Modeling PWM DC/DC converters out of basic converter units

An alternative approach to modeling pulsewidth-modulated (PWM) DC/DC converters out of basic converter units (BCUs) is presented in this paper. Typical PWM DC/DC converters include the well-known buck, boost, buck-boost, Cuk, Zeta, and Sepic. With proper reconfiguration, these converters can be represented in terms of either buck or boost converter and linear devices, thus, the buck and boost converters are named BCUs. The PWM converters are, consequently, categorized into buck and boost families. With this categorization, the small-signal models of these converters are readily derived in terms of h parameter (for buck family) and g parameter (for boost family). Using the proposed approach, not only can one find a general configuration for converters in a family, but one can yield the same small-signal models as those derived from the direct state-space averaging method. Additionally, modeling of quasi-resonant converters and multiresonant converters can be simplified when adopting the proposed approach     

A systematic and unified approach to modeling PWM DC/DC convertersbased on the graft scheme

A systematic and unified approach to modeling pulsewidth modulated (PWM) DC/DC converters based on the graft scheme is presented in this paper. With the graft scheme, the typical PWM switch-mode converters, such as buck-boost, boost-buck (Cuk), Sepic, and dual Sepic, can be generated from the two basic converters, buck and boost. The small signal models of these converters can, therefore, be derived by properly combining those of the buck and boost. Using the proposed approach can help to yield highly related dynamic models of the converters in a family and, in addition, physical insights into the converters can be readily identified. This has made the proposed modeling method valuable and viable     

Averaged modeling of PWM converters operating in discontinuousconduction mode

Various aspects of averaged modeling of hard-switching pulse-width modulated (PWM) converters operating in the discontinuous conduction mode (DCM) are studied. A more streamlined modeling procedure is proposed which serves as a general framework for comparing different models. A duty ratio constraint that defines the diode conduction interval is identified to be the key to accurate prediction of high-frequency behavior. A new duty-ratio constraint is proposed that leads to full-order averaged models of DCM converters. Numerical analyses and experimental measurements confirm that the new models correctly predict the small-signal responses up to one third of the switching frequency and are more accurate than all previous models. Moreover, new analytical results are included to show the origin of the high-frequency pole in DCM operation and to explain why the full-order model is capable of accurately predicting it. Averaged circuit counterparts of the new models are developed in the form of averaged switch models to facilitate circuit simulation     

Application of the current-injected modeling approach toquasi-resonant converters

This paper describes how the current-injected (CI) method, which has been applied only to pulse-width modulation (PWM) DC-DC power converters, can be extended to quasi-resonant (QR) power converters. The methodology for extending this small-signal modeling approach is described in detail. It is also shown that QR dynamic models are easy to obtain since they are derived directly from PWM power converter models. These new models result in a unified block diagram from which zero-voltage-switching (ZVS) or zero-current-switching (ZCS) transfer functions of the basic topologies, such as buck, boost, and buck-boost operated in half-wave (HW) or full-wave (FW) modes, are found. As an application of this method, a ZVS boost power converter and ZCS boost power converter were fabricated and tested. In addition, small-signal models of these power converters were derived with the help of the state-space averaging (SSA) method. The agreement of the CI method simulations with the experimental results for the two QR power converters is comparable or better than that of the SSA method     

Spectral characteristics of randomly switched PWM DC/DC convertersoperating in discontinuous conduction mode

This paper addresses a comparative study of the spectral characteristics of four random-switching schemes that apply to the basic pulsewidth-modulation (PWM) DC/DC converters operating in discontinuous conduction mode (DCM). They include randomized pulse position modulation, randomized pulsewidth modulation, and randomized carrier frequency modulation with fixed duty cycle and with fixed duty time, respectively. Mathematical models that characterize the input current and output voltage of the three basic PWM converters operating in DCM are derived. In particular, the effectiveness of spreading the dominant switching harmonics in the input current that normally exist in the standard PWM scheme and the introduction of low-frequency harmonics in the output voltage with respect to the randomness level are investigated. The validity of the models and analyses are confirmed experimentally by using a DC/DC buck converter     

Computer-aided modeling of quasi-resonant converters in thepresence of parasitic losses by using the MISSCO concept

The DC and small-signal models of quasi-resonant converters, operating in both half-wave and full-wave modes, are developed in a suitable form for computer simulation. The starting step is the extraction of a minimum separable switching configuration (MISSCO) containing all power switches but a minimum number of other components (resonant ones). By using the step-response analysis and average technique, and by perturbing and separating the DC and AC components in the resulting equations, the equivalent models of MISSCO are derived. They are introduced in the converter structure to replace the circuit initially extracted. Models of different quasi-resonant converters can be obtained by this general approach. The analysis takes into account the conduction losses of the switching devices and reactive elements, which improves considerably the model accuracy. Model-based computer simulation agrees with the experimental results     

Voltage and current stress reduction in single-stage power factorcorrection AC/DC converters with bulk capacitor voltage feedback

