Simple Control Approach Research Articles

A Simple Control Approach for Buck Converters With Current-Constrained Technique

The output voltage tracking problem with overcurrent protection for a pulse width modulation-based dc–dc buck converter is investigated in this brief. On the one hand, large transient current during the start-up phase is required for fast dynamics. On the other hand, overlarge transient current may lead to a risk of hardware damage. Conventionally, this problem is solved by choosing conservative control parameters, while the dynamic performance is sacrificed to a certain extent. Besides, the load uncertainty is inevitable in practical applications. Hence, a control design that keeps a good balance between dynamic performance, overcurrent protection, and robustness is desired. To this end, a novel and simple current-constrained controller is constructed. Both dynamic performance and current constraint are taken into account. The low complexity of the proposed current-constrained controller yields a higher reliability of dc–dc buck converter control system, and reduces cost of hardware. Moreover, it shows a nice property of robustness against load uncertainty. Control action is penalized by adjusting controller gains automatically when inductor current tends to the barrier bound. Rigorous stability analysis is given under the presented controller. Comparative simulation and experimental results between the proposed control scheme and the classic proportion–integration–differentiation control scheme on the buck converter system are illustrated to verify the feasibility and effectiveness of the proposed control scheme.

Simulating Eastern- and Central-Pacific Type ENSO Using a Simple Coupled Model

Severe biases exist in state-of-the-art general circulation models (GCMs) in capturing realistic central-Pacific (CP) El Nino structures. At the same time, many observational analyses have emphasized that thermocline (TH) feedback and zonal advective (ZA) feedback play dominant roles in the development of eastern-Pacific (EP) and CP El Nino–Southern Oscillation (ENSO), respectively. In this work, a simple linear air–sea coupled model, which can accurately depict the strength distribution of the TH and ZA feedbacks in the equatorial Pacific, is used to investigate these two types of El Nino. The results indicate that the model can reproduce the main characteristics of CP ENSO if the TH feedback is switched off and the ZA feedback is retained as the only positive feedback, confirming the dominant role played by ZA feedback in the development of CP ENSO. Further experiments indicate that, through a simple nonlinear control approach, many ENSO characteristics, including the existence of both CP and EP El Nino and the asymmetries between El Nino and La Nina, can be successfully captured using the simple linear air–sea coupled model. These analyses indicate that an accurate depiction of the climatological sea surface temperature distribution and the related ZA feedback, which are the subject of severe biases in GCMs, is very important in simulating a realistic CP El Nino.

A Soft Bionic Gripper with Variable Effective Length

This article presented a four-fingered soft bionic robotic gripper with variable effective actuator lengths. By combining approaches of finite element analysis, quasi-static analytical modeling, and experimental measurements, the deformation of the single soft actuator as a function of air pressure input in free space was analyzed. To investigate the effect of the effective actuator length on the gripping performance of the gripper, we conducted systematical experiments to evaluate the pull-off force, the actuation speed, the precision and error tolerance of the soft gripper while grasping objects of various sizes and shapes. A combination of depressurization and pressurization in actuation as well as applying variable effective actuator length enhanced the gripper’s performance significantly, with no sensors. For example, with tunable effective actuator length, the gripper was able to grasp objects ranging from 2 mm – 170 mm robustly. Under the optimal length, the gripper could generate the maximum pull-off force for the corresponding object size; the precision and the error tolerance of the gripper were also significantly improved compared to those of the gripper with full-length. Our soft robotic prototype exhibits a simple control and low-cost approach of gripping a wide range of objects and may have wide leverage for future industrial operations.

On Robustness and Perfect Tracking with Simple Adaptive Control in Nonlinear Systems

A recent paper revisited and modified the use of various components of the simple adaptive control (SAC) approach of LTI systems and showed how one can use passivity concepts such that, while it maintains robustness with disturbances, it also allows asymptotically perfect tracking in ideal conditions. Using the extension of passivity conditions to nonstationary systems, this paper extends the analysis of robustness with disturbances and asymptotically perfect tracking in ideal conditions to nonstationary and nonlinear systems.

