U-model-based two-degree-of-freedom internal model control of nonlinear dynamic systems

This paper proposes a U-Model-Based Two-Degree-of-Freedom Internal Model Control (UTDF-IMC) structure with strength in nonlinear dynamic inversion, and separation of tracking design and robustness design. This approach can effectively accommodate modeling error and disturbance while removing those widely used linearization techniques for nonlinear plants/processes. To assure the expansion and applications, it analyses the key properties associated with the UTDF-IMC. For initial benchmark testing, computational experiments are conducted using MATLAB/Simulink for two mismatched linear and nonlinear plants. Further tests consider an industrial system, in which the IMC of a Permanent Magnet Synchronous Motor (PMSM) is simulated to demonstrate the effectiveness of the design procedure for potential industrial applications

Repetitive predictive control and its application to PMSMs

Repetitive Control is a learning control algorithm used to solve the problems of tracking the references and/or rejecting the disturbances that have repetitive nature. One of the challenging problems in repetitive control is to maintain the performance of the controller when the manipulated and/or state variables are hitting the constraints. Meanwhile, it is well known that Model Predictive Control (MPC) has its reputation in dealing with the constrained control problem through the use of optimization algorithms. This thesis incorporates the concept of repetitive control into the design of an MPC controller, resulting a new controller termed Repetitive-Predictive Control (RPC), so that the benefits of both controllers are combined, such as repetitiveness, constraints and multi-variable control. The design of the RPC controller is achieved by incorporating the dominant frequency components identified by the frequency decomposition of the reference signal into the receding horizon control of MPC. To further investigate the strength and weakness of the RPC, the design, tuning and performance of the RPC controller is thoroughly explored by its application to the control of Permanent Magnet Synchronous Motors (PMSMs) that have been broadly adopted for industrial control application due to their low volume and high efficiency. The decision to use PMSMs as the application of RPC is reflected by the increasing trend to apply the Repetitive Control (RC) and Model Predictive Controller (MPC) for the electric drives in recent years. The design of RPC for the position, speed and current regulation of a PMSM has been investigated under two different schemes based on the Field Oriented Control (FOC). The first scheme employs the cascade structure with constrained MPC and RPC replacing the PI controllers for the inner-loop current control and outer-loop speed/position control, respectively. The second scheme is to combine both speed and current controllers into one single multi-variable model predictive controller with operating constraints imposed. The experimental comparisons of the two control schemes with cascade PI controllers demonstrate the superior performance of cascade RPC/MPC in terms of the ability of constrained control, disturbance rejection and position tracking. All results in the thesis have been validated by an experimental test-bed with an industrial-sized PMSM

Energy-Optimal Control of Over-Actuated Systems - with Application to a Hybrid Feed Drive

Over-actuated (or input-redundant) systems are characterized by the use of more actuators than the degrees of freedom to be controlled. They are widely used in modern mechanical systems to satisfy various control requirements, such as precision, motion range, fault tolerance, and energy efficiency. This thesis is particularly motivated by an over-actuated hybrid feed drive (HFD) which combines two complementary actuators with the aim to reduce energy consumption without sacrificing positioning accuracy in precision manufacturing. This work addresses the control challenges in achieving energy optimality without sacrificing control performance in so-called weakly input-redundant systems, which characterize the HFD and most other over-actuated systems used in practice. Using calculus of variations, an optimal control ratio/subspace is derived to specify the optimal relationship among the redundant actuators irrespective of external disturbances, leading to a new technique termed optimal control subspace-based (OCS) control allocation. It is shown that the optimal control ratio/subspace is non-causal; accordingly, a causal approximation is proposed and employed in energy-efficient structured controller design for the HFD. Moreover, the concept of control proxy is proposed as an accurate causal measurement of the deviation from the optimal control ratio/subspace. The proxy enables control allocation for weakly redundant systems to be converted into regulation problems, which can be tackled using standard controller design methodologies. Compared to an existing allocation technique, proxy-based control allocation is shown to dynamically allocate control efforts optimally without sacrificing control performance. The relationship between the proposed OCS control allocation and the traditional linear quadratic control approach is discussed for weakly input redundant systems. The two approaches are shown to be equivalent given perfect knowledge of disturbances; however, the OCS control allocation approach is shown to be more desirable for practical applications like the HFD, where disturbances are typically unknown. The OCS control allocation approach is validated in simulations and machining experiments on the HFD; significant reductions in control energy without sacrificing positioning accuracy are achieved.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146104/1/molong_1.pd

