Reactive and Harmonic Current Compensation by Multifunction Converters

Over the last few decades, global energy consumption has continued to grow. According to the report (Key World Energy Statistics 2017), published in 2017 by the IEA (International Energy Agency), the total energy consumed worldwide in 2015 was around 13647 Mtoe (million tonnes of oil equivalent). Non-renewable energy accounts for 90.3% of this, with oil (31.7%) accounting for the largest share of consumption, followed by coal (28.1%), then natural gas (21.6%) and finally nuclear power (4.9%). Increased consumption of non-renewable energies not only leads to their depletion, but also to environmental pollution and global warming. What's more, prices for non-renewable energies are soaring as the time for their depletion approaches. This is the decisive reason why, in the near future, both nationally and internationally, electricity grids will increasingly integrate decentralized solar and wind power generation, as well as electrical energy storage devices. For this reason, several pilot research projects are currently focusing on the new microgrid concept. This can be described as an integrated energy system including local power generation facilities (microturbines, photovoltaic panels, mini-wind turbines, etc.), electrical loads, electrical energy storage facilities (batteries, supercapacitors) and an energy flow supervision and management system. Microgrids are designed to provide decentralized power generation and local power supply for a number of consumers.

The operation of a microgrid requires intelligent, communicative management of all its components to ensure the availability of electrical energy in a context of rising demand and a decentralized, intermittent and volatile energy supply. This has prompted several researchers and academics to carry out research into the new microgrid concept. The problem addressed in this article concerns the improvement of energy efficiency in a three-phase AC microgrid. It is motivated by the fact that, generally speaking, loads only benefit from the "active" part of the energy supplied, while they also consume a "reactive" and "harmonic" part of the energy, which overloads the microgrid. For this reason, it is advantageous to compensate for the reactive and harmonic parts of the energy via appropriate solutions. Conventional solutions used for this purpose can be divided into two categories: passive solutions such as capacitor banks or passive filters, and active solutions such as active power filters. That said, recent research has shown that reactive and harmonic energy compensation can be achieved with multifunction converters (MFCs). These converters are basically used to interface renewable energy sources (RES) with the transmission lines of a microgrid. Their functionality can be extended to include auxiliary functions to compensate for the...