Pitch Command Research Articles

Cooperative Output Regulation of Large-Scale Wind Turbines for Power Reserve Control

This paper develops a distributed control framework to coordinate large-scale wind turbines for fairly sharing the power reserve request on a wind farm. A cooperative output regulation problem is formulated in a multi-agent framework, where the synchronization of turbine system outputs are established regarding the heterogeneity of turbine models. For this purpose, a homogeneous virtual system is created first and embedded into each turbine to generate the agreed trajectories across the wind farm in a distributed manner. The local power tracking of individual turbines is then enforced by the synthesized output regulator, whose control gains are determined by a variant of the Sylvester equation. The proposed approach issues the generator torque and blade pitch commands in a unified manner and is resistant to wind disturbances. The case studies are carried out through simulations and in a real laboratory-scale distributed communication network. The simulation results demonstrate the effectiveness of coordinated actions of wind turbines in response to the changing demands, under both constant and turbulent wind scenarios with the plug-and-play capability.

Using Sensors for Player Development: Assessing Biomechanical Factors Related to Pitch Command and Velocity.

Pitching biomechanical research is highly focused on injury prevention with little attention to how biomechanical data can facilitate skill development. The overall purpose of this study was to explore how sensor-derived segment kinematics and timing relate to command and ball velocity during baseball pitching. We used a cross-sectional design to analyze a series of pitches thrown from 10 collegiate baseball pitchers. We collected biomechanical data from six inertial sensors, subjective command from the pitchers, and ball velocity from a radar device. Stepwise regression analyses were used to explore biomechanical variables associated with command for all pitches and ball velocity for fastballs only. We found that only peak forearm linear acceleration was significantly associated with command, whereas several segment kinematic measures were significantly associated with ball velocity. Our results suggest that different biomechanical variables are linked to specific pithing skills. Our findings suggest that end-effector (forearm) movement is more important for pitch command, whereas proximal-to-distal (pelvis, trunk, upper arm, forearm) segmental movement is important for ball velocity.

Nonlinear dynamics of flexible heliogyro subject to sinusoidal root pitch command

A heliogyro is a particular solar sail configuration whose reflective surface is divided into a number of long and slender blades, which are stiffened by a suitable spin-induced centrifugal force. The reflective blades can rotate around their longitudinal axes to change (either collectively or cyclically) the pitch angles and allow the spacecraft attitude (and so the thrust vector) to be effectively controlled. The aim of this paper is to perform implicit nonlinear finite element analyses of a heliogyro solar sail in order to investigate the dynamic response of the structure subject to a sinusoidal pitch command, while centrifugal stiffening and solar radiation pressure are acting on it. Using a parametric modeling approach, sensitivity studies relative to a set of design parameters are conducted for identifying possible solutions that improve the heliogyro maneuverability. In particular, by adopting the design of the proposed HELIOS spacecraft as a reference configuration, the influence of some geometric parameters and the effect of a number of structural arrangements are investigated. The performed analyses demonstrate that, compared to the reference configuration, the arrangement with a lower blade aspect ratio, same tip mass, and one traversal reinforcement at the tip is the only configuration without irreversible torsional instability of the blades when the pitch command has an amplitude of 25 deg.

Depth and Attitude Coordinated Control for Supercavitating Vehicle Avoiding Planing Force

Supercavitating vehicles have particular high speeds. This unique advantage is obtained by the cavity separation from water to eliminate most drag. However, this may lead to the tail-slap phenomenon and the planing force. In addition, there are large and unpredictable uncertainties in the hydrodynamics of the supercavitating vehicle. All these factors impose a big challenge to achieve satisfactory depth tracking capability. In this paper, a depth and attitude coordinated control strategy is proposed for the longitudinal dynamics in order to realize depth tracking without planing force. The timely adjustment of the attitude ensures a small vertical speed which can be far away from the threshold value that causes the planing force. By designing the cascade control structure, the depth is regulated by proportional control to generate the pitch command for the attitude loop controller. The vertical speed and the pitch angular rate are both controlled by using the linear active disturbance reject control to guarantee sufficient accuracy and robustness. The simulation results demonstrate the effectiveness and the superiority of the proposed strategy.

