Flexible Grid-connected Control Strategy Of Distributed Battery Storage System Using Multi-DC Port Converters

The multi-DC port converter can effectively combine the distributed power supply and the energy storage device,overcome the problems of randomness and intermittentness of the distributed power generation system,and has the advantages of high integration,high efficiency,low volume and low cost.Power generation and gridconnected,AC-DC microgrid and other aspects have been widely used.In this paper,based on the distributed energy storage flexible grid-connected control strategy of multi-DC port converters,the research focuses on the control strategy of two-stage multi-port energy storage converters and cascaded H-bridge multi-level converters.The main contents of this article are summarized as follows:In view of the large number of energy storage battery packs in the energy storage system,the battery characteristics vary greatly,and the battery charge and discharge levels are inconsistent,it is easy to cause circulation,battery overshoot and over discharge,and it is impossible to realize efficient use of the energy storage system.In actual demand,more DC ports are needed to independently control the power of each battery pack.Therefore,this paper proposes an improved two-stage multi-port energy storage converter that can realize distributed energy storage.The converter can realize multi-port charging of multi-distributed energy storage,independent control of multiple battery charging,reducing cost and improving flexibility.For the demand of multiple sets of energy storage batteries directly connected to the medium and high voltage power grid,the cascaded H-bridge converters have received extensive attention in recent years,but the output of each group of batteries is different,there is a common difference in SOC operation,and the three-phase power imbalance of the energy storage system may occur,resulting in asymmetry of the three-phase grid-connected current.This paper analyzes the mechanism of phase-to-phase power imbalance control of three-phase cascaded H-bridge grid-connected converters,and proposes a new closed-loop zero-sequence voltage injection method,which omits complex trigonometric function calculations with lower computational complexity and realizes zero under various operating conditions with lower computational complexity.The sequence voltage is generated quickly,which can better control the phase-to-phase power.In the process of generating zero-sequence voltage,the output power of each phase of the cascaded H-bridge converter is controlled by closed-loop control.The method has strong anti-interference ability,high control precision and certain engineering practical significance.Aiming at the problem that the power imbalance of the three-phase cascaded H-bridge grid-connected converter is large and the modulation signal is over-modulated after zero-sequence voltage injection,this paper optimizes the closed-loop zero-sequence voltage optimization injection method and proposes a closed-loop zero sequence voltage optimized injection method(CZSI).Compared with the traditional method,the method achieves the rapid generation of optimized irregular zero-sequence voltage with lower computational complexity,and the calculation is simple,which is beneficial to engineering implementation;the closed-loop form accurately controls the output power of each phase of the cascaded H-bridge converter;the amplitude of the modulated signal after zero-sequence voltage injection is reduced,and the occurrence of over-modulation is suppressed,thereby expanding the adjustment range of the power imbalance between the cascaded H-bridges,and having superior power balance capability.Finally,simulation and experiments are carried out to verify the effectiveness of the proposed new topology and control strategy.