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Journal Cover Control Engineering Practice
  [SJR: 1.354]   [H-I: 84]   [40 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0967-0661
   Published by Elsevier Homepage  [3039 journals]
  • Neural network models for virtual sensing of NOx emissions in automotive
           diesel engines with least square-based adaptation
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Ivan Arsie, Andrea Cricchio, Matteo De Cesare, Francesco Lazzarini, Cesare Pianese, Marco Sorrentino
      To meet current Diesel engine pollutant legislation, it is important to manage after-treatment devices. The paper describes the development of Neural Network based virtual sensors used to estimate NOx emissions at the exhaust of automotive Diesel engines. Suitable identification methodologies and experimental tests were developed with the aim of meeting the conflicting needs of feasible on-board implementation and satisfactory prediction accuracy. In addition, since the prediction of control-oriented models is typically affected by engine aging and production spread as well as components drift, least square technique features were exploited in order to overcome these issues by adapting the virtual sensor output. The NOx adaptive virtual sensor was tested via comparison with experimental data, measured at the engine test bench on a turbocharged common-rail automotive Diesel engine. Furthermore, besides model validation, the experimental measurements were modified to simulate a sensor drift in order to enable full assessment of the proposed LS-based algorithm adaptation capabilities.

      PubDate: 2017-02-16T09:27:47Z
       
  • Non-linear sliding mode load frequency control in multi-area power system
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Sheetla Prasad, Shubhi Purwar, Nand Kishor
      This paper addresses non-linear sliding mode controller (SMC) with matched and unmatched uncertainties for load frequency control (LFC) application in three-area interconnected power system. In conventional LFC scheme, as the nominal operating point varies due to system uncertainties, frequency deviations cannot be minimized. These lead to degradation in the dynamic performance or even system instability. In this paper, an effective control law is proposed against matched and unmatched uncertainties.. The proposed controller has ability to vary closed-loop system damping characteristics according to uncertainties and load disturbances present in the system. The frequency deviation converges to zero with minimum undershoot/overshoot, fast settling time, significantly reduced chattering and ensures asymptotic stability. In addition, the controller is robust in the presence of parameter uncertainties and different disturbance patterns. It also guarantees high dynamic performance in the presence of governor dead band (GDB) and generation rate constraint (GRC). Simulations are performed to compare the proposed controller with linear SMC. Using proposed control strategy, undershoot/overshoot and settling time gets reduced by approximately 30% with respect to linear SMC. The computed performance indices and qualitative results establish the superiority as well as applicability of the proposed design for the LFC problem. Further, the proposed controller scheme is validated on IEEE 39 bus large power system.

      PubDate: 2017-02-16T09:27:47Z
       
  • Moving window adaptive soft sensor for state shifting process based on
           weighted supervised latent factor analysis
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Le Yao, Zhiqiang Ge
      Process nonlinearity and state shifting are two of the main factors that cause poor performance of online soft sensors. Adaptive soft sensor is a common practice to ensure high predictive accuracy. In this paper, the moving window method is introduced to the supervised latent factor analysis model to capture the state shifting feature of the process. To make the moving window strategy more efficient, the weighted form of the supervised latent factor analysis approach is applied. In this method, contributions of training samples are expressed through incorporating the similarity index into the noise variance of the process variable, which renders strong adaptability of the method for describing nonlinear relationships and abrupt changes of the process. A numerical example and a real industrial process are provided to demonstrate the effectiveness of the proposed adaptive soft sensor.

      PubDate: 2017-02-16T09:27:47Z
       
  • A delay-aware cyber-physical architecture for wide-area control of power
           systems
    • Abstract: Publication date: Available online 15 February 2017
      Source:Control Engineering Practice
      Author(s): Damoon Soudbakhsh, Aranya Chakrabortty, Anuradha M. Annaswamy
      In this paper we address the problem of wide-area control of power systems using Synchrophasor measurements in the presence of network delays. We propose a novel cyber-physical architecture that uses an arbitrated network control systems approach for mitigating the destabilizing effects of delays in power systems. The approach consists of: (1) utilization of Synchrophasor measurements from distributed measurements across different buses in the power network, (2) estimation of delays that control messages experience, (3) a delay-aware control design that explicitly accommodates the delays and judiciously utilizes estimated system states when needed, and (4) a switching control strategy that aborts the computation of control signals when delays exceed a certain threshold to improve resource utilization. While the control gains are determined using a centralized power system model and state feedback, it is shown that the delay-aware aspects of the proposed architecture allow both distributed measurements and distributed implementation of the control law. The results are illustrated using a 50-bus, 14-generator, 4-area power system model. The results clearly demonstrate that the proposed controller recovers the ideal system performance (such as deviations in frequency < 3 mHz ) even in the presence of large intra-area and inter-area delays with a small amount of additional control effort. Using the proposed overrun strategy, the results also confirm that about 30% drops can be accommodated with the proposed arbitrated network control systems approach.

      PubDate: 2017-02-16T09:27:47Z
       
  • A unified observer for robust sensorless control of DC–DC converters
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Gionata Cimini, Gianluca Ippoliti, Giuseppe Orlando, Sauro Longhi, Rosario Miceli
      Due to the large variety of converters' configurations, many different sensorless controllers are available in the literature, each one suited for a particular converter. The need for different configurations, especially on the same power supply, make it clear the advantage of having a shared control algorithm. This paper presents a unified nonlinear robust current observer for buck, boost and buck–boost converters in synchronous and asynchronous configurations. The unified observer speeds up the design, tuning and the implementation, and requires a memory cheaper code, easier to certify. Simulation and experimental results are presented to validate the approach in different scenarios.

      PubDate: 2017-02-11T12:59:26Z
       
  • Corner-based estimation of tire forces and vehicle velocities robust to
           road conditions
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Ehsan Hashemi, Mohamamd Pirani, Amir Khajepour, Alireza Kasaiezadeh, Shih-Ken Chen, Bakhtiar Litkouhi
      Recent developments in vehicle stability control and active safety systems have led to an interest in reliable vehicle state estimation on various road conditions. This paper presents a novel method for tire force and velocity estimation at each corner to monitor tire capacities individually. This is entailed for more demanding advanced vehicle stability systems and especially in full autonomous driving in harsh maneuvers. By integrating the lumped LuGre tire model and the vehicle kinematics, it is shown that the proposed corner-based estimator does not require knowledge of the road friction and is robust to model uncertainties. The stability of the time-varying longitudinal and lateral velocity estimators is explored. The proposed method is experimentally validated in several maneuvers on different road surface frictions. The experimental results confirm the accuracy and robustness of the state estimators.

