Large Stator Research Articles

Novel Dual-Rotor Single-Stator Coreless Permanent Magnet Machine With Dual-Flywheel

Permanent magnet (PM) machines have attracted much attention in the field of flywheel energy storage system (FESS) due to their merits of high power density and high efficiency. However, the flux generated by the PMs would cause large stator core loss during the idling state of FESS, which would reduce the energy conversion ratio and limit the application of FESS in long-term energy storage occasions. Addressing this issue, a novel dual-rotor single-stator coreless PM machine (DSSCPMM) with dual-flywheel is proposed in this article. The stator of the DSSCPMM is made of ceramic material, which can effectively eliminate the stator core loss. The rotor of the DSSCPMM contains inner and outer rotors, which are used as the flywheels and can be helpful to improve the energy storage density. First, the structure and operation principle of the proposed DSSCPMM are illustrated. Then, the influences of the key structure parameters and arrangement of PMs, winding configurations, and magnetization method on the electromagnetic performance of the proposed DSSCPMM are investigated. Finally, the optimized structure of the DSSCPMM is obtained and the efficiency is calculated. The result shows that the proposed DSSCPMM is a promising candidate for the application of FESS.

Optimization study of the main parameters of different types of wind turbine generators * * This work was supported in part by the National Natural Science Fund under Grant 52071090, in part by the Doctoral Start-up and Postgraduate Fund under Grant R17062, and in part by the Young Innovative Talents in Colleges and Universities of Guangdong Province under Grant 2019KQNCX046.

The research and development of large-scale wind turbine generators have become a future trend in green renewable energy field from the dual perspectives of the environment and economics. In this work, an electrical design method is first proposed and applied to different types of wind turbine generators, including the high-temperature superconducting (HTS), the permanent magnet, and the traditional copper generators. The optimal electrical designs of the three types of 10 MW wind turbine generators are then created based on the developed design program. Second, the influences of the rated revolution on the basic performance parameters of the HTS generator are investigated, and the results are compared with those of the other two types of generators. It is found that the generator weight decreases with the increases of the rated revolution and the stator outer diameter, and the optimal rated revolution for a generator with a large stator outer diameter is determined to be 40 min−1. Moreover, the weight of the field parts is found to have the same regulation rule as the generator weight. Finally, the design results of the three types of wind turbine generators are comparatively discussed, and it is found that the HTS wind turbine generator is superior to its two counterparts.

Efficiency improvement of dual three-phase permanent magnet synchronous motor using modified switching table DTC for electric ship propulsion

A direct torque control using a classical switching- table ST-DTC can be used to control the torque and thus the speed of Dual Three-Phase Permanent Magnet Synchronous Motor (DTP-PMSM). The principle is based on direct application of control sequence by using two hysteresis regulators and a switching table. A large stator current containing low order harmonics is produced during the application of the classic ST-DTC technique, this leads to higher losses affecting the efficiency of the machine. To allow a reduction of these harmonics a modified switching-table approach based DTC technique is examined. Indeed, an improved ST-DTC strategy, which consist of replacing the vectors of the classical table with synthetic vectors, is discussed. The simulation results confirm the validity of the selected strategy.

Squirrel cage induction motor predictive direct torque control based on multi-step delay compensation

The squirrel cage induction motor direct torque control main problems due to torque and large stator flux pulsation. In this an improved model predictive direct torque control algorithm considering multi-step delay compensation is proposed. At each sampling moment, predict the stator flux linkage and torque at the next moment under each voltage vector. The optimal voltage vector deviation from the stator flux linkage reference value and torque reference value are selected as the minimum objective function. Aiming at the problem of one-shot delay in digital control systems, a multi-step predictive delay compensation measure is studied. Simulation shows that the algorithm can effectively reduce torque and stator flux pulsation, reduce current harmonic distortion, and solve the delay problem in digital systems.

