Showing papers on "Open-loop controller published in 2012"

On controller performance in software-defined networks

Abstract: Network architectures in which the control plane is decoupled from the data plane have been growing in popularity. Among the main arguments for this approach is that it provides a more structured software environment for developing network-wide abstractions while potentially simplifying the data plane. As has been adopted elsewhere [11], we refer to this split architecture as Software-Defined Networking (SDN). While it has been argued that SDN is suitable for some deployment environments (such as homes [17, 13], data centers [1], and the enterprise [5]), delegating control to a remote system has raised a number of questions on control-plane scaling implications of such an approach. Two of the most often voiced concerns are: (a) how fast can the controller respond to data path requests?; and (b) how many data path requests can it handle per second? There are some references to the performance of SDN systems in the literature [16, 5, 3]. For example, an oft-cited study shows that a popular network controller (NOX) handles around 30k flow initiation events1 per second while maintaining a sub-10ms flow install time [14]. Unfortunately, recent measurements of some deployment environments suggests that these numbers are far from sufficient. For example, Kandula et al. [9] found that a 1500-server cluster has a median flow arrival rate of 100k flows per second. Also, Benson et al. [2] show that a network with 100 switches can have spikes of 10M flows arrivals per second in the worst case. In addition, the 10ms flow setup delay of an SDN controller would add a 10% delay to the majority of flows (short-lived) in such a network. This disconnect between relatively poor controller performance and high network demands has motivated a

Anti-Windup PID Controller With Integral State Predictor for Variable-Speed Motor Drives

Abstract: The windup phenomenon appears and results in performance degradation when the proportional-integral-derivative (PID) controller output is saturated. Integral windup is analyzed on the PI plane, and a new anti-windup PID controller is proposed to improve control performance of variable-speed motor drives and is experimentally applied to the speed control of a vector-controlled induction motor driven by a pulse width-modulated voltage source inverter. The steady-state value of the integral state is predicted while the PID controller output is saturated, and this value is utilized as an initial value of the integral state when the PID controller begins to operate in a linear range. Simulation and experiments result in more similar speed responses against load conditions and step reference change over conventional anti-windup schemes. Control performance, such as overshoot and settling time, is very similar to that determined by PID gain in the linear range.

Current Controller Based on Reduced Order Generalized Integrators for Distributed Generation Systems

Abstract: This paper presents a current controller based on a stationary reference frame implementation of an integrator in the synchronous reference frame [called here reduced order generalized integrator (ROGI)], suitable for three-phase distributed generation systems. The proposed controller is compared with the traditional second-order generalized integrator (SOGI)-based current controller. It is confirmed that, in normal operation conditions, both controllers have similar performance, requiring the ROGI-based controller much less computational burden than the SOGI counterpart. The proposed controller injects sinusoidal currents synchronized with the grid voltage, without requiring any dedicated synchronization algorithm. Three different current injection strategies are realizable with the same controller structure: balanced current injection, constant instantaneous active power injection, and maximum instantaneous active power injection. A state-variable-based control methodology in the discrete-time domain is presented. It ensures the stability and performance of the closed-loop system, even for high-order controllers and large digital signal processor processing delay. Moreover, it is confirmed that the proposed controller works satisfactorily even on faulty grid conditions.

Intelligent storage controller

Abstract: An intelligent storage controller operating in conjunction with a computer running an application that uses the data managed by the intelligent storage controller, and requires data transformation operations to be performed on the data. The intelligent storage controller is adapted to directly perform the data transformation operations on the data controlled by the controller, under the direction of the computer running the application, thereby offloading this processing entirely to the intelligent storage controller. The intelligent storage controller may also provide an application programming interface for the computer running the application to use in directing commands to the intelligent storage controller. To accommodate varying workloads on the intelligent storage controller, data transformation tasks may be load balanced between the intelligent storage controller, the computer running the application, and/or other hosts.

