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

Magnetic bearings have been applied to high speed and high power electric machines for machine tools, turbomolecular pumps, etc. Bearingless motors can be expected to realize high speed and high power ratings because magnetic bearing functions are integrated into high-speed motors, which results in a simplified structure with short shaft length. In this paper, permanent magnet type bearingless motors, having built-in capability to achieve high power factor and high efficiency, are proposed. The shaft is suspended and centered by electromagnetic forces produced by currents in the additional radial force windings of the stator slots. At first the relationships of these radial forces, currents and voltages are derived analytically. Moreover, the relationships between radial forces and permanent magnet thickness are found. The optimal permanent magnet thickness is determined. The ratio of radial force over current as well as the peak air-gap flux density are discussed. These relationships are confirmed by prototype machines.

Design and analysis of permanent magnet-type bearingless motors

Polyoxometalates (POMs) have been developed as a class of promising smart material candidates not only due to their multitudinous architectures but also their good redox activities and outstanding electron and proton transport capacities. Recently, abundant studies on POMs composited with metal nanoparticles (NPs), carbon materials (e.g., carbon nanotubes (CNTs), carbon quantum dots (CQDs), graphene), and conducting polymers or highly-porous framework materials (e.g., MOFs, ZIFs) have been performed and POM-based composite materials (PCMs) undoubtedly show enhanced stability and improved electrochemical performances. Therefore, POMs and PCMs are of increasing interest in electrocatalysis, electrochemical detection and energy-related fields (such as fuel cells, redox flow batteries and so on), thus, developing novel PCMs has long been the key research topic in POM chemistry. This review mainly summarizes some representative advances in PCMs with electrochemical applications in the past ten years, expecting to provide some useful guidance for future research.

Polyoxometalate-based composite materials in electrochemistry: state-of-the-art progress and future outlook.

A general solution for levitation control applicable to permanent magnet (PM) synchronous and induction type rotating motors is presented. Levitation force is generated by the superposition of P+2 or P-2 pole magnetic flux with the usual motoring magnetic flux (pole number P). PM synchronous motors have the advantage that the control of rotation and levitation are independent, however, the levitation force is weak. Conversely, induction motors produce a strong levitation force, but their efficiency is poor and the control of rotation and levitation are coupled. This paper introduces an internal permanent magnet (IPM) type bearingless motor which has the merits of strong levitation force and relatively easy control properties. A simple experimental apparatus is made to confirm the properties of the proposed motor. The results obtained are discussed in detail.

Levitation and torque control of internal permanent magnet type bearingless motor

Nanoarchitectonics is a concept envisioned to produce functional materials from nanoscale units through fusion of nanotechnology with other scientific disciplines. For component selection, coordina...

Nanoarchitectonics for Coordination Asymmetry and Related Chemistry

Super high-speed and high-power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with the principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4 pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. It was found that radial forces are efficiently produced by employing thin permanent magnets on the surface of rotor iron core. A test machine was built in order to measure inductance functions as well as relationships between voltages and currents.

Characteristics of a permanent magnet type bearingless motor

Keggin-type polyoxometalate (POM)-based compounds have long been considered as one of the environmentally friendly candidates of solid electrolytes exhibiting high proton conductivity under high relative humidity (RH >95%). However, their application has been limited by the lack of structural stability and large decrease in conductivity with a slight decrease in RH. In order to overcome these disadvantages, we report a series of crystalline composites based on Preyssler-type POMs ([Na(H2O)P5W30O110]14-, [Bi(H2O)P5W30O110]12-), which are known to show higher acidity in comparison to Keggin-type POMs, and polymers (polyethylene glycol (PEG), polyallylamine (PAA)). Electrostatic interactions between POMs and polymers contribute to enhance the structural stability, and it has been widely known that polymer electrolytes promote cation transport via segmental motion of the polymer chain. In the crystalline composites, K+ acts as a linker to connect the POMs three-dimensionally, resulting in an all-inorganic framework, and polymers and waters of crystallization reside in the framework. The composites with PEG exhibit moderate proton conductivities of 10-4 S cm-1 under nonhumidified (RH <10%) and low-temperature (<368 K) conditions by the aid of segmental motion of PEG. The composite with PAA exhibits a high proton conductivity of 10-3 S cm-1 under humidified (RH 75%) and low-temperature (<338 K) conditions.

