【作者】 程路；

【导师】 陈乔夫；

【作者基本信息】 华中科技大学 ， 电机与电器， 2008， 博士

【摘要】 本文在总结当前谐振接地系统研究现状的基础上,针对中性点经消弧线圈接地电网存在的主要问题,重点从消弧线圈本体、即可调电抗器的结构和控制,谐振接地系统的自动调谐和单相接地故障选线三个方面展开研究。现有的消弧线圈主体结构及控制方式均存在一定的缺陷,如电感不能快速连续调节或是谐波比较严重等,影响了消弧线圈的补偿效果,使其应用受到一定的限制。针对这些问题,本文提出了一种新型的可调电抗原理及控制方法。这种新颖的电抗调节方法的基本原理是:使用电压型PWM逆变器作为变压器二次侧的负载,通过对负载电流的控制,可以实现变压器一次侧等效阻抗的任意调节。其核心是PWM逆变器的输出电流对变压器一次侧电流的跟踪控制,本文对逆变器及变压器建立了整体的控制系统模型,推导了系统的稳定判据及该控制方式下逆变器直流母线电压的设计原则,并运用仿真工具分析了电流跟踪的稳态性能和动态性能,提出了适用于本系统的电流跟踪控制方法。通过采用变压器二次侧多绕组的结构,还可以大大提高可调电抗器的容量。实验结果证明该新型可调电抗器具备电感线性连续可调、响应速度快、谐波电流小的优良性能,这也是消弧线圈补偿装置所追求的理想性能。准确检测电网对地电容是谐振接地系统有效补偿的基础。注入变频信号法具有不需要启动电感调节装置,不改变系统运行状态,二次回路测量等诸多优点,是目前应用较多的一种检测方法。但中性点位移电压的存在会影响注入信号的质量,同时给注入信号的相位判断带来困难。针对这些问题,结合变压器负载可控型消弧线圈的结构特点,首次构建了电网不对称时注入信号的电路和控制系统模型。基于对控制模型的分析,提出了一种新的注入变频信号的消弧线圈自动调谐方法:通过电压前馈校正控制的引入,有效抑制了50Hz工频电压对注入信号的干扰,使得注入信号不受电网不对称及中性点位移电压的影响;提出以中性点注入信号电压幅值最大做为新的谐振判据,有效提高了谐振状态判断的灵敏度和准确度。实验结果证明,所提方法极大的提高了不对称电网及中性点位移电压异常升高系统的电容检测精度,对各种形式的电网均具有良好的适应性。谐振接地电网的故障选线问题一直以来没有得到很好的解决。本文在总结了谐振接地电网现有的选线方法及最新进展的基础上,对应用广泛的基于零序电流有功分量的选线方法进行了重点分析,论述了线路对地电容不平衡对零序有功电流方向的影响,以此提出了一种新的基于零序有功分量的选线方法。该方法以线路瞬时功率的直流分量作为零序有功判据,解决了传统零序有功分量法信号小、检测困难等问题;针对线路不平衡电流对零序有功方向辨别存在的干扰问题,提出利用零序电流变化量与零序电压变化量之间的相角作为辅助判据的解决方法,并提出了一种计算该相角的算法。消弧线圈补偿与选线一体化并协调控制是谐振接地电网的发展方向。结合本文提出的基于瞬时功率的直流分量的选线方法及变压器负载可控型消弧线圈所具备的电阻调节特性,提出接地故障后微调消弧线圈等效电阻的控制方法,以增大故障线路的零序有功分量,使得故障特征更为明显,有利于提高选线判据的准确性。仿真研究证明所提方法原理可行、实现简单,对于高阻接地和线路不平衡的情况,亦能准确选线。在补偿电容电流的同时实现故障选线,构成了一体化的接地补偿与保护装置。研制了一套800kVA变压器负载可控型消弧线圈补偿装置,设计了基于DSP和CPLD微处理器的数字控制系统。对系统软硬件设计方面的关键问题进行了研究,提出了多种实用的硬件改进方法和软件优化算法,包括PWM触发脉冲抗干扰、开关噪声抑制、缓冲电路设计以及提高电流跟踪性能的核心控制算法等,理论分析和实测波形验证了所提方法的有效性。首次对800kVA消弧线圈样机进行了完整的三相动模试验,试验结果表明,该新型消弧线圈成套装置具备电容检测精度高、补偿范围广、响应速度快、谐波电流小等一系列的特点。经国家权威鉴定机构认定,其各项性能均能满足国家标准。目前10kV系列产品已挂网运行,情况良好。可以预见这种新型消弧线圈接地系统在我国城网改造中有着广阔的应用前景。更多还原

