Search

Three-phase permanent-magnet synchronous motors (PMSMs) are widely used in renewable energy applications such as wind power generation, tidal energy and electric vehicles owing to their merits such as high efficiency, high precision and high reliability. To reduce the cost and volume of the drive system, techniques of reconstructing three-phase current using a single current sensor have been reported for three-phase alternating current (AC) control system using the power converts. In existing studies, the reconstruction precision is largely influenced by reconstructing dead zones on the Space Vector Pulse Width Modulation (SVPWM) plane, which requires other algorithms to compensate either by modifying PWM modulation or by phase-shifting of the PWM signal. In this paper, a novel extended phase current reconstruction approach for PMSM drive is proposed. Six novel installation positions are obtained by analyzing the sampling results of the current paths between each two power switches. By arranging the single current sensor at these positions, the single current sensor is sampled during zero voltage vectors (ZVV) without modifying the PWM signals. This proposed method can reconstruct the three-phase currents without any complex algorithms and is available in the sector boundary region and low modulation region. Finally, this method is validated by experiments.

Inductively coupled power transfer (ICPT) systems are now being used in applications where their efficiency and stability are critically important. In this paper, an ICPT pick-up is analyzed under conditions where the pick-up tuning is assumed to be essentially perfect, and all diodes are assumed to have continuous current flow in them. The analysis proceeds by replacing the existing parallel resonant tank and rectifier circuit with a DC source and transformer equivalent, thereby reducing the complexity of the circuit, and eliminating the diodes. The DC equivalent is shown to have the same energy storage and power capability as the original circuit and is accurate under all loadings for both transient and steady-state conditions. With this simplification, analytic transfer functions for the pick-up with respect to its excitation current and its control switch duty cycle are developed. The ICPT system model is shown to have multiple poles, with complex zeroes on the right half plane. The model allows a sophisticated controller to be designed to give the ICPT system the required stability at high efficiency.

Superpower electric propulsion requires a high-reliability high-torque and low-speed electric machine. Generally, multi-phase windings topology has been widely used to enhance the capacity and reliability of the traditional permanent magnet synchronous motor (PMSM) in the propulsion, but the usage of the multi-phase windings could bring much more complex engineering problems including controlled strategy and motor design. This paper presents a multi-unit topology low-speed high-torque PMSM, and the traditional three-phase control strategy can be simplified used in this novel motor. When all unit motors work, there is no difference of mechanical properties between multi-unit PMSM and ordinary three-phase PMSM. However, the electrical torque ripple will be produced due to asymmetry windings inductance matrix when only part of the unit motor is running. The torque ripple mechanism of multi-unit PMSM is be described in this paper, and the improved method reducing torque ripple are provided which has been verified by the finite element calculations and experiments.

This paper presents an approach for enhancing the thrust force of a tubular transverse flux permanent magnet linear machine (TFPMLM) which has been developed for electromagnetic applications. It is shown that by introducing auxiliary cores to suppress the leakage flux, the thrust force of the tubular TFPMLM has been significantly enhanced, by ∼130% under the same volumetric constraints. The effectiveness of the proposed technique is validated by extensive 3-dimensional finite element computations.

This paper investigates the thermal characteristics of the transverse flux tubular linear machine (TFTLM) for electromagnetic launcher (EML), including numerical calculation and temperature rise in the short-time overload test. Firstly, it estimates the various components of heat sources i.e. electromagnetic losses, including core loss in the stator as well as copper loss and eddy-current losses in the mover, and then presents the heat parameters according to the convective heat exchanges. Secondly, it establishes numerical model of the three-dimensional (3-D) for the transient temperature field in TFTLM. The validity of the numerical analysis is proved by the temperature rise in the short-time overload test.

This paper analyses the influence of orifice distribution on the damping characteristics of Elastic Ring Squeeze Film Dampers (ERSFD) for Flywheel Energy Storage System (FESS). Finite element method is employed to calculate the oil-film force of the ERSFD with different orifice distribution. The relationship of the oil-film force versus the orifice location in both axial and circumferential direction is drawn. The principle for the optimum orifice location is summarized, verified via varying the orifice radius. It is shown that orifices with the optimum distribution can play the greatest role in adjusting the damping coefficient, providing guidelines for the design and application of ERSFD.

