Coil design for induction cooking system
You should use one additional inductor Lr (L resonant) in series, both capacitor C2 and C3 could be also marked as Cr. Then, in your formula L1C becomes LrCr.

L1 should have just minimum effect on resonant frequency L1 &lt;&lt; Lr.

However if you don't want to use additional Lr, then the resonant frequency is dependant of the load applied. The inductor acts like a tranformer N:1, where the N is the equvalent number of primary turns (coli) and 1 is the secondary single turn (the pot). The load (resitance of the pot) is connected to the secondary. Depending of the load applied (different pot) also the resonating frequncy will change, therefore you need to have a switching device capable of measuring phase difference between voltage and current and adapt the frequency. If you want to stay above resonating frequency then you could acheive this by having a setpoint in a phase angle, this is done with PLL. Some induction heating devices use PLL, you can also check tesla coil builders forum as they alsu use this self resonant (quasi resonant) techniques.