Power injection of renewable energy sources using modified model predictive control

This paper presents a simple model predictive control (MPC) approach to control the power injection system (PIS) for renewable energy applications. A DC voltage source and a single-phase inverter that is connected to the grid by an LCL filter form the PIS. Grid voltage is considered a disturbance for the system. For eliminating this disturbance, a modified model is proposed. It is usual to control output current to inject a desired power to grid. But due to the presence of the LCL filter, we face a third-order system and other states should be bounded during operation. In this work, we ensure the stability of other state variables and, consequently, system stability, by defining a proper cost function. In this regard, reference signals are calculated for all state variables. For getting the benefit of the switching nature of the inverter, we use a finite control set model predictive control (FCS-MPC). Proposed predictive control is implemented in a digital scheme and, thereby, the discrete model of the system is extracted. The proposed controller does not require any other control loop or modulation method. Simulation results show the effective performance of the proposed control scheme.

From adaptive control to variable structure systems – seeking harmony

From adaptive control to variable structure systems – seeking harmony

Control approach of three‐phase grid connected PV inverters for voltage unbalance mitigation in low‐voltage distribution grids

Low-voltage distribution grids (LV) experience unbalanced voltage condition due to the high penetration levels of rooftop mounted single-phase photovoltaic (PV), the existence of single-phase transformers, unbalanced cable impedances and different load levels on each phase. The voltage unbalance (VU) has a harmful impact on the loads and equipment connected to grid that leads to overheating and fast thermal ageing. There are several solutions proposed to mitigate the VU, that requires the installation of extra hardware components or incorporate complex type of controllers that need special tuning procedures and special arrangements. Therefore, in this study a new and simple control approach of three-phase grid connected PV inverter is proposed to mitigate the unbalanced voltage. The new control approach is able to fully mitigate the unbalanced voltage without the need to extra hardware installation or negative sequence voltage magnitude and phase angle measurements, provided that the ampacity of the converter is high enough. The new system is tested in a LV grid with high PV penetration from Germany. The results show that the VU factor did not exceed 0.8% at the feeder connection point.

Efficient Control Scheme for Five-level (NPC) Shunt Active Power Filters Based on Fuzzy Control Approaches

This paper present simple fuzzy control approaches for shunt active power filter based on five-level (NPC) inverter which can mitigate current harmonics generated by nonlinear loads and compensate reactive power. Today, five-level inverter is strongly used in the medium and high voltage applications; these advantages are low harmonic distortions, low switching losses, low electromagnetic interference and low acoustic noise. Second, fuzzy logic techniques have been successfully employed in several power electronic applications. To benefit from these advantages a novel control scheme based on fuzzy current controller is adopted; it is designed to improve compensation capability by adjusting the current error using a fuzzy rule. The reference current signals required to compensate harmonic currents use the synchronous current detection method, this technique is easy to implement and achieves good results. To maintain the dc voltage across capacitor constant and reduce inverter losses, a proportional integral voltage controller is used. The simulation of global system control and power circuits is performed using Matlab-Simulink and SimPowerSystem toolbox. The results obtained in transient and steady states under various operating conditions show the effectiveness of the proposed shunt active filter based on five-level (NPC) inverter using fuzzy control.

Hierarchical aggregation of multiple fuzzy controllers for global complex control problems

In this paper, we illustrate a proposed method for control that combines the outputs of several individual controllers to improve global control of complex nonlinear plants. In the first part of this paper, we illustrate the proposed method that consists of two levels, where in the top level a fuzzy system represents a superior control that is designed for adjusting the behavior of the individual fuzzy controllers at the lower level. To test the approach, we consider the problem of flight control because it requires several individual controllers. Also a comparison is performed, where the hierarchical control strategy is compared with a simple control approach using the t student test. In this paper, we show that the proposed method outperforms the conventional fuzzy control approach. In the optimal design of the proposed control architecture a genetic algorithm was also applied to tune the parameters of the fuzzy systems in an optimal fashion.

Type-2 fuzzy logic aggregation of multiple fuzzy controllers for airplane flight control

This paper presents a proposed new approach for complex control combining several simpler individual fuzzy controllers. This method is particularly useful when the case of study is a multivariable control system. The proposed method has a hierarchical architecture with 2 levels (individual fuzzy systems and a superior control to adjust the global result). The behavior of the proposed method is illustrated with a problem of flight control that requires several individual controllers. In addition a statistical comparison is performed using the t student test, where the proposed control strategy is compared against a simple fuzzy control approach. Finally, an optimization method is also applied to achieve an optimal design of the fuzzy systems.

