Optimal Rotor Research Articles

Output Power Smoothing of Doubly Fed Induction Generator Wind Turbine Using Very Short Term Wind Speed Prediction Based on Levenberg–Marquardt Neural Network

Wind energy is a renewable energy with great potential. Unlike fossil fuels, wind energy is clean, pollution-free from CO2 emissions, and inexhaustible. However, wind speed is not constant, it fluctuates rapidly, and is uncontrollable. Fluctuating wind speed causes fluctuating output power at the wind turbine. Fluctuating wind power causes the grid frequency to fluctuate, which in turn reduces the quality of the transmitted power and generates instability in the power system. To reduce wind power fluctuations, the output power smoothing method can be used. This paper proposes the smoothing power output method without using energy storage devices to produce a constant output power of the doubly fed induction generator. The fluctuating wind speed generates constant output power based on wind speed predictions. Predicted average wind speed using neural networks with the Levenberg–Marquardt learning algorithm is based on the measurement data of wind speed in Indonesia, Nganjuk prefecture. Simulations are performed using Matlab Simulink. Simulation results show that the output power can be kept constant for a certain period of time. The speed of the rotor with this proposed method has an average above optimal rotor speed.

Experimental Investigation of Micro Air Vehicle Scale Helicopter Rotor in Hover

This paper describes a fundamental experimental study, which involved systematic performance and flowfield measurements (PIV) to understand and optimize the hover performance of a MAV-scale helicopter rotor operating at Reynolds numbers lower than 30,000. The rotor parameters that were varied include blade airfoil profile, blade chord, number of blades, blade twist, planform taper and winglets at blade tip. Blade airfoil section had a significant impact on the hover efficiency and among the large number of airfoil sections tested, the ones with the lower thickness to chord ratios and moderate camber (4.5% to 6.5%) produced the highest rotor hover figure of merit. Increasing the solidity of the rotor by increasing the number blades (with constant blade chord) had minimal effect on efficiency; whereas, increasing the solidity by increasing blade chord for a 2-bladed rotor, significantly improved hover efficiency. Moderate blade twist (−10° to −20°) and large planform taper (larger than 0.5) marginally improved rotor efficiency. Rotor blades with small winglets (height ≈ 6% of rotor radius) at the tip also improved hover performance. While using winglets, the flowfield measurements showed a diffused tip vortex, which could reduce the induced aerodynamic losses. Spanwise lift distribution obtained using sectional bound circulation computed from the measured flowfield correlated well with the load cell measurements. The optimal rotor designed based on the understanding gained from the present study produced a figure of merit of 0.67, which is the highest value of FM ever reported in the literature for micro-rotors operating at these low Reynolds numbers.

Optimum Design of Compound Helicopters that Use Higher Harmonic Control

The optimal design of a compound helicopter comprised of counterrotating coaxial rotors, a propeller, and optionally a fixed wing is investigated. The blade geometry, azimuthal blade pitch inputs, optimal shaft angle (rotor angle of attack), and division of propulsive and lifting forces among the components that minimize the total power for a given flight condition are determined. The optimal design problem is cast as a variational statement that minimizes the sum of induced and viscous power losses for a prescribed lift, propulsive force, and vehicle trim condition. The rotor, propeller, and wing geometry and control inputs are related to the far-field circulation through a lifting-line model that accounts for experimentally or computationally determined nonlinear lift and drag polars. The variational statement is discretized using a vortex lattice wake, and the resulting nonlinear constrained optimization problem is solved via Newton iteration. Results show that varying the prescribed propulsive force of the system affects the optimal shaft angle and rotor design, that higher harmonic control reduces the total vehicle power loss (inefficiency) in high-speed flight by as much as 15%, and that imposing a maximum allowable lateral lift offset can greatly increase the power loss of the coaxial rotors.