High Proton Conduction in Crystalline Composites Based on Preyssler-Type Polyoxometalates and Polymers under Nonhumidified or Humidified Conditions

Polyoxometalate based solids are promising candidates of proton-conducting solid electrolytes. In this work, a Preyssler-type polyoxometalate is crystallized with potassium ions and poly(allylamine), which is also a good proton conductor, from aqueous solutions. Here we show that the hygroscopicity induced low durability of polyoxometalate and poly(allylamine) can be circumvented by the electrostatic interaction between the polyoxometalate and protonated amine moieties in the solid state. Crystalline compounds are synthesized with poly(allylamine) of different average molecular weights, and all compounds achieve proton conductivities of 10−2 S cm−1 under mild-humidity and low-temperature conditions. Spectroscopic studies reveal that the side-chain mobility of poly(allylamine) and hydrogen-bonding network rearrangement contribute to the proton conduction of compounds with poly(allylamine) of low and high average molecular weights, respectively. While numbers of proton-conducting amorphous polyoxometalate-polymer composites are reported previously, these results show both structure-property relationship and high functionality in crystalline composites. Polyoxometalate based solids are promising candidates for proton-conducting electrolytes but their low durability and low proton conductivities remains an on-going challenge. Here the authors describe the preparation of polyoxometalate-based solids with much improved stability and proton conductivities.

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Confinement of poly(allylamine) in Preyssler-type polyoxometalate and potassium ion framework for enhanced proton conductivity

Effect of molecular weights of confined single-chain poly(allylamine) toward proton conduction in inorganic frameworks based on Preyssler-type polyoxometalate

Proton conduction in crystalline porous materials has received much attention from basic scientific research through to practical applications. Polyoxometalates (POMs) can efficiently transport protons because of their small superficial negative charge density. A simple method for enhancing proton conductivity is to introduce NH4+ into the crystal structure, because NH4+ can form hydrogen bonds and function as a proton carrier. According to these considerations, NH4+ was introduced into the porous structure of A2[Cr3O(OOCH)6(etpy)3]2[α-SiW12O40]·nH2O (A = Li, Na, K and Cs; etpy = 4-ethyl­pyridine) (I-A+) via topotactic cation exchange. The resulting compound, di­ammonium tris­(4-ethyl­pyridine)­hexa­formatooxidotrichromium α-silicododecatungstate hexahydrate, (NH4)2[Cr3(CHO2)6O(C7H9N)3]2[α-SiW12O40]·6H2O, showed high pro­ton conductivity and low activation energy under high relative humidity (RH), suggesting that protons migrate efficiently via rearrangement of the hydrogen-bonding network formed by the NH4+ cations and the waters of crystallization (Grotthuss mechanism). The proton conductivity and activation energy greatly decreased and increased, respectively, with the decrease in RH, suggesting that protons migrate as NH4+ and/or H3O+ under low RH (vehicle mechanism).

Satoru Miyazawa

Papers

Characteristics of a permanent magnet type bearingless motor

High Proton Conduction in Crystalline Composites Based on Preyssler-Type Polyoxometalates and Polymers under Nonhumidified or Humidified Conditions

Confinement of poly(allylamine) in Preyssler-type polyoxometalate and potassium ion framework for enhanced proton conductivity

Effect of molecular weights of confined single-chain poly(allylamine) toward proton conduction in inorganic frameworks based on Preyssler-type polyoxometalate

Effect of the ammonium ion on proton conduction in porous ionic crystals based on Keggin-type silicododecatungstate.