• Enhanced design of an offgrid PV-battery-methanation hybrid energy system for power/gas supply

      Xu, Xiao; Hu, Weihao; Cao, Di; Liu, Wen; Huang, Qi; Hu, Yanting; Chen, Zhe
      Extensive studies have been carried out on various hybrid energy systems (HESs) for providing electricity to off-grid areas. However, a standalone HES that is capable of providing power and gas, has been less studied. In this paper, a standalone Photovoltaic (PV)-battery-methanation HES is proposed to provide adequate, reliable and cost-effective electricity and gas to the local consumers. Identifying a potential solution to maximize the reliability of the system, asked by consumers, and to minimize costs required by the investors is challenging. Bi-level programming is adopted in this study to tackle the pre-mentioned issue. In the outer layer, an optimal design is obtained by means of particle swarm optimization. In the inner layer, an optimal operation strategy is found under the optimal design of the outer layer using sequential quadratic programming. The results indicate that 1) The bi-level programming used in this study can find the optimal solution; 2) The proposed HES is proved to be able to supply power and gas simultaneously. 3) Compared with the right most and leftmost points on Pareto set, the total costs are reduced by 17.77% and 2.16%.
    • Flicker mitigation strategy for a doubly fed induction generator by torque control

      Zhang, Yunqian Q.; Hu, Weihao; Chen, Zhe; Cheng, Ming; Hu, Yanting (IET, 2014-03)
      Owing to the rotational sampling of turbulence, wind shear and tower shadow effects grid connected variable speed wind turbines could lead to the power fluctuations which may produce flicker during continuous operation. A model of an megawatt (MW)-level variable speed wind turbine with a doubly fed induction generator is presented to investigate the flicker mitigation. Taking advantage of the large inertia of the wind turbine rotor, a generator torque control (GTC) strategy is proposed, so that the power oscillation is stored as the kinetic energy of the wind turbine rotor, thus the flicker emission could be reduced. The GTC scheme is proposed and designed according to the generator rotational speed. The simulations are performed on the national renewable energy laboratory 1.5 MW upwind reference wind turbine model. Simulation results show that damping the generator active power by GTC is an effective means for flicker mitigation of variable speed wind turbines during continuous operation. keywords: {asynchronous generators;oscillations;power generation control;torque control;wind power plants;wind turbines;GTC strategy;continuous operation;doubly fed induction generator;flicker emission;flicker mitigation strategy;generator active power;generator torque control;kinetic energy;megawatt-level variable speed wind turbine;power oscillation;tower shadow effects grid connected variable speed wind turbines;turbulence;upwind reference wind turbine model;variable speed wind turbines;wind shear;wind turbine rotor