Modeling and trajectory tracking control for flapping-wing micro aerial vehicles

This paper studies the trajectory tracking problem of flapping-wing micro aerial vehicles (FWMAVs) in the longitudinal plane. First of all, the kinematics and dynamics of the FWMAV are established, wherein the aerodynamic force and torque generated by flapping wings and the tail wing are explicitly formulated with respect to the flapping frequency of the wings and the degree of tail wing inclination. To achieve autonomous tracking, an adaptive control scheme is proposed under the hierarchical framework. Specifically, a bounded position controller with hyperbolic tangent functions is designed to produce the desired aerodynamic force, and a pitch command is extracted from the designed position controller. Next, an adaptive attitude controller is designed to track the extracted pitch command, where a radial basis function neural network is introduced to approximate the unknown aerodynamic perturbation torque. Finally, the flapping frequency of the wings and the degree of tail wing inclination are calculated from the designed position and attitude controllers, respectively. In terms of Lyapunov's direct method, it is shown that the tracking errors are bounded and ultimately converge to a small neighborhood around the origin. Simulations are carried out to verify the effectiveness of the proposed control scheme.

Adaptive non‐linear integral sliding mode fault‐tolerant control allocation scheme for octorotor UAV system

This study proposes a new active fault-tolerant control (FTC) and fault estimation scheme for a non-linear octorotor system. The proposed method utilises the idea of an online control allocation (CA) scheme to fully engage the rotors redundancy based on the information from the fault estimation unit. The nominal performance is first achieved using non-linear dynamic inversion (NDI) technique and then to incorporate the robustness, an adaptive non-linear sliding mode control is united with a baseline NDI controller. The proposed method is used to attain the desired altitude and attitude tracking control of an octorotor system. Furthermore, to control the un-actuated states (called internal dynamics) of octorotor system, a separate integral sliding mode-based NDI controller is designed that provides the translational axes control by generating the desired roll and pitch commands. Simulations on the non-linear model of octorotor system validate the dominant performance of the proposed scheme compared to the existing methods in the literature.

Optimization and Control of a Wind Energy Conversion System (WECS) Based on a Dual-Fed Induction Generator (DFIG) to Improve Wind Turbine Efficiency

This study is focused on the optimization and the control of a wind energy conversion system (WENS) by using Matlab/Simulink. It is based on a dual-fed induction generator (DFIG) connected to the fixed grid frequency through a back-to-back converter. The main objective is to develop a numerical model to extract the maximum energy power during the operation of the wind system, by presenting different strategies for controlling the electrical and the mechanical parameters of the wind-generated system. The Pitch Command has been used to control and limit the aerodynamic power in strong wind. The Maximum Power Point Tracking “MPPT” strategy consists of extracting the maximum power from the wind turbine and injecting it into the grid. The control of the Grid Side Converter (GSC) and the Rotor Side Converter (RSC) enables the adjustment of the reactive and active power according to the instructions determined by the grid manager. Vector control by orientation of stator flux of the generator has been applied to the independently control the reactive and active power between the network and the machine. The results of this research reveal the relevance of optimizing energy transfer in a wind power system. It proves that the control strategies used have a significant impact on the energy efficiency of the wind-generated system used.

