Eng Kee Poh - Academia.edu (original) (raw)
Papers by Eng Kee Poh
2021 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (APS/URSI)
This paper presents a simple Gaussian model for ionospheric scintillation in Singapore. The model... more This paper presents a simple Gaussian model for ionospheric scintillation in Singapore. The model is simple and consists of only one Gaussian term and a raised constant to characterize the S4 index. The model parameters are determined based on the 90th percentile of S4 scintillation data collected in Singapore. Comparisons of model and scintillation data over various months in Singapore indicates that the model predicts relatively well the scintillation activity in Singapore.
1993 American Control Conference, 1993
Higher Harmonic Control (HHC) is a method for cancelling the helicopter fuselage vibrations by in... more Higher Harmonic Control (HHC) is a method for cancelling the helicopter fuselage vibrations by introducing N/rev oscillations of rotor blades pitch angle (N is the number of rotor blades). This method is effective if both the amplitude and the phase of the oscillations introduced are chosen appropriately, depending on the flight conditions. It is shown in this paper that if the frequency of these oscillations is much greater than N/rev, the phase dependency disappears.
In this paper, an attitude determination system using three GPS antennas on the VELOX-CI microsat... more In this paper, an attitude determination system using three GPS antennas on the VELOX-CI microsatellite is presented. Attitude determination using GPS is typically challenging on a microsatellite due to its small form factor which limits the length of its GPS antenna baselines and the accuracy of the attitude fix. The baselines of the three GPS antennas mounted on the top platform of the VELOXCI satellite are only 26.5 cm, 26.5 cm and 47.8 cm. In addition, due to the dynamics and high velocity of a LEO satellite, the number of common satellites for antennas in a baseline is fast changing and may be insufficient for reliable integer ambiguity resolution. In order to perform the dual missions of GPS attitude determination as well as radio occultation for VELOX-CI, the centre GPS antenna is mounted facing up while the other antennas are mounted facing to the side at an angle of 25.9 degrees to the centre antenna. This configuration further reduces the number of common visible satellite...
Elements, 2019
32nd International Symposium on Space Technology and Science (ISTS), Fukui, Japan, 15-21 June 2019
Intelligent Systems, Control and Automation: Science and Engineering, 2016
This chapter presents two kinds of optimal control-based satellite formation keeping strategies.
[1991] Proceedings of the 30th IEEE Conference on Decision and Control
ABSTRACT The zeros of linear systems that ensure H2-optimal transmission characteristics from inp... more ABSTRACT The zeros of linear systems that ensure H2-optimal transmission characteristics from inputs to outputs are analyzed. Qualitative features of the resulting behavior are investigated, including controllability properties, optimal transmission properties, and nonminimum phase properties
AIAA Guidance, Navigation and Control Conference and Exhibit, 2008
AIAA Guidance, Navigation and Control Conference and Exhibit
2014 IEEE/ION Position, Location and Navigation Symposium - PLANS 2014, 2014
ABSTRACT Traditional NCO models in PLL update the local initial phase estimation at every update ... more ABSTRACT Traditional NCO models in PLL update the local initial phase estimation at every update interval based on the assumption that signal frequency estimation is accurate. The waveform generated by these models will be discontinuous at the update instant. We propose a new NCO model which adjusts both the frequency and phase of the local carrier to maintain waveform continuity. We denote the traditional method as phase feedback NCO, while our proposed method as frequency feedback NCO. Simulation results show that our proposed frequency feedback NCO model has wider pull-in range and larger equivalent bandwidth when compared with traditional phase feedback NCO model. The relationship between bandwidth and filter parameters is also derived. The formulas can be used to guide the selection of the filter parameters given desired bandwidth.
AIAA Guidance, Navigation, and Control Conference, 2010
ABSTRACT In this paper, model predictive control (MPC) with cost function which is non-quadratic ... more ABSTRACT In this paper, model predictive control (MPC) with cost function which is non-quadratic in control input is used to design a high level controller for fixed wing unmanned aerial vehicle (UAV). Given the kinematic model for UAV with low level autopilot, the control objective is to track straight lines defined by a set of way points. The path tracking problem is transformed to a problem of regulating the distance and heading error from desired straight lines. The optimization problem for MPC incorporates information on future paths. It is shown that under certain conditions the solution to MPC problem approaches the Dubins path. The simulation results also demonstrate that using our proposed scheme, the UAV follows the Dubins path. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
IEEE ICCA 2010, 2010
ABSTRACT This paper addresses a decentralized quaternion-based controller for attitude tracking s... more ABSTRACT This paper addresses a decentralized quaternion-based controller for attitude tracking synchronization in spacecraft formation, without angular velocity measurements. Passivity approach is deployed to remove the requirements for absolute angular velocity measurements and relative angular velocity measurements between neighboring spacecrafts. The proposed control law guarantees that each spacecraft approaches its desired time-varying attitude and angular velocity while achieving attitude synchronization among spacecrafts during formation maneuvers. The only assumption on inter-spacecraft communication topology is being bidirectional. The stability of the resulting closed-loop systems is proved by virtue of LaSalle's invariance principle. Simulation results demonstrate the effectiveness of the proposed attitude tracking synchronization controller for spacecraft formation in the absence of angular velocity measurements.