Coupling Effect Reduction of a Voltage-Balancing Controller in Single-Phase Cascaded Multilevel Converters

Abstract: This paper presents a new voltage-balancing controller for cascaded multilevel converters, especially for single-phase cascaded multilevel converters. It proposes a control algorithm that devotes itself not only to balancing the floating dc capacitors but also to eliminating the coupling effect between the voltage-balancing controller and the original system controller (controller without additional voltage-balancing controllers). Specifically, the average model in the d-q coordinate frame is derived and the control law is established. Then, the coupling effect between the voltage-balancing controller and the original system controller is identified and a new expression for duty cycle modification is proposed thus to eliminate the effect. Furthermore, this paper gives the design considerations of the pro- posed method, including the derivation of key transfer functions and effective voltage-balancing area, for the completeness of the discussion. Moreover, the reference generation techniques of the voltage-balancing controller are also discussed. This paper investigates the voltage imbalance in the soft-start process caused by an unsuitable reference, and presents a simple modified reference generation solution. Finally, both simulation and experimental results verify the performance of the proposed control system.

Design of PID controllers in double feedback loops for SISO systems with set-point filters

Abstract: A PID controller is widely used to control industrial processes that are mostly open loop stable or unstable. Selection of proper feedback structure and controller tuning helps to improve the performance of the loop. In this paper a double-feedback loop/method is used to achieve stability and better performance of the process. The internal feedback is used for stabilizing the process and the outer loop is used for good setpoint tracking. An internal model controller (IMC) based PID method is used for tuning the outer loop controller. Autotuning based on relay feedback or the Ziegler–Nichols method can be used for tuning an inner loop controller. A tuning parameter ( λ ) that is used to tune IMC-PID is used as a time constant of a setpoint filter that is used for reducing the peak overshoot. The method has been tested successfully on many low order processes.

Design and control of a decoupled two degree of freedom translational parallel micro-positioning stage

Abstract: This paper presents a novel decoupled two degrees of freedom (2-DOF) translational parallel micro-positioning stage. The stage consists of a monolithic compliant mechanism driven by two piezoelectric actuators. The end-effector of the stage is connected to the base by four independent kinematic limbs. Two types of compound flexure module are serially connected to provide 2-DOF for each limb. The compound flexure modules and mirror symmetric distribution of the four limbs significantly reduce the input and output cross couplings and the parasitic motions. Based on the stiffness matrix method, static and dynamic models are constructed and optimal design is performed under certain constraints. The finite element analysis results are then given to validate the design model and a prototype of the XY stage is fabricated for performance tests. Open-loop tests show that maximum static and dynamic cross couplings between the two linear motions are below 0.5% and -45 dB, which are low enough to utilize the single-input-single-out control strategies. Finally, according to the identified dynamic model, an inversion-based feedforward controller in conjunction with a proportional-integral-derivative controller is applied to compensate for the nonlinearities and uncertainties. The experimental results show that good positioning and tracking performances are achieved, which verifies the effectiveness of the proposed mechanism and controller design. The resonant frequencies of the loaded stage at 2 kg and 5 kg are 105 Hz and 68 Hz, respectively. Therefore, the performance of the stage is reasonably good in term of a 200 N load capacity.

Complementary PID Controller to Passivity-Based Nonlinear Control of Boost Converters With Inductor Resistance

Abstract: Since the DC-DC boost converter exhibits highly nonlinear and non-minimum phase properties, it is not an easy task to design a controller that is robust against load perturbations. This paper presents a dynamic output feedback controller for a DC-DC boost converter that has a practical inductor and a series resistance. In order to maintain its robust output voltage regulation, the proposed controller adopts a simplified parallel-damped passivity-based controller (PD-PBC). A complementary proportional-integral-differential (PID) controller to the PD-PBC has been designed for removing the steady state error owing to the parasitic resistance. We present sufficient conditions for the asymptotic stability of the augmented system with an additional dynamic system. Computer simulations and experimental tests under reference step changes and load perturbations confirm the improved performance of the proposed approach.

