【作者】 易杨；

【导师】 毛承雄； 陆继明；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2013， 博士

【摘要】 电力系统是现代社会不可缺少的重要组成部分，而电力变压器广泛应用于电力系统中，承担着电位隔离、电压变换等功能。近几十年，电力网络的规模日趋扩大、结构日趋复杂、运行方式日趋繁琐，导致电力系统稳定问题日趋明显；大量非线性和非对称负荷接入电网，导致电能质量下降，使电力系统不能为对电能质量敏感的负荷提供高品质供电；21世纪初学者提出了“智能电网”的概念，作为“智能电网”的重要组成部分，交/直流微网的智能化运行方式和灵活电网结构成为研究热点，其需要灵活的交直流变换的电力接口。传统电力设备尤其是传统电力变压器的智能控制手段和交直流电力接口功能非常有限，不能改善系统稳定性问题，不能解决电能品质问题，不能提供智能控制，不能提供灵活交直流电力接口功能。电子电力变压器是一种基于电力电子变流技术的新型电力变压器，不仅可以完成传统电力变压器的功能，还具有完全的可控性、并能提供多种电能形式，所以电子电力变压器具备解决未来电网面临的诸多问题的能力。本文从电力电子技术、电力系统应用需求和高压大功率工程样机等三个主要方面，详细介绍了电子电力变压器的建模、分析、仿真、设计、实现以及相关实验。本文首先分析了适合应用于电力系统的高压大功率领域的电子电力变压器的基本拓扑结构。基于此电力电子变换器拓扑结构，本文建立了电子电力变压器内部参数结构模型，详细分析了其内部电气参数的计算方法并给出计算公式，该计算公式描述了电子电力变压器目标参数（原副方直流电压纹波和中频变压器绕组电流）与原副方交流电压和电流相位的关系，最后通过仿真和实验验证该模型和计算方法的正确性。基于此模型及其分析，本文提出了电子电力变压器硬件设计原则与流程，各个元件必须按照其电压和电流可能出现的最大值设计。根据电子电力变压器目标参数与原副方交流电压和电流相位的变化规律，本文提出了原副方交流电压和电流相位优化控制策略，该控制策略可以显著抑制电子电力变压器主要元件的纹波电压和最大电流，进而减小装置体积、降低设计成本。电子电力变压器具有较强的谐波抑制能力，原副方交流电压和电流的谐波不能相互影响；通过多电平技术、并联控制技术和开关时刻优化控制技术，可以显著抑制电子电力变压器自身产生的谐波。在开关时刻优化控制的基础上，本文提出优化调整直流电压的控制方法，更进一步抑制电子电力变压器交流侧谐波。最后通过仿真和实验验证优化调整直流电压控制方法的谐波抑制效果。针对级联多电平电子电力变压器拓扑结构在解决电力系统三相不对称问题和灵活的并网接口问题的不足，本文提出并分析了基于模块化多电平换流器（MMC）结构的自平衡电子电力变压器（MMC-AEPT）。该拓扑结构可以有效地隔离副方三相负荷不对称对原方三相电流的影响，并有效地隔离原方三相电源不平衡对三相负荷的影响。同时，MMC-AEPT可以提供高压直流母线和低压直流母线，提供灵活智能的电力网络接口，为交/直流微网等新型电网结构和智能运行方式提供核心的电力设备。最后，本文详细介绍了10kV/400V0.5MVA电子电力变压器的研制，详细介绍电子电力变压器关键环节的设计要求和设计原则；同时详细介绍其主要元件的测试实验方法与流程。所述的内容适用于指导各种类似电子电力变压器拓扑的装置的设计与实验。更多还原

【Abstract】 The power system is one of the most important parts in the modern society, and powertransformers are widely used in that as the extremely important electrical components,which realize the voltage level change and the galvanic isolation. During the past severaldecades, power system is larger in the scale, more complicated in the network structure andmore complex in the operation mode, so that the stability problem becomes more serious.And larger unbalanced non-linear loads are connected to the grid which would generatenon-sinusoidal currents and deteriorate the grid voltage, so that it affects the power qualityseriously and even affects the reliability of power supply for those loads which are sensitiveto power quality. Recent year, the concept of “Smart-Grid” is expounded in some papers,and the network structures and the smart operation modes of “AC&DC Micro-grids” havebeen a hot topic. However, the traditional power transformers cannot resolve the stabilityproblem, cannot improve power quality, and cannot provide flexible operation modes andpower grid interfaces for “Micro-grids”.Electronic power transformer (EPT) is an entirely new type of power transformer.Based on power electronics technology, EPT retains the basic functions of traditional powertransformer and extends additional functions, such as the fully controllable of theactive/reactive power and the flexible DC&AC power grid interfaces. Hence, EPT can meetthe demands of “Smart-Grid”.In the dissertation, several topologies of EPT are introduced firstly, and themodularized cascaded multilevel topology of EPT is well suited for the high-voltage andhigh-power applications. Based on the conventional topology, the internal model isestablished for EPT, and the formulas of calculating the electrical parameters are derived.Finally, the experiment is carried out and the experimental results could verify therationality of the model analysis. In succession, the dissertation provides guidance on thedesign and selection of the key elements of EPT for the designers. According to the modelanalysis, the optimal control strategy on the phase angles of AC voltage/current isdeveloped to restrain the electrical parameters in order to reduce the size and cost of EPT. EPT provides a new harmonic suppression scheme for power system. Firstly, theharmonic voltage/current from primary/secondary side cannot flow through EPT. Secondary,EPT itself do not produce excess harmonic current by Cascaded Multilevel circuit, byparallel operation and by optimal control strategy. Based on the optimal control strategy, theoptimal regulation of DC-bus voltage can better suppress harmonic current of rectifier ofEPT.There are several shortcomings of the Cascaded Multilevel topology of EPT, so that theModular Multilevel topology of EPT (MMC-AEPT) as a novel auto-balancing topologyshall be found, and it has many benefits. It can make one side balance if the other side isnot. In addition, MMC-AEPT can provide DC-voltage power grid interfaces for other grids,and becomes the key component of “Smart-Grid”. The simulation results show thatMMC-AEPT can keep the system auto-balancing.Finally, the hardware of10kV/400V0.5MVA EPT is proposed in detail. The designmethods and the design principles of each component are proposed in the dissertation, andthey can also be used in the other similar devices.更多还原