Transient Performance Requirements Research Articles

Fixed-Time Event-Triggered Control of Nonholonomic Mobile Robots with Uncertain Dynamics and Preassigned Transient Performance

In this paper, a novel adaptive control scheme is proposed for the path-following problem of a nonholonomic mobile robot with uncertain dynamics based on barrier functions. To optimize communication resources, we integrate an event-triggered mechanism that avoids Zeno behavior and ensures that the tracking error of the closed-loop system converges to a small neighborhood around zero within a fixed time, while consistently satisfying predefined transient performance requirements. Extensive simulation studies demonstrate the effectiveness of the proposed approach and validate the theoretical results.

Adaptive Sliding-Mode Disturbance Observer-Based Nonlinear Control for Unmanned Dual-Arm Aerial Manipulator Subject to State Constraints

The unmanned dual-arm aerial manipulator system is composed of a multirotor unmanned aerial vehicle (UAV) and two manipulators. Compared to a single manipulator, dual-arm always provides greater flexibility and versatility in both goods delivery and complex task execution. However, the practical application of the system is limited due to nonlinearities and complex dynamic coupling behavior between the multirotor and the manipulator, as well as the one between the inner and outer loop of the multirotor. In this paper, a holistic model of the dual-arm aerial manipulator system is first derived with complete model information. Subsequently, an adaptive sliding-mode disturbance observer (ASMDO) is proposed to handle external disturbances and unmeasurable disturbances caught by unmeasurable angular velocity and acceleration of the manipulators. Moreover, for safety concerns and transient performance requirements, the state constraints should be guaranteed. To this end, an auxiliary term composed of constrained variable signals is introduced. Then, the performance of the designed method is proven by rigorous analysis. Finally, the proposed method is validated through two sets of simulation tests.

Underactuated Mechanical Systems With Both Actuator and Actuated/Unactuated State Constraints: A Predictive Control-Based Approach

Underactuated systems are widely used in practice. Due to actuator saturation and transient performance requirements, it is necessary to keep the control inputs and system states within safe limits. However, with fewer control inputs, the state constraints, especially for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">unactuated</i> states, are usually difficult to guarantee. Model predictive control (MPC), as a method that can handle constraints naturally, unfortunately, still struggles to deal with unactuated variable constraints directly. To this end, this article proposes a general MPC algorithm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">for a class of underactuated systems</i> . First, an MPC method considering actuator saturation constraints is designed, based on which, different velocity constraint-related matrices are constructed to convert both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">actuated</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">unactuated</i> velocity constraints into control input constraints. Then, by delicately analyzing the coupling relationship between actuated and unactuated variables, the displacement/angle constraints of unactuated variables are theoretically ensured. To our best knowledge, it is the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">first</i> MPC approach designed for a class of underactuated systems with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">both</i> actuated and unactuated state constraints as well as actuator saturation. Finally, the proposed MPC approach is applied to two typical underactuated systems, i.e., tower cranes and boom cranes, and a series of experiments are investigated to verify the effectiveness and superiority of this approach.

Singularity-Avoidance Prescribed Performance Control for Spacecraft Attitude Tracking

The attitude tracking control problem with preassigned performance requirements has earned tremendous interest in recent years, and the Prescribed Performance Control (PPC) scheme is often adopted to tackle this problem. Nevertheless, traditional PPC schemes may suffer singularity problems when the expected state constraint is violated. This may cause a decrease in the control effect or even the unstable of the system. Motivated by this issue, this paper proposes a Singularity-Avoidance Prescribed Performance Control scheme (SAPPC) to deal with these problems, of which the core is a shear mapping-based error transformation procedure that globally transforms the original error state without singularity. Based on the presented non-singular error transformation, this paper presents a perspective to guarantee the satisfaction of given transient performance requirements by leading the state trajectory converging along a preassigned smooth trajectory called Reference Performance Function (RPF). Based on the concept of the RPF, this paper naturally adopts an error-defined-type state constraint, providing a time-varying constraint boundary and alleviating the potential over-control problem at the steady state. Further, in order to validate the proposed SAPPC scheme, a simple backstepping controller is developed by employing the predefined-time stability technique and the dynamic surface control technique. Finally, theoretical analysis and numerical simulation results are presented to validate the proposed control scheme's effectiveness and robustness.

