Byungcho Choi

In an active clamp forward converter (ACFC), an oscillatory upsurge or ringing of the clamp capacitor voltage directly elevates the voltage stress of the main switch and the risk of saturating the isolation transformer. The magnitude of the voltage upsurge has been known to be largely affected by the loop gain characteristics of the converter. However, detailed analytical relations between them have not been fully revealed yet. Previous studies have addressed this issue via complex mathematical computations with limited engineering insights. This work demonstrates that the magnitude of the ringing is collectively influenced by both the 0 dB crossover frequency and the gain margin of the converter loop gain. The ringing could be alleviated when the loop gain crossover frequency is extended to a vicinity of the output filter double pole frequency, while retaining a sufficient gain margin. In some cases, a considerate design trade-off is necessary between the crossover frequency and gain margin, in order to soften the oscillatory rise of the clamp capacitor voltage. Such a design guideline is proposed to reduce the voltage stress of main switch and danger of transformer saturation. The proposed design strategy is empirically verified with a 50 W experimental prototype ACFC, as well as extensive computer simulations.

This letter proposes a modified double-dual-boost (DDB) high-conversion-ratio dc–dc converter. The proposed converter is derived from the existing DDB converter by a simple yet effective circuit modification and inherits all the advantages of the existing DDB converter. In addition, the input and output can share a common ground due to the circuit modification, enabling the use of low-side gate drivers for all switching devices. When compared with the existing DDB converter, the proposed converter requires only one more capacitor, and the seemingly two inductors can be integrated into a single inductor. Thus, the overall magnetic volume is the same as the conventional converter. To validate the performance of the proposed converter, a 2-kW prototype was fabricated and tested.

This paper proposes a new load impedance specification for multi-stage dc power conversion systems. The proposed specification avoids drawbacks of the existing specifications, such as the lack of explicit connections to the dc link dynamics and the unnecessary conservativeness. The new specification offers a direct command/ supervision of the frequency- and time-domain dynamics of the intermediate dc link, while being less conservative than the existing specifications. This paper also presents procedures for redesigning ill-conditioned load impedances to comply with the specification. The validity and utility of the proposed specification are demonstrated using an experimental two-stage dc power conversion system.

This paper proposes a new load impedance specification for multi-stage dc power conversion systems. The proposed specification avoids drawbacks of the existing specifications, such as the lack of explicit connections to the dc link dynamics and unnecessary conservativeness. The proposed specification offers a direct command/supervision of the frequency- and time-domain dynamics of the intermediate dc link, while being less conservative than the existing specifications. This paper also presents procedures of redesigning ill-conditioned load impedances to comply with the specification. The validity and utility of the proposed specification are demonstrated using an illustrative example.

This paper investigates the impacts of the load subsystem on stability and performance of the upstream converter in multistage Dc-to-Dc power conversion systems. This paper demonstrates that an appropriate load subsystem can be constructed to provide both stability and intended performance for the upstream converter at the brink of instability before being coupled with the load subsystem. These stabilizing effects of the load subsystem are theoretically analyzed and experimentally validated using a two-stage power conversion system, consisting of an upstream boost converter, downstream buck converter, and two filter stages. This paper also presents the design procedures for the stabilizing load subsystem, along with the performance verification of the upstream boost converter and the downstream buck converter.

Input Impedances of PWM DC-DC Converters: Unified Analysis and Application Example Current mode control;Dynamic interaction;Input impedances;Middlebrook's extra element theorem;Middlebrook's feedback theorem;Pulse width modulated dc-to-dc converters;Voltage mode control; The input impedances of pulse width modulated (PWM) dc-to-dc converters, which dictate the outcomes of the dynamic interaction between dc-to-dc converters and their source subsystem, are analyzed in a general and unified manner. The input impedances of three basic PWM dc-to-dc converters are derived with both voltage mode control and current mode control. This paper presents the analytical expressions of the 24 input impedances of three basic PWM dc-to-dc converters with the two different control schemes in a factorized time-constant form. It also provides a comprehensive reference for future dynamic interaction analyses requiring knowledge of the converters' input impedances. The theoretical predictions of the paper are all supported by measurements on prototype dc-to-dc converters. The use of the presented results is demonstrated via a practical application example, which analyzes the small-signal dynamics of an input-filter coupled current-mode controlled buck converter. This elucidates the theoretical background for the previously-reported eccentric behavior of the converter.

This paper investigates the impacts of the load subsystem on stability and performance of the upstream converter in multi-stage dc-to-dc power conversion systems. The paper demonstrates that an appropriate load subsystem could offer both stability and predictable performance for the upstream converter that was at the brink of instability before being coupled with the load subsystem. This stabilizing effects of the load subsystem are theoretically analyzed and experimentally validated using a two-stage power conversion system, consisting of an upstream boost converter, downstream buck converter, and two filter stages. The results of this paper can be used to stabilize the upstream converter that was initially well designed but later became destabilized due to the detrimental interaction stemming from unknown source subsystems.

This study presents the design and performance evaluation of the digital control adapted to an LLC series resonant dc‐to‐dc converter operating with wide input and load variations. The proposed control design correctly incorporates the wide‐varying power stage dynamics and variable small‐signal gain of a digitally controlled oscillator, thereby offering satisfactory converter performance for all the operational conditions. The proposed digital controller adopts the push–pull mode control scheme, which executes the control action two times in one switching period, to minimise the time delay and enhance the performance. Using a 150 W experimental converter, the performance of the proposed push–pull mode digital control is demonstrated in comparison with that of the conventional complementary mode digital control, which performs the control action only once in one switching period.

DC-to-DC converters are usually intended for general applications where the load impedance characteristics are unknown or undefined. This paper establishes the control design procedures for DC-to-DC converters in the absence of any prior knowledge on their load impedance. The proposed control design can be universally adapted to all the DC-to-DC converters regardless of the impedance characteristics of their actual load. This paper also presents the loop gain analysis of the converter combined with an actual load whose impedance characteristics are only available afterward. A graphical analysis method is proposed, which enables us to predict the loop gain of the converter in the presence of an arbitrary load impedance. The validity of the analysis method is demonstrated using a current-mode controlled buck converter coupled with an inductive load, capacitive load, and converter load. Theoretical predictions are verified with both computer simulations and experimental measurements.