      PubDate: 2017-02-11T12:59:26Z
       
  • A Voronoi-diagram-based dynamic path-planning system for underactuated
           marine vessels
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Mauro Candeloro, Anastasios M. Lekkas, Asgeir J. Sørensen
      The main contribution of this paper is the development of a rapid, dynamic path-planning system for 3-DOF marine surface vessels navigating in environments where other marine vehicles might be operating too. The method is based on the Voronoi diagram and generates the initial path while ensuring that clearance constraints are satisfied with respect to both land and shallow waters. Fermat's Spiral (FS) segments are used to connect successive straight lines, hence, resulting in curvature-continuous paths that are rapidly computed. When a ship is detected, the range of its position during a given time frame is estimated, and the path-planning system produces in real time a new safe and smooth path. The International Regulations for Preventing Collisions at Sea (COLREG) are taken into account in the replanning procedure. An indirect adaptive Line-Of-Sight (LOS) guidance algorithm from the existing literature is implemented to ensure the underactuated vessel will counteract the effects of unknown environmental forces, such as ocean currents, while converging to the safe path. Simulations show the effectiveness of the proposed approach.

      PubDate: 2017-02-11T12:59:26Z
       
  • Robust adaptive speed regulator with self-tuning law for surfaced-mounted
           permanent magnet synchronous motor
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Seok-Kyoon Kim
      This study exhibits a self-tuning speed control scheme for the surface-mounted permanent magnet synchronous motor (SPMSM) against the parameter variations through the multivariable approach. The proposed method has two novelties. The first one is to combine the adaptive controller with the self-tuning algorithm so as to make the decay ratio of the tracking errors higher in the transient period. The second one is to provide a systematical way to find a robust stabilizing control gain corresponding the speed and current tracking errors by solving an optimization problem. The efficacy of the proposed method was experimentally investigated using a 3-kW SPMSM.

      PubDate: 2017-02-11T12:59:26Z
       
  • Nonlinear tracking control for sensorless permanent magnet synchronous
           motors with uncertainties
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): C.M. Verrelli, P. Tomei, E. Lorenzani, G. Migliazza, F. Immovilli
      The recent advanced solution in Marino, Tomei, and Verrelli (2013) to the tracking control problem for sensorless IMs with parameter uncertainties is translated on the basis of letter swap connections between the models of (nonsalient-pole surface) permanent magnet synchronous motors (PMSMs) and induction ones (IMs). The (stability proof-based) nonlinear adaptive position/speed tracking control for sensorless PMSMs (with simultaneous estimation of uncertain constant load torque and stator resistance), which is accordingly obtained by exploring and decoding the design paths in Marino et al. (2013) and which surprisingly represents a simple generalization of the controller in Tomei and Verrelli (2011), constitutes an innovative solution to the related open problem. Illustrative experimental results are included.

      PubDate: 2017-02-11T12:59:26Z
       
  • Angle tracking of a pneumatic muscle actuator mechanism under varying load
           conditions
    • Abstract: Publication date: April 2017
      Source:Control Engineering Practice, Volume 61
      Author(s): Hongjiu Yang, Yang Yu, Jinhui Zhang
      In this paper, an active disturbance rejection control approach is proposed for a pneumatic muscle actuator mechanism to achieve angle tracking precisely under varying load conditions. The varying load conditions are treated as external disturbances which are estimated by a linear extended state observer. An active disturbance rejection controller is presented to compensate negative impacts induced by the varying loads. Moreover, stabilization of the closed-loop system are performed for the pneumatic muscle actuator mechanism. Finally, experimental results show the effectiveness of the developed technique in this paper.

      PubDate: 2017-02-04T12:44:04Z
       
  • Performance evaluation of nonlinear Kalman filtering techniques in low
           speed brushless DC motors driven sensor-less positioning systems
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Ardeshir Mazaheri, Ahmad Radan
      Appropriate position estimation of electric actuator is one of the most important stages in the control and automation processes. Considering various applications including robotics and automotive systems, Brushless DC (BLDC) motors sensor-less positioning is substantial in two major aspects. Electric commutation on the electric side should be performed precisely as well as motion control on the mechanical side. The mathematical models which befit precise applications are inherently nonlinear and require specific control techniques to deal with. Nonlinear Kalman filtering methods are considered as suitable solutions to estimation problems where uncertainty and noise exist. Three major and basic algorithms are Extended (EKF), Unscented (UKF) and Cubature Kalman filtering (CKF). In this paper, the application of these methods in estimation of rotor angular position with emphasis on low speed state is presented. Performance measures are compared using experimental setup. A typical 3-phase low voltage BLDC motor is implemented in the setup so that system noise could deteriorate quality of Back-EMF signal in low speed mode. It is shown that UKF and CKF techniques yield better results and performance in comparison to EKF according to measures. Estimated model states diagrams indicate the superior performance of Unscented and Cubature types regarding both accuracy and convergence.

      PubDate: 2017-02-04T12:44:04Z
       
  • Simultaneous COD and VFA unmeasured process inputs estimation in actual
           anaerobic wastewater treatment processes
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): V. Alcaraz-Gonzalez, E.A. Jauregui-Medina, J.Ph. Steyer, J.P. García-Sandoval, H.O. Méndez-Acosta, V. Gonzalez-Alvarez
      A Virtually Controlled Observer (VCO) was proposed to estimate both, the unmeasured states and the unknown inputs (influent substrate concentrations: Chemical Oxygen Demand (DCO) and Volatile Fatty Acids (VFA) in a 1m3 up-flow fixed-bed anaerobic digestion (AD) pilot plant. The VCO is developed without the full knowledge of the AD kinetics and consists of an asymptotic observer and an output feedback controller, in which, one of the observer inputs (the hypothetical -unmeasured- influent substrate concentration) is updated by a feedback control law, which is devised to regulate the estimation error of a measured output. Results show that the proposed observer is robust in the face model mismatch, load and operating conditions changes and sensor faults as it was able to reconstruct the influent substrate concentration.
      Graphical abstract image

      PubDate: 2017-01-29T01:00:21Z
       
  • Efficient hardware implementation of radial basis function neural network
           with customized-precision floating-point operations
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Helon Vicente Hultmann Ayala, Daniel M. Muñoz, Carlos H. Llanos, Leandro dos Santos Coelho
      This paper aims at the proposition of novel architectures for radial basis function neural networks implementation on hardware with custom-precision floating-point operations for black-box system modeling. An analysis tool was built to establish the trade-off between the consumption of hardware resources and the precision of the outputs, on the basis of the usage of the logic blocks on a field-programmable gate array and output quality. The architectures have been tested with a standard system identification benchmark and the speedup factors, when compared to a C implementation, are on the order of hundreds, what shows the importance of ad-hoc hardware architectures for improving computational efficiency.

