Assumed-strain finite element technique for accurate modelling of plasticity problems

In this work a linear hexahedral element based on an assumed-strain finite element technique is presented for the solution of plasticity problems. The element stems from the NICE formulation and its extensions. Assumed gradient operators are derived via nodal integration from the kinematic-weighted residual; the degrees of freedom are only the displacements at the nodes. The adopted constitutive model is the classical associative von-Mises plasticity model with isotropic and kinematic hardening; in particular a double- step midpoint integration algorithm is adopted for the integration and solution of the relevant nonlinear evolution equations. Efficiency of the proposed method is assessed through simple benchmark problem and comparison with reference solutions

Single pulse avalanche robustness and repetitive stress ageing of SiC power MOSFETs

This paper presents an extensive electro-thermal characterisation of latest generation silicon carbide (SiC) Power MOSFETs under unclamped inductive switching (UIS) conditions. Tests are carried out to thoroughly understand the single pulse avalanche ruggedness limits of commercial SiC MOSFETs and assess their aging under repetitive stress conditions. Both a functional and a structural characterisation of the transistors is presented, with the aim of informing future device technology development for robust and reliable power system development

Device loss model of a fully SiC based dual active bridge considering the effect of synchronous rectification and deadtime

It is becoming a great interest to employ SiC based power devices in dual active bridge (DAB) converter as an alternative to conventional Si-IGBT, due to its higher switching frequency potential, smaller switching losses as well as the capability to operate at synchronous rectification (SR) condition. This paper introduces the device loss model of a SiC MOSFET power module based DAB converter considering the effect of synchronous rectification, and the dead-time effect is also discussed. The calculated device loss for both SiC-MOSFET and Si-IGBT are discussed. The results show that the overall device loss is reduced by 40%, where the conduction loss is reduced by 38% because of SR capability of SiC-MOSFET, and the switching loss is reduced by 48% due to the faster transient of SiC-MOSFET during dead-time. On the other hand, the device losses are not even between the primary bridge and the secondary bridge of the DAB converter, and it is more significant for SiC-MOSFET based DAB due to the effect of SR with a maximum of 20%. At last, the dead-time range is given based on the device properties

Trade-off study of heat sink and output filter volume in a GaN HEMT based single phase inverter

This paper presents the trade-off study of heat sink and output filter volume of a GaN HEMT based single phase inverter. The selected topology is three-level Active Neutral point Clamped (ANPC) inverter, and the main aim is to explore the benefits of the GaN HEMTs at 600 V blocking class on the system level efficiency, and power density under wide range of operating conditions. The paper starts by introducing the inverter topology, selected PWM scheme and followed by the device features, static and dynamic characterisation and continues with presenting and discussing the results of extensive experimental and analytical characterisation. After this, the impact of GaN HEMTs on inverter volume is discussed in terms of heat sink and output filter volume analysis under different switching frequency and heat sink temperature conditions. The calculation of heat sink volume and single stage LC output filter volume are presented with respect to experimental results of single phase prototype. The findings from static, dynamic characterisation and single phase prototype results clearly show that GaN HEMT has excellent switching performance under wide load current and heat sink temperature conditions. The high performance of the inverter lead to reduction of the combined total volume, including output filter and heat sink volume

A physics-based compact model of SiC power MOSFETs

The presented compact model of SiC power MOSFETs is based on a thorough consideration of the physical phenomena which are important for the device characteristics and its electrothermal behavior. The model includes descriptions of the dependence of channel charge and electron mobility on the charge of interface traps and a simple but effective calculation of the voltage-dependent drain resistance. Comparisons with both physical 2-D device simulations and experiments validate the correctness of the modeling approach and the accuracy of the results

Optimization of thermal management and power density of small-scale wind turbine applications using SiC-MOSFETs

This paper presents an optimized design of 12kW 2L-FB inverter for small-scale wind turbine, taking into account some specific behavioral features of SiC power MOSFETs. Power converters used in renewable energy conversion have to deal with intermittent and variable power availability from the source, which implies that they actually work at their maximum rated power for only a small fraction of their operational time. Still, traditional thermal management design of power modules has to refer to maximum load conditions. SiC-MOSFETs exhibit a very stable performance over a broad temperature range [1-3]; this feature enables to design the cooling device for nominal operational conditions, typically corresponding to a much lower than maximum power rating. When this capability is added to the decrease in the size of passive filter elements, which can be gained by the higher switching frequency capability of SiC MOSFETs, the result is a significant increase of the converter powe, density

Modular plug-in high performance integrated single-phase inverter

The recent research exercises have targeted the transfer of the sandwich package benefits to application bespoke switch design, including flip-chip and device stacking topology [1]. This work presents the development of a highly integrated power switch, based on 70μm thin IGBTs and diodes rated at 600V/200A along with customized connectors to interface quickly the gate driver, the input, and the load side PCBs. This modular system has been designed with the aim to achieve high performance including the modularity and maintainability of power converter that can be worse in a system integrated into a single package

Extracting structure functions of power devices in induction motor drives

This paper proposes the extraction of structure function from power devices on-board induction motor drives. It puts forward the issues and methodology related to on-board measurement of the cooling curve and derivation of the structure function during idle times in induction motor drives for maintenance purposes. The structure function uses the thermal resistances and capacitances in the Cauer form to identify changes in the device structure. The advantage of the structure function is that it does not only reveal the value but also the location of the thermal resistance and capacitance in the heat flow path. The novelty in this work is the methodology used to achieve the measurement of the cooling curve and the derivation of the structure function despite issues related to freewheeling current due to energy stored as a result of motor inductance

Prognostic System for Power Modules in Converter Systems Using Structure Function

This paper proposes an on-board methodology for monitoring the health of power converter modules in drive systems, using vector control heating and structure function to check for degradation. It puts forward a system that is used on-board to measure the cooling curve and derive the structure function during idle times for maintenance purposes. The structure function is good tool for tracking the magnitude and location of degradation in power modules. The ability to keep regular track of the actual degradation level of the modules enables the adoption of preventive maintenance, reducing or even eliminating altogether the appearance of failures during operation, significantly improving the availability of the power devices. The novelty in this work is the complete system that is used to achieve degradation monitoring; combining the heating technique and the measurement without additional power components except the measurement circuit which can be integrated into the gate drive board and the challenges encountered. Experimental results obtained from this show that it is possible to implement an on-board health monitoring system in converters which measures the degradation on power modules