Optimal Rotor Research Articles

Optimal rotor design of novel outer rotor reluctance synchronous machine

This paper presents the optimal design and performance analysis of a novel synchronous reluctance motor with outer rotor for determination of the effect of the rotor pole shape on the machine’s performances. The investigation has been made in order to find the possible ways to improve the power factor with refining the rotor geometry without using permanent magnets. Starting from the design of the machine with classical rotor pole that was implemented in FLUX 2D, a finite element analysis software coupled with an optimal design procedure implemented in MATLAB was performed. The purpose of this complex co-simulation was to obtain several outer rotor structures that increase the performances of the machine: saliency ratio, power factor and torque density. For the proposed structures, especially for the modular topology, the obtained results of saliency and power factor have never been presented in the past literature. Hence, this represents a useful starting point for the following analysis of outer rotor synchronous reluctance machines with improved power factor.

Comparative Study of Wound-Field Flux-Switching Machines and Switched Reluctance Machines

In this paper, comparisons between two permanent-magnet-free machines, namely a wound-field flux-switching machine (WFFSM) and a switched reluctance machine (SRM), are carried out. The topologies and operation principles of the WFFSM are illustrated first. Then, the effects of rotor skewing angle on static characteristics, e.g., open-circuit phase flux-linkage and back electromotive force due to field currents, electromagnetic torque, and torque ripple, have been investigated in depth by finite-element analysis (FEA). Consequently, the optimal rotor skewing angle is determined. After that, comparisons at the rated speed 1500 r/min and at the rated RMS current density of 5 A/mm2 among the 6-armature-slots/5-rotor-poles (6/5) straight- and skewed-WFFSMs, and two representative SRMs, namely conventional 12/8 SRM and the short-flux 12/10 SRM with the same stator outer diameter and stack length are conducted in terms of phase flux-linkage, inductance, and torque performance. The results indicate that for these two PM-free machines, at the rated speed and the rated RMS current density, the skewed-rotor WFFSM exhibits considerably larger torque capacity, much smaller torque ripple, stronger saturation withstand ability. In addition, the experiments of the skewed-WFFSM and the 12/8 SRM prototypes working at the mechanical character curve are conducted. The experimental results present that the power factor of the WFFSM is much higher and the efficiency is slightly lower than that of the 12/8 SRM.

Optimal segmented rotor design for the embedded electrical machine for the more electric aircraft

This study presents the design and analysis of the segmented rotor design for an electrical machine embedded onto the more electric aircraft gas turbine engine shaft. The high-speed operational environment imposes high stress levels due to centrifugal forces; thus, the feasibility of this segmented rotor topology for such application is explored and a suitable design is proposed to overcome mechanical stresses. Finite element structural analysis was performed to compare the mechanical behaviour of a different rotor segment fixing structure and the proposed design. Also, electromagnetic analysis is carried out on a high-speed switched reluctance machine to study the impact of a new design on machine electromagnetic performance.

Variable rotor speed and active blade twist for civil rotorcraft: Optimum scheduling, mission analysis, and environmental impact

The concepts of variable rotor speed and active blade twist constitute promising technologies in terms of improving the operational performance and environmental impact of rotorcraft. Modern civil helicopters typically operate using nearly constant main and tail rotor speeds throughout their operational envelope. However, previous research has shown that decreasing the main rotor speed within salient points of the operational envelope can result in a notable reduction of rotor power requirement, resulting in more efficient aircraft. This work aims to develop an integrated approach able to evaluate the potential improvements in fuel economy and environmental impact through optimum implementation and scheduling of variable rotor speed combined with active blade twist. A comprehensive rotorcraft analysis method is utilized, comprising models applicable to flight dynamics, rotor blade aeroelasticity, engine performance, gaseous emission prediction, and flight path analysis. A holistic optimization strategy comprising methods for Design of Experiment (DOE), Gaussian Process-based (GP) surrogate-modeling, and genetic optimization is developed. The combined framework is used to predict globally optimum variable rotor speed and active blade twist schedules resulting in minimum fuel consumption. The overall method is employed to assess the impact of the investigated concepts for a representative Twin-Engine Light (TEL) helicopter operating within realistic mission scenarios. The optimizations carried out suggest that variable rotor speed combined with active blade twist may result in mission fuel consumption and nitrogen oxides emission (NOx) reductions of the order of 5% and 8%, relative to the fixed rotor speed case. The developed method constitutes an enabling technology for the investigation of novel technologies at multiple levels of assessment including aircraft-engine and mission levels.

