Total output power variation of several small wind turbines

Abstract

There is a concern that connection of several small wind turbines may cause severe voltage fluctuation and voltage flicker in low-voltage distribution lines due to their output power variations. In this study, output power variations of four 5-kW-class small wind turbine systems were measured with an interval of 0.1 s at a site in Wakkanai, Hokkaido, and their correlations and smoothing effect in the frequency range from [Formula: see text] to 5 Hz were analyzed and compared with those of five residential photovoltaic power systems. The results indicate that a smoothing effect occurs more in small wind turbines than in photovoltaic systems, because of lower correlation coefficients in lower frequency ([Formula: see text] Hz) components. Voltage flicker at the point of common coupling was also measured and it was confirmed that the impact of small wind turbines on voltage flicker is low enough at the site. In addition, the upper limits of the installation number and/or the system resistance are estimated theoretically using the measured flicker values.

An Evaluation of Flicker Emissions from Small Wind Turbines

“…In Figure 12b, all of the bin averages and 95th and 99th percentiles of the ∆V 10 distribution change smoothly, depending on the mean total output power P tot , with the peak at P tot = 16 ∼ 17 kW (5/6 of the total power rating). The peak value of the 95th percentile is 0.122 V at 12:45 on 15 April, which is 0.04 V lower than that evaluated in the previous report [17], owing to the extraction treatment. The peak value is 1.4 times higher than that at the site in Minami-Osumi.…”

“…The relationship between the increments of the PCC voltage ∆V t and the total output power ∆P tot over four days is illustrated in Figure 11. The dispersion of the data is much smaller than the scatter plot of the relationship between V t and P tot depicted in a previous report [17]. The values of slopes ∆V t /∆P tot of the straight lines drawn by the least-squares method for the respective days have slight errors, with an average of 0.242 V/kW.…”

“…Although the authors have already reported the measurement results from another site in Wakkanai in [17], they re-evaluated the same results in this section to compare them with the results obtained from the Minami-Osumi site described in Section 4. The following improved methods were used in this study for the re-evaluation process:…”

“…Figure 12a indicates that the ∆V 10 at the PCC was rather calm and always lower than the tolerable limit (0.45 V). Thus, in a previous report [17], the flicker emission was evaluated using the raw data. In contrast, in this study, the data in Figure 12b were extracted in terms of the V h /P h threshold of 1.3 V/kW as described in Section 4.3, and the rate of extracted data was 87.1% of all the data under the power-generating condition, which is a much higher rate than at the site in Minami-Osumi.…”

“…While such analyses effectively estimate the energy yield or probability and magnitude of overvoltage, they are devoid of the information for the faster output power variation that directly impacts the voltage quality, such as flicker emissions. Thus, this study first analyzed the impact of SWTs on voltage quality using time-series data measured over a period of four months, with an interval of 0.1 s from an operational site in Wakkanai, the northernmost city in Japan [17]. Subsequently, the data collected for a year from another site in Minami-Osumi, the southernmost town in mainland Japan, was analyzed and compared to identify the general features of the impact of SWTs on the voltage quality, especially flicker emissions, that is then described in this paper.…”