Application and Validation of Peak Shaving to Improve Performance of a 100 kW Wind Turbine

In this study, a peak shaving algorithm known as a control method to reduce peak mechanical loads in multi-megawatt wind turbines was designed and implemented to a medium capacity 100 kW wind turbine to solve overspeeding shutdown problem due to low moment of inertia of the rotor. The algorithm consists of a look-up table having an input of measured rotor speed and an output of blade pitch angle, and the output is added to the pitch command of the controller. The algorithm was firstly validated using a commercial aero-elastic simulation code, GH-Bladed, under low and high turbulence conditions. The simulation results clearly showed that the maximum rotor speed value causing an overspeed shutdown was reduced and that the mean power was slightly increased. In addition, the damage equivalent loads for the blade out-of-plane bending moment and tower fore-aft bending moment were reduced in the rated wind speed region. Field tests were also performed to confirm the validity of the simulation results. For the field test, the peak shaving algorithm was implemented to the original power control algorithm and it was uploaded to the programmable logic controller of the 100 kW wind turbine. It is concluded that applying the peak shaving method for multi-megawatt wind turbines to a medium capacity wind turbine with much lower rotor moment of inertia is effective in reducing overspeed shutdown problems and helps annual energy production as the result. In wind conditions where the average wind speed is 4.55% higher and the turbulence intensity is 11.81% higher, the maximum rotor speed and standard deviation causing an overspeed shutdown were reduced by − 2.06% and − 8.08%, respectively, with the proposed peak shaving algorithm. The results demonstrate convincingly that predicted improvement in simulation can be achieved in practice.

Predator-Prey Pigeon-Inspired Optimization for UAV ALS Longitudinal Parameters Tuning

This paper presents a predator-prey pigeon-inspired optimization (PPPIO) algorithm for an automatic landing system of a fixed-wing unmanned aerial vehicle (UAV) in the longitudinal plane. A pitch command autopilot and two types of approach power compensators are presented and evaluated in automatic landing. The design of a glide slope command system and an approach power compensator are converted to a finite-dimensional optimization problem. The longitudinal flight controller parameters are optimized by the proposed PPPIO algorithm. The differences between the two proposed approach power compensators are also analyzed. The proposed optimization process can guarantee the control gains vector converge to an approximate optimal solution, and it is computationally much more efficient. Simulation results are presented to demonstrate that this approach helps solve control system optimization problems for different criteria and attains a rather accurate result. As verified by these simulation results, the proposed automatic landing system can help improve UAV's performance during the landing phase.

Integral Barrier Lyapunov Function Based Saturated Dynamic Surface Control for Vision-Based Quadrotors via Back-Stepping

In this paper, we present an attitude restricted dynamic surface (DSC) controller for the vision-based quadrotor to ensure that visual target remains in the camera’s field of view all the time. To ensure stable quadrotor motion, proper perspective image moments are first extracted from the defined virtual image plane to derive the decoupled vision-quadrotor dynamics. Then, by developing a novel saturated DSC controller to limit the roll and pitch commands and employing an integral barrier Lyapunov function to guarantee the boundness of attitude responses, an attitude restricted DSC controller is devised under a back-stepping framework for quadrotors. The designed control scheme can regulate the moment features to their desired values without the violation of visibility constraint with both the attitude inputs and responses of quadrotor keeping inside the predefined state space. The boundedness and convergence of the closed-loop system are proved by the Lyapunov theory. Then, the satisfaction of the pre-specified constraints on the roll and pitch states can be guaranteed. The effectiveness and superiority of the proposed method are validated through extensive simulations and comparisons.

Proportional–integral–derivative attitude control subject to dynamic rate saturation of elevator through explicit command reshaping: An engineering approach

In this article, an explicit pitch command governor for a kind of proportional–integral–derivative attitude control system is proposed based on the model predictive control philosophy to avoid the dynamic rate saturation in the elevator. In this command governor, the control horizon of the model predictive controller is selected as 1 such that the predicted saturations can be represented by a set of linear inequalities, which can significantly reduce the computational complexity, and the optimal solution can be calculated in real-time. The effectiveness of the proposed method is validated via numerical simulations. In addition, the limitations of this pitch governor are also revealed through investigating its scope of application in terms of uncertainties, nonlinearities and coupling effects.