Spherically optical components of small diameters have found wide applications in many fields. Radius of curvature (ROC) is an important parameter as it determines their optical characteristics. For measuring the ROC of a mini spherical surface, a static microscopic carrier interferogram is taken, and virtual grating phase shift technique (VGPT) is adopted in this paper. By using the computer, four virtual gratings are generated, their reference frequency being the same as the carrier frequency of the test interferogram, and their modulation phases being 0, π/2, π and 3π/2, respectively. By multiplying the test interferogram separately with the four virtual gratings in intensity, four moire fringe images are obtained. By applying Furrier transform and low pass filtering, a set of four carrier-free phase shift fringe images are obtained. And finally by applying four step phase shifting algorithm and least square fitting (LSF), the ROC of the test spherical surface is obtained. Furthermore, the result agrees well with its nominal value and measurement result by Zygo interferometer. This indicates that adopting VGPT for measuring ROCs of mini spherical surfaces is practicable and has relatively a high accuracy.

The dynamic response of cameras affects the image quality apparently, characterized by the image blurring, the distortion of geometrical size and gray of image, when shoot a dynamic scene. A particular experimental setup was designed upon the mechanism of cameras, the gray data containing the response information were extracted from the concerned pixels of the motion image, and then the dynamic response was modeled by processing the extracted gray data with Least-square algorithm. The result indicates that the dynamic response of cameras can be expressed as a first-order system, a model with agreeable accuracy due to the fitting error approximating to 0.2. The proposed method can be readily used for testing the dynamic response of cameras in general application, and the dynamic response can be applied to resolve some related problems in machine vision.

The split ratio of the permanent magnet motor is one of the most important design parameters. It can not only influence the motor electrical torque and efficiency, but also can influence the motor thermal behavior. According to the high torque, short duty permanent magnet brushless motor, the thermal behavior should be investigated carefully. In this paper, the influence of the split ratio on the motor characteristics is investigated by field and circuit coupling finite elements analysis firstly. Then the influence of the split ratio on the motor thermal behavior of is analyzed, emphasis on the high torque short duty operation. The optimal design results are verified experimentally.

A novel flywheel reaction torque measurement system is proposed to measure the output torque of flywheels. The system structure and principle of the measurement system are presented. Finite-element method is applied to compute the magnetic field and characteristics of the measurement system. An improved disturbance observer is applied in the position closed loop control system. Simulation and experiment show that the system dynamic characteristics can be improved by the disturbance observer.

Permanent magnet brushless motor used for deep-sea Human Occupied Vehicle's (HUV's) propeller was studied in this paper. Based on analyzing the influences of waveform of phase current on flux density in air gap, rotor eddy-current losses were determined in BLAC and BLDC modes. This paper proposed that rotor loss is the minimum in BLAC mode. In BLDC mode, with optimal commutation advance angle (20°), rotor loss is the lowest. Finally the temperature distribution of the motor was gained considering the rotor eddy-current loss.

In temporal phase-shifting interferometer, environmental vibrations can induce the wobbling of fringes pattern that usually results in erroneous surface measurement. In order to actively compensating for the external vibration, wave-front phase variation, in proportion to the variation of optical path difference between reference and test arm of the interferometer, should be measured firstly. So, an optical heterodyne interferometric vibration measuring system is embedded in the interferometer, the real-time wave-front phase variation due to vibration is measured by comparing phase difference of two heterodyne signals at 40MHz, one is from reference arm, another is from test arm. An acousto-optical modulator (AOM) is used as optical frequency shifter. After wave-front phase measuring, secondly, a vibration servo compensating system is built. In this system, if real-time wave-front phase is differ from preset phase, an adaptive feedback signal is formed to drive a piezoelectric transducer (PZT), and the PZT drives the standard reference mirror to shift optical path difference in order to pulling wave-front phase to the preset value, thus, vibration is compensated and fringes pattern is stabilized. Thirdly, if preset phase value is periodically changed, a series of phase-shifting interferograms can be sampled. In the end, vibration-compensated effect of this adaptive interferometer is evaluated by an actual optical surface testing, results show this system works very well in the presence of vibrations which amplitude-frequency product is greater than 100 wave-Hertz. Frequency response of this system is restricted by PZT driven reference mirror.

With the rapid development of fiber communications, the fiber optic connector has become an indispensable no-source device, among which PC-type connector is most commonly used. As radius of curvature (ROC) of the connector end face is one of the three main geometric parameters affecting insertion and return losses, how to measure accurately the ROC has become an important issue in the field. In this paper, an algorithm, overlapping averaging 4-bucket method (OAF), is introduced to measure the parameter. Correspondingly, calculation of the phase principal values of the object wave-front and reconstruction of the spherical profile of the connector end face are analyzed, with simulation results given. Also analyzed is the influence of the shifting error of the phase shifter on the ROC measurement, with a curved surface figure for their relationship obtained. Meanwhile, a comparison is made between the errors developed by the 4-bucket algorithm (FBA) and OAF. It is indicated by the results that, OAF is superior to FBA in the suppression of the shifting error, and that, over a general range of calibration error and nonlinear displacement error both equal to or less than 8%, the ROC measurement error with OAF is less than 2.3×10-4.