IEEE ICCA 2010, 2010
ABSTRACT This paper introduces a decentralized design technique for satellite formation using alg... more ABSTRACT This paper introduces a decentralized design technique for satellite formation using algebraic graph theories. Each satellite controls itself using the relative states describing its position and velocity relative to neighboring satellites it can sense. The formation control problem with n satellites is thus reduced into stabilization problem of single satellite with the identical relative dynamics, individualized by a specific scalar parameter. This scalar parameter takes the nonzero eigenvalues of a Laplacian matrix which represents the topology of relative measurements among all satellites. The modified relative dynamics can be viewed as linear system with uncertain parameters and an optimal guaranteed cost control law can be applied. Simulation results show the efficiency of the proposed decentralized formation control strategy for satellite formation flying.
Guidance, Navigation, and Control Conference and Exhibit, 1998
In this paper, we present an approach to integrated steering and control design for flight vehicl... more In this paper, we present an approach to integrated steering and control design for flight vehicles. In this approach, input-output linearization is applied to derive the integrated controller, which performs the function of both autopilot controller and steering law. The nonlinear six degree-of-freedom dynamics together with aerodynamics model of vehicle is considered. Simulation shows that the design has excellent performance and is robust against unmodelled actuator dynamics and uncertainties.
Proceedings of 32nd IEEE Conference on Decision and Control
ABSTRACT In this paper, we give a parametrization of a class of stabilizing vibrational controlle... more ABSTRACT In this paper, we give a parametrization of a class of stabilizing vibrational controllers for single-input single-output systems. In particular, we show that, for the averaged system, Youla parametrization takes place and use this parametrization to design a controller that satisfies unit step response specifications for the original (non-averaged) system
2008 2nd International Symposium on Systems and Control in Aerospace and Astronautics, 2008
ABSTRACT A simulation method with a modeling error index are introduced for comparing and evaluat... more ABSTRACT A simulation method with a modeling error index are introduced for comparing and evaluating various theories of relative motion of satellite formation dynamics. The index captures error components of relative position and velocity between a selected satellite relative model and a precise propagator. It is applicable to evaluate the accuracy performance of any valid relative dynamic model including both linear and nonlinear models. In this paper, we study the evaluation of satellite relative dynamic models described by differential equations in LVLH coordinate. Five widely used models are analyzed in different orbits in perturbed Earth environment. The results show that, when the Earth aspherical gravity and the air drag are present, the accuracy of some models is affected tremendously by eccentricity, semi-major axis, inclination, and formation size. The numerical results provide valuable information for formation design.
AIAA Guidance, Navigation and Control Conference and Exhibit, 2008
Design of kernel control laws is an important step in autonomous ∞ight control design for UAVs, b... more Design of kernel control laws is an important step in autonomous ∞ight control design for UAVs, because the function of kernel control laws is to guarantee asymptotical innerloop stability of aircraft motion relative to the surrounding air. The design can be further complicated by nonlinear ∞ight dynamics. In this paper, we propose a hierarchical dynamic inversion (HDI) method for design of the kernel control law for a flxed-wing UAV based on quasi-steady states. HDI is more generally applicable to some non-a‐ne nonlinear systems. The designed kernel control law is incorporated into an autonomous ∞ight controller and verifled in simulation based on the high-fldelity 6-DOF nonlinear model of a UAV. The simulation results demonstrate that the UAV with the designed kernel control law successfully execute super maneuver and is robust against actuator gain variation.
International Journal of Robust and Nonlinear Control, 2012
This paper addresses attitude synchronization and tracking problems in spacecraft formation in th... more This paper addresses attitude synchronization and tracking problems in spacecraft formation in the presence of model uncertainties and external disturbances. A decentralized adaptive sliding mode control law is proposed using undirected interspacecraft communication topology and analyzed based on algebraic graph theory. A multispacecraft sliding manifold is derived, on which each spacecraft approaches desired timevarying attitude and angular velocity while maintaining attitude synchronization with the other spacecraft in the formation. A control law is then developed to ensure convergence to the sliding manifold. The stability of the resulting closed-loop system is proved by application of Barbalat's Lemma. Simulation results demonstrate the effectiveness of the proposed attitude synchronization and tracking methodology. Copyright
The views, opinions and/or findings contained in this report are those of the author(s) and shoul... more The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other documentation. 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution unlimited.
