Physical origins of input filter oscillations in current programmedconverters

Addition of an input filter to a current-programmed converter can cause the controller to oscillate. Two instability mechanisms can typically occur: (1) the current programmed controller effective current feedback loop may become unstable, or (2) the controller effective input voltage feedforward loop, which becomes a positive feedback loop when an input filter is added, may oscillate. Three design criteria for preventing oscillations are derived and interpreted. When all three criteria are well satisfied, then the output voltage regulation loop gain is unchanged. Hence, input filters of current programmed converters can be designed in essentially the same manner as for duty-ratio programmed converters. Results are summarized in tabular form for the basic buck, boost, and buck-boost converters. Experimental measurements for a buck converter with different input filters support the theoretical predictions     

Extending the tapped-inductor DC-to-DC converter family

Two new members of the family of switched mode converters employing tapped inductors are identified. The input to output voltage ratio for buck, boost and buck-boost converters with all possible tapping arrangements are analysed in terms of the tap position and switch duty cycle. Practical test results for the new converters are presented     

几种新型的Buck—Boost变换器的合成

从传输机制说明单管升降压变换器（如Buck-Boost、SPEIC、Cuk）中元件承受的电压和电流应力高的原因,并根据这一机制,采用变换器合成的方式,提出了一系列的双管Buck-Boost变换器。这类变换器根据输入输出条件,可以分别工作于Boost模式和Buck模式,起到降低元件应力的作用。     

A Compensation Technique for Smooth Transitions in a Noninverting Buck–Boost Converter

With the advent of battery-powered portable devices and mandatory adoption of power factor correction, noninverting buck-boost converters are garnering lots of attention. Conventional two-switch or four-switch noninverting buck-boost converters choose their operation modes by measuring input and output voltage magnitude. The criterion for the selection of the operation mode can cause higher output voltage transients in the neighborhood, where input and output are close to each other. For the mode selection, due to the voltage drops raised by the parasitic components, it is not enough just to compare the magnitude of input and output voltages. In addition, the difference in the minimum and maximum effective duty cycles between controller output and switching device yields discontinuity at the instant of mode change. Moreover, the different properties of output voltage versus a given duty cycle of buck and boost operating modes contribute to the output voltage transients. In this paper, the effect of the discontinuity due to the effective duty cycle derived from the device switching time at the mode change is analyzed. A technique to compensate the output voltage transient due to this discontinuity is proposed. In order to attain additional mitigation of output transients and a linear input/output voltage characteristic in buck and boost modes, the linearization of DC gain of the large-signal model in boost operation is analyzed as well. Analytical, simulation, and experimental results are presented to validate the proposed theory.     

Switched-Capacitor/Switched-Inductor Structures for Getting Transformerless Hybrid DC–DC PWM Converters

A few simple switching structures, formed by either two capacitors and two-three diodes (C-switching), or two inductors and two-three diodes (L-switching) are proposed. These structures can be of two types: ldquostep-downrdquo and ldquostep-up.rdquo These blocks are inserted in classical converters: buck, boost, buck-boost, Cuk, Zeta, Sepic. The ldquostep-downrdquo C- or L-switching structures can be combined with the buck, buck-boost, Cuk, Zeta, Sepic converters in order to get a step-down function. When the active switch of the converter is on, the inductors in the L-switching blocks are charged in series or the capacitors in the C-switching blocks are discharged in parallel. When the active switch is off, the inductors in the L-switching blocks are discharged in parallel or the capacitors in the C-switching blocks are charged in series. The ldquostep-uprdquo C- or L-switching structures are combined with the boost, buck-boost, Cuk, Zeta, Sepic converters, to get a step-up function. The steady-state analysis of the new hybrid converters allows for determing their DC line-to-output voltage ratio. The gain formula shows that the hybrid converters are able to reduce/increase the line voltage more times than the original, classical converters. The proposed hybrid converters contain the same number of elements as the quadratic converters. Their performances (DC gain, voltage and current stresses on the active switch and diodes, currents through the inductors) are compared to those of the available quadratic converters. The superiority of the new, hybrid converters is mainly based on less energy in the magnetic field, leading to saving in the size and cost of the inductors, and less current stresses in the switching elements, leading to smaller conduction losses. Experimental results confirm the theoretical analysis.     

