Current-mode Controlled DC-DC Converters Research Articles

Complex non‐linear phenomena and stability analysis of interconnected power converters used in distributed power systems

Distributed power systems are considered to be a key element of future power grids. Their main characteristic is the local production and consumption of energy that is accomplished using a number of power converters that interconnect local sources and loads. In this paper, a current mode controlled dc-dc converter which feeds another current mode controlled dc-dc converter is considered to meet the demands of the load. It shows that the existence of the second converter at the output has destabilising effect on the overall system. Such a system may also exhibit interactions of various types of instability that conventional modeling methods cannot predict. Slow-timescale oscillation in standalone switching converters is usually attributed to the occurrence of a Neimark-Sacker bifurcation of the fundamental periodic orbit of the discrete-time model of the system. But in the studied cascaded system, the underlying mechanism is quite different. This paper fully explains the mechanisms as well as the conditions of the occurrence of such instabilities by employing the analytical and numerical tools of the exact switched model of the system. These results can be useful for developing design guidelines to avoid such problems. Finally, the results have been validated experimentally.

An optimal current observer for predictive current controlled buck DC-DC converters.

In digital current mode controlled DC-DC converters, conventional current sensors might not provide isolation at a minimized price, power loss and size. Therefore, a current observer which can be realized based on the digital circuit itself, is a possible substitute. However, the observed current may diverge due to the parasitic resistors and the forward conduction voltage of the diode. Moreover, the divergence of the observed current will cause steady state errors in the output voltage. In this paper, an optimal current observer is proposed. It achieves the highest observation accuracy by compensating for all the known parasitic parameters. By employing the optimal current observer-based predictive current controller, a buck converter is implemented. The converter has a convergently and accurately observed inductor current, and shows preferable transient response than the conventional voltage mode controlled converter. Besides, costs, power loss and size are minimized since the strategy requires no additional hardware for current sensing. The effectiveness of the proposed optimal current observer is demonstrated experimentally.

Complex Interaction Between Tori and Onset of Three-Frequency Quasi-Periodicity in a Current Mode Controlled Boost Converter

It is known that power electronic circuits like dc-dc converters are highly nonlinear systems, and that period doubling and Neimark-Sacker bifurcations are common sources of instability in such systems. It has also been shown that these two types of bifurcation may interact, giving rise to interesting dynamical phenomena. In this paper we show that in a current mode controlled dc-dc converter, periodic, quasi-periodic, and saturation behavior can coexist for the same parameter value, and there can be complex interactions between them. Furthermore, abrupt exit to saturation mode can be triggered by a torus-torus collision. Finally, we report the first observation of three-frequency quasi-periodicity in a power electronic system.

Fast-Slow Scale Bifurcation in Higher Order Open Loop Current-Mode Controlled DC-DC Converters

Higher order converters, without an external voltage control loop, have been known not to exhibit a fast-slow scale bifurcation interaction, as the slow-scale bifurcation has generally been believed to be caused by parameter changes in the outer loop. In this paper, it is shown that a current-mode controlled Ćuk converter can exhibit an interaction between fast-scale and slow-scale bifurcations even in the absence of this closed outer voltage control loop. The phenomenon is probed using an approach based on the system's monodromy matrix that does not only predict this instability but also provides a systematic method for the development of new control strategies to avoid the onset of this bifurcation. Analytical and numerical results prove that the new controller greatly extends the stable region of operation of the converter.

Analysis of Piecewise Constant Models of Current Mode Controlled DC-DC Converters

Buck, boost, and buck-boost converters constitute large class of dc-dc converters used in practice and are interesting nonlinear dynamical systems. It has been shown earlier that various nonlinear phenomena including subharmonics and chaos can be observed in these converters. In this paper we show that with the simplifying assumption that voltage regulation is achieved in high frequency modulation, a very simple dimensionless model can be derived that explains the dynamic phenomena in both continuous conduction mode as well as the discontinuous conduction mode. Using this model, we analyze some peculiar aspects of the dynamics in discontinuous conduction mode like the occurrence of superstable orbits.

A Design Method for Paralleling Current Mode Controlled DC–DC Converters

This paper proposes a new current sharing method. It is based on current mode controlled dc-dc converters and achieves the current sharing by forcing all inner current loops to have the same current reference. Meanwhile, this method decouples control loops from the voltage regulation and current-sharing regulation instead of adding control loops as in traditional master-slave methods. Therefore, the large signal performance is good while its stability is guaranteed. Further, unlike multi-module methods, the modularity of single dc-dc converter is retained. Design rules and small signal analysis are presented. The advantages of the proposed method are verified by experimental results.