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类型 基础研究 预答辩日期 2017-12-07
开始(开题)日期 2016-05-19 论文结束日期 2017-10-27
地点 动力楼102 论文选题来源 省(自治区、直辖市)项目    论文字数 6 (万字)
题目 弱电网条件下多逆变器并联控制关键技术研究
主题词 弱电网,多逆变器并联,锁相环,稳定性,协调控制
摘要 如何实现电能的可靠供应以及保障供电质量,是目前国内外学者的研究热点。电能供应方面,以光伏、风电等为主要代表的新能源发电技术是应对化石能源危机、解决环境保护问题的有效途径。供电质量方面,以高度可控和快速响应为主要特性的有源电力滤波器、静止无功发生器等有源型滤波装置,是改善电能质量的理想方案。随着风力发电、太阳能发电的占比逐年升高,以及电网中其他非线性电力电子设备的广泛使用,采用多逆变器并联技术是新能源发电、有源滤波装置实现容量扩展的最佳途径,但是需要解决多逆变器间的协调、稳定性、开关次纹波抑制等关键技术问题。大量光伏、风力发电的远距离电能输送、多级升压必然会导致电网阻抗的增加,并且这些新能源发电的集中或分布式并网会给电网带来闪变、谐波污染等问题。除此以外,大量冲击性负荷(例如电弧炉、轧钢设备等)的投入使用,导致电网公共点电压的幅值、相位和频率都有可能发生突变。上述三方面问题将导致电网呈现弱电网特性,即:1)电网阻抗不可忽略,且随电网的运行方式变化;2)并网点电压存在严重的背景谐波。一方面,非线性电力电子设备的广泛使用,将会使得电网呈弱电网特性;另一方面,弱电网特性将反过来影响新能源并网、电能质量治理等应用场合下逆变器的控制性能,例如:弱电网条件下,由于存在不平衡分量及谐波分量,作为逆变器控制关键技术之一的锁相环,其电网同步性能将会受到影响;由于电网阻抗不可忽略,并联系统中的逆变器间通过电网阻抗交互耦合,容易产生失稳现象。本文选取电能质量治理为应用背景,针对多逆变器并联控制关键技术展开研究,综合考虑弱电网存在背景谐波、电网阻抗不可忽略的特性,围绕电网同步、稳定性分析及控制、并联协调控制以及高频开关次纹波抑制策略展开研究,为实现多逆变器并联系统的高效、可靠运行提供技术支持。 首先,在弱电网条件下的电网同步策略方面:提出了基于多前向数字复数谐振器的单三相通用电网锁相方法。将单三相输入信号通过各自信号变换统一为复数信号,从广义频域角度分析复数周期信号,得出其本质为各正、负频次旋转复数量的叠加,单三相通用锁相环的本质是提取其中的基波正序分量即+1频次分量。前置滤波环节采用由多前向数字复数谐振器构成的闭环结构,+1频次谐振器输出作为滤波器输出。通过广义频域分析可看出,该结构对+1谐振频次分量即基波正序分量无静差输出,其他谐振频次分量无静差滤除,谐振频次以外分量近似一阶低通带宽外滤除。复数谐振器本质是由复数积分器频移得到,其中前向数字复数谐振器构成闭环结构不形成代数环,可实际实现。另外,还介绍了前向数字复数谐振器的相关运算简化方法,包括基于k阶泰勒展开的谐振因子运算简化、单相系统的运算简化。另外,从多逆变器并联系统层面出发,分析了锁相环与电网阻抗、输出电流、PCC电压的耦合关系,定性分析了锁相环与并联系统稳定性的关系。 其次,在考虑电网阻抗不可忽略条件下的多逆变器并联稳定性分析及控制策略方面:提出了基于全局导纳频域分析的稳定性判据、失稳责任评估及抑制方法。通过建立全导纳形式的并联系统两端口诺顿等效电路,得到了电网阻抗不可忽略条件下的并联系统电流响应表达式;从全局导纳频域特性的角度,揭示了多模块并联系统存在失稳现象的本质原因;以改善全局导纳谐振点阻尼特性为目标,提出了基于导纳重塑的失稳抑制方法;进一步的,提出了弱电网条件下公共点处多逆变器并联谐振失稳评估及定责方法,将每台逆变器对并联系统失稳造成的影响进行量化,得到了单台逆变器对某频次失稳谐振点的定量责任因子,从而实现了并联系统中各台逆变器谐振失稳责任的有效评估和划分。 然后,在多模块并联系统协调控制策略方面:提出了开环多机均流+闭环多机分次相结合的谐波补偿方式,整机系统采用单CT采样、双补偿点并网,并介绍了相应的实现方法;考虑实际非线性负载的谐波含量及频谱分布,提出了多模块并联系统的动态协调控制方法,实现了整机补偿系统容量利用及补偿精度的综合优化;利用电流环生成的调制波信号,以一个系统周期内的最大调制比为控制对象,提出了基于直流侧电压控制的多模块并联系统功率损耗与补偿精度综合优化策略,在满足补偿精度要求的前提下,最大限度降低并联系统的功率损耗,使得整机补偿系统的综合性能达到最优。在开关次纹波抑制方面,介绍了4B-LCL型并网接口,以及有源载波移相+无源滤波相结合的多模块并联系统开关次纹波抑制策略。 最后,在实验平台设计和实验结果分析方面:介绍了三相四桥臂式(3P4L)主电路拓扑结构、功率器件及驱动模块,给出了四支路LCL型并网接口参数设计方法;介绍了基于DSP+FPGA双核心架构的控制系统,包括控制器结构、主要元器件以及多模块并联冗余故障重启策略;分别针对前文所提出的电网同步、开关次纹波抑制、多模块并联谐波补偿策略进行了验证,实验结果进一步说明了所提方法的有效性和合理性。
英文题目 Research on the Key Techniques of Parallel Control for Multi-Inverters Under Weak Grid Condition
英文主题词 Weak Grid,Paralleled Multi-Inverter System,Phase-Locked Loop,Stability Analysis and Control,Coordinated Control
英文摘要 The method of achieving reliable power supply and guaranteeing the power quality is currently a research hotspot for domestic and foreign scholars. In terms of power supply, as the main representative of renewable energy sources, photovoltaic or wind power is an effective way to deal with the fossil energy crisis and solve the environmental protection problems. In terms of power quality, due to a high controllability and rapid dynamic response, active power filter (APF), static var generator (SVG) and other active filter device, are the optimal solutions to