Single-stage power factor correction (PFC) AC/DC converters integrate a boost-derived input current shaper (ICS) with a flyback or forward DC/DC converter in one single stage. The ICS can be operated in either discontinuous current mode (DCM) or continuous current mode (CCM), while the flyback or forward DC/DC converter is operated in CCM. Almost all single-stage PFC AC/DC converters suffer from high bulk capacitor voltage stress and extra switch current stress. The bulk capacitor voltage feedback with a coupled winding structure is widely used to reduce both the voltage and current stresses in practical single-stage PFC AC/DC converters. This paper presents a detailed analysis of the bulk capacitor voltage feedback, including the relationship between bulk capacitor voltage, input current harmonics, voltage feedback ratio, and load condition. The maximum bulk capacitor voltage appears when the DC/DC converter operates at the boundary between CCM and DCM. This paper also reveals that only the voltage feedback ratio determines the input current harmonics under DCM ICS and CCM DC/DC operation. The theoretical prediction of the bulk capacitor voltage as well as the predicted input harmonic contents is verified experimentally on a 60 W AC/DC converter with universal-line input     

Analysis and Design for a Novel Single-Stage High Power Factor Correction Diagonal Half-Bridge Forward AC–DC Converter

By means of components placement, the buck-boost and diagonal half-bridge forward converters are combined to create a novel single-stage high power factor correction (HPFC) diagonal half-bridge forward converter. When both the PFC cell and dc–dc cell operate in DCM, the proposed converter can achieve HPFC and lower voltage stress of the bulk capacitor. The circuit analysis of the proposed converter operating in$ DCM+ DCM$mode is presented. In order to design controllers for the output voltage regulation, the ac small-signal model of the proposed converter is derived by the averaging method. Based on the derived model, the proportional integral (PI) controller and minor-loop controller are then designed. The simulation and experimental results show that the proposed converter with the minor-loop controller has faster output voltage regulation than that with the PI controller despite the variations of line voltage and load. Finally, a 100-W prototype of the proposed ac–dc converter is implemented and the theoretical result is experimentally verified.     

A unified SPICE compatible average model of PWM converters

A simple, unified, and topology-independent model of basic pulse-width modulated (PWM) power converters is developed using the switched inductor approach presented by S. Ben-Yaakov (1989). The model is compatible with SPICE or other similar general-purpose electronic circuit simulators. It can be used to simulate DC, small signal, and transient behavior of PWM converters operating in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). During simulation, the model automatically follows the CCM and DCM operation, with fewer convergence problems compared to previous simulation models. An effective measurement technique using the HP3562A dynamic signal analyzer (DSA) is presented and applied to compare simulation runs with experimental data. The two were found to be in good agreement     

Characterization of single-stage three-phasepower-factor-correction circuit using modular single-phase PWM DC-to-DCconverters

The complete DC characteristics of three-phase modular power-factor-correction (PFC) converters using single-phase pulsewidth modulation (PWM) DC-to-DC converter modules for high-power applications are studied. Using circuit averaging, the converter input and output quantities are determined numerically. Both the continuous and discontinuous output current modes of operation (CCM and DCM) are studied in detail. Near-unity power factor can be achieved with the converter modules operating in the DCM. An averaged model was used to study and determine the boundaries between DCM and CCM over the full period of the three-phase input voltage. It is found that high power factor is inherent in the converter system provided that the converters are operated in the DCM and the voltage conversion ratio is selected properly. The criteria for obtaining high power factor are analyzed and the optimal circuit parameters are determined to obtain the best achievable power factor. Both simulations and experimental results from a 1.5-kW prototype using full-bridge converter modules have confirmed the analysis     

Output plane analysis of load-sharing in multiple-module convertersystems

This paper explores the origin of the DC current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems. Both problems may be studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems. Furthermore, a broad class of converters whose output voltage is load-dependent, i.e., those that have a moderate value of output resistance, all exhibit good voltage- and current-sharing characteristics. Such converters are often suitable for a×b arrays of converters that can meet a large range of power-conversion requirements. The output planes of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A simple small-signal model of the modular converter system is developed. Experimental confirmation of load sharing and the small-signal model is given for the clamped series resonant converter and the series resonant converter for various configurations of four converters     

New multi-output switching converters with MOSFET-rectifier postregulators

A new multi-output switching power converter is proposed. The new power converter can reduce conduction losses and achieve tight regulation. The small-signal model of the new power converter has also been developed and experimentally verified. Based on the proposed scheme and the analysis of the small-signal model, high-performance and high-efficiency multi-output switching power converters can be achieved     

Modeling, analysis, and design of the quasi-charge control

A current-mode control technique, quasi-charge control (QCC), is studied. A small-signal model is developed for QCC. The model is derived for converters operating in the continuous conduction mode. The model is accurate up to half of the switching frequency. The proposed small-signal model is used to assess the dynamics of pulse-width-modulated (PWM) power converters with QCC, and to compare their performance to the current-injected control (CIC) and charge control (CC) schemes. As in CC, the QCC converges to CIC at light loads close to the boundary between continuous and discontinuous conduction modes. The dynamics of power converters with QCC or CC are more sensitive to load change and less sensitive to line change than those of power converters with CIC, especially the current loop dynamics. However, unlike in the case of CC, the dependency on the load/line can be controlled when the QCC is designed. Control design guidelines for DC-DC power converters and power factor correction rectifiers are presented, and experimental measurements are performed to verify the proposed model     

