We can find the first harmonic current component is1 of injecting to the nonlinear networks by using fundamental-wave balance principle

when sinusoidal voltage source Us is applied to the proper port of the nonlinear network.The frequency and amplitude of sinusoidal voltage source is called fundamental harmonic solution

when is1=0.If n-fundamental harmonic solution can be found

then n-periodic solution of original network certain exist correspondingly.If first harmonic solution is nonexistent

the original network has no periodic solution also.Taking the Colpitts circuit as example

the close relation between reactive power balance and periodic oscillation can be shown.Chaotic oscillation shape and properties of Chua’s circuit can be explained by the fundamental-wave balance principle.The universality of the conclusion can be extended to the three dimensional nonlinear network .Its correctness can be verified by the Simulink.