Collective control strategy for a cluster of stall-regulated offshore wind turbines

The power converter is one of the most vulnerable components of a wind turbine. When the converter of an offshore wind turbine malfunctions, it could be difficult to resolve due to poor accessibility. A turbine generally has a dedicated controller that regulates its operation. In this paper, a collective control approach that allows a cluster of turbines to share a single converter, hence a single controller, that could be placed in a more accessible location. The resulting simplified turbines are constant-speed stall-regulated with standard asynchronous generators. Each cluster is connected by a mini-AC network, whose frequency can be varied through a centralised AC–DC–AC power converter. Potential benefits include improved reliability of each turbine due to simplification of the turbines and enhanced profit owing to improved accessibility. A cluster of 5 turbines is assessed compared to the situation with each turbine having its own converter. A collective control strategy that acts in response to the poorest control is proposed, as opposed to acting in response to the average control. The strategy is applied to a cluster model, and simulation results demonstrate that the control strategy could be more cost-effective than each turbine having its own converter, especially with optimal rotor design.

Analytical solution of optimized energy consumption of Double Star Induction Motor operating in transient regime using a Hamilton–Jacobi–Bellman equation

The problem of energy optimization of a DSIM (Double Stator Induction Motor) using the concept of a RFOC (Rotor Field Oriented Control) can be treated by an OCS (Optimal Control Strategy). Using OCS, a cost-to-go function can be minimized and subjected to the motor dynamic equations and boundary constraints in order to find rotor flux optimal trajectories. This cost-to go function consists of a linear combination of magnetic power, copper loss, and mechanical power. The dynamic equations are represented by using a reduced Blondel Park model of the DSIM. From the HJB (Hamilton–Jacobi–Bellman) equation, a system of nonlinear differential equations is obtained, and analytical solutions of these equations are achieved so as to obtain a time-varying expression of a minimum-energy rotor flux. This analytical solution of rotor flux achieved maximum DSIM's efficiency and was implemented in the ORFOC (optimal rotor flux oriented control) and compared to the conventional RFOC at different dynamic regime of the DSIM. Simulation results are given and improved the effectiveness of the proposed strategy.

Direct Power Control of Dfig by Using Nonlinear Model Predictive Controller

AbstractThis paper proposes a nonlinear model predictive direct power control (PDPC) strategy for a double fed induction generator (DFIG)‐based wind energy generation system. Active and reactive power variations of DFIG are calculated based on machine rules, and a nonlinear model of DFIG is given. A nonlinear model predictive controller (NMPC) is presented based on the useful cost function and constraint that it results in more proximity between simulations and reality. The power and current ripples are reduced and the optimal rotor voltage is generated based on an objective function and the constraints. The rotor voltage vector is calculated in the synchronous reference frame and transferred into the rotor reference frame. Simulation results of a 2 MW DFIG system show good performance of the proposed method during variation of active and reactive powers, machine parameters, and wind speed. Also, the transient responses of active and reactive powers are within a few milliseconds.

Vibration reduction Design of Permanent Magnet Motor Using Level Set Based Shape Optimization Method

This paper presents a new optimization method to design a rotor structure for a permanent magnet motor that can reduce vibration. The optimization problem is formulated with a multi-objective function to minimize the fluctuation of the radial magnetic force and the torque ripple. To obtain the optimal rotor shape consisting of a permanent magnet and ferromagnetic material, a multiple level set model is employed to express the structural boundaries and magnetic properties of each material. The updating process of the level set function based on the adjoint sensitivity and the time evolutional equation makes it possible to obtain a novel rotor configuration of the motor. To verify the usefulness of the proposed method, a rotor design example of the surface-mounted permanent magnet motor for electric power steering system is performed.

Wound Rotor Machine With Single-Phase Stator and Three-Phase Rotor Windings Controlled by Isolated Three-Phase Inverter

This paper proposes a single-phase grid-connected wound rotor machine that has the single-phase stator and three-phase rotor windings. The machine has no auxiliary winding or capacitor unlike conventional single-phase machines. Nevertheless, it can operate in all four quadrants of the torque–speed plane with a three-phase inverter. For adjustable speed drives, an isolated three-phase inverter is applied to the rotor windings while the stator winding is directly connected to a single-phase source. The grid filter and rectifier of the conventional system are eliminated and the rotor-side slip rings can be also removed by the inverter integration. So the overall structure of the proposed drive system is simple and cost effective. In this paper, the proposed machine is modeled into a modified d – q model considering the absence of q -axis stator coil. Its characteristics are analyzed and vector control methods of the grid power factor, dc-link voltage, and speed are proposed. For more efficient control, the optimal rotor current set is calculated from the minimum copper loss condition. The system has wider operating areas than other single-phase drive systems. The feasibility of the proposed system is verified by experiments.

