Commutation process; Fast periodic steady state; Limit cycle; Newton method; Numerical differentiation; Unified power flow controllers Approximation theory; Electric control equipment; Electric power systems; Electric power transmission networks; Flow control; Fourier analysis; Fourier series; Functions; Harmonic analysis; Newton-Raphson method; Numerical analysis; Power quality; Power transmission; Commutation process; Fast periodic steady state; Limit cycle; Newton method; Numerical differentiation; Unified power flow controllers; Process control