Christian Kral

• Dr.
• Instructor at Technologisches Gewerbemuseum TGM

This paper presents the new open source Modelica library WindPowerPlants. For the economic assessment of either a wind power plant or an entire wind park, the accurate prediction of the energy output is essential. Such prediction is usually performed by means of calculations based on statistical wind data. The proposed WindPowerPlants library is ca...

Transient models of multi phase electric machines are already implemented in the Modelica Standard Library (MSL). However, advanced effects like saturation and skin effect are not taken into account. As an extension to the MSL models, the new EMachines library is presented. This package will be released as a supplemental library to the commercial E...

In this work the fuel consumption of two vehicles is compared. For investigating the fuel consumption a whole vehicle simulation is developed with the Smart- PowerTrains library and the SmartElectricDrives li- brary. Both librarys are written in Modelica language. As a reference vehicle a conventional vehicle with manual transmission is modeled. A...

A new quasi static fundamental wave machines library will be included in the magnetic domain package of the next Modelica Standard Library (MSL). The provided classes of machine models omit all transient electrical effects, but m echanical dynamics are fully taken into account. By including the new machine models new classes of problems can be trea...

Electric machine theory and electric machine simulations models are often limited to three phases. Up to the Modelica Standard Libray (MSL) version 3.2 the provided machine models were limited to three phases. Particularly for large industrial drives and for redundancy reasons in electric vehicles and aircrafts multi phase electric machi nes are de...

A thermal model for the determination of the temperatures of interior permanent magnets and stator windings is presented in this paper. The innovation of the model relies on one temperature sensor being located in the stator core of the machine. Such sensor is simple to implement in many applications such as traction or EV, where reliability is cri...

A model is presented in this work which is capable to calculate the magnetic behavior and iron losses of a ferromagnetic lamination in a wide frequency range. It is based on an energetic hysteresis model and extends its static approach with eddy-currents in a finite-difference simulation of a lamination sheet. This will also consider the field disp...

This paper focuses on different calculation methods of Joule losses in a winding and Halbach magnet arrays for air cored axial flux motors. The classical approach (I) for winding losses results in eddy current losses without proximity effect but with induced currents for the passing magnetic field. The second method (II) derives the frequency depen...

This paper describes the comparison and parameterization process of dynamic battery models for cell and system simulation. Three commonly used equivalent circuit battery models are parameterized using a numeric optimization method and basic electrical tests with a lithium-ion polymer battery cell. The maximum model performance is investigated, and...

This paper focuses on simulation of permanent magnet synchronous machine (PMSM) with fractional-slot windings (FSW) in Modelica. Modeling of the electrical machines with object-oriented approach is shortly described, and a new Modelica library for simulation of electrical machines is introduced. The results of simulation of PMSMs with fractional sl...

The work proposes an improved method for estimating the magnet temperature in permanent magnet synchronous machines (PMSM's) without using any temperature sensors. Originally the method implies an intermittent injection of a voltage pulse in the positive d-axis of the motor while keeping the load current zero. Thus, the resulting d-current response...

The work focuses on tuning issues of a recently presented sensorless rotor temperature estimation technique for Permanent Magnet Synchronous Motors (PMSMs). The method implies an intermittent injection of a voltage pulse in the d-axis of the motor while keeping the load current zero. Thus, the resulting d-current response depends on both the initia...

In this paper an innovative thermal model for the determination of the temperatures of the permanent magnets and stator windings is presented. This model relies on one temperature sensor located in the stator core of the machine. The estimated stator winding and perma- nent magnet temperatures are determined by a simpli?ed thermal lumped element ne...

Magnet material prices has become an uncertain factor for electric machine development. Most of all, the output of ironless axial flux motors equipped with Halbach magnet arrays depend on the elaborated magnetic flux. Therefore, possibilities to reduce the manufacturing cost without negatively affecting the performance are studied in this paper. Bo...

Monitoring of airgap eccentricity for induction motors is important for guaranteeing motor reliability, since eccentricity can eventually lead to motor failure due to stator rotor contact. However, there are many limitations to applying existing test methods such as motor current signature analysis (MCSA) in the field, especially for variable frequ...

This paper proposes a multi domain physical model of permanent magnet synchronous machines, considering electrical, magnetic, thermal and mechanical effects. For each component of the model, the main wave as well as lower and higher harmonic wave components of the magnetic flux and the magnetic potential difference may be considered. The permanent...

In this paper a new model for the estimation of the stator winding and rotor cage temperatures of induction machines is presented. This model can be used in series applications of machines operated under dynamic load conditions where stator and rotor temperature shall be monitored. The proposed model relies on a simplified lumped element thermal eq...

