Rotor Control Research Articles

Dual direct torque control of doubly fed induction machine using second order sliding mode control

In this paper a dual direct torque control (DDTC) strategy with second-order sliding mode control (SOSMC) controller of the doubly fed Induction motor (DFIM) is presented in order to overcome some drawback such as ripples in torque, flux and to improve dual direct torque control (DDTC) performance toward the electrical parameters variations. This control strategy used in the doubly fed induction machine supplied, coupled by two voltage source inverters in rotor and stator sides witches are linked to two switching tables in order to determined the rotor and stator flux vector control. This controller based on super-twisting algorithm (STA). Comparative results between a classical controller (PI) and the proposed controller can prove the very satisfactory performance and robustness of this new controller.

Optimal Segment Control of Active Twist Rotor for Power Reduction in Forward Flight

The segment control of active twist rotor is investigated to evaluate the effectiveness in rotor power reduction. A numerical model for predicting the isolated rotor power and loads in steady level flights is deployed and validated. A parametric sweep of the amplitude and phase angle for uniform single-harmonic active twist control is conducted to demonstrate the mechanism of active twist control in rotor power reduction. The optimal control schedules and segment layouts of the segment twist control for power reduction while considering saturation limits are obtained using an optimization framework based on genetic algorithm. Up to 5-seg configuration is considered. The results indicate that the segment twist control reduces the rotor power more than the uniform twist control by applying divergent control schedules to each segment. The load distribution of the rotor disk is harmonized in both circumferential and spanwise directions. The 2-seg and 3-seg control configurations are appropriate, while the configurations with more segments yield limited benefits and they may be penalized with an increase in system complexity.

Active balancing control for time-delay rotor via linear-quadratic regulator

Many imaging platforms, e.g., robotic devices and autonomous systems, require timely reaction to external events. The active balancing control is important to suppress rotor vibration and hence acquire stable videos and imagery. However, there is an inevitable delay in active balancing control of the high-speed, time-delay rotor systems. Eliminating this delay is crucial in real-world applications. The integral transformation term is introduced to transform the dynamic model of the time-delay rotor system into a dynamic model of the rotor system without time delay. Based on the linear-quadratic optimal control method, the influence of weight matrix is discussed. Moreover, an active balancing control strategy of the time-delay rotor is designed. The simulation model of the time-delay rotor control system is implemented with MATLAB, and a real device is fabricated to conduct both simulations and real-world experiments. Our results demonstrate that our proposed online active balancing control method effectively suppresses the vibration of the time-delay rotor system under different time-delay. The convergence time is short, and the system is agile.

Applications of adaptive stiffness suspensions to vibration control of a high-speed stiff rotor with tilting pad bearings

The current paper discusses the optimum parameter setting of asymmetric high-static low-dynamic stiffness (HSLDS) suspensions to reduce vibrations of a high-speed symmetric rotary system, excited by an unbalance force. The rotating system consists of a shaft that is supported by tilting pad journal bearings on the asymmetric HSLDS suspensions. The Reynolds equation is solved numerically to obtain the oil pressure distribution for each pad of bearing. With the aim of calculating the hydrodynamic forces applied to each pad, an analytical approach is presented. Its results are validated using a numerical integration approach. Given the considerable difference between the shaft mass and pads moment of inertia, the mathematical equations governing the motions of disk, journal, bearing and pads are solved implementing a routine specified for stiff ordinary differential equations in MATLAB. The optimum parameters of HSLDS suspensions are obtained, using a multi-objective genetic algorithm. Design objectives are considered to minimize the vibrations of rotor, journal, and bearing and bearing force transmission to the external supports. The efficiency of optimum HSLDS suspensions in reducing the vibrations of journal, bearing and rotor within the operating speed range is shown. The high performance of the designed suspensions in decreasing the bearings force transmission is proved as well. In addition, the design robustness to uncertainties in HSLDS suspensions parameters is studied.

Tiltrotor Conversion Maneuver Analysis with RCAS

Aeromechanics analysis is performed using the comprehensive analysis code RCAS (Rotorcraft Comprehensive Analysis System) to study the transient conversion maneuver of a tiltrotor. The analytical model is based on the XV-15 research tiltrotor aircraft in size and dynamic characteristics. A generic (not representative of XV-15) tiltrotor control system is developed to simulate a conversion maneuver. Hover and cruise performance of the present XV-15 analytical model is validated against available test data. The conversion calculation begins with a trim analysis at hover, which is followed by the conversion maneuver. During the maneuver analysis, the pilot control model is activated to fly the aircraft following a desired airspeed profile and minimum altitude change. Time histories of vehicle dynamics, rotor controls, rotor flapping, rotor performance, and blade structural loads are investigated for various transient conversion maneuvers. The aircraft acceleration during the transient maneuver has a significant influence on the rotor performance and loads.

