Ivana Kovacevic

New physical model for lifetime estimation of power modules

In this paper a physical model for lifetime estimation of standard power modules is proposed. The lifetime prediction is based on the assumption that the solder interconnections are the weakest part of the module assembly and that the failure cause is the inelastic deformation energy accumulated within the solder material. Unlike the well-known Coffin-Manson model, the proposed model can be used to physically explain the dependency of lifetime on the various properties of a temperature profile i.e. frequency, dwell-ramp time, minimum/maximum temperature. The model is based on Clechs algorithm for simulation of stress-strain solder response under cyclical thermal loading and on the solder deformation mechanism map used to define the dominant failure mechanism under observed stress-temperature conditions. Either accelerated cycling tests or existing field databases are needed to parameterize the model. To verify the approach, the results of power cycling tests for a high power IGBT module found in literature are applied and the impacts of two mission profiles on the module lifetime are examined.

3-D Electromagnetic Modeling of Parasitics and Mutual Coupling in EMI Filters

The electromagnetic compatibility (EMC) analysis of electromagnetic interference (EMI) filter circuits using 3-D numerical modeling by the partial element equivalent circuit (PEEC) method represents the central topic of this paper. The PEEC-based modeling method is introduced as a useful tool for the prediction of the high frequency performance of EMI input filters, which is affected by PCB component placement and self- and mutual-parasitic effects. Since the measuring of all these effects is rather difficult and time consuming, the modeling and simulation approach represents a valuable design aid before building the final hardware prototypes. The parasitic cancellation techniques proposed in the literature are modeled by the developed PEEC-boundary integral method (PEEC-BIM) and then verified by the transfer function and impedance measurements of the L-C and C-L-C filter circuits. Good agreement between the PEEC-BIM simulation and the measurements is achieved in a wide frequency range. The PEEC-BIM method is implemented in an EMC simulation tool GeckoEMC. The main task of the presented research is the exploration of building an EMC modeling environment for virtual prototyping of EMI input filters and power converter systems.

3-D Electromagnetic Modeling of EMI Input Filters

In this paper, a novel 3-D electromagnetic modeling approach which enables electromagnetic compatibility (EMC) analysis of power converter systems in an accurate and computationally efficient way is presented. The 3-D electromagnetic modeling approach, implemented in the EMC simulation tool GeckoEMC, is based on two numerical techniques, the partial element equivalent circuit method and the boundary integral method (PEEC-BIM). The developed PEEC-BIM coupled method enables comprehensive EMC analysis taking into account different effects of the PCB layout, self-parasitics, mutual coupling, shielding, etc., which in turn provides a detailed insight into the electromagnetic behavior of power electronic systems in advance to the implementation of hardware prototypes. The modeling features of the GeckoEMC simulation tool for virtual design of electromagnetic interference (EMI) filters and power converters is demonstrated on the examples of a single-phase two-stage EMI filter and a practical EMI filter for a single-phase PFC input stage. Good agreement between the PEEC-BIM simulation and the small signal transfer function measurement results is achieved over a wide frequency range, from dc up to 30 MHz. The EMC simulation environment enables a step-by-step EMC analysis distinguishing the impact of various electromagnetic effects on the EMI filter performance and allowing an optimal EMI filter design.

An extension of PEEC method for magnetic materials modeling in frequency domain

An extension of the partial element equivalent circuit (PEEC) method for magnetic materials modeling in the frequency domain applied on toroidal magnetic inductors with rectangular cross section is presented in this paper. The extension is performed by coupling the PEEC method and the boundary element method (BEM). The influence of magnetic material is modeled by distributions of “fictitious magnetic currents and charges” existing on the surface of a magnetic body. To verify the developed 3-D PEEC model, calculated and measured impedances are compared for two winding arrangements employing a ferrite T38 core. A good agreement between the PEEC simulation and measurements is presented up to the first resonant frequency. The described PEEC modeling approach enables 3-D electromagnetic simulations with much less computational effort than given for existing finite element method (FEM) simulators.

