Nonlinear controller design for wall inspection by a quad rotor helicopter under wind disturbance

Distributed tracking control of unmanned aerial vehicles under wind disturbance and model uncertainty

The so-called "New Space era" has seen a disruptive change in the business models and manufacturing technologies of launch vehicle companies. However, limited consideration has been given to the benefits that innovation in control theory can bring; not only in terms of increasing the limits of performance but also reducing mission preparation or "missionisation" efforts. Moreover, there is a gap between the current state-of-practice that still relies on linear controls and other modern control techniques that could bring relevant improvements in launcher attitude control; this is the case for nonlinear control algorithms, especially those based on Nonlinear Dynamic Inversion (NDI). NDI is a technique that basically 'cancels' the nonlinearities of a class of nonlinear systems, allowing for a single linear control law to be applied without the need for gain-scheduling across different operational points. Incremental NDI (INDI) is a variation of NDI that generates incremental commands and employs acceleration feedback to reduce model dependency, making it easier to design, and results in being more robust in closed-loop. While INDI has been applied successfully to several aerospace applications, its applicability to launch vehicles has not yet been adequately investigated. The objective of this paper is therefore to introduce and raise awareness of the INDI method among the launcher guidance, navigation, and control (GNC) community, showcasing its implementation on a representative launch ascent application scenario which highlights INDI's strengths and challenges. We present a new, practical approach for stability analysis of INDI for attitude control, and compare INDI with scheduled PD controllers with-and without angular acceleration estimates. Results show that, while INDI controllers are generally more sensitive to sensor noise and actuator delay than linear controllers, their potential benefits outweigh these limitations in terms of robustness and performance.

Visible Light Communication (VLC) has emerged as a powerful technique for wireless communication systems. Providing high data rate and increasing capacity are the major problems in VLC. Recent evidence suggests that Multiple Input Multiple Output (MIMO) technique can offers improved data rates and increased link range. This paper describes the design and implementation of visible light communication system in indoor environment exploring the benefits of MIMO. The specific objective of this research was to implement a 4×4 Multiple Input (LEDs) Multiple Output (photodetectors)-VLC communication system, where a 16 white power LEDs in four arrays are setting up at transmitter and four RX modules are setting up at receiver side without the need for additional power or bandwidth as well as analyze a mathematical model for a VLC- 4×4 MIMO with different modes such as the suitable angles to cover the entire room. The research designs practically an electronic circuit for the transmitter and receiver with inexpensive components. The power distribution of different propagation modes is calculated for Single Input Single Output (SISO) and MIMO channels in typical room dimensions. The results in this paper indicate that the power is distributed uniformly for entire room when implemented VLC-MIMO as compared to VLC-SISO. Furthermore, a 4×4 MIMO implementing VLC is compared in term of BER vs. SINR with SISO communication system for both Line of Sight (LOS) and Non Line of Sight (NLOS) propagation modes. Comparing the two results of LOS and NLOS, it can be seen that a 4×4 MIMO implementing VLC for LOS perform better than the same system with NLOS due to decreasing in the received power resulted from the multipath effect.

An experimental approach to multi-input multi-output nonlinear active vibration control of a clamped sandwich beam

Dynamical systems are often nonlinear in nature. It motives people to explore various theoretical nonlinear analysis and control design tools, of which constructive nonlinear design methods are the most celebrated ones. However, applying a constructive tool faces up a big hurdle that the tool deals only with a certain dynamical structure, often not possessed by the natural dynamics. Nonlinear constructive control designs heavily relies on the identification of a particular structure via coordinate transformation and control transformation. To be realistic, these theoretical tools are not general to all of the nonlinear systems. Here, a challenging benchmark example–a four degrees of freedom inverted pendulum under the influence of a planar force–is considered that is nonlinear, multiple input and multiple output, underactuated and unstable. The benchmark is also of practical interests because it is an abstract of several applications. Three challenging control objectives are envisaged for the first time in the literature in order to how to apply various cuttingedge theoretical nonlinear control tools. In fact, the key step of all of the nonlinear designs is to identify spectral structures– certain “normal” forms. From this aspect, a sequence of preliminary designs will accompany the existing tools to construct nonlinear controllers, which is quite different from the linear control designs.

