Research And Application Of Online Power Supply Technology Based On Battery Energy Storage

As the main power of emergency power supply,the emergency protection system plays an increasingly prominent role in many small and medium-sized electric fields.At present,off-grid emergency power supply based on diesel generator can not achieve seamless switching.Flywheel energy storage power supply system has high output power quality,but it has many shortcomings,such as high cost of investment and operation and maintenance,large workload of debugging,etc.Most of them can only provide temporary emergency support within minutes,and need to cooperate with diesel generator.In order to achieve many needs of low loss,zero noise,uninterrupted online operation and high reliability in the important power supply occasions,the lithium ion battery is used as the energy storage carrier,and the bidirectional converter is used as the interface of the energy exchange between the grid,the energy storage battery and the load in this paper.According to different scenarios,a multi-mode power supply strategy of lithium ion energy storage system with series,parallel and double loops is proposed.It can realize online power supply based on high-power battery energy storage and power supply system,and flexibly meet the uninterrupted power demand of important users under multi-scenarios.The main work of this paper is as follows:(1)An on-line guaranteed power supply topology based on battery energy storage and two stage AC-DC converter structure is proposed.According to different working conditions,it can realize on-line protection of power supply in series mode,and reserve power supply of two modes in parallel and double circuit,which can meet the demand of power supply in important occasions.Based on the topology of the power supply system,a reliability redundancy strategy is proposed.The system can automatically switch to redundant scheme to protect the power supply,realize flexible switching between the three modes,and improve the reliability of the system itself.(2)The control strategy of grid connected and off grid energy storage converter is studied respectively,and then a compound control method combining repetitive control with double-loop control is proposed.This method adds a repetitive control loop on the basis of V/f double loop,which can effectively improve the power quality when the nonlinear load is connected to the power supply system.On this basis,a series of pre-merger network,network and off-network three-step strategy is proposed.Then,the seamless switching strategy in parallel mode and the power supply strategy of double loop mode in single and double distribution network are analyzed.Thus,the overall control strategy of the online power supply system is formed,which can be used to protect the power supply of the important loads in the multi scenarios.(3)The accumulated value of grid voltage sampling value is used as the judgment basis of power grid drop point detection.Meanwhile,an improved active frequency shift detection method with positive feedback is used to detect islands.Through comprehensive judgment,the power grid fault can be detected timely and effectively.Then,the dual synchronous coordinate system software phase-locked loop is used to ensure accurate phase locking under normal voltage and various faults,and to provide accurate phase tracking for energy storage system.(4)Experimental platform is built by the laboratory to test the three access modes,and the test results meet the theoretical analysis.The series mode can be realized without flashing Os power supply,and basic parallel mode can be seamlessly switched,double loop mode can provide power supply service for two or even multi loop.Three models all can achieve uninterrupted power supply for the important load.Based on theoretical analysis,an on-line power supply device based on battery energy storage is developed,which is used in a sports park and a mountain villa.