Harmonic Distortion in Renewable Energy Systems: Capacitive Couplings

Abstract

Renewable energy systems such as wind farms and solar photovoltaic (PV) installations are being considered as a promising generation sources to cover the continuous augment demand of energy. With the incoming high penetration of distributed generation (DG), both electric utilities and end users of electric power are becoming increasingly concerned about the quality of electric network (Dugan et al., 2002). This latter issue is an umbrella concept for a multitude of individual types of power system disturbances. A particular issue that falls under this umbrella is the capacitive coupling with grounding systems, which become significant because of the high-frequency current imposed by power converters. The major reasons for being concerned about capacitive couplings are: a. Increase the harmonics and, thus, power (converters) losses in both utility and customer equipment. b. Ground capacitive currents may cause malfunctioning of sensitive load and control devices. c. The circulation of capacitive currents through power equipments can provoke a reduction of their lifetime and limits the power capability. d. Ground potential rise due to capacitive ground currents can represent unsafe conditions for working along the installation or electric network. e. Electromagnetic interference in communication systems and metering infrastructure. For these reasons, it has been noticed the importance of modelling renewable energy installations considering capacitive coupling with the grounding system and thereby accurately simulate the DC and AC components of the current waveform measured in the electric network. Introducing DG systems in modern distribution networks may magnify the problem of ground capacitive couplings. This is because DG is interfaced with the electric network via power electronic devices such as inverters. These capacitive couplings are part of the electric circuit consisting of the wind generator, PV arrays, AC filter elements and the grid impedance, and its effect is being appreciated in most large scale DG plants along the electric network (Garcia-Gracia et al., 2010).