直流微网混合储能控制及系统分层协调控制策略

Hybrid Energy Storage Control and System Hierarchical Coordinated Control Strategy for DC Microgrids

为了充分利用超级电容动态响应快、锂电池能量密度高的特点来提高微网储能系统的动态特性和运行寿命,利用这2种储能器件构成了光伏型直流微网的混合储能系统(HESS)。基于对超级电容和锂电池储能下垂特性的分析和工作区间的划分,提出改进型混合储能控制策略;再根据直流微网系统的功率方程、母线电容储能变化与电压变化方程,导出直流母线电压变化与系统功率流向之间的关系,提出对光伏型直流微网的电压分层协调控制策略。实验结果表明,该策略根据电压变化将直流微网的运行划分为5个层区,通过检测直流母线电压的变化量来决定系统的运行层区及光伏、超级电容和锂电池功率变换器的工作方式,保证各层区都有相应变换器来调整直流母线电压、平衡系统功率,实现直流微网电压稳定的控制目标。因此,基于混合储能系统的电压分层协调控制策略能够有效调节直流母线电压,保证直流微网的功率平衡。

The ultra-capacitor has high ramp rate and the lithium battery has high energy density, in order to make full use of the complementary performances, to improve the dynamic characteristics and to extend the operating life of energy storage system in DC microgrids, a hybrid energy storage system（HESS） composed of lithium batteries and ul- tra-capacitors was connected to the DC microgrid. By analyzing the energy storage droop characteristics of ultra-capacitor and lithium battery and the division of operating zone, we proposed an improved coordination control strategy for HESS. Then, according to the power equation of DC microgrid system and the equation about stored energy change of bus capacitor as well as voltage change, we derived the relationship between DC-bus voltage variation and the power flow in the DC microgrid. Thus the voltage hierarchical coordination control strategy was proposed. The experimental results indicate that, using the proposed strategy, the operation of DC microgrid can be divided into five levels according to the variation of voltage. The operation modes of photovoltaic converter, lithium battery converter and ultra-capacitor converter shifting correspondingly with the different levels are determined by detecting the change of the DC-bus voltage, therefore, the corresponding converter to tune the DC-bus voltage and balance the power system in each level is ensured, and the aim of the proposed control strategy is realized. The DC-bus voltage can be adjusted effectively to achieve the power balance of the DC microgrid system by the HESS based voltage hierarchical coordination control strategy.