In this paper, a lightweight ironless axial flux permanent magnet drive concept is presented. The in-wheel hub motor has a high torque to weight ratio and achieves a high efficiency, which extends the operation range of battery powered vehicles. The steps from preliminary design to manufacturing of the components are described. The paper includes F...

Die vorgestellte Arbeit behandelt das Phänomen defekter Rotorstäbe im Kurzschlussläufer einer Asynchronmaschine einschließlich der Detektion durch die Vienna Monitoring Method. Elektrische Asymmetrien im Rotorkäfig führen neben der zusätzlichen thermischen Belastung des Rotors auch zu Drehmomentpendelungen an der Welle sowie zu harmonischen Kompone...

Thermal models offer great advantages for enhancement of design, protection and control of electric machines. Detailed thermal models take a great number of time constants into account and provide accurate prediction of the temperatures. However, to parameterize such models detailed geometric data are needed. Whenever such detailed information is n...

An averaged model of a two-level IGBT inverter with consideration of temperature dependent switching and conduction losses is presented and compared to two other inverter models. In the presented model the influence of the conduction losses on the output voltage waveforms is considered and power balance is guaranteed. The model is not restricted to...

The work proposes a method for estimation of the magnet temperature in permanent-magnet synchronous machines by exploiting the d-axis saturation effects in the steel stator core produced by the d-current and rotor flux excitation. The method implies an intermittent injection of a voltage pulse in the d-axis of the motor. The resulting d-current res...

In this paper an accurate and fast thermal equivalent circuit (TEC) model of an interior permanent magnet synchronous machine (IPMSM) is presented. This model is capable of simulating transient thermal effects. The key parameters of the presented model are the heat transfer coefficients which consider heat transfer from the solid to the fluid regio...

This paper presents a method to control the current of each battery cell in a serially connected battery stack according to each cell capacity. With this method, the performance of a battery stack can be increased significantly. In a second life concept, battery cells with different capacities and even battery cells with different chemistries can b...

This article describes the parameterization process of dynamic battery models for cell and system simulation. Three commonly used equivalent circuit battery models are parameterized using a numeric optimization method and basic electrical tests with a lithium-ion polymer cell. The maximum model performance is investigated and a reasonable simplific...

The majority of the work performed for detecting eccentricity faults for permanent magnet synchronous motors (PMSM) focus on motor current signature analysis (MCSA), as it provides continuous on-line monitoring with existing current sensors. However, MCSA cannot be applied under nonstationary conditions and cannot distinguish faults with load torqu...

Unlike single cage rotor fault detection, FFT-based steady state spectrum analysis techniques can fail to detect outer cage faults in double cage induction motors due to the small outer cage current under running conditions. Double cage motors are typically employed in applications that require loaded starts. This makes the outer cage vulnerable to...

Condition monitoring of rotor problems such as demagnetization and eccentricity in permanent magnet synchronous motors (PMSM) is essential for guaranteeing high motor performance, efficiency, and reliability. However, there are many limitations to the off-line and on-line methods currently used for PMSM rotor quality assessment. In this paper, an i...

Unlike single cage rotor fault detection, FFT- based steady state spectrum analysis techniques can fail to detect outer cage faults in double cage induction motors due to the small outer cage current under running conditions. Double cage motors are typically employed in applications that require loaded starts. This makes the outer cage vulnerable t...

This article presents a method to control the current of each battery cell in a serially connected battery stack according to each cell capacity. With this method battery cells with different capacities and even battery cells with different chemistries can be serially connected. Therefore, significantly more energy can be extracted from the battery...

The majority of industrial controlled induction ma-chine drives are connected to the mains via a diode bridge. However, if reduction of harmonic currents and / or regenerative operation is desired, replacing the diode bridge by an active front-end (AFE) is required. This paper describes two models of an AFE: a power balance model disregarding switc...

This article gives an overview of the Electric Energy Storage (EES) library, which is proposed for inclu-sion in the Modelica Standard Library. The library contains models with different complexity for simu-lating of electric energy storages like batteries (sin-gle cells as well as stacks) interacting with loads, bat-tery management systems and cha...

This paper introduces the new FundemantalWave library which is included in the Modelica Standard Library 3.2. The presented Modelica package pro-vides models and components of rotating electrical three phase machines. The presented electrical machine models are fully compatible with the original Machines library of the electrical domain but rely on...

This paper examines the performance loss of lithium ion (LiIo) batteries as a result of aging effects. For this purpose, the state of merit (SOM) is introduced as a novel parameter. The SOM can be calculated as an inherent quantity considering both the increase in impedance as well as the loss in capacity of a battery cell. This is realized by meas...

