Algorithm Research Of Electromagnetic Characteristics For Transformer In AC-DC Hybrid Mode

It is very important to take research of electric transformer in AC-DC hybrid mode, which is caused by geomagnetically induced current and monopole-earth system of high voltage direct current. The electromagnetic characteristics of transformer will be changed significantly in AC-DC hybrid model causing a series of internal and external abnormal or fault, then destroying the security and stability of electromagnetic devices and the whole power network.The time-domain magnetic field-electrical circuit coupled method based on the edge finite element method is applied for DC-biased transformer. The electromagnetic characteristics of transformer in AC-DC hybrid mode is studied using this method, which takes the dynamic inductance and the time-domain current as key coupling parameters to reflect magnetic saturation and circuit’s change respectively. It is valid for the analysis of working characteristics of transformer in AC-DC hybrid mode by solving the nonlinear magnetic and equivalent circuit model.The magnetic field and electric circuit coupled model is applied for the stability analysis. And the absolutely stable region is determined to judge the convergence of computation. According to the stable boundary, the time step is researched with state matrix. Variation function of dynamic inductances is established to evaluate the magnetic changing. Meanwhile, the magnetic solving frequency is defined to handle the efficiency. On the basis of stability analysis, impacts of time step and magnetic solving frequency on accuracy and efficiency are discussed. Furthermore, an improved self-adaptive time-varying algorithm is proposed, in which, the iterative step can be revised to deal with the time-varying nonlinear excitation. Compared with the fixed-step algorithm, the efficiency and accuracy can be enhanced.Finally, the experiment is carried out to prove the self-adaptive method, which will be a new way for time-domain computation of practical electro-magnetic devices such as transformers in AC-DC hybrid model.