Study On The Controlled Operation And Planning Of The Hybrid Energy Storage System In Wind Farm

In recent decades,the large-scale wind power systems in China have been developed signing high-efficiency and low-cost.However,the utilization of wind energy was restricted by its stochastic nature and the transmission capacity of the power grid.As a result,various energy storage systems(ESSs)were proposed by researchers in order to transform the wind power system into a controllable and dispatchable system.These ESSs could eliminate the adverse influence of the grid-connected operation of the wind turbines so that the economic efficiency of the wind farm was improved.The existing ESSs can be formally categorized as power-based type and energy-based type according to the level of power exchange(LPE)and the level of energy capacity(LEC).The power regulation ability of the hybrid energy storage system(HESS)is better than that of a single ESS.In this dissertation,the key technical problems around the HESS consisting of the energy-based phase change energy storage system(PCESS)and the power-based supercapacitor energy storage system(SESS)are analyzed in order to improve the stability of the wind power.Firstly,the classic proportion-integration(PI)control strategy of the PCESS and the SESS is introduced.Secondly,the optimal operation modes of the cascaded PCESS based on the dynamic matrix control(DMC)algorithm and the energy management strategy of the SESS in the linearized charging-discharging mode are formulated.Thirdly,the optimal LPE and LEC of the parts of electric heating,the thermal energy storage,the evaporation,the thermoelectric conversion and the SESS are planned.Hence that the frame of researches on on-time control,optimizing operation and planning of the HESS is accomplished.These research results should suffice to prove the feasibility and economy of the HESS.The main works of this dissertation are as follows:(1)The synchronism of wind power regulation is emphasized when analyzing the real-time control of the HESS.Firstly,the HESS consisting of PCESS and SESS which dominats the technical advantage of both energy-based type and power-based type of ESSs is proposed.The coordination control mechanism of the HESS is analyzed from unit stage,function stage,device stage to control variates of the system during the process of compensating the wind.Secondly,the PI control strategy of the PCESS and SESS is formulated on the basis of thermodynamics and contrology.Here,the researches on the PCESS include modeling and analyzing the delay characteristic and steaty-state gain error of the parts of electric heating,the thermal energy storage,the evaporation and the thermoelectric conversion.The researches on the SESS include developing the fast power compensation strategy of the SESS considering the characteristics of the wind turbines output and the power load based on the real-time power balancing theory and the transfer characteristic of the invertors.Finally,the simulation results show that the SESS helps eliminating the power error of the PCESS so that the response speed of HESS is improved under the proposed coordination control mechanism.(2)The more efficient operation modes and nore advanced control strategies are emphasized when analyzing the optimal operation of the HESS.Firstly,the thermodynamic properties of the steam-based double screw expande and the organic Rankine cycle(ORC)double screw expande are compared under cascaded operation modes.The influence factors of the energy grad and the utilization of the energy storage are indicated.Secondly,the cascaded PCESS is equivalently modeled according to its step response characteristic.This model reflects the efficiency and the delay of the PCESS under different optimal operation modes.Accordingly,the frequency-domain model of the PCESS is transformed into a predictive matrix type based on the DMC algorithm.The characteristic of the model is also used to off-line plan a controlled smooth trajectory of the exchange power of the SESS.The control increment sequence of the PCESS input is planned on-line in use of rolling optimization and feedback correction mechanism.Meanwhile,the linearized energy management strategy of the SESS which takes the original state of capacity and three external constraints into consideration is generated.Finally,the simulation results show that the power error caused by the model mismatch of the screw expander according to its geometrical characteristic parameters under the DMC actions of PCESS and SESS so that the veracity of the HESS is improved.(3)The importance of the combination between the calculating rules of the LPE,LEC and the energy storage object,the control method and the optimal operation strategies is emphasized when planning the HESS.Firstly,the fluctuating wind power is decomposed into stable component and pulsating component.The LPE of the PCESS is optimized according to the probability density characteristic of the pulsating component under the given confidence level of the dispatchable wind power(CL-DWP).Secondly,the evaluation index of the sustainable operating ability(EI-SOA)of the HESS is defined.The economic model which takes the cost of the power investment,the energy investment and the SOA investment into consideration is established as the objective function.On the basis,the LES of the PCESS is optimized by solving the function with steepest descent method.Thirdly,the LPE and LEC of the SESS are optimized according to the balancing principle of supply and demand in energy of the HESS for a long term.Here,the installed capacity and the creep speed of the expander-generators are both considered.Finally,the evaluation index of the firm power escalation(EI-FPE)is defined and the relationship between the conversion rate of the energy storage and the FPE is analyzed under the given LPE and LEC of the HESS.Simulation results show that the stability of the active wind power output could be significantly improved even if the conversion rate of the energy storage is low through optimizing the LPE and LEC of the HESS.