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 design criteria for the current gain in current-programmedregulators

The design of the inner loop for current-programmed regulators is discussed in this paper. The effect that current gain has on the quality factor Q of the LC filter is shown. A methodology is derived to reduce this value that, in most cases, can be very high. A high quality factor can produce drastic changes with undesirable effects on regulator stability. A low quality factor will produce two real poles with a consequent reduction in the current response. After the proper selection of the current gain is done, the design procedure for the proportional integral controller of the outer loop can be continued. The design-oriented analysis is applicable to the three basic switch-mode pulsewidth modulation converters, i.e. buck, boost and buck-boost. At the end, the procedure is applied to a 280 W boost regulator that shows the simplicity of this approach     

一种车用恒流/恒压模式的四开关Buck-Boost变换器控制策略研究

对一种车用恒流/恒压模式的四开关Buck-Boost变换器的控制策略进行了研究。在输入输出电压接近时引入Buck-Boost模式,从而在不同输入输出电压大小关系下,通过检测功率管占空比大小,实现Buck模式、Boost模式和Buck-Boost模式之间的平滑切换,提高了系统的稳定性。通过设计最大值选择电路,使变换器在充电应用中自动从恒流模式切换到恒压模式,模式切换平滑稳定。仿真结果表明,在24 V输出电压下,变换器从Buck模式切换到Buck-Boost模式时,输出电压下冲为9.2 mV,变换器从Boost模式切换到Buck-Boost模式时,输出电压下冲为92 mV。变换器在Buck模式与Boost模式下均能实现恒流/恒压模式的自动平滑切换。     

Practical switch based state-space modeling of DC-DC converterswith all parasitics

All parasitics such as switch conduction voltages, conduction resistances, switching times, and ESRs of capacitors are counted in a proposed DC-DC power convertor state-space modeling based method on nonideal switching functions. An equivalent simplified model is derived from the complex circuit with parasitics. The modeling procedure is shown for the buck-boost converter as the general converter among the buck, boost, and buck-boost converters. The pole frequency, DC voltage gain, and efficiency are analyzed and verified by experiments that show good agreement with theory. The procedures for determining the gain margin of the controller, the turn ratio of an isolation transformer, the optimum duty factor, and the switching frequency are given for an example flyback converter     

Function control-a novel strategy to achieve improved performanceof the DC-to-DC switching regulators

The control strategy of the DC-to-DC switching converters is studied to obtain the switching regulators with zero-voltage regulation. A novel control strategy, the function control, is presented for the DC-to-DC switching converters to achieve this objective. The control law and the corresponding feedback are derived directly from the equations governing the switching converters. With the function control strategy presented in the paper, the switching regulators become robust, i.e., the output is independent of the disturbances from either the supply voltage or the load and exhibits other desirable advantages. The strategy is applicable to all the four basic PWM converters, i.e., buck, boost, buck-boost, and Cuk. The analysis is confirmed by experiments and computer simulations     

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     

A unified approach to the design of PWM-based sliding-mode voltage controllers for basic DC-DC converters in continuous conduction mode

This paper presents a simple unified approach to the design of fixed-frequency pulsewidth-modulation-based sliding-mode controllers for dc-dc converters operating in the continuous conduction mode. The design methodology is illustrated on the three primary dc-dc converters: buck, boost, and buck-boost converters. To illustrate the feasibility of the scheme, an experimental prototype of the derived boost controller/converter system is developed. Several tests are performed to validate the functionalities of the system.     

Modeling current-programmed buck and boost regulators

A general small-signal model for current-programmed switching power stages is used for design-oriented analysis of a 150 W buck regulator and a 280 W boost regulator. The model, into which the current-programming minor feedback loop is absorbed, exposes the desired tendency towards 'constant' output current. The regulator voltage loop remains the only explicit feedback loop, allowing the regulator closed-loop properties to be easily obtained from those of the open-loop current-programmed power stage. The design-oriented analytic results allow easy inference of the effects of element changes on the regulator performance functions. Results are obtained for the regulator line-to-output transfer function (audio susceptibility) and output impedance     

Sustained Slow-Scale Oscillation in Higher Order Current-Mode Controlled Converter

