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Ventilation cooling design is one of the key technologies during the design of large hydrogenerator. With the increase of hydrogenerator capacity, the overheating problem of rotor region become more and more serious. In this paper, a 250 MW hydrogenerator is analyzed. The transient electromagnetic field of the hydrogenerator is calculated. The losses (heat sources) of rotor components in the rotor region of the hydrogenerator are determined. Three-dimensional fluid and thermal coupled mathematic model of the hydrogenerator rotor region is established. The rotor rotation of the hydrogenerator is considered. The distribution of complex fluid velocity in the rotor region is calculated using the finite volume method. The influence of fluid velocity in the different directions on the temperature of the rotor excitation winding is studied under the different flow rates in the rotor region. The surface heat-transfer coefficient distribution of the rotor components is determined. The temperature distribution of the rotor excitation winding, rotor pole body, rotor press plate, rotor damping bar, and rotor end ring is obtained. The calculated temperature results match well with test values. These provide an important reference for the rotor structural design and optimization of larger hydrogenerator.

This paper is focused on a design and simulation of a 3D printed double rotor machine using Halbach array permanent magnets. This machine’s is supposed to be a learning tool for demonstration of behavior and properties of electrical machines’ magnetic field. Design of this machine according to the presumed way of production technology is described. A validation of the final design is verified by finite element analysis.

A measurement setup is designed and constructed to experimentally investigate the thermohydraulic performance of a novel direct rotor cooling method for an interior permanent magnet synchronous machine, where oil is pumped through weight saving channels of the rotor iron close to the magnets. The setup consist of a stationary rotor assembly where heat is dissipated in an aluminum sleeve surrounding the rotor outer surface. Measurements are performed for different oil inlet temperatures, flow rates and heat losses. It is shown that tangential temperature variations can be neglected and axial variations are as expected. The conductive resistance within the rotor assembly is similar for each measurement point as the differences are within the measurement uncertainty. The convective resistance decreases with an increasing flow rate, inlet temperature and heat dissipation. From correlations in scientific literature, it is expected that the convective resistance will further reduce with increasing rotational speed of the rotor. A comparison of these results to a standard hollow shaft cooling method shows a great potential of the novel direct rotor cooling method to further increase the power density of electric machines.

This work is on deriving precise lumped parameter thermal networks for modeling the transient thermal characteristics of electric machines under variable load conditions. The goal is to facilitate an accurate estimation of the temperatures of critical machines' components and to allow for running the derived model in real time to adapt the motor control based on the load history and maximum permissible temperatures. Consequently, the machine's capabilities can be exhausted at best considering a highly-utilized drive. The model shall be as simple as possible without sacrificing the exactness of the predicted temperatures. Accordingly, a specific lumped parameter thermal network topology was selected and its characteristics are explained in detail. The measurement data based optimization of its critical parameters through an evolutionary optimization strategy, and the therefore utilized experimental setup will be described in detail here. Measurement cycles were recorded for modeling and verification purposes including both static and dynamic test cycles with changing load torque and speed requirements. Applying the proposed hybrid approach for determining the model's parameters through involving physics-based equations as well as numerical optimization followed a significant improvement of the preciseness of the predicted motor temperatures compared to solely determining the networks's coefficients based on expert knowledge. Thereby, the validation included both the original measurement data as well as extra measurement runs. The proposed and applied strategy provides an excellent basis for future thermal modeling of electric machines.

This paper presents analytical thermal models of 7 different rotors with permanent magnets, which are used as sub-models in universal thermal management software, which is currently being developed at our university. Whole software is created as script in MATLAB interface and is based on equivalent thermal network. For each of the rotor topology is created thermal circuit, which can accurately calculate temperature distribution, and fits into software algorithm. All analytical models are verified by numerical finite element analysis.

The design of high-speed machines requires extensive multidisciplinary approach to achieve a high-performance machine. The design process is highly iterative, and analytical methods can accelerate it with faster design iterations at low computational efficiency to find the optimum parameters at conceptual stage. In this study, an analytical design method for obtaining rotor mechanical limits is developed for squirrel-cage slitted high-speed induction machine rotors. In high-speed electric machines, the design is made specifically to meet the application requirements and the objective is to reach a high efficiency. This means that the design needs to be made often from the scratch and existing designs can rarely be used as a starting point. The method developed in this study enables rapid design iterations, especially considering the mechanical limits in the conceptual and layout design phase. The proposed analytical design method is validated with three different case studies.

This article presents a new adaptive vision-based method (AVBM) of performing automatic detection for rotor balancing, and the online implementation proved that the method achieved rapid real-time optimization of system balancing configuration for a rotor dynamic balance machine. The proposed AVBM integrated 3D sensors and dynamic balancing platform using 3D computer vision technique and dynamic balance algorithm to improve the efficiency of rotor dynamic balancing. AVBM applied 3D ToF sensors on active rotor dynamic balance machines to grab 3D point cloud of rotor shaft and balance sprues. By 3D depth data, the background noise can be removed to detect the positions of shaft center, key phasor and balance sprues of rotor automatically. After combining with unbalance vector from dynamic balancing machine, the AVBM system calculated the optimal balance configuration by the vector analysis algorithm. Compares to conventional methods, conventional rotor dynamic balancing process relies on technicians to mount washers on particular balance sprues based on their experience, therefore uncertainty causes productivity decline. Experiments in industrial examples showed that the proposed AVBM required fewer rounds to achieve acceptance, whereas the conventional industrial rotor balancing method performed by operators required more than three rounds in average. Consider the overall dynamic balancing process for the motor, the processing time required for each motor without AVBM was 348.9 seconds, and the daily rotor balancing count of each dynamic balancing machine was 83. The processing time with AVBM was shortened from 348.9 to 283.9 seconds, the daily rotor balancing count had increased from 83 to 101, and the production improvement had reached 22 %. That is, the proposed AVBM can accurately analyze the dynamic balance and greatly reduce the redundant dynamic balance operations. The main advantage of the proposed AVBM over conventional methods is its efficiency, effectiveness and robustness in online optimization of rotor dynamic balance.