Research on vibration compensation control of electromagnetic bearings rotor

Research on vibration compensation control of electromagnetic bearings rotor

Research on vibration compensation control of electromagnetic bearings rotor

Research on vibration compensation control of electromagnetic bearings rotor

Hybrid gas-magnetic bearings: An overview

This paper presents a state-of-the-art survey on the development of the hybrid gas-magnetic bearing (HGMB) technology. HGMBs are proposed to complement the advantages of gas bearings and magnetic bearings for enhanced bearing performance. Nevertheless, there are a number of inherent challenges in their designs, analyses, and performance characteristics that must be taken into account for proper functionality and reliable operation. For this purpose, substantial results in theory, numerical simulations, and experiments concerning rotor dynamics, mechanical structures, control systems, and operation modes are discussed to help further investigation and implementation of HGMBs. In addition, future developments of HGMBs in industries and remaining challenges are discussed.

Erratum to: Analytical Estimate of Rotor Controls Required for a Straight Vortex Disturbance Rejection

Correction to:Journal of the American Helicopter Society, Vol. 62, (1), January 2017, pp. 1-4,http://dx.doi.org/10.4050/JAHS.62.015001

Simulation of step input in collective pitch for hovering rotor

Advanced CFD tools are nowadays used routinely for analysis and design of rotorcraft with the research community shifting towards simulations of rotorcraft during maneuvering flight. One of the impediments of this effort is the lack of data for validation, evaluation and thorough assessment of CFD methods when it comes to rotors with time-varying control inputs. This paper presents a first effort to validate CFD tools for step-inputs in rotor control angles against previously un-published experimental data. The experimental study was carried out at the Nanjing University of Aeronautics and Astronautics in China and consists of time varying control inputs for a hovering rotor. The agreement between the simulation and experimental study is good and quantify the overshoot in loads for this dynamic case. The results examine the lag in loads response to and the dynamic response of the wake with recommendations on spatial and temporal resolution to capture these effects.

Measurement based parameters estimation of large scale wind farm dynamic equivalent model

For the past few decades, the drastic increase in the installed capacity of wind farms (WFs) has necessitated a computationally efficient dynamic equivalent model of a WF, which can be used for accurate power network simulations. Various doubly-fed induction generators (DFIGs) with sophisticated power control, rotor, and grid side converter control based models for wind turbine (WT) exist in the literature. However, these models are computationally burdensome and restrict their application for modeling large WFs. Thus, an equivalent DFIG based model of a WF, with the rotor circuit modeled as a constant current source, is proposed in this paper. The proposed model is simple and computationally efficient as no rotor measurements are required, and voltage and current measurements at the point of common coupling (PCC) of the WF are used in extended Kalman filter (EKF) to evaluate the dynamic parameters of the equivalent DFIG. A Ybus based reduction is also proposed for the equivalent collector system’s impedance. Simulation results on a test WF in MATLAB Simulink and DIgSILENT prove the proposed model’s efficacy over the existing equivalent models for different operating conditions like wake effect and contingencies in the interconnected power system network.

Effect of active camber morphing on rotor performance and control loads

A computational investigation of a helicopter main rotor with an active-camber morphing mechanism was conducted to identify the capability to simultaneously save rotor power and reduce pitch-link loads using as low as possible camber deflection magnitudes. Comprehensive rotor aeromechanics analysis with elastic blade modeling and a free vortex wake for the aerodynamics model was used to ensure computational efficiency. The investigation was based on a full-scale Bo 105 helicopter main rotor in level flight condition at μ=0.3 and CT/σ=0.089. In addition to a variation of the radial position and length of the active-camber section, the capabilities and system behavior were investigated in an extensive parametric study using practical actuation inputs. The same computational framework was used to obtain optimal control inputs that led to best performance in terms of power savings using two-per-rev (2P) individual blade control (IBC) via pitch-link inputs and 2P active-twist control. The relative potential of the three active mechanisms and the aerodynamic phenomenology was compared. All of the investigated active-rotor mechanisms contributed to rotor power savings via a more uniform distribution of thrust over the rotor disk. Both IBC and active twist yielded maximum performance improvement of about 1.8% over the baseline in terms of power reduction. With active camber, simultaneous rotor power reduction of 3.8% and a peak-to-peak pitch-link load reduction of 20% were obtained using a nonharmonic camber deflection deployment schedule with a half-peak-to-peak magnitude of 2∘. The global maximum of power savings observed with active camber was 4.4%, which resulted in an increase of peak-to-peak pitch-link loads by 35% and a required half-peak-to-peak camber deflection magnitude of 3.6∘.

