A changing forgetting factor RLS for online identification of nonlinear systems based on ELM–Hammerstein model

Abstract

In this paper, an online identification method is proposed for nonlinear system identification based on extreme learning machine (ELM)–Hammerstein model. The ELM–Hammerstein model comprises an ELM neural network followed by a linear dynamic subsystem. This model is linear in parameters and nonlinear in the input. To speed up the convergence and meanwhile improve identification accuracy, a changing forgetting factor recursive least squares (CFF-RLS) method is proposed as online learning algorithm. The algorithm can identify the parameters of linear dynamic subsystem and the weights of ELM neural network simultaneously. Simulation results verify the effectiveness of the proposed method.