Performance Analysis of an Island Power System Including Wind Turbines Operating under Random Wind Speed

With continuous rise of oil price, how to develop alternative energy source has become a hot topic around the world. This study discussed the dynamic characteristics of an island power system operating under random wind speed lower than nominal wind speeds of wind turbines. The system primarily consists of three diesel engine power generation systems, three constant-speed variable-pitch wind turbines, a small hydraulic induction generation system, and lumped static loads. Detailed models based on Matlab/Simulink were developed to cater for the dynamic behavior of the system. The results suggested this island power system can operate stably in this operational mode. This study can serve as an important reference for planning, operation, and further expansion of island power systems. Keywords—Diesel engine power generation system, constant-speed variable-pitch wind turbine, small hydraulic induction generation system, penetration, Matlab/Simulink, SimPowerSystems. I.INTRODUCTION N recent years, with continuous rise of oil price, how to develop alternative energy source has become a hot topic around the world. After the Kyoto Protocol has been exercised, a new trend of international environment protection has emerged, and various industries in Taiwan have proposed suggestions for new energy policy. Since “The 2nd National Energy Conference,” the government has set CO2 control mechanism actively and expected decrease of 38 million MT by the end of 2015, 58.68 million MT by 2020, and 78.41 million MT by 2025. The utilization of renewable energy is expected to reach 7,000~8,000MW by 2020 and 8,000~9,000MW by 2025, to attain the goal for total installed capacity penetration 12% or energy structure penetration 4~6%. The renewable energy development projects include biomass, wind power, photovoltaic system, solar heat, hydrogen energy, fuel cell, oceanic energy, geothermal heat, etc. The projects also cover planning offshore wind farms with scale of economy and fostering the development of the domestic wind industry [1]. Diesel engine power generation systems are commonly used to supply relatively small capacity systems such as island Meng-Jen Chen is with the Department of Electrical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan (e-mail: [email protected]). Yui-Chi Wu is with the Department of Electrical Engineering, National United University, Miao-Li, Taiwan (corresponding author: +886-37-381362; fax: +886-37-327887; e-mail: [email protected]). Guo-Tsai Liu and Sen-Feng Lin are with the Department of Electrical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan. power systems, industrial power systems, and marine power systems. Especially, in many remote regions or islands, the electric power from central power stations is difficult to be transmitted to these places. The diesel engine power generation becomes the most commonly used power generation technology in these regions because the diesel engine has advantages of easy start-up, low equipment cost, short plant construction period, and stable voltage and frequency control. However, the power quality problem resulted from small capacity ratio between the power generation system and load has to be concerned. Combining the diesel engine with other renewable energy power supplies to form a hybrid system to maintain acceptable power quality and reliable electricity supply is an economical way to reduce the fuel cost and the pollution caused by fossil fuels [2], [3]. Many studies have been done on island power systems and hybrid power systems. Reference [4] proposed an algorithm for optimizing the assemblies of stand-alone wind-diesel hybrid power generation system and used a prototype system to verify the dynamic characteristics of two generators under optimal load distribution. Reference [5] discussed the power quality problem of a stand-alone island power system with high penetration of wind energy and indicated that the torque variation in diesel engine was the main cause for voltage flicker. Reference [6] proposed an automatic reactive power control strategy for stand-alone wind-diesel hybrid power system which consisted of a wind power generation system with permanent magnet generator and a diesel engine power generation system with synchronous generator. Reference [7] discussed the dynamic behavior simulation of a hybrid system comprising diesel engine and variable-speed wind turbine and proved that the power quality could be improved by controlling the frequency. Reference [8] discussed the dynamic characteristics of wind-diesel hybrid systems used in remote regions, including coupling problem, mutual interference of interconnected systems, improvement on reactive power, reduction of wind turbine output loss, etc. Reference [9] analyzed and designed the control method for a stand-alone wind-diesel hybrid system at different frequencies. Reference [10] discussed the influence of power quality on the wind-diesel hybrid system and the problems caused by load and frequency switching. Reference [11] used genetic algorithm to adjust static reactive power compensator, so the system could control the reactive power within an ideal range automatically. Reference [12] discussed the control system used for wind-diesel hybrid system with high wind power. Few of these Meng-Jen Chen, Yu-Chi Wu, Guo-Tsai Liu, and Sen-Feng Lin Performance Analysis of an Island Power System Including Wind Turbines Operating under Random Wind Speed I World Academy of Science, Engineering and Technology International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering Vol:7, No:7, 2013 860 International Scholarly and Scientific Research & Innovation 7(7) 2013 scholar.waset.org/1999.5/16364 In te rn at io na l S ci en ce I nd ex , E le ct ri ca l a nd C om pu te r E ng in ee ri ng V ol :7 , N o: 7, 2 01 3 w as et .o rg /P ub lic at io n/ 16 36 4 studies have used detailed dynamic pitch analyze the dynamic characteristics of an island power system with high renewable energy penetration. This study discussed the dynamic characteristics of an island power system under random wind speed. This study is essential for planning, operation, and further expansion of systems. II. ISLAND POWER SYSTEM A.Configuration of an Island Power System Fig. 1 shows the configuration of a simplified island power system. The system consists of three diesel engine power generation systems, three constant-speed variable turbines, a small hydraulic inductive generation system, and lumped static loads. Each diesel engine power generation system is rated 5MVA, consisting of a diesel engine, a synchronous generator, an excitation system, and a transformer. Each constant-speed variablerated 2MW, consisting of blades, a mechanical transmission system, an induction generator, and a transformer. The small hydraulic power generation system is rated 1M of a small hydraulic turbine, an induction generator, and a transformer. The diesel engine power generation systems are the main power sources, and the output voltage is 11.4kV. The minimum load of this system is 4MVA, and the maximum load is 12MVA. Fig. 1 Configuration of a simplified islan B.Diesel Engine Model The diesel engine prime mover model is usually developed by using the engine performance data provided by the manufacturer. Fig. 2 shows the schematic diagram of a diesel engine prime mover. This model consists of three s thermodynamic model, speed governing model, and shaft model [13]. -control models to