Figure 20 illustrates the typical analysis results. Starting from the time zero, the transformer core operates in the linear region and the unsaturated circuit of Figure 19(a) is solved, based on the corresponding initial conditions. When the core flux reaches the knee point flux λk, the solution is obtained by switching to the saturated circuit
of Figure 19(b). At the switching instant, the already calculated quantities of the unsaturated circuit are considered as new initial conditions for the saturated circuit to maintain the solution continuity. At the first saturation instant, i.e. t
1 in Figure 20, the core enters the saturation region, the magnetizing current abruptly increases, and the capacitor starts charging. Furthermore, due to the significantly smaller Lsat as compared with Lunsat, the circuit experiences a high frequency half-cycle oscillation starting at t 1. The oscillation frequency is