Machine Stator Research Articles

BTT & RFLB - THE OPTIMUM SET FOR STEAM TURBINE BLADES MONITORING

BTT, Blade Tip Timing system, is a commercially available system generating files of precise times of blade tips when passing sensors attached in a machine stator. RFLB, Residual Fatigue Life of Blades, is a postprocessor of those files evaluating estimates of fatigue lives of all blades fitted to the wheel. The set reduces a danger of unexpected blade failures.

Implementation of direct power control based on stator flux estimation using low-pass filter estimator for doubly fed induction generator–wind energy conversion system

This article deals with the direct power control strategy applied for a grid-connected variable speed wind turbine based on doubly fed induction generator. The proposed method is based on a stator flux estimation algorithm which allows to control the rotor-side converter of the doubly fed induction generator. Several methods of stator flux estimation are based on the integration of the stator back electromotive force signal. However, in practice, the pure integration can cause various problems due to noises, stator resistance uncertainty, unknown initial conditions and measurement errors. Several algorithms, reported in the literature and used to estimate machine stator fluxes, are reviewed and compared. Particular attention is drawn to the low-pass filter–based algorithms that show good performances. In this article, the novelty of the proposed approach is the development of the direct power control–based stator flux estimation method with a low-pass filter. Theoretical analysis and implementation procedures of the proposed method are developed in detail. Simulation results of a variable speed wind turbine based on doubly fed induction generator are performed in MATLAB/Simulink software in order to evaluate the dynamic performances of the proposed control method under wind speed variations. The adopted control strategy is implemented using dSPACE 1104 board and tested for a wind turbine emulator. Experimental results show the effectiveness and the originality of the proposed control strategy.

A Nine-Phase Permanent Magnet Electric-Drive-Reconstructed Onboard Charger for Electric Vehicle

This paper presents a novel approach for an electric-drive-reconstructed onboard charger (EDROC) for electric vehicles incorporating a symmetrical nine-phase permanent magnet machine. To implement three-phase power factor correction and propulsion battery voltage/current regulation, an exclusive utilization of the nine-phase propulsion system is developed. First, a paralleled three-phase pulsewidth-modulated voltage source rectifier is reutilized from six inverter legs and is directly connected to the three-phase utility grid through six-phase out of the machine stator windings. Second, a three-phase buck-type converter is reconstructed by the remaining three-phase inverter legs and machine windings. Third, to realize zero electromagnetic torque production during the three-phase charging mode, the rotor parking position is applied in the decoupling transformation matrix. Moreover, control schemes for a charging mode including current balancing and interleaving strategy are elaborated. To evaluate the steady-state and dynamic behavior of the proposed EDROC system under different operation scenarios, 3.3-kW laboratory prototype based tests have been conducted.

Stator Winding Internal Thermal Monitoring and Analysis Using In Situ FBG Sensing Technology

This paper reports a novel thermal monitoring scheme for on-line internal temperature measurement in low-voltage random wound machine stator windings. The scheme is based on utilizing electrically nonconductive and electromagnetic interference immune fiber optic sensing technology embedded in close proximity of hot spots of interest to create a robust distributed thermal monitoring network within the machine windings. The key design and implementation features of the proposed system are presented and applied on a prototype mains-fed induction motor. The on-line thermal monitoring performance is examined in a number of typical continuous and periodic running duty tests, as defined by the relevant IEC standards for rating and performance of rotating electrical machines. It is shown that the presented scheme has the potential to provide competent on-line measurement of critical machine thermal hot spots that are largely beyond the effective reach of conventional thermal monitoring solutions. Furthermore, the proposed scheme underpins a higher fidelity understanding of the distribution and propagation of winding thermal stress, demonstrated by the experimental analysis reported in the paper.

Experimental Characterization and Modeling of Thermal Contact Resistance of Electric Machine Stator-to-Cooling Jacket Interface Under Interference Fit Loading

Cooling of electric machines is a key to increasing power density and improving reliability. This paper focuses on the design of a machine using a cooling jacket wrapped around the stator. The thermal contact resistance (TCR) between the electric machine stator and cooling jacket is a significant factor in overall performance and is not well characterized. This interface is typically an interference fit subject to compressive pressure exceeding 5 MPa. An experimental investigation of this interface was carried out using a thermal transmittance setup using pressures between 5 and 10 MPa. The results were compared to currently available models for contact resistance, and one model was adapted for prediction of TCR in future motor designs.

