【作者】 李斌；

【导师】 周林；

【作者基本信息】 重庆大学 ， 电气工程， 2018， 博士

【摘要】 微电网作为一种小型智能化的发配电系统,通过与电网的交互补充可缓解大量分布式电源接入对电网造成的冲击,是实现传统电网向智能电网过渡的有效手段。然而,目前微电网中各分布式电源的并网逆变器大多仍采用传统的刚性控制手段,只能实现单位功率因数的并网控制,无法满足微电网对供电灵活性和可靠性的技术要求。论文以实现微电网与大电网的实时交互以及微电网孤岛模式下的安全稳定运行为目标,深入研究适用于微电网逆变器的虚拟同步发电机控制策略,并针对微电网的不同运行模式探讨虚拟同步发电机的功率解耦、一次调频调压和二次调频调压等关键控制技术的实现方法,使得微源逆变器在控制上变得更加柔性、功能上更加丰富,进而保证了微电网的安全稳定运行,具有一定的理论研究价值和工程实际意义。论文首先研究了现行虚拟同步发电机算法的实现机理,分析了虚拟同步发电机算法的功率控制结构,并利用小信号分析方法建立了虚拟同步发电机的功率输出模型以及功率环路的等效数学模型。基于建立的模型,提出一种关键控制参数包括转动惯量、阻尼转矩,无功电压下垂系数以及惯性系数等的选择方法,该方法兼顾控制器内外环解耦与相位裕度的设计要求,可快速准确的计算出相应参数的可行域,保证系统具有良好的稳定性和动态性能,为虚拟同步发电机的进一步研究奠定了基础。由于微电网多位于中低压配电网侧,其线路阻抗呈现阻性或者阻感性特点,使得虚拟同步发电机输出的有功和无功功率之间存在较强耦合,严重影响系统的控制性能。论文重点研究了功率耦合产生的机理以及虚拟同步发电机控制技术对功率解耦的控制要求,提出对角阵补偿矩阵与耦合点电压估测相结合的功率解耦控制策略,其中对角阵补偿解耦法属于系统工作点附近的静态解耦方法,通过计算输出功率的耦合分量并给予补偿,可提高虚拟同步发电机输出功率的控制精度,由于未改变原始控制通道的增益,该策略不会影响控制系统的稳定性以及参数设计方法;同时,利用耦合点电压估测单元,为微电网各微源逆变器的无功电压控制引入全局变量,可实现微源输出无功功率的均分控制,避免了无功环流的产生。目前的虚拟同步发电机控制技术只能模拟同步发电机的一次调频调压功能,当微电网运行在孤岛模式时,由于缺少大电网为其提供频率和电压支撑,虚拟同步发电机控制将无法满足此时系统对电压和频率的运行要求,不利于孤岛微电网的正常工作。针对该问题,论文改进了虚拟同步发电机功率环路的控制结构,提出基于虚拟同步发电机控制技术的二次频率电压控制手段。对于频率的二次控制,论文提出基于改进功频控制结构的二次调频本地化解决方案,该方案利用逆变器的本地信息实现频率的无差控制,且无需通信环节的引入,提高了系统的可靠性;同时论文利用频率的全局变量属性,提出多机协调参与二次调频控制的实现方法,使多台虚拟同步发电机可以按照既定的规则分配系统的有功缺额,有利于微电网总调频容量以及微电网系统容量的扩展;此外,利用二次控制对频率的无差调节能力,论文探讨了二次频率控制参与微电网离并网无缝切换的实现过程。对于电压的二次控制,论文引入微电网分布式架构的控制思想,借助相邻逆变器的信息交互,提出基于无功功率一致性协议的多机协调控制策略。该策略可使各微源逆变器在同步时钟的作用下与相邻微源交换电压、电流信息,通过本地的分布式控制器迭代评估全网的平均无功功率,实现各微源按照自身容量权重分配系统无功缺额的控制目标,保证系统无功功率的供需平衡,进而快速消除微电网的电压偏差,增强了微电网的运行稳定性与供电可靠性。由于没有微电网中央控制器参与调节,减少了通信量,一定程度上提高了系统的鲁棒性。论文通过算例仿真验证了以上所提控制策略的可行性和有效性,并对部分控制方案进行了实验验证。更多还原

【Abstract】 Microgrid is a kind of small scale generating and distribution system.Through interacting and supplying the grid,microgrid can remit the impact of a mass of distributed generators access to the grid.However,the traditional grid-connected inverters in the microgrid can just generate active current.It cannot satisfy the requirement of the microgrid on the high reliability and flexibility.The main focus of this study is based on the research of the inverter control of the microgrid and multi-machine coordinated control.Through simulating the performance characteristics of the traditional synchronous generator,the mathematical model of virtual synchronous generator(VSG)algorithm is constructed and borrowing from the hierarchical control thoughts of the power system,the issues of the power decoupling control and the frequency and voltage regulation of the microgrid under different operation mode are analyzes.This thesis firstly researches the control principle and ontology algorithm of VSG.The mathematical model consists of the main circuit topology,the power/frequency controller,the excitation controller and the voltage and current controllers is established.Based on the small signal approach,the equivalent mathematical model of the power loop is set up.The selection of related parameters is also confirmed based on the system design requirement,which can guarantee the stability and performance of the system and implement the request of the decoupling between the internal and external loop of the controller.All of above design establishes the foundation for further research of virtual synchronous generator.The line impedance in a microgrid generally presents resistance-inductance or resistive property,which can result in a strong coupling between the control of the active and reactive power.For the power decoupling control,this thesis analyzes the mechanism of the power coupling and points out that in the microgrid,the power decoupling control must accomplish the power approximate decoupling and the sharing control of the reactive power on the premise of the system stability.Then based on the output power model of the microgrid,a combination of the diagonal decoupling matrix and the estimated voltage of the point of common coupling is proposed.It can implement the power approximate decoupling and improve the accuracy of the power control.Furthermore,it can also implement the sharing control of the reactive power and avoid the generation of the reactive circulating current.Up to now,only primary frequency modulation and primary voltage modulation of VSG can be realized.However,the primary modulation incurs static error and cannot guarantee the power supply quality under the islanded mode of the microgrid.Hence,the distributed generators(DGs)in the microgrid are required to implement the secondary modulation.In this thesis,an improved control structure of virtual synchronous generator is proposed to realize the function of secondary frequency and voltage modulation for the islanded microgrid.In the power/frequency controller,an integrator is introduced to the damping element of VSG,which enables the realization of non-error frequency adjustment and secondary frequency with multiple inverters.It uses local information of the inverter and improves the dependability of the system.In addition,multi-inverter participation facilitates the allocation of power shortage of microgrid according to the capacity each inverter.In this manner,the extension of the total frequency regulating capacity is possible.For the excitation controller,the distributed control thought is introduced to implement the secondary voltage control.With the help of the nearest-neighbor communication,a new method based on reactive power consensus of the multi-agent model is proposed.Through evaluating the average reactive power of the whole network,it can regulate the microgrid voltage to its nominal value while maintaining the reactive power sharing among the VSGs.The distributed architecture allows for flexibility and redundancy and eliminates the need for a central microgrid controller.To verify the effectiveness and correctness of the above control strategies,some simulated and experimental results are carried out.更多还原