In view of the fact that the hybrid energy storage systems of optical storage and DC microgrids are susceptible to intermittent energy input, random load perturbations, and power flow switching, which may cause the problems of bus voltage fluctuations and system power instability, a complementary sliding mode control strategy based on a finite-time observer is proposed. First, according to the high-low frequency characteristics of the hybrid energy storage elements, the current equivalent distribution of the system differential power is carried out. Then, a finite-time dilated state observer is designed to observe the total disturbance to the system, and the disturbance observations are fed into the complementary sliding-mode controller as feedforward terms to compensate for the system disturbance, ensuring that the system state reaches convergence in finite time, improving the fast and anti-disturbance performance of the system, and proving the stability of the control system according to Lyapunov theory. Finally, based on the MATLAB simulation platform, the simulation results show that the proposed control has faster response speed and better immunity to disturbances than the traditional control strategy.
随着能源危机与环境问题的日益凸显,可再生能源的发展越来越受重视.直流微电网[1]作为一种高效的能源利用措施,因其结构简单、控制方便、效率高等优点,在各行业中的应用越来越广泛.其中采用太阳能发电的光伏微网[2],减少了对传统能源的依赖,具有节能环保的优点.但由于太阳能资源的随机性,系统运行常受到电压质量问题的影响.因此,有必要接入储能装置[3-4],补偿光伏间歇性的功率波动,增强光伏直流微网系统运行的稳定性.蓄电池和超级电容分别作为高能量密度和高功率密度的储能元件,具有互补的工作特性,构成的混合储能系统(Hybrid Energy Storage System,HESS)在光储直流微网[5-6]中得到了广泛应用.
裴斯诺等[18]针对传统PI控制下,储能变流器跟踪滞后以及抖振幅度大的问题,提出一种超螺旋滑模控制,提高了变流器的响应速度和鲁棒性,但由于电网运行情况复杂,微源以及负荷的扰动会造成系统抗扰性能变差.张世欣等[19]针对自抗扰控制中的PD控制鲁棒性差的问题,设计改进型滑模自抗扰控制,提升了直流微网系统的稳定性.董锋斌等[20]针对双馈风力发电机运行中的不确定性,引入扩张状态观测器(Expanded State Observer,ESO),通过估计系统总扰动并采用滑模控制进行补偿,减小抖振的同时也提高了系统抗干扰能力.但普通ESO的观测能力有限,只能达到渐进收敛.为了提高观测器的收敛性能,沙磊等[21]为二质量系统设计了有限时间滑模控制策略,提高了系统的跟踪性能以及抗扰能力.
图6为负荷功率扰动时不同控制策略下蓄电池荷电状态(State of Charge,SOC)容量变化对比图.分析图6仿真结果可知,当遭到负荷功率扰动,母线电压发生波动时,混合储能系统补偿差额功率.由于蓄电池循环次数有限,为减小蓄电池充放电次数、保护电池寿命,蓄电池的容量变化应越小越好.当蓄电池初始SOC为80%时,FTESO+CSMC控制策略下的蓄电池SOC容量变化最小,优于其它控制策略.
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