Automatic modeling of PWM DC-DC converters

Different small-signal models are available for describing the dynamics of pulse width modulators (PWM) dc-to-dc converters. Discrete time models reach the best compliance in real life situations. Some converter control modes, in particular phase shifting, provide advantages of modeling in discrete time. On the other hand, the burden of getting such exact models is often tedious. Currently, automatic tools are available that are able to provide the state-space model in discrete time of any PWM dc-dc converter switching at constant frequency. The authors claim that the use of these tools is advisable for the analysis and control optimization of switching power supplies. To support their opinion, this letter refers to a new, very accurate small-signal model of a phase-shifting converter which has been published recently. Its excellent performance, as well as the difficulties of the derivation procedure, are compared with the precise forecasts and the short processing time of an automatic modeling tool. The paper concludes in favor of automatic modeling.     

Modeling the closed-current loop of PWM boost DC-DC converters operating in CCM with peak current-mode control

This paper derives the transfer function from error voltage to duty cycle, which captures the quasi-digital behavior of the closed-current loop for pulsewidth modulated (PWM) dc-dc converters operating in continuous-conduction mode (CCM) using peak current-mode (PCM) control, the current-loop gain, the transfer function from control voltage to duty cycle (closed-current loop transfer function), and presents experimental verification. The sample-and-hold effect, or quasi-digital (discrete) behavior in the current loop with constant-frequency PCM in PWM dc-dc converters is described in a manner consistent with the physical behavior of the circuit. Using control theory, a transfer function from the error voltage to the duty cycle that captures the quasi-digital behavior is derived. This transfer function has a pole that can be in either the left-half plane or right-half plane, and captures the sample-and-hold effect accurately, enabling the characterization of the current-loop gain and closed-current loop for PWM dc-dc converters with PCM. The theoretical and experimental response results were in excellent agreement, confirming the validity of the transfer functions derived. The closed-current loop characterization can be used for the design of a controller for the outer voltage loop.     

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     

Novel zero-Voltage-transition PWM DC-DC converters

A new family of zero-voltage-switching (ZVS) pulsewidth-modulated (PWM) converters that uses a new ZVS-PWM switch cell is presented in this paper. Except for the auxiliary switch, all active and passive semiconductor devices in the ZVS-PWM converters operate at ZVS turn ON and turn OFF. The auxiliary switch operates at zero-current-switching (ZCS) turns ON and OFF. Besides operating at constant frequency, these new converters have no overvoltage across the switches and no additional current stress on the main switch in comparison to the hard-switching converter counterpart. Auxiliary components rated at very small current are used. The principle of operation, theoretical analysis, and experimental results of the new ZVS-PWM boost converter, rated 1 kW, and operating at 80 kHz, are provided in this paper to verify the performance of this new family of converters.     

降压PWM DC/DC开关稳压系统仿真分析

集成CMOS脉冲宽度调制开关电源系统因为高效率、高集成度等优点在通信、计算机系统方面被广泛应用.文中通过分析建立一个PWM DC/DC稳压系统的闭环响应传输函数,研究如何在瞬态响应速度和稳定性方面进行取舍;在此基础上用Matlab建立小信号模型仿真,并通过Hspice 实现仿真验证.     

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     

On the periodic behavior of PWM DC-DC converters

In this paper, we present a method to compute the periodic behavior of PWM DC-DC converters. The method is based on Fourier series and can be seen as a generalization of the state space averaging techniques that are well-known in the field of DC-DC converters. The method of this paper can be used to compute the periodic behavior of a DC-DC converter up to any degree of accuracy. This can be done in open loop as well as in closed loop situations. In an open loop situation the method only requires the solving a set of linear equations in the Fourier coefficients. It is shown that the periodic behavior in an open loop situation always is stable. In a closed loop situation the method requires the solving of a set of equations consisting of the previously mentioned set of linear equations in the Fourier coefficients, combined with an additional nonlinear equation in the relative pulse width (duty ratio). In both situations the method of this paper can be implemented in an efficient way. The method is illustrated by means of known examples taken from the literature and is shown to be useful in establishing whether or not a periodic behavior in a closed loop situation is stable     

