Design and Analysis of Electric Powertrains for Offshore Drilling Applications

Doktorgradsavhandling ved Institutt for ingeniørvitenskap, Universitetet i Agder, 2016The global energy market is challenged with an ever increasing need for resources to meet the growing demands for electric power, transportation fuels, etc. Although we witness the expansion of the renewable energy industry, it is still the fossil fuels, with oil and gas dominating the scene of global energy supply sector, that provide majority of worldwide power generation.However, many of the easily accessible hydrocarbon reserves are depleted which requires from the producers of drilling equipment to focus on cost-effective operations and technology to compete in a challenging market. Particularly high level of activity is observed in both industry and academia in the field of electrical actuation systems of drilling machines, as control methods of alternating current (AC) motor drives have become an industrially mature technology over the past few decades. In addition, state-of-the-art AC motors manufacturing processes allow to conform to the strict requirements for safe operation of electrical equipment in explosive atmospheres. These two main reasons made electric actuation systems a tough competitor to hydraulic powertrains used traditionally by the industry. However, optimal design of induction motor drives and systematic analysis of factors associated with operation in harsh offshore conditions are still considered as a major challenge. In this thesis, effective methods for design and analysis of induction motor drives are proposed, including aspects of optimization and simulation-based engineering. The first part of the thesis is devoted to studying methods for modeling, control, and identification of induction machines operating in offshore drilling equipment with the focus to improve their reliability, extend lifetime, and avoid faults and damage, whereas the second part introduces more general approaches to the optimal selection of components of electric drivetrains and to the improvement of the existing dimensioning guidelines. A multidisciplinary approach to design of actuation systems is explored in this thesis by studying the areas of motion control, condition monitoring, and thermal modeling of electric powertrains with an aspiration to reach the level of design sophistication which goes beyond what is currently considered an industrial standard. We present a technique to reproduce operation of a full-scale offshore drilling machine on a scaled-down experimental setup to estimate the mechanical load that the designed powertrain must overcome to meet the specification requirements. The same laboratory setup is used to verify the accuracy of the estimation and control method of an induction motor drive based on the extended Kalman filter (EKF) to confirm that the sensorless control techniques can reduce the number of data acquisition devices in offshore machines, and thus decrease their failure rate without negatively affecting their functionality. To address the challenge of condition monitoring of induction motor drives, we propose a technique to assess the expected lifetime of electric drivetrain components when subjected to the desired duty cycles by comparing the effects of a few popular motion control signals on the cumulative damage and vibrations. As a result, the information about the influence of a given control strategy on drivetrain lifecycle is made available early in the design stage which can significantly affect the choice of the optimal powertrain components. The results show that some of the techniques that have a well-proven track record in other industries can be successfully applied to solve challenges associated with operation of offshore drilling machines. One of the most essential contributions of this thesis, optimal selection of drivetrain components, is based on formulating the drivetrain dimensioning problem as a mixed integer optimization program. The components of powertrain that satisfy the design constraints and are as cost-effective as possible are found to be the global optimum, contrary to the functionality offered by some commercially available drivetrain sizing software products. Another important drawback of the dimensioning procedures recommended by the motor drives manufacturers is the inability to assess if the permissible temperature limits given in the standards do not become violated when the actuation system experiences overloads different than these tabulated in the catalogs. Hence, the second most significant contribution is to propose a method to monitor thermal performance of induction motor drives that is based exclusively on publicly available catalog data and allows for evaluating whether the standard thermal performance limits are violated or not under arbitrary load conditions and at any ambient temperature. Both these solutions can effectively enrich the industrially accepted dimensioning procedures to satisfy the level of conservatism that is demanded by the offshore drilling business but, at the same time, provide improved efficiency and flexibility of the product design process and guarantee optimality (quantitatively, not qualitatively, measurable) of the final solution. An attractive direction for additional development is to further integrate knowledge from different fields relevant to electric powertrains to enable design of tailored solutions without compromising on their cost and performance

