Doctor of Philosophy (PhD), Wright State University, 2020, Electrical Engineering

The pulse-width modulated (PWM) dc-dc converters play a vital role in several industrial applications that include motor drives, electric vehicles, dc distribution systems, and consumer electronics. The switched-mode power converters step the input voltage up or down based on their typology and provide a regulated output voltage. The stability and regulation performance of a power converter can tremendously be improved via a suitable control design. However, due to the nonlinearity of the power converters and the presence of the line and load disturbances, the design of a robust and low-cost control circuit becomes a challenging task. The sliding-mode control of the dc-dc converters has been studied for decades because of its robustness, design simplicity, and suitability for variable structure systems. Despite the merits of the sliding-mode control method, the linear controllers are still dominant and attractive to the commercial applications since they require less design efforts and can be implemented using simple analogue circuits. This research aims to develop simplified sliding-mode control circuits for the classical PWM dc-dc converters in continuous-conduction mode (CCM). The control objectives are to maintain a constant switching frequency, enhance the transient response, provide wide operating range, and track the desired reference voltage under large disturbances. In order to design and test the control circuit, an accurate power converter model should be derived. Hence, large-signal non-ideal averaged models of dc-dc buck and boost converters in CCM are developed. The models are simulated in MATLAB/SIMULINK and compared with the corresponding circuits in SaberRD simulator for validation purpose. Next, PWM-based simplified sliding-mode voltage and current control schemes are designed for the dc-dc buck and boost converters in CCM, respectively. The design procedure and the analogue realization of the control equations are presented, where the control c (open full item for complete abstract)

Committee: Marian K. Kazimierczuk Ph.D. (Advisor); Raúl Ordóñez Ph.D. (Committee Member); Saiyu Ren Ph.D. (Committee Member); Yan Zhuang Ph.D. (Committee Member); Xiaodong Zhang Ph.D. (Committee Member) Subjects: Electrical Engineering

MS, University of Cincinnati, 2024, Engineering and Applied Science: Mechanical Engineering

This work explores the application of Control Moment Gyroscopes (CMGs) to enhance the stability and comfort of electric Vertical Take-Off and Landing (eVTOL) aircraft. Our study encompasses not only the development of a dynamic model for the eVTOL aircraft by integrating CMGs but also the implementation of a backstepping sliding mode-based controller for translation and attitude control. To simulate realistic disturbance scenarios, wind generation, and effect models are considered. Alongside these, a motor dynamics model is taken into account to replicate practical rotor responses. A comprehensive analysis of control performance and passenger comfort is conducted, incorporating a fast Fourier transform frequency domain-based analysis of aircraft oscillations and the corresponding passenger response. The simulation results demonstrate that the use of CMGs not only significantly improves disturbance rejection with low power consumption but also enhances passenger comfort accordingly. Finally, to validate the simulation findings and assess the practical effectiveness of CMGs in mitigating oscillations in eVTOL, hardware experiments are conducted.

Committee: Donghoon Kim Ph.D. (Committee Chair); Daegyun Choi Ph.D. (Committee Member); Tamara Lorenz Ph.D. (Committee Member); Manish Kumar Ph.D. (Committee Member) Subjects: Aerospace Materials

PhD, University of Cincinnati, 2020, Engineering and Applied Science: Aerospace Engineering

