Three-phase Excitation Research Articles

Development of a flexible arrayed eddy current sensor with three-phase excitation for inspection of rail rolling contact fatigue cracks

A Flexible Arrayed Eddy Current (FAEC) sensor can inspect a large area in a single probe pass, which is beneficial for customizing the profile of the inspected part. This paper presents the development of a flexible arrayed eddy current sensor with three-phase excitation for inspection of Rolling Contact Fatigue (RCF) cracks in rail. The excitation coils are driven by three-phase currents that are 120° apart in phase. The induced eddy current in the conductive rail sample shifts electrically along the phase variation direction of the excitation currents. The sensor measures a small background signal to determine if there is no defect in the rail sample. Therefore, the sensor has a high relative sensitivity to defects. We study the operating principle of the sensor using a 3D finite element method (FEM) model. The numerical results demonstrate the sensor's viability for fast inspection and characterization to detect RCF defects in conductive rail steel samples.

Fast excitation structure for improving the transient time of magnetic controlled reactors

With the increasing proportion of renewable energy usage, the randomness and volatility of renewable energy have led to a corresponding increase in the demand for reactive power regulation in the power system. Magnetic controlled reactor (MCR) is one of the technical and economic means used to solve problems such as reactive power compensation and voltage regulation in the power system. However, the transient time of traditional MCR is relatively long compared to other reactive power compensation devices, which limits the further application of MCR. At present, most methods for optimizing the dynamic response time of MCR are to add additional circuits or change control strategies, which will increase the difficulty of MCR control and reduce stability. Therefore, without adding additional circuit structure and control difficulty, this paper proposes a three-phase MCR fast excitation structure that changes the winding connection method, which can improve the DC voltage in the control circuit and reduce the transient time of the MCR. A magnetic circuit model in the MCR core under the fast excitation structure is built and analyzed, based on which, the transient time of the MCR is mathematically calculated. A fast excitation MCR simulation model was constructed based on MATLAB/Simulink platform for dynamic response test simulation. Compared with typical MCR simulation results, the transient time was reduced from 400 ms to 37.1 ms. Dynamic response tests were conducted on a three-phase MCR prototype of 35 kV/18 Mvar, and drop test indicates that the fast excitation structure could reduce the transient time of the three-phase MCR prototype to 36.6 ms, which substantiate the precision of mathematical and simulation results and the efficacy of the fast excitation structure.

Robust-Oriented Optimization Design of Dual Three-phase Slotted Permanent Magnet Hybrid Excitation Generator Considering Manufacturing Tolerances

Robust-Oriented Optimization Design of Dual Three-phase Slotted Permanent Magnet Hybrid Excitation Generator Considering Manufacturing Tolerances

Parameter Estimation of Multiphase Machines Applicable to Variable Phase-Pole Machines

Variable phase-pole machines are envisioned in applications requiring a large torque-speed operating area. The control of these machines relies on accurate models and parameters but research on their parameter identification is scarce. This paper presents an offline parameter-identification method for variable phase-pole machines adopting a harmonic-plane decomposition model. The method employs standard tests with single-frequency three-phase excitation in multiple pole configurations and uses the results to minimize a constrained, regularized weighted least-squares problem. It relies on identifying a set of parameters common to all phase-pole configurations and transforming them into the adopted model. Good agreement is exhibited when comparing experimental results to an analytical harmonic-plane decomposition model using the inferred parameters. Steady-state, as well as pole transitions, are compared. The paper emphasizes the importance of performing measurements in multiple pole configurations and weighing these measurements appropriately to render an accurate set of parameters.

Finite-Time Control for Dual Three-Phase Hybrid Excitation Synchronous Machine Based on Torque Sensorless Current Coordinative Strategy

In this paper, the finite time speed regulation problem is investigated for a dual three-phase hybrid excitation synchronous machine (DTP-HESM) without a torque meter. The electromagnetic torque estimation required in the current coordinative strategy is obtained through the disturbance estimation technology. This method increases fault tolerance and reduces the cost as well as complexity of the DTP-HESM system. In contrast to the existing controllers in the speed loop, the non-singular terminal sliding mode control method is adopted to ensure the finite-time convergence of speed tracking in the whole speed region. To achieve better dynamic performance in the presence of lumped disturbances, including unknown load torque and unmodeled dynamics, the disturbance estimations are introduced into the sliding mode variable to establish a composite speed regulating controller. Simulations and experiments are carried out to validate the feasibility and effectiveness of the proposed control scheme.

