Depression Strategy Of IGBT Junction Temperature Fluctuation Of Power Modules For Wind Power Converter

Wind power converter, as a key control part of wind power generation system when power feedback to the grid, the reliable operation is of great importance to the grid power quality and stability of wind turbines. Junction temperature of power electronic devices in power module is one of the critical factors to the operation reliability of wind power converters. Due to sustained low frequency operation, large junction temperature and its fluctuation amplitude greatly reduce the fatigue life of rotor side converter in a doubly fed wind power generation system. To further improve the reliability of doubly fed wind power converter focusing on depressing the junction temperature of IGBT modules, the IGBT thermoelectric coupling model and the change rules of junction temperature were studied in this paper, and the junction temperature and its fluctuation depression strategies were further proposed.The main contents of this thesis are followings:(1) In view of the existing finite element models of IGBT module are difficult to consider the influence of the control strategy of double fed induction generator(DFIG) on the IGBT junction temperature, a combined simulation model of doubly fed wind turbine generation system considering the thermoelectric coupling characteristics of the converter was established. First, based on the equivalent thermal network of IGBT modules, thermoelectric coupling theory and multidimensional method, a junction temperature calculation model of three-phase converter was established, and the model was verified by experiments. Secondly, based on the rotor and grid side converter control strategy of doubly fed wind turbine, the simulation model of doubly fed wind turbine and its control system was established. Finally, by using the combined simulation platform based on PLESC and Simulink, the junction temperature analysis model of doubly fed wind power converter was established, and the thermoelectric performance of the converter under different operation conditions was simulated.(2) According to the different modulation strategies will affect the power loss of IGBT, and further affect its junction temperature, a combined segment modulation strategy was proposed to depress the junction temperature of IGBT modules. First, the power factor angle of the converter was analyzed under different DSVPWM strategies when it owns a minimum power loss. Secondly, according to the power factor angle range of DFIG rotor side converter, a combined segment modulation strategy was proposed. Finally, the thermoelectric performance and harmonic performance of the wind power converter were analyzed to verify the effectiveness of the proposed modulation strategy.(3) Regarding with issues of the large fluctuation of IGBT junction temperature in DFIG rotor side converter under synchronous operation condition, a IGBT junction temperature fluctuation depression strategy was proposed based on the speed control of DFIG. Firstly, based on the maximum power tracking curve, the control thought of IGBT junction temperature fluctuation was proposed by reducing the low frequency operation time of converter through controlling the speed of DFIG, and a rotor side converter control strategy was established to depress the junction temperature fluctuation based on speed and power control. And then, simulation and comparison of junction temperature of rotor side converter, stator output power and annual power generation of DFIG under different operation conditions were carried out, and further through the equivalent experiment, the effectiveness and feasibility of proposed control strategy were analyzed.The combined junction temperature simulation model of wind power converter established in this paper can provide support for the accurate calculation and analysis of the junction temperature, the proposed junction temperature depression strategies can provide technical support for the improvement of the control strategy of both DFIG and its converter, as well as the improvement of the reliable operation of wind power converter.