Loss separation analysis in ferromagnetic sheets under PWM inverter supply

As increasing frequency and capacity of the power semiconductor devices, the induction heating comes to use generally in the industrial fields. The induction pipe welder is the machine that beads the plate by roller and welds the seam by concentrated induction current in order to make pipes from plates. That is constructed from the inverter which has several hundred [kHz] and several hundred [kW] power source, the heating coil and the ferromagnetic bar inserted into the bent plate. As the technical theme, it is wanted to obtain the uniformity heating at the seam of pipe. In this paper, we analyzed the distortion of the eddy current induced in the plate by the three-dimensional finite element method which adopted a tetrahedral linear edge element in order to analyze complicated construction and considered the magnetic material. A computation mode is shown in Fig. I and the eddy current distribution on the pipe surface without the ferromagnetic bar is shown in Fig. 2. We also analyzed the relation between eddy current losses and the relative position of end of the ferromagnetic bar and the seam.