Harmonic Emission of Large PV Installations Case Study of a 1 MW Solar Campus

Abstract

Abstract. Extensive measurements were carried out at a 1 MW photovoltaic (PV) installation with focus on the analysis of harmonic emission both for classical harmonics below 2.5 kHz and higher frequency emission in the range of 2-150 kHz. The installation consists of multiple inverters with different rated power. Beside the measurement of total emission of all inverters, in one part of the measurement the inverters were switched off and on stepwise following a predefined schedule. This provides a comprehensive basis for a detailed characterisation of the interactions between the inverters in terms of harmonic emission. After a description of the measurement setup the paper discusses the total emission of the installation, the dependency of the emission on the supply voltage distortion and the potential of harmonic cancellation due to phase angle diversity between the different inverters. The results enable a better understanding of the harmonic emission behaviour of large PV installations. The paper is intended to be an contribution to the development and improvement of respective harmonic models. Key wordsPhotovoltaic inverter, Harmonics, cancellation effect, Higher frequency emission Measurement SetupThe PV installation comprises of nine large inverters with rated power of 100 kVA and eleven small inverters with rated power in the range between 1 kVA and 10 kVA (total output of nearly 50 kVA). All large inverters are three phase while all small inverters are single phase.For the measurement of low order harmonics, eleven PQ instruments complying with IEC 61000-4-30 Class A were used. The voltage and current spectra (magnitude and phase angle related to voltage fundamental) were measured with each instrument for almost two days using an averaging interval of 150 periods (three seconds). Each of the large inverters, the sum of all small inverters and the total sum of the installation were monitored. Calibration measurements were carried out to assess the accuracy of the PQ instruments. For voltage harmonics larger than 0.2% and current harmonics larger than 0.2 A the error for magnitude is smaller than ±2% and the error for phase angle is smaller than ±1°.Voltages and currents in the higher frequency range (2 -150 kHz) were measured at one large inverter (three phases) and four small inverters (each single phase). Two specific network analysers with a sampling rate of 1 MS/s and a resolution of 16 bits were used. The current was measured using current clamps. During the switching of inverters raw data in time-domain was stored continuously. Otherwise three seconds every minute were stored to reduce the data size. Afterwards, a high pass filter (elliptic, 3 rd order, 2 kHz passband) was applied to the measured data. Subsequently it was split in 200-msblocks (5-Hz-resolution) and for each block a discrete Fourier transformation was performed. All values are presented in the logarithmic unit dB µV , where 120 dB µV corresponds to 1 V and 0 dB µV to 1 µV. For currents the unit dB µA is used respectively. The network...

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