Dual mode control of tri-state boost converter for improved performance

A tri-state boost converter with an additional boost-inductor free-wheeling interval was proposed earlier to eliminate the right-half-plane (RHP) zero that occurs in the control-to output transfer function of a classical boost converter under continuous-conduction mode of operation. A ´constant-D_o´ control scheme, in which the ´capacitor-charging´ interval of the converter was kept constant, was employed. This resulted in a relatively large inductor current, especially under high line and load conditions, thereby causing high circuit losses. This paper proposes two variations of a novel dual-mode control (DMC) scheme that vary both the ´boost´ and the ´capacitor charging´ intervals. Control analysis, design, and limitations of the proposed DMC schemes are presented. Through computer simulations and hardware experiments the performance of the tri-state boost converter with DMC schemes are compared with those of the tri-state boost converter with ´constant-D_o´ control scheme, and the classical PI-controlled boost converter. The DMC schemes achieve a significant (about 10%) improvement in converter´s efficiency for a wide load range over the ´constant-Do´ control scheme.