Optimal energy saving of doubly fed induction motor based on scalar rotor voltage control and water cycle algorithm

PurposeThis paper aims to present an optimal variable speed drive of a doubly fed induction motor (DFIM) with minimum losses and reduced inverter capacity. The operation with minimum losses ensures that the DFIM develops the required load torque at desired speed with maximum energy saving. Moreover, the control of rotor voltage ensures the reduced inverter capacity. The water cycle algorithm (WCA) as one of meta-heuristic optimization techniques is used to estimate the optimal rotor voltages to drive the DFIM with minimum losses. The results of WCA are confirmed with other well-known and reliable optimization method such as particle swarm optimization along with classical method.Design/methodology/approachThe DFIM is an efficient alternative solution of synchronous motor (SM) because of its speed is synchronized with both stator and rotor frequencies regardless the load torque. As a result, the speed of variable speed drive associated with DFIM can be controlled through a rotor inverter with reduced capacity rather than SM. The output voltage of rotor inverter is controlled to develop the demanded output power with minimum motor losses.FindingsA complete DFIM drive model is developed under MATLAB/SIMULINK environment using d-q dynamic model to verify the strength and significance of the proposed controller. An experimental setup using a 300 W three-phase wound rotor induction motor is established to validate the mathematical models and theoretical results. The motor performances with proposed rotor voltage control (minimum losses) are compared with conventional method of constant voltage to frequency ratio (V/f constant). It is found that the proposed WCA based on controller achieves significant reductions in motor losses, input power and rotor inverter power.Originality/valueThe paper presents an efficient method to maximize the energy saving of DFIM with a reduced inverter capacity using WCA.

The structural optimum design of laminated slender beam section with arbitrary material distribution using a genetic algorithm

In this paper, a study on optimum design methodology of a section structure of a composite material rotor blade using genetic algorithm is conducted, in order to calculate repetitive optimum design, analysis of strength, fatigue and vibration on blade section. In the analysis, the minimum mass of the rotor blade was defined as objective function; stress damage index, center of mass on blade section and fatigue life of blade were set as constraints. By applying genetic algorithm, laminate angle and thickness of skin, thickness, location and width of torsion box were established as design variables; the optimum design methodology on section structure of the composite material rotor blade was validated. The integrated design program of the section structure of the composite material rotor blade based on this study deals with designing the optimal rotor blade section which meets the design load and constraints given by the random position of rotor blade. By using blade’s section design variables derived from this, it can be facilitated for basic information on detailed design of rotor blade.

Analytical Power Limits Curves of High-Speed Synchronous Reluctance Machines

The aim of this paper is to tackle the design of synchronous reluctance machines with transverse laminated rotor for high-speed applications by means of an analytical model. In high-speed applications, the mechanical design greatly affects the motor performance in terms of torque density and power factor. In fact, as the rated speed increases, the radial ribs thicknesses increase as well to ensure the rotor structural integrity against the centrifugal force. This increases the quadrature flux and, therefore, the rotor anisotropy gets worse. Hence, the optimal rotor design is the result of a compromise between mechanical and magnetic aspects. The purpose of this paper is twofold: First, to develop an analytical model that links the maximum average torque to the rated speed, and second, to determine the maximum power that can be generated by a specific rotor geometry. The analytical approach allows a fast motor design and analysis so that a rapid extrapolation of the results to different machine size is possible. Finite element analysis is used only to validate the final results.

