Two-pole Motor Research Articles

Influence of Slot Number on Electromagnetic Performance of 2-pole High-Speed Permanent Magnet Motors With Toroidal Windings

This article investigates the influence of stator slot number on electromagnetic performance of two-pole high speed permanent magnet (HSPM) slotted motors with toroidal (TO) windings. Four two-pole slotted motors with different slot numbers, i.e., 3, 6, 9, and 12, are globally optimised for maximum torque, and their electromagnetic performance are compared, including winding factor, air-gap flux density, back electromotive force, cogging torque, electromagnetic torque, winding inductances, unbalanced magnetic force (UMF), and various loss components. It shows that the six-slot/two-pole HSPM motor with TO windings is eminently suitable for high speed application due to no UMF and easy to realise a modular structure. In addition, TO and tooth-coil windings are compared in the three-slot/two-pole motors, and the results confirm that TO windings are not suitable for use in the three-slot/two-pole HSPM slotted motor due to large airgap field harmonics. Finally, a six-slot/two-pole prototype motor is manufactured and tested to validate the finite element predictions.

Eddy Current Losses in Solid Pole Shoes in a Two-Pole Permanent Magnet Motor

The aim of this paper is to present the eddy current losses in solid pole shoes in a permanent magnet two-pole electric motor. In the presented paper, the authors have chosen to work with three different analytical models, Carter’s theory, Gibb’s theory and Lawrenson’s theory, each with different degree of accuracy and simplifications. The results from the analytical models all present relatively low eddy current losses, giving the designer valuable arguments to utilize solid pole shoes, as a rotor with solid poles is from a construction point of view a more suitable choice, increasing the mechanical stability and reducing the production cost, compared to the laminated design.

Ensuring the Low Vibration of Two-Pole Motors on Flexible Foundations: A Manufacturer-System Integrator Collaboration

Motor vibrations are tested as a part of factory acceptance testing (FAT), normally on a massive foundation. In two-pole motors, there are two main sources of vibration: rotor unbalance and electrical twice-line frequency excitation. Low vibration implies that the natural frequencies of the motor are separated from the corresponding excitation frequencies. Usually, if the site foundation is rigid, the vibration levels repeat FAT values with minor changes and are well within the initial limits for condition monitoring. However, if the foundation is flexible, the motor vibration may produce unexpected results. The aim of this article is to introduce a procedure to help ensure low vibration in site conditions in these cases. The procedure relies on early cooperation between the motor manufacturer and the system integrator based on the horizontal and vertical stiffness of the foundation. The most cost-effective solution can be reached by incorporating proper motor design features in conjunction with the design of the mounting base.

1 kW/60,000 min−1bearingless PM motor with combined winding for torque and rotor suspension

A comprehensive description of a bearingless permanent magnet synchronous machine is presented including simulation, design, control and measurement focusing on a 1 kW/60,000 min -1 machine. A combined six-phase winding is used for the excitation of the two-pole motor field wave and the four-pole levitation field wave by applying two parallel three-phase current systems. The decomposition into the individually controllable current systems for motor torque and lateral rotor position control and the calculation of the relevant control parameters is explained. Measurements give an insight on the controlled motor performance. Thus, it is shown that the combination of torque and lateral force production with a single six-phase winding, fed by two three-phase inverters, not only leads to advantages in winding manufacturing but can be operated with a conventional field-oriented control also at high speed.

Impacts of Reduced Motor Cooling on Reliability

It has been well documented that bearing failures are the leading cause for grease lubricated motor repairs, and grease service life deterioration is a leading cause of bearing failures. Grease service life deteriorates rapidly with elevated operating temperatures, so it may be ascertained that a design change significantly reducing motor cooling would result in elevated bearing temperature, marginal lubrication, premature bearing failures, and reduced motor reliability. In recent years, the ever increasing drive for higher motor efficiencies has resulted in motor designs with less cooling capacity. A recent refinery motor reliability study confirms this correlation and highlights the issue with inadequately cooled motors. Results of the study reveal why new IEEE Standard 841 high-efficiency motors are at greater risk of a drive end bearing failure than the older motors they are replacing. The current IEEE Standard 841 allowable bearing temperature rise is exceedingly high (50 °C/90 °F rise on two-pole motors). To optimize bearing service life and motor reliability, this allowable temperature rise should be reduced significantly.

Evaluation of the Influence of Rotor Magnetic Anisotropy on Condition Monitoring of Two-Pole Induction Motors

If nongrain-oriented rotor laminations are punched and stacked in a uniform direction, magnetic asymmetry is present in the rotor core due to the nonideal magnetic anisotropy. In this paper, it is shown that the influence of rotor core anisotropy can be misinterpreted as rotor faults in two-pole induction motors when performing motor current signature analysis. A detailed analysis of the influence of rotor core anisotropy shows that components produced by the rotor fault and rotor anisotropy interact, making reliable fault detection difficult. It is also shown that offline testing is currently the only available means of detecting the fault, and online monitoring of the space harmonics-induced current components is proposed as a viable solution for providing reliable rotor fault detection for two-pole motors with rotor anisotropy. The analysis and conclusions presented in this paper are verified through testing on custom-built lab motors and on 3.3-kV motors.