Quasi-linear modeling and control of DC-DC converters

A quasi-linear approach is proposed for modeling and control of DC-DC power converters. The method presented is derived by perturbing an approximate large signal equation around a varying operating point in a reduced variable space. This differs from the usual practice of applying the perturbation technique around a fixed operating condition. In the proposed algorithm, the control equation and the control parameter are constantly adjusted according to environmental changes to meet the specified dynamical requirement     

Random discrete PWM method for DC-DC power converters

A random discrete pulse-width modulation (RDPWM) scheme is examined and compared with the randomised pulse-position modulation (RPPM) method for DC-DC power conversion. The RDPWM method has no switching harmonics while the RPPM method has significant switching harmonics. Power spectral characteristics of the two methods are presented and discussed     

三电平DC-DC变换器的统一建模研究

三电平变换器的统一建模是对变换器进行控制和优化的基础.但是,对于三电平变换器而言,其开关数目多,工作模态复杂,用传统建模方法对之进行统一建模相当困难.脉冲波形积分法是一种新的统一建模方法,为此,本文首次采用脉冲波形积分法,对三电平变换器的统一建模进行了研究.以非隔离三电平变换器为例,详细阐明了其统一建模原理,并给出了输入输出共地和输入输出不共地的Buck变换器的统一建模方法.仿真分析与实验结果表明,脉冲波形积分法是一种对三电平变换器进行统一建模的有效工具,为三电平变换器的有效控制奠定了基础.     

Large-signal modeling and simulation of switching DC-DC converters

A general nonlinear continuous formulation procedure for large-signal analysis of switching DC-DC converters is presented. The method can be applied in either of the two conduction modes, and it is easily programmed for computer-aided analysis with small simulation time. A boost regulator operating in constant-frequency current-programmed mode is used to illustrate the application of the method. A stability graph is subsequently developed to facilitate the design of DC-DC switching regulators for large-signal applications. The graph provides an estimation of the values of input voltage and load resistance leading to a stable regulator behavior     

Zero-Voltage-Switching Control for a PWM Buck Converter Under DCM/CCM Boundary

A new zero-voltage-switching (ZVS) control approach is presented for pulsewidth modulation (PWM) buck converters under discontinuous conduction mode (DCM)/continuous conduction mode (CCM) boundary. This proposed technique compensates for control circuit delay, and hence, turns on power MOS at the instant exactly when drain-to-source voltage becomes zero. No complicated timing calculation circuits or additional external components are required. This proposed integrated ZVS control can be applied to other dc–dc converters as well. The corresponding circuit analysis, implementation, and die photograph are presented in this paper. Simulation and experimental results for an example circuit with $V_{{rm IN}}$ of 5 V and $V_{{rm OUT}}$ of 3.3 V reveal that buck converters with the presented ZVS technique have higher efficiency than conventional ones, especially at higher frequencies. At about 3.6 MHz operation, the measured conversion efficiency of the PWM buck converter under DCM/CCM boundary mode with the proposed ZVS approach is 11$%,$ higher.      

Complex state-space modeling and nonlinear control of active front-end converters

This paper presents the modeling and control of active front-end (AFE) converters using complex state-space representation, a technique developed and thus far mostly employed for the analysis of ac machines. Particularly, three-phase PWM voltage-source and current-source rectifiers are thoroughly studied using the graphical capabilities of this approach, namely, complex signal flow graphs. These are used to directly and intuitively derive high-performance nonlinear control laws based on input-output feedback linearization. Specifically, a cascaded and a paralleled control scheme are investigated for the voltage-source rectifier, whereas a cascaded scheme is considered for the current-source rectifier. Under these strategies both converters exhibit linear and decoupled d-q axes dynamics, while also attaining a reactive power compensation capacity. Moreover, linearization of their respective dc-link voltage and current loops utterly enforces and ensures their operating stability. All this is achieved without the elaborate mathematical complexity of input-output linearization, effectively shunned out by the proposed complex state-space approach. Finally, experimental results from 5-kVA digital-signal-processor-based laboratory prototypes verify the analysis and downright performance evinced by these AFE converters.     

