Abstract -We investigated a small isolated hybrid power system that used two types of power generation; wind turbine and diesel generation. The interaction of diesel generation, the wind turbine, and the local load is complicated because both the load and the wind turbine fluctuate during the day. These fluctuations create imbalances in power distribution (energy sources are not equal to energy sinks) that can affect the frequency and the voltage in the power system. The addition of energy storage will help balance the distribution of power in the power network. For this paper, we studied the interaction among hybrid power system components and the relative size of the components. We also show how the contribution of wind energy affects the entire power system and distribution and the role of energy storage under the transient conditions caused by load changes and wind turbine startups.
Index Terms - wind turbine, diesel generator, hybrid power system, renewable energy, energy storage.
I. INTRODUCTION
Windmills were used to pump water and mill grain, along with many other uses [1, 2, 3, 4].
Today, wind turbines are used for similar purposes (i.e., water or oil pumping, battery charging, and utility generation). One important aspect of wind turbine applications, especially in an industrial environment, is that wind turbines generate electricity without creating pollution. Wind turbines are also well suited for generating electricity in isolated places with no connections to the utility grid [2,3,4]. However, in isolated applications, especially very small applications, the power system components (sources and loads) are limited, and the system networks are weak in many cases. Thus, any changes in the power input or output of one component may affect the rest of the system more dramatically than in a larger system where the smoothing effect of many components benefits the overall system. In this paper, we analyze a hybrid power system consisting of a wind turbine, a diesel generator, a local load, and energy storage. We also present the impact of energy storage on the power system performance. The results and conclusions of this analysis apply to similar hybrid power systems.
II. SYSTEM CONFIGURATION
The system has two types of generation: the diesel generator and the wind turbine generator (Figure 1). The
energy storage can act as a load or as a generator depending on the need. The diesel generator provides smooth output power, whereas the output power of a wind turbine depends on the wind velocity. As the wind velocity varies, so does is the power generation. For example, if the wind speed changes very smoothly, the output power of the wind turbine will also change very smoothly. On the other hand, wind turbulence causes the output power to fluctuate. Figure 1 is a single line diagram that represents the analyzed power system. The wind turbine has an induction generator with a capacity ranging from 40 kW to 225 kW. At low wind speeds, the generator operates at 900 rpm with a rated capacity of 40 kW. At high wind speeds, the generator speed is 1,200 rpm with a rated capacity of 225 kW. We used 150 kW of energy storage as a buffer to operate as a load or a source depending on the need. This paper discusses only fixed-speed wind turbine generation and does not cover variable-speed wind turbine generation [5]. The diesel engine, which has a rated capacity of 400 kW, is operated in parallel with the wind turbine to supply the load. The local loads are mostly residential and light loads. Other loads include water pumps, compressors, and heavy equipment. An 80-kW water pump represents the transient condition of a heavy load.
Fig 1. One line diagram of power system
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