Investigation on large turbo-generator stator end winding dynamic characteristics based on response surface method

Investigation on large turbo-generator stator end winding dynamic characteristics based on response surface method

Direct Torque Control for a Bearingless Induction Motor Based on Model prediction

Purpose The purpose of this paper is to address the large stator flux linkage ripple and electromagnetic torque ripple caused by the hysteresis comparator in traditional direct torque control for a bearingless induction motor (BIM). Design/methodology/approach Model predictive direct torque control (MPDTC) strategy is adopted. On the basis of the mathematical model of BIM, the stator current and stator flux observational values are obtained, and the electromagnetic torque and stator flux at the next moment are predicted. Then, based on the relationship between the stator flux and the electromagnetic torque, the predicted stator flux can be transformed into an equivalent flux linkage vector, which eliminates the weighting coefficients problem among multiple variables in traditional objective functions. The objective function and torque PI controller will output the optimal stator flux linkage and the increments of the torque phase angle. Through the phase angle increments, the space voltage vector can be obtained by the reference flux linkage controller instead of the stator flux linkage and the torque hysteresis controller. Findings The proposed MPDTC method can effectively improve the stator flux linkage and the torque ripple. It can implement the stable suspension of the rotor and improve the dynamic performance and steady-state accuracy of the BIM system. Originality/value A MPDTC strategy is proposed to reduce the ripple of stator flux and electromagnetic torque. The phase angle increment angle of stator flux linkage and electromagnetic torque is optimized by model prediction, and the optimal space voltage vector is obtained by designing the reference flux controller.

Current harmonic elimination for dual three‐phase PMSM based on a spatial analytical model of flux linkage

Compared with the conventional three-phase motors, the dual three-phase permanent magnet synchronous motors (PMSMs) have many advantages and have been widely used in various drive fields. However, one major disadvantage of these machines is that they are easy to generate large stator current harmonics, which makes it difficult to have an excellent performance in the drive field. To solve this problem, this study introduces a current harmonic elimination method based on a spatial analytical model of flux linkage. The study reconstructed the analytical model of flux linkage from finite element analysis. The analytical model can describe the spatial harmonics of flux linkage by considering the rotor position information. Based on the model, an active feedforward controller was proposed to eliminate current harmonics by actively injecting the corresponding voltage harmonics, the voltage harmonics are calculated by the model of flux linkage. The performance of the proposed method in eliminating current harmonics is verified by simulations and experiments.

Design and Performance Analysis of Segmented Three-Phase IPMSM for EVs Integrated Battery Charger

A segmented three-phase interior permanent magnet synchronous motor (IPMSM) can bring a significant advantage in the development of electric vehicles (EVs) since it can be used as a simple inductor filter for an integrated battery charger without torque production during charging/vehicle-to-gird (V2G) mode. However, unlike an induction machine, majority of IPMSMs have low value of stator inductance, possibly below the minimum limit of the pulsewidth modulation rectifier requirement; therefore, the integrated battery chargers based on these types of IPMSMs may have difficulty dealing with grid current harmonics during charging/V2G mode. This article presents the method to design a suitable segmented three-phase IPMSM with nine windings (S3-IPMSM-9W) for integrated battery chargers. The optimization of stator winding inductance is proposed in order to get a large stator inductance capable of achieving acceptable ripple during charging and does not degrade the traction mode performance. Therefore, an optimized inductance, which is eight times greater than the nonoptimized stator inductance value was obtained. 96% of the efficiency of the optimized machine was achieved during the motoring mode. Moreover, with the help of optimized leakage inductance acting as a grid-side filter, the total harmonic distortion below 5% is reached during charging. Simulation and experimental results are provided to validate the theoretical analysis.

Current Harmonic Suppression in Dual Three-Phase Permanent Magnet Synchronous Machine With Extended State Observer

Dual three-phase (DTP) permanent magnet synchronous machines (PMSM) have been utilized in many applications due to their outstanding performance. However, large stator current harmonics limit the further application of the DTP-PMSM due to the low impedance in the harmonic subspace. To solve this problem, this article proposes a current harmonic suppression strategy based on an extended state observer (ESO). A detailed analysis is carried out to demonstrate the disturbance rejection ability and robustness of the proposed method. The theoretical analysis also shows that the ESO strategy outstands the conventional proportional-integral controller and advanced proportional resonance (PR) controller in terms of harmonic reduction. The advantages are verified by simulation and experimental results under different operating conditions. The proposed strategy still works well when considering other factors that may cause harmonic distortion, such as magnetic circuit saturation, saliency ratio, over-modulation of the inverter, the voltage drop caused by electric devices, and dead time. Meanwhile, some limitations are also pointed out. The proposed strategy can also be easily applied to other multiphase PMSM types.