A novel three-phase excitation piezoelectric motor for macro-micro actuation: integration design, systematic modeling, and experimental evaluation

Macro-micro actuators require complex feedback control systems to obtain high positioning cooperativeness. However, the mechanical connections of macro-micro actuators are generally redundant in terms of their size, which is highly unfavorable for both miniaturization and integration. This paper presents an approach to address this problem based on a novel integration design for a three-phase excitation piezoelectric motor (TPM) that is capable of performing macro-micro actuation by switching its operating mode from resonant to nonresonant. The load capacity of the proposed TPM can reach 0.39 Nm with a maximum speed of 3.82 rad s−1 (36.5 rpm). This performance is achieved by using a unique triangular flexible stator that contains three piezoelectric stack actuators acting as vibrators and is excited by a three-phase electrical signal. A time-domain electromechanical coupling dynamic model is developed to determine the dynamic behavior of the proposed motor, and the modeling results are validated successfully by experimental results obtained from a fabricated prototype. The proposed motor is expected to be helpful for integration design of piezoelectric devices that require macro-micro actuation.

A High-Speed Chip-Scale Rotary Polygon Optical Scanner Based on a Micromotor Integrated With a Micro-Polyhedron Mirror

Micro-opto-electro-mechanical systems (MOEMS) based mirrors with a suitable actuation range are often used for optical beam scanning applications. While several MOEMS scanners have been reported, they often have limitations with respect to their range of motion, field of view, mass, size and fabrication cost. In this work, we present a rotary micro-polygon scanner based on an electrostatic variable capacitance micromotor for laser beam steering applications. The miniaturized scanner consists of a hollow micro-polyhedron mirror with a base radius of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200 {\mu }\text{m}$ </tex-math></inline-formula> and a height of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400 {\mu }\text{m}$ </tex-math></inline-formula> . It is mounted on the rotor of a variable capacitance micromotor using an epoxy-based adhesive. The rotor has a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$600 {\mu }\text{m}$ </tex-math></inline-formula> and is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5 {\mu }\text{m}$ </tex-math></inline-formula> thick. The micromotor was fabricated using a commercial three-layer polysilicon surface micro-machining process (PolyMUMPs) and the micro-polyhedrons were fabricated using a commercial bulk micro-machining process (PiezeoMUMPs). After fabrication of the components, the micro-scanner was assembled and operated under atmospheric conditions using a three-phase square wave excitation ranging from 0 V to 200 V and achieved rotational speeds of up to 2100 rpm. An optical laser beam with a wavelength of 632 nm was reflected off the sidewall of the rotating micro-polyhedron, achieving an experimentally measured scanning angular range of 57.88°, an angular scan rate of 220 radians per second and a scan speed of 25,200 lines per minute or 420 lines per second with a 12 sided micro-mirror. The ratio of the output power over the input optical power is measured over a scanning range of 22°, which is limited by the size of the photo-detector, yielding a ratio spanning from 0.18 to 0.22. This rotary micro-scanner can provide high scanning speeds and a wide scanning field of view with a footprint of 1.25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a thickness of 0.83 mm, which is suitable to implement chip-level high-performance micro-beam steering systems for various applications. [2022-0020]

Research on Single-phase Power Supply in Short-circuit Test of Transformer on Magnetic-force Coupling Field

The short-circuit test is a test of the comprehensive technical ability of transformer manufacturing. The three-phase power supply is usually used for short-circuit test of transformer. To investigate the feasibility of using a single-phase power supply in the short-circuit test of transformer, in this paper, we modeled a 200 kVA power transformer in three dimensions, using the finite element method to calculate the short-circuit current and short-circuit electromagnetic force of the windings under different excitation modes when the three-phase short-circuit occurs in the low-voltage windings. Analyze and compare the short-circuit current and short-circuit electromagnetic force distribution characteristics of windings under different working conditions. The results show that when the three-phase short-circuit condition occurred in the low-voltage windings, regardless of the three-phase excitation or single-phase excitation exerted on the high-voltage windings, the short-circuit current and the short-circuit electromagnetic force of the voltage zero-crossing closing phase is basically the same. This proves that a single-phase power supply can be used instead of a three-phase power supply for short-circuit tests. the analysis result has certain reference significance for improving the short-circuit test of transformer.