Stable Control of Nutation and Precession for the Radial Four-Degree-of-Freedom AMB-Rotor System Considering Strong Gyroscopic Effects

The stable control of the active magnetic bearing rotor (AMB-rotor) system is the key technology for a magnetically suspended control moment gyroscope, which is used in the spacecraft attitude control system. The nutation and precession instability caused by strong gyroscopic effects is the principal issue of the AMB-rotor system. In order to solve the gyroscopic effects problem, in this article, a state-space model of the radial four-degree-of-freedom AMB-rotor system is established, and the strong gyroscopic effects term varying with the rotor speed is regarded as a bounded perturbation. The regional pole assignment method of an uncertain system is used to design a robust controller to maintain the system stability over the full rotor speed range. However, the controller designed by the regional pole assignment method does not consider the influence of closed-loop stiffness of the magnetic bearing, which will lead to the start-up oscillation and structural mode self-excited oscillation problems. Therefore, on the basis of the regional pole assignment, the system stiffness is further constrained and a robust controller is solved. Experiments show that the designed controller can not only deal with the start-up oscillation and the structural modal vibration problems, but also can achieve the stable control of the nutation and precession.

Blade Structural Load/Airload Correlation on a Slowed Mach-Scaled Rotor at High Advance Ratios

To expand the cruise speed of a compound helicopter, alleviating the compressibility effects on the advancing side with reduced rotor RPM is proved to be an effective design feature, which results in high advance ratio flight regime. To investigate the aerodynamic phenomena at high advance ratios and provide data for the validation of analytical tools, a series of wind tunnel tests were conducted progressively in the Glenn L. Martin Wind Tunnel with a 33.5-inch radius fourbladed articulated rotor. In a recent wind tunnel test, the rotor blades were instrumented with pressure sensors and strain gauges at 30% radius, and pressure data were acquired to calculate the sectional airloads by surface integration up to an advance ratio of 0.8. The experimental results of rotor performance, control angles, blade airloads, and structural loads were compared with the predictions of comprehensive analysis and computational fluid dynamics (CFD) analysis coupled with computational structural dynamics (CSD) structural model. The paper focuses on the data correlation between experimental pressure, airload, and structural load data and the CFD/CSD predicted results at various collective and shaft tilt angles. Overall, the data correlation was found satisfactory, and the study provided some insights into the aerodynamic mechanisms that affect the rotor airload and performance, in particular the mechanisms of backward shaft tilt, the effect of hub/shaft wake, and the formation of dynamic stall in the reverse flow region.

Study the system with innovative rotor control in drilling of deviated and horizontal wells

Controllable rotor systems are the innovation of the drilling tool enabling to manage the well path decreasing failure and complication risk. The rig in this system moves by set path with continuous motion of drill string. The rotation of drilling tool provides the effective well cleaning, reduces the drilling tool sticking and allows drilling deep wells and those with complicated profile compared to the drilling with bottomhole engine. The most complicated circumstance for obtaining required drilling rate is the maintenance of enough load transmission from the earth surface to the rig regardless the boundary conditions between the well and drilling tool.

The influence of leading edge roughness, rotor control and wind climate on the loss in energy production

This study investigates how losses in energy production from wind turbines are influenced by leading edge roughness, rotor control and wind climates using computations. The performance of a NACA633-418 airfoil with five different damage types was predicted using Computational Fluid Dynamics (CFD) with bumps at the leading edge and grooves into the leading edge. Also, one type corresponding to a repair of a leading edge with an “overbite” was investigated. These airfoil characteristics were used in rotor computations where three different wind climates and five different maximum tip speeds were investigated. The rotor computations reflected that the Annual Energy Production (AEP) increased significantly with the average wind speed on the site. They also reflected that the relative AEP losses due to leading edge damages reduced with increasing average wind speed on sites. For the low wind speed site the losses were between 1% and 4% depending on the extent and the type of the blade damage. For the high wind speed site the losses were between 0.5% and 3%. Furthermore, the bigger the extent of the damages were the bigger the losses were. Finally, it was shown that increasing the maximum tip speed increased AEP and decreased the losses.