Modified Switching Table-Based Direct Torque Control of Six-Phase Induction Motor Drive

This paper presents “Switching Table based Direct Torque Control” of Six-Phase Induction Motor (SPIM) Drive. The SPIM consists of two sets of stator windings spatially shifted by an angle of 30°. The extension of DTC technique of three-phase induction motor for a six-phase induction motor yields conventional DTC, in which one large voltage vector per sampling period is utilized. This technique suffers from large stator current harmonics of the order of 6k ± 1 (k = 1, 3, 5..). Initially, the conventional DTC technique has been implemented for comparison purpose. Further, its performance is improved by using two voltage vectors in each sampling period. In order to investigate the performance of ST-DTC based SPIM, a simulation study is carried out under different operating conditions. To validate the simulation results, a prototype model of six-phase induction motor rated for 1.5 kW, 200 V, 50 Hz is developed. Results obtained during simulation and experimentation show the effectiveness of modified ST-DTC technique in the reduction of stator current harmonics.

Effect of Tip Clearance on Flow Field and Heat Transfer Characteristics in a Large Meridional Expansion Turbine

The large meridional expansion turbine stator leads to complex secondary flows and heat transfer characteristics in the blade endwall region, while the upstream tip clearance leakage flow of the rotor makes it more complex in flow and heat transfer. The influence of the upstream rotor tip clearance on the large meridian expansion stator is worth studying. The flow and heat transfer characteristics of the downstream large meridional expansion turbine stator were studied by comparing the tip leakage flow of 1.5-stage shrouded and unshrouded turbines using a three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solver for viscous turbulent flows. Validation studies were performed to investigate the aerodynamics and heat transfer prediction ability of the shear stress transport (SST) turbulence model. The influence of different tip clearances of the rotor including unshrouded blade heights of 0%, 1% and 5% and a 1% shrouded blade height were investigated through numerical simulation. The results showed that the upper passage vortex separation was more serious and the separation, and attachment point of horseshoe vortex in the pressure side were significantly more advanced than that of non-expansion turbines. The tip leakage vortex obviously increased the negative incidence angle at the downstream inlet. Furthermore, the strength of the high heat transfer zone on the suction surface of the downstream stator was significantly increased, while that of the shrouded rotor decreased.

On the Influence of Increased Stator Leakage Inductance in Single-Tooth Wound Synchronous Reluctance Motors

This paper explores the leakage inductance of a single-tooth wound synchronous reluctance motor and its influence on motor performance. It is shown that the stator leakage inductance heavily influences the true saliency ratio in synchronous reluctance motors and a large stator leakage inductance has a serious detrimental impact on the operating power factor. It is also shown through analytical and finite element analysis analysis that synchronous reluctance motors with single-tooth windings suffer an inherent high stator leakage inductance that is dominated the air-gap harmonic leakage component, derived from the significant stator MMF harmonics experienced with this winding type. This explains for the first time the experimental results showing a low operating power factor compared to a distributed wound machine. Measurement of the stator leakage inductance is attempted on a prototyped machine and the standardized method is found to be lacking when single-tooth windings are employed.

Predictive Torque and Rotor Flux Control of a DFIG-DC System for Torque Ripple Compensation and Loss Minimization

The severe torque ripple normally occurring in the doubly fed induction generator dc (DFIG-dc) system can cause premature failure of mechanical components and shorten the life of the drive train. This paper addresses the torque ripple issue by proposing a predictive direct torque control strategy, which delivers at the same time torque ripple suppression and minimization of losses. The existing control algorithms for torque ripple mitigation are mostly based on resonant controllers and repetitive control forcing the compensation signal either through the current chain or directly into the rotor voltage commands. All these techniques lead to structures with multiple controllers whose tuning is not straightforward. Furthermore, they are very sensitive to the operating frequency, making optimized operation with variable frequency highly challenging. Conversely, the proposed algorithm predicts directly the best rotor voltage space vector to minimize torque ripple and track a prescribed rotor flux amplitude to minimize losses, with no current control chain. As confirmed by simulations and experiments, the strategy allows large stator frequency variations as required by the optimal flux command for minimum losses, whilst ensuring effective torque ripple compensation.