Multiple Input - Multiple Output (MIMO) is a new communications paradigm which brings significant benefits to future communication systems. In contrast to conventional wireless communication systems, MIMO systems exploit the spatial diversity available in multipath propagation to create parallel channels within a common bandwidth. The multiple channels can be used for capacity enhancement, coverage improvement, lower radiated power spectral density, interference/jammer suppression, multi-beam communication and battery power savings. Research, development and exploitation of MIMO technology for tactical communication systems is significantly limited by lack of mobile, real-time MIMO testbeds to verify and validate extensive theoretical results. We report a 4x4 mobile, wideband, real-time MIMO-OFDM testbed designed and developed by the team of San Diego Research Center (SDRC) and Brigham Young University (BYU). Using this testbed we have successfully demonstrated the feasibility of peer-to-peer Mobile MIMO by closing 1000m links, at 50 mph speeds, at 12 bps/Hz spectral efficiency.

A decentralized PID neural network (PIDNN) control scheme was proposed to a quadrotor helicopter subjected to wind disturbance. First, the dynamic model that considered the effect of wind disturbance was established via Newton-Euler formalism. For quadrotor helicopter flying at low altitude in actual situation, it was more susceptible to be influenced by the turbulent wind field. Therefore, the turbulent wind field was generated according to Dryden model and taken into consideration as the disturbance source of quadrotor helicopter. Then, a nested loop control approach was proposed for the stabilization and navigation problems of the quadrotor subjected to wind disturbance. A decentralized PIDNN controller was designed for the inner loop to stabilize the attitude angle. A conventional PID controller was used for the outer loop in order to generate the reference path to inner loop. Moreover, the connective weights of the PIDNN were trained on-line by error back-propagation method. Furthermore, the initial connective weights were identified according to the principle of PID control theory and the appropriate learning rate was selected by discrete Lyapunov theory in order to ensure the stability. Finally, the simulation results demonstrate that the controller can effectively resist external wind disturbances, and presents good stability, maneuverability and robustness.

Robust Nonlinear EGR and VGT Control with Integral Action for Diesel Engines

This thesis describes the analytical design and the performance analysis of optimum receivers for Multiple Input - Multiple Output (MIMO) fading channels. In particular, a novel Optimum Receiver for separately-correlated MIMO channels is proposed. This novel pilot-aided receiver is able to process jointly the pilot symbols, transmitted within each time frame as a preamble, and the information symbols and to decode the transmitted data in a single step, avoiding the explicit estimation of the channel matrix. The optimum receiver is designed for the following two scenarios, corresponding to different transmission schemes and channel models: 1) Narrowband Rician fading MIMO channel with spatial separate correlation; 2) MIMO-OFDM Rician fading channel with space and frequency separate correlation. For each system the performance of the optimum receiver is studied in detail under different channel conditions. The optimum receiver is compared with: - the ideal Genie Receiver, knowing perfectly the Channel State Information (CSI) at no cost; - the standard Mismatched Receiver, estimating the CSI in a first step, then using this imperfect estimate in the ideal channel metric. Since the optimum receiver requires the knowledge of the channel parameters for the decoding process, an estimation algorithm is proposed and tested. Moreover, a complexity analysis is carried out and methods for complexity reduction are proposed. Furthermore, the narrowband receiver is tested in realistic conditions using measured channel samples. Finally, a blind version of the receiver is proposed

Multiple Input – Multiple Output (MIMO) architectures are essential in 4G and 5G mobile communications. They are capable of providing both multiplexing gain and diversity gain depending on the use case. Indeed, they can provide high data rate by simultaneous transmission of data streams through multiple independently faded, uncorrelated, channels. On the other hand, they can be employed as phased arrays exhibiting directive multi-antenna characteristics with dynamic beam-patterns to boost capacity via higher SNRs. Those “hybrid systems” came in play to provide the advantages of both MIMO and phased array. In this path in order to increase the gain of an antenna without altering its layout, meaning that the dimensions of the radiating aperture remain the same, we need to use the overlapping element concept. At the same time we need to assess whether or not other parameters of MIMO performance are compromised. This assessment is presented in the current work through the provision of a MIMO channel model incorporating the overlapping concept.