      PubDate: 2017-01-29T01:00:21Z
       
  • Parameter identification of a multi-stage, multi-load-demand experimental
           refrigeration plant
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): David Rodríguez, Guillermo Bejarano, José A. Alfaya, Manuel G. Ortega, Fernando Castaño
      Parameter estimation of a multi-stage, multi-load-demand refrigeration plant is addressed. It is shown that dominating system dynamics are those of heat exchangers, and their heat-transfer-related parameters affect system statics but barely influence system dynamics. A novel identification procedure focused on the heat exchangers is presented. It is based on non-measurable refrigerant phase-change zones, considering an overall heat transfer coefficient at each zone. Consistent values of all parameters are obtained considering only steady-state experimental data and some orders of magnitude found in the literature. The identified parameters are validated considering the two-stage, two-load-demand plant configuration.

      PubDate: 2017-01-29T01:00:21Z
       
  • Performance analysis of a new energy-efficient variable supply pressure
           electro-hydraulic motion control method
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): C. Du, A.R. Plummer, D.N. Johnston
      Electro-hydraulic actuation is used in many motion control applications due to its high power density, excellent dynamic response and good durability. However fluid power actuation has been shown to be very energy inefficient, with an average efficiency for fluid power systems across all industries of 22% in the USA. This is a very significant problem, given that 3% of the energy used by mankind is transmitted in this way. The key challenge for researchers is to reduce energy losses in hydraulic actuation systems without increasing weight, size, and noise, and without reducing speed of response. Conventional high performance electro-hydraulic motion control systems use a fixed supply pressure with valve-controlled actuators (FPVC). This is inherently inefficient due to the need to use a valve to throttle the flow required by each actuator in the system down to match its load pressure. In this paper, a new load-prediction based method is proposed, in which the supply pressure is varied to track the pressure required by any actuator branch. By implementing this model-based approach using a high response servomotor-driven pump, it is shown that the dynamic response remains excellent. The load model not only allows feedforward control for servomotor speed based on the motion demand, but also feedforward for the control valves to supplement conventional proportional-integral feedback control. The new variable supply pressure valve-controlled (VPVC) method is investigated in simulation and experimentally using a two-axis hydraulic robot arm supplied by an axial piston pump. The performance has been rigorously compared with the same robot arm using a fixed supply pressure and proportional-integral joint position control. Experimental results showed that up to 70% hydraulic power saving was achieved, and that the dynamic tracking errors for VPVC were about half that for FPVC as a result of using feedforward control.

      PubDate: 2017-01-22T00:39:05Z
       
  • Real-time implementation of an explicit MPC-based reference governor for
           control of a magnetic levitation system
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Martin Klaučo, Martin Kalúz, Michal Kvasnica
      This paper deals with the design and real-time implementation of an Model Predictive Control (MPC)-based reference governor on an industrial-like microcontroller. The task of the governor is to provide optimal setpoints for an inner Proportional-Summation-Difference (PSD) controller. The MPC-based governor is synthesized off-line as a Piecewise Affine (PWA) function that maps measurements onto optimal references. To achieve a fast and memory-efficient implementation, the PWA function is encoded as a binary search tree. This allows the reference governor to run on a sub-millisecond scale even on a very simple hardware. The proposed concept is experimentally verified on a laboratory device involving a magnetic levitation system. Here, the PSD controller is responsible for controlling the vertical position of the ball in the magnetic field. By using the reference governor, control performance can be significantly improved and input/output constraints enforced in a systematic manner.

      PubDate: 2017-01-22T00:39:05Z
       
  • Pulse-coupled time synchronization for distributed acoustic event
           detection using wireless sensor networks
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Felipe Núñez, Yongqiang Wang, David Grasing, Sachi Desai, George Cakiades, Francis J. Doyle
      Time synchronization has proven to be critical in sensor fusion applications where the time of arrival is utilized as a decision variable. Herein, the application of pulse-coupled synchronization to an acoustic event detection system based on a wireless sensor network is presented. The aim of the system is to locate the source of acoustic events utilizing time of arrival measurements for different formations of the sensor network. A distributed localization algorithm is introduced that solves the problem locally using only a subset of the time of arrival measurements and then fuses the local guesses using averaging consensus techniques. It is shown that the pulse-coupled strategy provides the system with the proper level of synchronization needed to enable accurate localization, even when there exists drift between the internal clocks and the formation is not perfectly maintained. Moreover, the distributed nature of pulse-coupled synchronization allows coordinated synchronization and distributed localization over an infrastructure-free ad-hoc network.

      PubDate: 2017-01-22T00:39:05Z
       
  • Disturbance rejection control of a fuel cell power plant in a
           grid-connected system
    • Abstract: Publication date: Available online 20 January 2017
      Source:Control Engineering Practice
      Author(s): Guiying Wu, Li Sun, Kwang Y. Lee
      Interface of a fuel cell plant to power grid is challenging because of the high nonlinearities of the fuel cell plant and the power conditioning system (PCS). This paper focuses on the control of grid-connected solid-oxide fuel cell (SOFC) power plant that is subject to varying load and uncertain network parameters. To this end, Active Disturbance Rejection Control (ADRC) is utilized to improve the performance of the PCS consisting of a dc-dc converter and a dc-ac inverter. ADRC is used in the dc-dc converter to stabilize the dc link voltage and yield a robust performance against the nonlinearity. Used in the dc-ac inverter, ADRC eliminates the steady-state error and is insensitive to the high-frequency noise. Simulation results show that, for grid current control, ADRC achieves a more robust performance than the conventional proportional-integral (PI) controller. Moreover, the total harmonic distortions (THDs) of the output current controlled by ADRC are always below 5% in spite of the variation in the load demand and network parameters.