【Abstract】 On the basis of comprehensively summarizing the current development and unsolved problems in neutral resonant grounding power system, this dissertation focus on following three parts to carry out studying, these are: new structure and control method of variable reactor, automatic tuning of resonant grounding system and fault line detection in single phase to ground faults.The existing structures and control strategies of variable reactor have some drawbacks, such as the inductance can not be regulated rapidly and continuously or generate serious harmonics. These shortages take negative influence on arc-suppression coil, which limit the compensation effect in practical application. Aim at these problems, a novel variable reactor structure with its control method has been proposed in this dissertation. The reactance tuning principle of this reactor is: using voltage source PWM inverter to be the secondary load of linear transformer, by controlling the inverter’s output current, which is also the transformer’s load current, the equivalent impedance of transformer’s primary winding can be regulated arbitrarily. The key point of this method is real-time control of inverter’s output current, which should trace transformer’s primary current rapidly and accurately. The holistic control model concerning the inverter with the transformer is founded. By analyses on the model, the criterion of system stabilization and design principle of the inverter’s DC link voltage are derived. Furthermore, the steady-state performance and dynamic performance of current tracing are analyzed by simulation tools, on the basis of which an effective arithmetic for this control system is presented. Large capacity variable reactor can be realized by adopting the structure of transformer with multiple secondary windings. Experimental results verified the excellent characteristic of this new type reactor, such as reactance linear and continuous tuning, fast response and few harmonic currents, which are also the ideal performance pursuing in arc-suppression coil application.Accurately detection of distribution network line-to-earth capacitance is the fundamental of effective compensation in neutral resonant grounding system. Injecting variable-frequency signal method has many advantages such as no need to adjust inductance of arc-suppression coil, unchanging running status of power utility, secondary measurement, etc, which is a widely used method in capacitive current detection. However, the existence of neutral point displacement voltage could take influence on the injected signal, which may make the phase judgement inaccurate. These problems have been analyzed basing on the presented novel arc-suppression coil. The equivalent circuit and control model of injecting signal method in unbalanced power networks are given out for the first time. With analysis on the control model, an improved automatic tuning method for arc-suppression coil is proposed, that is: adopting voltage feed forward control to restrain interfere of 50Hz displacement voltage, which can improve the characteristic of the injected signal significantly, make the injected signal without reference to unbalanced network and neutral displaced system. Another innovation is detecting the magnitude of neutral point signal-frequency voltage to judge the resonant state, which improves the sensitivity and accuracy of resonant judgement effectively. The experiments verified that the proposed method faithfully enhanced the capacitance detection capability and precision in unbalanced network or neutral with high displacement voltage network, which proved to have excellent adaptability in all type distribution networks.The fault line selection problem in neutral resonant grounding distribution network has not been well settled until now. On summarizing current fault line selection techniques and state-of-art developments in resonant grounding system, the technique based on zero-sequence active current is mainly researched in this dissertation. By analyzing the influence on the zero-sequence active current polarity while line-to-earth capacitance is unbalance in distribution network, a new fault-line selection method based on zero-sequence active power have been proposed. This method uses the DC component in line instantaneous power to be the criterion, which effectively solved the problem of precise detection of small active signal. To eliminate the interfere of inherent unbalanced current in the feeder, an auxiliary criterion is presented, which used the angle between zero-sequence varied current with zero-sequence varied voltage to judge the direction of active power. Additionally, arithmetic to calculate the phase angle has been proposed in the dissertation.A trend in the resonant grounding system is to make an integrated and coordinated control between the compensation of arc-suppression coil and the single phase to ground fault line selection. A new control strategy is presented by combining the proposed fault line selection method with the unique feature of resistance tuning capability of the novel arc-suppression coil. The fundamental principle is that properly varying the equivalent resistance of the arc-suppression coil to increase the active component in the fault line, which make the character of the fault line more evident, lead to the advance of high selection accuracy. Simulation results proved the validity and practicability of the presented method, the accuracy is satisfactory even in high-resistance grounding situation and in unbalanced system. The fault line selection is synchronous with capacitive current compensation, which fulfills an integrated compensation and protection equipment.A prototype based on the transformer with load controllable theory has been constructed, the capacity of which is up to 800kVA. A full digital control system based on DSP and CPLD microchip has been developed. The pivotal aspects in hardware and software design have been researched and discussed. Manifold optimized techniques in system design have been proposed, e.g. anti-jamming of PWM trigger signal, suppression of switching noise, design of snubber circuit and some kernel control arithmetic. The actual waveforms verified the validity of the proposed improvements.Three phase simulative experiments have been carried out on the 800kVA prototype. Experimental results proved that the novel arc-suppression apparatus has the characteristic of high precision in capacitance detection, wide compensation range, fast response and few harmonics. Authorized by national professional identify institution, the performances of this new type arc-suppression coil satify national standards. Now the 10kV series products have been well running in the power utility, it can be anticipated that this new arc-suppression coil grounding system have expectable future in medium-level distribution networks.更多还原