45 - High-Frequency Induction Heating Analysis of an IH Cooking Heater
Module: FQ, HT
An IH cooking heater cooks food by heating a pot that acts as a conductive body. It heats this pot with an induction heating method that uses electromagnetic induction. Eddy currents flow in the iron pot when a high frequency current is applied to the coil. These eddy currents produce joule loss, which acts as a heat source to raise the temperature of the iron pot. When designing the heating coil, the main points to look out for are: What kind of magnetic circuit design will raise heating efficiency, and whether it is generating uniform heat in the iron pot. Another factor is controlling leakage flux to the circuit component in the board box that surrounds the apparatus.
A magnetic field analysis simulation that uses the finite element method (FEM) is best for studying a three dimensional combination of the geometry, number, and alignment of the magnetic material that adjusts the magnetic circuit, and for quickly obtaining the electric circuit constant of the high frequency circuit that performs the heating.
This Application Note shows how to obtain the magnetic flux density surrounding an IH cooking heater that uses high frequency induction heating and the temperature distribution of its iron pot.
Magnetic Flux Density Distribution
Fig. 1 shows the magnetic flux density distribution of the IH cooking heater. The aluminum plate on the board box shields it from magnetic flux, reducing the amount of leakage flux that flows to it.
Eddy Current Loss Density Distribution and Temperature Distribution of the Iron Pot
Fig. 2 shows the eddy current loss density distribution of the iron pot. The magnetic field generated by the coil produces eddy currents on the surface of the iron pot. The iron pot is then heated because its electric resistance produces joule heat.
Fig. 3 shows the temperature distribution of the iron pot at 10 s, 30 s, and 60 s. The iron pot is heated by eddy currents. The temperature of the bottom of the iron pot rises over time, reaching 100 deg C at 60 s. In this analysis, the temperature rise of the bottom of the iron pot is not uniform. To heat the bottom of the iron pot uniformly during heating, the coil arrangement and the core geometry need to be improved.