      PubDate: 2017-01-22T00:39:05Z
       
  • Nonlinear control of coal-fired steam power plants
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Nahla Alamoodi, Prodromos Daoutidis
      This work proposes a nonlinear control strategy for steam power plants that efficiently controls the superheated steam temperature while accommodating large and frequent variations in power demand. The variables to be controlled are the pressure in the boiler, power generation, and superheater/reheater temperatures. The proposed strategy decomposes the overall plant into three separate subsystems and applies decoupling with deadtime compensation for each one of them. The derived strategy is implemented within a MATLAB/Simulink environment for different setpoint tracking and disturbance rejection cases, showing excellent performance and robustness.

      PubDate: 2017-01-15T00:12:35Z
       
  • Damage-tolerant active control using a modal H∞-norm-based
           methodology
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Helói F.G. Genari, Nazih Mechbal, Gérard Coffignal, Eurípedes G.O. Nóbrega
      A new approach for vibration reduction of flexible structures subject to damage is here proposed, based on modal H ∞ -norm control. Considering that structural damage provokes different effects on each vibration mode, the proposed method concentrates the control action on modes that are indeed suffering the worst damage consequences. For this purpose, a new modal H ∞ norm is introduced, weighing each mode according to control design convenience. Based on this norm, a regular H ∞ controller design is applied, using the linear matrix inequality approach. Simulated and experimental results show significant advantages of the proposed methodology over the regular H ∞ approach, including damage tolerance.

      PubDate: 2017-01-15T00:12:35Z
       
  • Rapid development of modular and sustainable nonlinear model predictive
           control solutions
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Sergio Lucia, Alexandru Tătulea-Codrean, Christian Schoppmeyer, Sebastian Engell
      While computational complexity is often not anymore an obstacle for the application of Nonlinear Model Predictive Control (NMPC), there are still important challenges that prevent NMPC from already being an industrial reality. This paper deals with a critical challenge: the lack of tools that facilitate the sustainable development of robust NMPC solutions. This paper proposes a modularization of the NMPC implementations that facilitates the comparison of different solutions and the transition from simulation to online application. The proposed platform supports the multi-stage robust NMPC approach to deal with uncertainty. Its benefits are demonstrated by experimental results for a laboratory plant.

      PubDate: 2017-01-06T19:58:17Z
       
  • Time-optimal flatness based control of a gantry crane
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Bernd Kolar, Hubert Rams, Kurt Schlacher
      This contribution deals with the flatness based control of a gantry crane, where the control objective is to transfer the load from an initial rest position to a final rest position in a minimal transition time. It is well-known that the type of crane model we consider is a differentially flat system, and that the position of the load is a flat output. We exploit this property both for the design of a tracking control as well as for planning time-optimal reference trajectories for the load. We discuss the design of the tracking control in detail, and show in particular how a standard approach which can be found in the literature can be modified systematically such that instead of measurements of certain time derivatives of the flat output we can use measurements of the state of the system. We also present a new approach for the design of time-optimal reference trajectories. In order to solve the resulting nonlinear optimization problem numerically, we use a primal-dual interior point method. Finally, we conclude with measurement results that stem from an implementation on a laboratory model.

      PubDate: 2016-12-28T08:18:46Z
       
  • Multi-experiment state-space identification of coupled magnetic and
           kinetic parameters in tokamak plasmas
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): B. Mavkov, E. Witrant, C. Prieur, D. Moreau
      This paper describes an identification technique for control-oriented linear time-invariant models of the coupled dynamics of the electron temperature and the poloidal magnetic flux for advanced operational tokamak scenarios. The actuators consist of two neutral beam injectors, an electron cyclotron current drive and the ohmic coil that provides the loop voltage at the plasma surface. The model is identified using a combination of subspace and output-error methods for state-space multiple-input and multiple-output system identification. This identification is applied on sets of simulated data from the METIS tokamak simulator with parameters typical of the DIII-D tokamak, and the results of the identification are presented.

      PubDate: 2016-12-28T08:18:46Z
       
  • Nonlinear observer design for GNSS-aided inertial navigation systems with
           time-delayed GNSS measurements
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Jakob M. Hansen, Thor I. Fossen, Tor Arne Johansen
      Global navigation satellite system (GNSS) receivers suffer from an internal time-delay of up to several hundred milliseconds leading to a degeneration of position accuracy in high-dynamic systems. With the increasing interest in GNSS navigation, handling of time-delays will be vital in high accuracy applications with high velocity and fast dynamics. This paper presents a nonlinear observer structure for estimating position, linear velocity, and attitude (PVA) as well as accelerometer and gyro biases, using inertial measurements and time-delayed GNSS measurements. The observer structure consists of four parts; (a) attitude and gyro bias estimation, (b) time-delayed translational motion observer estimating position and linear velocity, (c) input delays for inertial and magnetometer measurements, and (d) a faster than real-time simulator. The delayed PVA and gyro bias estimates are computed using a uniformly semiglobally exponentially stable (USGES) nonlinear observer. The high-rate inertial measurements are delayed and synchronized with the GNSS measurements in the state observer. The fast simulator integrates the inertial measurements from the delayed state estimate to provide a state estimate at current time. The sensor measurements are carefully synchronized and the estimation procedure for the GNSS receiver delay is discussed. Experimental data from a small aircraft are used to validate the results.

