Propagation of harmonic emission from the turbines through the collection grid to the public grid

Abstract

Abstract-This paper addresses the harmonic emission from a large off-shore wind farm. An overview is given of the issues, where a distinction is made between frequencies below and above 2 kHz. Three different approaches are presented: a simplified mathematical model; a more detailed mathematical model; and measurements and the point of connection for an off-shore wind farm. It is concluded from both models and measurements that the emission is small for frequencies above a few kHz. However, specific resonances at higher frequencies involving the power transformers, when coinciding with switching frequencies or harmonics of switching frequencies, could result in high emission even at these high frequencies.

Effect of wind turbine converter control on wind power plant harmonic response and resonances

“…Power quality problems arise in large WPPs because of the harmonic emissions of WTs equipped with power electronics [1][2][3][4][5][6][7][8][9]. These harmonic emissions are amplified by parallel resonances in the collector grid if they are close to the resonance frequency [1,[6][7][8][9][10][11][12]. A summary of the most important WPP harmonic and resonance issues is presented in [6,8,11].…”

Study of resonance in wind parks

“…• Although, in order to consider the influence of WT control on consumed harmonic currents, WTs are better characterized as Norton equivalent sources [7], the typical WT harmonic model as ideal current source is used in the study because it is commonly chosen to perform frequency scan studies and it offers a useful insight into parallel resonance analysis [1,8,[11][12][13][14]16]. However, further research is required to analyze the impact of WT control on this resonance.…”

“…Most research works model converters as harmonic current sources and analyze the influence of WP parameters on parallel resonance [1,7,8,[11][12][13][14][15][16][17][18]. These studies are mainly based on frequency scan simulations which allow the frequency range and peak impedance values of parallel resonances to be established.…”

“…1(a) shows a generic WP layout where WTs are supplied through low voltage (LV) underground cables and medium to low voltage (MV/LV) transformers and are interconnected with an N r × N c collection grid of medium voltage (MV) underground cables from the MV collector bus [7,8,[11][12][13][15][16][17]. Capacitor banks in onshore WPs can also be connected to this bus and harmonic filters are usually installed on the line side of WT converters to mitigate frequency switching harmonics [7,8].…”

Harmonics - another aspect of the interaction between wind-power installations and the grid

“…The relation between the emissions from individual turbines and from the park as a whole is discussed in a companion paper [3]. There it is concluded that the emission from a park can be higher as well as lower than the emission that would be obtained by adding the harmonic magnitudes of the individual turbine emissions.…”