Thermal analysis of asynchronous machines under intermittent loading

ArticleThe operation of electric machines is accompanied by losses which are mostly converted to heat. The heat needs to be dissipated from the machine. With a properly dimensioned motor, the arising heat is balanced with dissipated one. After the motor is started at ambient temperature, all functional parts of the machine are gradually warmed until stabilized. Any overloading of the machine leads to stabilization at temperatures higher than expected by the designers. High temperatures in the machine could cause a crash by damaging an insulation. In case of machines with permanent magnets, the temperature affects their magnetic properties and can leads to demagnetization at the Curie temperature. Therefore, the measuring of temperature is so important for verifying the allowed warming of the motor. Contact and noncontact methods could be used for temperature measuring. Thermal warming and temperature distribution in an electric machine can be also determined by theoretical calculations based, for example, on the finite element method. This method is used by a number of computer software such as Ansys. The article deals with generation and propagation of heat in electric motors and with measuring of warming characteristics with a variable value of a load factor for intermittent periodic loading of asynchronous machine. The loading is carried out by the dynamometer. The temperature measurement is implemented by temperature sensors which are located on the stator winding of the asynchronous motor and are in operation for the whole time the motor is loaded

Thermography-based methodology for multifault diagnosis on kinematic chain

The procedures for condition monitoring of electromechanical systems are undergoing a reformulation, mainly, due to the current thermographic affordability of infrared cameras to be incorporated in industrial applications. However, high-performing multifault data-driven methodologies must be investigated in order to infer reliable condition information from the thermal distribution of not only electrical motors but also of shafts and couplings. To address this issue, a novel thermography-based methodology is proposed. First, the infrared capture is processed to obtain a thermographic residual image of the kinematic chain. Second, the thermal distribution of the image's regions of interest is characterized by means of statistical features. Finally, a distributed self-organizing map structure is used to model the nominal thermal distribution to subsequently perform a fault detection and identification. The method provides a reliability quantification of the resulting condition assessment in order to avoid misclassifications and identify the actual fault root-causes. The performance and the effectiveness of the proposed methodology is validated experimentally and compared with the classical maximum temperature gradient procedure.Peer ReviewedPostprint (published version

Feasibility study of electromechanical cylinder drivetrain for offshore mechatronic systems

Currently, there is an increasing focus on the environmental impact and energy consumption of the oil and gas industry. In offshore drilling equipment, electric motors tend to replace traditionally used hydraulic motors, especially in rotational motion control applications. However, force densities available from linear hydraulic actuators are still typically higher than those of electric actuators. Therefore, usually the remaining source of hydraulic power is thereby the hydraulic cylinder. This paper presents a feasibility study on the implementation of an electromechanical cylinder drivetrain on an offshore vertical pipe handling machine. The scope of this paper is to investigate the feasibility of a commercial off-the-shelf drivetrain. With a focus on the motion performance, numerical modeling and simulation are used when sizing and selecting the components of the considered electromechanical cylinder drivetrain. The simulation results are analyzed and discussed together with a literature study regarding advantages and disadvantages of the proposed solution considering the design criteria of offshore drilling equipment. It is concluded that the selected drivetrain can only satisfy the static motion requirements since the required transmitted power is higher than the recommended permissible power of the transmission screw. Consequently, based on the recommendation of the manufacturer, avoidance of overheating cannot be guaranteed for the drivetrain combinations considered for the case study presented in this paper. Hence, to avoid overheating, the average speed of the motion cycle must be decreased. Alternatively, external cooling or temperature monitoring and control system that prevents overheating could be implemented

Design, taking into account the partial discharges phenomena, of the electrical insulation system (EIS) of high power electrical motors for hybrid electric propulsion of future regional aircrafts

