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This paper presents a new design approach to the type 3 compensator for voltage-mode controlled (VMC) buck converter for good closed-loop performance over a wide input voltage and load current range. The new design method offers superior load and line transient responses to the existing methods, such as K factor method and computer-aided iterative technique. A design example is presented to show the superiority of the proposed design technique to the existing designing techniques. The effectiveness of proposed design technique is verified using PSpice and PSIM time-domain simulations.

In this paper, we propose a new design method for multistage dc power distribution systems, which employ several pulsewidth modulated (PWM) converter stages and intermediate line filters in a cascaded manner. In the proposed method, individual PWM converter stages are initially built as a standalone converter, powered from an ideal voltage source and loaded with a current sink. Once the individual PWM converters are properly engineered based on the standard procedures, the intermediate filters are then designed and fabricated to provide the desired converter performance, dc link dynamics, system stability, and system dynamics. Thus, the task of designing a dc power distribution systems is reduced to the design problem of intermediate line filters. The validity of the proposed method is confirmed with an experimental dc power distribution system.

The output 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 load subsystem, are analyzed in a general and unified manner. This paper presents the analytical expressions of the output impedances of three basic PWM dc-to-dc converters operating with current mode control. It also provides a comprehensive reference for future dynamic interaction analyses requiring knowledge of the converters output impedances. The theoretical predictions are all supported by measurements on prototype dc-to-dc converters. The use of the presented results is demonstrated via practical application examples, which deals with current-mode controlled buck and boost converters connected with practical load subsystems.

This paper investigates the loading effects on the input impedance of the upstream converter stage in multistage dc power distribution systems. The paper shows that the loading effects depend on the topology of the converter stage. The loading effects are not observable in the input impedance of the buck converter. On the other hand, the loading effects are apparent in the input impedances of the boost and buck/boost converters. The outcomes of the paper can be used to analyze the stability of the whole power system. Theoretical results are all validated by both PSpice and PSIM time-domain simulations.

This paper presents a new design technique for multi-stage dc power distribution systems, which consistently offers the pre-programmed performance for dc distribution bus, irrespective of detrimental interactions among subsystem components. The paper demonstrates that the proposed design technique provides the aimed performance, even for cases in which the conventional design encounters instability due to adverse interactions from an ill-conditioned source subsystem. The performance of the proposed technique is theoretically validated and experimentally supported using a prototype two-stage dc power distribution 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 presents the performance evaluation of an interleaved boundary conduction mode (BCM) boost power factor correction (PFC) converter employing three different switching devices: the super junction silicon (Si) MOSFET, silicon carbide (SiC) MOSFET, and gallium nitride (GaN) high electron mobility transistor (HEMT). An experimental 500 W interleaved BCM boost PFC converters is built and its performance is evaluated while adopting each of the three semiconductor devices as the main switch. The overall efficiency and thermal performance of the experimental boost PFC converter are analyzed under three different operational conditions: one operational condition with the baseline switching frequency of fs base = 65 kHz and the other two conditions with fs base = 130 kHz and 200 kHz. The three baseline frequencies are selected in consideration of IEC 61000-3-2 and CISRR 22 EMC standards for conducted emission noise. This study confirms that the GaN HEMT exhibits the superior switching characteristics and pronounces its merits at high frequency operations. The current paper highlights the efficiency improvement with the GaN HEMT and demonstrates its application potentials to high power density/low profile BCM boost PFC converters.

This paper investigates stability of dc-to-dc converters deriving another dc-to-dc converter through a filter stage. The impacts of the downstream filter/converter stage on the absolute and relative stabilities of the upstream converter are analyzed. The absolute stability is examined using the minor loop gain, defined as the ratio of the impedances seen at the output port of the upstream converter. The relative stability is assessed using the loop gain expression of the upstream converter. This paper reveals that the downstream filter/converter stage rarely destabilizes the upstream converter, but usually dictates the loop gain characteristics of the upstream converter and frequently determines the phase margin and 0 dB crossover frequency of the loop gain. This paper proposes a simple method to determine the stability margins of the converter from the minor loop gain. The theoretical predictions are supported by both small-signal simulations and experimental measurements.

