High-speed Solid-rotor Induction Research Articles

Increasing the Performance of High-Speed Solid Rotor Induction Motor by Plunge Type Electrical Discharge Machining

Increasing the Performance of High-Speed Solid Rotor Induction Motor by Plunge Type Electrical Discharge Machining

Design and Manufacturing of a Modular Low-Voltage Multimegawatt High-Speed Solid-Rotor Induction Motor

High-speed solid-rotor induction machines (HSIMs) are popular within high-speed (HS) applications because of their high rotor structural integrity and their fairly well-established manufacturing process guaranteeing high quality series products. Designing a new HS electric machine requires a multidisciplinary team to accomplish the machine performance desired. In case of a HS machine design, the components and applied materials often reach their physical limits at the rated operating condition. Therefore, the design process is highly iterative and, thus, a systematic approach has a high potential to reduce the time of the design phase significantly. In this article, a systematic design process is proposed for a modular, multimegawatt (MMW) HSIM with three radial active magnetic bearings. The process includes a traditional multidisciplinary design flow with extra critical aspects of MMW HS machines: manufacturability, bearing system, housing, and operating unit. In addition, the manufactured machine is reported. The proposed systematic design process is described, including several multidisciplinary critical design aspects of HS machinery.

Accounting for Slot Harmonics and Nonsinusoidal Unbalanced Voltage Supply in High-Speed Solid-Rotor Induction Motor Using Complex Multi-Harmonic Finite Element Analysis

Solid rotor induction machines are still used in high-speed systems. A two-dimensional field-circuit model based on the finite element method and the complex magnetic vector potential has been shown as a very time-effective tool in the analysis of their steady states compared to time-domain models. This continuation work presents a validated computational algorithm that enables the inclusion of the nonsinusoidal and/or asymmetrical voltage supply in the multi-harmonic field-circuit model of these machines that was presented in the previous works by the authors. The extended model accounts for both spatial harmonics due to slotting and/or winding distribution and the time-harmonics due to voltage waveform. The applicability range of the model therefore increases to cases when the machine is supplied with a nonsinusoidal three-phase system of voltages with symmetry or asymmetry that can be decomposed into three symmetrical components. Its short execution time characteristic allows for much more insightful design studies of the contribution of voltage supply- and slotting-related harmonics to the overall efficiency of the machine than is possible with the time-consuming time-domain models. The proposed computational framework has never been presented in the literature. The model is verified positively by the comprehensive time-domain model. It is especially useful in design studies on solid rotor induction motors related to the optimisation of the efficiency of induction motor-based drive systems.

Faults diagnosis in stator windings of high speed solid rotor induction motors using fuzzy neural network

The paper deals with faults diagnosis method proposed to detect the inter-turn and turn to earth short circuit in stator winding of three-phase high-speed solid rotor induction motors. This method based on negative sequence current of motor and fuzzy neural network algorithm. On the basis of analysis of 2-D electromagnet field in the solid rotor the rotor impedance has been derived to develop the solid rotor induction motor equivalent circuit. The motor equivalent circuit is simulated by MATLAB software to study and record the data for training and testing the proposed diagnosis method. The numerical results of proposed approach are evaluated using simulation of a three-phase high-speed solid-rotor induction motor of two-pole, 140 Hz. The results of simulation shows that the proposed diagnosis method is fast and efficient for detecting inter-turn and turn to earth faults in stator winding of high-speed solid-rotor induction motors with different faults conditions

Application of Nonlinear Complex Polyharmonic Finite-Element Models of High-Speed Solid-Rotor Induction Motors

In this article, the application of a nonlinear complex De Gersem-type polyharmonic finite-element (FE) model in the steady-state analysis of three-phase solid-iron rotor induction motors is discussed. Effective magnetic permeability, dependent on the fundamental time harmonic of the magnetic field, is used for the representation of the magnetic saturation effects. A new coupling scheme for the air-gap mesh nodes is proposed in order to make the model more time-competitive with the time-stepping model in cases where the number of air-gap nodes must be high. By means of comparative analysis of computed electromagnetic torque and harmonic losses, it is shown that omitting some nodes at the interface boundary results in the reduction of the execution time by a factor of 100 with only a slight loss of accuracy.

