State Plane Feedforward Control for LLC Converter With Geometric Simplification

This article proposes a state plane feedforward (SPF) control to improve the dynamic response performance of LLC converters. In contrast to the traditional state-plane-based control, the proposed SPF control aims at the steady state analysis of state plane. The proposed SPF control predicts the switching period under specific operating conditions through state plane analysis with geometric simplification, and feedforward it to the conventional linear controller. The switching period predicted by SPF shows good agreement with the actual switching period. Moreover, because the state plane analysis is geometrically simplified, no complex high-order equations need to be solved, and online computation is available. Meanwhile, the SPF control guarantees greater stability compared with other state plane based nonlinear controls, as a result of no transient control structure switching is required during transient states. Finally, both simulation and experiments are carried out to validate the feasibility of the SPF control, the result demonstrates SPF control features a rapid dynamic response to all types of transient.