Francesco Iannuzzo

Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview

Reliability is one of the key issues for the application of Insulated Gate Bipolar Transistors (IGBTs) in power electronic converters. Many efforts have been devoted to the reduction of IGBT wear out failure induced by accumulated degradation and catastrophic failure triggered by single-event overstress. The wear out failure under field operation could be mitigated by scheduled maintenances based on lifetime prediction and condition monitoring. However, the catastrophic failure is difficult to be predicted and thus may lead to serious consequence of power electronic converters. To obtain a better understanding of catastrophic failure of IGBTs, the state-of-the-art research on their failure behaviors and failure mechanisms is presented in this paper. Moreover, various fault-tolerant design methods, to prevent converter level malfunctions in the event of IGBT failure, are also reviewed.

Reliability Oriented Design Tool For the New Generation of Grid Connected PV-Inverters

This paper introduces a reliability-oriented design tool for a new generation of grid-connected photovoltaic (PV) inverters. The proposed design tool consists of a real field mission profile (RFMP) model (for two operating regions: USA and Denmark), a PV panel model, a grid-connected PV inverter model, an electrothermal model, and the lifetime model of the power semiconductor devices. An accurate long-term simulation model able to consider the one-year RFMP (solar irradiance and ambient temperature) is developed. Thus, the one-year estimation of the converter device thermal loading distribution is achieved and is further used as an input to the lifetime model. The proposed reliability-oriented design tool is used to study the impact of mission profile (MP) variation and device degradation (aging) in the PV inverter lifetime. The obtained results indicate that the MP of the field where the PV inverter is operating has an important impact (up to 70%) on the converter lifetime expectation, and it should be considered in the design stage to better optimize the converter design margin. In order to have correct lifetime estimation, it is crucial to consider also the device degradation feedback (in the simulation model), which has an impact of 20-30% on the precision of the lifetime estimation for the studied case.

Series connection of high power IGBT modules for traction applications

IGBT series-connected power switching circuit is presented. Voltage balance on IGBTs is ensured by means of a simple auxiliary circuit applied directly on the high power inverter used in hard switching applications. Analysis in terms of dissipated energy, collector overvoltage and switching frequencies, comparing performances of a single high voltage IGBT (3300 V) module and two series connected 1700 V IGBTs is reported. An extended experimental analysis is also reported. Both analysis confirm the advantages in using two series connected IGBT in substitution of a single high voltage module in terms of power losses and switching performances

Physical CAD model for high-voltage IGBTs based on lumped-charge approach

A new insulated gate bipolar transistor (IGBT) model developed on a physical basis is presented. The Lumped-Charge method has been revised in order to point out a more general methodology for implementing the model into a circuit form. As an example, a version of the model for the popular PSPICE simulator is presented. The N-channel IGBT structure is described by means of an evolution of the PSPICE level-1 metal oxide semiconductor field effect transistor model. An accurate mobility model has been included to precisely predict the voltage drop in the ON state. Simulation results agree well with the experiments both in static and in switching operations. The comparison between the proposed and the native IGBT PSPICE model shows the better behavior of the former. The reasons for this result have been verified by means of two-dimensional MEDICI simulations. Moreover, the proposed model is able to predict the device behavior also in critical operations like its latchup during a turn-off under short-circuit conditions.

A 3-D-Lumped Thermal Network Model for Long-Term Load Profiles Analysis in High-Power IGBT Modules

The conventional RC-lumped thermal networks are widely used to estimate the temperature of power devices, but they lack of accuracy in addressing detailed thermal behaviors/couplings in different locations and layers of the high-power insulated gate bipolar transistor (IGBT) modules. On the other hand, a finite-element (FE)-based simulation is the other method, which is often used to analyze the steady-state thermal distribution of IGBT modules, but it is not possible to be used for a long-term analysis of load profiles of power converter, which is needed for reliability assessments and better thermal design. This paper proposes a novel 3-D RC-lumped thermal network for the high-power IGBT modules. The thermal coupling effects among the chips and among the critical layers are modeled, and boundary conditions, including the cooling conditions, are also considered. It is demonstrated that the proposed thermal model enables both accurate and fast temperature estimation of high-power IGBT modules in the real loading conditions of the converter while maintaining the critical details of the thermal dynamics and thermal distribution. The proposed thermal model is verified by both the FE-based simulation and the experimental results.

MAGFET based current sensing for power integrated circuit

Abstract A new on-chip non-invasive integrated current sensing, compatible with standard CMOS technology, has been developed, using a 1.2 μm BiCMOS ALCATEL technology, to sense the current in the drain side of a power MOSFET. The circuit is based on a split-drain magnetic sensor, implemented on the same chip of an integrated gate driver for a power MOSFET. A CMOS biasing circuit with a differential current output is also developed. The simulation results of the current sensing show a conversion gain of 1.25 mV/mT.

Experimental and numerical investigation on MOSFET's failure during reverse recovery of its internal diode

The failure of the power MOSFET during the reverse-recovery of its intrinsic body-source diode used as a fly-back element in a half-bridge configuration has been investigated. The experimental waveforms have been studied based on the analysis carried out by a mixed device and circuit simulator. According to the test conditions, it is shown that during the diode reverse recovery either a carrier current or a displacement current contribute to the activation of the parasitic BJT, which may cause the failure of MOSFETs. Among the parasitic elements inherent in the MOSFET structure, the capacitance associated to the gate oxide and the resistance of the polysilicon gate are shown to play a relevant role in the activation of the parasitic BJT due to a displacement current. The activation of the BJT due to carrier current, on the other side, is essentially dependent upon the resistances of the distributed base and of the body-source contact.

Non-destructive high temperature characterisation of high-voltage IGBTs☆

An experimental investigation about the behaviour of 3300V – 1200A IGBT modules both at high temperature and for large output currents is presented. The real IGBT turn off limits in terms of maximum switchable current and the short circuit behaviour at larger different environmental temperatures are identified. The experimental study has been performed by means of a non-destructive experimental set-up where IGBT modules are switched on an inductive load in presence of a protection circuit. It is activated at the occurrence of a dangerous operating conditions thus preventing the IGBT module failure.

Online junction temperature measurement via internal gate resistance during turn-on

A new method for junction temperature measurement of power semiconductor switches is presented. The measurement exploits the temperature dependent resistance of the temperature sensitive electrical parameter (TSEP): the internal gate resistance. This dependence can be observed during the normal switching transitions of an IGBT or MOSFET, and as a result the presented method uses the integral of the gate voltage during the turn-on delay. A measurement circuit can be integrated into a gate driver with no modification to converter or gate driver operation and holds significant advantages over other TSEP based measurement methods, primarily being: an absence of any dependence on operating conditions such as load current, and the potential to achieve higher sensitivity (20mV/C or more) than alternative TSEPs.

Power converters for future LHC experiments

The paper describes power switching converters suitable for possible power supply distribution networks for the upgraded detectors at the High Luminosity LHC collider. The proposed topologies have been selected by considering their tolerance to the highly hostile environment where the converters will operate as well as their limited electromagnetic noise emission. The analysis focuses on the description of the power supplies for noble liquid calorimeters, such as the Atlas LAr calorimeters, though several outcomes of this research can be applied to other detectors of the future LHC experiments. Experimental results carried on demonstrators are provided.