分布式非线性负载谐波阻尼特性及其对系统谐波谐振影响的研究

Power system harmonic issue is always the concern. Massive loads equipped with power electronic converter are turning the linear harmonic damping characteristic of loads to the nonlinear one, and weakening the damping effect on the system harmonic resonance..This project proposes to conduct research on the nonlinear damping characteristics of this type of loads, reveal the mechanism of harmonic damping of nonlinear loads and the coupling effect with voltage distortion and the damping effect on the power system harmonic resonance. The research will focus on the analytical harmonic frequency model and study the composition of nonlinear load damping factors and the factors affecting the damping characteristics, by introducing the concept of controlled virtual harmonic damping and employing the multi-factor analysis method and nonlinear regression method. The form of uniform damping model and the modelling method for nonlinear loads then will be proposed. With the help of the proposed model and Monte-Carlo method, the massive simulation studies will be conducted to investigate the effects of nonlinear loads on the harmonic resonance. Based on above mentioned research results, a method for identifying harmonic resonance source, which is a system component, will be proposed by borrowing the Blind Signal Separation theorem and harmonic resonance mode method. All the analysis and simulation results will be verified by experimental or field measurements..The proposal raises a foresight power quality problem. The objective of this research is to establish the entire approach, including modelling, theory and analysis method, to study nonlinear harmonic damping problems and prevent power system from harmonic stress caused by reduced load damping ability. The achievement of this project is also beneficial to the design of power electronic devices, application of capacitor banks and assessment of system transient process.

配以电力变换器前端负载的大量使用，改变了传统线性负载的阻尼性质，导致系统谐波谐振阻尼弱化。本项目提出对该类负载的非线性谐波阻尼特性展开研究，揭示其谐波阻尼产生机理、与系统电压的耦合关系、对系统谐波谐振的阻尼效应。基于这类负载的频域模型，引入受控虚拟阻尼概念，采用多因素分析和非线性回归方法，研究负载阻尼构成和影响因素，提出可用于谐波阻尼研究的负载阻尼模型表述方式和构建方法；借助负载谐波阻尼模型，采用蒙特卡洛法模拟该类负载在配电系统中的不同分布，研究系统谐波谐振阻尼弱化状况；结合盲信号分离法和谐波谐振模态概念，提出谐波谐振源评估指标和方法。理论分析和仿真结果通过实验实测数据验证。本项目是具有前瞻性的配电系统电能质量问题，拟提出一套探索非线性阻尼问题的模型、理论和方法；研究成果可有效预防日趋严重的配电系统弱阻尼问题，对电力变换器设计、系统中并联电容器应用、电磁暂态过程长短判断等均有积极的意义。

配电系统由大量阻、感和容性元件组成。当系统局部容、感元件契合时，在谐波源作用下，产生局部谐波谐振。传统配电系统中大量线性负载具有较强谐波阻尼，系统局部谐振强度因此受到抑制。目前大量负载配以变换器前端，成为非线性负载，极大降低系统中线性负载比例，是否会严重弱化系统谐波阻尼值得研究；同时，如何评估PCC点谐波电压成因（即由于谐波源或谐波谐振），以寻求合适的谐波抑制方法，也是亟待探讨的课题。.项目主要研究内容及结论：（1）研究变换器类单相负载谐波阻尼特性的统一谐波频域模型描述方式，并在此基础上研究该类负载的谐波阻尼影响因素及模型构造方法。该研究对非线性负载的基波和谐波阻尼进行了定义，建立了带变换器单相负荷的解析谐波阻尼模型，分别针对基波和主要低次谐波，解析分析了其阻抗表达式构成，对谐波阻尼特性主要影响因素进行的研究表明，在常规平顶畸变电压波形下，单相非线性负载在谐波频率显现比基波阻尼稍强的阻尼特性。（2）研究配电系统含有不同规模和分布的变换器负载时，局部谐波谐振条件下的负载阻尼状况及其与系统元件和谐波源的交互影响。该研究利用单相变换器负荷谐波阻尼模型，对其谐波阻尼在不同系统参数下的特性进行了研究，主要结论为该类负载的谐波阻尼比基波阻尼受到系统谐波环境的影响更大，在局部谐波谐振电路中引发较小的谐振频率偏移，且偏移量随负载增加而变大；对某次谐波而言，谐振点越接近谐波频率，谐振阻尼越强，仿真和实验证实了该类负荷对谐波阻尼的影响。（3）基于系统电压电流测量数据，研究PCC点谐波电压的成因（谐波负荷或者谐波谐振）及评估的方法。该研究基于系统侧谐波电压源和负荷侧谐波电流源的假定，结合单相变换器类负荷的谐波电流特性，分析PCC点两侧网络函数，提出了基于PCC点电流电压测量数据的3次谐波成因辨识方法，通过仿真实验对该方法进行了验证。.该项研究及相关结论对配电系统谐波谐振及抑制方法研究的进一步开展提供了理论依据。