Signal flow graph modelling of interleaved buck converters

This paper presents a systematic development of unified signal flow graph model for an interleaved buck converter system operating in continuous inductor current mode. From this signal flow graph small, large‐signal and steady‐state models are developed, which are useful to study the converter dynamic and steady‐state behaviour. Converter performance expressions like steady‐state voltage gain, efficiency expressions and other small‐signal characteristic transfer functions are derived. Development of unified signal flow graph is explained for a 3‐cell interleaved converter system. Derivation of large, small‐signal and steady‐state models from the unified signal flow graph is demonstrated by considering a 2‐cell interleaved buck converter system. Large signal model was programmed in TUTSIM simulator, and the large‐signal responses against supply, load disturbances were predicted. Signal flow graph analysis results are validated with PSIM simulations. Further, the mathematical models obtained from the signal flow graph modelling are in agreement with those obtained from the state‐space averaging technique. Copyright © 2003 John Wiley & Sons, Ltd.     

Signal flow graph modeling of two-cell cascade buck converters

This paper presents signal flow graph nonlinear modeling of two-cell cascade buck converters. A systematic procedure for developing the unified flow graph model of the cascade converter is discussed. A simplified procedure is described that can be used to deduce large, small-signal and steady-state models from the unified signal flow graph of the converter. Converter performance expressions, and small-signal and steady-state transfer functions are derived. The large-signal model is developed and programmed into a TUTSIM simulator. Converter large-signal responses are obtained against supply and load disturbances. The validity of the proposed signal flow graph modeling of cascade converters is verified and comparisons are made via PSIM simulator results. A few experimental results are provided to verify the proposed method.     

Design and analysis of power‐CMOS‐gate‐based switched‐capacitor DC–DC converter with step‐down and step‐up modes

A unified multi‐stage power‐CMOS‐transmission‐gate‐based quasi‐switched‐capacitor (QSC) DC–DC converter is proposed to integrate both step‐down and step‐up modes all in one circuit configuration for low‐power applications. In this paper, by using power‐CMOS‐transmission‐gate as a bi‐directional switch, the various topologies for step‐down and step‐up modes can be integrated in the same circuit configuration, and the configuration does not require any inductive elements, so the IC fabrication is promising for realization. In addition, both large‐signal state‐space equation and small‐signal transfer function are derived by state‐space averaging technique, and expressed all in one unified formulation for both modes. Based on the unified model, it is all presented for control design and theoretical analysis, including steady‐state output and power, power efficiency, maximum voltage conversion ratio, maximum power efficiency, maximum output power, output voltage ripple percentage, capacitance selection, closed‐loop control and stability, etc. Finally, a multi‐stage QSC DC–DC converter with step‐down and step‐up modes is made in circuit layout by PSPICE tool, and some topics are discussed, including (1) voltage conversion, output ripple percentage, and power efficiency, (2) output robustness against source noises and (3) regulation capability of converter with loading variation. The simulated results are illustrated to show the efficacy of the unified configuration proposed. Copyright © 2003 John Wiley & Sons, Ltd.     

Dynamic model development and control for multiple‐output flyback converters in DCM and CCM

Multiple‐output flyback converters are widely used in switching power supplies due to their low component count and cost‐effective structure. The main problem of this structure is how to balance output voltages in different load conditions. This paper proposes a new approach for single‐input multiple‐output flyback converters operating in DCM and CCM by a small‐signal averaged model. The averaged model is derived by presenting the piecewise‐linear waveform for the inductor currents inside the converter. In DCM, the magnetizing current and currents through the output windings reach zero when the switch is turned off. In CCM, the magnetizing current of the converter is continuous over a switching interval and this possibility exists that only some of the output diodes completely conduct when the switch is off. The proposed model of the converter can be used in a wide range of operations within identical and non‐identical loading conditions. Using a laboratory prototype, several case studies and input‐to‐output transfer functions are considered to verify the proposed model. The controller design is performed for the both CCM and DCM, and then dynamic characteristics of the overall system are evaluated.     

MMC型级联变换器阻抗建模和稳定性分析

工程中常通过不同类型的变换器灵活级联以实现不同的功能,然而变换器级联系统中前、后级变换器之间的相互作用可能会导致系统稳定裕度不足甚至失稳,不同类型的模块化多电平变换器(modular multilevel converter,MMC)级联也将面临稳定性问题。建立了MMC型级联变换器的稳定性分析模型,并提出了一种基于串联阻尼电阻的稳定性提升策略。首先,建立了MMC型AC/DC变换器和DC/DC变换器的阻抗模型,在稳态工作点附近推导出两种MMC型变换器的小信号模型,从而获得前级变换器的输出阻抗和后级变换器的输入阻抗。其次,分析了MMC型级联变换器的稳定性,结果表明,当前级变换器输出阻抗与后级变换器输入阻抗不匹配时,级联系统稳定性裕度可能不足导致系统失稳。进而,分析了MMC型级联变换器的平波电感、桥臂电感和子模块电容等一次参数对级联系统稳定性的影响。最后,提出了一种基于串联阻尼电阻的稳定性提升方法,并给出了串联阻尼电阻的选择建议。仿真结果表明提出的稳定性控制方法可有效提升MMC型变换器级联系统的稳定性。     