Attitude control/momentum management and payload pointing in advanced space vehicles

The design and evaluation of an attitude control/momentum management system for highly asymmetric spacecraft configurations are presented. The preliminary development and application of a nonlinear control system design methodology for tracking control of uncertain systems, such as spacecraft payload pointing systems are also presented. Control issues relevant to both linear and nonlinear rigid-body spacecraft dynamics are addressed, whereas any structural flexibilities are not taken into consideration. Results from the first task indicate that certain commonly used simplifications in the equations of motions result in unstable attitude control systems, when used for highly asymmetric spacecraft configurations. An approach is suggested circumventing this problem. Additionally, even though preliminary results from the second task are encouraging, the proposed nonlinear control system design method requires further investigation prior to its application and use as an effective payload pointing system design technique

Robust and Decentralized Control of Web Winding Systems

This research addresses the velocity and tension regulation problems in web handling, including those found in the single element of an accumulator and those in the large-scale system settings. A continuous web winding system is a complex large-scale interconnected dynamics system with numerous tension zones to transport the web while processing it. A major challenge in controlling such systems is the unexpected disturbances that propagate through the system and affect both tension and velocity loops along the way. To solve this problem, a unique active disturbance rejection control (ADRC) strategy is proposed. Simulation results show remarkable disturbance rejection capability of the proposed control scheme in coping with large dynamic variations commonly seen in web winding systems. Another complication in web winding system stems from its large-scale and interconnected dynamics which makes control design difficult. This motivates the research in formulating a novel robust decentralized control strategy. The key idea in the proposed approach is that nonlinearities and interactions between adjunct subsystems are regarded as perturbations, to be estimated by an augmented state observer and rejected in the control loop, therefore making the local control design extremely simple. The proposed decentralized control strategy was implemented on a 3-tension-zone web winding processing line. Simulation results show that the proposed control method leads to much better tension and velocity regulation quality than the existing controller common in industry. Finally, this research tackles the challenging problem of stability analysis. Although ADRC has demonstrated the validity and advantage in many applications, the rigorous stability study has not been fully addressed previously. To this end, stability characterization of ADRC is carried out in this work. The closed-loop system is first reformulated, resulting in a form that allows the application of the well established singular perturbation method. Based on the decom

Robust and Decentralized Control of Web Winding Systems

This research addresses the velocity and tension regulation problems in web handling, including those found in the single element of an accumulator and those in the large-scale system settings. A continuous web winding system is a complex large-scale interconnected dynamics system with numerous tension zones to transport the web while processing it. A major challenge in controlling such systems is the unexpected disturbances that propagate through the system and affect both tension and velocity loops along the way. To solve this problem, a unique active disturbance rejection control (ADRC) strategy is proposed. Simulation results show remarkable disturbance rejection capability of the proposed control scheme in coping with large dynamic variations commonly seen in web winding systems. Another complication in web winding system stems from its large-scale and interconnected dynamics which makes control design difficult. This motivates the research in formulating a novel robust decentralized control strategy. The key idea in the proposed approach is that nonlinearities and interactions between adjunct subsystems are regarded as perturbations, to be estimated by an augmented state observer and rejected in the control loop, therefore making the local control design extremely simple. The proposed decentralized control strategy was implemented on a 3-tension-zone web winding processing line. Simulation results show that the proposed control method leads to much better tension and velocity regulation quality than the existing controller common in industry. Finally, this research tackles the challenging problem of stability analysis. Although ADRC has demonstrated the validity and advantage in many applications, the rigorous stability study has not been fully addressed previously. To this end, stability characterization of ADRC is carried out in this work. The closed-loop system is first reformulated, resulting in a form that allows the application of the well established singular perturbation method. Based on the decom