Autonomous Landing of an UAV Using H∞ Based Model Predictive Control

Possibly the most critical phase of an Unmanned Air Vehicle (UAV) flight is landing. To reduce the risk due to pilot error, autonomous landing systems can be used. Environmental disturbances such as wind shear can jeopardize safe landing, therefore a well-adjusted and robust control system is required to maintain the performance requirements during landing. The paper proposes a loop-shaping-based Model Predictive Control (MPC) approach for autonomous UAV landings. Instead of conventional MPC plant model augmentation, the input and output weights are designed in the frequency domain to meet the transient and steady-state performance requirements. Then, the H∞ loop shaping design procedure is used to synthesize the state-feedback controller for the shaped plant. This linear state-feedback control law is then used to solve an inverse optimization problem to design the cost function matrices for MPC. The designed MPC inherits the small-signal characteristics of the H∞ controller when constraints are inactive (i.e., perturbation around equilibrium points that keep the system within saturation limits). The H∞ loop shaping synthesis results in an observer plus state feedback structure. This state estimator initializes the MPC problem at each time step. The control law is successfully evaluated in a non-linear simulation environment under moderate and severe wind downburst. It rejects unmeasured disturbances, has good transient performance, provides an excellent stability margin, and enforces input constraints.

Observer‐based consensus tracking control for a class of nonstrict‐feedback nonlinear multi‐agent systems with prescribed performance and input quantization

AbstractThis article investigates the consensus tracking problem with predefined transient and steady performance requirements for a class of nonstrict‐feedback nonlinear multi‐agent systems (MASs) with input quantization under a directed graph. Based on prescribed performance error transformation methods and command filtered backstepping techniques, a novel observer‐based adaptive control protocol is proposed, where neural observers are designed to estimate unmeasurable states and radial basis function neural networks are constructed to compensate command filter errors. The proposed protocol can be applied to a more general class of nonlinear MASs with nonstrict‐feedback nonlinear dynamics and unmeasurable states information. It is strictly proved that all signals in the whole MAS are semi‐globally uniformly ultimately bounded and both the transient and steady performances of the consensus tracking errors satisfy prescribed performance requirements. Finally, three numerical examples are presented to validate the effectiveness of the proposed protocol.

H-Infinity Loop-Shaped Model Predictive Control With HVAC Application

We formulate a model predictive control (MPC) for linear time-invariant systems based on H-infinity loop-shaping. The design results in a closed-loop system that includes a state estimator and attains an optimized stability margin. Input and output weights are designed in the frequency domain to satisfy steady-state and transient performance requirements, in lieu of standard MPC plant model augmentations. The H-infinity loop-shaping synthesis results in an observer-based state feedback structure. An inverse optimal control problem is solved to construct the MPC cost function, so that the control input computed by MPC is equal to the H-infinity control input when the constraints are inactive. The MPC inherits the closed-loop performance and stability margin of the loop-shaped design when constraints are inactive. We apply the methodology to a multizone heat pump, and validate the results in simulations and laboratory experiments. The design rejects constant unmeasured disturbances, tracks constant references with zero steady-state error, meets transient performance requirements, provides an excellent stability margin, and enforces input and output constraints.

An experimental assessment of robust control and estimation of acetate concentration in Escherichia coli BL21(DE3) fed-batch cultures

Avoiding acetate accumulation is a major challenge in Escherichia coli fed-batch cultures, since it leads to an inhibition of the cell respiratory capacity. A closed-loop regulation ensuring a low acetate concentration offers a practical solution to maintain the cultures near the optimal operating conditions. In this work, a robust Generic Model Controller (GMC) is designed and implemented to regulate the acetate concentration in E. coli BL21 (DE3) fed-batch cultures. To compensate for model mismatch, disturbances, and measurement noise, a robust design using the LMI formalism is achieved, considering robustness and transient performance requirements. Since the acetate concentration is not available for on-line measurement, an Unscented Kalman Filter (UKF) is also designed and implemented to estimate the acetate concentration based on an on-line biomass measurement. The proposed GMC-UKF strategy is validated through simulation runs and experimental tests at lab-scale. The control strategy shows good performance in regulating the non-measured acetate concentration. The estimation of this latter signal from the biomass measurement is performed accurately by the UKF.

Design of type-1 servo controller for grid voltage modulated direct-power control of single-phase grid-connected PV inverter

This paper presents direct control of active and reactive power using grid voltage modulation for single-phase grid-connected photovoltaic inverter. A design of type-1 servo system based on pole-placement method is proposed to control the power flow using a simplified multiple-input multiple-output (MIMO) model of the system. Phase-locked loop (PLL) with a quarter cycle time delay is used to estimate the grid phase angle for the purpose of performing the stationary and synchronous reference frame transformation. Unipolar pulse width modulation (PWM) technique is used to control a single-phase inverter with 2.7 KVA capacity connected to the photovoltaic system. The proposed controller can simply be tuned using minimum number of controller gains to achieve the transient and steady-state performance requirements. The proposed system, was capable of operating for a wide range of solar irradiance levels with a power factor in the range of 0.95 (leading/lagging), for the reactive power compensation purposes.