A high efficiency input/output magnetically coupled interleaved buck–boost converter with low internal oscillation for fuel-cell applications: Small signal modeling and dynamic analysis

Dynamic behavior of DC–DC converters plays a crucial role in stability of renewable energy exploitation systems. This paper presents small signal modeling of an input/output magnetically coupled interleaved buck–boost converter for fuel-cell applications to help the designers with the better understanding of converter dynamics. Aiming to have a continuous converter transfer function for a smooth transition between the operation modes and an improved inner dynamics, a damping network and an input/output coupling have been added to the interleaved structure of well-known cascaded buck–boost converter. Having the same step-up/step-down voltage transfer ratio, smooth transition and improved inner dynamics make this converter quite suitable for renewable energy applications. The paper presents a small signal ac equivalent circuit model of the proposed converter based on state space averaging (SSA) method. Simulation results show remarkable improvements in converter dynamic behavior in both time and frequency domains. Prototype setup of 360 W and 36 V output voltage for a fuel cell with a brand of “FCgen 1020ACS” Ballard Power Systems, Inc. was implemented. Experimental results are presented to verify the theoretical model and its expected merits.     

一种燃料电池发电系统直直变换器的研究

本文针对燃料电池的外特性较软这一特性，研究了一种推挽正激变换器。通过对变换器的小信号建模，设计了其双环控制参数。实验表明在燃料电池稳态输出及动态变化时，控制器均能保证了此变换器能够稳定工作，从而有效地利用了电能。     

Exact and explicit expressions for the small‐signal dynamics and frequency response of switching converters

In this paper, exact and explicit expressions for the dynamics and small‐signal responses of piecewise linear switching converters are derived. The results are very useful for the exact simulation and analysis of converter circuits. These expressions can also be used to develop simplified (approximate) models of converters for practical design purposes. An example is given to show that the well‐known state‐space averaging model is in fact the first‐order approximation of our exact model. Copyright © 2004 John Wiley & Sons, Ltd.     

直流微电网中变换器阻抗特性及系统稳定性研究

针对直流微电网中变换器阻抗特性及稳定性问题,从系统级高度将变换器的输出阻抗作为研究对象,对适用于光伏系统中的连续导电模式（CCM）下Boost型变换器进行小信号建模,得到变换器的开环输出阻抗。分析了变换器在下垂控制方式下的闭环输出阻抗的小信号模型及其影响因素,总结出规律性结论,便于对直流微电网的稳定性进行分析。最后,根据阻抗比判据,分析了线路中不同寄生电容对系统稳定性的影响。仿真结果验证了上述分析的正确性。     

规则法和混合法相结合的遥信错误辨识方法

针对遥信错误辨识问题,提出了一种基于规则和混合法的遥信错误辨识方法。首先制定规则剔除简单的遥信错误;对于无法通过简单规则辨识的遥信,提出采用转移潮流法和新息图法相结合的拓扑错误混合辨识方法进行辨识,该混合辨识方法具有如下特点:以前一断面的状态估计结果作为基态,避免转移潮流法在实际工程中基态选择的困难;通过新息图法中的修正预估比判断拓扑可疑支路,避免转移潮流法中用转移潮流判定拓扑可疑支路可能导致的误判;引入转移潮流法中注入功率对转移潮流的影响量,避免采用新息图法出现较大负荷预测误差产生负荷突变问题。最后,以算例证明了所述方法的有效性。     

同步整流Buck变换器断续工作模式建模分析

作者运用能量守恒原理 ,考虑电感电流的纹波和开关器件的导通损耗 ,把非理想功率开关等效为理想开关与开通电阻的串联 ,理想开关由受控源替代 ,推导了同步整流Buck变换器在断续工作模式下的大信号平均模型、DC和小信号电路模型 ,导出了开环传递函数 ,进行了计算机仿真分析 ,结果令人满意。该建模分析方法的优点是考虑了电感电流的纹波和变换器的寄生电阻 ,模型直观、物理意义清晰 ,具有实用价值     

Analysis and design of a half‐bridge LLC series resonant converter employing two transformers

This paper presents a two‐transformer LLC series resonant converter (SRC), which is derived from incorporating two identical converters. The proposed converter allows a low‐profile power supply design for liquid crystal display (LCD) TVs and servers. The presented converter can equally share the total load current between two transformers and the output rectifier modules. Therefore, the heat problem can be effectively relieved. The steady‐state analysis and design of this new two‐transformer LLC SRC are described. The experimental results are recorded for a prototype converter with an output voltage of 12thinspaceV, an output power of 300 W, and a resonant frequency of 74 kHz. Copyright © 2011 John Wiley & Sons, Ltd.     

