【作者】 黄涛；

【导师】 陈民铀；

【作者基本信息】 重庆大学 ， 电气工程， 2018， 硕士

【摘要】 在国家大力推动新能源发展的浪潮下,我国风电场建设规模越来越大,风电机组的可靠性问题受到广泛关注。作为风电机组的核心装置,变流器受随机风速产生的老化应力影响,其可靠性随运行时间逐渐降低。统计发现50%以上的变流器故障是由功率模块和电容器失效引起的,而变流器的组成器件都属于串联运行,任意器件失效都会引发变流器整体失效,因此在进行风电变流器可靠性评估时应重点考虑功率器件和电容器等核心部件的健康状态。通过监测变流器核心部件不同运行时间后的健康状态,研究评估不同老化程度的变流器整体可靠性水平,对于优化指导风电变流器的检修维护有着重要作用。现有的风电变流器可靠性评估模型,大都只考虑大载荷作用下的功率模块累积损伤,却忽略了无源器件、交变小载荷作用以及不同健康状态对变流器可靠性的影响。本文综合考虑以上因素,结合寿命预测解析模型和电力电子器件可靠性评估手册,建立了一种反映变流器整体的可靠性评估模型。首先,分析了变流器核心部件失效的主要原因及其失效演化过程,通过器件结温、壳温、饱和压降、功率损耗、纹波电流等在线监测数据与器件特征量的关系,确定各器件的健康状态。之后,建立计及疲劳累积的功率模块、电容器的寿命预测模型,该模型能表征交变小载荷作用下器件特征量参数变化。最后,结合可靠性评估手册,建立反映变流器整体可靠性水平的评估模型。并根据实际风速产生的热载荷,对不同健康状态下的风电变流器可靠性进行评估。本文的主要内容包括:(1)建立考虑健康状态和小载荷作用的功率模块可靠性评估模型。从模块焊料层失效角度出发,探寻不同运行工况和健康状态下,IGBT模块失效过程中热阻的变化过程。建立了能表征小载荷作用下功率模块物理失效演化过程的分段式疲劳累积模型,并通过试验验证了该模型的准确性。同时基于功率模块电热损耗关系和瞬态热阻曲线,建立功率模块电热耦合模型。在随机设置的热载荷作用下,对不同健康状态下小载荷对功率模块可靠性的影响进行了详细分析。(2)建立考虑健康状态和非线性损伤的电容器可靠性评估模型。对电容器主要失效方式和失效机理进行分析,确定其主要影响因素。同时建立铝电解电容器有限元模型,模拟电容器热失效过程。通过对电容器热老化失效过程中等效串联电阻ESR的变化分析,提出了一种能反映电容器热失效过程的非线性寿命预测模型。最后基于变流器直流环节中的电容器电热损耗关系及其稳态热阻曲线,建立电容器电热耦合模型。在随机设置的电容器核温曲线下,对不同健康状态下的电容器进行可靠性评估。(3)建立一种基于核心部件状态监测的变流器整体可靠性评估模型。在MATLAB/Simulink环境下建立1.5MW双馈风电变流器模型,通过提取变流器的导通电流、风机转速、输出功率等在线运行参数,获取功率模块和电容器的热载荷信息,结合提出的寿命预测模型和可靠性评估手册对变流器故障率展开计算。分析了不同风速输入下,机、网两侧变流器的运行特性及其故障率分布。最后,在变流器运行老化一段时间后,定量化对比分析了不同健康状态和运行参数对变流器可靠性的影响。更多还原

【Abstract】 Under the tide of the vigorous development of new energy,the construction scale of wind farms in China is getting larger and larger,and the reliability of wind turbines has received widespread attention.As the core device of the wind turbine,the converter is affected by the aging stress generated by the random wind speed,and its reliability gradually decreases with the running time.It is found that more than 50% of converter faults are caused by the failure of power modules and capacitors.While the constituent components of converters are all in series operation,any device’s failure will cause the overall failure of the converter.Therefore,the reliability assessmen of wind power converter should focus on the health status of core components such as power devices and capacitors.By monitoring the health status of the converter core components after different operating periods,the overall reliability level of converters with different ageing levels can be evaluated,which plays an important role in optimizing the maintenance of wind power converters.Most of the existing reliability assessment models for wind power converters only consider the cumulative damage of power modules under large loads,but ignore the effects of passive components,alternating small loads,and different health states of components.This article comprehensively considers the above factors,combines the life prediction model and the reliability evaluation manual,establishes a reliability evaluation model for the entire converter.Firstly,the main failure reasons and the failure evolution process of the converter are analyzed.Through the relationship between the on-line monitoring data,like junction temperature,shell temperature,saturation voltage drop,power loss,ripple current,and the device feature quantity,the health status of the device is determinded.Afterwards,the life prediction models of the power module and capacitor that considering fatigue accumulation are established.The model can reflcet the change of the device characteristic quantity parameter under the small load.Finally,associating with the reliability assessment manual,an overall reliability evaluation model for the converter is established.Based on the thermal load generated by the actual wind speed,the reliability of wind power converters under different health conditions is evaluated.The main content of this article includes:(1)A reliability evaluation model of power module considering health status and small load is established.From the point of the failure of the module solder layer,the change process of the thermal resistance of the IGBT module under different operating conditions and health conditions is explored.A segmented fatigue accumulation model is established to characterize the evolution of the physical failure of the power module under small loads.The accuracy of the model is verified by experiments.At the same time,the electrothermal coupling model of the power module is established based on the electric heating loss relationship and transient thermal resistance curve of the power module.Under the effect of random set thermal loads,the influence of small loads on the reliability of power modules under different health conditions is analyzed in detail.(2)A reliability assessment model of capacitor considering health status and nonlinear damage is established.To confirm the main failure factors of the capacitor,the main failure mode and failure mechanism of the capacitor are analyzed.At the same time,the finite element model of aluminum electrolytic capacitor is established to simulate the thermal failure process of the capacitor.By analyzing the change of equivalent series resistance(ESR)during thermal aging of capacitors,a nonlinear life prediction model reflecting the thermal failure process of capacitors is proposed.Finally,based on the electric heating loss relationship of the capacitor in DC link of the converter and the steady-state thermal resistance curve,the electrothermal coupling model of the capacitor is established.Under the effect of random set core temperature,the reliability of the capacitor under different health conditions is evaluated.(3)An overall reliability evaluation model of the converter based on the core component condition monitoring is established.In the MATLAB/Simulink environment,a 1.5MW double-fed wind power converter model is established.By extracting the on-line operating parameters such as converter’s current,rotor speed and output power,the thermal load information of power modules and capacitors can be obtained.Then,combined with the life prediction model and the reliability assessment manual,the calculation of converter failure rate is carried out.The operation characteristics and the distribution of the failure rate of the converters on both sides of the generator and the grid are analyzed under different wind speeds.Finally,after a period of aging operation of the converter,the effects of different health conditions and operating parameters on the reliability of converter are quantitatively analyzed.更多还原