This paper presents a methodology to deal with the control design for PWM converters in dc-to-dc power conversion systems. The concept of uncoupled dc-to-dc converter is established, which allows dc-to-dc converters to be designed independently from the source and load impedances. The control design strategy of the uncoupled dc-to-dc converters is formulated to offer good and robust closed-loop performance when the converters are coupled with the actual source and load subsystems. A peak current-mode controlled buck converter is used as an example throughout this paper to verify the proposed control design technique. We compare the control design of the uncoupled dc-to-dc converters with that of the converters coupled with resistive and non-resistive loads. The validity of the conventional design intended for a resistive load is also be discussed.

This paper 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 main theme of this paper is to highlight the advantage of using the push-pull mode of digital pulse width modulation (DPWM) operation over the complementary mode operation for the implementation of digital control to the resonant converters using a low cost digital signal controller (DSC). Conventionally, the complementary mode of DPWM operation is used for resonant converter. However, the push-pull mode of DPWM operation is chosen for the resonant converter circuit to improve closed-loop performance. Design procedures and performance evaluation are illustrated for both DPWM operational modes using an experimental 150 W LLC converter.

Conventional phase-shift full-bridge converters use high leakage inductance of transformer to achieve ZVS over wide load range of converter. But high leakage inductance causes drawbacks such as high circulating current, reduced voltage gain, severe voltage spike and parasitic ringing of secondary rectifier diode. So, phase-shift full-bridge converter using saturable inductor is usually used to solve drawbacks of conventional converter. Although use of saturable inductor solves drawbacks of phase-shift full-bridge converter, but reduced core size to get good performance causes high core temperature at high current due to increased core loss. This paper proposes a phase-shift full-bridge converter using MR(Magneto-rheological) fluid gap inductor which has advantages over conventional phase-shift full-bridge converters. MR fluid gap inductor has variable inductance characteristic caused by changing inductor current. Structure of MR fluid gap inductor and its properties were analyzed by using reluctance model. The principle, implementation and performance of the phase-shift full-bridge converter using MR fluid gap inductor are investigated to verify converter performance compared with conventional phase-shift full-bridge converter and phase-shift full-bridge converter using saturable inductors.

Conventional voltage mode control only offers limited performance for LLC series resonant dc-to-dc converters experiencing wide variations in operating conditions. This paper presents average current mode control which could consistently provide good closed-loop performance for LLC resonant converters for the entire operational range. The proposed control scheme employs an additional feedback from the current of the resonant tank network to overcome the limitation of the existing voltage mode control. The principles, implementation and performance of the average current mode control scheme are investigated to identify their respective merits and limitations compared with conventional control schemes. The accuracy of dynamic analysis and validity of control design are confirmed with both computer simulations and experimental measurements using 150W prototype converter.

Multi-module interleaved resonant converters have been widely adapted to low-profile power supplies for flat-panel display electronics. In this multi-module approach of resonant converter, individual modules tend to have different circuit characteristics due to unavoidable resonant component mismatch, resulting in noticeable imbalance in the module currents and considerable ripple component in the output current. Many researchers have been studied on methodologies for an effective load current sharing for multi-module dc-to-dc converters. But, most of their results were confined to the treatments of passive components. This paper proposes a new average current mode control which actively controls the individual modules to share equal current at the presence of mismatches in their circuit components. The validity and performance of the proposed average current mode control is demonstrated using a 150 W two-module interleaved LLC series resonant dc-to-dc converter designed for LCD TV sets.

This paper represents the digital current mode control for a multi-module bidirectional converter intended for battery charging/discharging applications. The digital current mode control is adapted to achieve equal current sharing and good dynamic performance. The predictive control is used for the digital current compensation and the direct method is adapted to the digital voltage compensation. The control parameters for the digital compensations are designed and fine-tuned using the SISO tool in MATLAB software. Theoretical predictions are confirmed with both MATLAB simulations and measurements on an experimental prototype converter.

