【作者】 周国梁；

【导师】 石新春；

【作者基本信息】 华北电力大学（河北） ， 电力电子与电力传动， 2009， 博士

【摘要】 作为新一代直流输电技术,基于电压源换流器的高压直流输电凭借其独特的技术优点取得了飞速的发展,并已在新能源发电系统联网、电网非同步互联、无源系统供电、无功补偿等场合得到实际工程应用。在我国,VSC-HVDC的研究尚处于起步阶段。本论文着重开展了VSC-HVDC技术的数学建模和控制策略的研究。论文的主要工作和取得的创新性成果如下:1.建立了系统标幺值模型,分析了VSC-HVDC的运行原理和稳态功率特性。明确了系统主电路参数对运行特性的影响,在此基础上提出了一种功率定义下的换流电抗、直流电压和直流电容以及频域下的交流滤波器参数设计方法。2.设计了一种基于无差拍控制的VSC-HVDC直接电流离散控制器。针对控制系统存在的VSC电压输出能力限制、PI控制器积分饱和现象和离散采样时间延迟问题,提出了相应的解决方法,推导了其电流内环控制器与功率外环离散控制器的设计原则。3.推导了换流站网侧与VSC交流侧功率节点以及换流电抗与损耗电阻上的瞬时功率方程,在此基础上提出了一种换流站网侧功率节点控制并补偿换流电抗与损耗电阻瞬时二倍频功率的不平衡控制策略,设计了该控制策略下的双序矢量控制器模型。同时针对传统dq软件锁相环在电压不平衡时锁相速度慢的缺点,提出了一种基于前置相序分解的频率自适应dq锁相环,提高了不平衡控制算法的动态性能与稳态特性。4.对VSC阀在交流电网低电压故障下的过流现象进行分析并提出了一种考虑正负序分量影响的指令电流限制器,保证了故障限流效果。分析比较了VSC阀电流裕度穿越法和指令电流限制器穿越法的特性,在此基础上提出一种结合正负序指令电流限制器与控制模式切换的交流电网低电压穿越控制方法,从而解决交流电网低电压故障时系统稳定与VSC过流问题。5.在分析现有VSC-HVDC拓扑的基础上,从降低电力电子器件直接串联数目、器件开关频率和简化主电路拓扑结构三个方面出发,将传统直流输电中常用的变压器隔离式多模块结构引入VSC-HVDC系统,并针对该模块级联式拓扑提出一种系统协调控制与模块独立运行相结合的新型控制策略。针对该拓扑下送端站存在的各模块直流侧电容电压均衡问题,提出了一种基于有功分量调节的直流侧电压控制方法。更多还原

【Abstract】 As the next generation of DC transmission technology, VSC-HVDC has made rapid progress due to its unique technical merits and it has been put into commercial applications such as the connection of island networks and renewable sources to a main grid, asynchronous connection of two grids for power market, reactive power compensation, etc. However research of the VSC-HVDC technology is still in its infancy in China. In this dissertation, the mathematical modeling and control strategy are studied, and the main contents are as below.1. Per-unit based mathematical model of VSC-HVDC is built up. The operating principle and the steady-state power characteristic of VSC station are analyzed, and then the influence of main circuit parameters on the operating characters of VSC station is made clear. On this basis, the detailed design principles of the phase reactors, DC capacitors and the DC voltage under the limit of power are obtained. Frequency domain model of VSC station is also built up to carry out the research of AC filter so as to gain its design principles.2. Based on the transient-state mathematical model of VSC-HVDC, the direct-current control dead-beat based discrete-time controller in dq synchronous rotation coordinate system is proposed. VSC voltage limiter, anti-windup controller, Smith predictor are selected to solve the corresponding problems of discrete-time controller. The detail design principles of inner current loop controller and the outer power loop controller are deduced.3. The power character of VSC station which takes both the negative and positive components into account is analyzed. On this basis, the system side control is adopted which takes the power on the L and R into account so as to cut off the spread of 2nd order DC voltage fluctuation from one station to the other through the DC cables. A novel anti-SSM (Sequence Separation Method) based dq-PLL with frequency adaptive character is proposed to gain better performance in unbalanced conditions.4. LVRT (Low Voltage Ride Through) methods of VSC-HVDC system are studied. Over-current phenomena of VSC valves in AC low voltage fault conditions are analyzed and then a novel reference current limiter for DVCC controller is proposed. Two LVRT methods are compared in this dissertation. One is to use VSC valve with larger current capacity, and the other is to use reference current limiter in control system. On this basis, a LVRT method with the novel reference current limiter is proposed, which is to switch the station function when in reference current limiting condition so as to ride through the faults without over-current phenomena.5. A transformer-isolating multi-module topology is proposed which is aiming to decrease the device number in series and its operating switching frequency and at the same time to simplify its topology. Then a novel control strategy for VSC-HVDC with this topology is proposed which consists of two parts, one is the independent control in module level and the other is the coordinated control in system level. Furthermore, an active power component adjusting method is proposed to balance DC voltages of different modules for sending-end station with this topology.更多还原