DBS分层控制下直流微电网离网运行稳定性分析
发布时间：2018-11-19 11:31
【摘要】：离网运行的直流微电网运行控制简单,安装地点灵活,且在大电网故障时可保证重要负荷可靠供电。本文针对离网运行的光储直流微电网,采用直流母线电压(DBS)分层控制策略实现多源协调、能量自主管理以及直流母线电压稳定等目标。分析DBS分层控制下直流微电网的小信号稳定性并探讨其影响因素,采用无源阻尼法提高直流微电网的稳定性。具体内容如下:首先,设计DBS分层控制策略,根据母线电压将光储直流微电网运行状态分为3种工作模式:模式1时轻载,母线电压较高,光伏单元下垂控制以限制功率输出并维持母线电压稳定,同时蓄电池单元限流充电吸收多余功率并防止蓄电池过充;模式2时负载增加,母线电压降低,光伏单元采用最大功率点跟踪(MPPT)控制实现最大功率输出,同时蓄电池单元下垂充电以补充剩余能量并维持母线电压稳定;模式3时重载,母线电压较低,光伏单元MPPT控制输出最大功率,同时蓄电池单元下垂放电补充不足的功率需求并维持母线电压稳定。仿真和实验验证了在DBS分层控制下直流微电网可以实现在3种工作模式的稳定运行和模式间平滑切换。其次,多变换器并联交互所引起的稳定性问题是直流微电网领域的一个研究热点。DBS分层控制下的直流微电网是一个多点平衡系统,目前单一控制模式的稳定性分析不适用于该控制策略下的直流微电网。本文在确定光储直流微电网架构及DBS分层控制策略的基础上建立了各单元在不同控制模式下的小信号模型,推导出各接口变换器的闭环阻抗表达式,并得出直流微电网分别运行在3种工作模式的等效阻抗模型。利用幅值-相角裕量(GMPM)阻抗比禁止区判据,判定得出直流微电网在3种工作模式均可保证小信号稳定。最后,针对直流微电网运行在模式2时,负载总阻抗中存在的负谐振尖峰不利于稳定的问题,采用无源阻尼法,通过增加阻尼电路来削减谐振尖峰,改善负载阻抗特性,使直流微电网稳定性得到提高,同时分析了滤波参数对稳定性的影响以指导滤波器的设计。仿真结果表明无源阻尼法可降低母线电压、负载电流纹波,提高直流微电网的稳定性及负载供电质量。
[Abstract]:The off-grid DC microgrid has the advantages of simple operation control, flexible installation location and reliable power supply for important loads in the event of large power grid failures. In this paper, the multi-source coordination, independent energy management and DC bus voltage stability are realized by using DC bus voltage (DBS) layered control strategy for off-grid optical storage DC microgrid. The small signal stability of DC microgrid controlled by DBS is analyzed and the influencing factors are discussed. The passive damping method is used to improve the stability of DC microgrid. The main contents are as follows: firstly, the DBS hierarchical control strategy is designed. According to the bus voltage, the operation state of the optical storage DC microgrid is divided into three working modes: mode 1, light load, high bus voltage, Photovoltaic unit droop control to limit power output and maintain bus voltage stability, while battery unit current limiting charge to absorb excess power and prevent battery overcharge; Mode 2 load increases, bus voltage decreases, photovoltaic unit uses maximum power point tracking (MPPT) control to achieve maximum power output, while battery unit sagging charging to replenish residual energy and maintain bus voltage stability; Mode 3 heavy load, low bus voltage, photovoltaic unit MPPT control output maximum power, while battery unit sag discharge to supplement the insufficient power demand and maintain bus voltage stability. Simulation and experiments show that DC microgrid can operate stably in three operation modes and smooth switch between modes under DBS layered control. Secondly, the stability problem caused by the parallel interaction of multi-converters is a hot topic in the field of DC microgrid. The DC microgrid based on DBS hierarchical control is a multi-point balancing system. At present, the stability analysis of single control mode is not suitable for DC microgrid with this control strategy. Based on the structure of optical storage DC microgrid and the layered control strategy of DBS, the small signal model of each unit in different control modes is established, and the closed-loop impedance expression of each interface converter is deduced. The equivalent impedance model of DC microgrid operating in three working modes is obtained. By using the criterion of (GMPM) impedance ratio of amplitude-phase margin, it is determined that the stability of small signal can be guaranteed in three operation modes of DC microgrid. Finally, aiming at the problem that the negative resonance peak in the load total impedance is not stable when the DC microgrid operates in mode 2, the passive damping method is adopted to reduce the resonant peak and improve the load impedance characteristic by adding damping circuit. The stability of DC microgrid is improved and the influence of filter parameters on the stability is analyzed to guide the design of the filter. The simulation results show that the passive damping method can reduce the bus voltage, load current ripple, improve the stability of DC microgrid and the quality of load supply.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727
本文编号：2342181
[Abstract]:The off-grid DC microgrid has the advantages of simple operation control, flexible installation location and reliable power supply for important loads in the event of large power grid failures. In this paper, the multi-source coordination, independent energy management and DC bus voltage stability are realized by using DC bus voltage (DBS) layered control strategy for off-grid optical storage DC microgrid. The small signal stability of DC microgrid controlled by DBS is analyzed and the influencing factors are discussed. The passive damping method is used to improve the stability of DC microgrid. The main contents are as follows: firstly, the DBS hierarchical control strategy is designed. According to the bus voltage, the operation state of the optical storage DC microgrid is divided into three working modes: mode 1, light load, high bus voltage, Photovoltaic unit droop control to limit power output and maintain bus voltage stability, while battery unit current limiting charge to absorb excess power and prevent battery overcharge; Mode 2 load increases, bus voltage decreases, photovoltaic unit uses maximum power point tracking (MPPT) control to achieve maximum power output, while battery unit sagging charging to replenish residual energy and maintain bus voltage stability; Mode 3 heavy load, low bus voltage, photovoltaic unit MPPT control output maximum power, while battery unit sag discharge to supplement the insufficient power demand and maintain bus voltage stability. Simulation and experiments show that DC microgrid can operate stably in three operation modes and smooth switch between modes under DBS layered control. Secondly, the stability problem caused by the parallel interaction of multi-converters is a hot topic in the field of DC microgrid. The DC microgrid based on DBS hierarchical control is a multi-point balancing system. At present, the stability analysis of single control mode is not suitable for DC microgrid with this control strategy. Based on the structure of optical storage DC microgrid and the layered control strategy of DBS, the small signal model of each unit in different control modes is established, and the closed-loop impedance expression of each interface converter is deduced. The equivalent impedance model of DC microgrid operating in three working modes is obtained. By using the criterion of (GMPM) impedance ratio of amplitude-phase margin, it is determined that the stability of small signal can be guaranteed in three operation modes of DC microgrid. Finally, aiming at the problem that the negative resonance peak in the load total impedance is not stable when the DC microgrid operates in mode 2, the passive damping method is adopted to reduce the resonant peak and improve the load impedance characteristic by adding damping circuit. The stability of DC microgrid is improved and the influence of filter parameters on the stability is analyzed to guide the design of the filter. The simulation results show that the passive damping method can reduce the bus voltage, load current ripple, improve the stability of DC microgrid and the quality of load supply.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727
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