Analysis on Electromagnetic Force of Armature in Asynchronous Induction Coil Launcher

The armature is driven forward by induced electromagnetic force in asynchronous induction coil launcher, and the space–time characteristics of force on the armature affect the exit velocity and energy conversion efficiency. Affected by the driving current, velocity, displacement, and other factors, the electromagnetic force received by the armature has obvious nonlinear characteristics. In this article, simulation and analysis of the electromagnetic volume force (EVF) distribution of the armature under different initial positions in the transient model using the field-circuit coupling theory and finite element method are studied. The characteristics of the armature force during the propulsion process are summarized. The structure of armature is optimized according to the simulation results and experiments. It is found that depending on the initial position, the electromagnetic force distribution also varies. There is an optimal initial position that allows the armature to greatly reduce the value of peak force under the premise of ensuring exit velocity. During the period of propulsion, there are two concentrated areas of EVF on the armature. Because of the three-phase excitation, there are three peaks in each of the two areas. The distance between the peaks is about the width of single driving coil, which can be used to optimize the structure of armature.

A New Small-Scale Self-Excited Wound Rotor Synchronous Motor Topology

In this article, a new low-cost small-scale three-phase brushless motor topology is proposed. This is a new topology for self-excitation of brushless wound rotor synchronous motor investigated initially for rated speed. For brushless excitation, the stator is designed to contain two windings, namely, three-phase armature winding and exciter winding. The rotor consists of two windings, that is, harmonic winding and field winding, and a diode rectifier. An inverter feeds the three-phase armature winding which is connected in series through an uncontrolled three-phase rectifier to a single exciter winding. When the current is supplied from the inverter, both the armature and exciter windings are energized eventually producing a flux in the air gap. Since the flux produced by the exciter winding is not synchronized with the field winding, it produces a harmonic to be intercepted by the harmonic winding on the rotor. Eventually, the voltage produced in the harmonic winding is used to feed dc current to the field winding for brushless operation. The results obtained by 2-D finite-element analysis (FEA) validate the brushless operation of the motor. The proposed motor is analyzed basically for topology verification with the FEA results. Since the topology can be verified, further effort can be put to investigate such low-cost topologies for brushless wound rotor synchronous motor. It can be an alternative to a costly permanent magnet synchronous motor for specific applications.

Eddy Current Probe With Three-Phase Excitation and Integrated Array Tunnel Magnetoresistance Sensors

Detecting defects in metal structures quickly and robustly is critical to maintaining safe operation in industry. This work discloses an eddy current (EC) testing probe with coils carrying three-phase currents as excitation and integrated array tunnel magnetoresistance (TMR) sensors measuring the magnetic field as receiver. The three-phase currents in the planar layout coils induce EC that migrates electrically in the material under test. This excitation method does not require multiplexing of the coils and is sensitive to defects of any orientations. The TMR array contains 64 sensors, which are microfabricated and packaged in a line. Within single probe pass, the sensors generate magnetic field image with high sensitivity ( $\text{1.99}\;\text{nT}/\sqrt {\text{Hz}} @\text{30}\;\text{kHz}$ ) and fine spatial resolution (0.5 mm pitch). By analyzing the output image, defects are identified and localized. The operating principle of the probe was investigated based on a finite-element method model. A prototype probe was developed and tested, with which machined defects in aluminum samples were inspected. Experimental results show that the probe has comparable sensitivity for horizontal and vertical defects, and it can recognize a small defect with length × width × depth = 1 × 0.2 × 1 mm3. The defects are located within 1 mm with an artificial neural network.

