Analysis, evaluation, and design of passive elements used in power conversion circuits

In addition to power semiconductor switching devices, passive elements such as reactors and capacitors are essential in power conversion circuits for smoothing input/output voltage and current, filtering harmonics, and suppressing overvoltage and overcurrent. In particular, high-frequency switching and operation at high temperatures are increasingly required for the application of wide bandgap semiconductors in power conversion circuits, and circuit design using passive elements accordingly is becoming necessary. Therefore, it is not sufficient to consider passive elements as mere L and C, but it is necessary to understand various characteristics before applying them to circuits. Funaki Laboratory evaluates the frequency characteristics of various reactors and capacitors and the dependence of their characteristics on temperature, operating current, and voltage, and conducts research to realize optimal power conversion circuit design by modeling based on their operating principles and structures. The iron loss of magnetic components can be evaluated by the hysteresis loop drawn by the trajectory of the magnetic flux in relation to the applied magnetic field. However, the conventional two-winding method is difficult to evaluate with high accuracy because the phase difference between the voltage and current is around 90 degrees for a magnetic core with low iron loss. By canceling the phase difference between voltage and current using the 2-winding method or the capacitor resonance method, only the loss can be evaluated, enabling highly accurate iron loss evaluation of low-loss iron cores.

Research work