Maine Campus September 26 1957

In traction applications, electrical drivetrain components are subjected to unpredictable load and temperature variations depending on the driving cycle and ambient conditions. As performance and power density requirements are getting increasingly stringent, the power electronic devices and electromagnetic actuators are stressed heavily due to temperature cycling effects and face the risk of overheating, compromising lifetime and reliability. To protect the drivetrain from thermally induced failure, a model-based thermal management strategy is proposed in this paper. Critical component temperatures are calculated online with a combined loss and thermal model and are limited progressively by applying constraints to loss-influencing operating variables. Starting from the requested torque, the dq-current setpoint calculation is formulated as a constraint optimization problem in order to protect all drivetrain components while maximizing overall efficiency over the entire torque speed operating range, including field weakening at elevated speed. Unlike conventional approaches, which are often adhoc or based on de-rating, the proposed strategy allows the drivetrain to operate safely at maximum performance limits, without unnecessarily degrading performance.status: publishe

Inferring transcriptional modules from ChIP-chip, motif and microarray data

'ReMoDiscovery' is an intuitive algorithm to correlate regulatory programs with regulators and corresponding motifs to a set of co-expressed genes. It exploits in a concurrent way three independent data sources: ChIP-chip data, motif information and gene expression profiles. When compared to published module discovery algorithms, ReMoDiscovery is fast and easily tunable. We evaluated our method on yeast data, where it was shown to generate biologically meaningful findings and allowed the prediction of potential novel roles of transcriptional regulators

Traditional and digital literacy. The literacy hypothesis, technologies of reading and writing, and the ‘grammatized’ body

This article discusses, from a theoretical and philosophical perspective, the meaning and the importance of basic literacy training for education in an age in which digital technologies have become ubiquitous. I discuss some arguments, which I draw from the so-called literacy hypothesis approach (McLuhan, Goody, Havelock, Ong), in order to understand the significance of a ‘traditional’ initiation into literacy. I then use the work of Bernard Stiegler on bodily gestures and routines, related to different (traditional and digital) technologies, in order to elaborate and criticize the claims the literacy hypothesis makes. Bringing together insights from both the literacy hypothesis approach and Stiegler's work, I defend the view that there exists an essential difference between traditional and digital literacy, and I try to argue for the introduction of a spelling and grammar of the digital in the educational curriculum

Genetic and lifestyle risk factors for MRI-defined brain infarcts in a population-based setting.

OBJECTIVE: To explore genetic and lifestyle risk factors of MRI-defined brain infarcts (BI) in large population-based cohorts. METHODS: We performed meta-analyses of genome-wide association studies (GWAS) and examined associations of vascular risk factors and their genetic risk scores (GRS) with MRI-defined BI and a subset of BI, namely, small subcortical BI (SSBI), in 18 population-based cohorts (n = 20,949) from 5 ethnicities (3,726 with BI, 2,021 with SSBI). Top loci were followed up in 7 population-based cohorts (n = 6,862; 1,483 with BI, 630 with SBBI), and we tested associations with related phenotypes including ischemic stroke and pathologically defined BI. RESULTS: The mean prevalence was 17.7% for BI and 10.5% for SSBI, steeply rising after age 65. Two loci showed genome-wide significant association with BI: FBN2, p = 1.77 × 10-8; and LINC00539/ZDHHC20, p = 5.82 × 10-9. Both have been associated with blood pressure (BP)-related phenotypes, but did not replicate in the smaller follow-up sample or show associations with related phenotypes. Age- and sex-adjusted associations with BI and SSBI were observed for BP traits (p value for BI, p [BI] = 9.38 × 10-25; p [SSBI] = 5.23 × 10-14 for hypertension), smoking (p [BI] = 4.4 × 10-10; p [SSBI] = 1.2 × 10-4), diabetes (p [BI] = 1.7 × 10-8; p [SSBI] = 2.8 × 10-3), previous cardiovascular disease (p [BI] = 1.0 × 10-18; p [SSBI] = 2.3 × 10-7), stroke (p [BI] = 3.9 × 10-69; p [SSBI] = 3.2 × 10-24), and MRI-defined white matter hyperintensity burden (p [BI] = 1.43 × 10-157; p [SSBI] = 3.16 × 10-106), but not with body mass index or cholesterol. GRS of BP traits were associated with BI and SSBI (p ≤ 0.0022), without indication of directional pleiotropy. CONCLUSION: In this multiethnic GWAS meta-analysis, including over 20,000 population-based participants, we identified genetic risk loci for BI requiring validation once additional large datasets become available. High BP, including genetically determined, was the most significant modifiable, causal risk factor for BI

Optimal Control of Traction Motor Drives under Electrothermal Constraints (Optimale controle van tractie aandrijvingen binnen elektrothermische limieten)