재생 면적비가 가정용 소형 제습로터의 성능에 미치는 영향에 관한 실험적 연구

During hot and humid weather, air-conditioners consume a large amount of electricity due to the large amount of latent heat. Simultaneous usage of a dehumidifier may reduce latent heat and reduce electricity consumption. In this study, dehumidification performance was measured for a small-sized dehumidification rotor made of inorganic fiber impregnated with metallic silicate within a constant temperature and humidity chamber. Regeneration to dehumidification depends on ratio, rotor speed, room temperature, regeneration temperature, room relative humidity and frontal velocity to the rotor. Results demonstrate an optimum area ratio (1/2), rotor speed (1.0 rpm), and regeneration temperature () to achieve a dehumidification rate of 0.0581 kg/s. As the area ratio increases, the optimum rotation speed and the optimum regeneration temperature also increase. Above the optimum rotor speed, incomplete regeneration reduces dehumidification. Above the optimum regeneration temperature, increased temperature variation between regeneration and dehumidification reduces dehumidification. Dehumidification rate also increases with an increase of relative humidity, dehumidification temperature and flow velocity into the rotor.

가정용 소형 제습로터의 성능에 대한 실험적 연구

In Korea, summer is hot and humid, and air-conditioners consume too much electricity due to large amount of latent heat. Simultaneous usage of dehumidifier may reduce the latent heat and save the electricity. In this study, dehumidification performance was measured in a constant temperature and humidity chamber for a small-sized dehumdification rotor made of inorganic fiber impregnated with metallic silicate. Variables were rotor speed, room temperature, regeneration temperature, room relative humidity and frontal velocity to the rotor. Results showed that there existed optimum rotor speed (1.0 rpm), and optimum regeneration temperature (100 o C). Above the optimum rotor speed, incomplete regeneration is responsible for reduced dehumidification. Above the optimum regeneration temperature, increased temperature difference between regeneration and dehumidification process is responsible for reduced dehumidification. The amount of dehumidification also increases with the increase of relative humidity, dehumidification temperature and flow velocity into the rotor.

The effect of blockage on tidal turbine rotor design and performance

The performance-enhancing effects of closely packing tidal turbines in single row arrays (tidal fences) are evaluated in this computational study. Infinitely long tidal fences are simulated with a range of lateral rotor spacings using a blade element momentum method embedded in a Reynolds averaged Navier–Stokes solver (RANS-BEM).First, a rotor design tool is applied to determine a hydrodynamically optimal rotor design for each lateral spacing. In the RANS-BEM method, the effect of blockage (the ratio of rotor swept area to channel cross-sectional area) on rotor optimization is accounted for. Increased blockage is found to result in increased optimal solidity and decreased optimal pitch. Next, each rotor design is simulated in its design spacing as well as several off-design spacings. The resulting power coefficient is largest when the rotor optimized for the highest blockage case operates in the array with the closest lateral spacing. Further, although a rotor's performance is improved through operation at a blockage higher than its design point, it still exhibits inferior performance relative to a rotor designed for that higher blockage. The results indicate that blockage must be considered in the rotor design process if the optimal rotor efficiency for a given spacing is to be achieved.

Backstepping sliding mode control of a variable speed wind turbine for power optimization

To optimize the energy capture from the wind, wind turbine (WT) should operate at variable speed. Based on the wind speed, the operating regions of the WT are divided into two parts: below and above the rated wind speed. The main aim at below rated wind speed is to maximize the energy capture from the wind with reduced oscillation on the drive train. At above rated wind speed, the aim is to maintain the rated power by using pitch control. This paper presents the control of WT at below rated wind speed by using backstepping sliding mode control (BSMC). In BSMC, generator torque is considered as the control input that depends on the optimal rotor speed. Usually, this optimal rotor speed is derived from effective wind speed. In this paper, effective wind speed is estimated from aerodynamic torque and rotor speed by using the modified Newton Rapshon (MNR) algorithm. Initially, a conventional sliding mode controller (SMC) is applied to the WT, but the performance of the controller was found to be less robust with respect to disturbances. Generally, WT external disturbance is not predictable. To overcome the above drawback, BSMC is proposed and both the controllers are tested with mathematical model and finally validated with the fatigue, aerodynamics, structures, and turbulence (FAST) WT simulator in the presence of disturbances. From the results, it is concluded that the proposed BSMC is more robust than conventional SMC in the presence of disturbances.

