SCESS-DFIG System And Its Key Technologies In Paticipating The Grid Frequency Inertia Responses

The promotion and application of renewable energy power generation systems is an effective way to solve problems such as resource depletion,environmental pollution,and climate warming in the utilization of petroleum and coal,and is highly valued in the field of energy and power.In the process of vigorously developing wind power generation in China,the installed capacity of wind power generation and the amount of grid-connected power generation increases year by year.The power system system faces the problem of power quality and operation stability caused by the high permeability of wind power generation.Some inherent defects of wind power generation systems also hindered the further increases in the total capacity of the grid system.In this paper,the existence of rotor-side converter(RSC)and grid-side converter(GSC)makes the doubly fed induction generator(DFIG)isolated from the power grid and has no inertial response capability.Therefore,additional control is needed to make it have analog inertia.There are two aspects in inertia simulation,one is the disturbance effect of wind characteristics,the other is the limited kinetic energy of the fan's own rotor,excessive absorption of kinetic energy will affect the normal operation of the fan.This paper presnted a wind power generation system with strong grid stabilization ability and strong wind wave anti-interference ability by adding a supercapacitor energy storage system(referred to as SCESS)in the conventional double-fed induction generator(DFIG)system,and made researches on the grid frequency inertia response related technologies based on the system construction.Firstly,on the basis of analyzing key problems affecting the grid-connectivity of wind power,it was proposed to combine the supercapacitor energy storage and the doubly-fed induction generator to form the SCESS-DFIG system to improve the inertia response capability of the wind power generation system.The dynamic mathematical model of the SCESS-DFIG system was established to provide technical conditions for the principle research and simulation analysis of the system.At the same time,the power flow of SCESS-DFIG under different operating conditions was analyzed,and the instantaneous power flow variation of SCESS-DFIG system and conventional DFIG system was simulated and compared,which proves that the instantaneous power of SCESS-DFIG system can be actively adjusted,and have the ability to participate in network frequency inertia response.Secondly,considering the SCESS-DFIG system participating in the network frequency inertia response,the real-time grid frequency fluctuation value was needed to quantitatively adjust the system output power.The research on the network frequency detection under complex grid conditions was carried out,and the DC offset of the complex grid voltage was analyzed.The effects of phase imbalance,higher harmonics disturbance and subsynchronous oscillation on ??-EPLL were proposed.The improved ??-EPLL network frequency detection method was proposed.The effectiveness of the method was verified by simulation and experimental verification under the condition of grid frequency drop.The DC-bus voltage fluctuation suppression method between RSC and GSC in SCESS-DFIG system was studied.In order to improve the dynamic response capability of the system,the power-energy balance relationship between multi-converters was analyzed.The coordinated control strategies were optimized and verified by simulations and experiments.Thirdly,considering the influence of wind characteristics on the inertia response capability of SCESS-DFIG system,the definition of inertia response of SCESS-DFIG considering wind speed change was proposed,and the power and energy quantitative method of inertia response of SCESS-DFIG system was proposed.By comparing the ability of the wind-driven DFIG rotor kinetic energy and the inertia of the energy storage device under different operating conditions,the coordinated control strategy of the kinetic energy of the rotor and the energy storage device was proposed.The SCESS-DFIG inertia response control strategy was considered to take into account the wind speed change,and the ESO method was applied to the SCESS-DFIG system inertia response control strategy.The simulation model of network frequency inertia response of multiple SCESS-DFIG system based on different wind speed changes was built.The proposed theory was verified by simulations.Finally,in order to experimentally verify the conclusions of theoretical analysis and simulation research,one physical simulation experimental platform was designed and built.The wind turbine parameters are scaled down to ensure that the wind turbine operating characteristics are constant,and a corresponding physical simulation experimental platform was established.Based on the physical simulation experiment platform,some key technologies in the SCESS-DFIG system research were experimentally studied,including: improved ??-EPLL performance verification experiment under ideal and complex grid conditions,SCESS-DFIG system and analog grid Network experiments,SCESS-DFIG system grid-connected power generation and power regulation experiments and SCEES-DFIG inertia response experimental verification and analysis.It was proved by experiments that the theoretical analysis and simulation calculations are correct.In this dissertation,one SCESS-DFIG system and its technical problems in participating the network frequency inertia response were studied theoretically and experimently,and some technical methods different from the conventional DFIG wind power generation were presented,and some improvement measures were proposed based on existing technologies.Hope these works can provide references for future researches and Applications.