Research On Control Method Of Cascaded Battery Energy Storage Inverter

With the continuous upgrading of energy structure,the proportion of renewable energy in total energy use continues to increase,but the problem of grid-connected absorption is becoming more and more prominent.Energy storage system has attracted wide attention because it can effectively improve the grid-connected power generation capacity of intermittent new energy sources.As the core component of energy storage system,energy storage inverters are the interface between energy storage devices and power grid,which is of great significance to the safe and stable operation of power grid.Cascaded H-bridge topology has great potential in the field of energy storage due to its modularity and scalability,and its distributed battery energy storage unit is easy to adjust system power.This paper takes cascaded battery energy storage inverters as the main research object,introduces the structure characteristics of cascaded H bridge topology,analyses its working principle and establishes relevant mathematical models,and introduces a method of adding zero sequence component to carrier modulation reference signal to equivalent space vector modulation.In addition,the corresponding zero-sequence injection correction algorithm is deduced and its linear modulation interval is discussed,because the cascaded battery energy storage inverters may have unbalanced three-phase DC link voltage.This algorithm can effectively improve the utilization of DC voltage when the three-phase DC link voltage is unbalanced.Based on the zero sequence injection correction method,the fault-tolerant control strategy of cascaded battery energy storage inverters is studied by means of software bypass principle,and the related validation is carried out by means of simulation platform.Secondly,based on the power calculation principle of power frequency sliding window,the three-phase power control and module power control algorithms are deduced.At the same time,the effectiveness of the related algorithms is verified by simulation.Finally,the experimental platform of cascaded battery energy storage inverters is designed.The hardware structure of the platform and the program design of the control system are introduced in detail.The experimental platform is used to compare SCPWM(Sector Correction Pulse Width Modulation)with NVM(Carrier-Based Neutral Voltage Modulation Strategy),ZSVIM(Zero Sequence Voltage Injection Methods)and SVPWM(Space Vector Pulse Width Modulation).The feasibility and effectiveness of the proposed algorithm are verified.On this basis,the three-phase power control strategy and the module power control strategy are verified experimentally.The experimental results show that the proposed power control strategy can effectively control the output power of each phase and each sub-module in the case of unbalanced DC link voltage.