Average Current Control with Asymmetrical Sawtooth or Peak Current Control

Abstract

Conductance control within SMPS (Switch Mode Power Supply) is typically implemented relying either on the ACC (Average Current Control) or on the PCC (Peak Current Control) technique. An in-depth analysis of the PCC dynamics has been published in the past, highlighting that such technique responds to a feedback control loop scheme covered by Laplace transfer functions properly modelling the limited switching frequency effects. The present paper consists in the dynamic analysis of ACC based on asymmetrical sawtooth, proceeding by similarity with the PCC analysis. It is shown that these ACC and PCC techniques are described by the same differential equations, hence that they pertain to a unique control technique. The bandwidth and stability margins of that closed-loop control technique are subsequently investigated, demonstrating that ACC has a phase margin larger than 60°, while PCC dynamic performance extends beyond ACC with larger bandwidth frequency at a price of lower phase margin. The paper further stresses the differences between Laplace transfer functions relevant to time-discrete and analogue systems, and why they shall be considered separately. Time simulations are finally reported and specific provisions for proper measurement of stability margins on electronic breadboard are indicated.