Characterisation and assessment of the harmonic emission of grid-connected photovoltaic systems

Abstract

This paper presents and discusses the results of several measurements carried out on photovoltaic systems connected to LV-grid, from the harmonic distortion viewpoint. The PV-system inverters are characterised by different ratings, in the range of 850 W up to 3 kW, and different structures, including low-frequency and high-frequency transformers. The harmonics emission and the total harmonic distortion (THD) were measured over a period of several days having different solar radiation and by this different generated power. The results indicated a strong dependency between the THD and the generated power, in such a way that the THD is always high when the generated power is low. The influence of network impedance measuring signal and of the modulation of the Pulse Width Modulation (PWM) is analysed and discussed. Procedures to assess the connection of the PV-systems to the grid as per international standards are presented. The results indicated that, in practical cases, the measured harmonic emission may exceed the typical values obtained in laboratory tests.

Comparison between Active power filter with selective control and conventional control for harmonic in photovoltaic systems

“…Consequently, the harmonic distortion generated by the photovoltaic systems depends strongly from the generated power, in such a way that when this power is low, the harmonic distortion is high; on the other hand, the harmonic distortion is low. This behavior is appreciated clearly in Figure 1 1 , which shows the change of the total harmonic distortion of current (THD i ) of a photovoltaic generator 2 in regard to the generation rate Gn PP , where P G is the generated power by the photovoltaic system and P n is the nominal power of the photovoltaic generator [2].…”

“…This conversion process happens across the inverters which are composed of power electronic devices that constitute a current source that inject harmonics to the network [2].…”

“…Nevertheless, also takes into account some peculiarities as the influence of climate variables as: the temperature, solar radiation and shadow effect. These variables impact significantly on the current and voltage waveform and establish the operating conditions and generation [2]. Fig.…”

Power Quality analysis in Renewable Energy Systems Supplying Distribution Grids

“…When the generated power is high (large value of RMS electrical current), the fundamental current is high and the THDI is small [7,8]. For small generated powers, the fundamental current is small and the THDI is high.…”

Power Quality Assessment in Small Scale Renewable Energy Sources Supplying Distribution Systems

“…In this paper, it is considered that harmonics are determined by converter at the interconnection point with the main supply. When the generated power is high (large value of RMS electrical current), the fundamental current is high and the THDI is small [16,17]. For small generated powers, the fundamental current is small and the THDI is high.…”