Conventional voltage mode control only offers limited performance for LLC series resonant dc-to-dc converters experiencing wide variations in operating conditions. This paper presents current mode control which could consistently provide good closed-loop performance for LLC resonant converters for the entire operational range. The proposed control scheme employs an additional feedback from the current of the resonant tank network to overcome the limitation of the existing voltage mode control. The superiority of the proposed current mode control over the conventional voltage mode control is verified using an experimental 150 W LLC series resonant dc-to-dc converter.

This paper presents the control design of a peak current-mode controlled multi-module bidirectional battery charging/discharging converter. The reduced-order modeling technique is combined with the small-signal model of current mode control, leading to design procedures for both current sensing network and voltage feedback compensation. Theoretical predictions are confirmed with both small-signal simulations and experiments.

This paper presents new soft-switched half-bridge dc-to-dc converters intended for applications where the input voltage varies widely. The proposed converters are presented in both non-isolated form and isolated form. The proposed dc-to-dc converters operate with zero voltage switching characteristics for MOSFET switches. The duty ratio of the proposed converter could expand to 100 % and its voltage gain is twice the voltage gain of conventional half-bridge converters. Accordingly, the proposed converters are well suited for applications requiring high conversion efficiency at the presence of wide input voltage variations. The operation and performance of the proposed converters are demonstrated with experimental converters that deliver a 12V/5A output from a 35–60 V input. The non-isolated converter recorded the maximum efficiency of 91 % at 1.5 A load current.

LLC series resonant converters for consumer or industrial electronics frequently encounter considerable changes in both input voltage and load current requirements. This paper presents theoretical and practical details involved with the dynamic analysis and control design of LLC series resonant dc-to-dc converters operating with wide input and load variations. The accuracy of dynamic analysis and validity of control design are confirmed with both computer simulations and experimental measurements.

This paper attempts to resolve some fundamental issues related to averaged modeling of peak-current controlled PWM converters. One issue to be addressed is the ability of averaged models to predict switching instability (also referred to as subharmonic oscillation) under peak-current control. It will be shown that, contrary to the widely held belief, such instability can be predicted by properly defined averaged models, and that incorporation of an additional second-order transfer function representing the so-called sample-and-hold effect is not necessary for this purpose. The averaged models capable of predicting such instability are developed by combining standard state-space averaged models with a properly defined duty-ratio constraint. A circuit approach based on general topological properties of PWM converters and a mathematical approach based on KBM ripple estimation algorithm to the derivation of the duty ratio constraint are reviewed and are shown to yield identical results. Implementation of the averaged models in circuit simulation programs using iterative method is also presented

This paper presents a qualitative method to analyze and interpret loop gain characteristics of switching power converters loaded with a practical load subsystem. Effects of the load subsystem's input impedance on the loop gain of switching power converters are investigated. Based on the analysis results, a simple qualitative method is established that facilitates the interpretation and prediction of the loop gain characteristics for switching power converters. Theoretical predictions of the paper are supported by both computer simulations and experimental results

This paper presents a new soft switching dc-to-dc converter that employs two separate transformers. Unlike previous topologies where two transformers are used as a functional substitute for one large transformer, the proposed converter utilizes two transformers as its key operational components. The proposed converter achieves high conversion efficiency by eliminating or minimizing the switching and conduction losses, while retaining all the benefits of using two small low-profile transformers instead of one large transformer. The operation and performance of the proposed converter are demonstrated with an experimental converter that delivers a 3.3V/20A output from a 44–52V input at the maximum efficiency of 94 %.

This paper presents average and small-signal models for a wide class of asymmetrically-driven double-ended (ADDE) pulsewidth modulated (PWM) dc-to-dc converters. In this paper, average models for the primary- and secondary-side circuits, commonly employed to most ADDE converters, are first derived using the circuit averaging technique. The principle of energy conservation is then invoked to systematically incorporate the effects of multiple parasitic resistances. The resulting average models are appropriately assembled to constitute an average model for a specific ADDE converter. Finally, the average model of an ADDE converter is linearized to yield the respective small-signal model. The validity and accuracy of the proposed models are experimentally verified using two prototype ADDE converters.

