V2 Controlled Buck Converter Research Articles

Study on high robustness and fast dynamic response synchronous rectifier buck converter

Here, a novel control strategy combined by constant-frequency V 2 control and H ∞ robust control is proposed and tested in a buck converter. The control strategy not only demonstrates the fast transient response of ordinary V 2 control, but also shows strong robustness with different input conditions. The main drawbacks of V 2 control, such as high interference susceptibility and low input perturbation stability margin, can be improved by introducing H ∞ robust strategy into the controller design. During the analysis and design process, the original controlled system based on the V 2 control is modelled at first, then the H ∞ weighting functions are calculated according to the small-signal analysis of V 2 controlled buck converter. After that, the H ∞ robust compensator parameters based on constant-frequency V 2 control are calculated. Finally, a buck converter controlled by the proposed control strategy is built and tested, with 48 V input voltage, 12 V output voltage, and 120 W output power. The experimental results demonstrate the effectiveness of the converter with the proposed control, which also proves the proposed method has great potential for high robustness and fast dynamic response applications.

Critical output‐capacitor ESR for stability of V 2 controlled buck converter in CCM and DCM

It has been reported that subharmonic instability exists in the V2 controlled buck converter in continuous conduction mode (CCM) when the duty ratio is above 0.5 (D > 0.5) and no stability issue exists in discontinuous conduction mode (DCM) when 0 < D < 1. However, the CCM and DCM instabilities will appear in the safe duty ratio range when the equivalent series resistance (ESR) of the output capacitor is below a critical value. The critical output-capacitor ESR for the stabiiity of a V2 controlled buck converter in CCM and DCM is investigated by using the discrete-time model and verified by circuit simulations.

Effect of output capacitance time-constant on dynamic characteristics of V2-controlled buck converter

The second-order discrete iterative map model of V2-controlled Buck converter is established, based on which, the bifurcation diagrams with variation of output capacitance and its equivalent series resistance (ESR) are obtained, and the effect of output capacitance time-constant on the dynamic characteristics of V2-controlled Buck converter is investigated. It is found that with gradual reduction of output capacitance time-constant, the V2-controlled Buck converter shows the evolutive dynamic behavior from continuous conduction mode (CCM) period-1 to CCM period-2, CCM period-4, CCM period-8, CCM chaos, and discontinuous conduction mode (DCM) chaos. Jacobi matrix at a fixed point is also derived. According to this, the converter stability is analyzed by using characteristic values and maximum Lyapunov exponent, which validates the correctness of bifurcation analysis. Finally, the simulation and experimental circuits are set up, and the correctness of the theoretical analysis is verified by simulation and experimental results.

Mechanism of instability behaviors and stabilization on V2 controlled buck converter

Along with the variation of the feedback amplify coefficient, V2 controlled Buck converter exhibits abundant nonlinear dynamical behaviors. By establishing the discrete-time model of the system, this paper has studied the instability phenomena based on the monodromy matrix method. With increasing feedback factor, the analysis indicated that the converter entered from a stable period-one statue into a period-doubling statue. Finally, it showed chaos. Mechanism of the bifurcation generated by the system was fully analyzed based on the monodromy matrix, which showed that as the increase of the feedback coefficient, an eigenvalue of the monodromy matrix went out of the unit circle; this was the reason why the system generated period-doubling bifurcation. Also presented was the sinusoidal voltage compensation method to extend the stability margin based on the monodromy matrix theory, by which the instability behavior was effectively handled. Simulation and experimental results confirmed the analytical method.

Equivalent modeling and bifurcation analysis of V2 controlled buck converter

After dimension reduction, two boundary voltages of V2 controlled buck converter are deduced under different operation mode, based on which, its equivalent one-dimensional discrete-time model is established and complex nonlinear bifurcation behaviors are emphatically studied. Two boundary conditions under which shift between stable period-one state and subharmonic oscillation state and shift between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) take place are derived by analyzing stability and operation mode. The research results show that in V2 controlled buck converter period-doubling bifurcation and border-collision bifurcation can occur with varying circuit parameters and the converter has different bifurcation routes at different circuit parameters. Simulation and experiment platforms are implemented and the corresponding results verify the validity of equivalent discrete-time model and theoretical analysis.

Comparative Studies of Common Fix-Frequency Controls for Reference Tracking and Enhancement by End-Point Prediction

This paper analyzes the dynamics of reference tracking in switched-mode power converters in terms of both large-signal and small-signal perspectives. Common control schemes, namely, voltage mode, current mode, and V2-control, are compared for their performance in reference tracking. For small-signal analysis, loop gains and reference-to-output transfer functions are analytically derived and verified by the proposed Matlab-based frequency response simulator. In the case of multiple-loop control like V2-control, different loop gains are clarified for their application in load transient or reference tracking. Practical circuit-level design considerations are given to current-mode control for achieving fast reference tracking, while end-point prediction (EPP) is used to improve V2-control, which is inherently slow in reference tracking. The effect of EPP on transfer function is then explained in details. A V2-controlled buck converter with EPP is fabricated. The measured reference-tracking response shows ten times improvement in tracking speed and verifies the effectiveness of EPP in V2-control.