Harmonic Problems in Renewable Energy and Microgrid Systems

The integration of renewable energy sources (RES) to the grid would not be possible without the use of power electronic devices (e.g., DC and AC inverters). These devices are essential to interface these RES and distributed generators (DG) to the distribution system. Using power electronic devices (e.g., inverters) in order to connect the RES and DGs to the grid exhibits many advantages, such as faster voltage and frequency regulation, but it also displays one major disadvantage. The switching operation of the semiconductors included in the inverters causes voltage and current harmonic distortion via the distribution transformer to the grid.

This distortion increases for a number of other reasons, such as the behavior of nonlinear loads (diode rectifier bridges, personal computers, induction machines, etc.) and the switching operation of their converters. Specifically, harmonic distortion occurs due to loads supplied by converters, as well as to RES, interfaced to the grid through inverters. Harmonic distortion leads to poor power quality to the end user of the distribution system, as well as to increased value of line current.

For this reason, a lot of active filters and power conditioners have been proposed to alleviate the distribution system problems of current and voltage high-order harmonics, and power quality. Only a few of these proposals deal with improving power quality. Instead, the majority focus on harmonic cancellation and power quality improvement of critical loads against the high-order harmonic distortion of the grid that they are connected to. In this section, we will discuss the impact of harmonics on renewable energy and microgrid systems.

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