An Optimization Approach for Smoothing Output Power of Variable Speed Wind Turbines

With the increasing penetration level of wind power, issues caused by this intermittent energy arouses extensive attention these years. How to mitigate the fluctuation of wind turbine output power is one of them. Variable speed operation of wind turbines, on the one hand, introduces electronic converters which can decouple the wind generator system with power system response and further bring many stability problems. On the other hand, wide rotor operation range makes it possible to flexibly adjust the rotor speed to meet with control objective. This paper introduced a detailed control method to smooth the power output of variable speed wind turbine with the strategy to optimize rotor speed. It was proved to be effective by the case study. Introduction Wind power, a relatively mature emerging technique, has been widely applied over last decades. The introduction of various emission reduction schemes led to the increase of wind power plants’ plan and installations in the world [1]. Like other countries, Australia government claimed the target that 23.5 percent of Australia’s electricity generation in 2020 will be from renewable sources and this target provides an incentive to build the lowest cost renewable energy projects [2]. Although wind energy advocates have spent decades obscuring the level of risk imposed on power system, the impacts of large amounts of new wind generation on power system stability can be significant. The impact of this intermittent power on the connected grid mainly attributed to the stochastic nature of wind energy, which directly influences the power generation. In other words, the output of conventional power plants needs to be adjusted more frequently to mitigate the fluctuations, and this also causes difficulties in estimating suitable system reserve to ensure secure and reliable operation. In order to provide gird as smoothing power as the conventional generators, energy storage technologies were utilized as a power reserve to smooth wind turbine power generation. Comparing these technologies, battery energy storage system (BESS) is the most cost-effective option for short-term wind farm dispatch purposes [3]. The cycle-life degradation of the battery, however, shrinks the life span of installed BESS and adds investment on the wind farm. Another way is to mitigate the power fluctuation by the control method design from the point of wind turbine control. The existing methods to control wind turbine power generations are classified into two ways in terms of control target. The one is levelling output power by advanced pitch angle control, which limits the power acquisition with the adjustable pitch angle. The other way is to adjust power generation by controlling tip speed ratio of wind generator. This method can be further achieved by three strategies, which are constant power control, linear slope control and optimal wind power acquisition [4]. In this paper, a modified optimal wind power acquisition strategy, which is based on the rotor speed optimization within the control horizon, is proposed to filter the wind turbine output power.