This paper presents a comprehensive computa- tional fluid (CFD) model of a radial flux permanent mag- net synchronous machine with interior magnets. In the CFD model the water jacket cooling and a simplified model of the topology of the distributed stator winding are considered. The heat sources of the CFD model are determined from a finite element...

Die wesentlichen Aufgaben und Herausforderungen der Simulation von Elektrofahrzeugen werden in dieser Arbeit erörtert. Die Anforderungen an die Simulationsumgebung, die eingesetzten Modelle und die Parametrierung werden diskutiert. Konkret wird für die vorgestellten Modelle die objektorientierte Modellierungsprache Modelica verwendet. Die eingesetz...

In this article a method to estimate the capacity of individual lithium ion battery cells during operation is presented. When having two different states of charge of a battery cell as well as the transferred charge between these two states, the capacity of the battery cell can be estimated. The method is described in detail and validated on a batt...

In this article a method to estimate the capacity of individual lithium ion battery cells during operation is presented. When having two different states of charge of a battery cell as well as the transferred charge between these two states, the capacity of the battery cell can be estimated. The method is described in detail and validated on a batt...

This paper presents a permanent magnet model which takes temperature dependencies and demagnetization effects into account. The proposed model is integrated into a magnetic fundamental wave machine model using the modeling language Modelica. For different rotor types permanent magnet models are developed. The simulation results of the Modelica are...

This article describes the parameterization of a simple, dynamic single cell battery model for cell and system simulation. It is shown how to parameterize the model based on basic electrical tests and publicly available data such as data sheets. The performance of the parameterized model is validated with test results gained from two different cycl...

This paper presents a physical model of a squirrel cage induction machine with rotor topology. The machine is modeled in Modelica, an object oriented multi physical modeling system. The presented machine model is used to investigate electrical rotor asymmetries in induction machines. For the case of a single broken rotor bar a simulation model is c...

From the rating plate data of an induction motor the nominal efficiency can be determined. Without detailed knowledge of equivalent circuit parameters, partial load behavior cannot be computed. Therefore, a combined calculation and estimation scheme is presented, where the consistent parameters of an equivalent circuit are elaborated, exactly match...

This paper presents two simulation models for two variants of a large chipper drive used in a paper mill. If a slip ring induction motor is used, the impact of a rotor circuit rheostat with respect to starting behavior and heavy duty load impulses can be examined. Furthermore a speed controlled squirrel cage induction machine will be investigated....

In this chapter state of the art fault detection methods for permanent magnet and induction machines are presented. The discussed methods rely on the evaluation of measured voltages, currents and speed, respectively. Each kind of fault gives rise to a specific fault pattern in either of the measured quantities. Advanced signal processing techniques...

The development procedure of permanent magnet drives for sensor less operation beginning from standstill under overload conditions has to consider different design aspects coevally. First, the robust rotor position sensing by test signal enforces a design with a strongly different behavior of the spatial dq-oriented differential inductance values....

From the rating plate data of an induction motor the nominal efficiency can be determined. Without detailed knowledge of equivalent circuit parameters, partial load behavior cannot be computed. Therefore, a combined calculation and estimation scheme is presented, where the consistent parameters of an equivalent circuit are elaborated, exactly match...

The development procedure of permanent magnet drives for sensor less operation beginning from standstill under overload conditions has to consider different design aspects coevally. First, the robust rotor position sensing by test signal enforces a design with a strongly different behavior of the spatial dq-oriented differential inductance values....

This paper presents how losses of electric machines are modeled as an extension of the Mode-lica.Electrical.Machines library. The theoretical background of the different loss models is elaborated and a Modelica implementation – the Ad-vancedMachines Library – is presented. Additional examples demonstrate the usage of the library.

Conventional models of squirrel cage induction machines do not consider interbar currents. For the accurate numerical investigation of electrical rotor asymmetries interbar currents have to be modeled. A mathematical model of such a machine with interbar conductances is presented in this paper. An approach for the parametrization of the interbar co...

This paper presents a simulation model for a large chipper drive used in a paper mill. If the chipper drive is a slip ring induction motor, several advantages arise from using a rheostat in the rotor circuit. This paper will investigate the impact of a rotor circuit rheostat with respect to starting behavior and heavy duty load impulses. The chippe...

From the rating plate data of an induction motor the nominal efficiency can be determined. Without detailed knowledge of equivalent circuit parameters, partial load behavior cannot be computed. Therefore, a combined calculation and estimation scheme is presented, where the consistent parameters of an equivalent circuit are elaborated, exactly match...