This research provides insights on the tilt-rotor quadcopter (TRQ) being a fully actuated system. The tilt-rotor quadcopters are a novel class of quadcopters with the capability of rotating each arm/rotor of the quadcopter to an angle using a servo motor. With the additional servo control inputs, the tilt-rotor quadcopters are fully actuated systems and hence can even hover with a non-zero attitude. Also, this type of a quadcopter can handle external disturbances better than a conventional quadcopter and is fault tolerant. The objective of this dissertation was to design a novel non-linear controller using sliding mode technique that enabled the TRQ to reach desired waypoints, perform robustly under wind disturbances and faults, and hold a commanded attitude and position simultaneously. Four different variants of the tilt rotor quadcopter, namely, TRQ v1, TRQ v2, TCop and TRQ v1H, are studied, and different non-linear control designs using sliding mode technique for each vehicle are presented. Firstly, in this study, the sliding mode control technique is utilized for the pitch, roll and yaw motions for the TRQ v1 while an independent PD controller provides the tilt angles to the servo motors. The dynamic model of the TRQ is presented, based on which sliding surfaces were designed to minimize the tracking errors. Using the control inputs derived from these sliding surfaces, the state variables converge to their desired values in finite-time. Further, the non-linear sliding surface coefficients are obtained by Hurwitz stability analysis. Numerical simulation results are presented that demonstrate the performance and robustness against disturbances using this proposed sliding mode control technique. Secondly, this dissertation studies the fault-tolerant behavior of tilt-rotor platforms. To achieve fault tolerance, the tilt-rotor quadcopter v2 transforms into a T-copter (TCop) design upon motor failure thereby abetting the UAV to cope up with the instabilities ex (open full item for complete abstract)

Committee: Manish Kumar Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Kelly Cohen Ph.D. (Committee Member); George T. Black M.S. (Committee Member) Subjects: Aerospace Materials

Master of Science in Electrical Engineering, Cleveland State University, 2020, Washkewicz College of Engineering

In this thesis, three control methods are developed for the impedance control of a linear pneumatic actuator for contact tasks using discrete valves. Linear pneumatic actuators, particularly with discrete valves, utilize compressed air to produce linear motion. It is a low cost and clean system with straightforward implementation compared to other actuators. Impedance control is applied to the pneumatic actuator to regulate not only force and position, but also the relationship between them. Specifically, the impedance control yields a desired air pressure based on the actual and desired positions, velocity, and force of a pneumatic cylinder to drive the dynamics of the actuator system. Three controllers including Active Disturbance Rejection Control (ADRC), Sliding Mode Control (SMC), and Extended State Observer (ESO) based SMC are implemented to control the pressure output of the actuator system. The control goal is to drive the actual pressure output to the desired pressure from the impedance control module despite the presence of parameter variations and external disturbances. The performances of these controllers are compared based on their abilities of regulating position, force, and pressure in contact and non-contact situations, as well as the amount of control efforts that excite the valve to achieve these goals. Simulation results demonstrate that ADRC provides the best solution to accomplish the control goals in terms of accurate tracking of position, effectively regulating impedance in the presence of an object, and requiring the least amount of control effort necessary to excite valves.

Committee: Lili Dong Ph.D. (Advisor); Petru Fodor Ph.D. (Committee Member); Siu-Tung Yau Ph.D. (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

As control techniques and optimization algorithms evolve, the spectrum of potential applications also broadens. Problems that previously were deemed intractable, now become amenable to practical control and optimization methods. Today, stand-alone wind turbines have been grouped with each other to form a wind farm. Characterizing and optimizing the overall performance of a wind farm requires a new generation of control and optimization techniques. This example and other newly emerged applications reveal the necessity to extend the classical control and optimization results to address the problems that arise in complex systems. Here, we are pursuing a new theoretical advancement in the field of sliding mode control. Having its basis on previous research on the use of sliding mode control in optimization. This dissertation proposes several sliding mode based extremum seeking control schemes for multivariable and distributed optimization problems. In the first scheme, a multivariable extremum seeking via sequential search is proposed. This approach recasts the problem of multivariable extremum seeking control into a sequence of single variable problems. The approach is suitable for non-separable problems, differentiating itself from existing work in this area. We determine stability and convergence conditions from the unidimensional case and derive a sufficient condition for the multivariable scheme to converge to the vicinity of the optimal points. Practical issues in implementation are discussed and several illustrative examples are presented to show the effectiveness of the scheme and highlight its potential use. Next, a simultaneous multivariable extremum seeking control scheme is proposed. Different from the first scheme, the presented approach addresses the problem in a concurrent manner using a single sliding surface. We determine a set of sufficient conditions under which the sliding mode will take place. Then, we demonstrate the convergence of the decision (open full item for complete abstract)

Committee: Umit Ozguner (Advisor); Vadim Utkin (Committee Member); Lisa Fiorentini (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, University of Akron, 2017, Mechanical Engineering