Integrated pitch control for wind turbine based on a novel pitch control system

A novel pitch control system is proposed for wind turbine to smooth output power and load fluctuations. This system is driven by a servo-valve controlled hydraulic motor and is precisely controlled to track the desired pitch angle trajectory. Nonlinear modeling and characteristics of this system are presented and analyzed. An adaptive nonlinear sliding mode pitch angle controller is designed to deal with the uncertainties and external disturbances in this system. An integrated pitch control strategy is proposed to generate the reference pitch commands for this system by considering the load reductions. The proposed system, pitch controller, and the control strategy have been validated for efficient and accurate pitch control performances by comparative experimental results under realistic wind speeds.

Optimal Control Framework for Estimating Autopilot Safety Margins

This paper presents an optimal control framework to determine a collection of open-loop command signals that mathematically guarantees operation of an aircraft within certain prescribed state constraints. The framework is specifically applied to estimate margins for the reference command inputs of aircraft autopilot systems so that safe operation within a given flight envelope can be assured under appropriate control action. Flight envelope excursions are generally considered as precursors to loss-of-control incidents; hence, these margins contain safety-critical information that can help improve the situational awareness onboard the aircraft. In off-nominal conditions, the computed safety margins provide indications of a degraded aircraft with reduced flying and handling qualities. These indications appear in the form of increasingly more strict limits on the autopilot reference command input. The entire framework is illustrated on an example problem involving a pitch dynamics model with state constraints on the pitch attitude. Simulations are conducted wherein margins are computed for the reference pitch command of the pitch hold system, while the aircraft enters an off-nominal condition with severely degraded system dynamics and reduced elevator effectiveness.

추력벡터제어 비행체의 일관된 탄도 성형을 위한 피치각명령 산출 방법

In this paper, we propose a method of generating pitch commands for consistent initial trajectories irrelevant to flight conditions in the initial boosting phase of a thrust-vector-controlled vehicle. After shape assumption of the pitch command profile, parameters of the profile are determined in real time in order for the summit height of the trajectory to be a desired value by deriving the summit height considering thrust performance, gravity, and other flight conditions. Computer simulation results demonstrate good performance of the proposed method.

Validation of Individual Pitch Control by Field Tests on Two- and Three-Bladed Wind Turbines

Further improvements in the cost-effectiveness of wind turbines drive designers toward larger, lighter, and more flexible structures, in which more intelligent control systems play an important part in actively reducing the applied structural loads. These improvements also help to eliminate the need for wind turbines to simply withstand the full force of the applied loads through the use of stronger, heavier, and therefore more expensive structures. One way to reduce the loads is to use individual pitch control (IPC), whereby each blade receives a different pitch command to compensate for asymmetrical loads caused by nonuniform flow across the rotor. Originating in helicopters, the use of IPC for wind turbines was suggested for many years. Although many simulation studies have shown that significant load reductions are possible, confirmation of this using field tests on a real turbine in natural turbulence is important to give wind turbine designers the confidence to design to the reduced loads that IPC can deliver. This paper presents the results of field tests on two different 600-kW wind turbines, one two-bladed and one three-bladed. The results demonstrate convincingly that the predicted load reductions can be achieved in practice.

Flight Control Laws Verification Using Continuous Genetic Algorithms

This work is concerned with the application of a continuous genetic algorithm (CGA) to solve the nonlinear optimization problem that results from the clearance process of nonlinear flight control laws. The CGA is used to generate a pilot command signal that governs the aircraft performance around certain points in the flight envelope about which the aircraft dynamics were trimmed. The performance of the aircraft model due to pitch and roll pilot commands is analyzed to find the worst combination that leads to a nonallowable load factor. The motivations for using the CGA to solve this type of optimization problem are due to the fact that the pilot command signals are smooth and correlated, which are difficult to generate using the conventional genetic algorithm (GA). Also the CGA has the advantage over the conventional GA method in being able to generate smooth solutions without the loss of significant information in the presence of a rate limiter in the controller design and the time delay in response to the actuators. Simulation results are presented which show superior convergence performance using the CGA compared with conventional genetic algorithms.