An analysis of generator trip caused by mistransmitting high temperature signal from excitation transformer

The excitation transformer is a device that specifically provides three-phase AC excitation power for the generator excitation system. The excitation system converts the three-phase power to the generator rotor DC power through the thyristor to form the generator excitation magnetic field, which is adjusted by the excitation system thyristor trigger angle, to achieve the purpose of adjusting the motor terminal voltage and reactive power. This article analyzes an accident in which the excitation transformer high temperature signal is erroneously caused to cause the unit to trip. The unplanned shutdown accident is specifically analyzed from the aspects of on-site situation investigation, cause analysis, main problems exposed, treatment and preventive measures.

Novel array ECT probe with three-phase excitation for steam generator tube inspection

Eddy current testing (ECT) is commonly used in steam generator tube inspection. Among multiple probes applied in this area, array probe shows the merit of the capability of obtaining a C-scan image in a simple linear scan. In this work, a novel array ECT probe with three-phase excitation is proposed. The probe consists of two rows of excitation coils and a row of pickup coils. The induced eddy current shifts electrically in the testing sample so that the necessity of multiplexer is eliminated, resulting in advantages of lower cost, less noise and faster inspection speed. Theoretical analysis indicates that the background signal of the array sensor would be small. A 3D finite element method (FEM) model is developed to study the operating principle and to predict the inspection performance of the probe. A prototype probe has been developed and tested, by which a steam generator tube sample with different kinds of defects was inspected. The experiment results validate the simulation model and further demonstrate the feasibility of the sensor.

An omnidirectional WPT platform for distributed fully implanted neural recording systems

Recent progress on human brain science requires developing advanced neural recording system to capture the activity of large neural populations accurately, across a large area of the brain, and over extended periods. Recently proposed distributed neural recording systems with numerous implanted devices require reliably energizing them wirelessly. Random distribution of these mm-sized implants and brain motion place them at different positions and orientations with respect to the power transmitter. Therefore, traditional wireless power transfer techniques fall short of reaching sufficient power for all implants simultaneously, rendering some implants nonfunctional. In this paper, a three-layer power transmitting array with three-phase coil excitation current is introduced, which is capable of producing omnidirectional and homogeneous magnetic field across the volume where the Rx coils are located. The individual coil dimensions in the array is optimized to improve the worst-case scenario in terms of homogeneity, which is further verified by the measurements using a scaled-up prototype system. The measurement results show that the minimum received voltages is improved from 0.34 V for 10-mm side-length hexagonal transmitting coil array to 0.83 V for the optimal case, i.e., 35 mm side-length hexagonal transmitting coil array.

Novel Array Eddy Current Sensor With Three-Phase Excitation

Array eddy current testing (AECT) sensor is capable of inspecting a large area in a single probe pass resulting in a C-scan image, which is beneficial for customizing the profile of the part being inspected. This paper presents a novel AECT sensor with three-phase excitation. The sensor has two rows of excitation coils and a row of pickup coils. The excitation coils are driven by three-phase currents that are 120° apart in phase. The induced eddy current in the conductive sample shifts electrically along the phase variation direction of the excitation currents. As a result, the sensor does not need multiplexer resulting in advantages of lower cost, less noise and faster inspection speed. The background signal measured by the sensor is small if there is no defect in the sample. Therefore, the sensor has high relative sensitivity to the presence of defect. A 3D finite element method (FEM) model is utilized to study the operating principle of the sensor. A prototype sensor has been developed and tested, with which aluminum sample and carbon fiber reinforced polymer (CFRP) sample with machined defects are inspected. The experiment results demonstrate the feasibility of the sensor for fast imaging of conductive materials.