Design of Automatic Steering Controller for Trajectory Tracking of Unmanned Vehicles Using Genetic Algorithms

Abstract: In this paper, an efficient strategy is proposed to design the automatic steering controller for trajectory tracking of unmanned vehicles, which is robust with respect to the inherent nonlinearities and uncertainties of vehicles. The proposed automatic steering controller consists of a feedback part and a feedforward part. First, a fuzzy controller is proposed as the feedback part, and the parameters of membership functions and rules are optimized by genetic algorithms (GAs) to guarantee high performance. Then, a feedforward controller is designed to assist the controller when the vehicle is engaged in a curved section of trajectory, which utilizes preview information regarding upcoming curvature of reference trajectory to calculate a preview steering angle so that it offsets the disturbance of curvature. Both simulation and experimental results show that the proposed strategy can robustly track the reference trajectories under various conditions with high accuracy.

Adaptive second-order sliding mode controller for a twin rotor multi-input-multi-output system

Abstract: In this study, an adaptive second-order sliding mode (SOSM) controller is proposed to control a laboratory helicopter called the twin-rotor multi-input-multi-output system (TRMS). The design objectives of the controller are to stabilise the TRMS in significant cross couplings, reach a desired position and accurately track a specified trajectory. The TRMS model is divided into a horizontal and a vertical subsystem (VS). The cross coupling existing between the two subsystems is considered as the system uncertainty. A simple adaptive tuning law is developed for the SOSM controller to deal with the bounded system uncertainty. The major advantage offered by this adaptive SOSM controller is that advance knowledge about the upper bound of system uncertainty is not a necessary requirement. The adaptive SOSM controller for the VS uses a proportional plus integral sliding surface to counter the offset present in the pitch angle. System robustness and the stability of the controller are proved by using the Lyapunov criterion. Apart from imparting robustness, the proposed adaptive SOSM controller reduces undesired chattering in the control input and thus is suitable for application in practical motion control applications. The proposed control scheme is validated by simulation results and is compared against the existing proportional-integral-derivative controllers to show that the overall performance of the proposed adaptive SOSM controller is better in the aspects of error and control indices.

Walking control of fully actuated robots based on the Bipedal SLIP model

Abstract: The goal of this paper is to generate and stabilize a periodic walking motion for a five degrees of freedom planar robot. First of all we will consider a biped version of the spring loaded inverted pendulum (SLIP), which shows openloop stable behavior. Then we will control the robot behavior as close as possible to the simple model. In this way we take advantage of the open-loop stability of the walking pattern related to the SLIP, and additional control actions are used to increase the robustness of the system and reject external disturbances. To this end an upper level controller will deal with the stabilization of the SLIP model, while a lower level controller will map the simple virtual model onto the real robot dynamics. Two different approaches are implemented for the lower level: in the first one, we aim at exactly reproducing the same acceleration that a SLIP would have when put in the same condition, while in the second one, we aim at a simpler control law without exactly reproducing the aforementioned acceleration. The latter case is equivalent to considering a SLIP with additional external disturbances, which have to be handled by the upper level controller. Both approaches can successfully reproduce a periodic walking pattern for the robot.

Virtual machine based controller and upgrade mechanism

Abstract: High availability for a network may be achieved, for example, during a hitless upgrade by creating a replica controller virtual machine of an operating controller virtual machine (source controller). The replica controller virtual machine may be on a same or different server as the source controller virtual machine. The replica controller virtual machine may be copied with processes present in the source controller virtual machine and synchronized for runtime state. Upgrades or changes to software applications run in the source controller virtual machine may be provided to the replica controller virtual machine. Once enabled, the replica controller virtual machine may be operated without suspension of the source controller virtual machine.

Controller for a power converter and method of operating the same

Abstract: A controller for a power converter and method of operating the same. In one embodiment, the controller includes an inductor-inductor-capacitor (“LLC”) controller configured to receive an error signal from an error amplifier to control a switching frequency of an LLC stage of the power converter to regulate an output voltage thereof. The controller also includes a power factor correction (“PFC”) controller configured to control a bus voltage produced by a PFC stage of the power converter and provided to the LLC stage so that an average switching frequency thereof is substantially maintained at a desired switching frequency.

