The power generated by wind turbines varies due to variations in the wind speed. A pack of rechargeable batteries could be used as a reserve power source to alleviate the intermittency in the wind turbine power. An integrated wind turbine and battery storage system is constructed where the wind turbine is electrically connected to a rechargeable battery system. Such a system can operate in two modes depending on the wind speed, power demand, and battery limit. The switching conditions for the wind turbine to operate in multi-input, single-output and single-input, single-output control mode are discussed. Linearized approximations of the closed loop wind turbine system are derived in order to analyze the switching stability between control modes. Common quadratic Lyapunov function (CQLF) is established for both control modes to prove the system stability. Simulation results demonstrating system stability are also presented.
The water vapor transfer across a Nafion® membrane exhibits an undesired non-minimum phase behavior. This paper will show that even in the disturbance-to-output loop, the non-minimum phase zero adversely affects the feedback controller design because of the coupling effect between the disturbance-to-output and the input-to-output loops. The non-minimum phase zero location is influenced by the channel plate structure and the membrane material property. The structural parameters examined in this research include channel plate dimensions and heat transfer coefficients. The membrane properties studied include membrane vapor transfer properties described in the Arrhenius’ equation. A governing equation to link the non-minimum phase zero and the parameters is developed in this paper. This equation shows that the non-minimum phase zero arises from the competing heat and mass transfer dynamics, and is determined by the structural parameters and membrane properties. A sensitivity study is presented and shows that structural and material property optimization can be used with the control system design to mitigate the non-minimum phase behavior in the PEM fuel cell humidification system.
Offshore wind farms in deep water are becoming an attractive prospect for harnessing renewable energy and reducing dependence on fossil fuels. One area of major concern with offshore wind turbines is stability control. The same strong winds that give deep water turbines great potential for energy capture also pose a threat to stability, along with potentially strong wave forces. We examine development of state space controllers for active stabilization of a spar-buoy floating turbine. We investigate linear state feedback with a state observer and evaluate response time and disturbance rejection of decoupled SISO controllers.
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