Tracking Control Loop Research Articles

Research on bidirectional beam tracking and performance analysis of optical communication system with microvibrations

AbstractThe impact of tracking errors over the vibration interference is investigated. A novel expression is presented for the bidirectional laser tracking mechanism which takes in account both periscope communication terminal and beam acquisition process with beaconless technology. In this paper, platform microvibrations are measured and compensated to improve the tracking characteristics of the optical communication terminal. An experiment was conducted to verify the high precision tracking system with the combination of coarse and fine tracking technologies, which represents that the fine tracking error is suppressed to 2.1 μrad. This high precision implementation demonstrates the effectiveness of the tracking control loop, and will contribute to the space laser communication.

Disturbance Attenuation and Pointing Control System Design for an Improved Disturbance-Free Payload Spacecraft

The low-frequency disturbances transmitted by flexible cables are difficult to be attenuated for a novel disturbance-free payload spacecraft, which decreases the payload’s pointing accuracy and stability. In this research, a new spacecraft configuration with a high-precision inertial reference unit composed of capacitive sensors and a spherical test mass is proposed. The disturbance attenuation and pointing control system is subdivided into four interconnected control loops. The payload can be isolated from disturbances in the all-frequency band by the active vibration isolation control loop and the drag-free control loops, and its high-precision pointing requirement can be satisfied with the attitude pointing control loop and the attitude tracking control loop. An integrated control strategy is proposed, and the control system is decoupled into 12 single-input single-output control loops by pre-compensating, which lays the foundation for feedback design. Through the amplitude-frequency response analysis, the control bandwidth is designed according to the Proportional-Integral-Differentive control algorithm. The numerical simulations show that the disturbance attenuation performance is better than −20 dB in the all-frequency band, and the pointing accuracy and the pointing stability are better than 10−6 deg and 10−7 deg/s, respectively. The new spacecraft configuration and the disturbance attenuation and pointing control system provide a general technical solution for payloads with high-precision and high-stability requirements.

Rate-Dependent Hysteresis Modeling and Displacement Tracking Control Based on Least-Squares SVM for Axially Pre-Compressed Macro-Fiber Composite Bimorph.

The new axially pre-compressed macro-fiber composite bimorph (MFC-PBP) can produce large displacement and output power. However, it has the property of strong rate-dependent hysteresis nonlinearity, which challenges the displacement tracking control of morphing structures. In this paper, the least-squares support vector machine (LS-SVM) is applied to model the rate-dependent hysteresis of MFC-PBP. Compared with the predicated results of the series model of the Bouc–Wen model and Hammerstein model (BW-H), the LS-SVM model achieved higher predication accuracy and better generalization ability. Based on the LS-SVM hysteresis compensation model, with the support vector pruning, the displacement tracking feedforward compensator is obtained. In order to improve the displacement tracking accuracy, the LS-SVM feedforward compensator combined with the proportional and integral (PI) controller and the feedforward plus feedback control experiment is carried out on the displacement tracking of MFC-PBP. The test results show that the feedforward plus feedback displacement tracking control loop based on the LS-SVM model also has a higher displacement tracking accuracy than that based on the inverse model of BW-H.

Current-Sensorless Control Strategy for the MPPT of a PV Cell: An Energy-Based Approach

A novel energy-based modelling and control strategy is developed and implemented to solve the maximum power point tracking problem when a photovoltaic cell array is connected to consumption loads. A mathematical model that contains key characteristic parameters of an energy converter stage connected to a photovoltaic cell array is proposed and recast using the port-Hamiltonian framework. The system consists of input-output power port pairs and storage and dissipating elements. Then, a current-sensorless control loop for a maximum power point tracking is designed, acting over the energy converter stage and following an interconnection and damping assignment passivity-based strategy. The performance of the proposed strategy is compared to a (classical) sliding mode control law. Our energy-based strategy is implemented in a hardware platform with a sampling rate of 122 Hz, resulting in lower dynamic power consumption compared to other maximum power point tracking control strategies. Numerical simulations and experimental results validate the performance of the proposed energy-based modelling and the novel control law approach.