Optimization of DC Starters Based on Reluctance Network Accounting for Armature Reaction Magnetic Field

In the new generation of “Stop & Start” starters, a DC series motor with high power density is used. In this application, non-symmetrical machines are used due to the single wave winding in brushed motors. The saturation of the iron core in this application reaches a really high level. Moreover, armature reaction in DC machine with a large stator pole spans makes this phenomenon even more enhanced. All these criteria lead to model the whole machine in highly saturated conditions which is time consuming. In this paper, a fast reluctance network (RN) model for an equivalent machine is proposed. It takes into account the armature reaction in high saturation conditions. It also allows a good accuracy and permits us to show the relevance of taking into account this phenomenon in torque calculation. This model is validated by a finite element (FE) method in many operating points, and by a statistical approach. It shows high robustness and low computation time. Finally, an optimization procedure using this reluctance network model and FE is presented in order to show the accuracy of the RN compared to FE model.

Inverse-Based Current Harmonic Controller for Multiphase PMSMs

Multiphase electric machines can provide significant advantages over conventional three-phase machines. Unfortunately, multiphase machines also have a notable disadvantage that even a small voltage excitation of certain frequency components can cause large stator current harmonics. This paper presents an inverse-based current harmonic controller to eliminate the current harmonics. A detailed theoretical analysis of the proposed harmonic controller is given including a comprehensive set of analytical design principles. The robustness of the method is studied with a multi-input multi-output approach based on a structured singular value and H∞ norm analyses. In addition to the theoretical work, the performance of the harmonic controller is investigated with experimental results from a dual three-phase permanent magnet synchronous machine (PMSM). The analysis and results of this paper show that the inverse-based current harmonic controller provides a robust and high-performance method to eliminate the current harmonics in multiphase PMSMs.

Current Harmonic Compensation in Dual Three-Phase PMSMs Using a Disturbance Observer

Dual three-phase electric machines are known to offer many important advantages compared with their conventional three-phase counterparts. However, these machines also suffer from a significant disadvantage of easily occurring large stator current harmonics. To solve this problem, this paper introduces a current harmonic elimination method based on a disturbance observer (DOB). The study provides a detailed analysis and design principles for the DOB. The performance of the proposed method is verified by experimental results. The results show that nearly complete elimination (> 99% reduction) of harmonic components is achieved. In addition, it is shown that the method is robust against uncertainties. The method provides a simple yet effective alternative for solving the issue of stator current harmonics in dual three-phase drives, and the results of this paper can be easily applied also to other multiphase machine types.

Consideration of Design and Operation on Rotational Flux Density Distributions in Hydrogenerator Stators

Core losses in an electrical machine vary depending on the type of material, frequency of operation, and flux density magnitude and waveform. Loss prediction using pulsating models is insufficient for estimating core losses in a machine, since it does not take into account rotational core losses. Moreover, superposition of pulsating losses in the radial and tangential direction overestimates losses especially at higher flux densities. The objective of this paper is to study rotational flux distribution in the stator of the generator under different operating conditions. Distribution of rotational flux in a large hydrogenerator stator is studied by plotting the aspect ratio. It was found that increasing the yoke length and reducing the air gap increases the area of the stator with rotational flux. Varying the output power showed slight changes in the rotational flux distribution. Different optimized machine designs are investigated for rotational flux distribution; moreover, rotational core losses are measured and used for a comparative study radially across the stator.

