【作者】 张波；

【导师】 颜湘武；

【作者基本信息】 华北电力大学(北京) ， 电力电子与电力传动， 2018， 博士

【摘要】 随着可再生能源在电网能源构成中所占比例的不断增加,电力系统正在逐步由集中式发电向分布式发电转变,大量的分布式电源通过电力电子变流装置接入电网,由于其缺乏传统同步发电机具有的转动惯量和系统阻尼,给电力系统安全稳定运行带来了巨大的挑战。虚拟同步机技术使得分布式电源或可控负荷在模拟同步发电机转动惯量的同时还具备了参与系统一次调频、调压的能力,从而实现对系统稳定运行的自主维护,对解决分布式发电系统的频率、电压稳定问题具有重要意义。本文依托国家高技术研究发展计划“863计划”项目“新型太阳电池、组件和系统部件技术”的课题“光伏微电网核心设备与控制系统研制及示范应用”(2015AA050603)和河北省自然科学基金项目“微网系统自同步电压源逆变器并联技术研究”(E2015502046),以分布式发电系统一次调节和惯量控制为核心问题开展研究,重点研究了计及源端动态特性的虚拟同步机控制策略,不同控制形式的分布式电源同步调节特性及其惯量匹配原则,然后建立了虚拟同步机多机并列系统的高精度小信号模型并进行了虚拟同步机核心控制参数的稳定性分析,最后搭建了基于dSPACE实时仿真系统的虚拟同步机半实物实验平台对相关控制方法进行了实验验证。本文主要研究内容和成果如下:(1)分析了可再生能源高渗透率的分布式发电系统面临的稳定性问题,以及系统一次调节和惯性支撑能力对系统频率和电压稳定运行的影响,对虚拟同步机基本思想、技术沿革、典型应用、发展方向等方面进行了梳理归纳,总结了虚拟同步机目前仍需深入研究的关键问题以及未来相关技术发展趋势。(2)提出了光伏运行工作点跟踪方向可变的变功率点跟踪控制方法,并阐述了该方法的具体实施过程,该方法在光伏阵列输出功率不足时能够保持MPPT的控制特性以实现对系统的最大功率支撑,而在光伏阵列输出功率过剩时能够自适应调节光伏输出以维持系统功率稳定;进而提出了基于变功率点跟踪控制的光伏虚拟同步机控制策略,该策略考虑了虚拟同步机源端分布式能源随机性和波动性对虚拟同步机输出特性的影响,克服了基于传统MPPT控制的虚拟同步机在光伏输出功率过剩时容易造成系统功率失衡、直流母线电压崩溃的技术缺陷。(3)建立了传统下垂控制DG逆变器与虚拟同步机相统一的数学模型,分别实现了下垂控制方程与转子运动方程、下垂控制系数与惯性时间常数在物理意义上的统一;研究了分布式发电系统在遭受负荷扰动或源端出力扰动后系统频率和功率动态调节过程的物理本质,指出了系统受到小干扰后维持稳定运行本质上取决于转子角加速度和转子相对角速度是否同时为零;提出了两台SG并联系统、两台VSG并联系统、下垂控制DG逆变器与VSG并联系统三种典型分布式电源并联结构的扰动功率分配规律和相应的核心控制参数配置原则;针对分布式电源多机并列系统频率和功率暂态同步性和一致性问题,提出了分布式发电系统多机并列运行惯量匹配方法。(4)提出了包含控制系统中所有中间控制环节状态变量的VSG单机以及VSG多机并列系统的小信号精确模型建立方法,该模型以基于虚拟阻抗和电压电流双闭环控制的VSG控制策略为对象,实现了对主电路参数、下垂控制参数、虚拟惯量参数、双闭环PI调节器参数、线路阻抗参数、虚拟阻抗参数等VSG核心参数进行准确的系统特征根轨迹分析及灵敏度分析,为VSG单机及VSG多机并列系统稳定性分析奠定理论基础,同时为VSG相关参数优化设计提供基本设计原则和稳定性判据。(5)在实验室环境下搭建了基于dSPACE实时仿真系统的VSG半实物实验平台,分别针对VSG单机独立运行和VSG双机并联两种工况,在不同特性负荷扰动、并离网切换情况下实验分析了虚拟同步机一次调频、一次调压、转动惯量、功率解耦、负荷功率分配等特性,验证了本文提出的分析方法和控制策略的正确性。更多还原

