Detailed analysis and modeling of an improved cascade buck converter

ABSTRACT

This paper presents ready-to-use nonlinear and linear averaged models of an improved cascade buck converter (ICBC) for the first time. A detailed steady-state analysis is also given, providing its operating modes, equilibrium values, and design guidelines. The modelling process consists of two stages. First, the nonlinear model is obtained using the state-space averaging technique. Subsequently, the averaged model is linearised by applying the small-ripple approximation and the small-signal model is achieved. Furthermore, the developed small-signal model is employed to derive three significant transfer functions of the converter. The proposed converter model is valid for the continuous conduction mode (CCM) when the duty cycle is lower than $0.5$. To be used in validation studies, an exemplary converter with $144\mathrm{W}$ rated power that steps down $320\mathrm{V}$ input voltage to $24\mathrm{V}$ is designed. The accuracy of theoretical analyses is confirmed by the simulation results of the designed converter. Similarly, all proposed models are validated with the simulations done in both frequency-domain and time-domain. The results show that the proposed parametric model response closely matches that of the switching (non-parametric) model and hence it can be safely used for controller design in feedback systems.

KEYWORDS:

• Cascade buck converter
• high step-down conversion ratio
• steady-state analysis
• state-space averaging technique
• small-signal model

Disclosure statement

No potential conflict of interest was reported by the author(s).