The implications of an upper limb deficiency, whether congenital or acquired, are great. Much research has been devoted to restoring these persons to a greater level of functionality, manifesting itself in a wide range of prosthetic devices that offer various levels of control, cosmesis, and utility. Recent efforts in this endeavor have ushered in a new generation of externally powered dexterous prosthetic hands and limbs that have great potential in helping to achieve this goal. Despite these improvements in mechanical dexterity, the ability to fully utilize this increased dexterity in an intuitive and robust way is lacking. Lack of such a control interface creates a circular problem in the area of upper limb prosthetic devices, where manufacturers of such devices have little incentive to provide improved dexterity for want of a sufficient control interface, and lack of more dexterous manipulators stifles the development of such a control interface that has real world practicality. The current study aims to bridge this gap via the development and testing of biologically inspired control mechanisms to increase the functionality of such devices in an intuitive and anthropomorphic manner.

Committee: Erik Engeberg PhD (Advisor); Celal Batur PhD (Committee Member); Forrest Bao PhD (Committee Member); Jiang Zhe PhD (Committee Member); Henry Astley PhD (Committee Member) Subjects: Biomedical Engineering; Engineering; Robotics

Doctor of Philosophy, The Ohio State University, 2017, Civil Engineering

Natural disasters are one of the constant challenges for designing new and strengthening existing infrastructures. Such hazards in the past have incurred significant loss of life and economic damage; therefore, further research is warranted in this area to enhance the health and minimize the cost of maintaining and upgrading infrastructures, improve residents' comfort, and enable achieving higher levels of life safety. To this end, the field of hazard mitigation and control focuses on performance improvement, safety, and cost effectiveness of structures mostly through minimizing large deformations of seismic-excited structures and suppressing the damage and collapse in dynamic systems due to excessive vibrations. Past developments in active and semi-active control designs, such as the commonly used state space controllers (e.g. linear quadratic regulator for fully observed systems and linear quadratic Gaussian for partially observed systems), consider linear feedback strategies. Meanwhile, such control strategies require linearization, and the system is usually linearized based on linear elastic properties. The control force is proportional to the state space vector and the dynamics and constraints of control devices are mainly ignored. The objective functions have restrictive forms, and are solely dependent on a second order convex function of the response variables. To overcome the aforementioned shortcomings, this dissertation develops new stochastic control algorithms for active and semi-active control strategies. This research concentrates on the development of frameworks that incorporate nonlinearity of the system, uncertainty of the excitation, and constraints and dynamics of the control device. Control designs are developed based on different objective functions such as higher order polynomials of response variables, reliability of the structure, and life cycle cost of the system considering hazard risks in seismic prone areas. In particular, a nonlinear (open full item for complete abstract)

Committee: Abdollah Shafieezadeh Dr. (Advisor); Natassian Brenkus Dr. (Committee Member); Halil Sezen Dr. (Committee Member); Wei Zhang Dr. (Committee Member) Subjects: Civil Engineering

Master of Science in Engineering, University of Akron, 2016, Mechanical Engineering

Grasping capabilities of a prosthetic hand adapted with sliding mode control was investigated with and without hand orientation feedback. Objects were grasped with a precision grip and repeatedly rotated in and out of the plane of gravity, while drop and break failures were recorded. The hand's grip force was controlled by computer generated input for benchtop tests as well as by electromyography muscle signals during human testing. An analysis of variance showed highly significant improvement in the number of successfully completed cycles for both the benchtop and human tests. Most performance metrics were not significantly affected by individual subjects, which indicates that the control scheme may be easily used by a large number of people. A sorting task, which was designed to serve as a distraction for the subjects while performing the task, had a significant impact on many of the performance metrics, but the impact caused by the Feedback-Sorting interaction suggests that the sorting task only affected the subject's performance without the assistance of the hand orientation feedback. Hand orientation feedback offered an effective method for reducing object drops while maintaining a minimum grip force.

