【作者】 刘晓杰；

【导师】 孙丽；

【作者基本信息】 哈尔滨工业大学 ， 能源动力（专业学位）， 2022， 硕士

【摘要】 微电网作为开发利用可再生能源的有效方式之一,在世界各国得到了广泛的关注。然而,微电网内分布式电源、电力电子设备和非线性负载的接入会产生大量的谐波,这些谐波严重影响了系统的输出电能质量。因此,设计有效的谐波补偿策略是保证微电网稳定运行的关键所在。而传统的微电网谐波补偿策略中一般采用的是基于周期采样的分布式二次控制方式,即每隔一个固定的采样周期都会进行一次数据的采集和信息的传输,这势必会在控制过程中会产生大量的通信冗余信息,并对有限的通信带宽造成不必要的占用。本文以孤岛交流微电网为研究对象,针对其电压谐波补偿和分布式二次控制通信问题,开展了以下研究:建立了三相逆变器的数学模型,分析了恒功率控制、恒压恒频控制和下垂控制等三种逆变器的基本控制策略,并对基于下垂控制的微电网一次控制层进行了详细的建模和分析。针对下垂控制无法抑制微电网内电压谐波的问题,分析了基于并网逆变器的谐波补偿原理,为后续实现微电网内电压谐波补偿奠定了理论基础。精确地对各阶电压谐波进行检测是实现微电网谐波补偿的关键,本文详细分析了基于多二阶广义积分器锁频环的谐波检测原理。该方法利用二阶广义积分器的带通滤波特性实现对电压各阶谐波分量的初步检测,并利用锁频环对其中心频率进行调整,以消除频率波动对滤波效果的影响。通过并联多个二阶广义积分器并加入交叉对消网络,可以实现各阶谐波分量的解耦控制,从而有效避免了低次谐波之间的互相扰动,进一步提升了谐波检测的准确性。仿真结果表明,采用该谐波检测方法可以快速准确地提取出输入电压中的各阶谐波信号。针对基于周期采样的微电网谐波控制中存在的通信负担过重问题,本文提出了基于事件触发的分布式谐波控制策略。该策略通过设置一个事件触发条件来决定是否进行谐波控制器的更新和通信,因此系统可以根据控制目标当前的状态自适应调整其采样频率,从而有效减少了通信冗余信息的产生,实现了对系统的计算和通信资源的高效利用。通过构建李雅普诺夫方程证明了所提事件触发控制策略的全局稳定性,并分析了任意两个事件间存在最小时间间隔,排除了芝诺现象。针对微电网内线路阻抗不一致引起的循环谐波电流问题,本文额外设计了基于动态一致性算法的谐波电流均衡控制环路,可以在实现微电网电压谐波补偿的同时,有效抑制循环谐波电流的产生。在RT-LAB实验平台上搭建了微电网的实验模型,在不同工况下对本文所提控制策略进行了有效性和鲁棒性验证。更多还原

【Abstract】 The microgrid,as one of the effective ways to utilize renewable energy,has caught common attention recently.However,a large number of harmonics will be generated because of the increasing proliferation of distributed generations,power electronic devices and nonlinear loads in the microgrid,which seriously deteriorate the output voltage quality.Therefore,designing an effective harmonic compensation strategy is the key to ensuring the stable operation of the microgrid.The traditional harmonic compensation strategy usually adopts a distributed secondary control method based on periodic communication,that is,data collection and information transmission are performed every fixed sampling period,which will generate a lot of redundancy information.And the limited communication bandwidth will also be unnecessarily occupied.This dissertation aims at the problem of voltage harmonic compensation and redundant communication,the major researches are listed as follows:The mathematical model of the three-phase inverter is established and its basic control strategies are analyzed.Detailed analysis of the primary control layer is carried out based on the droop control.Aiming at the problem that the droop control can not suppress the voltage harmonics,the principle of harmonic compensation based on the grid-connected inverter is analyzed in detail,which could effectively improve the output power quality.Accurate detection of harmonics is the key to realizing harmonic compensation.The principle of harmonic detection based on multiple second-order generalized integrator-frequency locked loop is analyzed in detail.This method makes use of the band-pass filtering characteristics of the second-order generalized integrator to realize the preliminary detection of the voltage fundamental and harmonic components.And the frequency locked loop is used to adjust the center frequency adaptively,which eliminates the influence of frequency fluctuation on the filtering effect.In addition,by connecting multiple second-order generalized integrators in parallel and adding a cross-cancellation network,the decoupling control of harmonic components of each order can be realized,thereby effectively avoiding the mutual disturbance between low-order harmonics and further improving the accuracy of harmonic detection.The simulation results show that the harmonic detection method based on the proposed strategy can extract the voltage fundamental and harmonic components quickly and accurately.In terms of redundancy information caused by the periodic sampling control in the existing islanded microgrid,a distributed harmonic compensation control strategy based on event-triggered control is proposed.The proposed strategy determines whether to trigger the harmonic controller by setting the event-triggered condition.The controllers will only be triggered to execute the data collection and signal transmission when the predefined event-trigger condition is satisfied.Therefore,The system can adaptively adjust its sampling frequency according to the current state of the control target,which effectively reduces the generation of redundant communication information and greatly saves the computing resources and communication bandwidth of the system.The global stability of the proposed strategy is proved by Lyapunov stability theory,and the Zeno phenomenon is ruled out by analyzing the existence of a minimum interval between any two events.In addition,in terms of the circulating harmonic current caused by inconsistent line impedance of the microgrid,a harmonic current sharing loop is proposed based on the consensus protocol,which could effectively eliminate the circulating harmonic current.An island AC microgrid test system is built on the RT-LAB experimental platform.The experimental results demonstrate that the proposed event-triggered strategy could effectively compensate for harmonic voltage under different working conditions.更多还原