| The power system with new energy as the main body is a key way to achieve the peaking carbon dioxide emissions and carbon neutrality.As an important "grid-forming" interface of the large-scale new energy system,the VSC-HVDC system needs to have the grid support function.Press pack IGBT module is the core component of the VSC-HVDC system,and improving its short-term overload capability can give full play to the grid support function of VSC-HVDC.The key to improving the short-term overload capability of press pack IGBT modules is to reduce the overload temperature rise and limit the junction temperature within the safe operating range(SOA).The existing methods of junction temperature management mostly adopt the loss control or external heat dissipation,while the heat dissipation inside the module is less considered,which is not conductive to suppressing the overload temperature rise in a short time,and it is necessary to study the new junction temperature management method.In addition,the junction temperature and pressure distribution within press pack IGBT modules are inhomogeneous,and local failures are prone to occur during short-term overload.Therefore,it is necessary to monitoring the junction temperature and pressure distribution within press pack IGBT modules.The existing monitoring methods of power modules mostly measure from the outside,which is inconvenient to obtain the junction temperature and pressure distribution within the module,and new monitoring methods need to be investigated.This thesis proposes a distributed junction temperature and contact pressure measurement method based on fiber Bragg grating(FBG)sensor integration,and a method of transient junction temperature management based on phase change material(PCM)integration.By establishing the converter test platform,the effectiveness and accuracy of the proposed junction temperature monitoring and management methods are verified.The main innovative work of this thesis includes:(1)The distributed transient junction temperature measurement of press pack IGBT modules is difficult,and a junction temperature online monitoring method based on FBG temperature sensor integration is studied.Firstly,by establishing the thermal network model of the heat dissipation system and deriving the transfer function between the temperature measurement point and the actual junction temperature,the influence of the sensor installation position on the measurement error of transient junction temperature is analyzed,indicating the necessity of integrating FBG sensors into the module packaging for the close measurement.Then,the mathematical model of FBG temperature sensors with different housings are established.The influence of housing parameters on the dynamic characteristic of FBG sensors is analyzed and validated with experiments,and the FBG sensor with small-size plate housing is shown to be more suitable for the transient junction temperature measurement,for a high sensitivity and a short thermal time constant.(2)The pressure sensor is too large to be integrated into press pack IGBT modules for the pressure measurement,and a distributed pressure monitoring method is proposed in this thesis.The mechanical pressure is converted into the mechanical strain,and the FBG strain sensor is integrated inside the module to measure the pressure indirectly.This realizes the online monitoring of contact pressure within press pack power modules for the first time.Given the low strain measurement sensitivity of FBG sensors,a sensitivity-enhancing structure is designed based on the flexible component inside the module.By establishing the mathematical model of pressure measurement structure,the factors of the pressure measurement sensitivity are analyzed.Given the FBG is sensitive to both temperature and strain,a temperature and strain decoupling scheme is proposed based on the sensitivity equations of FBG sensors.The validity and accuracy of the proposed method are verified with experiments.(3)Press pack IGBT module has low heat capacity,and the operating junction temperature may exceed the SOA during short-term overload.In this thesis,a method of transient junction temperature management that integrates PCMs into the module packaging is proposed,and the heat capacity of the power module is increased by utilizing the latent heat of PCMs.Based on the thermal characteristics of press pack IGBT module,a PCM integration scheme is proposed,which realizes both a low thermal resistance and a fast response.Combining the experiments and finite element analysis,the thermal diffusion inside press pack IGBT module during short-term overload is studied,and the heat absorption efficiency of the integrated PCM is evaluated.On these bases,a PCM integration scheme of multi-chip modules is proposed. |