Based on the receding horizon principle, cost function of nonlinear model predictive control (NMPC) becomes an accumulating type to extend prediction horizon. A nonlinear model predictive speed control (NMPSC) with prediction horizon self-tuning method is proposed in this paper, and applied into a permanent magnet synchronous motor (PMSM) rotor position control system with inner-loop of speed. The prediction horizon is improved as a positive integral discrete-time variable which needs to be adjusted according to operating states in each sampling period. Control performances such as rotor position and speed integral of time-weighted absolute value of errors (ITAEs), delay time and calculation burden are compared with the conventional control strategy, and advantages including ITAEs, delay time, weighting factor sensitivities and servo stiffness are obtained. The effectiveness and correctness are verified by simulation and experimental results.

In this paper a novel outer-rotor consequent pole permanent magnet machine (OR-CPPMM) with H-type modular stator core is proposed for higher average torque ( $T_{avg}$ ), flux linkage ( $\Phi$ ) and efficiency ( $\eta$ ) whereas low cogging torque ( $T_{cog}$ ), torque ripple ( $T_{rip}$ ) and harmonics content in flux linkage ( $\Phi _{THD}$ ) and back-EMF ( ${\mathrm {EMF}}_{THD}$ ). The proposed OR-CPPMM is investigated with different stator flux gaps width for static and dynamics electromagnetic performances. Analysis reveals that flux gaps in H-type stator core not only improve electromagnetic performance i.e., $\Phi $ is enhanced by 10.23%, $\Phi _{THD}$ is suppressed by 80.65%, diminished ${\mathrm {EMF}}_{THD}$ by 59.37%, truncate $T_{rip}$ by 44.37% and improve $T_{avg}$ by 15.99% but also exhibits better flux focusing effect to enhance flux linkage and diminish harmonic contents. In addition, H-type modular stator structure provide physical isolation of adjacent phase that de-couple the adjacent phase coupling flux which enhance self-inductance and weaken mutual-inductance and hence improve fault tolerant capability. In addition, to elaborate effectiveness of the proposed design and justification of OR-CPPMM novelty with H-type modular stator, electromagnetic performance is extensively compared with existing state of the art including E-core and C-core structure. Analysis and comparison with state-of-the-art reveals that proposed OR-CPPMM enhanced $\Phi $ by 65.35%, diminish $\Phi _{THD}$ by 67.24%, truncate $T_{cog}$ by 96.72%, suppresses ${EMF}_{THD}$ by 44.40%, diminish $T_{rip}$ by 77.23% whereas $T_{avg}$ is enhanced by 91.69%. Furthermore, the proposed design novelty is justified with comparison of OR-CPPMM with inner rotor and dual rotor permanent magnet flux switching machines. Comparison and analysis unveil that OR-CPPMM exhibits $T_{avg}$ higher up to 35.16%, truncate $T_{rip}$ up to 32.88%, enhanced $\Phi $ up to 22.13% and boost $T_{den}$ to 3.41 times at the cost of 2.58% increase in $T_{rip}$ .

This paper proposes a vector and a linear control strategy for wind turbines connecting to a DC collector grid. Two conversion schemes are considered for the wind turbine, (i) an active scheme where a dual rotor generator (DRG) is connected to a voltage source converter (VSC), and (ii) a passive scheme where a DRG is connected to a passive uncontrolled rectifier. The vector controller is implemented on VSC and DRG where the turbine rotor speed and output power are controlled via a VSC, and the wind turbine generator (WTG) rectified output DC voltage is controlled via a DRG DC filed current. A load-angle control and analytical modeling is discussed for the vector controller and evaluated via simulation results. In the passive scheme where the VSC is replaced with an uncontrolled rectifier the control is entirely shifted to DRG where a linear controller is implemented that controls the turbine rotor speed, power and voltage. A comparison of the vector and linear control is presented, and simulation results verify the effectiveness of the control strategy in steady-state and when turbine transitions between different wind velocities.

It’s essential to obtain the initial rotor position of PMSM to prevent the reversal of the rotor and to ensure the maximum electromagnetic torque output during the startup process. An improved pulse-voltage injection-based initial rotor position estimation method is proposed in this paper. Different from the conventional pulse-voltage-injection-based method that only utilizes the information about the virtual d-axis current for the voltage vector injected to PMSMs, the information about the virtual q-axis current is also utilized in the proposed method to reduce the estimation errors caused by the current sampling errors. The experimental results indicate that the estimation accuracy can be greatly improved.

In this paper two permanent magnet flux switching generator (PMFSG) is designed for 2 kW output power and 220 V phase voltage at 1500 rpm and comparatively analyzed for wind turbine applications. Both PMFSG share same C-core stator connected back-to-back through flux bridge ( $\beta$ ) with different rotor position i.e., inner rotor PMFSG (IR-PMFSG) and outer rotor PMFSG (OR-PMFSG). A detailed comparative analysis with various $\beta $ for both IR-PMFSG and OR-PMFSG are performed under static characteristics, rated condition, overload capability and over-speed capability for generating output voltage, current, power and efficiency. Comparison of the static characteristics reveal that IR-PMFSG offers 47.93% higher rated power, 2.83% higher efficiency, 22.78% more magnetic flux, 56.91% reduced cogging torque and 83.18% lower torque ripples at the cost of 62.69% higher voltage regulation factor. Furthermore, under rated operating condition and overload capability with same specifications it is found that IR-PMFSG exhibits 1.47 times power than that of OR-PMFSG counterpart. Finally, over-speed capability is investigated in term of the output power which shows that IR-PMFSG significantly generate almost 2.25 time of the specification power whereas OR-PMFSG exhibits nearly 1.25 times power. This analysis shows that IR-PMFSG can be operated at wide-speed rage for higher power specification requirements maintaining efficiency greater than 90%.