La réduction des émissions de CO2 est un enjeu majeur pour l'Europe dans les années à venir. Les transports sont aujourd'hui à l'origine de 24% des émissions globales de CO2. L'aviation ne représente que 2% des émissions globales de CO2. Cependant, le trafic aérien est en pleine expansion et, déjà, des inquiétudes apparaissent. A titre d'exemple, en Suède, depuis les années 1990, les émissions de CO2 dues au trafic aérien ont augmenté de 61%. Ce constat explique l'apparition du mouvement "Flygskam" qui se repend dans de plus en plus de pays Européen. C'est dans ce contexte que l'Union Européenne a lancé en septembre 2016 le projet Hybrid Aircraft Academic research on Thermal and Electrical Components and Systems (HASTECS). Le consortium regroupe différents laboratoires et Airbus. Ce projet s'inscrit dans le programme "Clean Sky 2" qui vise à développer une aviation plus verte. L'objectif ambitieux est de réduire de 20% les émissions de CO2 et le bruit produits par les avions d'ici 2025. Pour cela, le consortium étudie une architecture hybride de type série. La propulsion est assurée par des moteurs électriques. Deux cibles ont été définies. En 2025, les moteurs doivent atteindre une densité de puissance de 5kW/kg, système de refroidissement inclus. En 2035, la densité de puissance des moteurs sera doublée pour atteindre 10kW/kg. Pour atteindre ces cibles, le niveau de tension sera considérablement augmenté, au-delà du kilovolt. Le risque de décharges électriques dans les stators des moteurs électriques est considérablement accru. L'objectif de cette thèse est de mettre au point un outil d'aide au design du Système d'Isolation Electrique (SIE) primaire du stator de moteur électrique piloté par convertisseur. Elle est découpée en cinq parties. La première partie commence par préciser les enjeux et défis d'une aviation plus verte. Le SIE du stator de moteur électrique est développé. Enfin, les contraintes qui s'appliquent sur le SIE dans l'environnement aéronautique sont identifiées. La deuxième partie présente les différents types de décharges électriques que l'on peut retrouver. Le principal risque vient des Décharges Partielles (DP) qui détériorent peu à peu le SIE. Le principal mécanisme pour expliquer l'apparition des DP est l'avalanche électronique. Le critère de Paschen permet d'évaluer le Seuil d'Apparition des Décharges Partielles (SADP). Différentes techniques permettent de détecter et mesurer l'activité des DP. Des modèles numériques permettent d'évaluer le SADP. La troisième partie présente une méthode originale pour déterminer les lignes de champ électrique dans un problème électrostatique. Elle n'utilise qu'une formulation en potentiel scalaire. La quatrième partie présente une étude expérimentale pour établir une correction du critère de Paschen. Un bobinage de moteur électrique est très loin des hypothèses dans lesquelles ce critère a été originellement défini. Enfin, la cinquième partie est consacrée à l'élaboration de l'outil d'aide au design du SIE. Des abaques sont construites afin de fournir des recommandations sur le dimensionnement des différents isolants dans une encoche de stator. Une réduction du SADP due à une variation combinée de la température et de la pression est prise en compte.Reducing CO2 emissions is a major challenge for Europe in the years to come. Nowadays, transport is the source of 24% of global CO2 emissions. Aviation accounts for only 2% of global CO2 emissions. However, air traffic is booming and concerns are emerging. For instance, CO2 emissions from air traffic have increased by 61% in Sweden since the 1990s. This explains the emergence of the "Flygskam" movement which is spreading in more and more European countries. It is in this context that the European Union launched in September 2016 the project Hybrid Aircraft Academic research on Thermal and Electrical Components and Systems (HASTECS). The consortium brings together different laboratories and Airbus. This project is part of the program "Clean Sky 2" which aims to develop a greener aviation. The ambitious goal is to reduce CO2 emissions and the noise produced by aircraft by 20% by 2025. To do that, the consortium is studying a serial hybrid architecture. Propulsion is provided by electric motors. Two targets are defined. In 2025, the engines must reach a power density of 5kW/kg, including the cooling system. In 2035, the power density of the engines will be doubled to reach 10kW/kg. To reach these targets, the voltage level will be considerably increased, beyond one kilovolt. The risk of electric discharges in the stators of electric motors is considerably increased. The objective of this thesis is to develop a tool to assist in the design of the primary Electrical Insulation System (EIS) of the stator of an electric motor controlled by a converter. It is organized in 5 parts. The first part begins by clarifying the issues and challenges of a greener aviation. The electric motor stator EIS is developed. Finally, the constraints that apply to the EIS in the aeronautical environment are identified. The second part presents the different types of electric discharges that can be found. The main risk comes from Partial Discharges (PD) which gradually deteriorate the EIS. The main mechanism for explaining the appearance of PD is the electronic avalanche. The Paschen criterion makes it possible to evaluate the Partial Discharge Inception Voltage (PDIV). Different techniques are used to detect and measure the activity of PD. Numerical models are used to evaluate the PDIV. The third part presents an original method for determining the electric field lines in an electrostatic problem. It only uses a scalar potential formulation. The fourth part presents an experimental study to establish a correction of the Paschen criterion. An electric motor winding is very far from the hypotheses in which this criterion was originally defined. Finally, the fifth part is devoted to the development of the SIE design aid tool. Graphs are generated to provide recommendations on the sizing of the various insulators in a stator slot. A reduction in the PDIV due to a combined variation in temperature and pressure is taken into account