Committee: Erik Engeberg (Advisor); Graham Kelly (Committee Member); Choi Jae-Won (Committee Member) Subjects: Mechanical Engineering; Robotics

Doctor of Philosophy, The Ohio State University, 2013, Electrical and Computer Engineering

The aim of this dissertation is to conduct performance analysis for the modeling and control practices of photovoltaic (PV) systems. Different modeling techniques of PV systems are considered. The current existing modeling techniques are examined with further study, and the desired operating characteristics are achieved through the proposal of a simplified and accurate modeling process that estimates the PV model parameters for a PV module. This is done by taking a new approach that replaces the typical modeling practice in the literature. The main objective of this new approach is to avoid the need for complex calculation and tedious combination of equations to extract the PV system model parameters. The PV system behavior is studied under different environmental conditions. In addition, most PV system models in the literature have internal parameters that are not provided by the manufacturers. These parameters are not given in the PV module data sheet and require numerical methods for their determination due to the nonlinear nature of the PV system's output characteristics. This research presents an improved and comprehensive PV system characterization method that relies only on the values provided by the manufacturer. New improvements and modifications to some of the existing PV models are also presented. A control design strategy for control of the power generated by PV systems is suggested to provide effective energy extraction. The controller design ensures tracking of the maximum power point (MPP) for the PV system using a sliding mode control method of self-optimization. It offers fast and accurate convergence to the MPP in steady state and during varying weather conditions. Published research results and discussion are provided. The simulation in this research proposal is carried out using a Matlab/Simulink environment. Experimental verification of the simulated results are included to demonstrate the validity of the proposed controller design.

Committee: Vadim Utkin (Advisor) Subjects: Electrical Engineering

Master of Science, The Ohio State University, 2011, Civil Engineering

Structural control technologies have been widely accepted as effective ways to protect structures against seismic and wind hazards. Sliding mode control (SMC) is among the popular approaches for control of systems, especially for unknown linear and nonlinear civil structures. Compared with other control approaches, sliding mode control is invariant to disturbance such as wind and earthquake, and to system parameters such as the mass, stiffness, and damping ratio matrices if the uncertainties can be represented the linear combination of the control input, which is generally satisfied for most civil structures. For known linear civil structures subjected to wind excitation, a filtered sliding mode control approach is presented in order to reduce the response of civil structures. Rather than using a Lyapunov-function based control design, an alternative way is provided to find the control force based on the equivalent control force. A low pass filter is properly selected to remove the high-frequency components of the control force while remaining the structural stability. Simulation results of a 76-story wind-excited high-rising building show that this filtered sliding mode control method has better performance over Linear-quadratic-Gaussian (LQG), unfiltered SMC, and some other approaches with respect to maximum and root-mean-square (RMS) values of structural response. For unknown nonlinear civil structures, an adaptive and robust control algorithm for nonlinear vibration control of large structures subjected to dynamic loading is presented through integration of a self-constructing wavelet neural network with an adaptive fuzzy sliding mode control approach. It is particularly suitable when structural properties are unknown or change during the dynamic event which is the case for civil structures subjected to dynamic loading. In other words, the proposed control model has the advantages of not requiring accurate mathematical model of the controlled structure and good (open full item for complete abstract)

Committee: Hojjat Adeli (Advisor); Vadim Utkin (Committee Member); Shive Kumar Chaturvedi (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

Permanent-magnet-synchronous-machine (PMSM) drives have been increasingly applied in a variety of industrial applications which require fast dynamic response and accurate control over wide speed ranges. Two control techniques are proposed in this dissertation for PMSM drives, namely flux-weakening control incorporating speed regulation and sliding mode observer with feedback of equivalent control. The research objectives are to extend the operating speed range of the PMSM drive system and improve its control robustness and adaptability to variations of operating conditions as well as dynamic performance. First, a robust flux-weakening control scheme is studied. With a novel current control strategy, the demagnetizing stator current required for the flux-weakening operation can be automatically generated based on the inherent cross-coupling effects in PMSM between its direct-axis and quadrature-axis current in the synchronous reference frame. The proposed control scheme is able to achieve both flux-weakening control and speed regulation simultaneously by using only one speed/flux-weakening controller without the knowledge of accurate machine parameters and dc bus voltage of power inverter. Moreover, no saturation of current regulators occurs under any load conditions, resulting in control robustness in the flux-weakening region. Secondly, a sliding mode observer is developed for estimating rotor position of PMSM without saliency in the implementation of position-sensorless vector control. A concept of feedback of equivalent control is applied to extend the operating range of sliding mode observer and improve its angle-estimation performance. Compared to conventional sliding mode observers, the proposed one features the flexibility to design parameters of sliding mode observer operating in a wide speed range. The estimation error of rotor position can be reduced by properly selecting the feedback gain of equivalent control. In addition, a flux-based sliding mode obser (open full item for complete abstract)