Serving as a core component, the performance of the hydraulic transformer (HT) directly affects the energy-saving performance of the common pressure rail (CPR) system. The HT is capable of both amplifying and reducing pressure without throttle loss, in which the pressure ratio is a critical parameter controlled through adjusting the torques acting on the rotors. However, our understanding of it relies on simplified models due to the complicated operation mechanism. This study focuses on the pressure ratio characteristics of the novel double rotor hydraulic transformer (DRHT). Firstly, the key influencing factors of the DRHT are acquired through theoretical analysis. Secondly, a dynamic model of the DRHT is established allowing for mechanical and fluid properties. Thirdly, a specially designed DRHT prototype is manufactured and the test bench is built up to verify the model. The experimental and numerical results show that the pressure ratio varies nonlinearly with the control angle especially when the control angle is greater than 10 degrees, while it changes almost linearly with the increasing rotating speed. The test results are consistent with the simulation results, which credit the mathematical model feasible and effective. The parametric study show that the augment of the A slot wrap angle on the valve plate could enhance the driving torque, as a result larger pressure ratio can be acquired. The enlargement of the B slot on the valve plate could make the variation of the pressure ratio more linearly. The current work is also significant for further design and the application of the DRHT.

This paper proposed an improved full-order sliding-mode observer (IFSMO), applied to a sensorless control system of surface-mounted permanent magnet synchronous motor (SPMSM), to obtain a high-precision rotor speed and position. First, the IFSMO method, which combines the new sliding-mode function with the variable boundary layer function, is presented to suppress the chattering and accelerate the convergence speed of the system. Meanwhile, since the observer has the characteristics of a second-order low-pass filter, the high-frequency noise contained in the estimated back EMF signal can be effectively filtered out without an additional low-pass filter. Then, the proposed PLL is designed to obtain rotor position and speed. Finally, simulations and experiments of the SPMSM system based on the IFSMO method under different working conditions are implemented, which demonstrates the effectiveness of the proposed algorithm.

Triphibious robots can move in more complex environment compared with common mobile robots, which makes the triphibious robots have a wider movement space and better environmental adaptability. This paper proposes an innovative design solution of a triphibious robot with the tilting-rotor structure (TR-TRS), which can change its motion mode to perform smoothly transition between different media, such as land, water, and air. First, the mechanical structure of the triphibious robot is described with design diagrams. Two tilting-rotors are mounted on the left and right side of a quadrotor-like aerial platform, in which four legs with passive wheel are integrated to make the triphibious robot move on land. Tilting-rotor structure is used to change the orientation of the rotors on both sides of the robot’s fuselage, thus, through adjusting the orientation of these two rotors they can drive the triphibious robot to move on land and underwater. Next, according to the mechanical design, the motion modes in different environmental media are given, and the transition methods between different motion modes are explained in detail. Finally, the influence of tilting-rotor structure on the performance of the designed triphibious robot is analyzed and discussed by the results of virtual simulation. The superior performance of tilting-rotor structure in triphibious robots is demonstrated through the comparison of existing robots.

A perception-aware Nonlinear Model Predictive Control (NMPC) strategy aimed at performing vision-based target tracking and collision avoidance with a multi-rotor aerial vehicle is presented in this paper. The proposed control strategy considers both realistic actuation limits at the torque level and visual perception constraints to enforce the visibility coverage of a target while complying with the mission objectives. Furthermore, the approach allows to safely navigate in a workspace area populated by dynamic obstacles with a ballistic motion. The formulation is meant to be generic and set upon a large class of multi-rotor vehicles that covers both coplanar designs like quadrotors as well as fully-actuated platforms with tilted propellers. The feasibility and effectiveness of the control strategy are demonstrated via closed-loop simulations achieved in MATLAB., Comment: 6 pages, 6 figures, conference

The capability of a radar system to detect and identify the low-slow-small rotor unmanned aerial vehicle (UAV) is intensely important for management and control in low altitude, and it can be enhanced by the characteristics of UAV, which inherently carries micro-Doppler information. In this paper, we establish a micro-motion model of rotor UAV, and analyze the range walking and Doppler broadening caused by micro-motion. Hence, based on the characteristics of micro-Doppler of the rotors apart from the main body for the moving UAV, a micro-motion target detection and micro-Doppler parameters estimation method is proposed. Firstly, a method based on datashift in range dimension is used to compensate the translational component of the main body. Secondly, for the echo after translation compensation, a parameter estimation method of micro-Doppler based on the optimal demodulation operator is proposed. The operator contents the maximum likelihood criterion, which strengthens the difference between the micro-Doppler signal and the background clutters, so that more signal energy can be accumulated while the clutter is suppressed. Subsequently, the micro-Doppler parameters of the micro-motion component are obtained by the optimal demodulator, so that the detection and identification of the target are realized. Additionally, the performance of proposed method, including parameter estimation, signal-to-noise ratio (SNR) improvement and the calculation efficiency is analyzed. Finally, the simulation and experimental results reveal that the proposed method does possess the capability to improve the performance of detection and recognition of rotor UAV.