Overview of novel magnetically geared machines with partitioned stators

This study overviews recent development of a new class of magnetically geared machine topologies, i.e. partitioned stator (PS) machines. They are developed from magnetic gears and magnetically geared machines, as well as stator permanent magnet (PM) machines (switched flux, flux reversal, and doubly saliency PM), wound field, or hybrid PM and field winding machines. Based on the operating principle, i.e. magnetic gearing effect/air-gap field modulation and flux switching by the salient rotor iron poles, various PS machine topologies are developed. All have features of two stators, two air-gaps, and one segmented ferromagnetic rotor identical to a magnetic gear's modulating rotor. Their inherent relationships are revealed, while their electromagnetic performance is compared. Both PM and wound field PS machines are discussed, together with hybrid excited PS-PM machines and Vernier machines. It shows that all of these PS machines share the same torque production principle and the differences are mainly in PM configurations and relative positions of two stators. All PS machines have higher torque density per copper loss compared with their counterparts of single-stator machines. PS switched flux PM machines can produce the highest torque density per copper loss.

Fast predictive technique for reverse power detection in synchronous generator

Reverse power relays are utilised to trip turbine generators to avoid prime mover damage and directional relay is most widely used as the main protection for these conditions. An intentional time delay is ordinarily utilised to overcome the possible maloperation of these relays. However, the intentional time delay to prevent maloperation is not an ideal solution. As this time delay increases the reverse power relay operation time, which means that the motoring action of the synchronous generator persist for a longer time, making the prime mover more vulnerable to active power drawn by the generator. This study proposes a new flux-based approach to detect reverse power condition in the synchronous generators. The proposed scheme uses the analysis of angular velocity and acceleration data that are calculated from the estimated magnetic flux at the machine stator terminals. The basic idea of the technique stems from the principle that the stator and rotor magnetic fluxes rotate together at synchronous speed and will not be affected by system disturbances for a short interval according to highly inductive characteristics of the synchronous machine. The main advantage of this predictive algorithm is its speed, security and sensitivity to detect the reverse power conditions.

Postfault Operation of a Nine-Phase Six-Terminal Induction Machine Under Single Open-Line Fault

This paper studies the postfault control of a nine-phase six-terminal induction machine (IM) during single open-line fault, which was recently proposed for high-power medium-voltage applications as a promising alternative to conventional six-phase IMs. The required optimal reference currents to provide prefault loading conditions under one-line open are derived using the two most common optimization criteria employed in multiphase drives, namely, maximum torque and minimum loss modes. A postfault controller, based on conventional decoupling Clarke's transformation, is then used to ensure the same controller structure under all conditions. Consequently, the machine characteristic curves, achievable torque, and stator copper losses under these different modes are compared. A comparison with a conventional asymmetrical six-phase winding is also given. A 1.5-Hp prototype IM is used for experimental verification.

Anodic behavior of amorphous and nanocrystal alloys during the electrochemical processing

Magnetically soft alloys possessing unique characteristics, which determine corrosive, magnetic and other properties, are used as a construction material in the amorphous structural state. The amorphous alloys have a high hardness and unusual fragility along with unique magnetic properties. Due to this fact, there are some limitations in using these alloys as construction materials, which is related to the problems of their processing. Applying traditional methods of mechanical processing is impossible. Thus, the electro-diamond grinding based on the combined action of anodic dissolving and mechanical cutting by the diamond grains is used for processing the open surfaces, for instance, for grooving in the machine stator made of 5BDSR alloy. However, the use of the electrochemical size processing by the cathode-tool based on localizing the anodic dissolving of the machined material is considered to be perspective for processing geometrically complex cavities or holes with a small diameter. To develop the technology of surface forming in details made of 5BDSR and 82K3HSR alloys, the analysis of their anodic behavior during the electrochemical processing was conducted. The reasons for the anode surface passivation during the electrochemical processing of the investigated alloys were found both in amorphous and in amorpho-nanocrystal structural state in 10% electrolytes NaNO3, Na2SO4 and NaCl.

Improving network voltage unbalance levels by controlling DFIG wind turbine using a dynamic voltage restorer

This paper proposes a method to compensate the network voltage unbalance using the doubly fed induction generator (DFIG) wind turbine connected to a dynamic voltage restorer (DVR). In the configuration employed, a DVR based on a voltage-source converter is connected in series between the generator and the grid. The proposed control uses symmetrical components to calculate the negative sequence current to be injected in the network to compensate the voltage unbalance at the Point of Common Coupling (PCC), and the voltage to be applied at the stator, to avoid torque oscillations. The contribution of this paper consists on proposing a coordinated strategy for compensating the voltage unbalance at PCC and avoiding torque oscillations in the machine. Due to the coordinated use of all resources available for compensation, the proposed method increases the operational range of the existing methods. Basically, the strategy of the proposed method consists on using the remain capacity of the grid side converter of the DFIG for injecting compensating current and, when it reaches its limit, the rotor side converter is controlled to inject compensating current through the machine stator to the grid. The torque oscillations due to the unbalanced operation of the machine is avoided by applying a series voltage by the DVR. Simulation results have validated the proposed method, which maximizes the compensation at the PCC voltage unbalance and guarantees the machine operation with low oscillation in the electromagnetic torque.