Single-approximation-based adaptive control of a class of nonlinear time-delay systems

This paper presents a simple adaptive control approach for uncertain strict-feedback nonlinear systems with unknown time-varying delays. All nonlinear functions and time delays in the systems are assumed to be unknown. Compared with the existing works, the contribution of this study is the design of a simple adaptive control law using single function approximator, without the implementation of virtual controllers derived from the backstepping design procedure. Unlike the existing backstepping methods, virtual controllers are only used as intermediate signals for designing the actual control. Therefore, the proposed control scheme is simpler than the existing methods for strict-feedback time-delay systems because the problems of using multiple approximators and calculating virtual controllers are eliminated. In addition, it is shown that all signals in the closed-loop system are uniformly ultimately bounded.

Robustness and perfect tracking in simple adaptive control

SummaryAdaptive controllers have been developed to guarantee stability and asymptotically perfect tracking under ideal conditions. In particular, the simple adaptive control methodology has been developed to avoid the use of identifiers, observer‐based controllers and, in general, to avoid using large order adaptive controllers in the control loop. In spite of initially successful applications, it is known that the basic adaptive algorithm may lead to divergence of the adaptive gains in such non‐ideal conditions as the presence of disturbances. A sigma‐term adjustment has been used to maintain boundedness with disturbance, yet is known that it seems to also eliminate perfect following even in ideal situations. Furthermore, bursting and other chaotic‐like phenomena observed in connection with the sigma‐term may also give pause to potential users of adaptive control. This paper revisits and modifies the use of various components of the simple adaptive control approach and shows how one can use passivity concepts such that, while it maintains robustness with disturbances, it also allows asymptotically perfect tracking in ideal conditions. Copyright © 2015 John Wiley & Sons, Ltd.

A Low-Cost and Simple Control Approach for Two-Phase Induction Motors at High Speeds

This paper proposes a method to control two-phase induction motors using a two-leg inverter. This method represents superior dynamic behavior and is suitable for the field-weakening region and high speed applications. In the proposed Approximate Stator Flux Control (ASFC) method, mechanical sensors and current transducers are not required. Therefore, the implementation cost of ASFC drives is comparable with the conventional scalar control drives. In the ASFC method, a switching table controls the rotating field speed of the motor by adjusting its stator flux modulus. The relationship between the stator flux modulus and rotating field speed is derived. The average switching frequency of an ASFC drive is also derived. This parameter is controlled by the ASFC drive. Via simulation and experimental case studies, high-speed operation of a two-phase ASFC drive is compared with the performance of a conventional scalar drive in start-up and steady state conditions. The validity of the presented equations required to control two-phase induction motors is also demonstrated.

Flight Results of Vision-Based Navigation for Autonomous Spacecraft Inspection of Unknown Objects

This paper describes a vision-based relative navigation and control strategy for inspecting an unknown, noncooperative, and possibly spinning object in space using a visual–inertial system that is designed to minimize the computational requirements while maintaining a safe relative distance. The proposed spacecraft inspection system relies solely on a calibrated stereo camera and a three-axis gyroscope to maintain a safe inspection distance while following a circular trajectory around the object. The navigation system is based on image processing algorithms, which extract the relative position and velocity between the inspector and the object, and a simple control approach is used to ensure that the desired range and bearing are maintained throughout the inspection maneuver. The hardware implementation details of the system are provided. Computer simulation results and experiments conducted aboard the International Space Station during Expedition 34 are reported to demonstrate the performance and applicability of the proposed hardware, and related navigation and control systems to inspect an unknown spacecraft.

Fractional‐order repetitive control of programmable AC power sources

Programmable AC power sources that provide variable-frequency and variable-amplitude output voltages are widely used in automatic testing equipment and bench top applications. Under various load conditions, a high-performance programmable AC power source not only can generate very clean sinusoidal output voltages, but also to accurately synthesise specified harmonic distorted wave-shapes. Digital repetitive control (RC) can achieve zero steady-state error tracking of any periodic signal with known integer period, but usually fails to provide precise tracking of variable-frequency periodical waveform with fractional period. In this study, a frequency adaptive fractional-order RC (FORC) strategy at fixed sampling rate is proposed to track or eliminate any periodic signals with variable frequency, where a Lagrange interpolation-based fractional delay filter is used to approximate the factional delay items in RC. The proposed FORC that offers fast on-line tuning of the fractional delay and the fast update of the coefficients, provide a simple but high-performance real-time control approach to dealing with variable-frequency variable-magnitude periodic signals. A case study of FORC-based programmable AC power source is conducted. Experimental results are provided to show the effectiveness of the proposed FORC strategy. It can be widely used in extensive applications.

