煤层气抽采直流微网建模与稳定性分析

Modeling and Stability Analysis of DC Microgrid for Coal Bed Methane Extraction

针对目前煤层气抽采现场用电不合理现状,构建一种新型煤层气抽采直流微网供电系统,并对该直流微网系统稳定性及控制策略进行研究。煤层气抽采直流微网供电系统分三层结构:第一层由光伏和蓄电池组成能量供给层;第二层由双向Buck/Boost变换器构成能量传输和分配层;第三层由煤层气抽采机构成负荷层。基于此架构推导了第一、二层输出阻抗Zo(s),并建立第三层煤层气抽采机电动机输入阻抗Zin(s)与受控源K??m串联的小信号模型,在此基础上得到系统全局小信号模型。考虑到呈现负阻抗特性的煤层气抽采机电动机周期性动态交变负荷引起的系统不稳定,在能量传输和分配层分析并讨论了一种基于虚拟阻抗的直流微网稳定性控制策略,以及利用下垂控制实现负荷功率动态平衡分配的方法。进一步利用阻抗匹配原则求解多项式1/(1+Zo(s)/Zin(s))主导极点,比较采取该稳定性控制策略前后的主导极点位置并分析直流微网系统稳定性。最后基于Matlab/Simulink搭建由光伏阵列、储能单元和煤层气抽采机组成的煤层气抽采直流微网系统模型,系统仿真证明了稳定性控制策略的有效性。

According to the status of power consumption in the field of coal bed methane(CBM)extraction,a novel power supply system of DC microgrid for CBM extraction was set up,and itsstability issues and control strategy were also studied.The DC microgrid for CBM extraction hasthree-level configuration.The first is the power supply level consisting of PV arrays and battery banks.The second is the power transmission and distribution level comprised of bidirectional Buck/Boostconverter.The third is the load level including CBM-well pumping units.The output impedance Zo(s)of the first and second levels was established,as well as the input impedance Zin(s)in series with thecontrolled source K′m?of the third level.Thereafter,a global small-signal model was derived.Sincethe system instability will be induced by the dynamical and cyclical load of CBM-well pumping unitswith negative impedance characteristics,a stability control strategy based on virtual impedance wasanalyzed and discussed in the second level.Simultaneously,droop control was employed to achieve dynamic load power sharing.The impedance criteria were selected to evaluate the overall systemstability with and without this stability control strategy by solving the dominant poles of polynomial1/(1+Zo(s)/Zin(s)).Finally,the DC microgrid model comprised of PV arrays,battery banks andCBM-well pumping units was established in Matlab/Simulink,which verified this method.