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The fatigue damage and power generation of wind farms (WFs) is related to their service lifetime and economic benefits. In this paper, an asynchronous distributed optimal wake control (OWC) scheme is proposed to suppress fatigue load and increase power extraction in doubly-fed induction generator (DFIG)-based wind farm (WF). To improve control flexibility, the generator torque and pitch angle of a wind turbine (WT) is simultaneously controlled. Then, considering the influence of wake effect, the wind speed sensitivity is used to combine with the states of WTs for formulating the model predictive control (MPC)-based optimal control objectives. To deal with the higher computational complexity of the aerodynamic interactions efficiently, an asynchronous distributed alternating direction method of multipliers (AD-ADMM) is designed for the control system. A layout of a 3 × 5 wake WF is considered in the case studies to validate the outstanding performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

• A novel WT-ESS control model is proposed for WF. The upgrade WT-ESS control model can simultaneously control the generator torque, pitch angle, and ESSs output to improve the performance of the WT operation in a wider range. The virtual mechanical power control is proposed to regulate the ESSs output for clarifying the power interactions among WTs sand ESSs. • An OPC scheme is proposed for a novel WT-ESS control model to suppress the variations of T s , F t , and M f more flexibly and effectively. With the upgraded WT-ESS topology, the multiple state variables are adopted to formulate the MPC-based optimization objectives. • An AD-ADMM is designed for the OPC scheme to reduce the impact of communication delay for improving the time efficiency. At each iteration, the central controller can update a part of active global variables within boundary conditions based on the asynchronous update manner. It can enhance the system robustness by tolerating the different time-delay information. The convergence analysis has been done to ensure the stability of the proposed algorithm. An asynchronous distributed optimal power control (OPC) scheme is proposed to minimize fatigue load in the wind farms (WFs) in this paper. To better satisfy the grid code, each wind turbine (WT) in the scheme is equipped with an energy storage system (ESS) at the DC link of the WT converter. Based on the WT topology, a WT-ESS control model is established, thus developing an OPC scheme to control the generator torque, pitch angle, and ESS output simultaneously for reducing fatigue load. By formulating the model predicted control (MPC)-based optimal problems, the virtual mechanical power control is proposed to regulate the ESSs output for clarifying the power interactions among WTs and ESSs. In order to achieve more effective control of the above three parameters among multiple WTs-ESSs, an asynchronous distributed alternating direction method of multipliers (AD-ADMM) is developed to simultaneously minimize the variations of thrust force, shaft torque, and flapping moment load of the WTs in a wider range. Considering the impact of communication delays, the proposed AD-ADMM algorithm has the higher time efficiency and system robustness. The convergence of the proposed AD-ADMM algorithm is analyzed, and several cases are used to validate the performance of the OPC scheme. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

In order to resolve the starting problem for position sensorless interior permanent magnet synchronous motor, an improved initial rotor position estimation method based on square-wave signal injection is presented in this paper. Instead of the conventional sinusoidal voltage injection, square-wave voltage signals are injected into stator windings to obtain magnet pole position. On the basis of saturation and saliency principle, the voltage pulse injection method was adopted to identify the magnet polarity. Detecting the magnet pole position by using the square-wave voltage injection, the error signal can be calculated without low-pass filters and time delays. The proposed method is verified via a 1.5 kW interior permanent magnet synchronous motor drive platform. [ABSTRACT FROM AUTHOR]

This paper introduces a Permanent Magnet (PM) synchronous torque motor with an external rotor. Firstly, the basic structural features of this motor are described. Novel spiral magnetic poles and axial-cooling structure is designed to increase the energy density and make the motor compact. The width, thickness and spiral angle of the poles are determined by magnetic computing, in order to ensure the wave of gap magnetic density is sine. To provide an effect cooling structure, the motor side hoods are designed as centrifugal fans to cool the coil down. Multiple air channels are cut in the stator core to increase the ventilation of air. The spiral poles can also constitute spiral air channels and produces wind to cool the magnets. It is possible to choose high electromagnetic load to gain high energy density based on a good cooling effect. Next, the method is determined and the program is compiled for electromagnetic computing. The finite element analysis on magnetic field is conducted by applying ANSYS. Finally, according to the optimization of the structure, a 3 kW prototype is fabricated. The no-load and load experiments are carried out to proof the performance of the motor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cryogenic motors, as one of the key components of submerged liquefied natural gas (LNG) pumps, have gradually attracted the attention of researchers with the vigorous development of LNG industry. In this paper, the design, performance analysis, and experiment of a submerged cryogenic permanent magnet synchronous motor (PMSM) are investigated. Considering the effect of cryogenic temperature on material properties, the cryogenic temperature design method is proposed, and on this basis, an 18.5-kW cryogenic PMSM is designed. Then, the finite-element method is used to analyze the motor performance. The analysis is focused on the comparison of electromagnetic characteristics at two different cryogenic temperatures. A multiphysical field model coupling with electromagnetic, fluid, thermal, and stress is established and simulated, and the analysis results proved the rationality of the design. Finally, a prototype was fabricated and tested, providing measurement results that show a stable operation of the motor, which validated the theoretical design and analysis. [ABSTRACT FROM AUTHOR]