Permanent magnet synchronous motor (PMSM) drives combine an interesting set of characteristics including a high efficiency, a high torque-per-ampere ratio and a wide speed operating range. This makes them particularly suitable for application in (hybrid) electric vehicles. Future requirements on electric traction drives are getting increasingly stringent. A reduction of cost, weight and volume is required, while an increase of efficiency, power density and reliability is necessary as well. To achieve these goals, research and development mainly focuses on improved designs and materials. However, performance figures are not only determined by the properties of individual drivetrain components, but also in the way traction motors, power electronic converters and energy storage interact as a system. Because this interaction is (for a large part) determined by the applied control strategy, a large potential for improvement is situated in this area. This thesis investigates how advanced control algorithms can contribute to a better utilization of existing systems without change of the hardware, in order to meet the aforementioned requirements. This comes down to maximizing the drive's performance figures (torque, power and efficiency), while taking into account the electrical and thermal constraints.First, an enhanced current vector control (CVC) strategy for PMSM drives is elaborated. In each operating point, it generates optimal dq-current references to maximize the speed-torque envelope given the voltage and current constraints of the motor and/or inverter. The proposed algorithm is able to seamlessly switch between constant torque and flux-weakening control, allowing high-speed operation with a high degree of robustness to parameter variations and a fast transient response. Furthermore, a maximum-efficiency-per-Nm algorithm is included in the CVC-strategy to minimize overall motor and inverter losses.Because most failure mechanisms in motor drives are related to temperature, adequate thermal management is indispensable in meeting the conflicting future requirements on power density and reliability. Conventionally, the motor and inverter are rated assuming worst-case operating conditions, to safeguard switching devices and stator windings from excessive temperature amplitudes and variations. However, a conservative rating benefits lifetime on the one hand, but implies an (often unnecessary) restriction of performance on the other. As a solution, this thesis proposes an active approach to thermal management. Based on real-time estimates of switching devices and motor temperatures, losses are actively regulated by means of a dynamic switching frequency and current limit. In contrast to the conventional approach of applying a fixed (rated) current control limit and switching frequency, the deliverable (peak) torque output directly depends on the actual thermal state of the components. Torque is only curtailed in case the thermal constraints are effectively reached. Hence, active thermal management allows a better utilization of the drivetrain hardware, without jeopardizing reliability.The potential of dynamic DC-link voltage adaptation regarding thermal management of PMSM drives is investigated as well. With an additional converter, the bus voltage level can be adjusted to the required PMSM terminal voltage in each operating point. Doing so, switching losses can be reduced at low speed by lowering the bus voltage. At high speed, the voltage level is boosted and field-weakening operation with the associated additional losses is avoided. Because this implies a reduction of heat build-up in the switching devices, a higher torque and power output is allowed.Within the thesis, the different parts of the control algorithms are elaborated step by step. The emphasis is on the implementation aspects, with extensive experimental validation on a Matlab/Simulink-based rapid-prototyping platform. The experimental setup mimics a series-hybrid drivetrain, consisting of an 11 kW interior PMSM, an inverter and an active front-end converter. The PMSM is coupled to a dynamic load machine to test the algorithms under realistic driving conditions.nrpages: 232status: publishe

Synchronization and efficiency analysis of a direct-drive multi-motor application

This paper presents the results of a technical feasibility study concerning the direct-drive conversion of an existing four-axis wire processing machine. The objective is to obtain a considerable efficiency improvement, while maintaining equal speed and angle synchronization properties as the substituted gearbox mechanics. A control algorithm based on the method of electronic line shafting is implemented and verified with simulations and experiments on a test setup. The controller emulates the inter-shaft state feedback of a physical gearbox resulting in comparable synchronization performance during load disturbances, acceleration and emergency stop conditions. The efficiency improvement potential is verified with measured efficiency maps of all drivetrain components. In the nominal operating point, the direct-drive machine outperforms the conventional machine with 14% due to the avoidance of gearbox losses and the application of highly efficient permanent magnet synchronous motor technology.status: publishe

Electric Motors

The first section of this chapter focuses on the losses in electric motors. First the different loss components are described. Next, the influence of practical operating conditions on efficiency are addressed. The second section is devoted to standards on efficiency testing and classification. In the last section, the technology used in high efficiency motors is discussed briefly by looking at materials, design and manufacturing evolutions.edition: 1ststatus: publishe

2D Finite Element Analysis of a Solid Rotor Sector Motor

A solid rotor sector motor is a type of induction motor with a segmented stator rather than a ring-shaped or linear one. The operating principle and parasitic end effects are similar to those of a linear induction motor (LIM). A 2D finite element method model (2D FEM) including the 3D end effects is developed to calculate the torque and field distribution. A comparison with measurements is given and the simulation results are found to be a good prediction of the actual torque characteristics.status: accepte

Dynamic DC-link voltage adaptation for thermal management of traction drives

Power density and reliability specifications for motor drives in traction applications are getting increasingly stringent. The main challenge in meeting these conflicting requirements, is managing heat dissipation. A drive’s peak torque rating is limited by switching device temperatures which must be kept below critical values at all times for the sake of reliability, preferably without major hardware adaptations. In this challenge lies a large potential for advanced control algorithms. This paper proposes a PMSM drive control strategy which combines active thermal management with dynamic DC-link voltage adaptation. The bus voltage level is adjusted to the required PMSM terminal voltage in each operating point. Doing so, switching losses can be reduced at low speed by lowering the bus voltage. At high speed, the voltage level is boosted and field-weakening operation and the associated additional losses are avoided. An 11 kW PMSM drive, with an active front-end controlling the bus voltage, is used as a test setup to mimic a series-hybrid drivetrain. Compared to a fixed DC-link voltage, efficiency maps show a significant inverter loss reduction at low speed. This results in lower switching device temperatures which in turn allows a higher peak torque rating.status: publishe