HASTECS: Hybrid Aircraft: reSearch on Thermal and Electric Components and Systems

In 2019, transportation was the fastest growing sector, contributing to environmental degradation. Finding sustainable solutions that pollute less is a key element in solving this problem, particularly for the aviation sector, which accounts for around 2-3% of global CO2 emissions. With the advent of Covid-19, air traffic seems to have come to a fairly permanent halt, but this pandemic reinforces the need to move towards a "cleaner sky" and respect for the environment, which is the objective of the Clean Sky2 program (H2020 EU), the context in which the HASTECS project has been launched in September 2016

Improving Energy Efficiency and Motion Control in Load-Carrying Applications using Self-Contained Cylinders

Because of an increasing focus on environmental impact, including CO2 emissions and fluid spill pollution, inefficient hydraulic systems are being replaced by more environmentally friendly alternatives in several industries. For instance, in some offshore applications that have multiple diesel generators continuously running to produce electricity, all hydraulic rotating actuators supplied from a central hydraulic power unit have been replaced with AC induction motors containing a variable frequency drive and gearbox. However, hydraulic linear actuators are still needed in most load-carrying applications mainly because of their high reliability associated with external impact shocks. Moreover, their force capacity is higher than that of their linear electromechanical counterparts. Valve-controlled linear actuators (cylinders) supplied from a centralized hydraulic power unit are standard in offshore load-carrying applications. In addition to the advantages mentioned above of hydraulic linear actuators, they have, nevertheless, a number of important drawbacks, which include: 1) a high level of energy consumption due to significant power losses caused by flow throttling in both the pipelines and valves, 2) reduced motion performance due to the influence of load-holding valves, 3) high CO2 emissions and fuel costs related to the diesel generator that supplies electricity to the hydraulic power unit, 4) significant potential for hydraulic fluid leakage because of many leakage points, 5) demanding efforts with respect to installation and maintenance, as well as 6) costly piping due to the centralized hydraulic power supply. The work presented in this dissertation and the appended papers are devoted to replacing inefficient hydraulic linear actuation systems traditionally used in offshore load-carrying applications with more environmentally friendly solutions. Two alternative technologies are identified, namely electro-mechanical and electro-hydraulic self-contained cylinders. The feasibility of replacing conventional valve-controlled cylinders with self-contained cylinder concepts is investigated in two relevant case studies.publishedVersio

9th International Conference on Energy Efficiency in Motor Driven Systems

The 9th International Conference on Energy Efficiency in Motor Driven Systems (EEMODS'15) was be held in Helsinki (Finland) on 15-17 September, 2015. The EEMODS'15 conferences have been very successful in attracting distinguished and international presenters and attendees. The wide variety of stakeholders has included professionals involved in manufacturing, marketing, and promotion of energy efficient motors and motor driven systems and representatives from research labs, academia, and public policy. EEMODS’15 provided a forum to discuss and debate the latest developments in the impacts of electrical motor systems (advanced motors and drives, compressors, pumps, and fans) on energy and the environment, the policies and programmes adopted and planned, and the technical and commercial advances made in the dissemination and penetration of energy-efficient motor systems. In addition EEMODS covered also energy management in organizations, international harmonization of test method and financing of energy efficiency in motor systems. The Book of Proceedings contains the peer reviewed paper that have been presented at the conference.JRC.F.7-Renewables and Energy Efficienc