Asynchronous Torque of Line-Starting Permanent-Magnet Synchronous Motors

A modified theory and a proposed analytical approach clarified asynchronous torque characteristics of line-starting permanent-magnet (PM) motors, taking into consideration the mutual effect among the fields due to armature current, cage-bar current, and PMs. Theoretical and analyzed results revealed that cage torque had an oscillating component with slip frequency due to magnetic saturation. This component cannot be seen in the conventional theory. It was also found that the coupling effect between PM flux and cage-bar flux caused on magnet torque larger oscillation and more significant negative dc component, compared with the case in the conventional theory. The theoretical and analyzed results were validated on the basis of experimental approaches. Results are given for a two-pole prototype motor with $P_{N} = 5$ kW, $n_{N} = 3000$ min−1, $V_{N} = 200$ V, and Y-connection.

A Novel Speed Measurement Method for a High-Speed BLDC Motor Based on the Signals From the Rotor Position Sensor

The paper presents a digital algorithm of a speed control block for a dc brushless motor and a method for measuring the motor's rotational speed based on the signals from the rotor's position sensor. The proposed method allows an increase in the measurement frequency (six measurements per rotation for a two-pole motor or 12 measurements for a four-pole motor) and the measurement results are not affected by the misalignment mounting of the sensor. The paper describes a conceptual structure of a series PI controller.

Reluctance Torque Utility for Line-Starting Permanent Magnet Motors

This paper presents two types of prototype line-starting permanent magnet motors for compressor drives; one is a nonsalient-pole machine, and the other is a salient-pole machine. It is proved through both the analyses and experiments that the utility of reluctance torque not only boosts steady-state characteristics but also line-starting capabilities. It was also noteworthy that the salient-pole machine in the steady-state operation could achieve not only better efficiency but also a higher power factor. Finally, the designed motors achieved a 4% to 5% increase in efficiency over all operational points, which prevented a rise in temperature by 30 K, compared with a conventional two-pole induction motor. The results are given for a two-pole prototype motor with PN = 5 kW, nN = 3000 min -1, VN = 200 V, and Y-connection.

Design and Testing of a 45-MW 100-Hz Quadruple-Star Synchronous Motor for a Liquefied Natural Gas Turbo-Compressor Drive

Over the last few decades, the production of liquefied natural gas (LNG) has been pushing the development of electric drives with increasingly high power ratings, up to several tens of megawatts. A consolidated technology in this field entails dual-star two-pole synchronous motors fed by load-commutated inverters with supply frequencies between 50 and 80 Hz. This paper presents a novel drive concept for very high-power and high-performance LNG applications based on a 45-MW four-pole 100-Hz quadruple-star synchronous motor supplied by four pulsewidth modulation multilevel voltage source inverters. The genesis, development, and industrial implementation of this new design concept are outlined. Full-load drive system testing and commissioning results are presented which successfully validate the proposed solution.

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 degrees C during normal operation.

The effect of interbar currents in a permanent split capacitor motor

This paper demonstrates how the techniques of generalized harmonic analysis may be applied to a permanent split capacitor (PSC) motor, allowing for the effects of interbar currents. The analysis is verified using an extensive set of experimental measurements made on a 2.5-hp two-pole motor, which show excellent agreement with calculation, provided an appropriate interbar current flow model is adopted.

Optimum pole configuration of variable speed AC induction motors

Sometimes a user who is familiar with fixed speed AC induction motors may specify a variable speed AC requirement with a preconception of the number of motor poles. This is appropriate in the case of an application where the motor will be run "across-the-line", and is expected to run at the same speed and load as provided on inverter operation. If, on the other hand, "bypass" operation is not required, a more optimal choice of motor designs might be available. For example, an application requiring 3000 or 3600 RPM operation would demand a two-pole motor design if bypass (at 50 or 60 Hz) must be provided. However, when bypass is not required, it is often the case that a smaller motor can be provided in a four-pole design (utilizing 100 or 120 Hz base frequency) compared to a two-pole configuration. Another aspect of applying adjustable frequency power supplies to AC induction motors is that it allows an essentially infinite number of possible "base speeds", including base speeds in excess of 3600 RPM. In this paper the author discusses the number of poles required for fixed speed AC motors, DC motors, and adjustable frequency AC motors. Motor performance issues are also discussed.

