【作者】 金科；

【导师】 阮新波；

【作者基本信息】 南京航空航天大学 ， 电力电子与电力传动， 2006， 博士

【摘要】 随着人类生活水平的不断提高,对能源的需求大幅度增加。化石能源等不可再生能源正日益枯竭,而且它所造成的环境污染日益严重。氢能作为一种绿色新能源,得到越来越多的应用。氢能利用的一个重要方面就是燃料电池,它将氢和大气中的氧反应转换为电能,其反应产物为纯净水,对环境没有污染,而且噪声也很小。因此燃料电池供电系统的研究对新能源的发展和应用具有重要的意义。本文提出了燃料电池供电系统的通用结构,根据实际设计情况,通过分析和对比,确定了复合式燃料电池供电系统结构作为本文所要研究系统的结构。该系统由燃料电池、单向变换器、双向变换器、蓄电池和逆变器构成,其中蓄电池通过双向变换器与直流母线并联,该系统具有以下优点:1)由于蓄电池的引入,燃料电池的功率等级只需按照系统额定功率进行配置,从而降低整个系统的成本;2)当负载发生突变燃料电池来不及反应时,可由蓄电池通过双向变换器向负载供电,动态响应快。系统开机时,可以由蓄电池向负载供电,因此便于燃料电池的自启动;3)双向变换器可以控制蓄电池的充放电电流,延长蓄电池的寿命;4)双向变换器的一端与直流母线并联,而直流母线的电压相对比较稳定,因此双向变换器优于设计,可以减小电感大小,从而提高动态性能;5)可以通过选择双向变换器的工作模式来实现系统的能量管理,确保燃料电池和蓄电池协调工作,使得系统可以高效工作。燃料电池没有功率调节能力,外特性很软,这就要求单向DC-DC变换器可以在很宽的输入电压范围内高效工作。本文将LLC谐振网络引入到复合式全桥三电平变换器中,得到了适合于燃料电池供电系统的复合式全桥三电平LLC谐振变换器。该变换器集成了复合式全桥三电平变换器和LLC谐振变换器的优点:1)适合于宽输入电压范围的应用场合,可以在很宽的输入电压范围内高效工作;2)三电平桥臂的开关管电压应力只有输入电压的一半;3)输出整流二极管实现ZCS,而且其电压应力仅为输出电压;4)可以在全负载范围内实现ZVS;5)输入电流纹波和输出滤波器可以减小。实验结果验证了理论分析的正确性。在高压的燃料电池供电系统中可采用加箝位二极管ZVS PWM三电平变换器,但原有的变换器存在一定的缺点,本文对原变换器进行改进,将变压器和谐振电感交换位置,使变压器与滞后管相连。改进型加箝位二极管ZVS PWM三电平变换器保留了原变换器消除输出整流管反向恢复引起的电压振荡的优点,并且还具有以下优点:1)在一个周期中,箝位二极管只导通一次,因此其电流定额可以减小;2)零状态时导通损耗小,效率可以提高;3)占空比丢失小。此外,还讨论了隔直电容在不同位置时对变换器工作的影响,确定了一种最佳工程方案,即在改进后变换器的变压器中串联隔直电容,并以一个3kW的原理样机进行了实验验证。燃料电池动态响应慢,自启动困难,所以系统中引入了蓄电池和双向变换器。本文提出了适合于燃料电池供电系统的三电平Buck/Boost双向变换器。该变换器具有以下优点:1)电感可以大大减小,提高变换器的动态响应,从而优化整个系统的动态特性;2)开关管电压应力仅为高电压端输入电压的一半。由于系统中除了燃料电池外,还有蓄电池作为能量存储装置用来在不同的条件下给负载辅助供电或吸收多余的能量。为了确保系统具有很高的效率和可靠的稳定性,必须保证燃料电池和蓄电池协调工作,对整个系统的能量走向流进行管理。本文提出了系统的能量管理控制思路,其核心是根据燃料电池和蓄电池的状态来控制双向变换器,使其分别工作在Buck、Boost或关机模式,以此来控制蓄电池的充放电状态,从而对整个系统进行能量管理。本文确定了单向和双向变换器稳压和限流值,以及蓄电池切入切出系统的切换点,着重分析了系统在冷启动和过载时的情况。根据以上的分析,本文构建了一个1kW的燃料电池供电系统,并对该系统进行了深入的实验研究。实验结果表明,系统在稳态、冷启动、负载突变、过载等条件下均能很好的工作,验证了能量管理控制的有效性。更多还原

