【作者】 肖浩；

【导师】 段献忠； 李银红；

【作者基本信息】 华中科技大学 ， 电气工程， 2015， 硕士

【摘要】 换相失败是高压直流输电系统的常见故障,会导致直流设备承受过应力、输送功率减少以及逆变侧交流系统过电压等问题。随着高压直流输电技术的快速发展以及“西电东送”和“全国联网”能源战略的实施,受端落点于同一交流系统的多馈入直流输电系统已经在华东电网和南方电网中形成。多馈入直流输电系统结构可以将整体传输的容量增大和直流回路运行方式的灵活性增加,同时也使得交直流系统之间和直流系统之间的交互作用加强,导致换相失败的问题更加复杂。因此对于多馈入直流系统换相失败研究具有重要的现实意义。在介绍6脉动晶闸管型逆变器基本工作原理的基础上,分析了其换相失败的产生机理。基于PSCAD/EMTDC中CIGRE直流输电标准模型搭建了双馈入直流输电系统,并结合换相失败免疫因子(commutation failure immunity index,CFII)指标,分析了交流系统参数、直流系统参数和控制器参数对逆变器换相失败的影响,得出了在多馈入直流系统中各种因素影响逆变器发生换相失败的一般规律。提出了一种量化多馈入直流系统换相失败免疫水平的高效通用化方法。基于最小熄弧角判断标准,推导了多馈入直流输电系统中当地换相失败免疫因子(local commutation failure immunity index,LCFII)和同时换相失败免疫因子(concurrent commutation failure immunity index,CCFII)的解析表达式。同时为了进一步研究多馈入直流系统换流器间交互作用对同时换相失败的影响,定义了弱耦合多馈入交互作用因子(weak coupling multi-infeed inaction factor,WCMIIF)指标。基于CIGRE直流输电标准模型搭建了双馈入直流输电系统,仿真结果验证了表达式和所提指标的有效性和准确性。将交流线路故障点视为广义节点,并基于广义节点阻抗矩阵定义了电压关联因子(voltage correlation factor,VCF),根据最小熄弧角标准推导了临界电压关联因子指标(critical voltage correlation factor,CVCF)的解析表达式,通过此指标可以有效地表征直流系统抵御换相失败的能力。从理论上推导出交流线路故障位置差异性对于电压关联因子影响的表达式,并由此提出了一种影响多馈入直流系统换相失败的电网薄弱区域快速识别方法。南方电网多馈入直流系统算例的分析结果表明了所提指标的有效性以及电网薄弱区域快速识别方法的实用性。更多还原

【Abstract】 Commutation failre is a very frequent fault in HVDC transmission system,which can cause issues such as overstressing of dc equipments,reduction of transmitted power and overvoltage of the receiving ac system.With the rapid development of HVDC technology and the implementation of “West Power to East” and “national network” energy strategies,situations have arisen with two or more HVDC inverters terminated in close proximity of a common ac system in the East China Power Grid and the China Southern Power Grid. A multi-infeed HVDC system configuration can expand transmission capacity and increase the flexibility of system operating modes.However,it gives rise to the more complex commutation failure behaviors because of the inter-converter interactions as well compared to the single-infeed HVDC systems.So it is of important practical significance to study commutation failure behaviors in multi-infeed HVDC systems.On the basis of the baic operating principle of 6-pulse thyristor inverters,the mechanism of commutation failures was analyzed. Then,a dual-infeed HVDC system configuration was established based on “CIGRE HVDC Benchmark model” in PSCAD/EMTDC platform.And based on the “commutation failure immunity index”(CFII),the impact of ac system parameters,dc system parameters and controller parameters on commutation failure in inverters were analyzed in detail and the general rules of how various factors affect commutation failure in multi-infeed HVDC systems were also obtained.A general and efficient approach to quantify commutation failure immunity levels in multi-infeed HVDC systems was presented.Based on the minimum extinction angle criteria,the analytical expressions of “local commutation failure immunity index”(LCFII) and “concurrent commutation failure immunity index”(CCFII) were derived.Meanwhile, in order to give a profound insight into how inter-inverter interactions influence the concurrent commutation failure behaviors,a quantified index “weak coupled multi-infeed interaction factor”(WCMIIF) was proposed.The validity and accuracy of the analytical expressions and proposed index were verified by the simulated results based on a dual-infeed HVDC system.With the ac line fault location regarded as a generalized node,the “voltage correlation factor”(VCF) was defined based on generalized node impedance matrix.Based on the minimum extinction angle criteria,the analytical expressions of “critical voltage correlation factor”(CVCF) was derived,through which the immunity of inverters in HVDC systems to commutation failure could be effectively characterized.Moreover,the correlation between VCF and the variability of ac line fault locations was expressed,further,a rapid identification method of weak areas in power grid based on commutation failure analysis in multi-infeed HVDC systems was put forward.The validity of proposed index and the applicability of aforementioned method were verified by the calculation results based on the multi-infeed HVDC system model of China Southern Grid.更多还原