# Induction Coil Design Considerations for High-Frequency Domestic Cooktops
## 4 The Proposal of High-Frequency Induction Coil Design
### Simulation Results  
To design proper induction coils for domestic induction heating applications, a variety of FEMs were run. Some of the analyses were implemented following the FEM results. Firstly, the induction coil was designed for high-power applications. The target power rating was approximately 3.7 kW, which is widely used in mid-segment products. This application selected approximately 120 kHz switching frequency, which is nearly 5-6 times higher than conventional domestic induction heating applications. Conventional domestic induction cookers set the resonance frequency as approximately 18 kHz. Magnetic simulations were performed based on the fact that high-frequency induction cooktops operate between 100 and 120 kHz. In practical measurements, the operating frequency was approximately 100 kHz. As the switching frequency increased, it was obvious that the values of the passive components used in the power circuit decreased compared to conventional systems using low resonance frequency. FEM analyses of induction coils designed for high-power applications are given in Figure 12. In these analyses, in addition to conventional induction cooker coils, analyses of their high-frequency counterparts are also included. Results are given for different windings and magnetic core numbers, as well as for different air gaps. All of these analyses were carried out for a 210 mm induction coil and with a cast-iron pot. Cast-iron pots are made from a metal base plate through which induction cookers can transmit maximum power and have high induction compatibility. Figure 11: Step by step high-frequency induction coil design. Since new-generation high-frequency induction cookers require lower-value passive components compared to their conventional counterparts, the inductance value of the induction coil is much lower. The number of windings was reduced to decrease the inductance value of the induction coil. Reducing the amount of winding is important for reducing copper losses and increasing efficiency, as well as reducing product costs. Since decreasing the winding value for the same load current value will reduce the magnetomotive force, the magnetic field value that occurs for the same number of magnetic cores is much lower. Reducing the number of windings also provides the opportunity to reduce the number of magnetic cores. The high number of windings in conventional induction coils increases the risk of magnetic saturation if the number of magnetic cores decreases. Reducing the number of magnetic cores along with the number of windings reduces the resistance value in the coil-pot equivalent circuit and increases the inductance. In the previous sections, the effect of the equivalent resistance value on power transfer was discussed in detail. To increase the equivalent resistance value, the air gap must be reduced. When the air gap is reduced, the equivalent inductance value decreases and the resistance increases. Reducing the air gap is essential to designing a thinner induction cooker. FEM analyses of induction coils designed for low-power applications are given in Figure 13.  
Figure 12: FEM analyses performed for high-power applications. In addition to high-power applications, FEM analyses and measurements were carried out for low-power and very high-frequency applications. In Full-Flexi type induction cooktops, many low-power induction coils were used to cook on every surface of the cooktop. In this type of application, the switching frequency is much higher while the amount of power transferred by the induction coil is low. The target power rating was up to 1 kW, while operating frequencies ranged from 100 kHz to 1 MHz. The FEM model was used in a structured approach to optimize induction coil designs, focusing on material properties and field distribution. The process involves defining objectives, creating an initial design, and applying boundary conditions and loads. Iterative analyses refined the design, balancing accuracy with computational cost and considering material nonlinearities.