Myounggyu D. Noh

Design and implementation of a fault-tolerant magnetic bearing system for turbo-molecular vacuum pump

One of the obstacles for a magnetic bearing for use in a wide range of industrial applications is the failure modes associated with magnetic bearings, which are not expected for conventional passive bearings. These failure modes include electric power outage, power amplifier faults, position sensor faults, and the malfunction of controllers. Fault tolerant magnetic bearing systems have been proposed so that the system can operate in spite of some faults in the system. In this paper, we describe the design and implementation of a fault tolerant magnetic bearing system for a turbo-molecular vacuum pump. The system can cope with actuator/amplifier faults, as well as faults in position sensors, which are the two major fault modes in a magnetic bearing system.

Optimal Design of Radial-Flux Toroidally Wound Brushless DC Machines

Toroidally wound brushless dc (BLDC) machines are compact, economical, and can operate across large air gaps. In this paper, we provide analytical design equations for a radial-flux toroidally wound BLDC machine. The validity of the design equations is checked against finite-element analyses (FEAs) and experiments. It is found that the motor constant calculated by the design equations is off only by 5% from the results by the FEAs or experiments. We also provide an optimization metric that corresponds to the maximization of machine torque while maintaining minimum power loss. Two optimal design cases are presented.

Optimal design of micro flywheel energy storage system

We have designed a micro flywheel energy storage system in which the flywheel stores electrical energy in terms of kinetic energy and converts this kinetic energy into electrical energy when necessary. The flywheel is supported by two radial permanent magnet passive bearings. Permanent magnet passive bearings use the repulsive forces between two sets of permanent magnets so that contact free rotation is possible. A set of voice coil actuator provides the axial stability, resulting in a complete magnetic levitation. The toroidally-wound BLDC motor which has high efficiency and little additional negative radial stiffness is used for motoring and generation. Micro flywheel energy storage system is optimally designed to have the maximum energy storage capacity. In this paper, we present the design equation for the components in a micro flywheel energy storage system and the optimal design process for these components..

Toroidally-Wound Self-Bearing BLDC Motor With Lorentz Force

Self-bearing motors (SBM) use a single magnetic structure for rotational motoring as well as for noncontact levitation. They are sometimes referred to as bearingless motors or combined motor-bearings. In this paper, we propose a new type of self-bearing motors based on toroidally-wound brushless DC machines. This type of SBM can be made to be passively stable in the axial direction and for out-of-plane rotations. To achieve self-bearing operation, we derive a force-current model and show that the levitation force is decoupled from the rotational torque. To overcome the singularity problem in the force-current model, we propose a phase selection algorithm in which the phase that may cause singularity is counted out when inverting the force-current model. Through finite element analyses and experiments, we validate the force-current model and the phase selection algorithm.

Thermal Analysis of the PediaFlow pediatric ventricular assist device.

Accurate modeling of heat dissipation in pediatric intracorporeal devices is crucial in avoiding tissue and blood thermotrauma. Thermal models of new Maglev ventricular assist device (VAD) concepts for the PediaFlow VAD are developed by incorporating empirical heat transfer equations with thermal finite element analysis (FEA). The models assume three main sources of waste heat generation: copper motor windings, active magnetic thrust bearing windings, and eddy currents generated within the titanium housing due to the two-pole motor. Waste heat leaves the pump by convection into blood passing through the pump and conduction through surrounding tissue. Coefficients of convection are calculated and assigned locally along fluid path surfaces of the three-dimensional pump housing model. FEA thermal analysis yields a three-dimensional temperature distribution for each of the three candidate pump models. Thermal impedances from the motor and thrust bearing windings to tissue and blood contacting surfaces are estimated based on maximum temperature rise at respective surfaces. A new updated model for the chosen pump topology is created incorporating computational fluid dynamics with empirical fluid and heat transfer equations. This model represents the final geometry of the first generation prototype, incorporates eddy current heating, and has 60 discrete convection regions. Thermal analysis is performed at nominal and maximum flow rates, and temperature distributions are plotted. Results suggest that the pump will not exceed a temperature rise of 2°C during normal operation.

Validation of Flexible Rotor Model for a Large Capacity Flywheel Energy Storage System

When we design a controller for the active magnetic bearings that support a large rotor, it is important to have an accurate model of the rotor. For the case of the flywheel that is used to store energy, an accurate rotor model is especially important because the dynamics change with respect to the running speed due to gyroscopic effects. In this paper, we present a procedure of obtaining an accurate rotor model of a large flywheel energy storage system using finite-element method. The model can predict the first and the second bending mode which match well with the experimental results obtained from a prototype flywheel energy storage system.

Analysis and Modeling of a Voice-Coil Linear Vibration Motor Using the Method of Images

The vibration motors for smart phones with haptic interfaces require higher reaction rate and longer service life than what a typical rotational motor with eccentric mass provides. In this paper, a new type of a linear vibration motor is proposed. A voice-coil actuator is employed for high reaction rate. Permanent magnets replace mechanical springs, which would help increase the service life. For analyzing and modeling the proposed vibration motor, we use the method of equivalent current sheet and the method of images. These methods are validated against finite element analyses and experiments. A prototype motor is designed and fabricated. Tests with the prototype show the feasibility of the proposed linear vibration motor.

Design of a micro flywheel energy storage system including power converter

A flywheel energy storage system stores the electrical energy through a fast-spinning flywheel. When necessary, the kinetic energy of the flywheel is converted into the electrical energy by a power converter. In this paper, we present a design procedure of a micro flywheel energy storage system in which an effort is made to optimize not only the components but also the system. A power converter is also designed at the conceptual level. The performance of the power converter is checked through computer simulations.

Magnetic levitation design for the PediaFlow ventricular assist device

Over the past few decades, we have seen a tremendous progress in the development of implantable ventricular assist devices (VAD). However, these devices are mainly developed for adult patients. For the patients under age 5 who have chronic heart failures, physicians must resort to extracorporeal circulatory support devices which often result in infection, thromboembolism, or excessive blood transfusions. In this paper, we describe a design process for a pediatric ventricular assist device (PVAD). The central part of the device is a magnetically levitated rotating pump which creates a pressure rise (~100 mmHg) at a required flow rate (~0.5 L/min) suitable for infants and small children. We have considered several different pump topologies, of which an axial mixed-flow pump configuration was chosen for further development. The pump impeller is supported by two radial permanent-magnet passive bearings. The rotor-dynamics analysis of the pump shows that the critical speeds of the pump are affected by the radial and yaw stiffnesses of the PM bearings. Hence, analytical expressions for the stiffnesses are derived and verified through FEA. In contrast to the radial suspension, the axial motion of the impeller is actively controlled using a voice-coil actuator. A toroidally-wound motor drives the pump with high efficiency and little additional negative radial stiffness. The design process relies heavily on optimization at the component-level and system-level. The preliminary results of the design optimization are presented in this paper

Unbalanced Magnetic Forces Due to Rotor Eccentricity in a Toroidally Wound BLDC Motor

A common source of noise and vibrations in a permanent-magnetic synchronous motor is the radial forces due to rotor eccentricity. In this paper, we present entirely analytical models for the radial forces resulting from the eccentricity in a toroidally wound brushless dc motor by applying the perturbation theory. The air-gap magnetic field with eccentricity is first obtained. Then, the radial forces are obtained by integrating the Maxwell stress tensor. The radial force models are verified against the finite-element analysis (FEA). It is found that the maximum mismatch between the results by the model and by FEA is <;2%, which confirms the validity of the model.