Reliability Evaluation Of Wind Power Converter Based On State Monitoring Of Core Components

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.