Equivalent circuit models for resonant and PWM switches

The nonlinear switching mechanism in pulsewidth-modulated (PWM) and quasi-resonant converters is that of a three-terminal switching device which consists only of an active and a passive switch. An equivalent circuit model of this switching device describing the perturbations in the average terminal voltages and current is obtained. Through the use of this circuit model the analysis of pulsewidth modulated and quasiresonant converters becomes analogous to transistor circuit analysis where the transistor is replaced by its equivalent circuit model. The conversion ratio characteristics of various resonant converters and their relationship to a single function, called the quasi-resonant function, is easily obtained using the circuit model for the three-terminal switching device. The small-signal response of quasi-resonant converters to perturbations in the switching frequency and input voltage is determined by replacing the three-terminal switching device by its small-signal equivalent circuit model     

Quasi-square-wave converters: topologies and analysis

A class of converters with zero-voltage or zero-current switching characteristics is analyzed using a method originally developed for quasiresonant and PWM (pulsewidth-modulated) converters. The method relies on identifying simple three-terminal structures, called converter sections, that contain the switches and the resonant tank elements. The various zero-voltage-switched and zero-current-switched converters are obtained by permutation of these converter sections between source and sink. The method unifies the analysis of this class of converters in a single equivalent circuit model. The voltage and current waveforms in these converters are essentially squarelike except during the turn-on and turn-off switching intervals     

Engineering design of lossless passive soft switching methods for PWM converters. II. With nonminimum voltage stress circuit cells

This paper proposes the analysis and design methodology of lossless, passive soft switching methods for PWM converters. The emphasis of the design and analysis is for PWM converters that use nonminimum voltage stress (non-MVS) circuit cells to provide soft switching. PWM converters with non-MVS circuit cells have several distinct advantages over converters that use minimum voltage stress (MVS) cells. With the same relative size of the inductor and capacitor added for soft switching, the non-MVS cells have a substantially larger duty ratio range where soft switching is guaranteed. In addition, the overcurrent stress of the main switch, under most conditions, will be lower and an optimum value of inductor and capacitor added for soft switching can be used. Therefore, with proper design, the non-MVS cells provide higher efficiency. These advantages are obtained with the price of higher switching voltage stress and one additional inductor. The loss model for a MOSFET and optimum capacitor and inductor values are utilized in the design procedure. Examples of the design procedure are given for PFC and DC-DC applications. Experimental results backup the claim of higher efficiency.     

New family of zero-current-switching PWM converters using a new zero-current-switching PWM auxiliary circuit

A new family of zero-current-switching (ZCS) pulsewidth-modulation (PWM) converters using a new ZCS-PWM auxiliary circuit is presented in this paper. The main switch and auxiliary switch operate at ZCS turn-on and turn-off, and the all-passive semiconductor devices in the ZCS-PWM converters operate at zero-voltage-switching (ZVS) turn-on and turn-off. Besides operating at constant frequency and reducing commutation losses, these new converters have no additional current stress and conduction loss in the main switch in comparison to the hard-switching converter counterpart. The PWM switch model and state-space averaging approach is used to estimate and examine the steady-state and dynamic character of the system. The new family of ZCS-PWM converters is suitable for high-power applications using insulated gate bipolar transistors (IGBTs). The principle of operation, theoretical analysis, and experimental results of the new ZCS-PWM boost converter, rated 1.6 kW and operating at 30 kHz, are provided in this paper to verify the performance of this new family of converters.     

无源软开关电路拓扑的研究

提出一个研究无源软开关电路的新技术方法;其特征是对基本的单管隔离型PWM DC/DC变换器进行类比分析,由此直接导出可行的缓冲能量再生复位电路.该新方法能使DC/DC PWM硬开关变换器转变为软开关变换器.以新型Boost无源软开关变换器为例,进行了电路理论分析与中功率样机的实验测试;结果表明此新变换器具有较宽的软开关工作范围、较低的电应力、较小的缓冲元件量值等特点.由此认为,这种研究方法推导简单、物理意义清晰,还能深入地研究无源软开关的新电路拓扑.     