      PubDate: 2016-12-28T08:18:46Z
       
  • Special Section: IFAC Symposium on Biological and Medical Systems –
           BMS 2015
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Thomas Schauer, Berno J.E. Misgeld, Fabio Previdi


      PubDate: 2016-12-28T08:18:46Z
       
  • Controller design for neuromuscular blockade level tracking based on
           optimal control
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Juliana Almeida, Teresa Mendonça, Paula Rocha, Luís Rodrigues
      The contribution of this paper is to present and compare two state-feedback design methods for the automatic control of the Neuromuscular Blockade Level (NMB) based on optimal control. For this purpose a parsimoniously parameterized model is used to describe the patient's response to a muscle relaxant. Due to clinical restrictions the controller action begins when the patient recovers after an initial drug bolus. The NMB control problem, typically consisting of tracking a constant NMB reference level, can be associated with an optimal control problem (OCP) with a positivity constraint in the input signal. Due to the complexity associated with the introduction of a positivity constraint in the input, approximate solutions to this OCP will be found in this paper using two methods. In the first method, the optimal control problem is relaxed into a Semi-Definite Program (SDP) using a change of variables, whereas in the second method the OCP is approximated by an infinite horizon constrained Linear Quadratic Regulator (LQR) problem. These two controllers are compared with a classical PI controller in simulation. The PI exhibits a slightly worse performance in terms of the control magnitude but it was not optimized taking this magnitude into account. The simulation results show that the SDP relaxation and the saturated LQR methods lead to the same controller gains and therefore the same trajectory tracking using parameters from a patient's database, thus encouraging its application and validation in clinical trials. Although the performance of the proposed controllers can be compared in terms of how they work when applied to the patient's database models, the two proposed methods cannot be compared from an optimal control theoretical point of view because they correspond to the solution of two different relaxations of the original control problem using two different functions of merit.

      PubDate: 2016-12-28T08:18:46Z
       
  • Real-time insulin bolusing for unannounced meals with artificial pancreas
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Kamuran Turksoy, Iman Hajizadeh, Sediqeh Samadi, Jianyuan Feng, Mert Sevil, Minsun Park, Laurie Quinn, Elizabeth Littlejohn, Ali Cinar
      Post-prandial hyperglycemia can occur more frequently in artificial pancreas systems without meal announcements that trigger insulin boluses. Meal announcements are manual feedforward inputs. We have developed a meal-detection and meal bolusing algorithm based on continuous glucose measurements without manual information from patients. Bergman's minimal model is modified and used in an unscented Kalman filter for state estimations. The estimated rate of appearance of glucose is used for meal detection and calculation of meal boluses. The algorithm is tested in simulation and clinical environments. The proposed algorithm decreases the frequency, duration and magnitude of hyperglycemia without causing any additional hypoglycemia.
      Graphical abstract image Highlights fx1

      PubDate: 2016-12-28T08:18:46Z
       
  • Tracking the progression to type 2 diabetes with a proportional-derivative
           insulin secretion model
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Nor Azlan Othman, Paul D. Docherty, Nor Salwa Damanhuri, J. Geoffrey Chase
      Background Modelling insulin secretion as a function of peripheral C-peptide levels by mathematical deconvolution is widespread. However, the measurement resolution for successful deconvolution and high cost of C-peptide assays means measurement of insulin secretion can only be undertaken in small scale research endeavours. This research models the nature of insulin secretion (U N ) during the pathogenesis of type 2 diabetes. Methods A proportional-derivative U N model is based on the physiological, closed-loop insulin secretion response to increasing glucose ( ϕ D ) and glucose excursions ( ϕ P ). A total of 204 dynamic insulin sensitivity and secretion test (DISST) data sets from 68 participants in a 10-week dietary intervention trial were used to determine ϕ D and ϕ P values. The resulting gain values are used to classify subjects and thus the evaluation of U N over increasing insulin resistance. Results Participants with impaired fasting glucose (G 0 >5.56mmolL-1) had a lower median ϕ D value that becomes almost equal to ϕ P . In contrast, NGT participants (G 0 <5.56mmolL-1), ϕ D that tended to be much greater than ϕ P . Thus, as the metabolic state of a participant moves from NGT to pre-diabetes, the participant is loses first phase insulin burst secretion. The resulting gains are classified by easily measured basal glucose. Conclusions The simplicity of this PD U N model in a DISST model framework provides clear relationship between the U N profile and the readily available metabolic state of each participant. These relationships could significantly improve the cost and resolution of model-based tests like the DISST.

      PubDate: 2016-12-28T08:18:46Z
       
  • Closed-loop control of extracorporeal oxygen and carbon dioxide gas
           transfer
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): C. Brendle, K.-F. Hackmack, J. Kühn, M.N. Wardeh, T. Janisch, R. Kopp, R. Rossaint, A. Stollenwerk, S. Kowalewski, S. Leonhardt, M. Walter, B. Misgeld
      Additional extracorporeal gas transfer facilitates ultra-protective mechanical ventilation during treatment of severe lung disease. The proposed automation contributes to both patient safety and therapeutic success. A decentralized control system set the oxygen and carbon dioxide gas transfer rates. The controlled variables are estimated using standard measurement devices without direct blood contact. To reduce patient stress, an outer-loop integral controller adjusts the extracorporeal blood flow. The control system was first evaluated in silico and then in vivo using an animal model. Finally, the method is shown to be feasible and its response time is sufficient to meet patients' clinical needs.

      PubDate: 2016-12-28T08:18:46Z
       
  • A low-cost high-fidelity ultrasound simulator with the inertial tracking
           of the probe pose
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Saverio Farsoni, Marcello Bonfè, Luca Astolfi
      The authors developed a versatile ultrasound simulator. The proposed system achieves the main features of a high-fidelity device exploiting low-cost rapid prototyping hardware. The hand-guided ultrasound simulator probe includes a RFID reader, a 9-DOF inertial sensor unit, consisting of an accelerometer, a magnetometer and a gyroscope, and a microcontroller that performs the real-time data acquisition, the processing and the transmission of the estimated pose information to the visualization system, so that the proper ultrasound view can be generated. Since the probe orientation is the main information involved in the pose reconstruction, this work presents and investigates several tracking methods for the probe orientation, exploiting a sensor fusion technique to filter the noisy measurements coming from inertial sensors. The performances of a Kalman filter, a nonlinear complementary filter and a quaternion-based filter as inertial trackers have been tested by means of a robot manipulator, in terms of readiness, accuracy and stability of the estimated orientation signal. The results show that the nonlinear complementary filter and the quaternion-based filter match all the application requirements (RMSE < 3 deg , variance < 1 deg 2 , and settling time < 0.3 s ), and they involve a lower computational time with respect to the Kalman filter.

