An improved enhanced phase-locked loop based method for the measurement of harmonics/inter-harmonics

Measurement of harmonics/inter-harmonics based on the technique of enhanced phase-locked loop is unpractical dues to its slowly transient response speed. A new method which improves the technique of enhanced phase-locked loop by bringing in the theory of relaxation iteration is proposed: Taking the theory of relaxation iteration for the solution of nonlinear equation into account in the premise of convergence, and find out the optimum relaxation factor through proper transformation of the parametric expressions. Make sure the relaxation factor is updated after each step in order to ensure the iteration is carried out in the lest-error direction. Thus the new method exploits both the convergence of enhanced phase-locked loop and the fast speed of relaxation iteration. Results based on the simulations show that the proposed method has reduced the convergence time to less than 10% and the amount of computation to less than 20% as compared with enhanced phase-locked loop based method.