【作者】 沈国桥；

【导师】 徐德鸿；

【作者基本信息】 浙江大学 ， 电力电子与电力传动， 2008， 博士

【摘要】 燃料电池分布式电源系统具有广泛的应用前景,并网逆变是其中的一项关键技术,直接关系到电源系统的电能质量、安全和可靠性。迄今仍有不少并网逆变技术问题有待进一步研究解决,而燃料电池的特点又对并网逆变技术提出了新的要求。其中,并网发电的电能质量和本地负载的供电保障是两大关键问题。以往对这两个问题的研究常常是分开的,很少有人从结构上、功能上将两者放在一起考虑。作为并网发电电能质量核心要素的电流控制技术,也被LCL滤波器的谐振增益困扰日久,解决方案不甚理想;而保障本地负载连续供电的并网发电与独立运行的模式切换问题则更是一项新的研究课题。本文着眼于燃料电池分布式电源系统的运行特点,首先探讨了电源系统的运行模式和逆变系统结构要求,提出了兼具并网发电和独立运行功能的单逆变器型电源系统最佳线路结构以及运行模式与输出能量管理方法。给出了独立运行和并网运行逆变系统的模型、控制方法和输出滤波器设计。针对并网逆变的高频谐波抑制问题,本文通过模型和参数分析,详细探讨了LCL滤波器的传输特性和参数变化对并网逆变器滤波能力和控制性能的影响。给出了LCL滤波器的设计方法,为并网逆变系统分析和控制提供了依据。对于并网逆变系统电流控制问题,本文分析了并网逆变控制系统的特性和传统电流反馈控制方法存在的LCL滤波器谐振增益制约控制回路带宽和增益的问题。提出了电流加权平均值反馈和分裂电容法电流反馈控制新方法,使控制系统配置新的零点与极点作用抵消,从而使并网逆变控制系统由三阶系统降为一阶系统。新方法使控制系统带宽增大,易于实现输出电流稳态误差和谐波的抑制。给出了其理论依据、特性和实现方法。对于燃料电池电源系统并网运行与独立运行两种运行模式的切换问题,本文在传统运行模式切换控制策略的基础上,提出了四种强迫换流切换策略,即基于电压控制的电压幅值调节的切换策略、电压相位调节切换策略、电压瞬时值调节切换控制策略,以及基于电流调节的切换控制策略,实现了逆变运行模式的无缝切换。本文分析总结了各自的特性、适用条件,给出了仿真结果。最后,通过5kW燃料电池并网发电系统实验,验证了本文所给出的设计和提出的控制方法和控制策略,给出了试验结果。更多还原

【Abstract】 Fuel cell generation now is regarded as one of the most competitive energy sources for the distributed power generation systems (DG) due to its advantages of high efficiency, low emissions, and high power density. The grid-connected inverter is the main issue of the fuel cell DG because of its impact to the power quality, reliability and safety. Heretofore, many problems still need further studies, and the some new requirements are raised by the fuel cell DG. Among these, the power quality to grid and the power reliability to local loads are two most important aspects. These two aspects are used to study separately; seldom researches have been made on considering the system structures and functions. The current control strategies for the grid-connected inverters with LCL-filters were degraded by the resonance frequency without ideal solutions for long. On the other hand, the operating modes transfer is a new subject of ongoing researches.Focusing on the requirements for fuel cell DG, this paper has discussed the operating modes and the inverter structures for the power systems. A suitable system structure and the power managements have been presented. The system models, control strategies, and filter design methods for standalone or grid-connected operating modes are also given here.As to the switching frequency depression for the PWM inverter, the characteristics of the LCL-filter and impacts on inverter system control are analyzed in detail. For the current control of the grid-connected inverter, the problem of low bandwidth and gain resulted from the LCL-filter resonance frequency by traditional current feedback control has demonstrated. Novel current feedback control methods which appear as current weighted average and split capacitor method have been presented. The new control methods can create two zeros to contact the effects of the two poles in LCL-filter. Consequently, the V-I transfer function of the grid-connected inverter system with the LCL-filter is degraded from a third-order function to a first-order one, therefore the closed-loop current feedback control system can be optimized easily for minimum steady-state error and current harmonic distortions, as well as the system stability.For operating mode transfer control, this paper proposes four new transfer control algorithms based on voltage amplitude regulation, voltage phase regulation, instantaneous voltage regulation and current regulation for the fuel cell inverters, to implement forced current commutation between the grid and the inverter during the transition from grid-connected mode to stand-alone mode. The algorithms and their transition performances have been described and discussed. Simulations of the transfer control algorithms were carried out in PSpice to verify the methods.Finally, the inverter design and the presented control strategies have been experimentally verified on a 5kW DSP controlled fuel cell inverter.更多还原