      PubDate: 2016-12-28T08:18:46Z
       
  • Optimal learning control of oxygen saturation using a policy iteration
           algorithm and a proof-of-concept in an interconnecting three-tank system
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Anake Pomprapa, Steffen Leonhardt, Berno J.E. Misgeld
      In this work, “policy iteration algorithm” (PIA) is applied for controlling arterial oxygen saturation that does not require mathematical models of the plant. This technique is based on nonlinear optimal control to solve the Hamilton–Jacobi–Bellman equation. The controller is synthesized using a state feedback configuration based on an unidentified model of complex pathophysiology of pulmonary system in order to control gas exchange in ventilated patients, as under some circumstances (like emergency situations), there may not be a proper and individualized model for designing and tuning controllers available in time. The simulation results demonstrate the optimal control of oxygenation based on the proposed PIA by iteratively evaluating the Hamiltonian cost functions and synthesizing the control actions until achieving the converged optimal criteria. Furthermore, as a practical example, we examined the performance of this control strategy using an interconnecting three-tank system as a real nonlinear system.

      PubDate: 2016-12-28T08:18:46Z
       
  • An adaptive low-dimensional control to compensate for actuator redundancy
           and FES-induced muscle fatigue in a hybrid neuroprosthesis
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Naji Alibeji, Nicholas Kirsch, Nitin Sharma
      To restore walking and standing function in persons with paraplegia, a hybrid walking neuroprosthesis that combines a powered exoskeleton and functional electrical stimulation (FES) can be more advantageous than sole FES or powered exoskeleton technologies. However, the hybrid actuation structure introduces certain control challenges: actuator redundancy, cascaded muscle activation dynamics, FES-induced muscle fatigue, and unmeasurable states. In this paper, a human motor control inspired control scheme is combined with a dynamic surface control method to overcome these challenges. The new controller has an adaptive muscle synergy-based feedforward component which requires a fewer number of control signals to actuate multiple effectors in a hybrid neuroprosthesis. In addition, the feedforward component has an inverse fatigue signal to counteract the effects of the muscle fatigue. A dynamic surface control (DSC) method is used to deal with the cascaded actuation dynamics without the need for acceleration signals. The DSC structure was modified with a delay compensation term to deal with the electromechanical delays due to FES. A model based estimator is used to estimate the unmeasurable fatigue and actuator activation signals. The development of the controller and a Lyapunov stability analysis, which yielded semi-global uniformly ultimately boundedness, are presented in the paper. Computer simulations were performed to test the new controller on a 2 degrees of freedom fixed hip model after which preliminary experiments were conducted on one able-bodied male subject in the fixed hip configuration.

      PubDate: 2016-12-28T08:18:46Z
       
  • Contents list
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59


      PubDate: 2016-12-28T08:18:46Z
       
  • Robust control for voltage and transient stability of power grids relying
           on wind power
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Konstantin Schaab, Jannik Hahn, Maksim Wolkov, Olaf Stursberg
      Common practice in stabilization of power grids is to refer to different stability categories (transient stability, voltage stability, rotor angle stability) and to address these by designing dedicated controllers separately based on models linearized around nominal operation points. Furthermore, the controllers of a generating unit contained in the grid are usually synthesized without considering other grid nodes. This work, in contrast, proposes a scheme for unified synthesis of controllers which conjunctively address rotor angle stability and voltage stability for grids containing synchronous generators as well as wind energy conversion systems based on doubly-fed induction generators. First, a procedure is proposed to describe the generating units by linear-parameter-varying (LPV) systems, in which fluctuations imposed by the grid or the wind are mapped into time-varying model parameters. For appropriate ranges of these parameters, decentralized robust controllers can be synthesized by semidefinite-programming, such that the power grid is stabilized for the considered fluctuations and disturbances. The effectiveness of the approach is demonstrated for a multi-bus benchmark system, where the grid oscillations are well damped and the LPV-controller stabilizes the grid after permanent changes.

      PubDate: 2016-12-21T07:47:57Z
       
  • A method for setpoint alarming using a normalized index
    • Abstract: Publication date: March 2017
      Source:Control Engineering Practice, Volume 60
      Author(s): Timothy I. Salsbury, Carlos F. Alcala
      This paper describes a normalized index for assessing the performance of PID control loops. The index was developed with a focus on ease of implementation by making use of features that are commonly found in modern control systems. Exponentially-weighted moving averages (EWMAs) or equivalent first-order infinite-impulse response (IIR) filters are found in many control system algorithm libraries and the index is developed using two EWMAs. Because the index is normalized, this paper shows how a single threshold can be derived from generic performance metrics thereby providing a solution to replace traditional setpoint alarming. Results are presented from evaluating the index using data gathered from several different loop types in a building heating, ventilating, and air-conditioning (HVAC) system.

      PubDate: 2016-12-14T07:19:34Z
       
  • Series Active Variable Geometry Suspension application to comfort
           enhancement
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Carlos Arana, Simos A. Evangelou, Daniele Dini
      This paper explores the potential of the Series Active Variable Geometry Suspension (SAVGS) for comfort and road holding enhancement. The SAVGS concept introduces significant nonlinearities associated with the rotation of the mechanical link that connects the chassis to the spring-damper unit. Although conventional linearization procedures implemented in multi-body software packages can deal with this configuration, they produce linear models of reduced applicability. To overcome this limitation, an alternative linearization approach based on energy conservation principles is proposed and successfully applied to one corner of the car, thus enabling the use of linear robust control techniques. An H ∞ controller is synthesized for this simplified quarter-car linear model and tuned based on the singular value decomposition of the system's transfer matrix. The proposed control is thoroughly tested with one-corner and full-vehicle nonlinear multi-body models. In the SAVGS setup, the actuator appears in series with the passive spring-damper and therefore it would typically be categorized as a low bandwidth or slow active suspension. However, results presented in this paper for an SAVGS-retrofitted Grand Tourer show that this technology has the potential to also improve the high frequency suspension functions such as comfort and road holding.

      PubDate: 2016-12-07T13:04:31Z
       
  • Motion planning for robotic manipulators using robust constrained control
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Andrea Maria Zanchettin, Paolo Rocco
      Since their first appearance in the 1970's, industrial robotic manipulators have considerably extended their application fields, allowing end-users to adopt this technology in previously unexplored scenarios. Correspondingly, the way robot motion can be specified has become more and more complex, requiring new capabilities to the robot, such as reactivity and adaptability. For an even enhanced and widespread use of industrial manipulators, including the newly introduced collaborative robots, it is necessary to simplify robot programming, thus allowing this activity to be handled by non-expert users. Next generation robot controllers should intelligently and autonomously interpret production constraints, specified by an application expert, and transform them into motion commands only at a lower and real-time level, where updated sensor information or other kind of events can be handled consistently with the higher level specifications. The availability of several execution strategies could be then effectively exploited in order to further enhance the flexibility of the resulting robot motion, especially during collaboration with humans. This paper presents a novel methodology for motion specification and robust reactive execution. Traditional trajectory generation techniques and optimisation-based control strategies are merged into a unified framework for simultaneous motion planning and control. An experimental case study demonstrates the effectiveness and the robustness of this approach, as applied to an image-guided grasping task.