ADVANCED MANUFACTURING FOR NUCLEAR CORE DESIGN

Advanced manufacturing has the potential to revitalize US manufacturing, with valuable applications in several industries, including aerospace, automotive, and construction. Some of these applications have clear-cut objectives (e.g., maintain component performance while reducing mass). Applications of advanced manufacturing of nuclear components have aimed at recapturing lost manufacturing capabilities or addressing maintenance of legacy reactor components. Through the Department of Energy, Office of Nuclear Energy, Transformational Challenge Reactor design and analysis thrust, applications of advanced manufacturing, in particular, additive manufacturing, to core design has yielded reactor designs that are free from conventional manufacturing constraints. For applications in core design, the multiphysics nature of the key core metrics (e.g., peak temperature, peak power) in addition to transient safety performance requirements provides a more complex set of objectives that requires more advanced modeling and simulation tools. Additive manufacturing provides high dimensional control and design flexibility to produce complex coolant channel shapes for improved heat transfer properties and low peak material temperatures. Additional mechanisms for improved heat transfer characteristics and temperature-controlled feedback mechanisms have also been explored and incorporated into designs. While some of these enhancements are not directly beneficial for the current operating pressurized water reactor fleet, benefits may be realized in specific reactor applications that have a more constrained design space (e.g., mass, size, material type) or design metrics (e.g., fuel utilization).

Model-Based Design and Optimization for Large Bore Engines: Some Industrial Case Studies

Abstract Large bore reciprocating internal combustion (IC) engines are used in a wide variety of applications such as power generation, transportation, gas compression, mechanical drives, and mining. Each application has its own unique requirements that influence the engine design and control strategy. The system architecture and control strategy play a key role in meeting the requirements. Traditionally, control design has come in at a later stage of the development process, when the system design is almost frozen. Furthermore, transient performance requirements have not always been considered adequately at early design stages for large engines, thus limiting achievable controller performance. With rapid advances in engine modeling capability, it has now become possible to accurately simulate engine behavior in steady-states and transients. In this paper, we propose an integrated model-based approach to system design and control of reciprocating engines and outline ideas, processes, and real-world case studies for the same. Key benefits of this approach include optimized engine performance in terms of efficiency, transient response, emissions, system and cost optimization, and tools to evaluate various concepts before engine build thus leading to significant reduction in development time and cost.

Analytical Prediction and Minimization of Deadtime-Related Harmonics in Permanent Magnet Synchronous Motor

The current, torque, and speed harmonics caused by deadtime effect in voltage source inverter (VSI)-fed permanent magnet synchronous motor (PMSM) usually lead to undesired torque ripple and extra electrical loss, etc. In this article, a mathematical model is proposed to predict the deadtime-related harmonics in VSI-fed field-oriented control PMSM, and a deadtime-related harmonic minimization method is proposed based on proportional-integral (PI) controllers tuning and under the premise of keeping the same control strategy. The expressions of current, torque, and speed harmonics caused by deadtime effects are obtained based on the complex amplitude expression of the voltage error harmonic and the derivation of the closed-loop transfer function from the deadtime-related voltage error to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> axis current. Based on the derived expressions, optimization objective functions are built to search the optimal PI parameters for minimizing deadtime-related harmonics and reducing the torque ripple. The optimization constraint functions can be adjusted for transient performance requirements, so the transient performance can keep good even if the deadtime-related harmonics are minimized with the optimal PI parameters. Both simulation analysis and experimental data verify the correctness of the analytical prediction and the validity of the deadtime-related harmonic minimization method.

A method to account for transient performance requirements in the design of steam generators for concentrated solar power applications

Concentrating solar power plants are strongly characterized by recurring start-up and shut-down procedures. This imposes new challenges for conventional components such as the steam generator systems, as frequent load variations might lead to high thermal stress cycles, affecting their lifetime negatively. In this context, the header and coil design is a favourable configuration to reduce stresses. This paper introduces a method to design the heat exchangers of the header and coil steam generator type accounting for the dynamic performance, thermal stress sensitivity and impact on the performance of the power plant. Optimal designs were determined by minimizing the cost and total water-side pressure drop of the steam generator and the levelized cost of electricity of the power plant. The steam generator dynamic model was successfully validated using operational data. The results suggest that a steam generator design characterized by a tube outer diameter of 30 mm, high steam generator pressure drop and low investment cost is the optimal solution for the power plant under consideration. A configuration featuring a large number of tube layers is optimal in order to reduce the pressure drop at the superheater while at the same time, guaranteeing acceptable stresses and good transient response.

