**1. Introduction**

Most of the Russian and Finnish territories are located in a cold climate. Almost the entire northern part of these countries, as well as Central Siberia and Yakutia in Russia, fall within the cold polar zone of the Arctic, a zone of extremely low temperatures. In these areas, the duration of winter significantly exceeds that of summer with temperatures dipping close to −50 ◦C. Conditions here are unique, ye<sup>t</sup> approximately 2.5 million people live in these areas. This is more than the total number of people residing in the Arctic areas of the seven other Arctic nations, all of which have less severe climatic conditions [1].

A significant part of the Arctic territory belongs to the decentralized energy supply zone. This zone is characterized by weak infrastructure associated with its remoteness from regional centers, and electricity is mainly produced by diesel power plants operating on expensive imported fuel. In the Russian areas of this zone, there are approximately 900 diesel power plants in operation, which produce an energy output of about 3.0 billion kWh annually [1]. The main challenges of supplying power to isolated consumers are the high logistical costs associated with the delivery of fuel and equipment for diesel power plants, the limited transport infrastructure, and, consequently, the high cost of fuel. Additionally, the operating costs of diesel power plants and specific fuel consumption are

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**Citation:** Elistratov, V.; Konishchev, M.; Denisov, R.; Bogun, I.; Grönman, A.; Turunen-Saaresti, T.; Lugo, A.J. Study of the Intelligent Control and Modes of the Arctic-Adopted Wind–Diesel Hybrid System. *Energies* **2021**, *14*, 4188. https://doi.org/ 10.3390/en14144188

Academic Editor: Rafael Sebastián Fernández

Received: 1 May 2021 Accepted: 7 July 2021 Published: 11 July 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

high, and there is typically no monitoring or control automation. As a result, the levelized cost of electricity (LCOE) at diesel power plants in the Arctic regions is 0.25–2.0 Euro/kWh, which is much more expensive than in the centralized energy supply zones. To illustrate, the International Energy Agency estimates LCOE values of below 0.1 Euro/kWh in Europe for coal, gas, and nuclear energy [2]. In addition, significant damage to the vulnerable natural environment of the Arctic is being caused by the emissions from fuel combustion products (40 million tons of carbon dioxide (CO2), 80 thousand tons of sulfur oxides (SOx), 600 thousand tons of nitrogen oxides (NOx) annually), as well as by the storage of fuel barrels [3].

The Far North and the Arctic regions are characterized by high wind energy potential. In general, Russian and Finnish technical wind energy resources are 10<sup>16</sup> kWh/year, about 16% of which are concentrated in the European and Asian northern coastal zones, creating a solid foundation for their effective use [4]. Given this high wind energy potential, optimization and modernization of existing power supply systems and the construction of new ones can be effectively carried out based on modular wind–diesel–storage hybrid systems adapted to Arctic conditions. These systems offer a good opportunity to overcome the challenges related to the intermittent and fluctuating nature of wind energy production, and they can also reduce the use of fossil fuels in distributed energy generation [5,6]. The application of wind–diesel hybrid systems will reduce the use of diesel fuel by 10–60% and increase the standard service life of diesel generator sets by two to three times [7–10]. In terms of CO2 emissions, a study by Kazem et al. predicts an over 20% reduction in emissions when using a hybrid wind turbine–diesel engine system as compared with a diesel-only system [3]. It is worth mentioning that, in addition to the time-shifting role of the batteries in these systems, they can also improve the reliability and power quality as highlighted, for example, by Ansari and Velusami [11].

However, one of the key challenges to the optimal operation of Arctic wind turbines is icing. The impact of icing on wind turbine performance can be significant during the cold winter months. Turkia et al. [11] predict an approximately 17% reduction in turbine performance below nominal power due to icing, and Wei et al. [12] report power generation losses as high as 30%. Different passive and active anti-icing systems have been considered to reduce these effects, including special coatings, black paint, and heating [12]. One option that has not received much interest is airfoil pitch control. Nonetheless, several studies have shown that the optimal airfoil angle of attack can be affected by icing, for example, [13,14], introducing the potential to control the pitch differently during normal and icing operation modes.

Proportional integral (PI) control has traditionally been used in hybrid energy systems [9,15], but it poses problems regarding frequency regulation [11]. Increasing system stability has also been investigated recently [16]. The existing options to overcome the challenges described include, for example, the use of genetic algorithms [11] and fuzzy logic [17]. One potential approach to the control of a hybrid system is to use weather forecasts to help optimize the energy system's efficiency [18–20]. Under this approach, typically, wind forecast data are used to control the system, but icing, for example, is not considered although it can have a significant effect on performance especially in Arctic environments.

According to Elistratov et al. [4], wind–diesel hybrid systems should consider the following design constraints:


Additionally, the hybrid system must have a high degree of automation, including adaptive algorithms and intelligent control, and a remote monitoring and diagnostic system to optimize expensive diesel fuel usage.

Given the above, this study develops an existing field operating control system to improve its autonomous operation in Arctic conditions and maximize diesel fuel savings. It is shown that carbon-neutral technologies can be highly effective in Arctic zones subject to advanced control and reliable and safe operation. The study aims to identify how the system control approach affects system performance. Two control schemes are studied and compared with the use of a diesel engine only: 1. load following mode, and 2. cycle charge with short-term forecasting including icing effects. Additionally, a new wind turbine control method is proposed to decrease the effects of icing. The key novelties of the study are:


The article is structured as follows. First, the hybrid system's control methods are explained. Next, the icing modeling and the novel pitch control approach are presented. In the Results section, before the discussion and conclusions, the effects of the different control methods are examined. This analysis is followed by the demonstration of the potential of a combined pitch and tip-to-speed ratio control approach to reduce the effects of icing.