The Vienna monitoring method (VMM) is a model-based rotor fault detection method that utilizes the voltage and current models for the computation of a fault indicator. So far, the VMM was investigated with fixed rotor parameters only. In this paper, the parameters of the current model are provided by a parameter tracking technique. For this advance...

A thermal model of a totally enclosed water-cooled induction machine is presented. The axially and radially discretized physical regions of the machine are modeled in the object-oriented language Modelica. Additionally, the water-cooling jacket is modeled. The parameters of the thermal network are derived from geometric, physical, and empirical dat...

From the rating plate data of an induction motor the nominal efficiency can be determined. Without detailed knowledge of the equivalent circuit parameters, partial load behavior cannot be computed. Therefore, a combined calculation and estimation scheme is presented, where the consistent parameters of an equivalent circuit are elaborated, exactly m...

This paper investigates the impact of inertia on the fault signatures of squirrel cage induction machines. Rotor faults give rise to harmonic sideband currents and double slip frequency shaft torque oscillations, however. The total drive inertia thus influences the speed ripple which, again, influences the balance of the magnitudes of the lower and...

In this work an electrically operated water pump in a cooling circuit is implemented, simulated and op- timized. The presented simulation results are accom- plished with Dymola. This simulation tool is based on the modeling language Modelica. The model of the water pump is realized with time domain differential equations. The parameters of the diff...

An electric traction machine for an electric or a hybrid electric vehicle is usually designed for a specific operating point or cycle. For such an operating point or cycle, the masses and the cooling circuit of the electric machine determine the time dependent temperature distribution within the machine. For a specific load cycle, the thermal simul...

Three phase induction machines for traction applications in electric and hybrid electric vehicles can be used with a fixed gear due to the wide speed range enabled by field weakening. Although the induction machine is know as an extremely reliable and robust device, machine faults may occur. Machine faults which do not become detected may cause com...

This paper investigates the impact of inertia on the fault signatures of squirrel cage induction machines. Rotor faults give rise to harmonic side band currents and double slip frequency shaft torque oscillations, however. The total drive inertia thus influences the speed ripple which, again, influences the balance of the magnitudes of the lower an...

This contribution presents a Modelica library for the simulation of electrical asymmetries in multiphase machines -the ExtendedMachines library. Simulation models of squirrel cage and slip ring induction machines, permanent magnet and electrical excited synchronous machines and reluctance machines are introduced. The object oriented model approach,...

Thermal simulations are a very important tool for optimizing the design of electric machines. In this paper, two thermal simulation models for totally enclosed fan cooled (TEFC) induction machines are compared with thermal measurement results. For both one dimensional models of the induction machine a thermal equivalent circuit of the machine is pr...

The focus in this work is the evaluation and validation of the simulation model of a conventional thermal manage-ment for an internal combustion engine (ICE). A simu-lation software package for modeling thermal manage-ment of the ICE including mechanical and thermal parts of the cooling circuit is presented: the SmartCooling (SC) library. For the e...

The presented work proposes a simulation environment using Modelica programming language for full vehicle simulations. A special software library suitable for Mod-elica simulations is used -the SmartElectricDrives (SED) library. This software is developed to simulate all parts of the electrical drive systems, and furthermore, allows to choose diffe...

In this paper different models for simulating compo-nents of thermal power plants and other thermal or thermodynamic processes are presented. The different simulation results were performed with Dymola which is based on Modelica. The models were realized with time domain differential equations and algebraic equa-tions. For all components the was mo...

This paper presents a new technique for estimating the rotor position from the stator current by evaluating rotor saliency harmonics due to rotor slotting effects. These harmonics arise independent of speed and any time-varying machine parameters. Therefore, the proposed technique can be used to estimate the actual rotation of the rotor versus the...

The intention of this work is to compare fuel consumptions of conventional and hybrid electric vehicles as well as vehicles with conventionally and electrically operated auxiliaries. In this paper the investigated auxiliaries are the water pump and the cooling fan. For the purposed investigation a whole vehicle simulation model is developed. The si...

A new free Modelica library, called VehicleInterfaces, has been developed to promote compatibility between Modelica automotive libraries. The library provides standard system interface definitions that enable the whole vehicle system to be conveniently modelled. Example vehicle models are also provided to illustrate the use of the inferface definit...

In this work a new simulation software package for modeling drive systems including electric components as well as mechanical parts is proposed –the SmartElectricDrives (SED) library. The SED library is developed in Modelica programming language. All the presented simulations are performed with Dymola, which is a commercial tool for simulating Mode...