Current Injected Equivalent Circuit Approach to Modeling and Analysis of Current Programmed Switching DC-DC Converters (Discontinuous Inductor Conduction Mode)

The current injected equivalent circuit approach (CIECA) to modeling switching converter power stages is extended to model the current programmed converter power stages operating in fixed frequency discontinuous inductor conduction mode. To demonstrate the method, the modeling is carried out for the buck, boost, and buckboost converters to obtain small signal linear equivalent circuit models that represent both input and output properties. The results of these analyses are presented in the form of linear equivalent circuit models as well as transfer functions.     

开关变换器两端口网络建模、分析及设计

本文基于状态空间平均法,系统地给出开关变换器低频小信号传递函数推导算法。同时借助PWM开关模型,建立开关变换器平均模型。并根据小信号频域特性测试原理,给出一种借助电路仿真软件时域数值仿真数据作傅里叶分析,进而获得到低频小信号传递函数幅频相频曲线的建模方法。最后应用Agilent网络分析仪4395A在一台电压控制型Buck变换器原理样机上完成频域环路增益传函测试,验证了以上三种方法的正确性与一致性,并指出该方法可以推广至实际频域小信号传函测试较困难的场合,甚至是尚无精确模型的电路拓扑场合,供评估系统稳定性及动态性能使用。     

基于阻抗比判据的永磁直驱风力发电系统并网稳定分析方法

考虑永磁直驱风力发电系统(Permanent Magnet Synchronous Generator, PMSG)的动态特性,提出一种基于阻抗比判据的PMSG并网稳定性分析方法,以提高PMSG并网稳定分析的准确性。首先,基于阻抗比稳定分析原理,推导含变换器系统的并网稳定判据。然后,考虑PMSG的动态特性,在建立状态空间方程的基础上推导出PMSG的小信号模型,进而推导PMSG的输出阻抗表达式,据此分析PMSG并网稳定分析方法且得出具体实现流程。最后,利用PSASP分别搭建含PMSG的简单系统和WSCC-9节点仿真系统。仿真结果验证了所提方法的有效性和准确性。     

双母线直流微电网的级联稳定性分析

双母线直流微电网因具有供电可靠、负载匹配性高、接入中低压配电网系统灵活方便等特点,逐渐成为未来家庭和楼宇的主要供电架构之一,而级联稳定性分析是其设计中的重要问题.对双母线直流微电网在不同稳态运行模式下的级联小信号稳定性进行分析,利用广义状态空间建模法、传统状态空间平均建模法建立变换器的阻抗模型,根据系统各单元稳态运行模式的源荷属性提出4种模式,并利用阻抗比判据判定系统的小信号稳定性.仿真结果表明,在轻载模式下系统的稳定裕度最小,其中双有源桥、光伏变换器的阻抗特性不受功率交互的影响且一直具有负阻抗特性,而储能单元仅在作为负荷时具有负阻抗特性.对比3种无源阻抗方案以改善负载阻抗特性,提高系统的稳定裕度.实验结果表明:加入无源阻抗后轻载模式的负载电流纹波系数从14.3％下降至1.9％,可见无源阻抗可以改善负载阻抗特性,提高系统的稳定性和抗扰性能.     

基于虚拟同步发电机控制的分布式发电系统的阻抗边界分析

为解决采用虚拟同步发电机控制方法的分布式发电系统接入配电网运行的稳定性问题,提出一种虚拟同步控制变换器的并网运行阻抗边界确定方法,导出同时满足并网变换器的功率控制性能、稳定极限、系统负载允许变化范围和小信号稳定性的阻抗边界条件。给出了虚拟阻抗的配置方法,可使系统获得良好的动态控制性能与稳定性。采用Matlab/Simulink仿真验证了系统阻抗边界和虚拟阻抗配置方法的有效性,最后给出了部分实物装置实验案例结果。     

磁集成有源箝位正激变换器小信号建模分析

电感和变压器的集成可以有效地减小正激变换器电感电流纹渡,提高输出品质.为了对该变换器进行系统研究,论文提出小信号建模分析的一般方法,着重研究控制-输出传递函数的影响参数.研究表明:由于变压器和输出电感绕组耦合,在控制-输出传递函数中额外引入动态极点和动态零点,并且传递函数以输出零纹波为临界条件出现右半平面零点.     

A structural approach to synthesizing,analyzing, and modeling quasi‐resonant converters

This paper presents a structural approach to synthesizing, analyzing, and modeling quasi‐resonant converters (QRCs) based on the concept of basic converter units (BCUs). Typical QRCs include the well‐known topologies of buck, boost, buck‐boost, Cuk, Zeta, and Sepic. With proper reconfiguration, these QRCs can be synthesized from either buck‐QRC BCU or boost‐QRC BCU plus certain linear networks. Thus, the BCUs and general configurations of the converters can be identified. Analysis of steady state operation and derivation of small‐signal models for the converters then can be conveniently performed from the general configurations, reducing the complexity significantly. Moreover, the proposed structural approach can explore more physical insights into the converters in a family, and can reveal more relationships among converters over conventional approaches. Copyright © 2011 John Wiley & Sons, Ltd.