The quad tilt rotor (QTR) has the problem of manipulation redundancy due to the helicopter and fixed-wing manipulation mechanisms. Solving the problem of manipulation redundancy and develop an effective manipulation strategy is critical for QTR during conversion flight. A novel manipulation strategy based on states of QTR is proposed in this paper to solve the problem of manipulation redundancy in conversion mode. The longitude is controlled by the tilt angle of nacelle in helicopter mode and the course is controlled by the speed error of propellers in fixed-wing mode. The Active Disturbance Rejection Control (ADRC) is adopt into the flight control law, which can observe and compensate for internal and external disturbance. The simulation and flight test are carried out to verify the proposed manipulation strategy and the results show that the proposed manipulation strategy is effective and reasonable.

In this paper, the flight principle and accurate dynamics of three-rotor unmanned aerial vehicle (UAV) are detailedly analyzed and a nonlinear robust tracking control strategy is proposed considering unknown time-varying external disturbances. Aiming at the tracking control of the typical underactuated system, the dynamic model of the three-rotor UAV is divided into outer-loop position subsystem and inner-loop attitude subsystem. The feedback linearization algorithm is employed to design the outer-loop controller for the trajectory tracking of the UAV. For the inner-loop control of the UAV, the robust integral of the signum of the error (RISE) method is utilized to formulate the robust attitude controller to deal with the external disturbances. The stability of the closed loop system and the asymptotical tracking of the desired trajectory are proved via Lyapunov based stability analysis. Real-time experiments are implemented to validate the performance of the proposed control strategy.

The increasing penetration of renewable energies in the power system is demanding new services from wind farms. In particular, system operators are concerned about system restoration after a black-out and new grid codes are under consideration that demand the participation of wind farms in the restoration process. Black start requires the wind farms to be capable of controlling voltage and frequency in an isolated grid. This paper proposes the use of a novel grid forming control for doubly fed induction generators (DFIG) for restoring the system after a black-out. The proposed grid forming control uses the rotor flux orientation principle, that allows to generate an internal electromotive force for controlling in this way the terminal voltage and frequency. Then, it is demonstrated that the rotor flux magnitude and frequency can be controlled by means of the rotor voltage applied the rotor side converter of the DFIG. The paper also proposes a wind turbine control system for balancing the power demanded by the load at the wind turbine mechanical system. Black start capability of the proposed control system has been validated through a comprehensive simulation. The simulated system consists of a wind farm with two DFIG-based wind turbines connected in parallel to a point of common coupling that supplies an induction motor through a feeder. Also, the synchronization of the isolated system to a main grid has been simulated, demonstrating the ability of the proposed control system for successfully completing the restoration process.

Accurate rotor position estimation plays an important role in the start control for the aircraft three-stage Wound Rotor Synchronous Starter-Generator (WRSSG). In this paper, a novel exciter controller and rotor position estimation method for aircraft WRSSG were proposed. The exciter controller consists of a three-phase full-bridge converter and a full H-bridge converter, and it is used to inject high frequency voltage into the permanent magnet pre-exciter to estimate the rotor position in the starting mode, and regulate the field current of the main exciter to control the output voltage of the main machine in the generation mode. The proposed rotor position estimation method has the advantages of high stability and high estimation accuracy. Simulation analysis verified the feasibility and effectiveness of the proposed exciter controller and rotor position estimation method.

This paper proposes a resolver offset calibration algorithm that can detect offset with high precision just by configuring a very simple experimental environment. This use of a simple experimental environment holds a great advantage for large-capacity permanent magnet synchronous motors (PMSMs) that require substantial resources to configure an experimental environment, such as EV traction motors. The proposed algorithm is designed based on the PMSM voltage equation. The algorithm is first verified for its validity through simulation with Simulink. Subsequently, it is implemented based on the C-language and installed on an inverter for verification experiments. The implemented algorithm is very simple and requires little execution time and memory. The error in the calibrated offset is experimentally found to converge within 3-bits based on 12-bits (the resolution of the commonly used RDC), and the results have very little deviation.

Synchronous Condenser (SC) can provide the dynamic reactive power for the converter station of Ultra High Voltage Direct Current (UHVDC) during the short-circuit fault of the power system. However, the rotor loss and temperature rise restrict the operation of the SC. A key factor that affects the rotor loss distribution and temperature rise is the conductivity of the rotor slot wedges. For a SC with the rotor slot wedges made of aluminum, beryllium bronze and stainless steel, this paper presents the electromagnetic and temperature field calculation of the single-phase short circuit faults and the experimental validation. The influences of different materials of the rotor slot wedges on the rotor loss distribution and temperature rise of the SC are studied. The positions of the highest temperature rise on the rotor are obtained. According to the maximum permissible temperature of rotor, the duration of the single-phase short circuit is obtained under different materials of slot wedge. This study can provide the theoretic basis for improving the operating ability of the SC.

A hysteresis motor is an inherently synchronous motor in which accuracy is more important than efficiency. The rotor is a smooth cylinder type made up of permanent magnet material having high hysteresis loss in its simplest form. We use a hysteresis ring around a non-magnetic material to reduce the rotor's weight, say aluminum. Rotor ring material handles the efficiency of the motor to some extent. This paper involves designing a three-phase hysteresis motor using the scrap material for rotor ring, i.e., hard magnetic material, a composition of aluminum, cast iron, and Nichrome, and provide an alternative to the material currently used for manufacturing hysteresis motor. Further, this paper proposes to reduce the motor's size and improve the hysteresis motor's efficiency.

In an effort to increase the efficiency close to 0.97 for a power factor above 0.7, at maximum 70 tons (250,000USD) active weight (and cost) for 10 MW, 10rpm wind generator, a Ferrite spoke-PM and bonded NdFeB respectively, multi pole rotor, 3 phase radial air gap synchronous generator was designed here, with key FEM validation checks regarding the flux density distribution and torque waveform and L dm , L qm inductances for pure I q field-oriented control (FOC). The rotor was provided with flux barriers in axis q, to further reduce q axis inductance and thus increase power factor. Two variants of rotor core geometry have been considered: one with a single lamination (without and with additional radial magnets) and one with detachable poles with flux barriers; in all, 6 rotor variants. It has been also proved that the generator can survive approx. 2.00 p.u. load without serious PM demagnetization.

