Magnetic components are one of most important parts of the power converter system. In order to fully exploit the function of the magnetic components more knowledge about the loss of magnetic component must be gained. It is well known that the loss of the magnetic component consist of core loss and copper loss. Firstly, the dissertation analyzes the topologies of power converters, the configurations of the soft switching circuits and the working states of the magnetic components in these circuits. Then, the dissertation mainly focuses on some basic problems of core loss, including following aspects,1. Core loss model under sinusoidal waveform excitationThe parallel resistance model is proposed in this dissertation. Based on some reasonable simplification, the core loss of the inductor is represented by the loss of an equivalent resistor parallel with the inductor and the value of the resistor is just the function of the frequency. So the nonlinear core loss model can be represented by a linear model.At the same time, a comparison is made among the parallel resistance model, Steinmetz equation and Rayleigh relation model. It is found that among these three models Steinmetz equation is the most accurate one to calculate the core loss of the magnetic component. Rayleigh relation model, though un-accurate, is an important relation. And the parallel resistance model is simplest and practical, suitable for system simulation and the control system design of power converters.2. Core loss model under rectangular waveform excitationThe dissertation makes a research on the core loss model under rectangular waveform excitation. A ratio named KD is introduced and defined as the ratio of core loss under rectangular waveform excitation to that of under sinusoidal waveform excitation supposed both of which are under the same frequency and the same flux density. It is found in the experimental results that KD is concave function of duty cycle and it is axial symmetric across the duty cycle equal to 0.5. When the duty cycle equals to 0.5 KD reaches its minimum value. And if the duty cycle is within a certain space range KD smaller than 1, otherwise larger than 1. At last the core loss model under the influence of the duty cycle is proposed. This model is simple but practical and suitable for engineering calculation.3. Core loss model under the influence of DC bias magnetic fieldThe dissertation also makes a research on the influence of DC bias magnetic field to the core loss. Similarly, a ratio named KB is introduced, defined as the ratioof core loss of sinusoidal waveform excitation with DC bias to that of without DC bias, supposed that both under the same frequency and flux density. Besides, a variable named s is also introduced, .y is defined as the ration of DC flux density to AC flux density. It is found that KB is an increasing function of s and AC flux density and a formula to calculate KB is given in this dissertation.4. Research on the practical core loss problemThe filter inductor of the DC/DC converter works under rectangular waveform excitation and at the same time there exists DC bias magnetic field in this inductor. So both respects must be taken into account of. It is guessed that the ratio of core loss of DC/DC converter filter inductor to core loss under sinusoidal waveform excitation under the same frequency and same AC flux density is the product ofKo and Kg. The experimental results have proved that this guess is correct.DC/AC converters and AC/DC converters, both worked under rectangular waveform excitation, but the duty cycle and bias magnetic filed are changed in the line period. So firstly core loss of every switching period in one line period must be calculated, then these values should be add together and calculate the mean value. The result is the core loss value of these converter. The core loss model and the experimental results of DC/AC converter are given in the dissertation. As for the AC/DC converter it just need reference for the procedure of the DC/AC con