2021 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (APS/URSI)
This paper presents a simple Gaussian model for ionospheric scintillation in Singapore. The model... more This paper presents a simple Gaussian model for ionospheric scintillation in Singapore. The model is simple and consists of only one Gaussian term and a raised constant to characterize the S4 index. The model parameters are determined based on the 90th percentile of S4 scintillation data collected in Singapore. Comparisons of model and scintillation data over various months in Singapore indicates that the model predicts relatively well the scintillation activity in Singapore.
1993 American Control Conference, 1993
Higher Harmonic Control (HHC) is a method for cancelling the helicopter fuselage vibrations by in... more Higher Harmonic Control (HHC) is a method for cancelling the helicopter fuselage vibrations by introducing N/rev oscillations of rotor blades pitch angle (N is the number of rotor blades). This method is effective if both the amplitude and the phase of the oscillations introduced are chosen appropriately, depending on the flight conditions. It is shown in this paper that if the frequency of these oscillations is much greater than N/rev, the phase dependency disappears.
In this paper, an attitude determination system using three GPS antennas on the VELOX-CI microsat... more In this paper, an attitude determination system using three GPS antennas on the VELOX-CI microsatellite is presented. Attitude determination using GPS is typically challenging on a microsatellite due to its small form factor which limits the length of its GPS antenna baselines and the accuracy of the attitude fix. The baselines of the three GPS antennas mounted on the top platform of the VELOXCI satellite are only 26.5 cm, 26.5 cm and 47.8 cm. In addition, due to the dynamics and high velocity of a LEO satellite, the number of common satellites for antennas in a baseline is fast changing and may be insufficient for reliable integer ambiguity resolution. In order to perform the dual missions of GPS attitude determination as well as radio occultation for VELOX-CI, the centre GPS antenna is mounted facing up while the other antennas are mounted facing to the side at an angle of 25.9 degrees to the centre antenna. This configuration further reduces the number of common visible satellite...
Elements, 2019
32nd International Symposium on Space Technology and Science (ISTS), Fukui, Japan, 15-21 June 2019
Intelligent Systems, Control and Automation: Science and Engineering, 2016
This chapter presents two kinds of optimal control-based satellite formation keeping strategies.
[1991] Proceedings of the 30th IEEE Conference on Decision and Control
ABSTRACT The zeros of linear systems that ensure H2-optimal transmission characteristics from inp... more ABSTRACT The zeros of linear systems that ensure H2-optimal transmission characteristics from inputs to outputs are analyzed. Qualitative features of the resulting behavior are investigated, including controllability properties, optimal transmission properties, and nonminimum phase properties
AIAA Guidance, Navigation and Control Conference and Exhibit, 2008
AIAA Guidance, Navigation and Control Conference and Exhibit
2014 IEEE/ION Position, Location and Navigation Symposium - PLANS 2014, 2014
ABSTRACT Traditional NCO models in PLL update the local initial phase estimation at every update ... more ABSTRACT Traditional NCO models in PLL update the local initial phase estimation at every update interval based on the assumption that signal frequency estimation is accurate. The waveform generated by these models will be discontinuous at the update instant. We propose a new NCO model which adjusts both the frequency and phase of the local carrier to maintain waveform continuity. We denote the traditional method as phase feedback NCO, while our proposed method as frequency feedback NCO. Simulation results show that our proposed frequency feedback NCO model has wider pull-in range and larger equivalent bandwidth when compared with traditional phase feedback NCO model. The relationship between bandwidth and filter parameters is also derived. The formulas can be used to guide the selection of the filter parameters given desired bandwidth.
AIAA Guidance, Navigation, and Control Conference, 2010
ABSTRACT In this paper, model predictive control (MPC) with cost function which is non-quadratic ... more ABSTRACT In this paper, model predictive control (MPC) with cost function which is non-quadratic in control input is used to design a high level controller for fixed wing unmanned aerial vehicle (UAV). Given the kinematic model for UAV with low level autopilot, the control objective is to track straight lines defined by a set of way points. The path tracking problem is transformed to a problem of regulating the distance and heading error from desired straight lines. The optimization problem for MPC incorporates information on future paths. It is shown that under certain conditions the solution to MPC problem approaches the Dubins path. The simulation results also demonstrate that using our proposed scheme, the UAV follows the Dubins path. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
IEEE ICCA 2010, 2010
ABSTRACT This paper addresses a decentralized quaternion-based controller for attitude tracking s... more ABSTRACT This paper addresses a decentralized quaternion-based controller for attitude tracking synchronization in spacecraft formation, without angular velocity measurements. Passivity approach is deployed to remove the requirements for absolute angular velocity measurements and relative angular velocity measurements between neighboring spacecrafts. The proposed control law guarantees that each spacecraft approaches its desired time-varying attitude and angular velocity while achieving attitude synchronization among spacecrafts during formation maneuvers. The only assumption on inter-spacecraft communication topology is being bidirectional. The stability of the resulting closed-loop systems is proved by virtue of LaSalle's invariance principle. Simulation results demonstrate the effectiveness of the proposed attitude tracking synchronization controller for spacecraft formation in the absence of angular velocity measurements.