Sampled-data modelling and analysis of the power stage of PWM DC-DC converters

The power stage of the PWM DC–DC converter is modelled and analysed using the sampled-data approach. The work addresses both continuous and discontinuous conduction mode under voltage mode control, and continuous conduction mode under current mode control. For each configuration, nonlinear and linearized sampled-data models, and control-to-output transfer functions are derived. Using this approach, both current mode control and discontinuous conduction mode can be handled systematically in a unified framework, making the modelling for these cases simpler than with the use of averaging. The results of this paper are similar to results of Tymerski, but they are presented in a simpler manner tailored to facilitate immediate application to specific circuits. It is shown how sampling the output at certain instants improves the obtained phase response. Frequency responses obtained from the sampled-data model are more accurate than those obtained from various averaged models. In addition, a new (‘lifted’) continuous-time switching frequency-dependent model of the power stage is derived from the sampled-data model. Detailed examples illustrate the modelling tools presented here and also provide a means for comparing results obtained from the sampled-data approach with those obtained from averaging.     

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     

Voltage loop of boost PWM DC-DC converters with peak current-mode control

A new transfer function from control voltage to duty cycle, the closed-current loop, which captures the natural sampling effect is used to design a controller for the voltage-loop of a pulsewidth modulated (PWM) dc-dc converter operating in continuous-conduction mode (CCM) with peak current-mode control (PCM). This paper derives the voltage loop gain and the closed-loop transfer function from reference voltage to output voltage. The closed-loop transfer function from the input voltage to the output voltage, or the closed-loop audio-susceptibility is derived. The closed-loop transfer function from output current to output voltage, or the closed loop output impedance is also derived. The derivation is performed using an averaged small-signal model of the example boost converter for CCM. Experimental verification is presented. The theoretical and experimental results were in good agreement, confirming the validity of the transfer functions derived.     

Quadratic state-space modeling technique for analysis andsimulation of power electronic converters

This paper presents a quadratic state-space modeling technique for analysis of power electronic converters. The methodology is based on using a least-square-error fitting to derive a quadratic state-space representation for each topology, together with automatic determination of switching topology. The algorithm integrates the advantages of calculating topology responses at the circuit level and determining switching instants at the device level. Several key features of the new model that lead to significant improvements in computational efficiency include: (1) its simple quadratic polynomial representation for the state-transition matrix in solving the differential equations describing each topology; (2) its direct and single-step calculation of the switching instants; and (3) its generality in determining valid topology without a prior understanding of the switching relationships. Several examples illustrating the generality and simulation speed of the proposed approach are presented. The computational efficiency of the new approach is demonstrated by comparing its simulation time with commercial software using the stepwise integration algorithm. The accuracy is verified with the exact method and available literature     

Active voltage clamp in flyback converters operating in CCM mode under wide load variation

Active clamp topologies of low power dissipation have become a very attractive solution in order to limit overvoltages in flyback converters. Although many suitable topologies have been introduced for the case of discontinuous conduction mode (DCM), where the duty cycle value depends on the load level, in continuous conduction mode (CCM) it is more difficult to appropriately design such topologies so as to "sense" load changes-due to the small duty cycle divergence under wide load variation. Taking for granted that in order to achieve high power-factor correction in these converters, CCM is a more attractive mode of operation, a drastic solution for this case that will manage to eliminate voltage stresses under wide load changes has become very essential. For this purpose, this paper presents an active clamp topology with small power dissipation, suitable for flyback converters operating in CCM mode. Its main idea is the use of a load-dependent current source, consisting of an auxiliary converter operating in DCM mode. Experimental results highlight the effectiveness of the proposed topology under wide load changes, establishing it as an appropriate solution in order to develop flyback converters, even at the power range of 500 W.     

A COMPUTER-AIDED UNIFIED APPROACH TO MODELING PWM AND RESONANT CONVERTERS

This letter puts forward a method of modeling for the steady-state and small signal dynamic analysis on PWM, quasi-resonant and series/（parallel） resonant switching converters based on pulse-waveform integral approach. As an example, PWM and quasi-resonant converters are used to discuss the principle of the approach. The results are compared with those in the relative literatures. Computer aided analysis are made to confirm the correctness.     

NEW PERTURBATION TECHNIQUE FOR TRANSIENT ANALYSIS AND ITS APPLICATIONS IN DC-DC PWM SWITCHING POWER CONVERTERS

An improved perturbation technique proposed in a recent paper (Int. J. Electronics, vol. 63, pp.403-414) has been successfully applied to steady-state analysis of PWM switching converters. This paper extends the algorithm to transient analysis of a broader class of non-linear systems. As an example, the transient response of a Boost PWM switching converter is analyzed to demonstrate its simplicity and accuracy.