Research On Control Strategy Of Chain Energy Storage Converter

With the overall improvement of China’s industrial structure adjustment and economic level,the traditional fossil energy-based industrial production and consumption mode has been unable to meet the requirements of sustainable development.Renewable energy represented by wind and solar energy is an inevitable choice for China and even the global energy and economy to achieve sustainable development.However,such renewable energy has the characteristics of intermittent,volatility and randomness due to the influence of meteorological fluctuations.In order to greatly improve the adaptability of power grid to large-scale grid connection of such new energy,the new energy power resources are transformed into a resource that can be fully controlled and dispatched by using large capacity energy storage devices.This device can curb the imbalance between new energy output and load demand as much as possible,which leads to the occurrence of wind and light abandonment.At the same time,it can maintain the normal operation of the power system,better let users use clean energy,and more flexibly meet the needs of heating,power generation and industrial production.It is of great significance to reduce the consumption of fossil energy and actively respond to the dual-carbon strategy.In this thesis,the chain energy storage inverter is taken as the research object,and some control strategies are studied.Firstly,a two-stage cascaded energy storage inverter topology based on distributed inductance is used.Compared with the traditional chain-type energy storage inverter,this topology occupies a smaller area,is more convenient for later maintenance,the initial input cost of the battery is lower,and the utilization rate of battery capacity is higher.At the same time,the battery current can be independently controlled to prolong the operation life of the whole energy storage system.Secondly,the problem of poor phase tracking ability of traditional synchronous rotating coordinate phase locked loop under unbalanced grid conditions is improved.The cross self-decoupling complex filter is used to extract the positive sequence fundamental component of the power grid.At the same time,the new frequency and phase self-tuning link make the phase locked loop have better frequency and phase tracking ability than the traditional digital phase locked loop.Thirdly,the three-level DC voltage control strategy and the three-level SOC equalization control strategy are usd for the H-bridge converter in the battery charging state and the battery discharging state,respectively.The two control strategies ensure the stable and reliable operation of the chain energy storage inverter during the battery charging and discharging.At the same time,in order to make full use of the design capacity of the chain energy storage inverter,reduce the construction cost of the system and improve the operation efficiency of the device,a power quality control composite control strategy based on residual capacity is used.The reactive power of the power system is compensated and the harmonic current is compensated,and the power quality problem of the power system is moderately improved and solved.Fourthly,a three-stage charging control strategy suitable for the chain-type energy storage inverter and a simple secondary ripple current suppression control strategy on the battery side are used for the bidirectional DC/DC converter during the battery charging process and the battery discharge process,respectively.The former realizes the fast charging of the battery pack and the balanced control of SOC of each battery pack,improves the charging effect of the battery packs,inhibits the lithium dendrite phenomenon and improves the operation life of the battery packs.The latter suppresses the secondary ripple component of the voltage after the capacitor sampling at the high voltage side,so that the secondary ripple component in the reference value of the current inner loop is suppressed or even eliminated,and the characteristics of the current flowing into the battery pack are improved.Then,in view of the battery capacity decline and SOC pseudo-equilibrium caused by the unbalanced temperature of the battery pack in the chain energy storage system,the source of heat generation of the battery pack is analyzed,and a simple equivalent thermal resistance model of the battery pack is established.A battery pack temperature balancing control strategy based on energy adaptive transfer is proposed from a new perspective.The proposed strategy uses the second harmonic energy that the traditional strategy needs to suppress to effectively control the temperature of each battery pack,which not only avoids the malignant influence of the overshoot of temperature and SOC in the control process,but also improves the average operating life of the whole energy storage system.Finally,the MATLAB/Simulink simulation model of the chain energy storage inverter is established,and the control strategies for H-bridge converter and bidirectional DC/DC converter are simulated and verified.Then the low-voltage engineering prototype of the chain energy storage inverter is designed and built.The proposed control strategies are experimentally verified by engineering prototypes,and the correctness and effectiveness of the proposed control strategies are verified by comparing and analyzing the simulation and experimental results.