Effect of Control Method on Impedance-Based Interactions in a Buck Converter

Abstract

Abstract-All the interconnected regulated systems are prone to impedance-based interactions making them sensitive to instability and transient-performance degradation. The applied control method affects significantly the characteristics of the converter in terms of sensitivity to different impedance interactions. This paper provides for the first time the whole set of impedance-type internal parameters and the formulas according to which the interaction sensitivity can be fully explained and analyzed. The formulation given in this paper can be utilized equally either based on measured frequency responses or on predicted analytic transfer functions. Usually, the distributed dc-dc systems are constructed by using ready-made power modules without having thorough knowledge on the actual power-stage and control-system designs. As a consequence, the interaction characterization has to be based on the frequency responses measureable via the input and output terminals. A buck converter with four different control methods is experimentally characterized in frequency domain to demonstrate the effect of control method on the interaction sensitivity. The presented analytical models are used to explain the phenomena behind the changes in the interaction sensitivity.Index Terms-Buck converter, dynamic behavior, minor-loop gain, source/load interactions, stability.

Physical insight into the factors affecting the load-transient response of a buck converter

“…16. The usual reason for the phenomenon is that the LC filter impedance exceeds the short-circuit input impedance of the converter as explained and demonstrated explicitly in [27,28]. Such a resonance causes decaying oscillation in the output voltage during the load transient and resembles the condition where the output-voltage-feedback-loop margins are low as demonstrated in Fig.…”

“…It will be emphasized that the reason for the observed problems in the transient behavior can be either internal (i.e., power-stage component selection or feedback-controller design) or external (i.e., input-filter design or source impedance) as explained in [26: pp. 225-285], [27,28].…”

Review of PV Generator as an Input Source for Power Electronic Converters

“…The analysis methods are developed further in many publications (e.g., [28,42,[117][118][119][120][121][122][123][124][125][126][127]). The further developments are mainly concentrated on enlarging of the allowed area in complex plane, where the impedance ratio is allowed to lie without causing instability [117,118,122], on making the special parameters governing the interactions in the converters to be explicitly solvable [119,122], and on extending the methods into the grid-connected three-phase converters as well [123][124][125][126][127]. The interactions are caused by the source and load impedances through the different impedance ratios in the associated converters [122].…”

Single-Source Multi-Battery Solar Charger: Analysis and Stability Issues

“…Consequently, current-controlled buck power stages are considered in this paper as power processing interfaces, opposed to the conventional boost power stages typically used in grid-connected photovoltaic systems. Nevertheless, unlike in boost converter based power stages, stability issues were shown to arise when utilizing current-controlled buck converters as power electronic interfaces in photovoltaic applications [18,19] because of interactions between converter dynamics and solar array impedance [20], leading to open-loop instability.…”