A New Pitch Control System of Wind Turbine to Damp Power System Frequency Fluctuations Liu Junqiao, Marwan Rosyadi, Rion Takahashi, Junji Tamura Department of Electrical and Electronic Engineering Kitami Institute of Technology Kitami, Hokkaido, Japan Tomoyuki Fukushima, Atsushi Sakahara, Koji Shinya, Kazuki Yosioka Hokkaido Electric Power Co., Inc. Sapporo, Hokkaido, Japan Abstract—In this paper a new controller of pitch angle control system for fixed speed wind turbines based wind farm is proposed to smooth output power for damping frequency fluctuation of power system. The control system is designed in such way for the pitch controller to operate based on wind speed and load frequency deviation information. The wind farm is connected to a multi machine power system which is composed of 4 synchronous generators and a static load. Simulation analyses have been carried out to investigate the performance of the controller using real wind speed data. It is shown that the output power from the wind farm can be controlled smoothly damping the load frequency fluctuation effectively. Keywords - Pitch controller; wind power control; frequency control, wind farm, multi-machine system. I. INTRODUCTION Recently the huge penetrations of the wind generators into utility grid system have been increased significantly. It is well known that the wind generator output variations can have an influence on the power system frequency. As the frequency stability is an essential aspect of the power system security, it is important to design a suitable control strategy for smoothing output power from wind farm when it is connected to main grid. Traditionally, the frequency oscillation is damped by using conventional power plants with synchronous generators, which are equipped with governor system and load frequency control system. Power system frequency stabilization by synchronous generators is an established technology, which is applied all over the world [1]. In general, the Fixed Speed Wind Turbines with Squirrel Cage Induction Generator (FSWT-SCIG) is most widely used in wind farms. This type of wind turbine is very popular and it has the advantages such as mechanical simplicity, low specific mass, robust construction, and low cost [2]. However, this type of wind turbine is only equipped with conventional blade pitch angle controller. The conventional pitch controller is used, in general, to maintain the output power of the wind generator at its rated level when the wind speed is over the rated speed. However the output power from the wind farm cannot be controlled smoothly by using the conventional method. Some methods have been proposed in order to smooth wind generator output fluctuations. In [3, 4], a flywheel energy storage system is proposed for smoothing wind farm output, but the flywheel energy system has complicated control strategy. Superconducting Magnetic Energy Storage (SMES) is a very good system for wind power smoothing due to its response speed and high efficiency [5]. However its installation is still doubtful from a practical point of view for its large installation and continues maintenance cost. Some papers have proposed Battery Energy Storage System (BESS) integrated with a STATCOM [6, 7]. However, application of a STATCOM/BESS in wind farm is not good choice because BESS has some demerits such as its chemical process, low response speed, a short service life, etc. Moreover, the system overall cost will increase when such devices are installed in the wind farm. SMA (Simple Moving Average) and EMA (Exponential Moving Average) methods have been proposed to control pitch controller of the FSWT-SCIG based wind farm in order to reduce load frequency fluctuation [8]. In this concept, the reference output of wind generator is determined by using moving average of wind speed. Therefore, the oscillating components in the wind turbine output can be smoothed. However, the wind farm is operated by using the conventional pitch controller when the load is heavy during daytime and the farm is operated by the proposed controller when the load is light during midnight. In this paper a new pitch control system is proposed to smooth wind farm output power. The control system is designed in the central management system, which determines the power reference set point for each wind generator. By this system, the output power can be controlled smoothly; hence the frequency fluctuation in the power system can be damped effectively. In addition, the pitch control method can be simply switched from the conventional to the proposed one. The simulation studies have been performed using PSCAD/EMTDC. II. POWER SYSTEM MODEL The model system used in the simulation analyses is shown in Fig. 1. The model system consists of a wind farm (WF), a hydro power plant, SG1, with a salient pole synchronous generator (HG), two thermal power plants, SG2 and SG3, with