Near Optimal Controller Tuning in a Current-Mode DPWM Boost Converter in CCM and Application to a Dimmable LED Array Driving

A boost converter exhibits a nonminimum phase behavior while operating in continuous conduction mode. This is due to the existence of a right-half-plane zero that significantly restricts the closed-loop bandwidth. Using the phase- plane geometry, this paper proposes a nonlinear tuning approach in a digitally current-mode controlled boost converter with a proportional-integral voltage controller. Considering a load current feed-forward with a normalized gain k
_n
, optimal proportional gains are analytically derived in order to achieve near time optimal recovery under both load and reference step transients. The optimal gain is shown to be equally applicable for a (nonminimum phase) noninverting buck-boost converter by suitably updating k
_n
. Large-signal stability analysis is carried out, and the effects due to finite sampling and parameter variations are discussed. The proposed tuning significantly improves the transient response over existing small-signal-based tuning methods. The constraints on the current overshoot and/or voltage deviation are also considered, and their effects on the transient performance are studied. A boost converter prototype is tested using resistive and dimmable (white) LED array loads. The proposed tuning is realized using a field-programmable gate array device; improved performance and efficiency are demonstrated using test results.