A zero-voltage-switched PWM boost converter with an energyfeedforward auxiliary circuit

A zero-voltage-switched (ZVS) pulsewidth-modulated (PWM) boost converter with an energy feedforward auxiliary circuit is proposed in this paper. The auxiliary circuit, which is a resonant circuit consisting of a switch and passive components, ensures that the converter's main switch and boost diode operate with soft switching. This converter can function with PWM control because the auxiliary resonant circuit operates for a small fraction of the switching cycle. Since the auxiliary circuit is a resonant circuit, the auxiliary switch itself has both a soft turn on and turn off, resulting in reduced switching losses and electromagnetic interference (EMI). This is unlike other proposed ZVS boost converters with auxiliary circuits where the auxiliary switch has a hard turn off. Peak switch stresses are only slightly higher than those found in a conventional PWM boost converter because part of the energy that would otherwise circulate in the auxiliary circuit and drastically increase peak switch stresses is fed to the load. In this paper, the operation of the converter is explained and analyzed, design guidelines are given, and experimental results obtained from a prototype are presented. The proposed converter is found to be about 2%-3% more efficient than the conventional PWM boost converter     

一种新型软开关DC-DC PWM升压变换器设计

为提高转换效率并降低电源开关的电流应力,提出一种基于新型有源缓冲电路的PWM DC-DC升压变换器。该有源缓冲电路使用ZVT—ZCT软开关技术,分别提供了总开关ZVT开启及ZCT闭合、辅助开关ZCS开启及ZCT闭合。消除了总开关额外的电流及电压应力,消除了辅助开关电压应力,且有源缓冲电路的耦合电感降低了电流应力。另外,通过连续将二极管添加到辅助开关电路,防止来自共振电路的输入电流应力进入总开关。实验结果表明,相比传统的PWM变换器,新的DC-DC PWM升压变换器在满负荷时电流应力降低且总体效率能达到98.7%。     

Novel reduced-order small-signal model of a three-phase PWMrectifier and its application in control design and system analysis

A reduced-order (RO) small-signal model of three-phase pulse-width-modulation (PWM) rectifiers is proposed. By combining the PWM switch model and equivalent multimodule model techniques in DC-DC converters, a three-phase rectifier can be modeled as a DC-DC converter with equivalent power capability and small-signal characteristics. This model reduces the system order to two and greatly simplifies the control design and system analysis of three-phase converters. In this paper, the proposed model is also used for control design and for system interaction analysis on the three-phase interface of a boost rectifier. The RO model is verified with the d-q model, switching-model simulation, and experimental results     

A unified approach to modeling, synthesizing, and analyzingquasi-resonant converters

This paper presents a general method of modeling, synthesizing, and analyzing quasi-resonant converters (QRCs), including actively clamped QRCs. First, the concept of the pulse-width modulation (PWM) switch model is generalized to encompass all PWM (nonisolated) converters. Then, by adding inductor-capacitor (LC) elements and auxiliary switches into the PWM switch, QRC families are synthesized. DC and small signal analyses can be carried out based on these switch models. Furthermore, the duality relationship between zero-voltage-switching (ZVS) and zero-current-switching (ZCS) QRCs is established systematically and rigorously     

A systematic approach to developing single-stage soft switching PWMconverters

A systematic approach to developing soft switching PWM converters based on the synchronous switch scheme is presented in this paper. With the approach, several families of passive and active soft switching PWM converters, such as buck-boost, Zeta, Cuk, and Sepic, can be generated from the two basic converters, buck and boost. Also, the approach is used to integrate multiple converters to form a single-stage soft switching PWM converter. It has been shown that analysis of the converters can be conveniently performed from the derived general configurations, reducing the complexity significantly. Therefore, employing the technique can not only explore more physical insights into the converters in a family but reveal more relationships among the soft switching converters over conventional approaches. Measured results from a prototype have verified the feasibility of the derived single-stage converters     

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     

On the modeling of PWM converters for large signal analysis indiscontinuous conduction mode

Several methods have been developed until today for the analysis of PWM converters operating in discontinuous conduction mode (DCM) and many endeavours have been done in order to solve two well known problems: the nontrivial calculation of the internally controlled instant at which the current flowing into the diode falls to zero and the subsequent order reduction of the state-space model of the circuit due to the disappearance of one state variable. In this work a new approach to the modeling of PWM converters for the large signal analysis in DCM operation is presented. It is based on a closed-form discrete-time state-space model obtained by introducing a time-adaptive function for the calculation of the instant at which the diode current falls to zero, and an equivalent fictitious configuration of the circuit during the idle phase, in order to prevent the unconditioned order reduction of the state-space model. A four-terminal device is also introduced which allows a unified representation of the PWM buck, boost, buck-boost, and Cuk converters in DCM operation using the fictitious configuration. The model proposed can be used for circuit oriented simulations both in open and closed loop operation and for an accurate ripple inspection, automatically accounting for DCM to CCM (continuous conduction mode) transitions and vice versa     

A New Family of Zero-Current-Switching (ZCS) PWM Converters

A new family of zero-current-switching (ZCS) pulsewidth-modulated (PWM) converters which uses a new ZCS-PWM switch cell is presented in this paper. The main switch and auxiliary switch operate at ZCS turn-on and turn-off, and all the passive semiconductor devices in the ZCS-PWM converter operate at zero-voltage-switching (ZVS) turn-on and turn-off. Besides operating at constant frequency and with reduced commutation losses, these new converters have no additional current stress in comparison to the hard-switching converter counterpart. The new family of ZCS-PWM converters is suitable for high-power applications using insulated gate bipolar transistors (IGBTs). The PWM switch model and state-space averaging approach is used to estimate and examine the steady-state and dynamic character of the system. The principle of operation, theoretical analysis, and experimental results of the new ZCS-PWM boost converter, rated 1 kW and operating at 30 kHz, are provided in this paper to verify the performance of this new family of converters.     