A New Approach for Optimal Management of Solar Energy Systems

In this article, a solar-powered photovoltaic system offers a clean energy solution to this challenge; this system is rapidly developing worldwide. Solar energy is believed to be able to meet 2% of the world’s energy requirements, and this system are designed to generate electricity for specific needs, The global development of solar systems, as well as indicators, prices and efficiency of these systems, especially in Iraq, was studied, and a model and integrated system was designed to feed one of the homes in Iraq. proposed Maximum Power Point Tracking (MPPT) control loop and using the best techniques Perturb and Observe (P&O) Algorithm extracting maximum power from PV module under different solar irradiation. Various scenarios involving environmental parameters such as temperature and radiation are presented to demonstrate the theoretical analysis, effectiveness and feasibility of the proposed energy management technique.

A physics-, SCADA-based remaining useful life calculation approach for wind turbine drivetrains

This paper describes the development of a physics-, SCADA-based model able to predict the expected lifetime for wind turbine drivetrains. A real-time coupled torsional gearbox-generator model is developed using the bond graph approach in the software 20SIM. The model uses SCADA data with a sampling frequency of one hertz to impose a load reference on the wind turbine for the simulation model. From the SCADA measurements, rotor torque is estimated and used as input load to the wind turbine rotor, while generator speed is used as reference in the control loop for maximum power point tracking. Shaft torsion is used to predict highspeed shaft radial and axial bearing loads from static equilibrium. The load amplitude and the number of stress cycles are calculated using the load duration distribution method and damage is calculated using Miner’s rule. Expected lifetime is predicted by linear extrapolation of the accumulated fatigue damage to the fatigue limit. Results show that the model can capture the torsional and electrical dynamics and that the model results agree with the reference input. The radial bearing loads match well with literature where additional sensors are used to determine the loads.

A Simple and Effective Excitation Force Estimator for Wave Energy Systems

Wave energy converters (WECs) need to be optimally controlled to be commercially viable. These controllers often require an estimate of the (unmeasurable) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">wave excitation force</i> . To date, observers for WECs are often based upon ‘complex’ techniques, which are counter-intuitive in their design, additionally requiring an explicit model to describe the excitation as part of an (augmented) system. The latter imposes strong assumptions on the design of each observer, while also implying an additional computational burden associated with the necessity of augmenting the WEC model to include the dynamics of the input. We propose a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">simple</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">effective</i> excitation force estimator based on linear time-invariant (LTI) theory, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">without the need</i> for an explicit model of the input. In particular, we re-formulate the unknown-input estimation problem as a tracking control-loop, so that a wide-variety of LTI design techniques (arising from either classical or modern control theory) can be used to compute an estimate of the excitation force. We demonstrate performance, simplicity, and intuitive appeal of the proposed observer, by means of a case study based on a realistic computational fluid dynamics simulation, comparing the technique against a large set of WEC observers, showing that the approach is able to outperform available estimators.

Adaptive Trajectory Tracking Algorithm of a Quadrotor with Sliding Mode Control and Multilayer Neural Network

To improve the trajectory tracking accuracy, the anti‐jamming performance, and the environment adaptability of a quadrotor, the paper proposes a new adaptive trajectory tracking algorithm with multilayer neural network and sliding mode control method. The major difference between other related approaches is that the paper uses the multilayer neural network in the system and the neural network is online computing in the whole process. Firstly, the paper establishes the quadrotor dynamic model and introduces the conception of Sigma‐Pi neural network. Then, the paper adds the neural network to the attitude and trajectory tracking control loop. Moreover, the paper designs the adaptive neural network control law. At last, to illustrate the stability of the adaptive control law, the paper gives the Lyapunov stability analysis. Finally, to demonstrate the effectiveness of the method, the paper gives different types of simulation. Comparing with different cases, when increasing the layer of the neural network, the trajectory tracking performance becomes better. In addition, introducing multilayer neural network into the system could improve the anti‐interference ability of the system and has a high‐precision in tracking the desire trajectory.