基于动态相量法的PWM DC/DC变换器的建模与分析方法

文章从动态相量的概念以及基本性质出发,推导了动态相量法应用于PWM DC/DC变换器建模与分析的数学方法。首先介绍了纹波的计算方法,引入了选择模式分析法对PWM DC/DC变换器动态相量模型进行简化,建立了小信号模型,并以PWM BUCK/BOOST双向DC/DC变换器为例,用MATLAB软件建立了PWM DC/DC变换器的动态相量模型,将之与时域仿真模型进行了比较,验证了该方法的有效性。     

A general approach to synthesis and analysis of quasi-resonantconverters

A method for systematic synthesis of quasi-resonant (QR) topologies by addition of resonant elements to a parent pulse-width modulation (PWM) converter network is proposed. It is found that there are six QR classes with two resonant elements, including two novel classes. More complex QR converters can be generated by a recursive application of the synthesis method. Topological definitions of all known and novel QR classes follow directly from the synthesis method and topological properties of PWM parents. The synthesis of QR converters is augmented by a study of possible switch realizations and operating modes. In particular, it is demonstrated that a controllable rectifier can be used to accomplish the constant-frequency control in all QR classes. Links between the QR converters and the underlying PWM networks are extended to general DC and small-signal AC models in which the model of the PWM parent is explicitly exposed. Results of steady-state analyses of selected QR classes and operating modes include boundaries of operating regions, DC characteristics, a comparison of switching transitions and switch stresses, and a discussion of relevant design trade-offs     

Actively clamped bidirectional flyback converter

An actively clamped bidirectional flyback converter is proposed. The converter's operation is examined in detail. All switches in the converter have zero-voltage-switching characteristics. A low-frequency behavior model and small-signal transfer functions are derived. It is found that the flow of current is directly under the control of the duty cycle, and that the transformer's leakage inductance has a significant effect on the control characteristic of the converter. It is expected that such bidirectional converters will find wide applications in the interconnection of multiple sources of DC power to a common bus (e.g., in a DC uninterruptible power supply). Simulation and experiment results are also presented     

电压控制型BUCK变换器DCM的精确离散模型及分叉稳定性分析

本文建立了不连续运行模式下电压反馈型BUCK变换器精确的离散数学模型,在此基础上分析了BUCK 变换器的分叉稳定性问题,得到了变换器参数之间相互关系的解析表示式,改进了已有近似模型的结论,界定了变换器主要参数的稳定运行范围,并展现了BUCK 变换器从稳定到倍周期分叉甚或混沌的过程.本文的研究方法具有一般性,为DC/DC功率变换器非线性现象的分析建立数学模型基础.     

Nonlinear modeling of the PWM switch

The nonlinearity due to the switching action in pulse-width-modulated (PWM) DC-to-DC converters, DC-to-AC inverters, or amplifiers and input-current-shaping AC-to-DC converters can often conveniently be confined to three-terminal structure referred to as the PWM switch. The PWM switch represents a static nonlinearity for which circuit models can easily be derived for frequencies harmonically related to the frequency of perturbation. Converter analysis can thus be approached in a way analogous to ordinary transistor circuit analysis whereby the nonlinear three-terminal device is replaced by its circuit model. A first-order approximation of the model results in the small-signal model     

Signal flow graph modelling and analysis of interleaved DC?DC parallel converters

This paper presents a systematic development of a unified signal flow graph model for an interleaved DC–DC parallel converter system operating in continuous current mode. This signal flow graph approach provides a means to translate directly the switching converter to its graphic model, from which the steady-state and dynamic behaviour of the converter can be studied easily. The development of a unified signal flow graph is explained for a three-cell interleaved parallel converter system. Derivation of large-signal, small-signal and steady-state models from a unified signal flow graph is demonstrated by considering a two-cell interleaved converter system operating in complementary activation mode. Converter performance expressions such as steady-state voltage gain, efficiency expressions and small-signal characteristic transfer functions are also derived. A large-signal model was programmed in a TUTSIM simulator, and the large-signal responses against supply and load disturbances were predicted. Signal flow graph analysis results are validated with PSIM simulations. Experimental observations are provided to validate the signal flow graph modelling method. Further, the mathematical models obtained from the signal flow graph modelling are in agreement with those obtained from the state-space averaging technique.     

Large-signal modeling of hysteretic current-programmed converters

Large-signal dynamic models for hysteretic current-programmed buck, boost, and buck-boost converters are proposed. The model is expressed by a single differential equation. The small-signal transfer functions of these three converters are also derived, based on the large-signal model. The analysis shows that under the hysteretic current-programmed control, the output voltage of the buck converter is independent of the supply voltage, and there is a right-halfplane (RHP) zero in the control-to-output transfer function of boost and buck-boost converters. An experimental prototype is breadboarded to verify the analysis