Design and comparison of autopilots of an air-to-surface antitank missile and its terminal guidance study

The design of the autopilot is one of the most important algorithms of missiles. Performance of the autopilot and its robustness are significant matters to hit a target accurately. The autopilot should satisfy the desired performance under disturbances. In the scope of this study, three autopilots were offered for tracking pitch acceleration command using different control methods: three-loop classic control, pole-placement control and receding horizon predictive control. The aim of the autopilot designed by employing receding horizon predictive control is to minimize the flight control effort, and to make the close-loop system insensitive against modelling uncertainties and stochastic shattering factors. This study comes up with that the missile is able to move in desired performance under disturbances such as control surface misplacement, thrust misalignment, wind and aerodynamic uncertainties with more robustness, less control effort and minimum miss distance and terminal time using an alternative control method instead of classic and pole-placement control methods which are generally referred by the defence industry.

Autonomous terrain-following for unmanned air vehicles

This paper presents an integrated guidance and control design scheme for an unmanned air vehicle (UAV), and its flight test results. The paper focuses on the longitudinal control and guidance aspects, with particular emphasis on the terrain-following problem. An introduction to the mission, and the terrain-following problem is given first. Waypoints for climb and descent are defined. Computation of the reference trajectory in the vertical plane is discussed, including a terrain-following (TF) algorithm for real-time calculation of climb/descent points and altitudes. The algorithm is particularly suited for online computation and is therefore useful for autonomous flight. The algorithm computes the height at which the vehicle should fly so that a specified clearance from the underlying terrain is always maintained, while ensuring that the vehicle’s rate of climb and rate of descent constraints are not violated. The output of the terrain-following algorithm is used to construct a smooth reference trajectory for the vehicle to track. The design of a robust controller for altitude tracking and stability augmentation of the vehicle is then presented. The controller uses elevators for pitch control in the inner loop, while the reference pitch commands are generated by the outer altitude control loop. The controller tracks the reference trajectory computed by the terrain-following algorithm. The design of an electromechanical actuator for actuating the control surfaces of the vehicle during flight is also discussed. The entire guidance and control scheme is implemented on an actual experimental vehicle and flight test results are presented and discussed.

Autonomous Flight at Low Altitude Using Light Sensors and Little Computational Power

The ability to fly at low altitude while actively avoiding collisions with the terrain and objects such as trees and buildings is a great challenge for small unmanned aircraft. This paper builds on top of a control strategy called optiPilot whereby a series of optic-flow detectors pointed at divergent viewing directions around the aircraft main axis are linearly combined into roll and pitch commands using two sets of weights. This control strategy already proved successful at controlling flight and avoiding collisions in reactive navigation experiments. This paper describes how optiPilot can efficiently steer a flying platform during the critical phases of hand-launched take off and landing. It then shows how optiPilot can be coupled with a GPS in order to provide goal-directed, nap-of-the-earth flight control in presence of obstacles. Two fully autonomous flights of 25 minutes each are described where a 400-gram unmanned aircraft flies at approx. 10 m above ground in a circular path including two copses of trees requiring efficient collision avoidance actions.

Flight Testing of a Reconfigurable Control System on an Unmanned Aircraft

A radio-controlled aircraft was built and equipped with air-data and inertial sensors. A radio frequency link was added to transmit data and receive commands from a ground station. Data from several flight tests were used to characterize the dynamic response of the aircraft. Despite the high level of noise associated with the low-cost sensor suite, consistent identification of critical aircraft parameters was obtained. Flight tests were also conducted with actuator failures induced on one elevator, one aileron, and one engine. Recursive parameter identification produced parameters tracking the effects of the failures, such as reduced effectiveness of pitch commands due to a locked elevator, or roll and sideslip due to engine failure. The identified parameters were also used in reconfigurable control experiments, where knowledge of the aircraft parameters was used to compensate for the effect of failures, reducing the pilot's workload. Overall, the paper demonstrates that recursive identification and reconfigurable control algorithms are implementable in real-time, even in low-cost platforms. They can be designed to effectively compensate for actuator failures and aircraft damage.