【作者】 王晓蔚；

【导师】 任士焱；

【作者基本信息】 华中科技大学 ， 电工理论与新技术， 2007， 博士

【摘要】 直流大电流一般用在生产铝、铜、铅、锌、镁等有色冶金系统及生产烧碱的化工系统,这两个系统的企业是国家的支柱产业,也是重点的耗电大户。为了节能降耗,准确测量直流大电流是一个关键环节。长期以来,由于监视、计量、控制企业生产用电的大电流直流在线测量装置缺乏可靠的计量保证,仪器的指示值仅作为参考数值,这直接影响到这类国营大中型企业的节能降耗、经济效益。要改变这种状况,关键的是要集中现有几种测量原理的优点,克服其缺点,从原理上探索出一种新型的直流大电流传感理论与方法。基于这种新原理、新方法的装置要求测量准确性高、抗外磁场能力强、高稳定性、高可靠性。本课题的研究目标是建立一种磁势自平衡回馈补偿式直流大电流传感器。基于这种新原理和新方法的传感器,既具有直流闭环测量原理的优点,又具有直流开环测量原理的优点,测量准确性高,抗外磁场能力强,具有高稳定性和高可靠性的优点。为了对理论研究进行验证,制作了一台10000A/5A的模拟样机,对此模拟样机进行了实验研究。实验结果证明:被测直流中的大部分磁势可由平衡绕组来平衡,剩余磁势由检测回路进行检测并经过运算放大及驱动器后回馈到补偿线圈,就实现了对被测直流磁势和平衡电流磁势差的补偿。当直流大电流传感器用于工业现场时,不可避免地会受到电磁场的干扰,这些干扰会影响直流大电流传感器的正常工作。直流大电流传感器的设计中电磁屏蔽的设计是非常重要的。本文对直流大电流传感器的屏蔽问题做了以下三个方面的研究。首先讨论了直流大电流传感器的屏蔽技术。目前传统的直流大电流传感器均采用铜屏蔽和磁屏蔽的双层防磁结构,外层的铜屏蔽层同时具有对电场和高频磁场屏蔽的作用,内层的硅钢片对低频磁场的磁屏蔽效果很好。用两种材料做成双层屏蔽体可以得到高频磁场和低频磁场都满意的屏蔽特性。屏蔽技术可分为:电场屏蔽、磁场屏蔽和电磁场屏蔽。本章应用等效传输线法推导了屏蔽效能的计算公式。在设计磁屏蔽体时,采用了多通道防磁技术。其次,讨论了应用磁路法对直流大电流传感器磁屏蔽体的磁屏蔽效能进行计算。自从Moore提出了直流大电流传感器的磁屏蔽以来,磁屏蔽效能的计算问题一直是直流大电流传感器设计者所关心的问题。采用较为精确的方法来对磁屏蔽体的磁屏蔽效能作一个较为可靠的计算,具有相当大的现实意义。本文应用磁路法分别推导了外加径向磁场和外加轴向磁场时,磁屏蔽体的磁屏蔽效能的计算公式。为了验证磁路法计算的正确性,本文对直流大电流传感器的磁屏蔽效能进行了测试。因为磁导率μr在铁心上的各个部分并非常数,而是外加磁场强度的函数,为了便于计算结果与测试结果的比较,取外界磁场为20GS时,测试了磁导率的值。将测试所得的磁导率的值分别代入磁路法推导得到的公式。由测试结果和计算结果进行对比分可以得出结论:利用磁路法进行磁屏蔽效能计算,对直流大电流传感器的磁屏蔽效能估算具有一定的指导意义。最后,研究了多通道直流大电流比较仪的通道封闭问题。当多通道直流大电流比较仪的铁心是一个整体时,铁心有剩磁。在被测电流和干扰电流共同作用下,铁心磁化不均匀,当某些铁心分段的剩磁比较严重,该通道可能封闭。为了解决多通道直流大电流比较仪的通道封闭问题,本文设计的多通道直流大电流比较仪,每个通道铁心之间有一段空气隙,以消除铁心的剩磁。本文分析了多通道直流大电流比较仪的带气隙的环形铁心的磁特性。根据基尔霍夫定律可列出多通道直流大电流比较仪的状态方程,应用谐波平衡原理求解该非线性电路方程,从而得到多通道直流大电流比较仪的开环传输特性。由带气隙和不带气隙的直流大电流比较仪的开环特性计算曲线可以看出:当多通道直流大电流比较仪采用带气隙的环形铁心时,由于磁阻增加,在相同的输入安匝下,其输出直流电压要小一些。多通道直流大电流比较仪的磁路中开了气隙后,可减少铁心非线性的影响。但磁路中加入气隙后也有一些负面影响,会增加漏磁,有损安匝比的准确性。铁心的等效磁导率比完整铁心的磁导率减小,因而多通道直流大电流比较仪的灵敏度降低。最后应用劳斯判据,通过特征方程的根与各项系数的关系来判别系统的特征根是否全部具有负实部,从而分析了多通道直流大电流比较仪的稳定性。为了减小扰动信号对系统稳态误差的影响,提出了采用前馈补偿来抵消这种影响。更多还原