基于PWM的逆变电路分析

PWM控制技术是逆变电路中应用最广泛的技术.为了对PWM型逆变电路进行分析,从PWM控制的基本原理出发,首先建立了逆变器控制所需的电路模型,采用IGBT作为开关器件,并对单相桥式电压型逆变电路和PWM控制电路的工作原理进行了分析.使用双踪示波器对电路的输出波形进行分析,给出了仿真波形.实践表明:运用PWM控制技术能够很好地实现逆变电路的运行要求.     

PWM-switch modeling of DC-DC converters

The introduced PWM-switch modeling method is a simple method for modeling pulse-width-modulated (PWM) DC-DC converters operating in the continuous conduction mode. The main advantage of this method is its versatility and simple implementation compared to other methods. The basic idea is the replacement of the switches in the converter by their time-averaged models. These switch models have been developed in such a way that the converter model provides the same results as the state-space-averaging technique but not including nonlinear effects. Simple rules for determination of the switch models are obtained. The resulting model is a time-averaged equivalent circuit model where all branch currents and node voltages correspond to their averaged values of the corresponding original currents and voltages. The model also includes parasitics, second-order effects and nonlinearities, and can be implemented in any circuit-oriented simulation tool. The same model is used for the simulation of the steady-state and the transient behavior     

A unified approach to characterization of PWM and quasi-PWMswitching converters: topological constraints, classification, andsynthesis

Topological constraints are obtained for pulse width-modulation (PWM) (under both continuous and discontinuous current modes) and quasi-PWM (including families of quasi-resonant and quasi-square wave) converters by identifying their three structures. Switching sequences of these converters and a classification of quasi-PWM power converters are presented. A dual circuit of an ideal diode and an ideal switch are proposed and used to obtain duals of the switching converters in one step. A procedure for the synthesis of quasi-PWM converters is presented     

Self-commutated auxiliary circuit ZVT PWM converters

This paper introduces a novel class of zero voltage transition (ZVT) DC/DC pulse-width modulation (PWM) converters that use a resonant inductance-capacitance (L-C) circuit connected to the auxiliary switch, which is termed a self-commutated auxiliary circuit. It provides a simple and reliable means of achieving zero-current conditions (ZCS) for auxiliary switch commutations under wide line and load ranges, without the inclusion of any kind of DC voltage source. Furthermore, this auxiliary circuit is placed in parallel with the main power converter, retaining the ZVT characteristics. The self-commutated auxiliary circuit ZVT PWM boost is analyzed, and its feasibility and reliability are confirmed by experimental results obtained from laboratory prototypes rated at 1 kW and 100 kHz.     

A general unified large signal model for current programmedDC-to-DC converters

A general and unified large signal averaged circuit model for current programmed DC-to-DC converters is proposed. In the averaged circuit model, the active switch is modeled by a current source, with its value equal to the averaged current flowing through it, and the diode is modeled hy the voltage source, with its value equal to the averaged voltage across it. The averaged circuit model has the same topology as the switching converter. The large signal averaged circuit model for current programmed buck, boost, buck-boost and Cuk converters are proposed, from which the large signal characteristics can be obtained. The steady-state and small signal transfer functions of the current programmed DC-to-DC converters can all be derived from their large signal averaged circuit models. The large signal characteristics of the current programmed buck converter are studied by both the phase plane trajectory and the time domain analysis. Experimental prototypes for a current programmed buck converter, with and without an input filter, are breadboarded to verify the analysis     

Comparison of performance of single-loop and current-injectioncontrol for PWM converters that operate in both continuous anddiscontinuous modes of operation

An analysis of current-injection-controlled (CIC) power converters operating in both the continuous and discontinuous modes is performed using the PWM switch model and a new, continuous-time model of CIC. The stability, output impedance, audio susceptibility, and transient response are compared with single-loop control. The control of an example buck converter is designed with CIC and single-loop control. It is shown how single-loop controlled power converters exhibit a large change in the dynamic performance when crossing the boundary between continuous mode and discontinuous mode. This is especially true for the output impedance and transient response. The dynamic performance of CIC power converters remains relatively fixed when crossing this boundary. A significant performance improvement can be realized when CIC is employed in converters that operate over a wide load range     

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