Performance of a single-phase to three-phase cycloconvertor drive

The paper presents the performance of a three-phase induction motor driven by a new cycloconvertor consisting of six naturally commutated triacs and digital control circuits, which can generate a symmetrical variable voltage variable frequency (VVVF) three-phase supply from a single-phase mains. This inexpensive topology is particularly suitable for low power domestic and similar drives requiring full torque and/or regenerative operation over the full speed range. Using a double integral control technique, a single-phase to three-phase modulation strategy is proposed so the phase flux linkages follow sinusoidal references. The output frequency of this cycloconvertor can be up to half of the input frequency, giving a maximum synchronous speed of 1500 rev/min for a two-pole motor. The three phase currents are symmetrical, and the motor speed ripple is low. Despite a reduced efficiency and power factor, the torque-speed curve of the motor with the cycloconvertor supply is very close to that with a sinusoidal supply. Software was written in C for both simulation and control. The experimental results agree with the simulation.

Function Cost of Low-power, Three-phase Squirrel-cage Induction Motors

SUMMARY This short paper looks at the function costing of low-power, three-phase squirrel-cage induction motors. Function costing is the estimation of the costs of engineering systems from the quantified functions performed by their elements. For the motors considered, the cost is largely proportional to the full-load output torque, with only a small variation attributable to the pole number. However, two-pole motors are an exception; they cost up to 70% more per unit torque. An explanation of this result is proposed. At the date of the prices used ( February 1992), the approximate price of the sampled motors with four or more poles is£ 61 + £ 5.30 per newton metre of output torque, and that of the two-pole motors is £ 49 + £ 9.60 per newton metre.

Digital Simulation Of A Vector Current Controlled Axially-Laminated Anisotropic (ALA) Rotor Synchronous Motor Servo-Drive

ABSTRACT It has been recently demonstrated that axially laminated anisotropic (ALA) rotor reluctance motors have high torque density, power factor and efficiency due to unusually high Ld/Lq ratios. For variable-speed vector-controlled drives no starting cage on the rotor is required. Through digital simulations this paper explores the steady-state torque and power factor capabilities and the transient performance of a vector ac current-controlled ALA-rotor motor drive. Fast torque and speed responses are demonstrated for a two-pole motor up to a speed of 2500 rpm. Good performance down to 0.1 rpm is obtained through an adaptive proportional integral (PI) speed controller.

Peaked-MMF smooth-torque reluctance motors

The authors investigate the steady-state torque characteristics of reluctance motors with nonsalient stator punchings, but with peaked rotating magnetomotive forces (MMFs). The torque calculation includes the effects of saturation and fringing and groove fluxes. The peaked rotating MMF is produced by properly coordinated current waveforms and winding. Peaked-MMF reluctance motors have tow major advantages: the torque is smooth and the flux per pole required to produce a given torque is lower than that of conventional reluctance motors. This property is most beneficial to two-pole reluctance motors, for a given frame whose bore diameters and slot areas can be increased significantly for higher ratings or better performance. Unlike switched reluctance motors, shaft encoders are not required for peaked-MMF motors. >

Selection and Design of an Inverter-Driven Induction Motor for a Traction Drive System

The considerations and trade-offs involved in the selection and design of an inverter-driven induction motor for a traction drive system are described. The inverter is transistorized and operates in a pulsewidth modulation (PWM) mode in the constant torque region and in a six-step square wave mode in the constant power region. Drive system requirements establish the 50-hp peak motor rating and the motor voltage. The aspects of an induction motor designed to be driven from an inverter are presented. These include the number of poles and rotor bar shape of the motor. Expressions relating the motor performance to motor design parameters are derived. The aspects of the inverter power source are presented. These include the constant volt-ampere characteristics of the inverter and the relationship of motor inductance to the inverter design. A final motor design is reached, Contrary to previous expectations, the best design is a two-pole motor.

Controlling Two-Pole Induction Motor System Vibration

3600 r/min motors are particularly susceptible to involvement in a certain category of system vibration problems. Properly designed and manufactured two-pole motors, when mounted on flexible supports, can exhibit excessive vibration as a result of resonance. The system may be complex and difficult to analyze. Many of the problems can be avoided. When problems do arise, they are often easily corrected when the proper approach is used.

Electric power for airplanes

Electric-power loads are increasing rapidly on airplanes and auxiliary-engine-driven generators offer dependable power sources independent of main engines, Minimum weight for the required capacity is essential in the design of generators, motors, and control. The a-c 110-volt 400-cycle three-phase system has been developed for large airplanes with heavy motor loads. Alternators rating 12.5 kva at 75 per cent power factor and two-pole motors running at 22,500 rpm full-load speed are available. Control apparatus builds up the alternator, establishes accurate voltage regulation, and provides direct current for excitation and battery charging. The 24-volt system is applied on airplanes using d-c power which have relatively light motor loads. Generators rate 5 kw and are designed for speeds ranging from 3,200 to 6,000 rpm to conform to prime-mover requirements. Motors have been built which run at 7,500 rpm. The control effectively regulates the voltage, handles battery charging, and provides for starting the power plant.