Research Of Establishment Transformer Broadband Model Based On The Modified Image Method

In the power system electromagnetic transient simulation, the establishment of a stable power transformer simulation model can be crucial. And implementation of the passive circuit for the power transformer simulation model is one of the difficulties. Passivity of circuits can be divided into the port passive and strictly passive. The port passive refers to that the energy into the port is always non-negative at any time point. And strictly passive refers to that all of the parameters of circuit components are positive. Therefore, the establishment of a power transformer model which is consisted of only positive components has a great theoretical and practical significance.“Image method” is based on the amplitude of frequency-dependent parameters and the RLC circuit elements are used to the integration of the circuit. This method can make all of the parameters of components positive and realize the strict passivity of the circuit model. However, it only calculates for single resonance peak point of impedance amplitude frequency and cannot apply to calculate for the complex transformer frequency dependent which has several resonance peak points. In order to solve this problem, “image method” has been improved in this paper. The first step of the method is segmenting the admittance amplitude frequency dependent, the low-frequency part for the form of RL in series, the high-frequency part for the form of RC in parallel, and the resonance part for the form of RLC in series. Levenberg-Marquardt algorithm is used to determine the component values for each part. Then the imitative effect can reach the most optimal performance after the total elements’ parameters have been global optimized by the Origin. The modified method can realize the strict passivity of circuits as well as it can be widely used.The simulations and experiments are studied on 10 k V two-winding transformer and 110 k V three-phase three-winding transformer. Based on the above methods, the Simulink models are constructed for simulation. To verify the model, the experiments lightning overvoltage is conducted. The comparisons between the simulation and measurement results verify the feasibility and validity of the model.