Analysis And Suppression Of Junction Temperature Fluctuation Of Power Module For Doubly-fed Wind Power Converters

High reliability of electronic power module is the basic guarantee of safety and stability of wind power converter.However,the operation reliability of the power module is obviously affected by the complex operation conditions and the grid access conditions of the wind turbine.Existing studies have shown that due to the long-term low-frequency operation of the rotor side converter(RSC)of doubly-fed wind turbine,the junction temperature of its power module fluctuates more dramatically than that of the grid side converter(GSC),and its fatigue failure increases the risk of shutdown.In addition,the sub-synchronous oscillation(SSO)introduced by large-scale wind power interconnection generates inter harmonic current(IHC)in the rotor windings of a doubly fed wind turbine,reducing the operational reliability of the RSC.In order to improve the operation reliability of doubly-fed wind power converter under synchronous speed operation condition and subsynchronous disturbance,this paper takes the power module of RSC as the research object,analyzes the junction temperature distribution of the power module of RSC in different operating scenarios,and proposes the corresponding junction temperature fluctuation suppression strategy.The main research contents of this paper include:(1)In view of the difference in loss distribution caused by the uneven dynamic flow between the parallel chips in the power module,traditional junction temperature calculation method has difficulty in accurately reflecting the heat distribution in the module,a dynamic junction temperature calculation method of power module considering the influence of stray inductance is presented.Firstly,an insulated gate bipolar transistor(IGBT)equivalent circuit model with stray inductance is established,and the mechanism of the uneven current distribution between the parallel chips in the power module is proved by simulation.Secondly,the relationship between stray inductance and switching loss is quantitatively derived,and a method for calculating dynamic junction temperature of power module based on multi-chip electrothermal coupling is proposed,which is verified by experiments.Finally,the electro-thermal simulation model of the power module of the doubly fed wind power converter is established with the influence of stray inductance taken into account.And the junction temperature distribution of the power module of the converter is analyzed.(2)To solve the problem that the current junction temperature fluctuation suppression strategy is difficult to take into account the operation efficiency of the turbine under synchronous operating conditions,a new junction temperature fluctuation suppression strategy based on direct power predictive control(DPPC)is proposed.First,from the doubly-fed Induction Generator(DFIG)voltage and flux linkage equations,in order to realize the Maximum Power Point Tracking(MPPT),the prediction model and objective function is etablished.Secondly,Secondly,based on the DPPC strategy and combined with the dynamic junction temperature calculation model,the dynamic junction temperature fluctuation of the RSC power module was analyzed when the turbine was running reciprocally under sub-/super-synchronous conditions.And the steady-state junction temperature fluctuation and the operation efficiency of the turbine are also analyzed.Finally,the effectiveness of the proposed control strategy is verified by comparing it with the existing junction temperature fluctuation suppression strategy.(3)Aiming at the problem that SSO may reduce the operation reliability of doubly-fed wind power converter caused by large-scale wind farm being connected to the power grid,the junction temperature analysis of RSC power module under sub-synchronous disturbance and the suppression strategy are studied.Firstly,based on the voltage and flux linkage equations of DFIG,the analytical model of rotor IHC caused by sub-synchronous disturbance is derived,and its characteristics under different disturbance frequencies and operating conditions are analyzed.Secondly,the loss and junction temperature distribution of the power module under the influence of IHC are obtained and verified by experiments.Finally,a junction temperature fluctuation suppression strategy based on power compensation is proposed on the basis of DPPC strategy,and the junction temperature distribution of the power module based on the proposed control strategy under sub-synchronous disturbance is obtained by simulation,which is compared with that of the existing oscillation suppression strategy on the basis of additional filter control.The dynamic junction temperature distribution law and suppression strategy of power module of doubly-fed wind power converter studied in this paper lay a foundation for accurately analyzing the junction temperature change of the power module,effectively reducing the junction temperature fluctuation,and improving the reliability and operating efficiency of the doubly-fed wind power converter.