Nonlinear Control of Underactuated Systems Subject to Both Actuated and Unactuated State Constraints With Experimental Verification

In practice, underactuated systems are widely used, and their control problems have attracted much attention in recent years. For safety concerns or transient performance requirements, some state constraints should be guaranteed both theoretically and practically, particularly those exerted on unactuated states. To the best of our knowledge, there are few closed-loop control methods that can treat unactuated state constraints with theoretical guarantees (i.e., that can theoretically guarantee unactuated state variables to be always within the preset ranges). For this purpose, in this article, we propose a new control strategy for a class of underactuated systems that can treat the various constraints including actuated and unactuated state constraints and the constraints on some specific composite variables. Specifically, we elaborately design some new auxiliary terms that are composed of constrained variable signals and actuated velocity signals. These terms can enhance the couplings between unactuated and actuated states that are further utilized to tackle the unactuated state and composite variable constraints. Then, the performance of the designed method is proven by rigorous analysis. Finally, the proposed method is applied to a double pendulum crane system and a tower crane system to verify its superior performance by experiments.

Two-Degree-of-Freedom H$\infty$ Robust Control Optimization for the IPT System With Parameter Perturbations

Robust control can maintain robust stability and robust performance for an inductive power transfer (IPT) system in a comparatively larger perturbation range of parameters. However, it ignores the transient performance requirements and influence of open-loop properties on a resulting controller. So a method of improving two-degree-of-freedom (2DOF) H $\infty$ robust control for the IPT system is proposed. Based on the generalized state-space averaged model, the distribution of poles and zeroes under mutual-inductance and load perturbations with a bounded range is investigated in detail. An expected closed-loop transfer function is added in a 2DOF control structure with a prefilter and feedback controller, to introduce the transient performance requirements. Then, a generalized plant including the model of the IPT system is defined and its state-space realization for standard robust control configuration is also derived. Finally, controllers with different performances are designed referring to the mutual-inductance and load features. Simulation and experiment results show that the 2DOF H $\infty$ robust controller designed with parameters that maximize the modulus value of a dominant pole can reach the prescribed performances for the IPT system, with settling time and overshoot of no more than 5 ms and 2% in startup and reference tracking processes, and restoring time of no more than 5 ms when parameter perturbation occurs.

Multiobjective Robust Controller Synthesis for Nonlinear Mechanical System

In the paper multiobjective robust controller synthesis problem for nonlinear mechanical system described by Lagrange’s equations of the second kind is considered. Such tasks have numerous practical applications, for example in controller design of robotic systems and gyro-stabilized platforms. In practice, we often have to use uncertain mathematical plant models in controller design. Therefore, ensuring robustness in presence of parameters perturbations and unknown external disturbances is an important requirement for designed systems. Much of modern robust control theory is linear. When the actual system exhibits nonlinear behavior, nonlinearities are usually included in the uncertainty set of the plant. A disadvantage of this approach is that resulting controllers may be too conservative especially when nonlinearities are significant. The nonlinear H∞ optimal control theory developed on the basis of differential game theory is a natural extension of the linear robust control theory. Nonlinear theory methods ensure robust stability of designed control systems. However, to determine nonlinear H∞-control law, the partial differential equation have to be solved which is a rather complicated task. In addition, it is difficult to ensure robust performance of controlled processes when using this method. In this paper, methods of linear parameter-varying (LPV) systems are used to synthesize robust control law. It is shown, that Lagrange system may be adequately represented in the form of quasi-LPV model. From the computational point of view, the synthesis procedure is reduced to convex optimization techniques under constraints expressed in the form of linear matrix inequalities (LMIs). Measured parameters are incorporated in the control law, thus ensuring continuous adjustment of the controller parameters to the current plant dynamics and better performance of control processes in comparison with H∞-regulators. Furthermore, the use of the LMIs allows to take into account the transient performance requirements in the controller synthesis. Since the quasi-LPV system depends continuously on the parameter vector, the LMI system is infinite-dimensional. This infinitedimensional system is reduced to a finite set of LMIs by introducing a polytopic LPV representation. The example of multiobjective robust control synthesis for electro-optical device’s line of sight pointing and stabilization system suspended in two-axes inertially stabilized platform is given.