improve the power quality. With the proportion of wind power and photovoltaic generation increasing year by year, and the popularization of other non-linear power electronic equipment, the paralleled multi-inverter system is the best way to expand the capacity. However, some key technical issues such as coordination control for multi-inverters, stability analysis and instability suppression, and ripple suppression need to be solved. The long-distance power transmission and multi-stage voltage transformation of photovoltaic and wind power will inevitably lead to the increase of power grid impedance. And these renewable energy sources with centralized or distributed grid-connection will bring flicker, harmonic pollution and other issues to power grid. In addition, a large number of impact loads (such as electric arc furnace, rolling equipment, etc.) are put into use, which results in the potential mutation of amplitude, phase and frequency of PCC voltage. The above problems will result in the following characteristics of the power grid: 1) grid impedance cannot be ignored, and changes with the operation of the grid; 2) there are serious background harmonics in the PCC voltage. On the one hand, the widespread use of non-linear power electronic devices will lead to the weak grid characteristics. On the other hand, the weak grid characteristics will affect the control performance of inverters under the application of new energy generation and power quality control. Under weak grid condition, due to the existence of unbalanced and harmonic components, the synchronization performance of PLL will be affected,which is one of the key technologies of the inverter. Due to the non-negligible grid impedance, the inverter in the parallel system is coupled with each other, which is prone to instability. This paper selects power quality control as the research background and studies the key technology of paralleled multi-inverters including grid synchronization, stability analysis and control, coordination control and ripple suppression strategy under weak grid condition. Firstly, a novel unified digital PLL with multiple complex resonators for both single- and three-phase systems is proposed. Single-phase and three-phase voltage signal is transformed uniformly to a similar complex form that consists of positive and negative sequence components rotating in clockwise and counterclockwise directions, respectively. And synchronous rotating frame PLL with a generalized pre-filter is introduced. The proposed filtering structure consists of multiple complex resonators that can filter out harmonic frequency components and maintain fundamental positive sequence components accurately. Furthermore, a simplified structure of the complex resonator for single-phase system and an operation method for resonant factor are introduced. Secondly, stability analysis and control strategy is put forward based on the global stability criterion. By establishing the two-port NORTON