DC-DC converters under current-mode control have been known to exhibit slow-scale oscillation as a result of a Hopf-type bifurcation as one or more of the parameters of the outer voltage loop are varied. In the absence of the outer voltage loop (i.e., open loop), slow-scale oscillation was generally not observed in simple low-order dc-dc converters, i.e., buck, buck-boost, and boost converters. In this paper, slow-scale bifurcation in a higher order current-mode controlled converter is studied. It has been found experimentally that, even in the absence of a closed outer voltage loop, a current-mode controlled Cuk converter can exhibit a slow-scale Hopf-type bifurcation. The phenomenon was observed in a commercial low-ripple dc-dc converter which has been designed using the Cuk converter and the LM2611 controller. Such slow-scale oscillation of the inner current loop can also be observed in full-circuit SPICE simulations. An averaged model has been developed and implemented in SPICE to find the Hopf bifurcation boundaries. With this averaged model, the Hopf bifurcation can be explained conveniently using the traditional loop gain analysis. Specifically, the extra degrees of freedom in higher order dc-dc converters have opened up a new possible mode of instability which has not been found in simple low-order dc-dc converters.     

A nonlinear resonant switch

A resonant switch is introduced that uses linear tank elements. Zero-current switching is obtained even through the peak transistor voltage and current stresses can approach those of an equivalent ideal pulsewidth-modulated converter. Reduced switching loss without a substantial increase in conduction loss is therefore possible. An approximate analysis is outlined, and transistor peak-voltage and current stresses are shown to be much lower than those of linear resonant switch technologies. Single-transistor implementations of the buck, boost, and buck-boost nonlinear resonant switch converters are given. Results are presented which experimentally prove the validity of the nonlinear resonant switch concept, as well as that of the approximate analysis     

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     

A simple large-signal nonlinear modeling approach for fastsimulation of zero-current-switch quasi-resonant converters

A nonlinear modeling approach for zero-current-switch (ZCS) quasi-resonant converters (QRC) is proposed which can be derived easily using simple analytical techniques. The converter model obtained is readily absorbed by MATLAB for analysis and design of both the open- and closed-loop configurations in fast speed. Simulations have shown its accuracy, even for large-signal transient responses. Applications of this modeling approach to the three basic topologies of buck, boost, and buck-boost converters are given as illustrative examples. The condition for zero-current switching is identified from the model. The feasibility of applying this proposed modeling approach to the extended period QRC topologies is to be discussed. Simulation results for the three basic topologies are given to show the merits of the proposed modeling approach     

Optimal feed-forward compensation for PWM DC/DC converters with`linear' and `quadratic' conversion ratio

An analytical procedure to optimize the feedforward compensation for any PWM DC/DC power converters is described. Achieving zero DC audiosusceptibility was found to be possible for the buck, buck-boost, Cuk, and SEPIC cells; for the boost converter, however, only nonoptimal compensation is feasible. Rules for the design of PWM controllers and procedures for the evaluation of the hardware-introduced errors are discussed. A PWM controller implementing the optimal feedforward compensation for buck-boost, Cuk, and SEPIC cells is described and fully experimentally characterized     

Simple topologies of PWM AC-AC converters

This letter proposes a new family of simple topologies of PWM AC-AC converters with minimal switches. With extension from the basic DC-DC converters, a series of AC-AC converters such as buck, boost, buck-boost, Cuk, and isolated converters are obtained. By PWM duty ratio control, they become a "solid-state transformer" with a continuously variable turns ratio. All the proposed AC-AC converters in this paper employ only two switches. Compared to the existing circuits that use six switches or more, they can reduce cost and improve reliability. The operating principle and control method of the proposed topologies are presented. Analysis and simulation results are given using the Cuk AC-AC converter as an example. The analysis can be easily extended to other converters of the proposed family.     

State-plane analysis of zero-current-switching resonant DC/DC powerconverters

The state-plane analysis for the buck, boost, buck/boost, and Cuk zero-current-switching resonant DC/DC power converters is presented. Simple visual criteria are introduced to determine whether the converter is operating in a mode producing voltage conversion. It is shown that the voltage conversion takes place within the converters if and only if both horizontal and vertical straight-line segments are present in the state-plane graph. The boundary of energy conversion is identified from the state plane by the evaporation of one or both straight-line segments. Formulas are found for the normalized switching frequency at this boundary that depend on the value of normalized switching voltage