New Algorithms for MM-Estimation of Multivariate Scatter and Location

We present new algorithms for $M$-estimators of multivariate scatter and location and for symmetrized $M$-estimators of multivariate scatter. The new algorithms are considerably faster than currently used fixed-point and related algorithms. The main idea is to utilize a second order Taylor expansion of the target functional and to devise a partial Newton-Raphson procedure. In connection with symmetrized $M$-estimators we work with incomplete $U$-statistics to accelerate our procedures initially

Position estimation for PMSMs at any speed using the zero-sequence voltage and modified space vector modulation

Anisotropy-based estimation techniques enable position and speed estimation for synchronous and induction machines down to low speeds and standstill. One possible approach consists of exciting the machine with special pulse patterns and measuring the zero-sequence voltage which requires access to the neutral point of a star-connected machine but can in return enable high signal-to-noise ratios. This thesis focuses in particular on permanent magnet synchronous machines and aims to contribute to the understanding of fundamental relations through a mathematical analysis of the underlying anisotropy information as well as to practical aspects that include initial polarity detection, usable pulse patterns and investigations on certain non-ideal effects which real machines exhibit. Experimentally achieved estimation results using real machines are presented, which demonstrate in particular low noise content and little dependence on rotor speed.Anisotropiebasierte Schätzverfahren ermöglichen Positions- und Drehzahlschätzung für Synchron- und Induktionsmaschinen bis hin zu niedrigen Drehzahlen und Stillstand. Ein möglicher Ansatz besteht darin, die Maschine mit speziellen Pulsmustern anzuregen und die Nullspannung zu messen, was den Zugang zum Sternpunkt einer im Stern verschalteten Maschine erfordert, dafür aber hohe Signal-Rausch-Verhältnisse ermöglichen kann. Diese Arbeit konzentriert sich insbesondere auf Permanentmagnet-Synchronmaschinen und möchte durch eine mathematische Analyse der zugrundeliegenden Anisotropie-Information zum Verständnis grundlegender Zusammenhänge beitragen sowie zu praktischen Aspekten, darunter die Erkennung der anfänglichen Polarität, verwendbare Pulsmuster und Untersuchungen zu bestimmten nicht-idealen Effekten, welche bei realen Maschinen auftreten. Es werden experimentell erzielte Ergebnisse der Schätzung bei realen Maschinen vorgestellt, die insbesondere einen geringen Rauschanteil und eine geringe Abhängigkeit von der Rotordrehzahl aufzeigen

Improvement of Position Estimation of PMSMs Using an Iterative Vector Decoupling Algorithm

This paper presents an improvement of sensorless techniques based on anisotropy for the estimation of the electrical angular position of synchronous machines by means of an iterative algorithm. The presented method reduces the effect of the fourth saliency harmonics on the measured signals avoiding the use of an observer or filter, thus, no additional dynamics are introduced on the system. Instead, a static algorithm based on iterative steps is proposed, minimizing the angular position error. The algorithm is presented and applied using the DFC (Direct Flux Control) technique but it is not limited to this choice. The advantages and limitations of this method are presented within this paper. The proof of the algorithm convergence is given. Simulations and experimental tests are performed in order to prove the effectiveness of the proposed algorithm

Corrections to "Modulation Strategies for Anisotropy-Based Position Estimation of PMSMs Using the Neutral Point Voltage"

In the above article [1], there are a few errors that are corrected in the following

Modulation Strategies for Anisotropy-Based Position Estimation of PMSMs Using the Neutral Point Voltage

Information obtained about magnetic anisotropy via neutral point voltage measurements can be used to estimate the position of synchronous and induction machines at all speeds including standstill. Due to its usually high signal-to-noise ratio, this estimation method can be an attractive alternative to approaches that acquire anisotropy information via current measurements. The position estimation method looked at in this paper relies on anisotropy information in the form of position-dependent inductance ratios. These are obtained through measurement of the voltage between the machine’s neutral point and an artificial neutral point during the application of different voltage vectors via a two-level switching inverter. We analyze the conditions placed on and the consequences of implementing necessary modifications to a standard space vector modulation. Five different modified modulation strategies are compared and investigated, including two newly proposed strategies which use only a minimal set of active and zero voltage vectors for measurement of the inductance ratios and therefore allow high utilization of available voltage and a high update rate of the estimated position. Experimental results for three low-power threephase permanent magnet synchronous machines are presented which suggest that modulation strategies that use active measurement vectors in all three instead of only two axes of the machine are less susceptible to systematic deviations in the position estimation that presumably result from nonlinear machine properties. As part of the machine model, a normalizing inductance variation ratio is introduced, which simplifies expressions and supports the comparison of motors

GrassPlot - a database of multi-scale plant diversity in Palaearctic grasslands

GrassPlot is a collaborative vegetation-plot database organised by the Eurasian Dry Grassland Group (EDGG) and listed in the Global Index of Vegetation-Plot Databases (GIVD ID EU-00-003). GrassPlot collects plot records (releves) from grasslands and other open habitats of the Palaearctic biogeographic realm. It focuses on precisely delimited plots of eight standard grain sizes (0.0001; 0.001;... 1,000 m(2)) and on nested-plot series with at least four different grain sizes. The usage of GrassPlot is regulated through Bylaws that intend to balance the interests of data contributors and data users. The current version (v. 1.00) contains data for approximately 170,000 plots of different sizes and 2,800 nested-plot series. The key components are richness data and metadata. However, most included datasets also encompass compositional data. About 14,000 plots have near-complete records of terricolous bryophytes and lichens in addition to vascular plants. At present, GrassPlot contains data from 36 countries throughout the Palaearctic, spread across elevational gradients and major grassland types. GrassPlot with its multi-scale and multi-taxon focus complements the larger international vegetationplot databases, such as the European Vegetation Archive (EVA) and the global database " sPlot". Its main aim is to facilitate studies on the scale-and taxon-dependency of biodiversity patterns and drivers along macroecological gradients. GrassPlot is a dynamic database and will expand through new data collection coordinated by the elected Governing Board. We invite researchers with suitable data to join GrassPlot. Researchers with project ideas addressable with GrassPlot data are welcome to submit proposals to the Governing Board