Impedance with Finite-Time Control Scheme for Robot-Environment Interaction

For the robot system with the uncertain model and unknown environment parameters, a control scheme combining impedance and finite time is proposed. In order to obtain accurate force control performance indirectly by using position tracking, the control scheme is divided into two parts: an outer loop for force impedance control and an inner loop for position tracking control. In the outer loop, in order to eliminate the force tracking error quickly, the impedance control based on force is adopted; when the robot contacts with the environment, the satisfactory force tracking performance can be obtained. In the inner loop, the finite-time control method based on the homogeneous system is used. Through this method, the desired virtual trajectory generated by the outer loop can be tracked, and the contact force tracking performance can be obtained indirectly in the direction of force. This method does not need the dynamics model knowledge of the robot system, thus avoiding the online real-time calculation of the inverse dynamics of the robot. The unknown uncertainty and external interference of the system are obtained online by using the time-delay estimation, and the control process is effectively compensated, so the algorithm is simple, the convergence speed is fast, and the practical application is easy. The theory of finite-time stability is used to prove that the closed-loop system is finite-time stable, and the effectiveness of the algorithm is proved by simulations.

Observer-Based Adaptive Sliding Mode Control of NPC Converters: An RBF Neural Network Approach

This paper proposes a novel control strategy for three-level neutral-point-clamped (NPC) power converter. The proposed control scheme consists of three control loops, i.e., instantaneous power tracking control loop, voltage regulation loop, and voltage balancing loop. First, in the power tracking control loop, a set of adaptive sliding mode controllers are established to drive the active and reactive power tracking to their desired values via radial basis function neural network technology. In the voltage regulation loop, an efficient but simple adaptive controller is designed to regulate dc-link output voltage where the load is considered as an external disturbance. Moreover, a composite controller is developed in the voltage balancing loop to ensure imbalance voltages between two dc-link capacitors close to zero, in which a reduced-order observer is used to estimate sinusoidal disturbance improving the converter performance. The effectiveness and superiority of the proposed control strategy for the NPC power converter are compared with other control schemes through experimental results.

Optimal GNSS Signal Tracking Loop Design Based on Plant Modeling

Conventional research for signal tracking of the Global Navigation Satellite System (GNSS) uses a loop filter to minimize the effect of measurement noise. Although for a few decades, research into the optimal GNSS tracking loop has been based on similarity between signal tracking and general control loop theory, it has mainly focused on optimal estimator, or shown vulnerability for high dynamic signal tracking. To enhance the performance of the optimal signal tracking loop, this paper proposes new plant modeling for optimal GNSS signal tracking that consists of both optimal estimator and controller. The proposed plant modeling is able to maximize the performance of the optimal signal tracking loop due to the relationships between code and carrier tracking, and between the frequency and phase of the carrier. In addition, the plant clearly defines a relationship between the general control loop and GNSS tracking loop, so that the plant is ready to be applied to various control theories for GNSS signal tracking. To assess the performance of the proposed plant modeling, we implement a linear quadratic Gaussian (LQG) tracking loop based on the new proposed plant and process simulation data. Comparison of the processing results to those of conventional research shows improved performance of the proposed plant modeling.

Aerial-Underwater Systems, a New Paradigm in Unmanned Vehicles

Unmanned Aerial-Underwater Vehicles (UAUVs) arise as a new kind of unmanned system capable of performing equally well in multiple mediums and seamlessly transitioning between them. This work focuses in the modeling and trajectory tracking control of a special class of air-underwater vehicle with full torque actuation and a single thrust force directed along the vehicle’s vertical axis. In particular, a singularity-free representation is required in order to orient the vehicle in any direction, which becomes critical underwater in order to direct the thrust force in the direction of motion and effectively overcome the increased drag and buoyancy forces. A quaternion based representation is used for this purpose. A hierarchical controller is proposed, where trajectory tracking is accomplished by a Proportional-Integral-Derivative (PID) controller with compensation of the restoring forces. The outer trajectory tracking control loop provides the thrust force and desired orientation. The latter is fed to the inner attitude control loop, where a nonlinear quaternion feedback is employed. A gain scheduling strategy is used to deal with the drastic change in medium density during transitions. The proposed scheme is studied through numerical simulations, while real time experiments validate the good performance of the system.