Full PEEC Modeling of EMI Filter Inductors in the Frequency Domain

In this paper, the performance of a new method based on the coupling of the partial element equivalent circuit method and boundary integral method (the PEEC-BIM method) for 3D modeling of toroidal inductors, which are typically used in electromagnetic interference (EMI) filter applications, is presented. The presence of magnetic materials is modeled by replacing the surface of magnetic regions with an equivalent distribution of fictitious current loops. It is shown that the influence of the magnetic core on the impedance and the stray field of EMI filter inductors can be modeled and explained in detail by PEEC-BIM simulation results. The developed PEEC-BIM approach is verified by both 3D finite-element method (FEM) simulations and near-field measurements for different winding configurations and magnetic cores. Regarding computational complexity, the developed PEEC-BIM method applied to toroidal inductors performs extremely well. The PEEC-BIM simulation is at least twice faster than the corresponding FEM-based analysis. The PEEC-BIM method has been implemented in a PEEC-based simulation tool, which facilitates the simulation of entire EMI filter structures.

PEEC modelling of toroidal magnetic inductor in frequency domain

In this paper, a detailed 3D Partial Element Equivalent Circuit (PEEC) model of a toroidal coil with a magnetic core is developed. The PEEC problem in the presence of magnetic materials is solved in the frequency domain via a magnetic current/charge approach, i.e. replacing the magnetized objects by a distribution of equivalent fictitious magnetic currents/charges in free space. The simulation parameters are the winding and magnetic core properties. The permeability is either taken from datasheets or determined by measuring the series equivalent impedance. To verify the proposed 3D PEEC model, calculated and measured impedance values are compared for several winding arrangements and core materials. A good agreement between simulation and measurements is presented up to the first resonant frequency. For higher frequencies, a more accurate specification of the permeability is required, as well as the core dielectric property has to be considered.

PEEC-based virtual design of EMI input filters

The paper summarizes a step by step Partial Element Equivalent Circuit (PEEC) modeling approach for Electromagnetic Interference (EMI) filter components (e.g. foil capacitors, common mode and differential mode inductors) and PCB tracks, to design complete EMI input filters with an optimal selection and placement of the individual components. The presence of magnetic cores is modeled with the proposed PEEC-Boundary Integral Coupled Method (PEEC-BIM) by means of fictitious magnetic surface currents, using the core geometry and permeability as inputs. The developed PEEC based models are verified by transfer function measurements of several single-phase single/two-stage filter circuits. The resulting PEEC simulation time is determined by the time required to perform the surface mesh of the magnetic volume and is in the order of several minutes. The good results of the presented PEEC modeling approach enable a fast virtual design of EMI filters and help to accelerate the design process of power converter systems.

Multi-domain simulation of transient junction temperatures and resulting stress-strain behavior of power switches for long-term mission profiles

For lifetime estimation of power converters in traction applications, one method is to calculate numerically the stress-strain hysteresis curves of the interfaces silicon-solder-DCB and/or DCB-solder-baseplate inside the power modules. This can only be achieved if the transient junction temperatures in these layers are known for a defined mission-profile. Therefore, one has to couple circuit simulation with thermal simulation and stress-strain computation. The second challenge of this problem is to perform this transient simulation taking into account switching losses in the mus-range for mission profiles over a couple of minutes. In this paper we employ a new multi-domain simulation software to achieve results with reasonable computational effort.

Optimization of a wearable power system

In this paper the optimization of wearable power system comprising of an IC engine, motor/generator, inverter/rectifier, Li-battery pack, DC/DC converters, and controller is performed. The Wearable Power System must have the capability to supply an average 20 W for 4 days with peak power of 200 W and have a system weight less then 4 kg. The main objectives are to select the engine, fuel and battery type, to match the weight of fuel and the number of battery cells, to find the optimal working point of engine and minimizing the system weight. The minimization problem is defined in Matlab as a nonlinear constrained optimization task. The optimization procedure returns the optimal system design parameters: the Li-polymer battery with eight cells connected in series for a 28 V DC output voltage, the selection of gasoline/oil fuel mixture and the optimal engine working point of 12 krpm for a 4.5 cm3 4-stroke engine.

Practical characterization of EMI filters replacing CISPR 17 approximate worst case measurements

A common approach for selecting a suitable EMI filter is detailed based on the example of a realized single-phase 500W PFC rectifier. The presented work separates conducted EMI noise into Differential Mode (DM) and Common Mode (CM) components and derives expressions for the DM and CM insertion losses achieved if a given EMI filter is connected to a dedicated power converter. With the use of hardware measurement results it is shown that the impedances of the EMI filter and the PFC rectifier have a considerable impact on the realized insertion losses, which, at particular frequencies, may be even less than approximate worst-case estimations proposed in CISPR 17.