Research On Control Strategy Of Cascaded Energy Storage Power Conversion System

Cascaded energy storage power conversion system(PCS)has the advantages of modular structure and high security,which is widely concerned in high voltage and large capacity occasions.Its control strategy directly affects the performance and reliability of energy storage system.Therefore,the study of cascade energy storage PCS control strategy has theoretical value and practical significance.Taking cascade energy storage PCS as the research object,the control strategies of the system in different states are studied by using automatic control theory and small signal modeling method.The topology of cascaded energy storage PCS is determined according to the needs of the system.Based on the analysis of various modulation techniques,the unipolar frequency doubling SPWM is selected as the modulation technology through simulation analysis,and the small signal mathematical model of cascade energy storage PCS is established.According to the established mathematical model and automatic control theory,the control strategy of cascade energy storage PCS under charge/discharge state,SOC unbalance state and power module fault state is studied.When the system is in charge/discharge state,the PI regulator is used to control the power of the system,so that the system can realize charge/discharge according to the required power,and cut the peak and fill the valley of the power grid;When the system is SOC unbalanced due to the difference of battery production process and self-discharge during charge/discharge,the system needs to carry out clustered-balance control and individual-balance control.In clustered-balance control,when SOC unbalance between phases is large,aiming at the problem of slow balance speed of traditional zero sequence voltage injection strategy,in order to shorten the balance time,the relationship between balance coefficientΛand general vectorΔSOC_g is found by simulation analysis,the zero-sequence voltage injection strategy based on variable balance coefficient is proposed,that is,the zero sequence voltage injection strategy that changes the balance coefficientΛin real time to speed up the balance process is used to maintain the stable operation of the system;In individual-balance control,the reference voltage amplitude adjustment strategy is adopted to make the SOC of each battery in a phase tend to be consistent and the service life of the battery can be prolonged effectively.At the same time,in order to ensure the reliability of the system,when a power module fails,the zero sequence voltage injection strategy is used for fault-tolerant control of the system to achieve the balance of the residual battery SOC and stable operation of the system.To verify the rationality of the control strategy and the correctness of the proposed control strategy,the active-power control strategy,SOC-balance control strategy and fault-tolerant control strategy of the system are studied by Matlab/Simulink software,the simulation results demonstrate the rationality of the adopted control strategy and the correctness of the proposed strategy,and on the basis of debugging the experimental platform,the experimental research on avtive-power control and fault-tolerant control is carried out,the results verify the rationality of the control strategy.