Performance of ceramic superconductors in magnetic bearings

Magnetic bearings are large-scale applications of magnet technology, quite similar in certain ways to synchronous machinery. They require substantial flux density over relatively large volumes of space. Large flux density is required to have satisfactory force density. Satisfactory dynamic response requires that magnetic circuit permeances not be too large, implying large air gaps. Superconductors, which offer large magnetomotive forces and high flux density in low permeance circuits, appear to be desirable in these situations. Flux densities substantially in excess of those possible with iron can be produced, and no ferromagnetic material is required. Thus the inductance of active coils can be made low, indicating good dynamic response of the bearing system. The principal difficulty in using superconductors is, of course, the deep cryogenic temperatures at which they must operate. Because of the difficulties in working with liquid helium, the possibility of superconductors which can be operated in liquid nitrogen is thought to extend the number and range of applications of superconductivity. Critical temperatures of about 98 degrees Kelvin were demonstrated in a class of materials which are, in fact, ceramics. Quite a bit of public attention was attracted to these new materials. There is a difficulty with the ceramic superconducting materials which were developed to date. Current densities sufficient for use in large-scale applications have not been demonstrated. In order to be useful, superconductors must be capable of carrying substantial currents in the presence of large magnetic fields. The possible use of ceramic superconductors in magnetic bearings is investigated and discussed and requirements that must be achieved by superconductors operating at liquid nitrogen temperatures to make their use comparable with niobium-titanium superconductors operating at liquid helium temperatures are identified

Conserving Energy with No Watt Left Behind

Facilities managers for industrial and commercial sites want to develop detailed electrical consumption profiles of their electrical and electromechanical loads, including expensive physical plant for heating, ventilation, and air conditioning (HVAC) and equipment for manufacturing and production. This information is essential in order to understand and optimize energy consumption, to detect and solve equipment failures and problems, and to facilitate predictive maintenance of electromechanical loads. As energy costs rise, residential customers are also developing a growing interest in understanding the magnitude and impact of their electrical consumption quickly, easily, and informatively

Switched Reluctance Motor Drives for Hybrid Electric Vehicles

Because of the ever‐increasing concerns on the energy utilization and environmental protection, the development of hybrid electric vehicles (HEVs) has become a hot research topic. As the major part of HEV technologies, the electric motor drives have to offer high efficiency, high power density, high controllability, wide‐speed operating range, and maintenance‐free operation. In particular, the switched reluctance (SR) motor drive can achieve most of these goals; therefore, this motor type has drawn much attention in the past. This chapter aims to serve as an overview of the latest developments of the SR motor drive, purposely for HEV applications. To be specific, the discussions on motor structures for torque density enhancement and torque ripple minimization are covered

Architectural Model to Enable Power System Tradeoff Studies

We continue the development of an overall architectural model for an all-electric ship using a physics-based simulation environment to perform fully-integrated simulation of electrical, hydrodynamic, thermal, and structural components of the ship operating in a seaway. The goal of this architectural model is to develop an early-stage design tool capable of performing tradeoff studies on concepts such as AC vs. DC distribution, frequency and voltage level, inclusion of reduction gears, energy and power management options, and effect of arrangements and topology. The results of the studies will be presented in standard metrics including cost, weight, volume, efficiency/fuel consumption, reliability and survivability. We will specifically look at the hull, mechanical and electrical (HM&E) systems that support the ship and its missions; specifically, the electrical generation and distribution system, propulsion equipment, fresh- and saltwater pumping and distribution, control systems, and structural components

A Hierarchical Control Strategy With Fault Ride-Through Capability for Variable Frequency Transformer

