State Estimation And Active Balance Control For Distributed Energy Storage System

To achieve ”carbon peak” and ”carbon neutrality”,it is critical to promote the transition on the power generation side.Increasing the proportion of renewable energy resources can reduce carbon emissions from the source.However,renewable energy sources such as wind power and photovoltaics have intermittent and volatility,which brings difficulties to the operating control of the power system.The energy storage system(ESS)can make up for the defects of renewable generation and will play an important role in the future energy system.At the same time,the energy system architecture is also changing from centralized to distributed.The distributed clustering imposes challenges on state monitoring,coordination control,safe and stable operation.This thesis focuses on the distributed energy storage system(DESS).First,the state estimation of the lithium-ion battery is investigated.A framework for joint fault-tolerant estimation of the state of charge(SOC)and the state of health(SOH)is proposed.Under this framework,the unscented Kalman filter(UKF)is used to estimate the SOC online.After the discharge process,the historical SOC results are smoothed offline and then the SOH is calculated.In addition,the current sensor fault detection algorithm based on adaptive Kalman filter can diagnose and estimate the current sensor fault in real-time.Simulation based on experimental test data verifies the effectiveness of the framework.Then,aiming at the issue that the SOC may easily become inconsistent in the DESS,a distributed active balance control strategy is developed.Each energy storage unit(ESU)only uses the SOC information of its neighbors,and adjusts the virtual impedance of the interface DC/DC converter through the designed distributed control protocol.By doing so,it can change the current sharing of the entire distributed energy storage system to achieve SOC balance.In order to ensure the stability of the balancing process,the mixed potential function method is applied to derive the conditions for the stable operation.Simulations and experiments illustrate the effectiveness of the proposed strategy and stability conditions.Finally,the concept of region of attraction and its application in power system are discussed.On the basis of stability conditions in the above chapter,a method with the mixed potential theory to characterize the region of attraction under large disturbances of the DESS is further put forward and verified by simulation and experiments.