Harmonic power sharing between power electronics converters in islanded AC microgrid

Abstract

The dynamic evolution of renewable energy sources (RESs) with utilization of power electronics converters (PECs) caused the situation, where many energy generation units works parallel in local systems named microgrids (MGs). This distributed generation systems with many few kW micro-sources have to provide energy for linear and non-linear loads in grid connected mode of operation, but also in islanded mode of operation, which requires more advanced monitoring and energy management algorithms to ensure power balance and good voltage quality. The issues of power management in islanded AC microgrids are studied by many research centres and novel solutions are necessary to improve the reliability of MGs. In literature, there is still a gap for development of harmonic power sharing method in MG with most often used non-linear loads. Together with active and reactive power management algorithms the harmonic power sharing algorithm need to be implemented in control system to obtain complete solutions. The most often used approach in MG is hierarchical control structure, which includes the basic control loops at primary level, independent for each of PECs and outer control loops at secondary level, which allow to improve voltage amplitude and frequency in point of common coupling, as well as power sharing between PECs. Moreover, the hierarchical control structure is a great opportunity to implement a distributed control algorithm, which is able to execute many operations in the same time. Based on this idea, the novel proportional harmonic power sharing algorithm has been developed. It causes the harmonic power sharing between PECs proportionally to active powers, improving the output current waveforms of converters by decreasing the amplitude of selected current harmonics. The principles of hierarchical droop control and reactive power management has been presented in this paper. The developed solution has been implemented in simulation research together with proportional reactive power sharing algorithm. In order to present the advantage of harmonic power sharing, the results have been compared with non-controlled harmonic power.