Compared with internal-rotor switched reluctance motors (SRMs), external-rotor (ER) SRMs can show different vibration and acoustic noise behavior due to the differences in the designs, e.g. thinner rotor back iron to achieve smaller inertia, and longer stator pole height to improve the electromagnetic performance. This paper presents the considerations in the modeling and analysis of the acoustic noise sources of an ER SRM stator and rotor. The harmonic components of the stator tangential force density and rotor radial force density are analyzed and compared. The vibration modes, the vibration behavior, and acoustic noise of the stator and rotor are also compared. A 12/16 external-rotor SRM designed for a direct-drive E-bike application is used for the modeling, analysis, and experimental validation of vibration and acoustic noise. It is concluded that both the stator tangential vibration and the rotor radial vibration can be sources of the acoustic noise in an ER SRM.

The design, simulation and testing of an impulse magnetizer and the in-situ post-assembly magnetization of a permanent magnet (PM) rotor manufactured by a cold spray additive manufacturing (AM) using the prototyped magnetizer is presented in this paper. A software based finite element simulation is done to obtain the level of magnetization current required. An impulse magnetizer is built for this specification. A 4-pole rotor with cold-sprayed rectangular magnets is magnetized in this work after assembling it in the stator. Various stator terminal connection configurations are analyzed. The machine is magnetized and the back-EMF waveform and the rotor magnetization profile is obtained., IECON 2021: 47th Annual Conference of the IEEE Industrial Electronics Society, October 13-16, 2021, Toronto, ON, Canada

Induction machines are a popular choice for tractive applications due to inherent cost savings and performance benefits driving industry to search for an optimal rotor bar design. Induction machines suffer from low torque densities due to larger size and increased losses incurred in the rotor bars making these the performance objectives to be improved through optimization. Communicating through objective functions (OFs), a performance model to rapidly evaluate design parameters coupled with genetic algorithm (GA) can be used to produce an optimal rotor bar; however, conventional OF modeling may introduce function bias or complex coefficient calculations leading to dominated objectives, stalling and premature convergence leading to an unoptimized solution. In this paper, the rotor bar of a squirrel cage induction machine (SCIM) is modeled by a permeance based equivalent circuit model (ECM) creating a link between the rotor slot geometry and equivalent circuit parameters. The model considering skin and slotting effect as well as slot, zigzag, tooth top and overhang leakage reactance effects coupled with a multi- objective GA through novel hyperbolic tangent based OFs to optimize the rotor bar geometry. The optimal rotor bar shape proposed offers increased output torque and reduced total machine losses resulting in a higher operating efficiency.

In this work, an experimental test rig has been set up to enable the physical implementation of the stator and rotor interturn winding faults on a 5kW wound rotor induction machine (WRIM) that was developed and built in the university laboratory as a scaled-down version of a typical 2.5MW DFIG. To evaluate the performance of the developed test rig, experiments have been carried out by separately implementing the stator interturn short circuit faults (ITSCFs), rotor ITSCFs and a static eccentricity fault on the micromachine and capturing the real-time startup stator and rotor current signals for further analysis in MATLAB to diagnose the presence of these faults during both transient and steady state operating conditions. For fault diagnosis, two analysis techniques have been explored in this work: the conventional motor current signature analysis (MCSA) and the Discrete Wavelet Transform (DWT) analysis. To improve the fault diagnosis process, the Hilbert Transform (HT) technique has been applied on the captured transient stator and rotor current signals to remove the fundamental component that masks the fault-related components due to its higher magnitude. Therefore, the DWT analysis has been applied on the resultant Hilbert modulus of the stator and rotor currents to diagnose the faults under study. Moreover, spectrogram plots of the resultant signals have been used to indicate the evolution of the fault-related frequency components in the resultant Hilbert modulus of the stator and rotor current. The results have demonstrated that the analysis of the rotor current using either the MCSA, DWT or spectrogram technique provides a clearer indication of the presence of the stator ITSCF, rotor ITSCF and static eccentricity fault condition as compared to the analysis of the stator current signal. Therefore, it is concluded that the rotor current is best suited for diagnosing the different faults implemented on the micromachine.

The paper considers a complete magnetic suspension of a small-sized horizontal rotor in passive radial and active axial magnetic bearings. It describes experimental studies of the dynamics of a model rotor in a combined passive-active magnetic suspension. The studies were performed using the developed specialized software and hardware complex for measuring and analyzing the dynamic characteristics of rotors with magnetic suspension systems. Its software includes special algorithms of the mathematical data processing for measuring and evaluating the main parameters of the signals characterizing the vibration displacement of the rotor points. The results are presented in the form of vibrograms of rotor support section motion in the radial direction, spectrograms of these signals and amplitude-frequency characteristics. The work shows how the proposed experimental analysis of the vibration state of a rotor system with magnetic bearings allows modifying the rotor design to reduce the vibration amplitudes at rotation speed values close to the critical ones.