In this brief, a novel robust nonlinear motion controller with disturbance observer (DOB) for positioning control of a nonlinear single-input-single-output (SISO) mechanical system is proposed. The controller is designed in a backstepping manner. First, a proportional-integral (PI) controller is designed to stabilize the position error. Consequently, a novel robust nonlinear velocity controller with DOB is designed to stabilize the velocity error. With the help of nonlinear damping terms, the input-to-state stability (ISS) property of the overall nonlinear control system is proven, which leads to a major contribution of construction of a theoretically guaranteed robust nonlinear controller with DOB. The performance of the proposed controller is verified through application to a magnetic levitation system. Comparative studies with an adaptive robust nonlinear controller are also carried out. It is shown that the proposed novel controller while being simple is superior over the adaptive robust nonlinear controller for the experimental setup under study.

An adaptive dual control algorithm is presented for multiple-input, multiple output (MIMO) linear systems with input and output noise and unknown parameters. The system parameters are assumed to belong to a finite set on which a prior probability distribution is available. The difficulties in characterizing the future evolution if MIMO system information as required by the dynamic programming are overcome through a novel way of using preposterior analysis. This provides a probabilistic characterization of the future adaptation process and allows the controller to take advantage of the dual effect.

As the evolution of the 3G standards, multiple input and multiple output (MIMO) has been adopted to enhance the performance of 3G systems for the potential of beamforming, spatial multiplexing or spatial diversity. So far, no MIMO scheme has been adopted for time division-synchronous code division multiple access (TD-SCDMA). In this paper, 2times8 MIMO eigen beamforming is proposed to improve the performance of TD-SCDMA. As size limited, the antennas at the UE or Node B are correlated, only one eigen mode of the spatial correlation matrix is found to be useful, and only the beamforming gain and spatial diversity gain can be obtained efficiently. The simulation results of high speed uplink packet access (HSUPA) in the fixed reference channel show that, compared to single input and multiple output (SIMO) 1times8, 3 dB performance gain can be obtained by MIMO 2times8 eigen beamforming; while compared to that of single input and single output (SISO), the performance gain is 8-3 dB

In this paper, an optimal controller is investigate d based on the Linear Quadratic Control method. The controller simulation is execut ed based on a small-scale autonomous model helicopter, Yamaha R-50. Genetic algorithms are employed to generate weighting matrices by optimizing the performance index of the control system. As a result, this method produces optimal weighting matrices which further improve the Linear Quadratic Controller. A full state feedback approach is used in the control design process. A Kalman observer is integrated into the controller to predi ct full state variables, since only a limited number of state variables are measured. Finally, th e performance of the controller is evaluated in the time domain with and without disturbances when the model helicopter is in hovering flight and forward flight. I. Introduction utonomous helicopters offer special advantages for major operations in both civilian and military sect ors, particularly in cases that are considered either in accessible or dangerous for human beings, due to th eir vertical take-off and landing (VTOL) capabilities. The contr ol system of autonomous helicopters plays a key rol e in its ability to carry out the assigned task effectively. This has lead to a growing interest in the design and analysis of the control system of autonomous helicopters. In 1990s, classic control theory was widely used for autonom ous helicopter control systems, which is mainly a succe ssive loop closure approach. The control gains are selected separately using tools such as Root locus, Bode and Nyquist plots. The controller parameters are usual ly tuned based on the controller performance measured either in ti me domain or in frequency domain. This design procedure becomes increasingly difficult as more and more loo ps are added, specifically, when the dynamics invol ve multiple inputs, multiple outputs, or multiple feedback loop s with complex performance criteria. To control an autonomous helicopter modeled as a complex Multiple Input Multiple Output (MIMO) system, the performance criteria can not be easily met by the approach based on classis cont rol theory. Several researchers have developed a number of diff erent ways for the control system design of autonom ous helicopters in the literature. Shim et al 1 presented three different control methods using li near robust, fuzzy logic, and nonlinear tracking controls, for an autonomous helicopter in hover and low speed flight. Johnson a nd Kannan 2

This chapter presents a general adaptive inverse approach for control of plants with uncertain nonsmooth actuator nonlinearities such as dead-zone, backlash, hysteresis, and other piecewise-linear characteristics which are common in control systems and often limit system performance. This chapter gives an overview of various state feedback and output feedback control designs for linear, nonlinear, single-input and single-output, and multi-input and multi-output plants as well as open problems in this area of major theoretical and practical relevance. A key problem is to develop linearly parametrized error models suitable for developing adaptive laws to update the inverse and feedback controller parameters, which is solved for various considered cases. The chapter shows that control systems with commonly used linear or nonlinear feedback controllers such as a model reference, PID, pole placement, feedback linearization, or backstepping can be combined with an adaptive inverse to handle actuator nonlinearities.