基于饱和电抗器结构下的新型直流比较仪原理

Principle of a Novel DC Comparator Centered on the Structure of Saturable Reactor

在常规的可控饱和电抗器中增加检测绕组和反馈绕组构成一种新型直流比较仪,即它由4个绕组(检测绕组、激励绕组、直流绕组和反馈绕组)、环形磁心以及后续处理电路组成。利用电压源激励磁心,当直流偏磁磁势(即被测电流)不为0时,检测绕组的端电压是正负半波不对称的波形,研究得出,该电压的峰一峰值、总有效值以及正负半波有效值之差均与直流偏磁磁势(或被测电流)有关。利用正负半波有效值之差作为反馈控制的误差信号,并将该电压信号预处理之后,经过电压／电流变换,再由功率放大器扩流,最后送到反馈绕组中形成反方向直流磁势以平衡被测直流磁势,实现"零磁通状态",从而完成直流测量任务。仿真分析和实验结果均表明,该比较仪开环输出特性曲线不会出现虚假平衡点,因而控制可靠,仅含单磁心,结构简单,易于操作。

A novel DC comparator is proposed by adding the detection winding and the feedback winding to the saturable reactor (SR), which includes four windings, (viz. detection winding, feedback winding, DC winding and excitation winding), single toroidal magnetic core and peripheral circuits. The terminal voltage from the detection winding is asymmetric waveform when the SR is stimulated both by voltage source and DC biasing magnetic potential. Researches indicate that peak-peak value, full-wave root-mean-square (RMS) and differential RMS between positive and negative half waves of the terminal voltage have direct concerns with the biasing magnetic potential (or the measured current). The differential RMS above is adopted as feedback variance to balance the DC biasing magnetic potential via a series of processing that the differential RMS above is preconditioned and converted to current (V/I) and amplified by power circuit. Then the amplified difference current flows into the feedback winding to balance the biasing magnetic potential to form the zero flux condition and thus the DC measurement is achieved. Simulation and experimental results verify the DC comparator model has such performances as output characteristic without false-balance points, simple structure with single core and easy operation.