【作者】 孙国强；

【导师】 于永进；

【作者基本信息】 山东科技大学 ， 电气工程， 2023， 硕士

【摘要】 出于环境和经济的因素考虑,常规分布式电源(Distributed Energy Resource,DER)并网对我国绿色发展必不可少。为此,微电网(Microgrid,MG)的概念提出来用以高效管理分散的DER。但由于缺乏主电网的支持,运行在孤岛模式下的MG的频率稳定需由其内部发电设备维持。对于应用广泛的集中式二次频率控制(Secondary Frequency Control,SFC)方案而言,一个挑战性的问题是通信资源受限;另一方面,DER数量的增加会消耗大量的通信资源来维持系统的频率响应性能。具体而言,SFC对孤岛MG的稳定运营起到至关重要的作用。因此,一种有效的、通信成本低的SFC方案对于补偿可再生能源(Renewable Energy Sources,RES)发电与负荷之间的有功功率不平衡是必不可少的。本文以孤岛微电网的SFC系统为研究对象,考虑通信延迟,测量扰动等因素,综合研究多种事件触发机制(Event-Triggered Mechanism,ETM)下微电网的二次频率控制问题。具体内容如下:(1)为探究各发电设备运行对MG内频率稳定的影响,本文给出了可用于频率分析的各发电子系统、储能系统、负载模型。其中,将风光发电等RES发电功率波动性和间歇性视作扰动,并不将RES发电功率纳入SFC环节。随后分析集中式SFC方案的工作原理,阐明通信资源对集中式控制的重要性。(2)为解决孤岛MG中通信资源受限问题,提出一种动态事件触发机制(Dynamic Event-Triggered Mechanism,DETM)来克服带宽限制,该机制与前述成果不同,DETM的阈值可根据最新传输值和当前测量值的误差动态调整。基于此,本文构造了基于DETM的微电网二次频率控制系统框架,该框架以DETM作为是否进行数据传输的开关,以传统发电设备作为MG内维持功率平衡的核心,以PI型控制器进行频率控制,开展DETM对MG频率调整的研究。随后,选取合适的Lyapunov泛函,推导出上述构造的SFC系统渐近稳定且满足给定期望H_￥鲁棒性能的充分条件。然后,对控制器进行联合设计确保满足以上要求。不仅如此,为保证DETM可行性,得出相邻两次触发时刻的差值唯一非零正数,保证了Zeno现象不会出现。最后,通过4场景的仿真分析验证了所提方法的有效性和实用性。(3)为充分探讨网络化控制诱导的通信延迟对MG集中式SFC频率控制的影响,以进一步克服MG带宽限制,提高平均触发间隔,本文提出一种动态切换事件触发机制(Dynamic Switching Event-Triggered Mechanism,DSETM)以确保完成上述任务的同时避免发生Zeno现象。基于此,构建了计及通信延迟的DSETM的微电网二次频率控制闭环系统模型以充分挖掘DSETM对通信资源的利用率,对通信延迟的包容性和对扰动的鲁棒性。然后,利用合适的Lyapunov泛函并结合Lyapunov稳定性理论和不等式放缩技术,得到以线性矩阵不等式(Linear Matrix Inequality,LMI)形式的判据。提出的判据可以确保基于DSETM的MG二次频率控制闭环系统在容忍一定通信延迟的情况下具有渐近稳定性,并且能够满足给定期望的鲁棒性要求。而且,本文给出寻找满足系统稳定性的最小鲁棒指标的一般方法,以充分挖掘所提方法的抗扰能力。最后,所提方法的可行性通过4场景分析得以验证。更多还原

【Abstract】 Owing to environmental and economic factors,the integration of conventional distributed energy resources(DER)into the grid is essential for sustainable development in China.Microgrid(MG)is proposed as an efficient solution to manage the dispersed DER.However,in islanded mode,without the support of the main grid,frequency stability in the MG relies solely on the internal generating units.A challenging issue for widely applied centralized secondary frequency control(SFC)in MG is the limited communication resources;On the other hand,the increasing number of DERs will consume a large amount of communication resources to maintain the system’s frequency response performance.Specifically,SFC plays a crucial role in the stable operation of islanded MG.Therefore,an effective and low-cost SFC scheme is essential to compensate for the active power imbalance between renewable energy sources(RES)and load.This thesis focuses on the SFC system of islanded MGs,taking into account factors such as communication delay and measurement disturbance,and comprehensively studies the secondary frequency control problem under various event-triggered mechanisms(ETM).The specific contents are as follows:(1)To investigate the impact of operating various generating units on the frequency stability of MGs,this thesis presents various subsystems,energy storage systems,and load models that can be used for frequency analysis.Thereinto,the fluctuation and intermittency of the power generated by RES such as wind and solar power are regarded as disturbances,and the power generated by RES is not included in the SFC process.The working principle of centralized SFC is then analyzed to illustrate the importance of communication resources in centralized control.(2)To overcome the limited communication resources in islanded MGs,a dynamic event-triggered mechanism(DETM)is proposed to overcome bandwidth limitations.Unlike previous results,the threshold of DETM can be dynamically adjusted according to the error between the latest transmission value and the current measurement value.Based on this,this thesis constructs an MG SFC system framework based on DETM.The framework uses DETM as a switch for data transmission,traditional generating units as the core for maintaining power balance in the MG,and a PI controller for frequency control to research the frequency adjustment of the MG under DETM.Then,a suitable Lyapunov functional is selected,and the sufficient conditions for the asymptotic stability and robust performance of the constructed SFC system with the given expectation are derived.The controller is co-designed to meet the above requirements.Furthermore,to ensure the feasibility of DETM,the non-zero positive difference between adjacent triggered moments is unique to ensure that the Zeno phenomenon does not occur.Finally,the effectiveness and practicality of the proposed method are verified through simulation analysis of four scenarios.(3)To fully explore the impact of communication delay induced by networked control on centralized SFC frequency control in MGs,and to further overcome the bandwidth limitations and increase the average triggering interval,this thesis proposes a dynamic switching event-triggered mechanism(DSETM)to ensure completion of the above tasks while avoiding the occurrence of the Zeno phenomenon.Based on this,a MG SFC system model considering communication delay and DSETM is constructed to fully exploit the utilization of communication resources,the tolerance of communication delay,and the robustness to disturbances provided by DSETM.Then,by utilizing an appropriate Lyapunov functional and combining Lyapunov stability theory and inequality scaling techniques,a criterion in the form of a linear matrix inequality(LMI)is derived.The proposed criterion ensures the asymptotic stability of the MG SFC system based on DSETM under tolerable communication delay and satisfies the robustness requirement of the given expectation.Furthermore,a general method for finding the minimum robust performance index that ensures system stability is provided to fully test the disturbance rejection capability of the proposed method.Finally,the feasibility of the proposed method is verified through analysis of four scenarios.更多还原