Principal objective of the research paper is to develop and stimulate a Novel Dual Integrated Rotor-Stator System with Double Layered V-Shaped Magnetic Pole Six-Phase Permanent Magnet Synchronous Generator (NDIRSS-PMSG) for tidal energy extraction. The quest for generating electricity from tides using different technologies has resulted in the birth of tidal energy. While not commonly used, tidal energy has the potential to be a future source of power because it is more predictable than wind and sun. A multiphase Permanent Magnet Synchronous Generator (PMSG) is a better option for the aforementioned reason. The double rotor-stator configuration enhances the machine’s voltage regulation, as well as its stability and performance. The novelty of the designed PMSG is hidden in its magnetic pole structure. A double layered V-shaped magnet is inserted into the rotatory portions, which provides a higher flux density and contribute for a reliable operation of the proposed system. To construct the generator optimally and for evaluation, magnetostatic and transient analysis are used. As a result of the study, it can be concluded that the proposed novel system is authentic, robust and efficient.

Currently, wind energy occupies an important position in the world, which leads to a significant increase in the demand for wind turbines. Inexpensive power converters of energy, fast microprocessors, and automatic control of technological processes have made it possible to produce a high-tech wind turbine that can work efficiently in the power system, as well as in isolated remote areas. This article discusses the use of a wind turbine with an asynchronous generator, which has improved the performance of the turbine through mathematical modeling and confirmation of the results by experimental work. Also, a method has been developed to control the rotational speed of a generator with a wound rotor, based on the additional resistance in the rotor circuit and using a voltage rectifier and a chopper. The torque-speed characteristics of the induction generator were obtained for different rotor resistance values and similarly, characteristics of a turbine with a power of 1500 watts were obtained by pitch angle control.

Currently, wind energy occupies an important position in the world, which leads to a significant increase in the demand for wind turbines. Inexpensive power converters of energy, fast microprocessors, and automatic control of technological processes have made it possible to produce a high-tech wind turbine that can work efficiently in the power system, as well as in isolated remote areas. This article discusses the analysis of an asynchronous generator connected to wind turbines, which has improved the performance of the turbine through mathematical modeling and confirmation of the results by experimental work. Also, a method has been eveloped to control the rotational speed of a generator with a wound rotor, based on the additional resistance in the rotor circuit and using a voltage rectifier and a chopper. The torque-speed characteristics of the induction generator were obtained for different rotor resistance values and similarly, characteristics of a turbine with a power of 1500 watts were obtained by pitch angle control.

This paper presents a dq flux-linkage modeling approach and the virtual testing of a wound rotor synchronous machine that assures the propulsion of a battery electrical vehicle. The motor model, organised using Energetic Macroscopic Representation, is constructed based on a series of electromagnetic finite-element analysis defined by various armature and rotor excitation currents. The performances of the dq-model, together with its control and electronic units, are evaluated through virtual tests. Furthermore, the model accuracy is validated by comparing the simulation results with the experimental data obtained from different tests performed on a Renault ZOE Q90 car. Two test scenarios, an urban test and a highway one, are chosen in order to evaluate the precision and the reliability of the developed model under normal and maximum electrical vehicle speed conditions. The combination of dq-modeling and virtual testing represents a way to rapidly develop and validate high performance system models and accelerate time to market.

The analysis of motor currents under starting has proven to be a powerful method for enhancing the reliability of the diagnosis of several electromechanical failures in induction motors. Among other advantages, it enables to avoid false indications of conventional methods and, the same time, it provides a robust diagnosis regardless of the operating conditions or of the constructive characteristics of the machine. In particular, the method has proven its usefulness to detect rotor asymmetries, not only in cage motors (CM) but also in wound rotor induction motors (WRIM), in which this type of faults are more frequent. Nowadays, several research lines are oriented toward studying the extrapolation of this methodology for the detection of other types of faults. The present paper expands the applicability of the method to detect stator asymmetries in WRIM. This is done by using a field motor case, in which the application of the transient-based method enabled to detect the presence of certain levels of asymmetry both in the rotor and in the stator winding. The timely detection of this anomaly, thanks to the application of these methods, enabled to avoid a potential outage of the field WRIM with subsequent catastrophic consequences.

High heat losses are generated in the rotors of Axial-flux Permanent Magnet (AFPM) machines due to their high power density. Therefore, they require intensive cooling to maintain safe continuous and peak power operation. For ventilated-type machines, air cooling is the predominant cooling method that keeps the rotor magnets temperature below critical limits. Integration of air-cooling features such as protruding magnets, rotor vents, and rotor integrated fan blades into machines has been widely investigated. These features improve the overall cooling of the machine and eliminate the reliance on external cooling devices. This study investigates different rotor geometries, including either a single or a combination of the mentioned features, and assesses their thermal performance and cooling efficiency considering associated windage losses. From the simulated cases, it was found that rotors with geometrical features that allow though-flow ventilation to directly cool the magnets are more efficient compared to others that rely on indirect cooling.

In this paper, convolutional neural network (CNN) is used to classificate the rotor blade number of rotor targets micro-motion signal with deep learning’s strong feature extraction ability. Firstly, the scattering point model of the rotor blade echo is used to generate the target echo. Under the condition of different signal-to-noise ratio, time-frequency diagram of the echo with different number of rotor blades is constructed by using short-time Fourier transform, which is used as the test set and training set. Three convolutional neural network models of lenet, alexnet and vggnet are used for training. The performance of the network model is compared, and the recognition performance of the alexnet network model is analyzed under ambiguous, unambiguous and a method of Interpolation to resolve ambiguous. Through experiments, it can be found that the recognition rate of the proposed method can reach 95% under the condition of signal-to-noise ratio of 10dB. It has good recognition performance for classification of rotor blade number, and provides effective data and algorithm support for the rotor target recognition in the future.