Input impedances of pulse-width modulated (PWM) dc-to-dc converters, which dictate the outcome 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 (buck, boost, and buck/boost converter) with either voltage-mode control or current-mode control are derived using Middlebrook's extra element theorem and feedback theorem, and subsequently simplified into approximations using the graphical Bode plot analysis method. Analytical expressions for 24 input impedances are provided in a factorized time-constant form, thereby providing a comprehensive reference for dynamic interaction analyses requiring knowledge of converters' input impedances. Theoretical predictions of the paper are all supported by experiments performed on experimental dc-to-dc converters.

Three different current-mode control schemes, peak current-mode control, charge control, and average current-mode control, are investigated for the applications to asymmetrically-driven bridge-type pulse-width modulated DC-to-DC converters. The principles, implementation, and performance of the three control schemes are compared in an attempt to identify their respective merits and limitations. Design examples for feedback compensations are given for the three control schemes. The theoretical predictions of this paper are supported by computer simulations and experimental results

This paper presents the theoretical and practical details involved with the small-signal analysis of switching power converters under a strong influence of input filter interaction. A boost dc-to-dc converter controlled by voltage-mode control and the same boost converter controlled by current-mode control are used as illustrative examples. The theoretical predictions of this paper are supported by computer simulations and experimental results

Asymmetrical half-bridge dc-to-dc converters exhibit the fourth-order power stage dynamics. When the conventional voltage-mode control is employed, the fourth-order dynamics impose certain constraints on the feedback compensation design and the result could be poor closed-loop performance. This paper demonstrates that the current-mode control could alleviate the detrimental effects of the power stage dynamics and offer an improvement in the closed-loop performance. The principles, performance, and experimental results of current-mode control are presented in comparison with those of voltage-mode control.

A comprehensive system-level analysis is presented, and a systematic design procedure for a stacked power system is established. An effective load impedance of each converter is identified, incorporating all subsystem interactions in the system. Using the effective load impedances, the system is decoupled into three individual converters. The effective load impedance of the decoupled converter is simplified to a resistive value, an equivalent resistive load. The control loop of each converter is designed individually using its equivalent resistive load. It is shown that this design procedure offers a good small-signal performance and very stable transient responses for the entire system. To verify analysis results and to illustrate the design approach, computer simulations are performed in both frequency and time domain. Frequency-domain simulations are performed using ASTAP with a small-signal model of the system. Time-domain simulations are performed using EASY5 with an exact nonlinear model of the system. >

Multistage distributed power systems are analyzed, focusing on the dynamic interactions between two cascaded converter stages. An unterminated modeling and design approach is proposed to design a converter driving other converters downstream. Results of the analysis were verified by both frequency- and time-domain simulations. >

A systematic control-loop design procedure for a multimodule converter system for high-current, low-voltage applications is presented. A small-signal model of the system is derived using the PWM (pulse width modulation) switch model and the small-signal model of the current mode control. The small-signal model for the multimodule converter system is simplified to a equivalent single-module model. The control-loop design is implemented using the single-module model. A three-loop control strategy for the multimodule converter system with a secondary output filter is developed. Significant improvements of small-signal performance and module-failure response are achieved using additional feedback from the intermediate filter stage. The small-signal analysis of the three-loop controlled converter is performed, focusing on the effects of the local voltage feedback on the closed-loop performance of the system. It is shown that local voltage feedback minimizes any detrimental effect of the resonance between the power stage filter of each converter module and the common output filter. >

This paper presents the steady-state analysis and design of a forward-flyback converter that employs two transformers and an output inductor. By utilizing two separate transformers, the proposed converter allows a low-profile design to be readily implemented while retaining the merits of a conventional single-transformer forward-flyback converter with secondary center tap. By using an output inductor, the proposed converter efficiently reduces the output ripple to an acceptable level. The design and performance of the proposed converter are confirmed with experiments on a 100 W prototype converter.

This paper presents a new contactless battery charger that is well suited for the applications to the low-profile portable telecommunication/computing electronics such as cellular phones, Internet phones, palm-tops, and other hand-held electronics of the future. The performance of the proposed charger is confirmed with experiments on a prototype charger developed for cellular phones.