Optimal Rotor Design of IPM Motor for Improving Torque Performance Considering Thermal Demagnetization of Magnet

This paper proposes a new design technique for improving torque performance of interior permanent magnet (IPM) motors with consideration of the thermal characteristic of magnet. To verify the driving performance of IPM motor at operating temperature, a magnetic-thermal coupled analysis was performed with a heat source, such as iron loss and copper loss, and the thermal characteristics of permanent magnet (PM) is considered to define the magnetic property. The optimization problem is formulated to minimize the harmonics of magnetic flux, which cause iron loss, as well as to maximize the output torque for satisfying the design target. To obtain an optimal rotor shape of the IPM motor, which is composed of both PM and ferromagnetic material, a multi-phase level set model is employed for representing the precise boundaries of the magnetic materials. A design example of a motor with Nd-Fe-B magnet, which has a tendency to be demagnetized at high temperature, is provided to verify the effectiveness of the proposed method.

A Study on Optimal Design of the Triangle Type Permanent Magnet in IPMSM Rotor by Using the Box–Behnken Design

This paper proposes an optimal rotor design method of an interior permanent magnet synchronous motor (IPMSM) by using a permanent magnet (PM) shape. An IPMSM is a structure in which PMs are buried in an inner rotor. The torque, torque ripple, and safety factor of IPMSM can vary depending on the position of the inserted PMs. To determine the optimal design variables according to the placement of the inserted PMs, parameter analysis was performed. Therefore, a response surface methodology, which is one of the statistical analysis design methods, was used. Among many other response surface methodologies, Box-Behnken design is the most commonly used. For the purpose of this research, Box-Behnken design was used to find the design parameter that can achieve minimum experimental variables of objective function. This paper determines the insert position of the PM to obtain high-torque, low-torque ripple by using a finite-element-method, and this paper obtains an optimal design by using a mechanical stiffness method in which a safety factor is considered.

Study on the Optimal Rotor Retaining Sleeve Structure for the Reduction of Eddy-Current Loss in High-Speed SPMSM

In the case of designing high-speed surface-mounted permanent magnet synchronous motor (SPMSM), the rotor retaining sleeve is inserted into the rotor to prevent the permanent magnet’s damage. It is quite an efficient way to consider manufacturability, but the sleeve becomes the major source of ohm loss in high-speed operation. In this paper, the high-speed motor for a turbo blower at the rating of 100 kW, 20000 r/min was introduced. To improve its efficiency, the retaining sleeve’s optimal design was needed. For this, parametric analysis on the shape of the retaining sleeve was carried out in a different type of motor. Within a range that meets the mechanical safety, sleeve designs have been changed. The effect of changing design variables of the sleeve was studied. This paper presents the optimized sleeve’s advantages in electrical efficiency from the results of the electromagnetic finite element analysis software. Finally, it suggests the optimal sleeve design to reduce eddy-current loss, which is related to motor shape.

Aerodynamic design optimization of helicopter rotor blades including airfoil shape for forward flight

This study proposes a process to obtain an optimal helicopter rotor blade shape including both planform and airfoil shape for helicopter aerodynamic performance in forward flight. An advanced geometry representation algorithm which uses the Class Function/Shape Function Transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape was considered in terms of design variables. The optimization process was constructed by integrating several programs developed by the author. Airfoil characteristics are automatically generated by an analysis tool where lift, drag, and moment coefficients of airfoil are predicted for subsonic to transonic flow and a wide range of attack angles. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight, aerodynamic requirements (lift, drag and moment coefficients) for critical flow condition occurring on rotor blades. The trim condition must be attainable in any flight condition. Objective function is chosen as a combination expression of non-dimensional required power in hover and forward flight.

