# Investigation into the Yaw Control of a Twin-Rotor 10 MW Wind Turbine
## 1 Introduction  
In recent decades, the consumption of non-renewable energy sources, such as fossil fuel, coal, petroleum, and natural gas, has increased rapidly due to population growth and technological innovations. Non-renewables are limited in their sources and have a significant negative impact on the environment due to greenhouse gas (GHG) emissions from burning fossil fuels and natural gas, which is reflected in climate change and global warming [1, 2]. According to the Intergovernmental Panel on Climate Change (IPCC), CO\({}_{2}\) emissions have increased by 1.9% in the past three decades alone, and in 2007, a 40-110% increase in CO\({}_{2}\) emissions by 2030 was predicted [3]. Consequently, there have been great efforts to reduce GHG emissions by searching for alternative sources of energy production that are sustainable and environmentally friendly, in order to avoid the potential dangers of global warming and climate change, which are threats to the whole world. One of the mosteffective ways of eliminating fossil fuel usage is shifting toward using renewable energy (RE) sources [4], which have minimal negative impacts on the environment, as they are sustainable and clean [5]. Renewable energy sources, including biomass energy [6], tidal energy [7; 8], solar energy [9; 10; 11], and wind energy [12; 13], can be safe and economically feasible alternatives for generating power on a megawatt scale. Currently, solar and wind energy sources are considered to be the cleanest, cheapest, and fastest-growing RE sources in the world, and they are expected to play a dominant role in the transition to fully RE systems that cover global energy needs [14; 15]. A long time ago, it was concluded that 45% solar PV and 55% wind power would be the optimum balance for a 100% RE system [16]. Wind energy is considered to be one of the core pillars of RE sources, as it is the least polluting, most sustainable, efficient, and cost-competitive energy source compared with other sources [17]. The year 2022 was recorded as the third best year for wind power production, with a capacity of 78 GW added, resulting in a global cumulative wind power capacity of 906 GW, representing a year-over-year (YOY) growth of 9%. According to the 2023 Global Wind Energy Report (GWEC), it is expected that an additional capacity of 143 GW will be installed by the end of 2030 [18]. Therefore, wind energy is becoming an object of great research interest, and researchers are competing to find new sources and develop existing ones. In order to benefit from wind energy and utilize it to its full potential, new and innovative wind energy systems have been developed [19], including some novel unconventional technologies such as airborne wind energy devices like giant kites [20], aerial vehicles [21], and wings [22], which are tethered to the ground and fly high in the air where the wind is stronger and more consistent. Wind turbines (WTs) are conventional devices for harvesting energy from flowing wind, and they have the highest efficiency. Horizontal-axis wind turbines (HAWTs) are complex nonlinear systems with a single rotor consisting of three fiberglass blades that come in different sizes based on capacity. According to the general rule of WT power, the amount of energy produced is directly proportional to the cube of the wind speed and the swept area, which means that WTs of enormous sizes are required to produce more wind energy [23]. HAWTs such as the Haliade-X WT, which has a 220 m rotor diameter and a 107 m blade length, can typically produce up to 14 MW [24]. However, many major problems are associated with components of enormous size [25]. These problems include but are not limited to the design complexity due to stresses on longer blades and an increased rotor weight, which also increases the gearbox weight. These problems result in transportation, installation, and maintenance cost increases, with transportation accounting for about 10% of the capital cost of a WT, equivalent to USD millions [26; 27].