Z-domain modeling of peak current mode control for full-bridge DC-DC buck converters
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ORIGINAL ARTICLE
Z‑domain modeling of peak current mode control for full‑bridge DC‑DC buck converters Xiaohong Wang1 · Qisong Huang1 · Bo Zhang1 · Di Chen1 · Quanxue Guan2 Received: 1 August 2020 / Revised: 8 September 2020 / Accepted: 11 September 2020 © The Author(s) 2020
Abstract Traditional local-averaged state-space modeling for peak current mode (PCM) controls fails to explain the subharmonic oscillation phenomenon when the spectrum is higher than half of the switching frequency. To address this problem, this paper presents a small-signal modeling method in the z-domain, and builds a discrete linear model for the current loop of a full-bridge DC-DC converter. This discrete model is converted into a second-order continuous model that is able to represent the system performance with a wider frequency range. A frequency-domain analysis shows that this model can be used to explain the subharmonic oscillations and unstable characteristics. This provides an engineering guideline for the practical design of slope compensation. The effectiveness of the proposed modeling method has been verified by simulation and experimental results with a prototype working in the Buck mode. Keywords DC-DC converter · Peak current mode control · Slope compensation · Subharmonic oscillation · Z-domain modeling method
1 Introduction Peak current mode (PCM) control has been widely used in power electronic converters due to its accuracy, fast dynamic response and software flexibility [1, 2]. Flying capacitor Buck converters [3], flyback converters [4] and Buck LED drivers [5] are some examples of this PCM control. In fullbridge DC-DC converter applications, PCM control has a simple structure and an inherent built-in overcurrent protection mechanism [6]. Implementation is easy due to the absence of a large inertia filtering link in the current feedback control loop [7]. This also results in the PCM control having a fast response. In general, PCM control is implemented in cascaded double-loop control structures with the stability mainly depending on the inner current loop. However, when the steady-state duty ratio is higher than 50%, the converters have alternating wide pulses and narrow pulses, namely * Quanxue Guan [email protected] 1
School of Automation Science and Engineering, South China University of Technology, Guangzhou, China
Department of Electrical and Electronic Engineering, University of Nottingham, Nottingham, UK
2
subharmonic oscillations. These oscillations result in poor system stability. Thus, it is necessary to have an appropriate control [8, 9]. The key to a good PCM control is to accurately model and analyze the characteristics of the current control loop. The numerical calculation in [10–12] uses a piecewise linear discrete model to iteratively calculate the circuit response. However, this method, which ignores the influence of parasitic parameters such as the dead-time, and the on–off voltage drop of the switches, is only suitable for simulations. The state space averaging method eases the parame
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