Committee: Longya Xu (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

Optimal sliding mode control and stabilization of underactuated systems by using sliding mode control are studied in this dissertation. Sliding mode controls with time-varying sliding surfaces are proposed to solve the optimal control problem for both linear and nonlinear systems. The time-varying sliding surfaces are designed such that the system state is on the sliding surface from the beginning of the motion without reaching phase. Therefore, the behavior of the system is totally determined by these time-varying sliding surfaces. The original optimal control problem is also transformed into finding the optimal sliding surfaces. In some cases, the new problem is easy to solve than the original one. The main advantage of this kind of controls is that they can provide a more robust optimal control to the original problem. The optimal sliding mode control system should work in such a manner. In the region dominated by the system nominal part, the system behavior is mainly governed by optimal control. In the region where perturbation becomes dominant, sliding mode control will take over the main control task. Several approaches are applied to find the optimal solution or an approximation of the optimal solution for linear continuous-time, linear discrete-time and nonlinear optimal control problems. As a special kind of nonlinear systems, underactuated systems are of great interest in both theoretical research and real applications. For underactuated systems, which don't satisfy Brockett's necessary conditions, non-smooth sliding mode control could be used to robustly stabilize those underactuated systems. Two kinds of underactuated systems, those in the cascaded form and those in the chained form, are studied in the second part of the dissertation. Two sliding mode controllers are presented to stabilize those two kinds of underactuated systems with simulations of three benchmark examples.

Committee: Umit Ozguner (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2006, Electrical Engineering

In this dissertation, the adaptive seeking control strategy for nonlinear systems is investigated to solve control problems like online optimization and system stabilization. The adaptive seeking control strategy developed includes the gradient-seeking control method and the adaptive seeking sliding mode control method. The gradient-seeking control algorithm is designed to solve online convex optimization problems in which it adaptively locates and tracks a priori unknown optimal set-point that extremizes/optimizes the value of a nonlinear performance index function. The gradient-seeking control is applicable to systems that involve a continuous and convex nonlinearity. The proposed gradient-seeking strategy is consistently simple in structure. It is also robust to unknown disturbances and modeling uncertainties while adaptively locating and tracking an optimal set-point online. Based on the same concept of gradient-seeking control strategy, a new sliding mode control method, namely adaptive seeking sliding mode control, is proposed in this dissertation to solve system stabilization problems for a class of nonlinear systems. While reserving the properties of the sliding mode control, like insensitivity to parameter variations and complete rejection of disturbances, the adaptive seeking sliding mode control offers a promising robust sliding mode control solution for real-life engineering applications with continuous control input. The proposed sliding mode control method applies a floating feedback control gain and it helps to relieve the chattering problem accompanying some sliding mode control systems in the presence of parasitic dynamics and continuous disturbances. This method is especially promising for control systems with limited actuation capabilities and bandwidth. The dissertation concludes with a summary of the current work and a discussion on possible extensions of the proposed control strategy in future work.