Dynamic operability assessment : a mathematical programming approach based on Q-parametrization

Bibliography: pages 197-208.The ability of a process plant to guarantee high product quality, in terms of low variability, is emerging as a defining feature when distinguishing between alternative suppliers. The extent to which this can be achieved is termed a plant's dynamic operability and is a function of both the plant design and the control system design. In the limit, however, the closedloop performance is determined by the properties inherent in the plant. This realization of the interrelationship between a plant design and its achievable closed-loop performance has motivated research toward systematic techniques for screening inherently inferior designs. Pioneering research in the early 1980's identified right-half-plane transmission zeros, time delays, input constraints and model uncertainty as factors that limit the achievable closedloop performance of a process. Quantifying the performance-limiting effect of combinations of these factors has proven to be a challenging problem, as reflected in the literature. It is the aim of this thesis to develop a systematic procedure for dynamic operability assessment in the presence of combinations of performance-limiting factors. The approach adopted in this thesis is based on the Q-parametrization of stabilizing linear feedback controllers and involves posing dynamic operability assessment as a mathematical programming problet? In the proposed formulation, a convex objective function, reflecting a measure of closed-loop performance, is optimized over all stable Q, subject. to a set of constraints on the closed-loop behavior, which for many specifications of interest is convex. A discrete-time formulation is chosen so as to allow for the convenient hand.ling of time delays and time-domain constraints. An important feature of the approach is that, due to the convexity, global optimality is guaranteed. Furthermore, the fact that Q parametrizes all stabilizing linear feedback controllers implies that the performance at the optimum represents the best possible performance for any such controller. The results are thus not biased by controller type or tuning, apart from the requirement that the controller be linear

Continuous and discrete-time sliding mode control design techniques.

Sliding mode control is a well-known approach to the problem of the control of uncertain systems, since it is invariant to a class of parameter variations. Well-established investigations have shown that the sliding mode controller/ observer is a good approach from the point of view of robustness, implementation, numerical stability, applicability, ease of design tuning and overall evaluation. In the sliding mode control approach, the controller and/ or observer is designed so that the state trajectory converges to a surface named the sliding surface. It is desired to design the sliding surface so that the system stability is achieved. Many new methods and design techniques for the sliding controller/ observer are presented in this thesis. LQ frequency shaping sliding mode is a way of designing the sliding surface and control. By using this method, corresponding to the weighting functions in conventional quadratic performance, a compensator can be designed. The intention of observer design is to find an estimate for the state and, if the input is unknown, estimate a suitable input. Using the sliding control input form, a suitable estimated input can be obtained. The significance of the observer design method in this thesis is that a discontinuous observer for full order systems, including disturbance inputs, is designed. The system may not be ideally in the sliding mode and the uncertainty may not satisfy the matching condition. In discrete-time systems instead of having a hyperplane as in the continuous case, there is a countable set of points comprising a so-called lattice; and the surface on which these sliding points lie is named the latticewise hyperplane. Control and observer design using the discrete-time sliding mode, the robust stability of the sliding mode dynamics and the problem of stabilization of discrete-time systems are also studied. The sliding mode control of time-delay systems is also considered. Time-delay sliding system stability is studied for the cases of full information about the delay and also lack of information. The sliding surface is delay-independent as for the traditional sliding surface, and the reaching condition is achieved by applying conventional discontinuous control. A well-known method of control design is to specify eigenvalues in a region in the left-hand half-plane, and to design the gain feedback matrix to yield these eigenvalues. This method can also be used to design the sliding gain matrix. The regions considered in this thesis are, a sector, an infinite vertical strip, a disc, a hyperbola and the intersection ii of two sectors. Previous erroneous results are rectified and new theory developed. The complex Riccati equation, positivity of a complex matrix and the control of complex systems are significant problems which arise in many control theory problems and are discussed in this thesis