IEEE ICCA 2010, 2010
ABSTRACT This paper introduces a decentralized design technique for satellite formation using alg... more ABSTRACT This paper introduces a decentralized design technique for satellite formation using algebraic graph theories. Each satellite controls itself using the relative states describing its position and velocity relative to neighboring satellites it can sense. The formation control problem with n satellites is thus reduced into stabilization problem of single satellite with the identical relative dynamics, individualized by a specific scalar parameter. This scalar parameter takes the nonzero eigenvalues of a Laplacian matrix which represents the topology of relative measurements among all satellites. The modified relative dynamics can be viewed as linear system with uncertain parameters and an optimal guaranteed cost control law can be applied. Simulation results show the efficiency of the proposed decentralized formation control strategy for satellite formation flying.
Guidance, Navigation, and Control Conference and Exhibit, 1998
In this paper, we present an approach to integrated steering and control design for flight vehicl... more In this paper, we present an approach to integrated steering and control design for flight vehicles. In this approach, input-output linearization is applied to derive the integrated controller, which performs the function of both autopilot controller and steering law. The nonlinear six degree-of-freedom dynamics together with aerodynamics model of vehicle is considered. Simulation shows that the design has excellent performance and is robust against unmodelled actuator dynamics and uncertainties.
Proceedings of 32nd IEEE Conference on Decision and Control
ABSTRACT In this paper, we give a parametrization of a class of stabilizing vibrational controlle... more ABSTRACT In this paper, we give a parametrization of a class of stabilizing vibrational controllers for single-input single-output systems. In particular, we show that, for the averaged system, Youla parametrization takes place and use this parametrization to design a controller that satisfies unit step response specifications for the original (non-averaged) system
2008 2nd International Symposium on Systems and Control in Aerospace and Astronautics, 2008
ABSTRACT A simulation method with a modeling error index are introduced for comparing and evaluat... more ABSTRACT A simulation method with a modeling error index are introduced for comparing and evaluating various theories of relative motion of satellite formation dynamics. The index captures error components of relative position and velocity between a selected satellite relative model and a precise propagator. It is applicable to evaluate the accuracy performance of any valid relative dynamic model including both linear and nonlinear models. In this paper, we study the evaluation of satellite relative dynamic models described by differential equations in LVLH coordinate. Five widely used models are analyzed in different orbits in perturbed Earth environment. The results show that, when the Earth aspherical gravity and the air drag are present, the accuracy of some models is affected tremendously by eccentricity, semi-major axis, inclination, and formation size. The numerical results provide valuable information for formation design.
AIAA Guidance, Navigation and Control Conference and Exhibit, 2008
Design of kernel control laws is an important step in autonomous ∞ight control design for UAVs, b... more Design of kernel control laws is an important step in autonomous ∞ight control design for UAVs, because the function of kernel control laws is to guarantee asymptotical innerloop stability of aircraft motion relative to the surrounding air. The design can be further complicated by nonlinear ∞ight dynamics. In this paper, we propose a hierarchical dynamic inversion (HDI) method for design of the kernel control law for a flxed-wing UAV based on quasi-steady states. HDI is more generally applicable to some non-a‐ne nonlinear systems. The designed kernel control law is incorporated into an autonomous ∞ight controller and verifled in simulation based on the high-fldelity 6-DOF nonlinear model of a UAV. The simulation results demonstrate that the UAV with the designed kernel control law successfully execute super maneuver and is robust against actuator gain variation.
International Journal of Robust and Nonlinear Control, 2012
This paper addresses attitude synchronization and tracking problems in spacecraft formation in th... more This paper addresses attitude synchronization and tracking problems in spacecraft formation in the presence of model uncertainties and external disturbances. A decentralized adaptive sliding mode control law is proposed using undirected interspacecraft communication topology and analyzed based on algebraic graph theory. A multispacecraft sliding manifold is derived, on which each spacecraft approaches desired timevarying attitude and angular velocity while maintaining attitude synchronization with the other spacecraft in the formation. A control law is then developed to ensure convergence to the sliding manifold. The stability of the resulting closed-loop system is proved by application of Barbalat's Lemma. Simulation results demonstrate the effectiveness of the proposed attitude synchronization and tracking methodology. Copyright
The views, opinions and/or findings contained in this report are those of the author(s) and shoul... more The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other documentation. 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution unlimited.