混合发电用多端口输入DC-DC变换器

为了提高能量的转换效率,提出了一种用于新能源混合发电的高低压多端口输入DC-DC变换器。首先,分析了多端口输入DC-DC变换器合成法则;接着,以罗氏变换器复举变换器和Buck变换器为合成单元,设计了高低压双输入DC-DC变换器的拓扑结构;然后,分析了电路的各种工作状态;最后,运用Matlab对设计的变换器进行仿真分析。仿真结果表明,所设计的变换器的各个输入口既可以独立也可以同时给负载供电。     

ZCS BUCK变换器CM工作模式下的分岔和混沌现象

本文对零电流开关(ZCS—Zero-current-switching)BUCK变换器电压反馈控制的分岔和混沌现象进行了研究。建立了变换器在CM(Continuous mode)工作模态下的精确离散映射模型，进行分岔稳定性和混沌运动的仿真分析。研究结果表明，软开关BUCK变换器虽然减少了开关应力，改善了开关的工作条件，但它与硬开关BUCK变换器相比，混沌运动特点更加明显，这在一定程度上降低了变换器的运行稳定性。     

A prototype of a fuel cell PEM emulator based on a buck converter

After a brief introduction about fuel cell systems, and their modelling, this paper proposes a possible solution to emulate a proton exchange membrane fuel cell (PEM-FC) system by using a DC–DC buck converter. The fuel cell system, including all its auxiliaries and related control systems, is emulated by a buck converter realized experimentally and controlled in the DSPACE environment. The realization of the buck converter allows the behaviour of any fuel cells to be easily emulated since only the modification of the control law of the switch is necessary. The proposed emulator can be applied easily to other fuel cell systems if the polarization curve has the same current rate and maximum power. In this way it is possible to utilize the converter and perform the necessary tests to optimize a fuel cell system by avoiding the waste of hydrogen and the purchase of cells as well as any cell damage. With regard to current other types of emulators, the one presented here has the following characteristics: (1) all the auxiliaries of the system have been considered, each including its own control system, as in a real FCS, (2) the converter is a classical buck converter with a free-wheeling diode and is designed to have a high bandwidth and to be practically always in conduction mode (discontinuous mode appears only at very low currents) (3) the voltage control is made by a space-state controller, able to fix properly the closed loop poles of the system, thus guaranteeing the desired bandwidth of the control system and (4) it can be used in laboratory as a stand-alone low-cost system for design and experimental purposes.     

An integrated simulation model for PEM fuel cell power systems with a buck DC-DC converter

Fuel cell powered systems generally have a high current and a low voltage. Therefore, the output voltage of the fuel cell must be stepped-down using a DC-DC buck converter. However, since the fuel cell and converter have different dynamics, they must be suitably coordinated in order to satisfy the demanded load. Accordingly, this study commences by constructing a MATLAB/Simulink model of a proton exchange membrane fuel cell (PEMFC) system comprising a PEMFC stack, an air/fuel supply system, and a temperature control system. The validity of the PEMFC model is demonstrated by comparing the simulation results obtained for the polarzation curves of a single fuel cell with the corresponding experimental curves. A model is then constructed of the DC-DC buck converter used to step-down the PEMFC output voltage. In addition, a sliding mode control (SMC) scheme is proposed for the DC-DC buck converter which guarantees a low and stable output voltage given transient variations in the output voltage of the PEMFC. Finally, a model is constructed of a DC-AC inverter with a pulse width modulated (PWM) control scheme which enables the PEMFC stack to supply the grid or power AC applications directly. Overall, the combined PEMFC/DC-DC buck converter/DC-AC inverter model provides a powerful and versatile tool for the design and development of a wide range of PEMFC power systems.     

Reliability assessment of a stand-alone wind-hydrogen energy conversion system based on thermal analysis

Due to the stochastic behavior of the wind speed, accessing the wind energy would be problematic in some critical moments. One feasible solution lies in the use of wind turbines to produce hydrogen through an electrolyzer and by using wind-hydrogen hybrid systems. However, many of the issues related to these systems should be investigated to make landmark decisions about their performance. For instance, there is a lack of study on the reliability assessment of the wind-hydrogen systems; for this purpose, the main objective of this study is to evaluate the reliability of a stand-alone wind-hydrogen energy conversion system unconnected to the grid. The proposed system consists of two major parts: the rectifier and the buck converter. The primary task of the rectifier is to rectify the wind turbine output voltage to a constant DC voltage. Additionally, the buck converter is responsible to reduce the voltage level to a 48 V voltage, which meets the voltage requirement of the 3.6 kW electrolyzer. The results of the performed simulations showed that the rectifier is under more thermal stresses than the buck converter. The predicted mean time to failure (MTTF) of the hybrid system is approximately 7.6 years, and this estimation can affect the maintenance and refurbishment costs.     

基于混沌同步的Buck变换器并联均流控制

针对处于混沌状态的降压(Buck)变换器并联均流效果不佳且均流的稳态和动态特性差的现象。首先建立电压控制型Buck变换器的分段光滑开关模型以及离散模型,并分析系统通往混沌的道路。然后确立初值不同的驱动与响应系统。将所设计的终端滑模控制率施加到响应系统上从而实现并联系统的混沌同步控制。基于混沌的同步特性,可以实现电压控制型Buck变换器的并联均流控制。最后通过MATLAB/Simulink仿真平台搭建施加控制后的并联系统模型进行实验仿真。结果显示,并联系统均流误差接近于0,并当输入电压发生突变时,均流误差未发生改变,表明施加终端滑模控制后,Buck变换器并联均流误差小且具有较好的稳态和动态特性。     

基于未知系统动态估计器的Buck型变换器快速固定时间控制

针对存在参数不确定、输入电压波动以及负载变化等未知动态的Buck型变换器系统,提出一种基于未知系统动态估计器的快速固定时间控制方法.首先,设计基于一阶低通滤波器的估计器,实现对系统未知动态的前馈补偿.在此基础上,基于输出电压误差和未知动态估计值设计固定时间滑模面和反馈控制器,保证输出电压快速收敛至参考电压附近邻域内,且...     

流控型Buck变换器的动力学行为分析

针对光伏发电系统中电流控制型Buck变换器,利用不连续动力学理论分析了其非线性振荡行为. 通过调节控制电路的电压幅值和直流激励电源值,给出碰撞边界的和时钟脉冲触发的参数分岔图,获得了电流控制型Buck变换器从稳定的周期1到混沌状态的参数节点. 分别绘制周期和混沌运动的相轨迹和时序图,分析各子域内具有不同映射结构的系统类型. 研究结果表明,流控制型Buck变换器在参数变化时其运动行为丰富,边界碰撞现象明显,观测到倍周期分岔和阵发混沌. 通过分析映射类型,说明其边界的非线性振荡行为.     

分布式储能中大降压比Buck变换器的优化设计

研究一种具有大降压比、低开关电压应力的新型Buck变换器,主要用于适配分布式储能系统中可再生能源输出与电池组之间的大压差。该变换器由低侧开关型降压单元与开关电感型降压单元级联而成。在介绍其工作模式和稳态特性的基础上,着重分析了变换器中各器件的功率损耗和电气应力,根据分析结果进行器件的优化选择和电路的优化设计。利用SIMPLIS软件进行仿真分析的同时,测试了一台峰值效率为94.6%、功率为750 W的实验样机。测试结果表明,该变换器具有极强的降压能力和较低的元件电气应力,同时能维持较高的变换效率。