Energy storage systems (ESSs) play a very important role in recent years. Flywheel is one of the oldest storage energy devices and it has several benefits. Flywheel Energy Storage System (FESS) can be applied from very small micro-satellites to huge power networks. A comprehensive review of FESS for hybrid vehicle, railway, wind power system, hybrid power generation system, power network, marine, space and other applications are presented in this paper. There are three main devices in FESS, including machine, bearing, and Power Electronic Interface (PEI). Furthermore, advantages and disadvantages all of them have been presented. In addition a brief review of new and conventional power electronic converters used in FESS, have been discussed. Finally, practical ways to develop this technology in the future are presented.

A comprehensive review of Flywheel Energy Storage System technology

To effectively reject the influence of speed detection on system stability and precision for a bearingless induction motor, this paper proposes a novel speed observation scheme using artificial neural network (ANN) inverse method. The inherent subsystem consisting of speed and torque winding currents is modeled, and then its inversion is implemented by the ANN. The speed is successfully observed via cascading the original subsystem with its inversion. The observed speed is fed back in the speed control loop, and thus, the speed-sensorless vector drive is realized. The effectiveness of this proposed strategy has been demonstrated by experimental results.

Speed-Sensorless Vector Control of a Bearingless Induction Motor With Artificial Neural Network Inverse Speed Observer

Bearingless permanent-magnet (PM) synchronous motors (BPMSMs) are a new type of machines combining the characteristics of conventional PM synchronous motors and magnetic bearings. With ever-increasing concerns on applications, such as high-speed electric machines, canned pumps, high-speed-precision mechanical processing, aeronautics and astronautics, flywheel energy storage, life science, vacuum technique, and semiconductor and biotechnology industries, there is a fast growing interest in BPMSMs. In this paper, after a general description of the generation principle of radial suspension forces, a comprehensive overview of BPMSMs is presented, with particular emphasis on mathematical models, motor topologies, and control strategies. Moreover, several possible development trends of the BPMSM are also discussed.

Overview of Bearingless Permanent-Magnet Synchronous Motors

In this paper, a novel design of a one degree of freedom actively positioned bearingless motor, hereafter referred to as a single-drive bearingless motor, has been proposed. The concept is based on an axial flux motor where field weakening and strengthening with d-axis current modulation produce the suspension force for axial motion control. The single-drive bearingless motor requires neither additional windings, nor inverters for noncontact magnetic suspension. It has only one three-phase winding set and one three-phase inverter. To verify this novel concept, theoretical calculations, finite-element method analysis, and test machine development are carried out. The test results successfully demonstrate the magnetic suspension and noncontact rotation of the single-drive bearingless motor.

Proposal and Analysis of a Novel Single-Drive Bearingless Motor

This paper presents a novel exterior rotor topology of a bearingless brushless synchronous motor with rated power of 300 W. Owing to the large possible magnetic gap and the absence of mechanical bearings, this motor is especially qualified for high-purity and low-shear applications (e.g., bioreactor mixing). Both torque and magnetic bearing forces are created inside this disk-shaped motor using a sophisticated control (proportional-integral-differential vector control) with superimposed drive and bearing currents fed to the concentrated combined stator coils. Optimal design is derived based on an electromagnetic analysis using the three-dimensional finite element method (3D-FEM), and the simulation results are verified with a prototype mixer setup.

Bearingless 300-W PMSM for Bioreactor Mixing

The split ratio of an interior rotor permanent-magnet machine, which relates the rotor diameter to the total motor diameter, can be optimized with the goal of generating maximum torque for a given motor volume For that purpose, thermal constraints have to be considered that limit the producible magnetomotive force and, consequently, the torque output Both a maximum local current density in the coils and a maximum global copper loss density related to the motor surface are respected In this paper, the analytical calculations for torque and split ratio are derived and the influence of these thermal constraints is elaborated

Split Ratio Optimization for High-Torque PM Motors Considering Global and Local Thermal Limitations

This paper describes important design considerations for a bearingless brushless motor (permanent magnet synchronous motor, PMSM) in exterior rotor construction. In order to come up with a compact energy-dense setup which can provide both bearing forces and high torque, several parameters have to be accounted for while considering mutual dependences. Moreover, the magnetic bearing and the drive are interlinked for this disk-shaped bearingless motor (with combined concentrated windings). A detailed analysis about the design of the stator teeth has been undertaken, and the influence on torque and active and passive radial forces has been investigated.

Stator Tooth Design Study for Bearingless Exterior Rotor PMSM

The selection of a suitable topology is a crucial part of the design process of a machine. In particular, the slot/pole combination of a bearingless motor has a strong influence on the levitation and drive characteristics. In this paper, several feasible slot/pole combinations for a bearingless motor in exterior rotor construction are investigated, and the important characteristics of each possible topology are discussed in detail. In the end, a comparison between the presented topologies is undertaken, and the optimal motor topology is designed and implemented in a prototype setup.

Investigation of Exterior Rotor Bearingless Motor Topologies for High-Quality Mixing Applications

This article presents a novel topology for a bearingless permanent-magnet motor. This disk-shaped motor, featuring an exterior rotor, can be advantageously employed in delicate bioreactor processes. Both torque and bearing forces originate inside this magnetically levitated motor and are generated with concentrated combined windings. Using 3-D-FEM analysis, the optimal machine sizing parameters are evaluated with the goal to maximize torque while providing sufficient bearing forces to allow a precise and stable operation. The results from the sizing optimization and from the force and torque analysis have been implemented and tested with a real-size prototype setup.

Thomas Reichert

Papers

Bearingless 300-W PMSM for Bioreactor Mixing

Split Ratio Optimization for High-Torque PM Motors Considering Global and Local Thermal Limitations

Stator Tooth Design Study for Bearingless Exterior Rotor PMSM

Investigation of Exterior Rotor Bearingless Motor Topologies for High-Quality Mixing Applications

Bearingless Permanent-Magnet Motor with 4/12 Slot-Pole Ratio for Bioreactor Stirring Applications