Design and Analysis of a Novel Brushless Wound Rotor Synchronous Machine

Permanent magnet synchronous machines (PMSMs) utilize permanent magnets to generate the rotor flux needed to produce torque. They are ideal for high-accuracy fixed-speed drives. But rise in the price of rare earth magnet caused by its scarcity is a key consideration while developing such kind of machines. In this situation, wound rotor synchronous machines (WRSMs) have benefits compared to PMSMs as it does not need magnetic material and can be operated in a wide range of speeds [1]. In a WRSMs field windings are used, which is supplied with a DC current that generates the rotor flux. DC current can be applied to the rotor winding either using the brush and slip-ring structure or brushless excitation method. The brushes and slip rings have losses and maintenance issues, so they are used for small synchronous machines. For brushless excitation, additional (auxiliary) stator windings are used to excite the rotor field winding. Several patents are granted according to this excitation method [2]-[4]. The conventional method faces issues, since both the stator windings are located in the same stator core and require a large stator volume for making place for the both windings. Using a single winding in the stator to perform the brushless operation for the WRSMs is presented in [5]. But in that case concentrated windings are used to develop the higher harmonics for the excitation which will result in more losses. Thus a new idea for brushless WRSMs is proposed in which single stator winding is used to excite the rotor as well as generate the fundamental air gap harmonic for electromagnetic torque. A 2D finite element analysis (FEA) have been done to analyze and verify the proposed brushless WRSMs.

Influence of stator vane number on performance of the axial-flow pump

The interplay of impeller and stator is investigated for an axial-flow pump. Three stator vane numbers of 5, 7 and 9 are devised to match the same impeller. The renormalization group k-e turbulence model is used to simulate three-dimensional flows in three pumps with different vane numbers. Axial velocity distributions at impeller outlet and stator outlet are comparatively analyzed. Experiments assess operation performance of the three pumps. Vibration parameters and static pressure fluctuations are measured as well. It is indicated that the influence of vane number on both pump head and pump efficiency is insignificant. Large stator vane number contributes to the improvement of the uniformity of axial velocity distribution at impeller outlet. At stator outlet, similar tendency is revealed. Severe vibration occurs near the outlet bend of the pump, as is particularly remarkable at vane number of 9. For the three cases, blade passing frequency and its harmonics are predominant in the frequency spectra of pressure fluctuations. As flow rate increases from 0.8Q to 1.0Q, high-frequency pressure fluctuations are suppressed considerably at vane number of 9, while the other two cases also manifest a decline in overall pressure fluctuation amplitude. The 7-vane case is the most preferable one among the three cases in terms of both pump performance and pressure fluctuation between the impeller and the stator.

Winding topologies of flux-switching motors for in-wheel traction

Purpose – The purpose of this paper is to investigate winding topologies for flux-switching motors (FSMs) with various segment-tooth combinations and different excitation methods. Design/methodology/approach – For the ac winding of FSM, two winding topologies, namely the concentrated winding and the distributed winding, are compared in terms of the winding factor and efficiency. For the field winding of dc-excited FSM (DCEFSM), another two winding topologies, namely the lap winding and the toroidal winding, are compared in terms of effective coil area, end-winding length, and thermal conditions. Analytical derivation is used for the general winding factor calculation. The calculation results are validated using finite element analysis. Findings – Winding factors can be used as an indication of winding efficiency for FSMs in the same manner as done for synchronous motors. For FSMs with concentrated windings, the winding factor increases when the rotor tooth number approaches a multiple of the stator segment number. For FSMs with certain segment-tooth combinations, e.g. 6/8, the theoretical maximum winding factor can be achieved by implementing distributed windings. Furthermore, the toroidal winding can be an efficient winding topology for DCEFSMs with large stator diameter and small stack length. Research limitations/implications – This work can be continued with investigating the variation of reluctance torque with respect to different segment-tooth combinations of FSM. Originality/value – This paper proposes a general method to calculate the winding factor of FSMs using only the phase number, the stator segment number, the rotor tooth number, and the skew angle. Using this method, a table of winding factors of FSMs with different segment-tooth combinations is provided. Principle of design of FSMs with high-winding factors are hence concluded. This paper also proposed the implementation of distributed windings for FSM with certain segment-tooth combinations, e.g. 6/8, by which means a theoretical maximum winding factor is achieved. In addition, different winding topologies for the field winding of DCEFSM are also investigated.