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为验证相位调制激励与实际试验结果的一致性,使用西安中科智晶电力科技有限公司的LLG−1100光纤电流传感器按上述两种测试方法进行对比试验。LLG−1100光纤电流传感器的光纤匝数N=10,半波电压Dλ=32768,维尔德常量V=0.768×10−6 rad/A,解调周期为1.51 μs,输出频率为10 kHz,每个采样点的间隔为100 μs。高功率信号发生器可以产生10 A电流,在试验室中采用等安匝原理,将母线围绕光纤电流传感器传感头缠绕10圈,等效产生100 A的测试电流,线性度可以达到1 ppm (1ppm=10−6)[15]。通过设置信号发生器输出阶跃响应波形及不同频率的正弦波形,对比LLG−1100光纤电流传感器的试验结果与仿真结果。
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阶跃响应模拟±100 A电流下光纤电流传感器的输出响应,通过公式(8)计算得到阶梯波相位调制激励的固定台阶高度为16,在光纤电流传感器闭环控制算法中添加阶梯波相位调制激励,得到阶跃响应的输出如图7所示。
LLG−1100光纤电流传感器的阶跃响应试验数据与仿真数据如表1所示。
Data Overshoot percent Rise time/μs Experimental data 0% 100-200 Simulation data 0% 100-200 Table 1. Comparison of step response simulation data
由于采样周期限制,每个采样点的间隔为100 μs,由表1可以看出,采用激励的方式得到的仿真数据与试验数据一致。可以反映光纤电流传感器的阶跃响应特性。
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频率响应模拟频率范围50 Hz~2 kHz,额定电流100 A光纤电流传感器的输出响应,通过公式(8)计算得到阶梯波相位调制激励的幅值为16,在光纤电流传感器闭环控制算法中添加阶梯波相位调制激励,通过改变激励频率来得到不同频率下的输出响应。利用公式(16)~(17)分别计算添加激励仿真及等安匝测试的幅值误差:
式中: I0为设置电流值;I1为添加激励仿真的电流输出值;I2为等安匝测试电流输出值。
频率响应曲线如图8所示。由表2可以看出,采用相位调制激励的仿真数据与试验数据最大偏差为0.12%,满足0.5级光纤电流传感器的频率响应要求,可以反映光纤电流传感器的频率响应特性。
Frequency/Hz Experimental data error Simulation data error 50 −0.03% 0.01% 150 0.06% −0.05% 600 −0.06% −0.06% 800 −0.13% −0.11% 1200 −0.39% −0.27% 1600 −0.76% −0.73% 1800 −1.05% −1.08% 2000 −1.55% −1.52% Table 2. Experimental and simulation data of frequency response
Simulation research of the transient characteristics of a digital closed-loop fiber optic current sensor
doi: 10.3788/IRLA20210615
- Received Date: 2022-01-20
- Rev Recd Date: 2022-03-15
- Publish Date: 2022-08-05
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Key words:
- digital closed-loop fiber optic current sensor /
- frequency response /
- step response /
- modulation excitation
Abstract: Transient characteristics of digital closed-loop fiber optic current sensors (FOCSs) include the frequency response and step response which are important indexs in the industrial areas such as power system relay protection and fault recording. In engineering applications, due to the complexity of the test system and the poor accuracy of a small current signal, it is not conducive to evaluating the transient characteristics of an FOCS in a traditional way. According to the closed-loop control mechanism of a digital closed-loop optical fiber current sensor, a new method of adding phase modulation excitation to the feedback loop of a digital closed-loop FOCS was researched. First, the phase modulation principle of the digital closed-loop of FOCS was analysed, and a mathematical model was established to calculate and verify the equivalence of the phase modulation excitation; Second, based on the closed-loop control algorithm of the FOCS, the frequency response and step response modulation excitation generation method were proposed; Finally, use the existing digital closed-loop FOCS product platform was used to complete the simulation and test of frequency response and step response. The results show that the maximum error between simulation data and test data is 0.12%. The modulation excitation method can realize different current simulation tests of frequency response and step response on the existing hardware platform without building a complex test system.