Committee: Umit Ozguner (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2003, Mechanical Engineering

Electromagnetic actuators (EMA), which incorporate solenoids, are increasingly becoming the actuator of choice in industry lately, due to their ruggedness, low cost, and relative ease of control. Latest applications of solenoid based EMA's include Electromagnetic Valve Actuation (EMV) systems. This application presents challenges that require the improvement of the dynamic characteristics of the EMA. Some of these problems include, but are not limited to, quiet operation, reduced bounce, less energy consumption, trajectory shaping with a minimum number of measurements, and high actuation speeds. These demands, coupled with the nonlinear dynamics of the EMA, make the use of classical control strategies a less attractive option. A possible attempt to arrive at intermediate solutions to these problems should include some amount of model based robust control strategy. This includes the development of an accurate but simple control based model and a robust digital control strategy. In this study a basic nonlinear model for a solenoidal EMA will be developed, and validated, which will include bounce, leakage inductance and temperature effects. The model is formulated for the linear legion (region before saturation) of the actuator dynamics, but validation will include operation in the saturation region as well. This effectively means that a nonlinear model will be developed that is simple but accurate enough for control, neglecting hysteresis and magnetic saturation. Next, an EMV will be designed and built. A nonlinear model for the EMV will be developed and validated. This model will include secondary nonlinearities like saturation, hysteresis, mutual inductance and bounce. In this study a variable that is easier and cheaper to measure, current, will be measured and the information of the position and velocity variables will be estimated from this measurement. The position estimate will be used for control. This is called Sensorless Control. The control objective is to r (open full item for complete abstract)

Committee: Gregory Washington (Advisor) Subjects:

Master of Science in Mechanical Engineering, Cleveland State University, 2011, Fenn College of Engineering

Aircraft engine control has been evolving since its beginning. With advancements in technology more and more control methods are being applied to this area. This thesis presents the design of an adaptive PID sliding mode control (A-SMC) for a turbofan engine. The controller design methodology is presented. Using an aircraft engine simulation environment developed by NASA, called Commercial Modular Aero-Propulsion System Simulation, the developed controller is tested. The results from three simulations are analyzed to investigate the application of this new design scheme. The A-SMC is able to follow the demanded fan speed for short flight simulations. However, some of the adaptive gains continue to increase when operating away from the limits. It is shown that using an A-SMC is a feasible methodology for controlling an aircraft engine, although further studies are necessary to investigate the adaptive PID control and the technique chosen to eliminate the chattering phenomenon of sliding mode control.

Committee: Hanz Richter Ph.D. (Committee Chair); Jerzy Sawicki Ph.D. (Other); Daniel Simon Ph.D. (Other) Subjects:

Master of Science in Mechanical Engineering, Cleveland State University, 2011, Fenn College of Engineering

Many control theories are used in controlling aircraft engines. However, the multivariable sliding mode control is not yet established in this application even though it has a lot of potential in dealing with complex and nonlinear systems such as aircraft engines. Therefore, a guideline in developing multivariable sliding mode control law for an aircraft engine is presented in this thesis. The problem of chattering in the sliding mode control is suppressed by the use of the boundary layer method. The control logic is tested by implementing NASA's Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k). Simulation results are analyzed and compared to the results obtained from the baseline controller. The robust property of multivariable sliding mode control is also examined by altering the flight condition of the engine.

Committee: Hanz Richter PhD (Committee Chair); Jerzy Sawicki PhD (Committee Member); Lili Dong PhD (Committee Member) Subjects:

Master of Science in Mechanical Engineering, Cleveland State University, 2008, Fenn College of Engineering

General motion control of conveyor belts does not present difficulties. When theconveyor belt carries open containers filled with liquid, significant analysis needs to be carried out to design controllers. The objective of this thesis was to design a control system which will allow an open container filled with liquid to be transferred between two stations as fast as possible and without excessive slosh causing the liquid to spill out of the container. This control problem has applications to industrial processing facilities, where open containers are carried by a conveyor belt. The speed at which the open container can be transferred between stations has a direct impact on productivity. The thesis involves determination of the plant (conveyor belt dynamics and the container filled with liquid) model using system identification techniques and examination of candidate control techniques. Simulation results have been shown to validate the approach.

