous, because the staff that are doing maintenance tasks believe there is no voltage, when indeed there is, as the photovoltaic system continuous generating it. Obviously, that can cause serious accidents or even failures in the electrical system. Therefore, it is important to have a method that detects when occurs the island effect in order to switched off the photovoltaic system.

Due to the importance of the problem, the company INGETEAM of Pamplona, which designs and produces converters for photovoltaic systems, addressed to the team of researches of the Public University of Navarre in order to obtain an efficient algorithm to detect the operation in island then to be introduced in photovoltaic converters that they commercialise.

Once the different methods proposed in the scientific literature were studied, Pablo Sanchis focused on two of them, the impedance measurement method and the drift method in frequency. The research team ignored the capacity of the first one, required by the German regulation. As for the drift in frequency, they sensed it was one of the best methods.

Once the impedance measurement method was analysed, Pablo Sanchis developed a new valid technique to go beyond the German regulation. This new method allows ensuring the island detection in any real operation condition, which makes it an optimal method.