      PubDate: 2016-12-07T13:04:31Z
       
  • A framework for simulation-based engine-control unit inspection in
           manufacturing phase
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Won K. Ham, Minsuk Ko, Sang C. Park
      This paper proposes a framework for electronic engine-control unit (ECU) inspection in manufacturing phase. Although various methodologies have been developed for the ECU verification at the development phase, the ECU verification in the manufacturing phase has rarely been brought into focus. ECUs in the manufacturing phase need the verification process in the unified way of the ECU software and hardware components by three major causes: 1) ECU software revision, 2) incomplete installation of software, and 3) quality variation of hardware. For the effective ECU verification in the manufacturing phase, we propose a simulation-based ECU testing methodology. The proposed framework configures virtual vehicle environment to simulate an ECU using a “virtual engine system (VES) model” that specifies the operations of every ECU function during a simulation. The proposed framework employs a reverse engineering approach to identify the operation state transition of an ECU function by reference vehicle states from vehicle experimental data. The main objective of this paper is to design a VES model-based inspection system that simulates an ECU without software modification in brief time for set-up and execution. The proposed framework has been implemented and successfully applied to a Korean automotive company.

      PubDate: 2016-12-07T13:04:31Z
       
  • Transmission support using Wind Farm controls during voltage stability
           emergencies
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Costas Vournas, Ioannis Anagnostopoulos, Theodoros Souxes
      This paper investigates the effect of reactive support by Wind Farms (WF) on the maximum power transfer, and thus the voltage stability limit of a transmission system. An insecure snapshot in a weak area of the Hellenic Interconnected System is examined, as well as a simpler test system. MV feeder characteristics and substation controls (feeder resistance and reactance, switched capacitors, LTC controls) are modelled in detail. Most importantly, the converter current limits, as well as the overvoltage limitations on the MV feeder, are taken into consideration in assessing the effect of the WF support.
      Graphical abstract image

      PubDate: 2016-12-07T13:04:31Z
       
  • Robust pole location with experimental validation for three-phase
           grid-connected converters
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Luiz A. Maccari, Humberto Pinheiro, Ricardo C.L.F. Oliveira, e Vinícius F. Montagner
      This paper provides design and experimental validation of robust current controllers for three-phase grid-connected converters. The main objectives here are: (i) to show that a simple polytopic model can be used for designing robust controllers for predominately inductive grids; (ii) to help in the choice of the control design parameter, based on a trade-off between an upper bound of the transient settling times and the control gain sizes. Linear matrix inequality based conditions are used to design the robust control gains with lower numerical complexity than similar conditions on literature. It is shown that small values the radius of pole location lead to better bounds for the transient responses, at the price of higher control gains. Good tracking of references for the grid currents is also illustrated in practice, allowing the closed-loop system to inject active and reactive power into the grid. Simulation and experimental results prove that the system connected to the grid can provide three-phase currents complying with requirements of an important international standard.

      PubDate: 2016-12-01T00:42:40Z
       
  • An agent-based Decision Support System for resources' scheduling in
           Emergency Supply Chains
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Sarah Ben Othman, Hayfa Zgaya, Mariagrazia Dotoli, Slim Hammadi
      We propose a multi-agent-based architecture for the management of Emergency Supply Chains (ESCs), in which each zone is controlled by an agent. A Decision Support System (DSS) states and solves, in a distributed way, the scheduling problem for the delivery of resources from the ESC supplying zones to the ESC crisis-affected areas. Thanks to the agents’ cooperation, the DSS provides a scheduling plan that guarantees an effective response to emergencies. The approach is applied to two real cases: the Mali and the Japan crisis. Simulations are based on real data that have been validated by a team of logisticians from Airbus Defense and Space.

      PubDate: 2016-12-01T00:42:40Z
       
  • Fuzzy logic based adaptive admittance control of a redundantly actuated
           ankle rehabilitation robot
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Mustafa Sinasi AYAS, Ismail Hakki ALTAS
      Ankle rehabilitation robots have recently attracted great attention since they provide various advantages in terms of rehabilitation process from the viewpoints of patients and therapists. This paper presents development and evaluation of a fuzzy logic based adaptive admittance control scheme for a developed 2-DOF redundantly actuated parallel ankle rehabilitation robot. The proposed adaptive admittance control scheme provides the robot to adapt resistance/assistance level according to patients' disability level. In addition, a fuzzy logic controller (FLC) is developed to improve the trajectory tracking ability of the rehabilitation robot subject to external disturbances which possibly occur due to human-robot interaction. The boundary scales of membership functions of the FLC are tuned using cuckoo search algorithm (CSA). A classical proportional-integral-derivative (PID) controller is also tuned using the CSA to examine the performance of the FLC. The effectiveness of the adaptive admittance control scheme is observed in the experimental results. Furthermore, the experimental results demonstrate that the optimized FLC significantly improves the tracking performance of the ankle rehabilitation robot and decreases the steady-state tracking errors about 50% compared to the optimized PID controller. The performances of the developed controllers are evaluated using common error based performance indices indicating that the FLC has roughly 50% better performance than the PID controller.

      PubDate: 2016-12-01T00:42:40Z
       
  • Design of univariate alarm systems via rank order filters
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Wen Tan, Yongkui Sun, Ishtiza Ibne Azad, Tongwen Chen
      Filtering is one of the techniques used in alarm system design to improve the performance of an alarm system. Due to the fact that the filtered data is no longer independent, computation of the performance indexes (false alarm rate (FAR), missed alarm rate (MAR) and expected detection delay (EDD)) is hard for filters. In this paper, rank order filters are applied in alarm system design. The output of rank order filters is restricted to one of the input samples, thus the probability density function (PDF) of the filtered data can be computed directly from the PDF of the raw data. This feature makes it possible to compute FAR and MAR for rank order filters directly. Further, a method to compute the expected detection delay is proposed for rank order filters despite the dependence of the filtered data. Simulation results shows that the order of rank order filters provide another degree-of-freedom in alarm system design besides the window size, which can be used to improve the alarm performance.