Development of the Hydro Static Wind Turbine Powered RO System for Maximum Power Point and Maximum Permeate Flow Tracking

Wind energy is one of the cheapest sources of energy that may solve the Climate change problem and fresh water scarcity challenges. This article introduces a novel Desalination Wind Turbine that is cheaper and more efficient than the common wind turbine, especially offshore wind turbines. In this system, the wind energy transmitted to the water pump by a hydraulic transmission line. The RO module is used for fresh water production. The pressure recovery module is added to RO system, to increase the permeated flow. It can be increased the permeate flow up to 45%, which is significant. The Maximum Power Point Tracking (MPPT) based on the hydraulic oil pressure measurement is implemented. In addition, the Maximum Permeate Flow Tracking control loop, similar to MPPT, is introduced to optimized the pressure of the RO system. It is increased the annual permeate production up to 8%. The long term performance of the system, such as annual water production is calculated and the ability of the system to MPPT and the wind turbulence and gust is analyzed. The rotor speed overshoot of the closed loop system is less than 16%, which is acceptable.

Power Smoothing of a Variable-Speed Wind Turbine Generator in Association With the Rotor-Speed-Dependent Gain

This paper proposes a power-smoothing scheme for a variable-speed wind turbine generator (WTG) that can smooth out the WTG's fluctuating power caused by varying wind speeds, and thereby keep the system frequency within a narrow range. The proposed scheme employs an additional loop based on the system frequency deviation that operates in conjunction with the maximum power point tracking (MPPT) control loop. Unlike the conventional, fixed-gain scheme, its control gain is modified with the rotor speed. In the proposed scheme, the control gain is determined by considering the ratio of the output of the additional loop to that of the MPPT loop. To improve the contribution of the scheme toward maintaining the frequency while ensuring the stable operation of WTGs, in the low rotor speed region, the ratio is set to be proportional to the rotor speed; in the high rotor speed region, the ratio remains constant. The performance of the proposed scheme is investigated under varying wind conditions for the IEEE 14-bus system. The simulation results demonstrate that the scheme successfully operates regardless of the output power fluctuation of a WTG by adjusting the gain with the rotor speed, and thereby improves the frequency-regulating capability of a WTG.

Power-Smoothing Scheme of a DFIG Using the Adaptive Gain Depending on the Rotor Speed and Frequency Deviation

In an electric power grid that has a high penetration level of wind, the power fluctuation of a large-scale wind power plant (WPP) caused by varying wind speeds deteriorates the system frequency regulation. This paper proposes a power-smoothing scheme of a doubly-fed induction generator (DFIG) that significantly mitigates the system frequency fluctuation while preventing over-deceleration of the rotor speed. The proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while preventing over-deceleration of the rotor speed, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system clearly demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WPP under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.

Almost-Global Finite-Time Trajectory Tracking Control for Quadrotors in the Exponential Coordinates

This paper investigates the trajectory tracking problem for quadrotors with finite-time convergence via homogeneous feedback approach. Based on the inherent underactuated cascaded properties of a quadrotor, the tracking control is decomposed into the outer position tracking control loop and the inner attitude tracking control loop. And the orientation of the four thrust inputs for the position loop is determined by the attitude loop. Therefore, an inner geometric tracking controller based on exponential coordinates for the attitude loop is first proposed, which avoids kinematic singularity and redundancy. Then, a homogeneous feedback plus dynamics compensation scheme is utilized to construct the thrust magnitude control input for the position dynamics, which also provides a reference rotation matrix for the attitude tracking loop. The almost global finite time stability of the whole tracking control system is clearly proved. Numerical results are also presented to demonstrate the effectiveness of this finite-time control strategy.

Intelligent Controller Design for Quad-Rotor Stabilization in Presence of Parameter Variations

The paper presents the mathematical model of a quadrotor unmanned aerial vehicle (UAV) and the design of robust Self-Tuning PID controller based on fuzzy logic, which offers several advantages over certain types of conventional control methods, specifically in dealing with highly nonlinear systems and parameter uncertainty. The proposed controller is applied to the inner and outer loop for heading and position trajectory tracking control to handle the external disturbances caused by the variation in the payload weight during the flight period. The results of the numerical simulation using gazebo physics engine simulator and real-time experiment using AR drone 2.0 test bed demonstrate the effectiveness of this intelligent control strategy which can improve the robustness of the whole system and achieve accurate trajectory tracking control, comparing it with the conventional proportional integral derivative (PID).