The wind field has a great influence on the control stability of Tilt-rotor unmanned aerial vehicle (UAV), especially during the take-off and landing phase. The airspeed of UAV is so small during these phases that it cannot generate stable aerodynamic forces, which will significantly reduce the wind robustness of Tilt-rotor UAV. In this article, the disturbance of wind field is analyzed from two perspectives: the wind field acting on the UAV fuselage, which is regarded as external interference, and the wind acting on the propeller, which is considered as modeling error. After analyzing the interference mechanism of wind field, a generalized extended state observer (GESO) and a $H\infty $ robust control method with mixed sensitivity are proposed, which could empower the Tilt-rotor UAV with good interference suppression ability as well as better performance tracking ability. Finally, the laboratory simulation and flight experiment are studied. The results validate the theory and prove that the proposed method could resist the interference of wind field and shows excellent control effect.

In order to study the aerodynamic characteristics of a Hex-rotor micro aerial vehicle (MAV) with different rotor spacing, both experiments and numerical simulations are performed in this paper. First of all, a series of aerodynamic parameters to characterize the hover performance of the Hex-rotor MAV are analyzed theoretically. Secondly, tests on the Hex-rotor MAV with different rotor spacing ratios ( $i=0.5$ , 0.56, 0.63, 0.71, 0.83, 1.00) is presented in detail. The thrust and power of the Hex-rotor MAV are obtained from the self-designed test platform. In the meanwhile, pressure and velocity distribution of the Hex-rotor MAV are obtained by Computational Fluid Dynamics (CFD) simulation. The results show that the aerodynamic performance of the Hex-rotor MAV is varied with the rotor spacing. Specifically, the rotor interference is inclined to improve the aerodynamic performance of the Hex-rotor MAV with the proper rotor spacing. Owing to the increase of rotor spacing, the interactions between rotors are weakening gradually. In addition, the uniformity of velocity distribution, the stability of downwash distribution and the integrity of vortex are the necessary conditions for a larger thrust of the Hex-rotor MAV. Finally, combined with the test and simulation results, it is also found that there is larger thrust characterized with better aerodynamic performance at $i=0.63$ , which is assumed as the best rotor arrangement of the Hex-rotor MAV. Especially for ${{Re}}=1.16\times 10^{5}$ , the thrust increases by 6.09%, and the hover efficiency increases by about 9.17% in general.

In this study, an analytical technique for the rotor geometry optimization based on lumped magnetic parametric approach is used to design a two-pole, three-phase, 7.5-kW line-start permanent magnet (LSPM) synchronous motor. The permanent magnet shape substantially affects the air-gap flux density distribution, back electromotive force (EMF) as well as the copper loss, which have a great impact on the performance characteristics of the permanent magnet synchronous motors. Principal advantages involve in adjusting the rotor shape are to achieve the effective air-gap flux density and optimize the fundamental component of the back EMF with low harmonic content for minimum ripple torque. Therefore, to enhance the efficiency (η) and power factor, an optimized slot shape considering various design parameters is selected for the permanent magnet of the rotor in the prototype LSPM machine. A linear saturated lumped magnetic parametric model is developed to exhibit magnetic characteristics, and analytical equations are acquired under the open-circuit condition without considering the slotting effect for design simplicity. The influence of design variables on the air-gap flux density distribution and the flux leakage is investigated precisely using an analytical circuit model. A parametric study of the prototype model demonstrates that the steady-state performance of the LSPM motor are significantly influenced by the design variables. The inductance saliency ratio and electromagnetic torque components are carefully analyzed in terms of their effects on the load characteristics of the LSPM motor in order to determine the optimal shape of the PM slots and the magnetic flux barriers. The validity of the proposed method has been checked by evaluating the numerical solution of the analytical model using a two-dimensional finite element method.

Fault diagnosis of rotor systems is important to prevent unexpected failures. Recently, deep learning (DL) methods, such as a convolutional neural network (CNN), have been utilized in many research areas, including fault diagnosis. DL has gained significant attention thanks to its ability to efficiently learn proper features from input data. It is possible to learn enriched hierarchical features by making the DL architectures deeper; therefore, many studies have been conducted to stack the neural networks, which are the basic building blocks of DL, deeper. However, it becomes difficult to comprehensively train neural network architectures as they become deeper, due to problems in the flow of gradient information during the training phase. In this paper, a direct connection based CNN (DC-CNN) method is proposed to significantly improve training efficiency and diagnosis performance. DC-CNN connects feature maps of different layers within a CNN to improve the gradient information flow over the layers. These additional connections, however, can increase the number of trainable parameters within the network. To prevent problems that might be caused by an increased number of parameters, dimension reduction modules are also developed. Moreover, to consider the anisotropic characteristics inherent in rotor systems, the vibration images containing both spatial and temporal information are generated and utilized. The effectiveness of DC-CNN is validated using experimental data from a rotor testbed. The experimental results indicate that the proposed method outperforms other conventional approaches with a smaller number of parameters. Also, visualizations of the learned features indicate that the proposed method can learn much more effective and significant features. Furthermore, the proposed method outperforms other approaches under conditions of insufficient or noisy data.

In this paper, a salient-pole permanent magnet synchronous machine (SPPMSM) is introduced to high-speed trains, taking advantage of its high utilization of the reluctance torque from the unbalanced reactance. Torque characteristics, such as average torque and torque ripple, are rather important and should be carefully concerned during the optimal design of the SPPMSM. Both the eccentric air-gap and the advanced step-skewed rotor (ASSR) design are developed and implemented to reduce the torque ripple for comfort and safety issues. Compared to the conventional step-skewed rotor (CSSR), the ASSR takes advantage of the high utilization of permanent magnets (PMs), which are axial continuous assembled, and the easier manufacture with a single rotor lamination model, which is asymmetrically designed with pole shoes skewed by individual skewing angles. No skewing arrangement is applied to the rotor yoke and the PM chambers. The impacts of the eccentric air-gap and the ASSR on the torque characteristics are comprehensively investigated by finite element analysis. The results show that the proposed technique can significantly reduce the torque ripple with a slight expense of the average torque. Based on the optimal eccentric design, experiments of the SPPMSM with the non-skewed rotor, CSSR, and ASSR under various conditions are carried out to validate the estimated results.