Investigation of the causes behind the vibrations of a high-speed solid-rotor induction motor

This paper analyzes the causes of vibrations in a solid-rotor induction motor (SRIM) through electromagnetic Finite Element (FE) simulations and laboratory measurements. The computed results are compared with vibration measurements, and the electromagnetic causes of vibrations were discovered, including the fault related reasons. The machine under investigation is a 300 kW, 60 000 rpm, three-phase SRIM. The FE simulations are carried out in an open source FE library implemented in Matlab. Both magnetic forces and magnetostriction deformations are accounted for in the simulations. This magneto-mechanical coupling is implemented using a free-energy-based model. The harmonic analysis of the vibrations revealed that, the supply frequency components, the magnetic forces and the magnetostriction contribute to the electromagnetic causes of vibration, while there is a significant amount of vibration produced due to the rotor eccentricity in the motor.

Design of a High-Speed Solid-Rotor Induction Machine With an Asymmetric Winding and Suppression of the Current Unbalance by Special Coil Arrangements

High-speed solid-rotor induction machines (IMs) suffer from higher rotor eddy-current losses (as a result of the air-gap flux density harmonics) more than any other type of high-speed machines because of the solid-rotor steel. A double-layer short-pitch asymmetric winding arrangement with prefabricated coils is proposed in this paper to mitigate the solid-rotor losses and enable easier assembly. However, the asymmetric winding also brings some current unbalance because of three-phase asymmetric stator inductances, especially the winding leakage inductances. Current unbalance can cause harmful effects for both the machine and supply, e.g., torque ripples, unbalanced magnetic pulls, and unbalanced thermal loads of the supply network and supply power electronics. Additionally, a three-phase unbalanced current can cause an extra source of electromagnetic emission to the environment, which can be harmful to surrounding electronics and can cause extra eddy-current losses in surrounding solid surfaces (e.g., a metal terminal box). To mitigate the current unbalance, two methods are compared in this paper. The first method is a slight increase of the stator slot height and placing of the coil sides at the top or bottom within the slot height for different phases. The stator slot height is optimized based on the 2-D finite-element method (FEM) to achieve the best solution for mitigation of the current unbalance. The other method is based on the results of the first method, and the coil side position for a specific phase is further adjusted. Unlike conventional methods of mitigating the current unbalance by power electronics, the proposed method suppresses the current unbalance solely by adjusting the machine design, which avoids extra investments for power electronics devices. In addition, the machine control strategy remains unchanged compared with the traditional one.

Extraction of Rotor Eddy-Current Harmonic Losses in High-Speed Solid-Rotor Induction Machines by an Improved Virtual Permanent Magnet Harmonic Machine Model

High-speed induction machines equipped with a solid steel rotor are capable of achieving a high-rotating speed than other types of machines, because of their simpler and more robust rotor structure. At the same time, however, the eddy-current losses in the solid rotor may be critical, because of the high conductivity of the rotor material, which makes it easy for axial eddy currents to travel in the solid rotor. To efficiently mitigate the rotor eddy-current losses, it is important to accurately determine the rotor eddy-current losses induced by a particular harmonic in advance. In this paper, an improved virtual permanent magnet harmonic machine (VPMHM) model equipped with a sinusoidally magnetized virtual magnet based on the finite element method (FEM) is proposed for determination of the rotor eddy-current harmonic losses. The 2-D fast Fourier transform was used to accurately analyze the time-spatial air-gap flux density harmonics. The VPMHM model was enhanced to ensure that it was able to exactly produce the required flux density harmonics in the air gap. Two algorithms for the improved VPMHM models with different hybrid excitations were proposed to determine the harmonic losses together with the other important harmonic behavior. The model was further investigated to separate the electromagnetic transients from different harmonics. Finally, the simulation time for the harmonic losses required by the enhanced VPMHM model was significantly reduced by separating the harmonic transients. All the results and conclusions presented in this paper are based on the FEM analysis.

