CONTROL PLAN FOR AN INDEPENDENT WIND ENERGY SYSTEM (KEY IJP************890)

• U Srilatha

Abstract

ABSTRACT Conventional sources are mainly reliant on current energy needs. However, the focus now is on renewable energy sources because conventional sources are becoming more and more scarce and expensive. Wind energy is regarded as one of the most established alternative energy sources currently accessible. The wind energy conversion system (WECS) is presently used to address both grid-connected and stand-alone load needs since it has a competitive cost for electricity generation. However, wind flow is sporadic by nature. Power supply continuity is ensured by using proper backup storage technologies. In order to meet the demands of a 3-kW stand-alone dc load representing a base telecom station, a 4-kW hybrid wind and battery system's viability is examined in this article provides controlled charging and discharging of batteries, a charge controller for battery banks is created using tracking of the turbine maximum power point and battery state of charge. The pitch control approach ensures the mechanical security of the WECS. Both control strategies are combined, and their effectiveness is tested in MATLABSIMULINK using a variety of load and wind profiles.Keywords: Maximum power point tracking (MPPT), pitch control, state of charge (SoC), wind energy conversion system (WECS). 1.INTRODUCTIONThe ever-increasing demand for energy is currently being met by renewable sources due to the depletion of traditional supplies and concern over environmental deterioration 1. Wind energy is seen as one of the promising sources of renewable energy for the future 3 due to its comparatively low cost of electricity production 2. However, wind flow is stochastic by nature. Therefore, in-depth laboratory testing is required to create an effective control strategy for wind energy conversion systems (WECS). stand-alone loads are powered by renewable sources of energy. With this renewed interest in wind technology for stand-alone applications, a great deal of research is being carried out for choosing a suitable generator for stand-alone WECS. A detailed comparison between asynchronous and synchronous generators for wind farm applications is made in 4. The major advantage of asynchronous machines is that the variable speed operation allows extracting maximum power from WECS and reducing the torque fluctuations 5. An induction generator with a lower unit cost, inherent robustness, and operational simplicity is considered as the most viable option as a wind turbine generator (WTG) for off-grid applications 6. However, the induction generator requires capacitor banks for excitation at isolated locations. The excitation phenomenon of a self-excited induction generator (SEIG) is explained in 5 7. The power output of the SEIG depends on the wind flow which by nature is erratic. Both amplitude and frequency of the SEIG voltage vary with wind speed. Such arbitrarily varying voltage when interfaced directly with the load can give rise to flicker and instability at the load end. So, the WECS are integrated with the load by power electronic converters in order to ensure a regulated load voltage 8. Again, due to the intermittent characteristics of wind power, a WECS needs to have an energy storage system 9. An analysis of the available storage technologies for wind power applications is made in 9 and 10. The advantage of battery energy storage for an isolated WECS is discussed in 10. With battery energy storage it is possible to capture maximum power 11 from the available wind. A comparison of several maximum power point tracking (MPPT) algorithms for small wind turbines (WT) is carried out in 12 and 13. In order to extract maximum power from WECS the turbine needs to be operated at optimal angular speed 13. However, 11 do not take into account the limit on maximum allowable battery charging current nor do they protect against battery overcharging. In order to observe the charging limitation of a battery a charge controller is required. Such a charge control scheme for battery charging for a stand-alone WECS using MPPT is explained in 14. However, in this paper also the maximum battery charging current is not limited. The dis- continuous battery charging current causes harmonic heating of the battery. The terminal voltage instead of the state of charge (SoC) is used for the changeover from current mode to voltage mode. Also, the MPPT implementation is highly parameter-dependent and will be affected by variations of these parameters with operating conditions. Moreover, as the wind speed exceeds its rated value, the WT power and speed need to be regulated for ensuring mechanical and electrical safety 15. This is achieved by changing the pitch angle to the required value 16. The structure of the essay is as follows. In Section II, the power converter topology and a brief description of the hybrid wind-battery system that powers an off-gird dc load are provided. Section III discusses the control strategy that consists of the charge controller for the battery and the pitch controller for the turbine. The results of simulating the hybrid system with various wind profiles and load fluctuations are reported in Section IV, validating the effectiveness of the suggested control logic. The paper is concluded in Section V.