【Abstract】 With the increasing proportion of renewable energy in the energy composition of the grid,power system is gradually changing from centralized generation to distributed generation.A large number of distributed power sources are connected to the power grid through power electronic device,which poses an enormous challenge to the safe and stable operation of power systems because the device lacks inertia and damping as the traditional synchronous machines.The virtual synchronous machine technology enables the distributed power sources or controllable load to participate in the primary frequency modulation and voltage regulation of the system while mimicing the rotational inertia of the synchronous machine.Thus,it realizes the independent maintenance of the stable operation of the system,which is significant for solving the problems of frequency and voltage stability of distributed generation systems.With the support of National High-tech R&D Program(863 Program)"Development and Demonstration Application of Photovoltaic Microgrid Core Equipment and Control System"(2015AA050603)and Hebei Province Natural Science Fund Project "Research on Parallel Technology of Self-Synchronous Voltage Source Inverter in Microgrid"(E2015502046),the key technologies for the primary regulation and inertial control of distributed generation systems are focused on in this work.The virtual synchronous machine control strategy with considering the dynamic characteristics of primary source,and the synchronous regulation characteristics analysis method and inertia matching principle of distributed power sources with different control forms have been further studied.And then a high-precision small-signal model of multi-VSGs parallel system was established.Moreover,the stability analysis of the core control parameters of VSG have been performed.An semi-physical experimental setup based on dSPACE has been designed to demonstrate the excellent performance of the proposed control strategies and analyzes methods.The main research contents and achievements of this work are presented as follows:(1)The stability problem of distributed power generation system with high permeability of renewable power sources is studied.Meanwhile,the influence of primary regulation and inertial support ability to system frequency and voltage stable operation is analyzed.Then the general idea,evolution of technology,typical applications and development directions of the virtual synchronous generators are combed and summarized.The key issues of synchronous generator that need to be further studied and the related technology development trends in the future are summarized in this work,respectively.(2)A variable power point tracking(VPPT)control method with a variable tracking direction of the PV operation point is proposed,and then the specific implementation process of the method is described.The method can follow the MPPT control to realize the maximum power support for the grid when the output power of the PV array is insufficient,meanwhile,it also can adaptively adjust the PV output power to keep the grid power stability when the output power of the PV array is adequate.In addition,a photovoltaic virtual synchronous generator control strategy based on VPPT control is proposed,with consider of the influence of randomness and volatility of the renewable energy.The strategy overcomes the technical defects that the VSG based on the traditional MPPT control can easily cause system power imbalance and DC bus voltage collapse when the photovoltaic power is sufficient.(3)A unified mathematical model of virtual synchronous machine is established by the analogous way of traditional droop control DG inverter,with which the unity in the physical sense is realized between droop control equation and swing equation,and between the droop coefficient and the mechanical time constant.The physical nature of the frequency and power dynamic regulation process of the distributed generation system suffering from load disturbance or source output disturbance is studied.It is pointed out that the system can operate stably after receiving small disturbances essentially depends on whether the angular acceleration and the relative angular velocity of the rotor can be zero at the same time or not.The disturbance power distribution rules and the core control parameter configuration principles of three typical parallel structures of distributed generation such as two SGs parallel system,two VSGs parallel systems,and droop controlled inverter and VSG parallel system are proposed.Aiming at the problems of frequency and power transient synchronism and consistency in multi-generators parallel systems,an inertia matching method for multi-generators parallel operation in distributed power generation systems is proposed.(4)A method for establishing a precision small-signal model is proposed for VSG stand-alone system and VSG multi-machine parallel system,which includes all state variables in the control system.This model takes the VSG control strategy that based on virtual impedance control and voltage-current double-loop control as the object,through which accurate system characteristic root locus analysis and sensitivity analysis can be performed for VSG main circuit parameters such as droop control parameter,virtual inertia parameter,double closed loop PI regulator parameter,line impedance parameter,virtual impedance parameter etc.It lays a theoretical foundation for the stability analysis of VSG stand-alone and multi-VSGs parallel system,and provides basic design principles and stability criteria for the VSG parameter optimization design.(5)A semi-physical experimental platform of VSG based on dSPACE real-time simulation system is built in laboratory.The VSG characteristics such as primary frequency modulation,primary voltage regulation,rotation inertia,power decoupling and load power distribution are analyzed under the conditions such as different load disturbance and in grid-connected or island mode,for single VSG and two parallel VSGs respectively.Furthermore,the correctness of the analysis method and control strategy presented above is verified.更多还原