Design of Fuzzy PID controller for Brushless DC motor

Abstract: Brushless DC (BLDC) motors are widely used for many industrial applications because of their high efficiency, high torque and low volume. This paper proposed a improved Fuzzy PID controller to control speed of Brushless DC motor. The proposed controller is called proportional-integral-derivative (PID) controller and Fuzzy proportional-integral-derivative controller. This paper provides an overview of performance conventional PID controller and Fuzzy PID controller. It is difficult to tune the parameters and get satisfied control characteristics by using normal conventional PID controller. As the Fuzzy has the ability to satisfied control characteristics and it is easy for computing, In order to control the BLDC motor, a Fuzzy PID controller is designed as the controller of the BLDC motor. The experimental results verify that a Fuzzy PID controller has better control performance than the conventional PID controller. The modeling, control and simulation of the BLDC motor have been done using the software package MATLAB/SIMULINK.

A Neuro-Inspired Spike-Based PID Motor Controller for Multi-Motor Robots with Low Cost FPGAs

Abstract: In this paper we present a neuro-inspired spike-based close-loop controller written in VHDL and implemented for FPGAs. This controller has been focused on controlling a DC motor speed, but only using spikes for information representation, processing and DC motor driving. It could be applied to other motors with proper driver adaptation. This controller architecture represents one of the latest layers in a Spiking Neural Network (SNN), which implements a bridge between robotics actuators and spike-based processing layers and sensors. The presented control system fuses actuation and sensors information as spikes streams, processing these spikes in hard real-time, implementing a massively parallel information processing system, through specialized spike-based circuits. This spike-based close-loop controller has been implemented into an AER platform, designed in our labs, that allows direct control of DC motors: the AER-Robot. Experimental results evidence the viability of the implementation of spike-based controllers, and hardware synthesis denotes low hardware requirements that allow replicating this controller in a high number of parallel controllers working together to allow a real-time robot control.

Design Robust Backstepping on-line Tuning Feedback Linearization Control Applied to IC Engine

Abstract: Design a nonlinear controller for second order nonlinear uncertain dynamical systems (e.g., Internal Combustion Engine) is one of the most important challenging works. This paper focuses on the design of a robust backstepping adaptive feedback linearization controller (FLC) for internal combustion (IC) engine in presence of uncertainties. In order to provide high performance nonlinear methodology, feedback linearization controller is selected. Pure feedback linearization controller can be used to control of partly unknown nonlinear dynamic parameters of IC engine. In order to solve the uncertain nonlinear dynamic parameters, implement easily and avoid mathematical model base controller, Mamdani’s performance/error-based fuzzy logic methodology with two inputs and one output and 49 rules is applied to pure feedback linearization controller. The results demonstrate that the error-based fuzzy feedback linearization controller is a model-free controllers which works well in certain and partly uncertain system. Pure feedback linearization controller and error-based feedback linearization like controller with have difficulty in handling unstructured model uncertainties. To solve this problem applied backstepping-based tuning method to error-based fuzzy feedback linearization controller for adjusting the feedback linearization controller gain ( ). This controller has acceptable performance in presence of uncertainty (e.g., overshoot=1%, rise time=0.48 second, steady state error = 1.3e-9 and RMS error=1.8e-11).

Simulink Modeling and Design of an Efficient Hardware-Constrained FPGA-Based PMSM Speed Controller

Abstract: The aim of this paper is to present a holistic approach to modeling and field programmable gate array (FPGA) implementation of a permanent magnet synchronous motor (PMSM) speed controller. The whole system is modeled in the Matlab Simulink environment. The controller is then translated to discrete time and remodeled using System Generator blocks, directly synthesizable into FPGA hardware. The algorithm is further refined and factorized to take into account hardware constraints, so as to fit into a low-cost FPGA, without significantly increasing the execution time. The resulting controller is then integrated together with sensor interfaces and analysis tools and implemented into an FPGA device. Experimental results validate the controller and verify the design.

