Wind Engineering

An investigation of power law exponents (wind shear coefficients) was conducted using LiDAR data collected offshore in Lake Erie. The purpose was to investigate discrepancies found by previous studies between calculated power law exponents from measurements and recommended values from international standards. In this study, power law exponents were evaluated using the LiDAR measurements at heights of 80–200 m. The average power law exponent during the study period was found to be 0.09, which was lower than the 0.14 standard assumed by international standards. A detailed investigation of the distribution of power law exponents revealed a bi-modal distribution comprising the two most frequent exponent ranges between 0.01–0.02 and 0.19–0.20. The gap between these peaks was found to be dependent on the atmospheric stability of the boundary layer. Average power law exponents of 0.02 and 0.14 were found for atmospheric conditions indicating unstable regimes and neutral/stable regimes, respectively. Regime stability also showed directional dependence where winds from the 180° ± 45° directions were prevailing during neutral/stable conditions and winds from the 326° ± 67° directions were prevailing during unstable conditions.

In South Korea, where 64% of the national territory is mountainous, good wind resources in inland areas are mostly situated in high mountain regions. To develop a wind farm in a mountain region, the sloping of mountains and their shielding from wind by the surrounding topology should be considered. It is generally most advantageous to install wind turbines along a ridge that is open in all directions. This article presents a methodology for evaluating suitable sites for wind farm development by identifying suitable ridges using morphometric analysis, while excluding the geographical and social environmental exclusion factors and superposing them on the wind resource map to find the area having a specific level or higher wind power density. The result of the proposed suitable site analysis and existing wind farms was assessed to verify the feasibility of the method of analyzing suitable sites on ridges. The wind resource potential in Gangwon Province when calculated using a method based on conventionally suitable site and the method based on ridge analysis was 9 and 5 GW, respectively. The result confirmed that the conventional area-based potential calculation without consideration of the morphometric terrain characteristics overestimated wind resource potential by around 80% compared to the ridge analysis method of calculation presented in this article.

A control strategy has been proposed for minimising the machine loss by optimally sharing the reactive power at the stator and rotor terminals of stand-alone doubly fed induction generator. For achieving this, fixed capacitor along with static synchronous compensator at the stator terminals has been employed apart from battery inverter system at the rotor terminals. A TMS320LF2407A digital signal processor–based controller has been developed for maintaining the stator voltage magnitude and frequency. A method has been developed for calculating the optimal reactive power at the stator terminals using the steady-state equivalent circuit of the proposed system. An analogue circuit–based optimal reactive power controller has been designed and fabricated in the laboratory for supplying this optimal reactive power at the stator terminals for all operating conditions. The salient feature of the proposed optimal reactive power controller is that it needs to monitor only the reference value of reactive power at the stator terminals for any operating conditions. The successful working of the proposed controller has been amply demonstrated through extensive analytical and experimental results obtained on a three-phase, four-pole, 415 V, 50 Hz, 5 kVA doubly fed induction generator.