| In recent years,the proportion of new energy source generation is rise gradually such as wind power and solar energy power in the power system in our country,and energy storage system is able to smooth power fluctuations and improve the optimal allocation of energy resources for grid.Battery energy storage system has become a focus research topic in the field of electric power because of its high modularity and high power quality.However,reliability is one of the most important issue and the system may suffer from great financial loss after fault occurs.In this paper detailed research was carried out about flexible group battery energy storage system and mainly concentrated on the operation characteristics as well as fault tolerant control topologies under the failure of submodules.In the process of traditional battery group,the cause of battery pack inconsistencies and its adverse influence on the performance of the battery pack are analyzed,and then the concept of battery flexible group is put forward.The characteristics of flexible battery group technology are analyzed.Analysis the advantage of flexible battery group compared with traditional battery group.Meanwhile,the topology and control strategies of flexible group battery energy storage system are studied.The basic modulation method,the grid control strategy and charge and discharge current independent control strategy are analyzed in detail.Then,a fault-tolerant control system is established for the fault condition of the battery flexible energy storage system.The conventional methods of fault detection and fault diagnosis are described and the principle and application of traditional fault-tolerant control strategies as well as fundamental phase shift compensation fault-tolerant are analyzed.Though the system can operate well under conventional method application,there are still some defects existing in flexible group battery energy storage system.On basis of this,two improved fault-tolerant control strategies for faulty conditions of battery flexible energy storage systems for different fault operations are proposed.By injecting the third harmonic with the same amplitude and phase shift into three-phase fundamental waveforms after fault occurrence,the DC voltage utilization has been increased.Meanwhile,aiming to the "quasi-faul" problem of the battery energy storage system in charging and discharging process,a hybrid modulation fault-tolerant control strategy based on the fundamental phase shift compensation and third harmonic injection is also proposed to maintain the normal operation,thus improving the battery utilization and avoiding the capacity loss caused by the direct shutdown.The optimal redundancy solution under each fault condition is also elaborated comprehensively with a comparison of the proposed fault tolerant strategies,which taking full advantage of battery utilization and minimizes the loss of energy capacity.Finally,the flexible group battery energy storage system platform is designed.Then,software and hardware design of main circuit and control circuit are introduced.Firstly,the experimental verification of the oriented vector control method,the battery charging and discharging current independent control method and dead-zone compensation control are carried out on the experimental platform to ensure the system can be operated well in the normal condition.On basis of this,the fault tolerant control strategies have been analyzed and discussed in detail.The experimental results show that the proposed fault-tolerant control methods can maintain the stable operation of the system under fault conditions as well as maximizing the utilization rate of battery capacity. |
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