Sunplus Technology

Hsinchu, Taiwan

Sunplus Technology

Hsinchu, Taiwan
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Fang C.-C.,Sunplus Technology | Redl R.,Redl Consulting
IEEE Transactions on Power Electronics | Year: 2017

Closed-form subharmonic oscillation conditions are derived and experimentally verified for the current-controlled boost converter in continuous conduction mode with closed voltage feedback loop. Typical voltage-loop phase-lag and type-II compensators are analyzed. The well-known open-voltage-loop instability condition becomes a special case. It is found that, unlike in the buck converter, the ripple at the output of the compensator can improve the stability. The analysis is extended to other boost-like converters with pulsating output currents, such as buck-boost, flyback, and SEPIC converters. © 2016 IEEE.


Fang C.-C.,Sunplus Technology | Chen C.-J.,National Taiwan University
IEEE Transactions on Power Electronics | Year: 2016

General closed-form subharmonic oscillation conditions are obtained for 2-controlled buck converters. Both constant switching period and constant on-time operations are analyzed with the outer voltage loop closed or open. Once an arbitrary linear feedback is given, the associated closed-form stability condition of the converter is readily obtained. Past research results based on the describing function technique and the Floquet theory become special cases. This paper provides an alternative and easier method to analyze subharmonic instability. © 2015 IEEE.


Fang C.-C.,Sunplus Technology | Redl R.,Redl Consulting
IEEE Transactions on Power Electronics | Year: 2014

This paper presents the derivation and experimental verification of the closed-form subharmonic instability condition of the constant-frequency peak-current-controlled buck converter with closed voltage feedback loop. The well-known open-voltage-loop instability condition becomes a special case. The instability limits in the converter parameter space are readily obtained from the result. It is found that closing the voltage feedback loop tends to degrade the stability margin. One can clearly see the effects of all converter parameters (such as the pole, zero, and gain of the voltage-loop compensator, the equivalent series resistance of the output capacitor, the presence of a second output capacitor, and the switch turn-off delay) on the instability. © 2014 IEEE.


Fang C.-C.,Sunplus Technology
IEEE Transactions on Power Electronics | Year: 2015

A recent paper proposed I2 average-current control with constant switching period (CSP) or constant on-time (COT) operation in continuous conduction mode (CCM). The small-signal analysis was presented, but only for the COT case. No instability or its condition was reported. In this note, unified subharmonic oscillation conditions are derived for both CSP and COT buck converters. The effects of feedback gain, turn-off delay, and stabilizing ramp slope are considered. The results can be extended to other converters or control schemes. © 2014 IEEE.


Fang C.-C.,Sunplus Technology
International Journal of Circuit Theory and Applications | Year: 2015

This paper is an extension of the author's recent research in which only buck converters were analyzed. Similar analysis can be equally applied to other types of converters. In this paper, a unified model is proposed for buck, boost, and buck-boost converters under peak or average current mode control to predict the occurrence of subharmonic oscillation. Based on the unified model, the associated stability conditions are derived in closed forms. The same stability condition can be applied to buck, boost, and buck-boost converters. Based on the closed-form conditions, the effects of various converter parameters including the compensator poles and zeros on the stability can be clearly seen, and these parameters can be consolidated into a few ones. High-order compensators such as type-II and PI compensators are considered. Some new plots are also proposed for design purpose to avoid the instability. The instability is found to be associated with large crossover frequency. A conservative stability condition, agreed with the past research, is derived. The effect of the voltage loop ripple on the instability is also analyzed. Copyright © 2014 John Wiley & Sons, Ltd.


Fang C.-C.,Sunplus Technology
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2013

Based on a general critical condition of subharmonic oscillation in terms of the loop gain, many closed-form critical conditions for various control schemes in terms of converter parameters are derived. Some previously known critical conditions become special cases in the generalized framework. Given an arbitrary control scheme, a systematic procedure is proposed to derive the critical condition for that control scheme. Different control schemes share similar forms of critical conditions. For example, both V2 control and proportional voltage mode control have the same form of critical condition. A peculiar phenomenon in average current mode control where subharmonic oscillation occurs in a window value of pole can be explained by the derived critical condition. A ripple amplitude index to predict subharmonic oscillation proposed in the past research has limited application and is shown invalid for a converter with a large pole comparable to the switching frequency. © 2004-2012 IEEE.


Fang C.-C.,Sunplus Technology | Redl R.,Redl Consulting
IEEE Transactions on Power Electronics | Year: 2014

A general closed-form subharmonic stability condition is derived for the buck converter with ripple-based constant on-time control and a feedback filter. The turn-on delay is included in the analysis. Three types of filters are considered: low-pass filter (LPF), phase-boost filter (PBF), and inductor current feedback (ICF) which changes the feedback loop frequency response like a filter. With the LPF, the stability region is reduced. With the PBF or ICF, the stability region is enlarged. Stability conditions are determined both for the case of a single output capacitor and for the case of two parallel-connected output capacitors having widely different time constants. The past research results related to the feedback filters become special cases. All theoretical predictions are verified by experiments. © 1986-2012 IEEE.


Fang C.-C.,Sunplus Technology
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2014

Three types of bifurcations (instabilities) in the DC-DC converter under valley current mode control (VCMC) are analyzed, which is an extension of a recent paper on the peak current mode control (PCMC). The three bifurcations are border-collision, period-doubling, and saddle-node bifurcations. The corresponding critical (instability) conditions are derived. The derived conditions divide the parameter space into different operating modes. Contrary to the general belief that the critical conditions for VCMC and PCMC are symmetric with respect to the duty cycle D=1/2 , most critical conditions are actually asymmetric. The dynamics symmetry is converter, bifurcation, loading, and parameter dependent, verified by bifurcation diagrams and time-domain simulations. The VCMC boost converter has rich dynamics and it is extensively analyzed. © 2014 IEEE.

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