Characteristic frequencies in averaged description of step-down (BUCK) DC-DC power converter

Abstract

Abstract:In the description of small-signal transmittances of switch-mode power converters several characteristic frequencies are usually used, corresponding to poles and zeros of transmittances. The knowledge of these frequencies is important in the design of control circuits for converters and usually are assumed to be constant for a given power stage of a converter. The aim of the paper is to evaluate the influence of converter primary parameters and load conductance on characteristic frequencies. Analytical derivations and numerical calculations are performed for an ideal and non-ideal BUCK converter working in continuous or discontinuous conduction mode. Key words: switch mode DC-DC converter; step-down converter, BUCK power converter; small-signal transmittances; sharacteristic frequencies Selected symbols and abbreviations C -capacitance; C Z -equivalent capacitance; d A , D A -duty ratio and its steady-state value; f S -switching frequency; f (with other subscripts) -characteristic frequencies; G -load conductance; G A -equivalents conductance defined by Eq. 39; H (with subscripts) -small-signal transmittances of converter; L -inductance; M I -current static transmittance in DCM; Q -coefficient in H t (s) dependence; R -load resistance; R (with subscripts) -parasitic resistances; R Z -equivalent parasitic resistance; SW1, SW2 -ideal semiconductor switches; T S -switching period; θ -small-signal representations of duty ratio in s-domain; ω (with subscripts) -characteristic pulsations; CCM -continuous conduction mode; DCM -discontinuous conduction mode.

Archives of Electrical Engineering

“…3. It differs from the model discussed in [30] by the existence of the capacitor series resistance R C and different description of the current sources i X and i GS -see Eqs. ( 12) and ( 14).…”

“…An outline of the proposed method has been previously presented in the short paper [30] on the example of an ideal buck converter without small-signal analysis, and without verification of dynamic characteristics. The present paper is a substantial extension of [30], takes into account parasitic resistances of converter components and includes verification of the proposed model by measurements and full-wave simulations.…”

Influence of output conductance on characteristic frequencies of switch mode BUCK and BOOST converter

“…Control to output transmittances of BUCK and BOOST converters working in CCM with parasitic resistances (see Fig. 1) may be expressed as [7]:…”

“…Characteristic frequencies in given operation mode depend mainly on the parameters of an induction coil and capacitor used in the power stage. In typical description of these frequencies, their dependence on load current (or load conductance) is not taken into account [1][2][3][4][5][6] but it is shown in [7] that in some situations, this dependence may be important. The considerations in [7] are only theoretical and restricted to a step-down converter (BUCK).…”

“…In typical description of these frequencies, their dependence on load current (or load conductance) is not taken into account [1][2][3][4][5][6] but it is shown in [7] that in some situations, this dependence may be important. The considerations in [7] are only theoretical and restricted to a step-down converter (BUCK). In the present paper, formulas describing the influence of load conductance on characteristic frequencies of BUCK and BOOST converters are presented and theoretical results are verified by measurements.…”