The phenomenon of third-order harmonics in synchronous reluctance motors (SynRMs) with an axially laminated anisotropic (ALA) rotor is studied. The paper shows that a specific rotor geometry can distort the air-gap flux density and induce third-order currents in the stator winding if it is delta connected. The third-order currents in different phases have the same phase shift angle and cannot, therefore, produce a rotating air-gap flux. Instead, they produce an air-gap flux that pulsates in time, and thus, causes eddy current losses in the rotor conducting parts. The phenomenon was described and proven with finite element simulation (FEM) of a 12 kW high-speed ALASynRM. The research underlines the importance of considering the third harmonic phenomenon in the design of a two-pole ALASynRM intended for high-speed applications, where a specific rotor geometry with a wide magnetically conducting middle layer is required.

The necessity to align the rotor with the d-q magnetic axes is the main obstacle for the wide application of synchronous machine standstill parameter tests, especially for the high-power units. This paper presents an arbitrary rotor position parameter estimation method for standstill time-domain response (SSTRs) tests and applied on a 300 MVar, 20 kV large synchronous condenser, a DC step voltage signal is selected as the input signal. Firstly, a frequency-domain Dalton-Cameron transformation is demonstrated and used to simultaneously obtain both axes' operational inductances in an arbitrary rotor position, thus eliminating the need for the rotor prepositioning process. Then, a novel analytical parameter estimation method combined with an I/T transformation is proposed, all the parameters of both axes are determined without extra tests, the mutual leakage flux between the field winding and the d-axis damper winding is also taken in account. To validate the proposed method, this test is carried out and its parameter estimation results are compared against that of the three-phase sudden short-circuit test and the traditional SSTR test. Estimation results are given in the form of I-type and T-type circuits, the maximum relative error no more than 6% and 10%, respectively.

The brushless doubly fed generator (BDFG) has been a research focus of wind power generation due to its inherent promising features. Although it is important to consider the effect of losses on the design and analysis of the BDFG, there are a few related comprehensive studies. Moreover, a hybrid rotor is studied to improve the performance of BDFG, which brings greater challenges to the loss calculation. The aim of this paper is to propose the accuracy calculation methods of core loss and copper loss for the studied BDFG with hybrid rotor. The core loss calculation model which taken the influence of harmonics, alternating magnetization, rotating magnetization and two-dimensional magnetic property of material into account is proposed based on the analysis of the magnetic field characteristics. In order to calculate the copper loss considering the skin effect, the inductive current of the assisted cage bars which is difficult to obtain directly is calculated. The accuracy and correctness of the proposed approaches and models are validated by experimental results from a 25kW prototype BDFG with hybrid rotor. In addition, the proposed loss calculation method, especially the core loss calculation model, is also applicable to BDFG with other rotor structure which is operated by the magnetic field modulation mechanism.

Leakage magnetic field from the rotor end windings affects obviously the electromagnetic losses and temperature of end components in the turbine generator end zone with magnetic screen. As the capacity of turbine generator increases, this effect of rotor end windings has become more prominent. To investigate influence of the extension length of rotor end windings on the electromagnetic and thermal fields in the turbine generator end zone with magnetic screen, three-dimensional transient electromagnetic field model of 1250 MW turbine generator end zone is given. Leakage magnetic field and losses of end components are compared and studied in the end zone under the different extension lengths of rotor end windings. Based on the calculation results of electromagnetic losses (heat sources) and flow network (boundary conditions), three-dimensional fluid-thermal coupling field is calculated in the turbine generator end zone with magnetic screen. Distribution of complex fluid velocity in the end zone is obtained. Influence of the different extension lengths of rotor end windings on the stator-end copper coil, screen plate, finger plate, press plate, magnetic screen, and stator end core is researched in the turbine generator end zone. The accuracy of calculation results is validated by experimental values.

Due to poor heat dissipation of rotor, especially in flywheel energy storage system (FESS) for uninterruptible power supply (UPS), there is a higher risk of irreversible demagnetization by rotor temperature rising. Irreversible demagnetization of permanent magnets by rotor loss always is a critical problem of high-speed permanent magnet synchronous machine (PMSM). The stabilization and efficiency can be increased by reduction of rotor loss. By Finite Element Method simulations with experiment date, the rotor temperature rising of the prototype PMSM mainly comes from rotor loss induced by time harmonic. The distribution and components of prototype rotor loss are given. Rotor loss is analyzed by equivalent magnetic circuit with considering time harmonic magnetomotive force in this paper. According to analysis of rotor loss, this paper presents a method to reduce rotor loss without changing stator structure and winding current. This rotor structure optimization will not affect output performance of PMSM. The method has been proved to be available by the no-load experiment finally. It can greatly reduce the rotor loss in no-load operation when PMSM is driven in high-speed operation zone.

This study proposes a new topology for brushless operation of a wound rotor synchronous machine (WRSM) employing a stator harmonic winding. It is based on generating an additional six-pole magneto-motive force component without the use of an inverter. In this topology, six thyristor switches are used to create harmonic currents for brushless operation of the machine. The usage of stator harmonic winding has the advantage of configuring the winding for six poles or any other combination based on the output requirement. In the proposed topology, a six-pole winding arrangement is used to generate a six-pole air-gap flux component aimed at rotor excitation for brushless operation. On the rotor side, two windings, namely rotor harmonic winding (to intercept the air-gap harmonic flux) and field winding, along with a diode rectifier are mounted. 2-D finite element analyses and experiments were carried out to analyze the brushless operation of the WRSM.