Optimal control strategy of an induction motor for loss minimization using Pontryaguin principle

This paper presents a new design of loss-minimization optimization control for Induction Machine (IM) drives. It describes a closed-loop optimal control law and exploits the Pontryagin principle to get optimal energy consumption. This proposal is based on the Optimal Control Problem (OCP) which focuses on minimizing a cost function given as an integral of a weighted sum of the mechanical power, copper losses and magnetic power of the IM. In order to minimize the IM energy consumption, we consider a normalized cost function with respect to the optimization finite-interval [0,T]. This functional is subjected to dynamic constraints which are developed from a reduced IM model. The system depends on two state variables: the rotor flux and the motor speed. The proposed method provides an optimal rotor flux that performs the minimal energy consumption of an IM along a given torque and velocity. This OCP conducts to a system of combined nonlinear differential equations of state and co-state variables. Long and hard developments lead to many calculus steps. Finally, an optimal time-varying rotor flux is successfully turned out. This OCP satisfies also abrupt torque conditions and can cover dynamic operations when the proposed solution fulfills some criteria of sub-optimality. The validity of the suggested optimal control design is tested via simulation and then via experimental results by comparing a dynamic control law using the proposed optimal rotor flux trajectory with a conventional control utilizing the rated flux value.

Optimization of sensorless field-oriented control of an induction motor taking into account of magnetic saturation

This work deals with the optimization of sensorless field-oriented control of an induction motor taking into account of magnetic saturation effects. We propose a double optimization (in the point of view of dynamic and energetic performances) of sensorless field-oriented control of induction motor. This control is associated to a Luenberger type interconnected observers. Particle swarm optimization algorithm is used notably to determine the optimal gains of the observers as well as the optimal parameters of the regulators. This algorithm guarantees the stability and the global convergence of the system. The sensorless control takes into account all operating range of the machine (very low speed, low speed, high speed with or without load torque). Regarding the energetic optimization, the reference of the rotor flux is generated using another developed algorithm that permits us to dynamically determine the optimal rotor flux for each given value of motor load and speed. Numerical simulations are carried out each time to confirm theoretical predictions.

Communications and Control for Wireless Drone-Based Antenna Array

In this paper, the effective use of multiple quadrotor drones as an aerial antenna array that provides wireless service to ground users is investigated. In particular, under the goal of minimizing the airborne service time needed for communicating with ground users, a novel framework for deploying and operating a drone-based antenna array system whose elements are single-antenna drones is proposed. In the considered model, the service time is minimized by minimizing the wireless transmission time as well as the control time that is needed for movement and stabilization of the drones. To minimize the transmission time, first, the antenna array gain is maximized by optimizing the drone spacing within the array. In this case, using perturbation techniques, the drone spacing optimization problem is addressed by solving successive, perturbed convex optimization problems. Then, according to the location of each ground user, the optimal locations of the drones around the array’s center are derived such that the transmission time for the user is minimized. Given the determined optimal locations of drones, the drones must spend a control time to adjust their positions dynamically so as to serve multiple users. To minimize this control time of the quadrotor drones, the speed of rotors is optimally adjusted based on both the destinations of the drones and external forces (e.g., wind and gravity). In particular, using bang–bang control theory, the optimal rotors’ speeds as well as the minimum control time are derived in closed-form. Simulation results show that the proposed approach can significantly reduce the service time to ground users compared with a fixed-array case in which the same number of drones form a fixed uniform antenna array. The results also show that, in comparison with the fixed-array case, the network’s spectral efficiency can be improved by 32% while leveraging the drone antenna array system. Finally, the results reveal an inherent tradeoff between the control time and transmission time while varying the number of drones in the array.

A design methodology for quiet and long endurance MAV rotors

Over the last 10 years, the use of micro air vehicles has rapidly covered a broad range of civilian and military applications. While most missions require optimizing the endurance, a growing number of applications also require acoustic covertness. For rotorcraft micro air vehicles, combining endurance and covertness heavily relies on the capability to design new propulsion systems. The present paper aims at describing a complete methodology for designing quiet and efficient micro air vehicle rotors, ranging from preliminary aerodynamic prediction to aeroacoustic optimization to experimental validation. The present approach is suitable for engineering purposes and can be applied to any multirotor micro air vehicle. A fast-response and reliable aerodynamic design method based on the blade-element momentum theory has been used and coupled with an extended acoustic model based on the Ffowcs Williams and Hawkings equation as well as analytical formulations for broadband noise. The aerodynamic and acoustic solvers have been coupled within an optimization tool. Key design parameters include the number of blades, twist and chord distribution along the blade, as well as the choice of an optimal airfoil. An experimental test bench suitable for non-anechoic environment has been developed in order to assess the benefit of the new rotor designs. Optimal rotors can maintain high aerodynamic efficiency and low acoustic signature with noise reductions in the order of 10 dB(A).

