Time-domain Modelling of Low-power Transformer for Power Supply Applications

Abstract

The aim of this paper is to present a way of solving an electrical circuit of a single-phase transformer with a nonlinear hysteretic core in the time domain. The considered circuit consists of an AC power supply, a transformer with a ringshaped core and a resistor in the transformer primary and secondary circuit depicting the coil ohmic resistances. The secondary circuit also has a load impedance. Three working regimes of the transformer are considered – when it is loaded and when it is close to no-load and short-circuit working conditions. For the loaded regime, impedance has been varied from 10 Ω to 10 kΩ, with power factor from 0.01 to 0.99. In the no-load and short circuit regimes it is set to 10 MΩ and 0.01 Ω, respectively, with the power factor of 0.99. Calculations have been made at industrial frequency (50 Hz) using an iterative procedure based on Harmonic Interpolation Method (HIM) and Bertotti’s Statistical Theory of Losses (STL). The obtained results are compared with the results calculated using an equivalent transformer circuit and well-known RL model of the transformer core. The details regarding the calculation procedures, measurement setup and results, the comparison of the calculated results, as well as their appropriate analysis, are presented in this paper.