Linear near-equilibrium glide model for unpowered entry trajectory control

Trajectory control plays an essential part in development of entry guidance systems for unpowered gliding entry. From an engineering standpoint, a trajectory control law in a simple structure as well as capable of high adaptability and flexibility is very appealing. To this end, a linear near-equilibrium glide model (LNEGM) is developed using an empirical near-equilibrium glide condition (NEGC). Unlike the prior work on linear approaches, the LNEGM is a flexible model in that it can represent the majority of the linear dynamics of the unpowered gliding entry trajectories. Based on the LNEGM, a linear trajectory control law is naturally obtained, which is composed of a feed-forward part and a proportional-derivative (PD) feedback part. The unique feature of the proposed linear trajectory control law is that the feedback gains are analytical equations associated with desired profiles and transient guidance performance requirements. A state-of-the-art application is given in which the proposed linear trajectory control law satisfactorily solves a common trajectory shaping problem for a class of numerical predictor-corrector guidance.

Optimal-Behavior-Based Dynamic Calibration of the Automotive Diesel Engine

This paper presents a novel automotive engine management system (EMS) calibration methodology for rapid dynamometer test-bed data collection and mapping I.C. engine controllers with significant dynamic and transient performance requirements. This paper applies the methodology to an industrial state of the art WAVE-RT 1 model of a 1.5 L Turbo EU6.1 Diesel engine acting as a virtual dynamometer based engine. The approach directly yields a feedforward controller in a nonlinear polynomial structure that can be either directly implemented in the EMS or converted into a dynamic or static lookup table format. The methodology is based on multistage black-box modeling and dynamic system optimization. The process can exploit the power of global constrained numerical optimization codes and use system identification techniques with dynamic design of experiments. The objective of the engine controller optimization is to improve the fuel economy while maintaining specified (legislated) limits on emissions and map smoothness for driveability. The key contribution is a novel approach to obtaining a feedforward dynamic calibration controller from the system identification of the computed optimal behavior. Model structure selection techniques are shown to be usefully employed to further improve the accuracy of the system identification and so enhance the control performance of the dynamic controllers. The results indicate that the dynamic calibration methodology leads to a considerably reduced requirement for testing time and an improvement of between 1.9% and 2.6% in fuel economy over extra urban driving cycle without violating the emission constraints compared with current steady-state model-based calibration methods. 1 Ricardo PLC.

Output transient trajectory shaping control for a class of nonlinear systems

SUMMARYThis paper presents a transient trajectory shaping (TTS) control method for the SISO strict feedback nonlinear systems. The TTS control refers to explicitly constraining the system output tracking error transient trajectories within predesigned time‐varying boundaries while they are converging to equilibrium. By this method, the boundaries of system output transient trajectories can be designed a priori according to the system transient control performance requirements in both symmetric and asymmetric ways. With a class of time‐varying boundary functions, control laws can be devised by utilizing the enhanced differential unbounded function techniques. Such control laws can ascertain that the system output tracking errors travel within their respectively predesigned time‐varying boundaries while converging to origin. To handle the control input exaggeration issue in TTS, input constraint control techniques are proposed to effectively reduce the required control input magnitude for second‐order systems. A numerical example is utilized to show the effectiveness of the proposed TTS control methods. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Control of the dual mode operation of generator/motor in SOFC/GT-based APU for extended dynamic capabilities

The integrated solid oxide fuel cell (SOFC)/gas turbine (GT) system is an appealing power generation solution for mobile applications from energy conversion efficiency point of view. The relatively poor dynamic capabilities of the SOFC/GT system, which are often the results of system characteristics and SOFC operation safety considerations, limit their widespread applications and must be enhanced to meet safe, efficient and fast load following requirements. To this end, the SOFC/GT system can be augmented by an energy storage unit (e.g., battery) and a dual operating generator/motor (G/M). This paper focuses on investigating the G/M dual mode operation and its implications on system transient performance and battery requirements. Active shaft load control is achieved to manage the load transients through: (a) pre-conditioning of the generator power for load step-up transients; (b) absorbing the excessive power by motoring operation for load step-down transients. By taking full advantage of the bi-directional operation of G/M, we show that better trade-offs between power tracking and thermal management can be achieved, power and energy requirements for the energy storage (battery) can be reduced, and overall system performance can be enhanced.