Design & Performance Prediction of Integrated Vertical Axis Wind Turbine

The main propose of this paper is extracting the maximum power from low speed wind turbine. The power generated is directly proportionate to the wind speed obtainable. The maximum power can be obtained by tracking the optimal rotor speed. There are two main types of wind turbine, first one is horizontal axis and second one is vertical axis wind turbine reliant on the positioning of the turbine rotor and its generator. The primary objective of this research was to design and modelling of a small-scale integrated VAWT. Design the combination of Darrius and savonius type VAWT i.e. integrated VAWT. A graphical user interface is generated for a generic model of integrated vertical axis wind turbine that is used to determine its parameters. The aims were to analyze the turbine blade shapes, develop to establish the techno economic performance of the new hybrid VAWT shape design.

A Variable Droop Frequency Control Strategy for Wind Farms that Considers Optimal Rotor Kinetic Energy

A variable droop control strategy for wind farms (WFs) that considers optimal rotor kinetic energy (RKE) is presented in this paper. The process for the control strategy is as follows. First, an optimized scheduling reserve mode (OSRM) is executed by the WF control center (WFCC) according to the deloaded rate orders issued by the dispatching center. Through coordinated optimization control for over-speed control and pitch angle control, more available RKE can be stored in each wind turbine (WT) under the OSRM than can be stored in conventional over-speed reserve mode (CORM). Second, the optimization results will be sent to a variable droop coefficient set module for each WT by the WFCC. Then, the sum of the available RKE capacity and the mechanical load-shedding capacity (the wind power curtailment) of each WT can be computed in real-time and used as a practical spinning reserve capacity to adjust the droop coefficient. In this way, the optimized available RKE stored in the WT under the OSRM can be fully released to participate in the droop frequency control. Finally, simulations are performed in PSCAD/EMTDC to verify the proposed variable droop frequency control strategy for WFs. The simulation results indicate that the capability of the primary frequency regulation would be further improved, especially for low or medium wind speeds.

An improved robust MPPT control for variable speed wind turbine without mechanical sensor: Exprimental evaluation

This paper presents a robust sensorless control scheme of permanent magnet synchronous generators (PMSG) wind turbine with two full-scale controllable three phase converter connected to the grid. The main aim is to drive wind turbine at an optimal rotor speed in order to perform maximum power point tracking (MPPT) control of the wind generation system. The proposed strategy combine a nonlinear backstepping control of the PMSG which is based on both feedback laws and Lyapunov theory, and a non-linear sliding mode observer(SMO) to estimate the PMSG rotor position and to perform a sensorless control. The PMSG wind turbine is integrated to the grid through a three phase inverter which is controlled with classical proportional integral (PI) to control the active and reactive power. The proposed method was successfully tested with both simulation and experimental setup using MATLAB and a dSPACE 1104 platform. The obtained simulation and experimental results show clearly the accuracy and the effectiveness of the proposed method.

Determination of an Optimum Fictitious Air Gap and Rotor Disk Thickness for a Coreless AFPMM

Determination of an Optimum Fictitious Air Gap and Rotor Disk Thickness for a Coreless AFPMM

Tuning turbine rotor design for very large wind farms

A new theoretical method is presented for future multi-scale aerodynamic optimization of very large wind farms. The new method combines a recent two-scale coupled momentum analysis of ideal wind turbine arrays with the classical blade-element-momentum (BEM) theory for turbine rotor design, making it possible to explore some potentially important relationships between the design of rotors and their performance in a very large wind farm. The details of the original two-scale momentum model are described first, followed by the new coupling procedure with the classical BEM theory and some example solutions. The example solutions, obtained using a simplified but still realistic NREL S809 aerofoil performance curve, illustrate how the aerodynamically optimal rotor design may change depending on the farm density. It is also shown that the peak power of the rotors designed optimally for a given farm (i.e. ‘tuned' rotors) could be noticeably higher than that of the rotors designed for a different farm (i.e. ‘untuned' rotors) even if the blade pitch angle is allowed to be adjusted optimally during the operation. The results presented are for ideal very large wind farms and a possible future extension of the present work for real large wind farms is also discussed briefly.

