Study On Reliability Evaluation Of Power Semiconductor Devices In Wind Power Converter And Its Improvement Measures

The limitations of traditional fossil energy promote the development and application of the renewable energy sources, especially the wind power generation. However, research has shown that power converter is one of the most vulnerable parts in the wind turbine power converter system. The converter availability depends on the components reliability. The failure of power semiconductors is one of the easiest failure components. Consequently, it is urgent that a reliable lifetime estimation of power devices be well studied, and some targeted improvements are proposed.Power device failures mainly belong to Package-related failure modes, and are mainly caused by the thermal cycling swings which are crucial prerequisites for lifetime estimation of power devices. Reducing the fluctuations of thermal cycling is an effective way for improving the reliability of power devices. To consider the long-term mission profiles of wind power converter, this paper proposes a method for evaluating the long-term thermal cycling of power devices, and then establishes the multi-time sale lifetime evaluation model of power modules. Based on the multi-time sale lifetime consumption of power devices, this paper also presents a new idea which can guide the thermal management behaviors of power devices, and this idea can be applied to improve the lifetime of power devices. The main contents are as follows:Firstly, the failure primarily results from thermal cycling, which will be affected by the wind speed and ambient temperature. Besides, the external environment change with day and season, and the long-term mission profiles should be transformed into the thermal cycling of power devices. So this paper proposes a numerical IGBT junction temperature calculation method based on the analysis of the electric-thermal analogy theory. Performance comparison among the proposed method, the electro-thermal simulation, the analytical solution method, and the IGBT junction temperature online measure method based on the infrared camera is also conducted. Results show that when the long-term mission profiles will be included, the proposed method ensures the calculation accuracy, but greatly reduces the computational time.Secondly, the long-term thermal cycling of power devices has the characteristics of multiple-time scale. The thermal cycling with different time scale will result in different lifetime consumption. So the multi-time sale lifetime consumption of power devices are evaluated, and we may propose the targeted measures to improve the reliability of power devices. So this paper establishes the multi-time sale lifetime evaluation model based on the multi-time sale distribution of thermal cycling, and analyzes the distribution characteristics of lifetime consumption. The results show that the multi-time sale lifetime consumption can be evaluated through the proposed model, and the great majority of the lifetime of power semiconductors due to fundamental frequency thermal cycling is consumed when the wind speed is equal to and higher than the wind speed which is close to the rated wind speed, however, the probability of this wind speed range is much small. The lifetime consumption due to low frequency thermal cycling mainly attribute to the larger thermal cycling swings with lower probability.Finally, the thermal cycling swings can be reduced as far as possible to improve the reliability of power devices. However, the thermal management methods may affect the operation of power converter. So it is necessary to research some targeted improvement measures. Based on the multi-time sale lifetime consumption, this paper presents a new idea a new idea which can guide the specific thermal management behaviors of power devices. To verify the reasonability of this idea, the Pulse Width Modulation(PWM) schemes will be regarded as the variable. After the performance of the presented modulation scheme is verified and compared with that of other PWM schemes, this paper proposes a new hybrid modulation scheme. The results show that the lifetime of power devices with the presented hybrid approach is longer than that with the continuous Pulse Width Modulation(CPWM), and is shorter than that with the discontinuous Pulse Width Modulation(DPWM). Moreover, the power quality of the power converters with the hybrid modulation scheme can be guaranteed in all operation conditions, which may not be achieved with DPWMs.