Online Monitoring For Degradation Of IGBT Under Repetitive Over-Current Conditions

Recently, the power converter is more and more widely used in many industrial processes that require high reliability. Therefore, it is also required that the power converter is also with high reliability. According to the relevant industrial surveys, the power device is the most fragile component of a power converter because it undertakes the main thermal and electric shocks during practical operations. In addition, insulated gate bipolar transistor (IGBT) is the most popular type of power device because it has the advantage of voltage-controlled characteristic, high input impedance, high switch speed, low power dissipation, large current capacity and so on. Therefore, research on performance degradation of IGBT to put forward aging indicators, can realize online monitoring of the degree of degradation. According to the degree of the degradation of an IGBT, the plan of maintenance or the strategy of online adjusting can be developed to avoid the catastrophic consequences and economic losses brought by a sudden failure, which effectively improves the reliability of power converters.Due to the enclosed package of IGBTs, the internal degradation processes can hardly be measured directly. It is general to draw an aging indicator from terminal characteristics of IGBTs to indirectly monitor the degradation. Through the review of the existing aging indicators we discover that some of them cannot be measured online, and some of them can be effected by the change of load current or junction temperature. Based on the above shortcomings, we propose a new degradation index, on resistance, which can be measured on-line and hardly affected by the change of load current or junction temperature. Specific work is divided into the following sections:1. To provide theoretical basis, the normal degradation mechanisms, degradation phenomena and electrical characteristics of IGBTs in the practical processes are analyzed. Then, based on the electrical model of IGBT with a series of decoupling and simplification, the aging indicator, which is named on resistance, is proposed. The on resistance can be extracted online, the change of it can reflect the degree of the degradation of Al layer and bond-wire and has no relation with the change of load current.2. Since the proposed degradation index-on resistance is affected by the change of junction temperature, the index need to be optimized. Combined with the analysis of the relation between the junction temperature and the aging indicator, the indicator of junction temperature is proposed and the aging indicator can be further adjusted to remove the effect of the junction temperature. Otherwise, a complete scheme about online monitoring for degradation of IGBT is carried out.3. According to the above results of analysis and online monitoring scheme, an experimental platform is established for repetitive over-current experiments to degrade IGBTs in power cycling. The tendency curves of oral and adjusted on-resistance processed from the experimental data with aggravated degradation validate that the proposed aging indicator is effective and feasible to online monitoring.