equivalent circuit, the current response expression of the parallel system is obtained. From the perspective of global admittance frequency domain, the paper reveals the intrinsic reason of instability in paralleled multi-modules system. In order to improve the damping property of the global admittance resonance point, a method of instability suppression based on admittance is proposed. Further, an assessment method for instability is proposed, which quantizes the influence of each inverter on instability. Then, the coordination control strategy combining open-loop with closed-loop is proposed. The main feature of improved compensation system includes single CT sampling and double compensation points. The corresponding implementation method is introduced. Considering the harmonic content and spectrum distribution of the actual nonlinear load, the dynamic coordination control method with the optimal utilization is proposed. Based on DC side voltage control strategy, a new optimization method for comprehensive optimization of power loss and compensation precision is proposed. In the case of ripple suppression, the four-branch LCL-type (4B-LCL) filter is introduced, and the strategy combining active carrier phase shift with passive filter is proposed. Finally, the experimental platform and analysis of the experimental results are introduced. The parameters design method of four-branch LCL-type grid interface is proposed. Dual-core control system based on DSP and FPGA is introduced, including the structure, the main components, and restart procedures under redundant fault conditions. The experimental results further illustrate the effectiveness and rationality of the proposed methods.
学术讨论
主办单位时间地点报告人报告主题
东南大学 2014年10月9日 动力楼126 刘康礼 三相负荷不平衡治理技术方案
东南大学 2015年5月5日 动力楼316 张小平 全球电力能源互联网关键技术与挑战
东南大学 2016年5月10日 动力楼316 陈建妃 Beyond Technology: Why Social-Psychological Factors are Important in the Interdisciplinary Research of Energy and Technology
东南大学 2016年5月18日 动力楼110 刘康礼 多机并联型大容量APF相关技术
东南大学 2016年5月27日 动力楼316 文福拴 能源互联网及电转气技术的成本特征与运营经济性分析
东南大学 2016年9月25日 动力楼110 刘康礼 有源电力滤波器研究进展
东南大学 2017年4月20日 动力楼126 刘康礼 电压质量治理-国内外新技术与新设备的研究现状与趋势
东南大学 2017年7月20日 大礼堂 春晖堂 Thomas M. Jahns Understanding PM Machine Fault Behavior and the Impact of Excitation on Mitigation Techniques
     
学术会议
会议名称时间地点本人报告本人报告题目
The 2nd IEEE Southern Power Electronics Conference 2016年12月7日 新西兰.奥克兰大学 Optimized Current Control and Dynamic Coordination Strategy for Large-capacity Harmonic Compensation System
IEEE 8th International Power Electronics and Motion Control Conference 2016年5月23日 中国.合肥 Improved Parallel Operation for Multi-modular Shunt APF Using Dual Harmonic Compensation Loop
     
代表作
论文名称
Unified Digital Phase-Locked Loop with Multiple Complex Resonators for Both Single- and Three-phase
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
周波 正高 教授 博导 南京航空航天大学
赵晋泉 正高 教授 博导 河海大学
金龙 正高 教授 博导 东南大学
顾伟 正高 教授 博导 东南大学
陈武 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
杨燕 其他 讲师 东南大学