| Wind power output has a certain degree of randomness,intermittency and volatility.Adding energy storage equipment to absorb and compensate for wind power output,thus improving the smooth grid connection of wind power.Currently,the demand for energy storage for large-scale wind power grid connection has increased significantly.Traditional single energy storage battery system is difficult to meet the future demand of wind power smoothing.The hybrid energy storage system proposed in this paper can give full play to the advantages of different energy storage technologies and achieve complementary advantages.It both effectively reduces the wind power output power fluctuation rate to meet the requirements of grid connection,and reduces the cost required for energy storage.Firstly,the topology of the hybrid energy storage system with lithium battery energy storage system and flywheel energy storage system in wind power generation system is analyzed.The working characteristics,charging and discharging control and model simulation of lithium battery energy storage and flywheel energy storage are studied separately.The results show that the lithium battery energy storage system has a slower response rate with a longer discharge capacity;Flywheel energy storage system with fast response time and short discharge time.The two types of energy storage systems compensate for each other’s shortcomings.Secondly,to address the problem that the traditional wavelet packet method has a large difference in the smoothing effect in the wind power fluctuations of different time periods when extracting grid-connected power.An adaptive wavelet packet decomposition method for hybrid energy storage capacity configuration is proposed.The model of wind abandonment loss and energy storage deficit is constructed according to the charging and discharging power command and charge state of lithium battery energy storage and flywheel energy storage.The optimal number of layers for decomposition is determined adaptively in different time scales according to the wind power fluctuations.The grid-connected expected power,low-frequency power component and high-frequency power component are obtained by adaptive wavelet packet decomposition.According to the different characteristics of lithium battery and flywheel energy storage,the low-frequency power component is used as the charge/discharge power command for lithium battery energy storage;the high-frequency power component is used as the charge/discharge power command for flywheel energy storage for wind power leveling.Based on this,the capacity configuration results of lithium battery energy storage and flywheel energy storage are obtained through simulation.The method is also compared with the traditional wavelet packet decomposition method for smoothing effect index,and the results show that the proposed method has better smoothing effect.Finally,considering that the energy storage capacity configuration is too large to affect the cost and too small to achieve the leveling effect.A hybrid energy storage capacity optimization allocation method for wind abandonment loss and energy storage deficit is proposed.The model of wind abandonment loss and energy storage deficit is constructed according to the charging and discharging power command and charge state of lithium battery energy storage and flywheel energy storage.Under the condition of satisfying the wind power grid connection,the annual integrated cost of initial investment cost,operation and maintenance cost,abandoned wind loss cost and energy storage missing cost is minimized as the target function.Using genetic algorithm optimization iterations to find the critical point of energy storage capacity configuration.Matlab/Simulink simulations have verified that this capacity configuration is more economical.The research work in this paper helps to provide a reference for the capacity configuration of hybrid energy storage in wind power systems. |
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