| Application of power devices and power electronic devices in power system results in a large number of harmonics and inter harmonics and impact, non-periodic and high dynamic signal. There is no doubt that electric energy metering is faced with a new challenge. Current transformer is an important part of measurement device, and the transfer characteristics under the complex signal will directly affect the accuracy of electric energy metering. However, there is a lack of systematic research on the transfer characteristics of current transformer and its influence on electric energy metering system. According to this problem, this thesis has carried out the following research.This thesis has studied several common current transformer models, and found that J-A hysteresis model can reflect transfer characteristics of current transformer under complex signals, so it’s chosen. The thesis makes further analysis about the deficiency of the J-A model and makes further improvement. Besides, it identifies the parameters of the J-A model through the differential evolution algorithm. Finally, the improved J-A static hysteresis model is formed. In addition, from the basic principles of electromagnetic induction, the transfer equation is derived between the primary side and the secondary side of the current transformer. Moreover, it combines the J-A static hysteresis model under the theory of magnetic core, then establishes the numerical model of current transformer.The semi-physical simulation platform based on ds PACE simulation platform is established. From this experimental platform, the characteristics of current transformer in AC component of different amplitudes and different DC coefficient of current transformer is measured. And the transient and steady state process are analyzed. In addition, there are almost the same results of the hysteresis curve and transfer characteristics between the actual current transformer and the improved J-A model in the presence of the DC component. Therefore, it verifies the correctness of the model. In addition, this thesis also has analysed the influence on electric energy measurement of current transformer under DC component, and found that the nonlinear characteristics of current transformer will lead to the decrease of fundamental power and the increase of harmonic power.By using a single frequency method and the superposition of single harmonics, the frequency characteristics of current transformer is studied. The study makes clear that at rated current and rated load, the results in two kinds of test methods are similar, which indirectly proves that frequency is not sufficient to change the current transformer from the linear region to the non-linear region. Based on this conclusion, the thesis puts forward a more efficient method of measuring current transformer’s frequency characteristics. And that is multiple harmonics composited method. According to the equivalent circuit, the transfer function is derived. And measurement results are compared and analyzed in order to verify the correctness of the transfer function. In addition, the influence on the electric energy measurement under harmonic load is analyzed in theory, and the thesis also analyzes the error of current transformer through the actual data. Due to the influence of harmonic ratio and power factor angle in complex harmonic signal, the harmonic power error relative to harmonic ratio increases about ten times.In addition, the thesis also has carried on the analysis to the actual signal, summarized several common dynamic load models, studied the transfer characteristics of current transformer under the different dynamic load and put forward the ideas that the composite error quantizes the transmission error under the dynamic load. Besides, it has analyzed the influence of the current transformer on the electric energy measurement under the dynamic load with actual data. It is confirmed that the error caused by current transformer in the dynamic load cannot be ignored. |
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