Innovative power smoothing techniques for wind turbines using batteries and adaptive pitch regulation

To ensure a higher penetration of wind energy in local and national energy mixes, power variability induced by wind fluctuations needs to be limited. In this study, three power smoothing approaches are proposed and compared to the conventional unconstrained behavior. The first method makes use only of a state-of-the-art Li-Ion battery (BESS), while the second and the third also integrate a dedicated blade pitch regulation to control the power output; more specifically, in one case pitch regulation is used to curtail ramp-up violation, i.e. an abrupt increase in wind speed and power output that exceeds an imposed maximum variation threshold, if the BESS cannot be charged completely. In the third method, pitch actuators are exploited to contrast ramp-down violations in addition to ramp-up violations, by reducing the amount of power fed to the grid for specific wind speeds. The three methods have been applied to a hypothetical case study including the NREL 5 MW Reference wind turbine subject to a series of 20-year wind data synthesized based on experimental data coming from a wind farm in Greece. A power ramp rate limit equal to 10 % of the nominal power per minute has been considered, and the economic prospects of the system have been studied from the perspective of different penalties (0–500 €/MWh of violating energy) that could be applied in the future to ramp rate violations. Results obtained show that: i) below a 20 €/MWh penalty, it is not convenient to add any power smoothing method; ii) for a 20–60 €/MWh penalty, it is convenient to add a battery only; iii) for a 60–350 €/MWh penalty adding a pitch control system to the BESS to avoid ramp up violations if the battery is fully charged becomes convenient; iv) above 350 €/MWh, the best control method is a hybrid battery and pitch system which modifies the power curve of the turbine to obtain an optimal compromise between power smoothing and power production reduction. Focusing, however, on the quality improvement of wind turbine power output, abatement ratios for proposed innovative methods range from around 84 % to 88 %, and the average intensity of those violations is reduced to around 17–19 % compared to a standard operation. All these metrics are much higher than those achievable with the use of a battery alone.