Committee: Hanz Richter Phd (Advisor); Jerzy Sawicki Phd (Committee Member); Daniel Simon Phd (Committee Member) Subjects: Engineering; Mechanical Engineering

MS, University of Cincinnati, 2020, Engineering and Applied Science: Mechanical Engineering

The thesis focusses on formulating novel control algorithm architectures based off the sliding mode controller design. Three control designs are presented in this thesis. The three control architectures are tested on a quadrotor and their behaviour is observed when waypoint navigation is attempted. The first control architecture is to develop a control design that is effective against external disturbances. The theoretical design and working of the controller is first presented. Its ability to stabilize systems in the presence of disturbance is also presented theoretically. Consequently, to test its effectiveness, its reaction to wind and gust disturbance is observed when implemented on a quadrotor. The second and third control architecture deals with a certain type of controller known as the PD (Proportional Derivative) controller. The PD controller helps us control the dynamics of a system in a simple manner. However, in order to do so in a successful manner, there are certain parameters in its structure that need to be decided manually. This can be a difficult task for larger dynamical systems. The second and third control architectures present two methods in which these gains automatically take ideal values which help channel system dynamics. This rules out the need for determining them manually. A theoretical proof for this method is presented. Simulations to understand the working of the idea are also shown. Conclusions for the 3 control architectures are drawn out. Future work is also presented.

Committee: Manish Kumar Ph.D. (Committee Chair); Rajnikant Sharma Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2020, EECS - System and Control Engineering

A modern Multiprocess Arc Welding Power Source (MAWPS) is a Switched-Mode Power Supply (SMPS) that has been designed to produce waveforms used for multiple arc welding processes, such as Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Flux-Cored Arc Welding (FCAW). MAWPS control is challenging for a number of reasons, including the complex dynamics of switching power converters, transient conditions encountered in the metal transfer process, wide variations in load impedance, a need for tracking complex reference waveforms, incomplete or inaccurate models of the welding process itself, the difficulty of addressing the needs of several welding processes using a single machine, an electrically harsh environment with high levels of electromagnetic noise, and health and safety concerns. In this work, models of the equipment in a welding setup are developed that can be used for analysis and control system design. The models are used to develop a simulation environment and a new control strategy for a welding power source from Lincoln Electric, using Sliding Mode Control (SMC). While SMC has been applied to SMPS elsewhere in the literature, this work focuses on the particular needs of the welding power source and incorporates output current, voltage, and power reference tracking, switching frequency control, and output constraints. A hardware implementation of the SMC strategy is described, and its performance is compared against the existing control system and computer simulations. While some implementation details still need to be worked out, the SMC strategy is shown to be feasible to implement and to provide significant improvements in the current, voltage, and power tracking performance. These improvements should have a direct impact on the welding performance of the Multiprocess Arc Welding Power Source (MAWPS).

Committee: Kenneth Loparo Ph.D. (Advisor); Vira Changkong Ph.D. (Committee Member); Robert Gao Ph.D. (Committee Member); Wei Lin Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2019, Washkewicz College of Engineering

The CSU 4OptimX exercise robot provides a platform for future research into advanced exercise and rehabilitation. The robot and its control system will autonomously modify reference trajectories and impedances on the basis of an optimization criterion and physiological feedback. To achieve this goal, a robust impedance control system with trajectory tracking must be implemented as the foundational control scheme. Two control laws will be compared, sliding mode and H-infinity control. The above robust control laws are combined with underlying impedance control laws to overcome uncertain plant model parameters and disturbance anomalies affecting the input signal. The sliding mode control law is synthesized based on a nominal plant model due to its inherent nature of overcoming unspecified, un-modeled dynamics and disturbances. Implementation of the H-infinity control law uses weights as well as the nominal plant, a structured parametric uncertainty model of the plant, and a model with multiplicative uncertainty. The performance and practicality of each controller is discussed as well as the challenges associated with attempts to implement controllers successfully onto the robot. The findings of this thesis indicate that the closed loop controller with sliding mode is the superior control scheme due to its abilities to counter non-linearities. It is chosen as the platform control scheme. The 2 out of 3 H-infinity controllers performed well in simulation but only one was able to successfully control the robot. Challenges associated with H-infinity control implementation toward impedance control include determining proper weight shapes that balance performance and practicality. This challenge is a starting point for future research into general weight shape determination for H-infinity robust impedance control.

Committee: Hanz Richter (Committee Chair); Dan Simon (Committee Member); Jerzy Sawicki (Committee Member) Subjects: Electrical Engineering; Engineering; Mechanical Engineering; Rehabilitation; Robotics; Robots