      PubDate: 2016-12-01T00:42:40Z
       
  • Experimental sensorless control for IPMSM by using integral backstepping
           strategy and adaptive high gain observer
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): M.A. Hamida, J. de Leon, A. Glumineau
      In this paper a robust sensorless control for an Interior Permanent Magnet Synchronous Motor (IPMSM) is designed. The proposed control strategy uses a backstepping controller, whose robustness is improved by using integral actions added at each step of the original algorithm, and by a Maximum-Torque-Per-Ampere strategy (MTPA) to improve its energy efficient operation. Furthermore, to implement this controller in the framework of the mechanical sensorless control from the only measurements of the currents and voltages, an adaptive interconnected high gain observer is developed for estimating the rotor speed, the position and the load torque. Moreover, sufficient conditions are given to ensure the practical stability of the Observer-Controller system even if bounded uncertainties occur. Finally, the performance and the effectiveness of the designed method are tested experimentally throw a significant benchmark including different speed references and with significant robustness tests. A comparative evaluation of the computational effort of our scheme with respect to classical motor control is given.

      PubDate: 2016-12-01T00:42:40Z
       
  • A two-level control strategy with fuzzy logic for large-scale photovoltaic
           farms to support grid frequency regulation
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): Nguyen Gia Minh Thao, Kenko Uchida
      This study proposes a two-level coordinated control strategy with fuzzy logic for appropriately adjusting the total active power supplied to a grid by large-scale photovoltaic (PV) farms in order to regulate grid frequency. For a solar farm, the strategy includes a central coordinating controller and many local controllers at PV power assemblies, treated as agents. In detail, the central controller uses a frequency regulation module based on a new automatic-tuning fuzzy-logic controller scheme to compute the appropriate reference values according to the total power needed. Then, the individual reference value for each local controller is determined. Each local controller governs all power-electronic converters installed at the PV agent to inject power into the grid according to the individual reference value received. Additionally, each local controller uses an algorithm to manage the state-of-charge of the battery bank installed at the agent so that it remains in the safe range of 20–80% while operating and close to the desired idle value of 50% at the steady state. Besides, a special control mode is developed and integrated into the overall strategy to aid rapid recovery of the grid frequency under emergency conditions. Numerical simulations demonstrate that the suggested strategy has the good response in terms of injecting an appropriate amount of power into the grid to regulate the frequency deviation into acceptable ranges of ±0.2 (Hz) in the transient state and ±0.05 (Hz) at the steady state, even when the weather conditions (solar radiation, air temperature), AC system load, and important control parameters of the grid suddenly change. Furthermore, the effectiveness in improving the grid-frequency stabilization by using the proposed strategy is validated within a four-area power system, where four PV farms are connected and the operating parameters of the grids at the areas are fairly different.

      PubDate: 2016-12-01T00:42:40Z
       
  • Bridging the gap between designed and implemented controllers via adaptive
           robust discrete sliding mode control
    • Abstract: Publication date: February 2017
      Source:Control Engineering Practice, Volume 59
      Author(s): M.R. Amini, M. Shahbakhti, S. Pan, J.K. Hedrick
      Bridging the gap between designed and implemented model-based controllers is a major challenge in the design cycle of industrial controllers. This gap is created due to (i) digital implementation of controller software that introduces sampling and quantization uncertainties, and (ii) uncertainties in the modeled plant's dynamics. In this paper, a new adaptive and robust model-based control approach is developed based on a nonlinear discrete sliding mode controller (DSMC) formulation to mitigate implementation imprecisions and model uncertainties, that consequently minimizes the gap between designed and implemented controllers. The new control approach incorporates the predicted values of the implementation uncertainties into the controller structure. Moreover, a generic adaptation mechanism will be derived to remove the errors in the nonlinear modeled dynamics. The proposed control approach is illustrated on a nonlinear automotive engine control problem. The designed DSMC is tested in real-time in a processor-in-the-loop (PIL) setup using an actual electronic control unit (ECU). The verification test results show that the proposed controller design, under ADC and model uncertainties, can improve the tracking performance up to 60% compared to a conventional controller design.

      PubDate: 2016-11-18T12:53:07Z
       
  • Explicit hidden coupling terms handling in gain-scheduling control design
           via eigenstructure assignment
    • Abstract: Publication date: January 2017
      Source:Control Engineering Practice, Volume 58
      Author(s): H. Lhachemi, D. Saussié, G. Zhu
      This paper presents a novel method for the design of gain-scheduled output feedback controllers in the presence of hidden coupling terms, which naturally arise when endogenous signals are used as scheduling parameters. In this case, the controller gains vary with respect to system variables, leading to inner loops between the system and the linearized gain-scheduled controller dynamics. Such effects, also known as parasitic feedbacks, are inherently difficult to handle in classic gain-scheduling control design and are often omitted, which might result in performance degradations or even destabilization of the closed-loop system. This paper shows how such a pitfall can be avoided through the application of self-scheduling and eigenstructure assignment techniques. In this context, the main contribution of the present work is the extension of eigenstructure assignment-based self-scheduling techniques for explicit hidden coupling terms handling. The viability of the proposed method is illustrated through a pitch-axis missile autopilot benchmark problem.

      PubDate: 2016-11-11T04:16:42Z
       
  • A Light-Weight Fault Injection Approach to Test Automated Production
           System PLC Software in Industrial Practice
    • Abstract: Publication date: January 2017
      Source:Control Engineering Practice, Volume 58
      Author(s): Susanne Rösch, Birgit Vogel-Heuser
      A light-weight software-implemented fault injection (SWIFI) testing approach is introduced, focusing on technical process faults and system faults. The reaction of automated production systems (aPSs) and their programmable logic controller (PLC) software to these faults is tested. In order to tailor the testing approach to the aPS domain in industrial practice, our test generation is based on a classification of possible deviations, i.e. a classification of possible technical process and system faults as the PLC perceives them. As a result, both specification and test execution become more efficient for practitioners. Furthermore, the test specification is tailored for execution on IEC 61131-3 programming environments. In this, the execution of test cases both against simulation or the real aPS, is enabled.

      PubDate: 2016-11-11T04:16:42Z
       
 
 
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