Early Diagnosis of Induction Machine Stator Winding Faults by Discrete Wavelet Transform

AbstractElectrical machines are useful in nuclear power plants, military applications, domestic appliances and industrial utilities. The relevant literature indicates that the induction machine takes about ninety percent of all electrical machine globally used in the industry. The risk of the failure of this machine can be avoided if the proper diagnostic scheme is designed and implemented to detect failure/impending faults at an incipient stage. This paper describes Discrete Wavelet Transform (DWT) based diagnosis technique that analyses stator currents of induction machine under healthy and faulty conditions. This enables the extraction of harmonic components caused by each signal for further analysis. On one hand, the maximum energy for each signal gives information about the time a certain fault occurs in the machine and the time it starts deviating from the normal (healthy) state. On the other hand, a Fault Index (FI) is generated for each situation in order to classify the state of the machine into normal, medium or high. The colours; green, yellow and red are used to represent the normal, medium and high states respectively. Should the faults at medium state are not detected on time, it may lead a more serious fault (high state). Thus, this technique is robust to identify a fault of an induction machine at the incipient state with a very minimal time.

Current Sensorless MTPA for IPMSM Drives

In this paper, a maximum torque per ampere (MTPA) control strategy is presented for interior permanent magnet synchronous machines (IPMSMs) without current sensing or regulation. The developed control scheme achieves MTPA using a direct voltage control method, which varies the machine's stator voltage amplitude and angle. As such, no explicit current loop regulation is needed, which simplifies the control structure and unlike other control strategies, no parameter knowledge, voltage, or current transducer is required. Experimental comparison against the well-known MTPA vector control highlights the performance of the proposed controller in various conditions. Moreover, quantitative efficiency metrics are provided to better illustrate the MTPA trajectory tracking performance. Furthermore, the simplicity of the control scheme makes it a good candidate for low-cost implementation of real-time IPMSM drives.

Introductory assessment of a novel high‐torque density axial flux switched reluctance machine

A novel structure of switched reluctance machines (SRMs) is proposed in this study. The proposed structure uses the advantages of the axial flux path, short flux path, segmental rotor, and flux reversal free stator machines all together to improve the torque density of the SRMs. The main geometrical, electrical and physical specifications are presented. In addition, some features of the proposed structure are compared with those of a state-of-the-art radial flux SRM, considered as a reference machine. Achieved results reveal that, compared with the reference machine, the proposed machine delivers about the same torque, albeit employing considerably lower volume and active material mass. These make the proposed structures a potentially proper candidate for traction and propulsion applications demanding high-torque density machines.

Topology Evaluation of a Slotless High-Speed Electrical Machine with Stator Core Made of an Amorphous Alloy for the Aerospace Industry

The paper presents the experimental research of different slotless high-speed electrical machine topologies for integration into the auxiliary power unit gearless. It was shown that the 6-poles and 8-poles with the concentrated windings and the wound stator core are the most effective for aerospace industry. Based on the experimental and computer research of different slotless high-speed electrical machine topologies. It was found that for use in the gearless auxiliary power unit of modern and perspective aircrafts, the use of the 6-poles and 8-poles slotless high-speed electrical machines with concentrated windings and wound stator core is the most effective. This topology allows providing the sufficient rigidity of the slotless high-speed electrical machine stator core, the minimum length of the frontal part and the minimum weight and size parameters of the slotless high-speed electrical machine at the maximum efficiency. In addition, in this case, the slotless high-speed electrical machine windings have a high inductance, which leads to limit the magnitude of short circuit currents.

Partitioned Stator Machines With NdFeB and Ferrite Magnets

Partitioned stator (PS) machines employ two separated stators to accommodate armature windings and permanent magnets (PMs), respectively, alleviating the space conflict in stator-PM machines, and hence boosting the torque density. However, the PM usage volume in PS machines is relatively large, and thus the material cost is high, which is undesirable for the cost-sensitive applications. In this paper, a PS machine employing ferrite PM is presented, which takes advantage of larger available space for PMs while balances the performance and cost. The electromagnetic characteristics of an optimized ferrite PS machine and an NdFeB PS machine are evaluated together with a classic Prius2010 interior PM (IPM) machine as a baseline. Meanwhile, the economic issues are considered. The results reveal that the NdFeB PS machine has higher torque density than the Prius2010 IPM machine, but is more expensive, while the ferrite PS machine can significantly reduce the cost and still exhibit good performance. The demagnetization behavior of the ferrite PS machine is evaluated and a new method to improve the demagnetization withstand capability is proposed. Moreover, the mechanical analysis is conducted for the cupped rotor of PS machines. Finally, a pair of small-scaled prototypes are manufactured to validate the predictions.