Modeling and Mitigation of Rotor Eddy-Current Losses in High-Speed Solid-Rotor Induction Machines by a Virtual Permanent Magnet Harmonic Machine

Being much more rugged than a rotor made of traditional steel sheets, a solid rotor is frequently used in high-power high-speed induction machines (IMs). Furthermore, by a solid-rotor machine, a higher rotating speed can be achieved. However, the solid rotor also has certain disadvantages, the relatively high solid-rotor eddy-current losses being the most serious one. Basically, solid-rotor eddy-current losses are mainly induced by time–spatial air-gap flux density high-order harmonics. The suppression of the high-order harmonics is the key means to mitigate the rotor eddy-current losses. In this paper, a novel computational model is proposed for evaluating the rotor harmonic eddy-current losses of a 2 MW, 12 000 r/min IM. The model was built on a special machine referred to as a virtual permanent magnet harmonic machine (VPMHM). The model was constructed by applying the finite-element method (FEM), and it is based on the time–spatial harmonics produced by a rotating magnet with sinusoidal magnetization. The VPMHM model links the air-gap flux density harmonics directly to the specific rotor eddy-current losses. Furthermore, according to the proposed model, three options, namely, the use of air-gap permeance modifying notches on the stator teeth, semimagnetic wedges, and their combination, were investigated in detail for mitigating the rotor eddy-current losses in the motor nominal operating point. The results and conclusions in this paper are based on the FEM analysis.

Rapid Computation of Harmonic Eddy-Current Losses in High-Speed Solid-Rotor Induction Machines

In high-speed solid-rotor induction machines, space harmonics in the air gap flux density corresponding to the stator slots typically cause significant losses on the rotor surface. Since these slot harmonics rotate very fast with respect to the rotor, their corresponding skin depths are typically very small. Loss estimates obtained by transient finite-element (FE) analysis may, therefore, require very fine spatial and temporal discretization and consequently very long solution time. In this paper, we derive a time-harmonic analytical model for the multilayer cylindrical rotor. Since the effect of the stator slots on the eddy-current losses cannot be ignored, the analytic solution is coupled to a numerical FE solution covering the stator. The resulting method is very fast since time stepping and meshing of the rotor can be avoided. The results are compared to those obtained with full 2-D transient FE analysis.

Performance Calculation for a High-Speed Solid-Rotor Induction Motor

The paper deals with analytical method of design and prediction of performance characteristics for induction motors with solid steel rotor coated with copper layer. On the basis of the distribution of the 2-D electromagnetic field, the equivalent impedance of the rotor has been derived. The edge effect and nonlinear magnetic permeability of solid steel have been included. The presented analytical method has been verified with laboratory test results. A 300 kW, 60 000-rpm, three-phase solid-rotor induction motor for the next generation air compressor has been investigated. The accuracy of analytical approach is acceptable and can be recommended for rapid design of solid-rotor induction motors.

Electromagnetic and mechanical design aspects of a high-speed solid-rotor induction machine with no separate copper electric circuit in the megawatt range

The most crucial electro-magnetic and mechanical design aspects of an integrated electrical-motor–gas-compressor system in high speed and high power operation are presented. The electric motor type considered is a solid-rotor induction motor with properties of which are particularly well suited in high-speed operation. The effect of the electro-magnetic material properties of the solid rotor core material on the performance of the machine is discussed. Guidelines to improve the performance of the solid-rotor induction motor are given. Thermal design aspects of a solid-rotor induction motor are presented. The mechanical properties of a solid rotor are discussed. Bearing arrangements as well as the rotor dynamics of an integrated system are presented.

Electromagnetic and mechanical design aspects of a high-speed solid-rotor induction machine with no separate copper electric circuit in the megawatt range

Electromagnetic and mechanical design aspects of a high-speed solid-rotor induction machine with no separate copper electric circuit in the megawatt range

Calculating the effects of solid‐rotor material on high‐speed induction motor characteristics

AbstractA method for the analysis of high‐speed solid‐rotor induction motors is presented. The analysis is based on a new combination of the three‐dimensional linear method and the transfer‐matrix method. Both saturation and finite length effects are taken into account. The active region of the solid rotor is divided into saturated and unsaturated parts. The time dependence is assumed to be sinusoidal and phasor quantities are used in the solution. The method is applied to the calculation of smooth solid rotors manufactured of different materials. Five rotor materials are tested: three construction steels, pure iron and a cobalt‐iron alloy. The results obtained by the method agree fairly well with the measured quantities.