【Abstract】 The heavy direct current is applied in the metallurgic plant and the chemical plant commonly. The metallurgic plant and the chemical plant are important industries in our country. They consume a great deal of electricity. It is important to measure the heavy direct current precisely for energy conversation. For a long time the indication value of instrument is regarded as referenced value only because the online metrical instrument applying in monitoring and metering is short of reliability. It will affect the energy conversation and economic returns of these industries directly. It is important to collect the virtue and overcome the shortcoming of measurement theory in existence in order to change the situation. Then we search for a new kind of direct current sensing theory. The instrument based on this new kind of direct current sensor theory has high stability and high dependability. This paper establishes a kind of dc sensor based on self-balance of magnetic potential and feed-back compensation. The direct current sensor is divided into two types of principle based on open loop and closed loop measurement theories. The sensor based on open loop theory has many advantages such as simple construction, small volume, and lightweight. It doesn’t exist the oscillation and heavy driving power either. That based on closed loop theory has many advantages such as high accuracy, good linearity, and strong anti-interference and so on. A model machine is made in order to validate the correctness of theory. The experiment results have proved that the most of magnetic potential is balanced by the ac voltage source e. The system composed of the detecting and compensation coils and electronics module A is an automatic dc compensation system whose open loop gain is small. The zero ampere-turns compensation of the detecting core is realized by this circuit.When the heavy direct current sensor is applied in industry spot, it is inevitable to be disturbed by magnetic field. This disturbance will affect the heavy direct current sensor work naturally. It is very important to design the magnetic shielding body. Three ways of problem about magnetic shielding will studied in this paper.At first the magnetic shielding technology of heavy direct current sensor is discussed. The heavy direct current sensor applies magnetic shielding layer and copper shielding layer at the same time. The magnetic shielding effectiveness is the sum of every layer’s magnetic shielding effectiveness.The copper shielding layer can shield electric field and high-frequency magnetic field at the same time. The silicon-steel sheet layer can shield low-frequency magnetic field. When the magnetic shielding body is made of these two materials the satisfactory magnetic shielding effectiveness for low-frequency magnetic field and high-frequency magnetic field can be obtained. The magnetic shielding technology can be divided into electric shielding and magnetic shielding. The calculated formula of magnetic shielding effectiveness can be deduced by equivalent transmission line method. When the magnetic shielding body is designed the mutichannel technology is applied.Secondly the calculation of magnetic shielding effectiveness applied magnetic circuit method is discussed. Since Moore has put forward the magnetic shielding of dc sensor, the calculation of magnetic shielding effectiveness is concerned by the designer of dc sensor all the while. It is important to apply more precise method to calculate reliably. The calculation formula is deduced applying magnetic circuit method when adding radial magnetic field and axis magnetic field. In order to prove that the calculated result is truthfulness, the experiment is carry on to test the magnetic shielding effectiveness in this paper. The permeabilityμr isn’t constant in iron core. It is the intensity of magnetic field’s function. When intensity of magnetic field is 20GS, the permeability is tested. The tested permeability is substituted into formula deduce by magnetic circuit method. Compared the calculated result and the tested result we can see that the calculated result is close to factual situation. The conclusion can be obtained that magnetic circuit method can estimate the dc sensor’s magnetic shielding effectiveness.Finally the problem of multichannel comparator’s closed channel is studied. When the iron core of dc sensor is integral, the iron core has remnant magnetic potential. When the measured current and disturbed current operate on iron core at the same time, the magnetization of iron core is uneven. It will lead to closed channel of multichannel comparator. A new kind of multichannel comparator is designed in this paper in order to solve the problem of closed channel of multichannel comparator. An air gap between two channels can counteract remnant magnetic field in iron core. Every channel based on double magnetic detector sensing theory is an absolute dc comparator. The magnetic characteristic of annular iron core which has air gap and the open-loop characteristic of multichannel comparator for heavy direct current have studied. At first the length of air gap and equivalent intensity of magnetic field are calculated. Then the math model of multichannel comparator for heavy direct current is established. In the end the open-loop characteristic curve of multichannel comparator for heavy direct current is described. When the iron core of dc sensor has gas gap, the reluctance is increase. Compared the open-loop characteristic calculated curve the conclusion can be obtained that the output direct voltage of the dc sensor which has gas gap is lower than the dc sensor which has integral iron core when input ampere-turn is same.When the multichannel comparator has gas gap, it can reduce the effect of iron core’s non-linear. But it brings negative effect also. It can increase leak flux. It will reduce the veracity of ampere-turns ratio. The equivalent permeability of iron core is decrease also. Thus the sensitivity of mutichannel heavy direct current comparator is reduced. The stability of multichannel comparator for direct current sensor is analyzed applying Routh criterion. Whether the roots of character equation are all negative real part is judged by the relation of character equation’s root and every coefficient. The interferential signal will affect system’s stable error. The feed forward compensation is put forward to counteract the effect更多还原