Electromagnetic Performances and Main Parameter Sensitivity Effect on Unbalance Magnetic Flux in a New Single-Phase FEFSM with Segmental Rotor

Three-phase field excitation flux switching motor (FEFSM) with salient rotor structure has been introduced with their advantages of rotor easy temperature elimination and controllable FEC magnetic flux. Yet, the salient rotor structure is found to lead a longer magnetic flux path between stator and rotor parts, producing a weak flux linkage along with low torque performances. Hence, a new structure of single-phase FEFSM using segmental rotor with non-overlap windings is proposed with advantages of shorter magnetic flux path, light weight and robust rotor structure. Analysis on fundamental magnetic flux characteristics, armature and FEC magnetic flux linkages, cogging torque, back-Emf, various torque capabilities, refinement of unbalance magnetic flux, and torque-power versus speed characteristics are conducted using 2D FEA through JMAG Designer version 15. The results show that magnetic flux amplitude ratio has been improved by 41.2% while the highest torque and power achieved are 1.45 Nm and 343.8 W, respectively.

Optimal design of single-phase 12S-6P FEFSM using segmental rotor and non-overlap windings

&lt;span&gt;Recently, a three-phase Field Excitation Flux Switching Motor (FEFSM) using salient rotor has been introduced, suitable for high torque, high power as well as high speed diverse performances due to their advantages of easy rotor temperature elimination and controllable field excitation (FE) flux. However, existing FEFSMs are found to have low torque performance as the salient rotor structure has caused longer flux path, and consequently weak flux linkage. Therefore, a new structure of a single-phase FEFSM using segmental rotor and non-overlap windings is proposed. There are two valuable findings found in this topology, first is less copper loss due to the non-overlap windings between armature and FE coils, and secondly the segmental rotor structure has produces shorter flux path to produce high torque, less rotor weight as well as robust rotor at high speed condition. Flux linkage, back-emf, average torque and output power characteristics of the initial and optimized designs have been investigated and compared using 2D Finite Element Analysis (2D-FEA) through JMAG Designer version 15. Based on the 2D-FEA analysis, the average torque has increased by 81.3% to 1.65 Nm, while the output power of 466.5 W, increased of 68.2%. In conclusions, a FEFSM using segmental rotor and non-overlap windings is considered as the best single-phase motor due to their optimal performances and less copper loss.&lt;/span&gt;

Investigation of Static Characteristics in Six-Phase Switched Reluctance Motors under Different Winding Connections

The effect of the winding connections on the static torque in six-phase switched reluctance motors (SRMs) is investigated in this paper. Different winding connections for the six-phase SRMs are shown and compared. Under the conditions of different winding connections, the self-inductance and mutual inductance of a six-phase SRM are compared and analyzed. Six-phase SRMs can be running in two-phase excitation mode and three-phase excitation mode, and in these two modes, the static torque characteristics with different poles polarities arrangements are compared and analyzed. The comparison of the static torque in a six-phase SRM with different winding connections is obtained by the Maxwell 2D and experiments. Based on the results, an optimal winding connection mode for starting stage of the six-phase SRMs is proposed.

Determination Approach for the Parameters of Equivalent Circuit Model of Deep Saturated Three-Phase Integrative Transformers

Based on the analysis of the defects of the traditional methods for determining the equivalent circuit parameters of three-phase integrated transformers by single-phase excitation, an expression method of equivalent circuit parameters and their determination approach based on three-phase simultaneous excitation are presented in this paper. The parameters are expressed in terms of the phase of the excitation source, and the value of parameters is determined by calculating the reluctance of core segments based on the finite element method simulations. Then, the electric circuit parameters are obtained by converting the magnetic circuit into the electric circuit. This kind of electric circuit model is suitable for analyzing the problems of deep saturation of transformers and the concerning power grid problems.

Research on an online diagnosis for rotating diode faults in three‐phase brushless exciter with two coils

The rotating rectifier is prone to be damaged in the exciter of the brushless excitation system, wherein a diode open-circuit fault which is common can affect the normal and safe operations of a generator. On the basis of the structure of the brushless exciter, this study, analysed the effect that an open-circuit in one and two diodes had on armature current and armature field, and put forward a new online detection method for diode open-circuit fault. In this method, two magnetic field detection coils are installed on the stator iron yoke of the brushless exciter, and the open-circuit fault of the diodes can be reflected by the induced voltage difference of the two detection coils. Using a 16-pole, three-phase brushless exciter as an example, the performance of this new diagnosis method was verified by using a finite element simulation.