级联型储能系统中虚拟同步发电机控制及电池自均衡策略

为更好地应对可再生能源装机容量不断提升而传统分布式储能系统容量小、电压等级低的问题,提出采用级联H桥拓扑实现单机电池储能系统(BESS)的高压、大容量化。为增强储能系统入电网友好性,对虚拟同步发电机(VSG)控制技术进行了研究,结合同步发电机的一次调频特性及调压特性,详细分析了同步发电机的二阶等效模型和VSG控制策略,建立VSG控制的宽频带小信号动态模型,定量分析VSG控制的固有功率耦合特性及交流侧阻抗对VSG控制的影响,提高了VSG模型准确度。通过频域模型分析虚拟惯性和阻尼以及无功控制参数与BESS性能的关系,为VSG稳定性分析及关键参数的设计与优化提供了依据。针对VSG控制下BESS模块电池荷电状态均衡的问题,提出一种改进型最近电平调制方法并给出了调制原理,实现了相内模块间荷电状态的自均衡。最后,利用搭建的仿真模型,验证了VSG在级联型BESS应用中的可行性、参数分析以及调制方法的有效性。

Strategy of Virtual Synchronous Generator Control and Battery Balancing in Cascaded H-bridge Based Energy Storage System

Considering that the low voltage and small capacity ratings of traditional distributed energy storage system cannot meet the increasing capacity of renewable energy, the battery energy storage system(BESS)based on cascaded H-bridge topology is presented to achieve high-voltage and large-capacity. Moreover, in order to make BESS connected to grid friendly, the virtual synchronous generator(VSG)is investigated. Firstly, the second-order equivalent model of synchronous generator(SG)is analyzed and the VSG control strategy for BESS is given combined with primary frequency and voltage regulation of SG. Besides, the small signal dynamic model in wideband of VSG is established to analyze the inherent power coupling problem and the effect of AC side impedance on VSG control, also, the relationship between control parameters of VSG and performance of BESS is analyzed by frequency domain model, which provide the basis of stability analysis and the design and optimization of key parameters of VSG. Simultaneously, aiming to the problem of state of charge(SOC)balancing for sub-module batteries, a method based on improved nearest level modulation(I-NLM)is proposed and the modulation principle and implementation process are given. Finally, the effectiveness of VSG control on BESS and equalization method for SOC are verified through computer simulation.