Control Scheme for a Stand-Alone Wind Energy Conversion System

 

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. Of 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 formeeting both grid-connected and stand-alone load demands. However, wind flow by nature is intermittent. In order to ensure continuous supply of power suitable storage technology is used as backup. In this paper, the sustainability of a 4-kW hybrid of wind and battery system is investigated for meeting the requirements of a 3-kW stand-alone dc load representing a base telecom station. 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 WECS is assured by means of pitch control technique. Both the control schemes are integrated and the efficacy is validated by testing it with various load and wind profiles in MATLAB/SIMULNIK.

 KEYWORDS

  1. Maximum power point tracking (MPPT)
  2. Pitch control
  3. State of charge (SoC)
  4. Wind energy conversion system (WECS).

SOFTWARE: Matlab/Simulink

BLOCK DIAGRAM:

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Fig. 1. Layout of hybrid wind–battery system for a stand-alone dc load.

SIMULATION RESULTS:

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Fig. 2. (a) WT and (b) battery parameters under the influence of gradual variation of wind speed.

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Fig. 3. (a)WT and (b) battery parameters under the influence of step variation of wind speed.

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Fig. 4. (a) WT and (b) battery parameters under the influence of arbitrary variation of wind speed.

CONCLUSION

The power available from a WECS is very unreliable in nature. So, a WECS cannot ensure uninterrupted power flow to the load. In order to meet the load requirement at all instances, suitable storage device is needed. Therefore, in this paper, a hybrid wind-battery system is chosen to supply the desired load power. To mitigate the random characteristics of wind flow the WECS is interfaced with the load by suitable controllers. The control logic implemented in the hybrid set up includes the charge control of battery bank using MPPT and pitch control of the WT for assuring electrical and mechanical safety. The charge controller tracks the maximum power available to charge the battery bank in a controlled manner. Further it also makes sure that the batteries discharge current is also within the C/10 limit. The current programmed control technique inherently protects the buck converter from over current situation. However, at times due to MPPT control the source power may be more as compared to the battery and load demand. During the power mismatch conditions, the pitch action can regulate the pitch angle to reduce the WT output power in accordance with the total demand. Besides controlling the WT characteristics, the pitch control logic guarantees that the rectifier voltage does not lead to an overvoltage situation. The hybrid wind-battery system along with its control logic is developed in MATLAB/SIMULINK and is tested with various wind profiles. The outcome of the simulation experiments validates the improved performance of the system.

 REFERENCES

  • [1] Sahin, “Progress and recent trends in wind energy,” Progress in Energy Combustion Sci., vol. 30, no. 5, pp. 501–543, 2004.
  • [2] D. Richardson and G. M. Mcnerney, “Wind energy systems,” Proc. IEEE, vol. 81, no. 3, pp. 378–389, Mar. 1993.
  • [3] Saidur, M. R. Islam, N. A. Rahim, and K. H. Solangi, “A review on global wind energy policy,” Renewable Sustainable Energy Rev., vol. 14, no. 7, pp. 1744–1762, Sep. 2010.

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