Stability Analysis Based on Transient Magnetic-Circuit Coupled Method for DC-Biased Transformer

Combining with the hot problem of DC-biased transformer, the stability, accuracy, efficiency and magnetic changing characteristic are researched in transient magnetic- circuit coupled compute. The power-balanced method is improved to get the dynamic inductances. According to the high-order convergence of the fourth Runge-Kutta, the absolute stability region, which is a function of the critical time step, is determined, and the relation between state matrix and time step is also deduced. Simulation and case study about normal and DC biasing operation are given to work out the transient currents and dynamic inductances. The varying characteristics of coupling parameters are researched in accord with different saturated excitations. Result shows these parameters are feasible to reflect the variable magnetic saturation. Compared with the traditional and improved Euler methods, the fourth Runge-Kutta takes advantages in stability and precision. It can be found from simulation that the stable region is proved with validity. Meanwhile, not only the computing speed and accuracy are directly related to the time step, but also are the changing characteristics of the coupling quantities. On this basis, an adaptive algorithm of time-varying step in transient coupled computation is proposed and applied. The result coincides with experimental data. And this adaptive method is verified to gain more efficient and accurate computation.