The increasing share of single-phase distributed generation units in low-voltage grids causes voltage unbalance problems and overvoltages. Therefore, the need for power quality improving control strategies of grid-connected inverters emerges. Some control strategies require three-phase four-wire inverter topologies. The simplest way to connect the fourth wire is by connecting it to the mid-point of the dc-bus. This sometimes causes challenges in the stabilisation of the mid-point. In this article, two algorithms for stabilising the midpoint of a three-phase four-wire inverter are proposed. Both algorithms are described in detail and validated experimentally. The results showed that both algorithms perform well under perturbations and are able to maintain the midpoint potential close to zero, while the quality of the injected currents is not deteriorated.

Resonances in electrical distribution systems can result in amplification of harmonics, which is undesirable in electrical networks. To avoid intrusive measurement techniques, in the majority of the cases network modeling is used to validate if there is an issue with resonance. In this paper a new, innovative but simple, concept is presented which uses relatively basic measurements to segregate the power related to specific harmonics into active and non-active harmonic power. These results are subsequently used in order to find if there is resonance in the electrical network. In this paper the concepts are explained on a theoretical basis and are test cased by numerical modeling. The initial results look promising but additional research is needed to validate the method.

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In order to achieve the energy targets for 2020, further integration of renewable energy sources is required. Hence, there was a need to investigate possible solutions to achieve a reliable network without loss of production. An optimisation method is defined for integrating a residential solar-battery system. Based on the results of this research, it could be concluded that small battery storage systems of ±1 kWh/MWh consumption creates a considerable increase of both self-consumption and self-sufficiency ratio. Integrating a larger capacity will not contribute to a proportionate increase. In addition, an evaluation of centralised and decentralised storage systems is performed.

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