Optimum Actuator-Disk Performance in Hover and Axial Flight by a Compact Momentum Theory with Swirl

A new compact form of momentum theory is introduced for actuator disks including swirl. The new form unifies both the axial and angular momentum balances into a single momentum equation, applicable over the entire range of thrust and power coefficients. While completely consistent with earlier momentum theories, such as that of Glauert with swirl, the compact form allows analytic expressions for the parameters of a Betz actuator disk and reveals additional insight into the limiting efficiency of rotors, propellers, and wind turbines. The compact form also allows a completely closed form for the truly optimum Glauert rotor. We will also present results from the Betz hypothesis as practically optimum. Closed-form results presented here include the practically optimum values of induced flow, inflow angle, thrust, induced power, and efficiency. Closed-form expressions are also given for practically optimum twist, chord distribution, and solidity in the presence of profile drag (along with the resulting overall efficiencies). This report also gives a closed-form solution for the truly optimum rotor in hover, based on the Glauert optimality criterion.

J1030106 ロケット用ターボポンプのロータ形態の違いが軸振動特性に及ぼす影響

Turbopumps are high-speed turbomachinery which feed the cryogenic propellant to the combustion chamber for rocket engines. Rotor vibration problems caused by the increase of power have occurred under development of turbopumps. Authors had proposed the morphology design method as way of resolving the rotor vibration problems. In this study, superior solutions are investigated by the morphology design method. Besides, the effect of the rotor morphologies on vibration characteristics such as system damping ratios and vibration amplitudes are discussed. The optimal rotor arrangement for the suppression of the rotor vibration was proposed by the morphology design method. Trend of the vibration characteristics for the permutation and direction of the rotor elements was shown.

Sensitivity Analysis of Torque Ripple Reduction of Synchronous Reluctance and Interior PM Motors

The main drawback of reluctance machines is a high torque ripple, due to the interaction between the stator magnetomotive force and the rotor structure. Adopting a rotor configuration characterized by several flux barriers per pole, there is a high influence of the rotor geometry on the machine performance in terms of both average torque and ripple. An optimization is often required to determine the optimal rotor geometry so as to achieve a high and smooth torque. Then, the geometry determined earlier should guarantee good performance for various operating points (i.e., changing the current amplitude and phase), as well as for small variations of the geometry. This paper investigates this aspect, showing the results of optimizations carried out on various machines. The impact of the geometry parameters is taken into account, and the sensitivity of the optimal solution to the geometry variation is pointed out. This paper highlights the difficulty to get a robust geometry as far as the torque ripple reduction is concerned. Finally, a few experimental results on a synchronous reluctance motor prototype will be presented, compared with finite-element analysis simulations for validation.

Investigation of self-starting and high rotor solidity on the performance of a three S1210 blade H-type Darrieus rotor

Energy is an essential ingredient for socio-economic development and economic growth of a country. Energy is available in two different forms, fast depleting or non-renewable (coal, fuel, natural gas) and renewable (solar, wind, hydro etc). Wind is one of the potential renewable energy sources due to its abundance in the atmosphere in different scales of high, medium and low ranges. Vertical axis wind turbine (VAWT) can be installed in low wind speed regime for performing various small-scale functions ranging from electrifying a built environment to pumping water especially in remote places where grid-connected electricity is a scarce. Amongst various VAWT rotors, H-type Darrieus rotor has become more popular in the built environment for their straight blade designs and simpler construction features. However, the major problem facing such VAWT rotor is their non-self-starting characteristics due to symmetrical blade designs. Replacing VAWT's conventional blades with unsymmetrical blades and increasing rotor solidity could make potential solution to the above problem. However, there is still hardly any quantitative measure of the self-starting, torque, power coefficient etc. with increased rotor solidity so as to obtain some performance insights of high solidity unsymmetrical blade H-Darrieus rotor in low wind speed condition. In this paper a three-bladed H-type Darrieus rotor equipped with unsymmetrical S1210 blades is investigated first for its self-starting characteristics with different rotor solidities (from 0.8 to 1.2) at various azimuthal positions. Then the power coefficients (Cp) are evaluated for these solidities at various wind speeds. It will be shown that high blade solidity is in fact desirable for overall better performance of the rotor. There is an optimum rotor solidity at which power coefficient is the highest. And the maximum Cp of 0.32 is obtained for rotor solidity 1.0 and wind speed 5.7 m/s. The results are compared with some other symmetrical/unsymmetrical blade H-Darrieus rotors. Though the operating range is reduced but, for higher static and dynamic torque and comparable power coefficient with respect to existing rotors, the present rotor could be used for various small-scale applications especially that require high torque like pumping, grinding etc.