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Control and Energy Monitoring Scheme for a Stand-Alone Wind Energy Conversion System

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Abstract
Present energy need heavily relies on the conventional sources. But the limited availability and steady increase in the price of conventional sources has shifted the focus toward renewable sources of energy. Among the available alternative sources of energy, wind energy is considered to be one of the proven technologies. With a competitive cost for electricity generation, wind energy conversion system (WECS) is nowadays deployed for meeting both grid-connected and stand-alone load demands.
However, wind flow by nature is intermittent. In order to ensure continuous power supply, suitable storage technology is used as backup. A storage system such as a battery bank may be used. In this thesis, the sustainability of a hybrid wind energy and battery system is investigated for meeting the requirements of a stand-alone dc load. A charge controller for battery bank based on turbine maximum power point tracking and battery state of charge is developed to ensure controlled charging and discharging of battery. The mechanical safety of the wind energy conversion system is assured by means of pitch control technique. Both the control schemes are integrated and the efficiency is validated by testing it with various load and wind profiles in numerical computation software SCILAB.
The SCILAB model is intended to simulate the behavior of wind turbine using synchronous generators and control the wind electrical energy conversion processes. Rotational speed and torque become the controlled variables in wind energy and mechanical energy conversion process. Control scheme has been developed for switching DC-DC buck type converter. It is possible to predict the behaviour of the system by simulation using SCILAB-XCOS software.
I.Introduction
Wind Energy Conversion System (WECS) is one of the most versatile non-conventional resources of energy due to the ever-growing demand of electricity supply. Since wind is a natural source and its utility is based on the climatic variation, it is essential to tap this energy effectively for meeting the demand [1]. Due to the development of technology in the synchronous and asynchronous generators, it is possible to effectively employ these generators in WECS. The wind energy can be used for stand-alone load or connected to grid.
Nowadays, many stand-alone loads are powered by renewable energy [2][3]. With this interest on using wind energy technology for a stand-alone application, a great deal of research is being carried out for selecting a suitable generator for stand-alone WECS.
For optimizing the use of wind energy to a stand-alone or grid connected system, proper control strategy and energy monitoring scheme have to be developed. Since wind energy is intermittent, a hybrid system such as wind-battery system may be employed for effective utilization of wind energy.
Charge controller for battery bank based on turbine maximum power point tracking (MPPT) and battery state of charge is developed to ensure controlled charging and discharging of battery. Mechanical safety of WECS is assured by proposed pitch control technique. MPPT logic is used to operate at optimum tip–speed ratio (TSR).

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