A variable frequency transformer (VFT) is being considered as a new alternative to the classical back-to-back high voltage direct current (HVDC) link for interconnection of two asynchronous networks. The VFT is a retrospective form of frequency converter using the wound rotor induction machine (WRIM), which converts the constant frequency input into a variable frequency output. The prime objective of VFT is to achieve controlled bidirectional power transfer between the two asynchronous networks. This paper presents a detailed working principle of VFT technology and proposes a new hierarchical control strategy for establishing the VFT connection with two power systems to achieve bidirectional power transfer between them. Also, to restrict the grid fault propagation from one side of the VFT to the other side, a series dynamic braking resistor based fault ride-through (FRT) scheme is proposed. The performance of the VFT during the synchronization process, steady-state, dynamic, and the grid fault conditions is evaluated using the real-time hardware in-loop (HIL) system. The plant is simulated in real time using OPAL-RT real-time simulator while the control algorithm is implemented in digital signal processor to carry out HIL study. All the important results supporting the effectiveness of the proposed control strategy and FRT scheme are discussed

Design of the All-Electric Ship: Focus on Integrated Power System Coupled to Hydrodynamics

We present a detailed model of the integrated power system coupled to hydrodynamics that allows us to study global sensitivities in the All-Electric Ship. A novel element of our formulation is the stochastic modeling of the coupled system to account for uncertainty in the parameters or operating conditions. This new computational framework is applied to a model of the DDG- 51 destroyer that involves a 19 MW 15-phase induction machine and an indirect field oriented controller. In particular, we simulate extreme events corresponding to propeller emergence and firing of pulsed power weapons.United States. Office of Naval Research (N00014-02-1-0623 ESRD Consortium); United States. Office of Naval Research (N00014-07-1-0846); Massachusetts Institute of Technology. Sea Grant College Program (NA060AR4170019 NOAA/DOC

How Much DC Power Is Necessary?

Many proposals for future power systems for warships are extant. Anticipated improvements in capability, operating economy, and signature reduction may not be uniquely associated with these power systems. Alternatives are available for constructing variable speed drives and prime movers for ships with electric drives. These alternatives may open new design possibilities

Electric Machines

6.685 explores concepts in electromechanics, using electric machinery as examples. It teaches an understanding of principles and analysis of electromechanical systems. By the end of the course, students are capable of doing electromechanical design of the major classes of rotating and linear electric machines and have an understanding of the principles of the energy conversion parts of Mechatronics. In addition to design, students learn how to estimate the dynamic parameters of electric machines and understand what the implications of those parameters are on the performance of systems incorporating those machines

Modeling and Analysis of a Variable Speed Heat Pump for Frequency Regulation Through Direct Load Control

This paper presents a dynamic model of a variable speed heat pump (VSHP) in a commercial building that responds to direct load control (DLC) signals, updated every 4 s, for the improvement of grid frequency regulation (GFR). The model is simplified for real-time simulation studies with the time horizon ranging from seconds to hours, but still sufficiently comprehensive to analyze the operational characteristics such as the heat rate and coefficient of performance. A variable speed drive-controlled induction motor model is also established for the adjustment of the VSHP input power. A dynamic model of an experimental room is then developed to estimate the effect of the DLC application to the VSHP on its indoor air temperature for two different cooling systems. Furthermore, small signal analysis is performed to evaluate both the transient response of the DLC-enabled VSHP and its contribution to GFR. Finally, with an isolated microgrid implemented with Matlab/Simulink, simulation studies demonstrate that the VSHP can be effectively exploited as the DLC-enabled load while still ensuring building occupant comfort and long-term device performance

Pitfalls of modeling wind power using Markov chains

An increased penetration of wind turbines have given rise to a need for wind speed/power models that generate realistic synthetic data. Such data, for example, might be used in simulations to size energy storage or spinning reserve. In much literature, Markov chains have been proposed as an acceptable method to generate synthetic wind data, but we have observed that the autocorrelation plots of wind speeds generated by Markov chains are often inaccurate. This paper describes when using Markov chains is appropriate and demonstrates the gross underestimation of storage requirements that occurs at short time steps. We found that Markov chains should not be used for time steps shorter than 15 to 40 minutes, depending on the order of the Markov chain and the number of wind power states. This result implies that Markov chains are of limited use as synthetic data generators for small microgrid models and other applications requiring short simulation time steps. New algorithms for generating synthetic wind data at shorter time steps must be developed.MIT-Portugal Progra