Gernot Riedel

A study on IGBT junction temperature (Tj) online estimation using gate-emitter voltage (Vge) at turn-off

Abstract A novel method is presented for online estimation of the junction temperature (Tj) of semiconductor chips in IGBT modules, based on evaluating the gate-emitter voltage (Vge) during the IGBT switch off process. It is shown that the Miller plateau width (in the Vge waveform) depend linearly on the junction temperature of the IGBT chips. Hence, a method can be proposed for estimating the junction temperature even during converter operation – without the need of additional thermal sensors or complex Rth network models. A measurement circuit was implemented at gate level to measure the involved time duration and its functionality was demonstrated for different types of IGBT modules. A model has been proposed to extract Tj from Vge measurements. Finally, an IGBT module with semiconductor chips at two different temperatures has been measured using Vge method and this method was found to provide the average junction temperature of all the semiconductor chips.

Active thermal protection and lifetime extension in 3L-NPC-inverter in the low modulation range

The switches of multilevel inverters in high-power applications are mounted on dedicated heatsinks and there is no heat sharing among the devices. If one semiconductor device is exposed to excessive thermal stress, then the lifespan of the affected device is reduced significantly. This thermal overload may arise due to degradation of the cooling system, failures in firing or in the drivers, inappropriate placing of the semiconductor devices etc. In this paper, a control scheme is devised that can reduce the thermal stress of a particular semiconductor device; the benefit is that the reduction of the lifetime of this device is avoided. Thus, after detecting of the occurrence of a local thermal overload by temperature sensing on the particular heatsink, the control scheme modifies the pulse width modulation in such a way, that the power losses of the stressed device are redistributed among the other semiconductors without limitations of the inverter current. In previous works, this method was already presented for the higher modulation index range; it is now extended to the low modulation range and is validated by experiments.

Active lifetime extension — Demonstrated for voltage source converters

Many voltage source converters have no redundant power components (e.g. IGBT modules) built in. Therefore if one power component fails, the converter stops working. Here we introduce a generic approach that takes advantage of the inherent redundancies of voltage vectors in multilevel converters in order to actively extend the lifetime of converters. When detecting increased stress of one IGBT module, the switching strategy is altered in order to reduce the load of that particular IGBT module. The active lifetime extension (ALE) switching strategy aims to balance the remaining life of all IGBT modules at all times. In such way the lifetime of the converter is maximized.

Risk assessment using design review based on failure mode

In order to improve sustainability of industrial applications, big efforts are underway to increase efficiency of electrical power transmission, power conversion, or power usage. The availability of electrical converters used in these applications is crucial for high efficiency. Therefore, risk assessment has to be performed during product development to improve their reliability. The method typically used is Failure Mode and Effects Analysis (FMEA). In this paper another method called Design Review Based on Failure Mode (DRBFM) is applied to a typical power converter and evaluated. The DRBFM approach used was found to be much more efficient, if the focus lies on the identification of the critical problems and on improvements. On the other hand, FMEA is the method of choice for focusing on a complete list of possible failures.