Rejecting wake-rotor overlapping load disturbances: An extension to active power control of wind farms

This paper studies an extension to the active power control of wind farms for further structural load alleviation of waked wind turbines. We demonstrate that the structural fatigue loading of a downstream turbine, which its rotor overlaps with wakes of its upwind turbine, can be significantly alleviated, while the wind farm power production follows a power reference signal. A load variations model is proposed, based on the multi-rotor concept, to sense the variations of the wind velocity and the associated loading across the rotor area of a single wind turbine. Then, an individual rotor control is proposed to reject the rotor-wake overlapping load disturbances about an operating condition, commanded with the closed-loop APC at the wind farm level. The applicability and key features of the controller are discussed with a wind farm example consisting of 2×2 turbines. A large-eddy simulation model is employed for resolving the turbulent flow, the wake structures and its interaction with an atmospheric boundary layer. The effectiveness of the proposed load disturbance rejection is evaluated using the damage equivalent load of the tower base fore-aft bending and torsional moments of the individual wind turbines.

Reduction of the High-Speed Magnetically Suspended Centrifugal Compressor Harmonic Vibration Using Cascaded Phase-Shifted Notch Filters

In the active magnetic bearing (AMB)-rotor control system, rotor mass unbalance and displacement sensors runout will bring about harmonic current, which would further result in vibration force transmitted to machine housing. The undesired machine vibration would pose a potential threat to system stability and performance degradation. In order to attenuate harmonic current, this work has proposed a scheme of control system with cascaded mode phase-shift notch filters, and the system stability has been analysed. The harmonic current reduction performances of the system with cascaded mode notch filters are compared with that with parallel mode notch filters. Theoretical analysis has demonstrated that the proposed cascaded mode control system could achieve the same suppression performance as the commonly used parallel mode control system, which is also verified by simulation results. Experiments carried out on a high-speed magnetically suspended centrifugal compressor have validated that the proposed method is effective for harmonic current reduction.

Evaluation method and platform of vibrational disturbance test for ventricular assist devices.

For ventricular assist devices utilizing levitation bearing technology, collision and wear of the rotor would occur if the bearing cannot resist disturbances from patient activities and vibration/shock impacts. The reliability of ventricular assist devices can be seriously affected, potentially impairing blood compatibility (e.g. thrombus generation) and threatening patient safety. In this article, we proposed a vibrational disturbance test protocol for ventricular assist devices. Two kinds of vibrational disturbances-translational and rotational-were defined and the disturbance levels determined as 6G and 10 rad/s per possible patient activity impact. A test platform was built according to the disturbance level requirements. The test platform successfully generated the required disturbance. The vibration test evaluation criteria for ventricular assist device assistance (characterized by the pressure head, flow rate, and driving current waveform) were well verified. Compared with translational vibration, rotational vibration had a greater impact on the rotor. Accurate control of high-speed rotor is difficult because of the gyroscopic effect. As conventional random vibration tests cannot cover all risk situations, it is recommended that translational and rotational disturbance tests are carried out for levitation ventricular assist devices. We recommend that researchers and manufacturers pay attention to the vibrational impact of rotor-levitated ventricular assist devices.

Evaluation of an advanced slung load control system for piloted cargo operations

Helicopter operations with externally slung loads are highly demanding for the flight crew. As the pilot does not have a direct view of the load, assistance is required from an additional crew member to achieve operational requirements (e.g., for load handling to achieve precise load positioning). An automatic load stabilization and positioning system for cargo operations has been designed with the aim to reduce pilot workload, damp load pendulum motion and to improve the load positioning performance. This system uses the concept of load-motion feedback to the rotor control. To avoid degradation of Handling Qualities (HQs), as found in previous investigations, a function has been developed that monitors pilot control inputs. Dependent on the amplitude and duration of pilot control stick deflection, the feedback signal for slung load damping is blended between two different gain sets. One set provides improved HQs during piloted control and one set provides good load damping when the pilot is passive. A further novel aspect is the evaluation of an automatic load control system using a Translational Rate Command as a method of helicopter control. A piloted simulation study has been conducted using this advanced load control system with automatic load stabilization and positioning. Three test pilots evaluated the system in different control law configurations using a Mission Task Element simulating an external load cargo operation. HQs and pilot workload were evaluated using the Cooper-Harper Rating Scale and NASA Task Load Index, respectively. The results of the study show that improved HQs and reduced pilot workload in combination with improved task performance can be achieved with the advanced slung load control system.