Collision avoidance control for a human-operated four-wheeled mobile robot

Because the collision avoidance function is indispensable for providing safe and easy operation of human-operated robotic systems, this paper deals with the collision avoidance control for a human-operated mobile robot in unknown environments. A typical four-wheeled mobile robot with infrared distance sensors for detecting obstacles is considered. The robot cannot move in an arbitrary direction owing to a nonholonomic constraint. Therefore, we propose a simple control approach in which a human operator’s control input is modified in real time to satisfy the nonholonomic constraint and avoid collision with obstacles. The proposed controller has steering- and brake-like functions that are adjusted according to the distance sensor information. The stability of the proposed control system is analyzed with a linear model. The effectiveness of the proposed method is confirmed by experiments in which several operators control the robot in an environment with obstacles.

How teams use indicators for quality improvement – A multiple-case study on the use of multiple indicators in multidisciplinary breast cancer teams

A crucial issue in healthcare is how multidisciplinary teams can use indicators for quality improvement. Such teams have increasingly become the core component in both care delivery and in many quality improvement methods. This study aims to investigate the relationships between (1) team factors and the way multidisciplinary teams use indicators for quality improvement, and (2) both team and process factors and the intended results. An in-depth, multiple-case study was conducted in the Netherlands in 2008 involving four breast cancer teams using six structure, process and outcome indicators. The results indicated that the process of using indicators involves several stages and activities. Two teams applied a more intensive, active and interactive approach as they passed through these stages. These teams were perceived to have achieved good results through indicator use compared to the other two teams who applied a simple control approach. All teams experienced some difficulty in integrating the new formal control structure, i.e. measuring and managing performance, in their operational task, and in using their ‘new’ managerial task to decide as a team what and how to improve. Our findings indicate the presence of a network of relationships between team factors, the controllability and actionability of indicators, the indicator-use process, and the intended results.

A Site-Specific Index to Control the Total Effect of Point Sources Discharges and to Achieve ‘Good Chemical Status’ in Effluent Dependent and Effluent Dominated Water Bodies: Application on Ergene River Basin

In this study, a simple site-specific index entitled “Discharge Effect Index (DEI)” was developed to rank and control the potential risks of point sources discharges effects to Ergene River and its branches. The basin is densely populated and heavily industrialized and all the water bodies in the basin are effluent-dependent or dominated. A case study is presented to assess the most important pollution parameters in the water bodies and to evaluate relationship between toxicity to Vibrio fischeri organism and chemical parameters in receiving waters. The aim of the study was to develop a simple site-specific control approach for seriously polluted and effluent-dominated water bodies in this developing country, Turkey and guide to decision makers about controlling point sources pollution in such heavily industrialized basins and achieve ‘good chemical status’ in ambient waters. The results of the study should be useful to encourage site-specific policies on point sources pollution especially to who had such these pollution problems in their receiving water bodies.

Neural Internal Model Control for tracking Unknown Nonaffine Nonlinear Discrete-time Systems under External Disturbances

of nonlinear dynamic plants under external disturbances is presently an active area of research. The main difficulty felt in the tracking of nonlinear dynamic plants under external disturbances is the computational complexity in control design. This paper presents a simple neural network internal model control (IMC) approach for off-line tracking of unknown nonaffine nonlinear discrete time systems subject to external disturbances. The proposed control scheme is based on the neural network plant model and the inverse model. These models are determined using input output data. The final neural network IMC approach, including network plant model and the inverse model, is work off-line for tracking nonaffine nonlinear discrete time systems subject to external disturbances. Simulation results have been presented toward the end of the paper to illustrate the effectiveness of the proposed control strategy for tracking unknown nonaffine nonlinear discrete-time systems with and without external disturbances.

A simple hair control approach during intra-oral surgical procedures

A simple hair control approach during intra-oral surgical procedures