Research On Online Condition Monitoring Method Of Key Devices In Power Converter

The goal that overall quality of the ecological environment should be improved was put forward by thirteen five plan.The capacity of new energy power generation increased year by year,in order to solve the ecological environment and energy crisis and other issues,and to promote the development and application of new energy power generation technology.Especially the wind power generation,which as the representative of the new energy power generation.The engineering application data shows that power converter is one of the weakest components in wind power generation system.The reliability of grid-connected wind power generation system and the safe operation of great grid is directly influenced by power converters,which are the key components of wind power generation system.The failure of power converter is mainly caused by the degradation of IGBT module and DC-link capacitor.The solder fatigue and ageing of bond wires is directly caused by the large difference of thermal expansion coefficient(CTE)between the module package materials,and high temperature swing of chip,which caused by dynamic loading associated with the variable input.The electrolytic liquid of DC-link capacitor will be evaporated gradually during the working period of power converter,and that will cause the degradation of capacitor.The reliability of the wind power converter is gradually reduced with the ageing of the key components in the converter.In order to avoid the catastrophic consequences of wind power generation system,which caused by the sudden failure of key devices.Finding and replacing the defective devices by real-time monitoring the condition indicators of IGBT modules and DC-link capacitors is the urgent problem to be solved.An online condition monitoring method for the key devices of power converter has been presented in this paper,and the health level of both IGBT modules and DC-link capacitors can be evaluated online simultaneously by this method.The short-circuit current of IGBT module and the step voltage of DC-link capacitor should be detected,which produced by short-circuit test during the normal operation of power converter.The health level of IGBT module can be identified by the short-circuit current,and the failure prediction of DC-link capacitor is realized by the equivalent series resistance(ESR),which can be calculated by IGBT module short-circuit current and the step voltage of DC-link capacitor.The main work of this paper is as follows:Firstly,the ageing mechanism of IGBT module and electrolytic capacitor is analyzed in detail,and the condition monitoring method of IGBT module and DC bus capacitor is proposed.A condition monitoring method of IGBT module based on short-circuit current is proposed,and the influence of bond wires fatigue on the short-circuit current is analyzed in this section.The health level of IGBT module can be evaluated by short-circuit current only,and ignore the influence of junction temperature.At the same time,the ageing indicator and the condition monitoring method of the electrolytic capacitor are analyzed in detail.Secondly,an online condition monitoring method for both IGBT module and DC-link capacitor of power converter based on short-circuit current is proposed.The short-circuit current is used as the condition indicator of IGBT module,and the ESR is used as the condition indicator of DC-link capacitor.The online measurement method of short-circuit current and ESR is analyzed in detail.The online condition monitoring for IGBT module and DC-link capacitor is realized by short-circuit test during the normal operation of power converter,which makes the IGBT module work in the current saturation mode.At the same time,the impact of short-circuit test on key devices and the effect on the normal operation of power converter are analyzed in detail in this section.Finally,the effectiveness of this online condition monitoring method is validated by a confirmatory experiment.A special IGBT driver,which can output three different levels so that the IGBTs in the converter can operate in different mode,is designed for the online condition monitoring of key devices in power converter.The IGBT module is short-circuit tested in incubator by the special IGBT driver,at different bond wires fatigue condition,different junction temperature,and different driving voltage.The relationship between short-circuit current of IGBT module and the driving voltage,junction temperature,bond wires ageing state has also been analyzed.The short-circuit current of IGBT module and the ESR of DC-link capacitor is online measured by an single-phase converter,and the test results are consistent with the theoretical analysis.So,the correctness of the online condition monitoring method proposed in this paper is verified.