회전자 속도에 따라 변하는 게인에 기반한 가변속 풍력발전기 출력 평활화

Abstract - In a power grid that has a high penetration of wind power, the highly-fluctuating output power of wind turbine generators (WTGs) adversely impacts the power quality in terms of the system frequency. This paper proposes a power smoothing scheme of a variable-speed WTG that can smooth its fluctuating output power caused by varying wind speeds, thereby improving system frequency regulation. To achieve this, an additional loop relying on the frequency deviation that operates in association with the maximum power point tracking control loop, is proposed; its control gain is modified with the rotor speed. For a low rotor speed, to ensure the stable operation of a WTG, the gain is set to be proportional to the square of the rotor speed. For a high rotor speed, to improve the power smoothing capability, the control gain is set to be proportional to the cube of the rotor speed. The performance of the proposed scheme is investigated under varying wind speeds for the IEEE 14-bus system using an EMTP-RV simulator. The simulation results indicate that the proposed scheme can mitigate the output power fluctuation of WTGs caused by varying wind speeds by adjusting the control gain depending on the rotor speed, thereby supporting system frequency regulation.Key Words : Power smoothing, Rotor speed-dependent gain, Releasable kinetic energy, Frequency deviation loop.†Corresponding Author : Dept. of Electrical Engineering, WeGAT Research Center, and Smart Grid Research Center, Chonbuk National University, Korea E-mail : yckang@jbnu.ac.kr* Dept. of Electrical Engineering, Chonbuk National University, KoreaReceived : February 23, 2016; Accepted : March 1, 2016

A geometric approach for quadrotor trajectory tracking control

This paper investigates the trajectory tracking problem for quadrotor with attitude finite-time convergence via geometric approach. First, a global geometric dynamic description is presented on the special Euclidean group (SE(3)), and the trajectory tracking control is decomposed into two cascaded tracking control loops: the position tracking control loop and the attitude tracking control loop. Then, based on the fact that the attitude tracking loop is a fast loop, a finite-time controller based on the exponential coordinate is proposed to speed up the response rate of the attitude control loop, so that the artificial singularity and redundancy can be avoided. In addition, a backstepping controller is designed for the position tracking loop to construct the thrust magnitude control input for the position dynamics and the reference rotation matrix for the attitude tracking loop. Finally, the numerical simulation results are presented to demonstrate the effectiveness of this trajectory tracking strategy.

Waveform Aliasing in Satellite Radar Altimetry

The full deramp pulse compression scheme employed by satellite radar altimeters digitizes each radar echo at a sampling rate matched to the chirp bandwidth. Echo power is undersampled by a factor of 2 when the power samples are simply obtained by squaring the magnitude of the echo samples, without first resampling, as is done in all altimeters to date. This results in inadequate sampling of the leading edge of the waveform if the significant wave height (SWH) is low. For a typical Ku-band altimeter with a chirp bandwidth of 320 MHz, simple squaring should be inadequate over ocean surfaces with SWH less than 2 m, that is, half of the ocean. Simply zero-padding the digital samples prior to range Fourier transform alleviates the problem introduced by magnitude squaring. Data from the CryoSat altimeter are used to demonstrate this remedy, and it is found that this reduces the variance in estimated range by 10% and in SWH by 20%. These improvements are confined to a range of SWH values between 1 and 4 m. Zero-padding also seems to have some small impact on values estimated over very flat surfaces (SWH ≪ 1 m), although theory suggests that better resolution of such surfaces would require a bandwidth exceeding 320 MHz. The 500-MHz bandwidth of the Ka-band altimeter on the Satellite with ARGOS and AltiKa mission should encounter these difficulties at smaller SWH values. Onboard range tracking and automatic gain control loops in future altimeters might be improved if zero-padding were employed during onboard waveform processing.