This paper presents the design of cryogenic permanent magnet synchronous motor (C-PMSM) for submerged liquefied natural gas (LNG) pump. The motor is submerged in LNG with a cryogenic temperature (CT) of −161 °C, and its magnetic and electric characteristics differ greatly from that of the motor at room temperature (RT). So it is necessary to redesign according to the result of conventional design, considering the changes of materials under the cryogenic environment. The operating characteristics of the C-PMSM are investigated, and the redesign method is discussed. Finite-element method is used to analyze the motor performance. A prototype is fabricated and tested to verify the rationality of the design. [ABSTRACT FROM AUTHOR]

In this paper, a new modular multi-stage axial flux permanent magnet synchronous motor is proposed for the traction motor applications, which has the features of slotted north–south-pole topology, segmented and yokeless stator, ellipsoidal similar Somaloy teeth, and flexible power circuits. To minimize the cogging torque, a cost-effective asymmetrical bidirectional magnet skewing (ABMS) technique is adopted in the motor. Various ABMS combinations are studied with different skew angles and cross positions. Both the theoretical analysis and finite-element method (FEM) illustrate that ABMS has both the skewing and phase shifting effects. Based on a 2 kW-1000 r/min, 10-pole 12-open-slot prototype, the experiments are developed. The results measured by experiments agree well with the ones predicated by 3-D FEM, which verifies the conclusions and design. [ABSTRACT FROM PUBLISHER]

The precise estimation of position is an essential concern for the control of a switched reluctance motor (SRM). Given the prominent role of position, the promising sensorless control approach for an SRM drive should be capable of providing accurate position. An inductance-based approach has been widely applied in the position estimation. However, the estimated accuracy suffers from the magnetic saturation effect, resulting in the poor performance of sensorless operation. This paper presents a reversible synchronization of commutation with the corresponding rotor position for SRM. With the consideration of magnetic saturation, the proposed approach is taken as a suitable candidate and plays an essential role in accommodating the requirement of optimal control. The relationship between a typical inductance position and magnetic circuit saturation is investigated. The instant of the intersections is sensed by comparing the instantaneous inductance of adjacent phases. Thus, the predicted position is obtained with the information of the special point and the calculated average speed. Compared with other existing methods, the proposed approach has the certain advantages, such as the ability to update the estimated speed and position six times per electrical period, which guarantees the estimated accuracy. The proposed approach is also valid even when the motor is operated at an acceleration state and heavy load operation. In addition, the requirement of the educated inductance structure is not unnecessary, less memory space is needed in the chip, and the accumulated error is eliminated. The simulation and experimental findings demonstrate the feasibility and practicality of the proposed position estimation approach with carrying out the inertial operation, load mutation, and high-speed test. [ABSTRACT FROM AUTHOR]

The high current ripple and torque ripple are the main drawbacks of the switched reluctance motor (SRM) since the nonlinearity and double saliency, which limits its applications. In order to eliminate the current variation and torque ripple, an optimized pulse width modulation (PWM) control is presented in this paper. The voltage ratio duty is able to be predicted precisely according to the information of the motor running parameter. Based on torque sharing functions (TSFs), the current profile is pre-computed and four regions are defined according to the reference current profiles. The three modes, excitation, demagnetization and freewheeling, are flexibly chosen according to the characteristic of the current profile. It is indicated that it is better than that of conventional PWM modulation in terms of current ripple and the current tracing performance is improved without increasing the switching frequency or changing the hysteresis band. The current ripple is defined as the peak-to-peak value dividing the average value and it is reduced by 40%. A comparison in terms of the torque ripple and copper loss is also carried out: the torque ripple is significantly reduced via the proposed scheme under both magnetic linear and saturation conditions. The torque ripple and copper loss are reduced by about 70% and 12%, respectively. The validity and effectiveness of the proposed control strategy is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

The general method to suppress the axial force of the permanent magnet synchronous motor (PMSM) direct-drive turbine is to increase the number of balance devices, such as balance disks and special bearings, to counteract its influence, but this also leads to complex system structure and higher mechanical losses. Aiming to solve the above issue, this paper presents a novel PMSM structure with a conical-rotor (CR). Due to its adaptive equilibrium of axial force and simple structure of rotor with turbine, the CR-PMSM can help improve the system efficiency. Both surface-type and interior-type motors are analyzed, and the axial magnetic force of CR-PMSM is studied in detail. The 3-D finite-element method (FEM) is used to model and simulate the machine, and the magnetic-field distribution, axial magnetic force and driving performance are obtained. Also, the control rule of d-axis current is analyzed to achieve the adaptive equilibrium of axial force. A 2.0 kW, 6000 r/min prototype motor is fabricated and tested to validate the theory. [ABSTRACT FROM AUTHOR]