Harmonic and Reactive Currents Compensation in the Utility Grid

A power system is a complex system that essentially includes the generation, distribution and consumption of electrical energy. Despite its complexity, a power system must ensure that electrical energy is generated in line with instantaneous load consumption. As electrical energy is very difficult to store, the stability of the power network requires a permanent balance between generation and consumption. This is why, nowadays, the quality of electrical energy (QEE) in power grids has become a crucial issue. This is because improving QEE ensures :

• better control of electrical energy consumption;

• productivity gains in the generation of electrical energy.

Electrical energy is generally distributed in the form of a three-phase source of sinusoidal voltages, balanced in the ideal case. The waveform of the currents consumed by the loads determines the nature of the energy transmitted. This can be broken down into an "active" part, a "reactive" part and a "harmonic" part. In general, the end-user only benefits from the energy supplied by the "active" part of the transmitted electrical energy. The "reactive" and "harmonic" energies transmitted cannot be eliminated, but can be compensated for by appropriate devices that offer the following advantages:

• the ability to compensate for harmonic currents consumed by non-linear loads. This helps to improve power quality by reducing the TDH (harmonic distortion rate) of currents flowing through power distribution lines;

• the ability to compensate for the reactive current consumed by non-linear, reactive loads. This increases the power displacement factor.

In this case, we're talking about an improvement in power quality, and the total energy drawn from power grid sources will be reduced overall.

To this end, this article is a contribution to a better understanding of the problems associated with the consumption of harmonic and reactive currents in the power network. In addition, this article reviews the state of the art in conventional solutions for improving electrical power quality by compensating for the "reactive" and "harmonic" components of distributed electrical power. In this context, the authors wish to raise readers' awareness of the energy and economic potential offered by these solutions, but also of the technological challenges and limitations associated with them.