Optimal Rotor Fault Detection in Induction Motor Using Particle-Swarm Optimization Optimized Neural Network

This study examined and presents an effective method for detection of failure of conductor bars in the winding of rotor of induction motor in low load conditions using neural networks of radial-base functions. The proposed method used Hilbert method to obtain the stator current signal push. The frequency and signal amplitude of the push stator were used as the input of the neural network and the network outputs were rotor fault state, and the number of conductive bars with broken fault. Moreover, particle-swarm optimization algorithm was used to determine the optimal network weights and neuron penetration radius in the neural network. The results obtained from the proposed method showed the optimal and efficient performance of the method in detecting conductive bars broken fault in induction motor in low load conditions.

Optimal Power Reserve of a Wind Turbine System Participating in Primary Frequency Control

Participation of a wind turbine (WT) in primary frequency control (PFC) requires reserving some active power. The reserved power can be used to support the grid frequency. To maintain the required amount of reserve power, the WT is de-loaded to operate under its maximum power. The objective of this article is to design a control method for a WT system to maintain the reserved power of the WT, by controlling both pitch angle and rotor speed simultaneously in order to optimize the operation of the WT system. The pitch angle is obtained such that the stator current of the permanent magnet synchronous generator (PMSG) is reduced. Therefore, the resistive losses in the machine and the conduction losses of the converter are minimized. To avoid an excessive number of pitch motor operations, the wind forecast is implemented in order to predict consistent pitch angle valid for longer timeframe. Then, the selected pitch angle and the known curtailed power are used to find the optimal rotor speed by applying a nonlinear equation solver. To validate the proposed de-loading approach and control method, a detailed WT system is modeled in Matlab/Simulink (The Mathworks, Natick, MA, USA, 2017). Then, the proposed control scheme is validated using hardware-in-the-loop and real time simulation built in Opal-RT (10.4.14, Opal-RT Inc., Montreal, PQ, Canada).

Optimal Design of Rated Wind Speed and Rotor Radius to Minimizing the Cost of Energy for Offshore Wind Turbines

As onshore wind energy has depleted, the utilization of offshore wind energy has gradually played an important role in globally meeting growing green energy demands. However, the cost of energy (COE) for offshore wind energy is very high compared to the onshore one. To minimize the COE, implementing optimal design of offshore turbines is an effective way, but the relevant studies are lacking. This study proposes a method to minimize the COE of offshore wind turbines, in which two design parameters, including the rated wind speed and rotor radius are optimally designed. Through this study, the relation among the COE and the two design parameters is explored. To this end, based on the power-coefficient power curve model, the annual energy production (AEP) model is designed as a function of the rated wind speed and the Weibull distribution parameters. On the other hand, the detailed cost model of offshore turbines developed by the National Renewable Energy Laboratory is formulated as a function of the rated wind speed and the rotor radius. Then, the COE is formulated as the ratio of the total cost and the AEP. Following that, an iterative method is proposed to search the minimal COE which corresponds to the optimal rated wind speed and rotor radius. Finally, the proposed method has been applied to the wind classes of USA, and some useful findings have been obtained.

A comparative study between optimal metal and composite rotors for flywheel energy storage systems

Most recent research on flywheel rotors has focused on high-speed composite rotors as the storage element of the flywheel energy storage system (FESS). Literature research indicates that this is primarily due to the high specific energy of composites compared to metals. However, a quantitative comparison of the performance of flywheels made from these materials has not been conducted. This paper aims to answer the question - ‘Are composite flywheels better suited for energy storage than metal flywheels?’. This study uses three different performance indices: kinetic energy; specific energy; and, energy per cost, to compare the corresponding rotor designs. A plain-stress, linear elastic mathematical model of the flywheel rotor described by Krack et al. (2010) is used for analysis. Different optimization formulations corresponding to performance indices chosen based on the FESS application are then solved to study optimal FESS designs. The study indicates that for applications where the energy-per-cost is to be maximized, metals are superior to composite rotor materials. On a total energy basis, metals and composites are on par with each other. Composite rotors are however, superior for applications requiring high specific energy. A hybrid rotor, with a metallic energy storage element and a thin composite burst-rim, is also optimally designed and found to be a viable solution, because it offers the cost benefit of metal rotors, as well as the burst-safety provided by composites.