近年来，规模化储能技术成为智能电网发展的重要方向。规模化储能系统的接入可通过电力调峰提高电力资产利用率，通过功率平滑控制平抑新能源并网波动，通过四象限运行解决电网安全稳定运行问题。在各类储能技术中，电池储能技术发展最成熟，应用最广泛。论文结合大容量电池储能工程应用需求，对链式电池储能功率转换系统（PCS）关键技术进行了深入研究。论文对基于变压器降压NPC 三电平逆变器和链式逆变器的PCS主电路性能和成本进行了对比研究，表明链式PCS在效率、成本、占地面积、谐波特性等方面具有优势，更适合大容量电池储能应用场合。在此基础上建立了链式PCS的数学模型和控制策略，给出了主电路参数设计方法，通过四象限运行的数字仿真对主电路参数设计及控制策略进行了验证。针对链式PCS的SOC均衡控制，首先提出了注入零序电压的相间SOC均衡控制策略，并分析了传统单位功率因数下相内SOC均衡控制策略在SOC极度不均衡状况下，导致极端模块过调制的失效条件；接着提出了一种注入无功功率的相内SOC均衡控制策略，通过在各H 桥模块调制信号上同时叠加一个有功和无功电压偏移分量，保证极端电池组主要进行有功交换，其余电池组主要进行无功交换，充分协调各模块调制比，避免过调制的同时实现均衡控制；然后推导出注入无功功率前后临界均衡状态时各模块调制比公式，得到注入无功功率后可在SOC极度不均衡情况下实现均衡控制，扩大适用范围，并分析了其应用范围边界。针对链式PCS的低压穿越控制策略，首先结合光伏发电站PCS接入电力系统的LVRT技术标准，给出了电网故障下链式PCS低电压穿越控制策略的设计目标；综合考虑变流器过流限制、三相峰值电流限制、故障阶段无功支撑要求、故障清除后有功恢复速度要求，设计了平衡电网故障下链式PCS低压穿越控制策略、不平衡电网故障下分别控制输出三相电流平衡和输出有功功率稳定的链式PCS低压穿越控制策略。在PSCAD数字仿真平台中建立了链式电池储能系统及论文所提出的各相关控制策略的仿真模型，对所提链式PCS四象限运行控制策略、SOC均衡控制策略和低电压穿越控制策略的有效性进行仿真验证。
In recent years, large-scale energy storage technology has become an important direction of smart grid development. The access of large-scale energy storage system can improve the utilization ratio of power assets and stabilize the fluctuation of new energy power. Among all kinds of energy storage technologies, battery energy storage technology has the most mature development and the most extensive application. The paper considers the needs of large-capacity battery energy storage engineering applications and conducts in-depth research on the key technologies of the chain battery energy storage power conversion system (PCS).Firstly, this paper compares the large capacity PCS based on NPC three-level inverter and the cascaded PCS. It shows that the cascaded PCS has great application potential in large capacity applications due to its advantages in cost, efficiency and harmonic characteristics. On this basis, the mathematical model and control strategy of the cascaded PCS are established, and the main circuit parameter design method is given. The PSCAD simulation results of the four-quadrant operation verify the effectiveness of the main circuit parameter design and control strategy.Secondly, to address the issue of SOC unbalance, this paper proposes a phase to phase SOC balancing control strategy with zero sequence voltage injection. According to the traditional in-phase SOC balancing control strategy with unit power factor, the boundary condition of over-modulation when SOC is extremely unbalanced is analyzed. Then, a novel in-phase SOC balancing control strategy with injection of reactive power is proposed. By superimposing the active and reactive voltage component on each H-bridge modulation signals, this strategy can ensure that the batteries with extreme SOC mainly exchange active power, while other batteries mainly exchange reactive power. Then, the modulation ratios of the batteries with extreme SOC before and after reactive power injection is derived, which proved injecting reactive power can expand application scope of SOC balancing control.Thirdly, to address the issue of overcurrent during power grid faults, the design goal of cascaded PCS low voltage ride-through control strategy is given by referring to the LVRT standard of photovoltaic power station. Considering the converter current limitation, the average transmission power limitation and reactive power support requirement, cascaded PCS low voltage ride-through control strategies under power grid symmetrical and asymmetrical faults are proposed. The LVRT control targets during asymmetric faults are set to control PCS output three-phase current symmetry and control PCS output active power stability.The simulation model of the cascaded battery energy storage system and the related control strategies proposed in this paper are built in PSCAD. The cascaded PCS four-quadrant operation control, SOC balancing control and low voltage ride-through control are simulated. The simulation results verify the correctness and effectiveness of the proposed control strategies.