Analysis and Detection of Inter-Turn Short-Circuit Fault Through Extended Self-Commissioning

This paper presents a comprehensive analysis of permanent magnet synchronous machine stator winding impedance variation in inter-turn short-circuit and eccentricity faults. The phase impedances are monitored through an extended self-commissioning procedure at the standstill mode before or after operation, and hence are agnostic to well-known issues caused by transients, load/speed level, or controller coefficient dependency. Moreover, the effect of stator iron core saturation on the electrical parameters is analyzed in depth. In order to distinguish the inter-turn shorts from the eccentricity fault which exhibits similar behaviors, a classification algorithm based on the saturation effect is introduced and analyzed on the machines with different pole–slot combinations. Both two-dimensional finite element analysis simulation and experimental test results are provided to show the efficacy of this analysis.

Thermal analysis of Double Stator Switched Reluctance Machine (DSSRM) with and without a squirrel cage rotor

Abstract Double Stator Switched Reluctance Machine (DSSRM) is a novel switched reluctance machine with limited information about its heat distribution and dissipation. This paper presents a two dimensional (2-D) thermal analysis of Double Stator Switched Reluctance Machine (DSSRM) to observe actual heat distribution in the parts of the machine, using Finite Element Method (FEM). Two topologies for the rotor of DSSRM are considered, Non-Squirrel Cage Double Stator Switched Reluctance Machine (NSC-DSSRM) and Squirrel Cage Double Stator Switched Reluctance Machine (SC-DSSRM). The heat distribution of these two topologies is analyzed, using Computational Fluid Dynamics (CFD). Finally the results are presented and compared.

Inductor Machines with Longitudinally-Transversal Comb-Wise Tooth Zone

Abstract The method considered in the present paper concerns the operational efficiency of the inductor electric machine, which can be improved by placing on the stator and rotor teeth the combs combined from differently shaped teeth and slots. The use on the inductor electric machine stator and rotor teeth of combs as a combination of differently shaped hills (teeth) and valleys (slots) allows raising the specific power of the machine. This effect is determined by the chosen type of a comb element as well as by technological possibilities of the manufacturer. The proposed method could be used moderately in the inductor machines with longitudinally-transversal combing.

Optimal Pulsewidth Modulation for Common-Mode Voltage Elimination Scheme of Medium-Voltage Modular Multilevel Converter-Fed Open-End Stator Winding Induction Motor Drives

Multilevel converter topologies for open-end stator winding medium-voltage (MV) induction motor drives have been researched from the last two decades. In this paper, a dual $n$ -level modular multilevel converter (MMC) topology has been proposed for open-end stator winding MV induction motor drives. The control requirements of the proposed system are low device switching frequency, minimal harmonic distortion of machine stator currents, elimination of common-mode voltages in machine stator windings, and maintaining floating capacitor voltages around their nominal value. Based on these requirements, an emerging modulation technique for MV induction motor drives known as synchronous optimal pulsewidth modulation has been developed for the proposed dual $n$ L-MMC topology. The laboratory measurements from a dual three-level MMC fed 1.5-kW open-end stator winding induction motor drive demonstrate the performance of proposed technique.

On-Line Stator Open-Phase Fault Detection and Tolerant Control for Permanent Magnet Machines Using the Neutral Point Voltage

Conventional machine stator open-phase fault detection methods rely on the detection of current harmonics from the sensing of phase currents. Because the magnitudes of current harmonics are proportional to the machine load condition, it is a challenge for the phase fault detection at the light load condition when fault-induced current harmonics are too small to detect. This paper proposes an improved stator phase fault detection for permanent magnet (PM) machines based on the use of neutral point (NP) in Y-connected windings. It is shown that the first-order voltage harmonic is resultant once the open-phase fault occurs. Comparing with prior detection methods based on the current measurement, the fault detection using NP voltage is insensitive to the load condition, because the proposed fault signal is induced by the voltage unbalance as a result of the open phase. In addition, considering the fault tolerant control, a single-phase drive is developed by connecting the machine NP to one of the inverter legs. The machine can drive at the most efficient condition using standard three-leg inverters under phase fault. A 50-W PM machine with the accessible NP is used to evaluate the proposed open-phase fault detection and tolerant control method.