In this work a drive train simulation of a four wheel hybrid electric vehicle (HEV) is presented. The results of the simulation show an optimized configuration of electric power source compo-nents in the HEV drive train system. All initial parameters used for the specific models of the simulation correspond to the measures of components in a typica...

An electric traction machine for an electric or hybrid electric vehicle is usually designed for a specific operating point or cycle. For such a operating cycle, the masses and the cooling circuit of the electric machine determine the time dependent temperature distribution within the machine. For a specific load cycle, the thermal simulation of the...

Stator winding failures are a serious problem of induction machines. In the case of bearing failures or rotor faults, fault-specific signatures increase slowly. An induction machine with such failures still can be operated for a certain time without taking strict precautions. Stator faults may occur much faster due to insulation breakdown or overlo...

Mechanical rotor imbalances and rotor eccentricities give rise to specific mechanical vibration, and certain electric, electromagnetic and mechanical harmonics. The extent and location of these harmonics depends on the actual severity of the imbalance, machine supply and load torque. Many fault detection techniques evaluate the spectral components...

This contribution investigates the Vienna monitoring method during transient operation. The Vienna monitoring method is a rotor fault detection technique based on two space phasor machine models. These models derive quantities such as flux and torque. An induction machine with rotor asymmetries gives rise to double slip frequency oscillations of sh...

This contribution proposes an algorithm for automated partial discharge (PD) pattern recognition for synchronous turbo generators. PD patterns indicate faults in the mica insulation of the stator windings of high voltage synchronous turbo generators. Usually these patterns can only be interpreted by experienced test engineers. The presented diagnos...

In this paper a cooling circuit with an electrically operated water pump was examined and simulated. The presented simulation results were performed with Dymola. This simulation tool is based on the modelling language Modelica. The model of the water pump was realized with time domain differential equations. The parameters of the differential equat...

Electrical rotor asymmetries such as broken rotor bars give rise to well known side band currents in the vicinity of the fundamental as well as double slip frequency torque modulation. An externally caused low frequency load torque modulation may therefore also cause similar effects such as side band currents and modulation of the electromechanical...

Stator and rotor temperature of a motor drive are important quantities with respect to the utilization and the overload capability. Permanent thermal stress and disregard of the temperature class specification may cause insulation deterioration with subsequent failure as well as rotor faults. Since the on-line measurement of rotor temperature is ve...

This paper presents two libraries, the basic Ma- chines library which is released with Modelica standard library 2.1 as well as an ExtendedMa- chines library, both for modelling electric ma- chines. The basic library provides the basic ma- chines types such as dc machines, three phase in- duction machines, three phase permanent magnet synchronous m...

Mechanical rotor imbalances and rotor eccentricities are reflected in electric, electromagnetic, and mechanical quantities. Therefore, many surveillance schemes determine the Fourier spectrum of a single line current in order to monitor the motor condition. Mechanical imbalances give rise to two first-order current harmonics. Due to the interaction...

So far, some freight cars have a detection device attached in order to be able to detect a derailed car. This work was carried out in order to investigate the possibility of the detection of derailments only by means of the evaluation of various signals at the locomotive. Several cases of short trains were examined, both by simulation and in realit...

The Vienna monitoring method (VMM) is a model based rotor fault detection technique for squirrel cage induction machines. It compares the torques calculated by a voltage and a current model, respectively. The voltage model evaluates the voltage and the current space phasor, whereas the current model processes the current space phasor ill the rotor...

This paper describes the experiences with partial discharge diagnoses of high voltage turbogenerators. After a short introduction of the structure of a high voltage winding with Roebel-bars the sources of partial discharge in the winding are described. The phase resolved partial discharge pattern analysis as well as the applied method for online an...

Mechanical rotor imbalances and rotor eccentricities are reflected in electric, electromagnetic and mechanical quantities. Therefore, many surveillance schemes determine the Fourier spectrum of a single line current in order to monitor the motor condition. Mechanical imbalances give rise to two first-order current harmonics. Due to the interaction...

This contribution compares rotor fault detection techniques of squirrel cage induction machines such as motor current signature analysis, Park's vector, motor power, torque, search coils, vibrations and acoustic emissions. Innumerable papers have been published about those techniques so far. Yet, the assessment of the severity of the actual fault h...

This paper addresses the possibility of integration of an induction machine rotor fault monitoring technique into batch tests. Conventional monitoring techniques are designed for operating conditions near nominal speed and load. Generally, load torque is not available at batch test as the test sample should not or cannot be clutched. However, at st...