Current Comparator Bridge Based On FPGA

Current Comparator Bridge(CCB) is commonly used to measure thecapacitance and dielectric loss factor(tan) of high voltage electricalequipment. CCB has a higher accuracy and more secure operation.This paper analyzed the basic theory of the CCB and deduced theformula of calculating the capacitor value. It reduced the uncontrolledfactor by using current from the bridge arm to generate balancing currents.Based on this principle this paper finds an auto balancing algorithmwhich realized the bridge internal electrical quantities analysis. Twobalancing currents are achieved after knowing the circuit, and the balancestate can be gradually approached with feedback of null detector andNewton-Raphson iteration. The whole test progress can be doneautomatically. The control quantities can be reduced to two bysimplification of the auto balancing algorithm: standard capacitor bridgearm winding N2and gain factor β and it will be less complicate. The finalvalue of Cxand tan can be calculated with the balancing parameters andformula. Examples of the algorithm are based on SOPC system build withFPGA platform. The program is carried on embedded IP core processor.The whole system is well user-defined and easy to expand to more complicated system.This paper also designed the peripheral interface circuit of FPGAand focused on analog-digital circuit. The paper coded with Verilog HDLlanguage to generate control module of AD7895and packaged it into theSOPC system. And we achieved the analog signal sampling based onFPGA platform.