【Abstract】 The environment concern is now the driving force for seeking new clean energy such as geothermal, photovoltaic, hydroelectric, wind generation, etc. Fuel cell is an electrochemistry device, it uses hydrogen, propane, natural gas, or other fuels to generate electricity without increasing pollution. The emission of fuel cell is only water, and the noise is very low. Therefore, it has been receiving more and more attention in distributed generation power system and electrical vehicles.This paper proposes a universal fuel cell power system structure. Based on the system specifications we design, a hybrid fuel cell power system structure is employed in this system. It consists of a fuel cell, an isolated uni-directional converter, a bi-directional converter, an inverter and a battery. The proposed system has several advantages as follows: 1) Fuel cell is the most expensive component in the system. Thanks to the introduction of battery, the power rating of fuel cell can be decreased, so the total cost of the system is reduced. 2) When the load varies, the fuel cell cannot response immediately, battery will provide or absorb the dynamic energy, so the dynamic characteristic of the system can be improved. Battery also powers the system during the system start process, which make the system be easy to cold start.3) Bi-directional converter can limit battery charge and discharge current and lead to a longer life of battery. 4) One side of bi-directional converter is connected to DC bus, whose voltage is steady, thus the inductor of bi-directional converter can be minimized, leading to a good dynamic characteristic.5) Power management can be employed to ensure that fuel cell and battery cooperate well and improve system efficiency.Zero-voltage-switching pulse-width-modulation three-level converter (ZVS PWM TL converter) is widely used in high voltage applications. But it has some shortages. This paper proposes a improved ZVS PWM TL converter, which is improved from the original ZVS PWM TL converter just by exchanging the position of the resonant inductor and the transformer, such that the transformer is connected with the lagging switches. The improved converter not only keeps the advantages of original converter, but also has several advantages over the original one, e.g., the clamping diodes conduct only once in a switching period, and the resonant inductor current is smaller in zero state, leading to a higher efficiency and reduced duty cycle loss. A blocking capacitor is usually introduced to the primary side to prevent the transformer from saturating, this paper analyzes the effects of the blocking capacitor in different positions, and a best scheme is determined. A 3kW prototype converter verifies the effectiveness of the improved converter and the best scheme for the blocking capacitor.The output voltage of fuel cell fluctuates with the load significantly, which is too wide to power the inverter. Therefore, a uni-directional DC-DC converter is needed to convert the variable output voltage of the fuel cell to a constant one. The DC-DC converter should be adaptive to the wide input voltage range. This paper proposes a novel hybrid full-bridge three-level LLC resonant converter. It integrates the advantages of the hybrid full-bridge three-level converter and the LLC resonant converter. It can operate under both three-level mode and two-level mode, so it is very suitable for wide input voltage range application, such as fuel cell power system. Compared with the traditional full-bridge converter, the input current ripple and output filter can be reduced. In addition, all the switches can realize zero-voltage- switching from zero to full load, and the switches of the three-level leg only sustain half of the input voltage. Moreover, the rectifier diodes can achieve zero-current- switching, and the voltage stress across them is the output voltage. A 200-400V input, 360V/4A output prototype is built to verify the operation principle of the proposed converter.Fuel cell has slow response and it is difficult to cold start. Therefore, a battery and a bi-directional converter are employed in the system. This paper proposes a new three-level Buck/Boost bi-directional converter, which is suitable for fuel cell power system. Compared with the traditional Buck/Boost bi-directional converter, the inductor also can be reduced significantly, so the dynamic response can be improved. The voltage stress on the switch of the proposed converter is just half of the voltage on the high voltage side. Therefore, it is very suitable for fuel cell power systems. This paper illustrates the operation principle and implementation of the control circuit. A 1kW prototype converter is built to verify the theoretical analysis. In the system, there are two power sources: fuel cell and battery. Therefore, it needs to manage two sources to ensure the system operate with high efficiency and high reliability. This paper proposes a power management scheme. The key point of this power management scheme is to control bi-directional operates under Buck, Boost or Shut-Down mode according to the conditions of fuel cell and battery. Cold start and overload processes are analyzed in detail.According to the theoretical analysis, a 1kW fuel cell power system is built in lab to verify the theoretical analysis. Experimental results illustrate that system operates well under steady, cold start, overload, load step up and down.更多还原