Methodology of Mathematical Error-Based Tuning Sliding Mode Controller

Abstract: Design a nonlinear controller for second order nonlinear uncertain dynamical systems is one of the most important challenging works. This paper focuses on the design of a chattering free mathematical error-based tuning sliding mode controller (MTSMC) for highly nonlinear dynamic robot manipulator, in presence of uncertainties. In order to provide high performance nonlinear methodology, sliding mode controller is selected. Pure sliding mode controller can be used to control of partly known nonlinear dynamic parameters of robot manipulator. Conversely, pure sliding mode controller is used in many applications; it has an important drawback namely; chattering phenomenon which it can causes some problems such as saturation and heat the mechanical parts of robot manipulators or drivers. In order to reduce the chattering this research is used the switching function in presence of mathematical error-based method instead of switching function method in pure sliding mode controller. The results demonstrate that the sliding mode controller with switching function is a model-based controllers which works well in certain and partly uncertain system. Pure sliding mode controller has difficulty in handling unstructured model uncertainties. To solve this problem applied mathematical model-free tuning method to sliding mode controller for adjusting the sliding surface gain ( λ ). Since the sliding surface gain ( λ) is adjusted by mathematical model free-based tuning method, it is nonlinear and continuous. In this research new λ is obtained by the previous λ multiple sliding surface slopes updating factor �α�. Chattering free mathematical error-based tuning sliding mode controller is stable controller which eliminates the chattering phenomenon without to use the boundary layer saturation function. Lyapunov stability is proved in mathematical error-based tuning sliding mode controller with switching (sign) function. This

Type-2 fuzzy model based controller design for neutralization processes.

Abstract: In this study, an inverse controller based on a type-2 fuzzy model control design strategy is introduced and this main controller is embedded within an internal model control structure. Then, the overall proposed control structure is implemented in a pH neutralization experimental setup. The inverse fuzzy control signal generation is handled as an optimization problem and solved at each sampling time in an online manner. Although, inverse fuzzy model controllers may produce perfect control in perfect model match case and/or non-existence of disturbances, this open loop control would not be sufficient in the case of modeling mismatches or disturbances. Therefore, an internal model control structure is proposed to compensate these errors in order to overcome this deficiency where the basic controller is an inverse type-2 fuzzy model. This feature improves the closed-loop performance to disturbance rejection as shown through the real-time control of the pH neutralization process. Experimental results demonstrate the superiority of the inverse type-2 fuzzy model controller structure compared to the inverse type-1 fuzzy model controller and conventional control structures.

Design and performance comparison of variable parameter nonlinear PID controller and genetic algorithm based PID controller

Abstract: In this study, design and performance comparison of variable parameter nonlinear PID (NL-PID) and Genetic Algorithm (GA) based PID controller are achieved. To begin with the proposed method, an error function depending on the system input and output are defined to determine variable coefficients of the nonlinear PID controller. A new type non linear PID controller is designed by using defined error function. By this way, the nonlinear PID controller changes its own parameters over time according to the output response. Secondly, genetic algorithm based PID controller are defined to performance comparison of the proposed NL-PID controller and Ziegler-Nichols PID controller. Simulation results show that the effects of the PID controllers; nonlinear, GA based and Ziegler-Nichols.

Development of a Self-Tuning TSK-Fuzzy Speed Control Strategy for Switched Reluctance Motor

Abstract: This paper presents a novel adaptive Takagi-Sugeno-Kang (TSK)-fuzzy controller (ATSKFC) to regulate the speed of a switched reluctance motor (SRM). The proposed controller comprises two parts: a TSK-fuzzy controller and a compensated controller. The TSK-fuzzy controller is the main controller, which is used to approximate an ideal control law. The compensated controller is designed to compensate the approximation error between the TSK-fuzzy controller and the ideal control law. The parameter variations and the external load of the SRM drive are considered to ensure the robustness of the proposed scheme. An on-line tuning methodology based on Lyapunov is utilized to adjust the parameters of the ATSKFC, so that the stability of the control system can be guaranteed. Three control schemes, ATSKFC, fuzzy control, and PI speed control, are experimentally investigated and the performance index, root-mean-square error, is used to evaluate each scheme. The results reveal that the ATSKFC outperforms other comparison schemes. In addition, the robustness of the proposed scheme to the parameter variations and external load torque disturbance has been verified via simulation and experiments.

Digital Charge Balance Controller to Improve the Loading/Unloading Transient Response of Buck Converters

Abstract: A linear/nonlinear digital controller is presented that allows a Buck converter to recover from a load transient event with near-optimal voltage deviation and recovery time. A novel digital double accumulator calculation block is used to calculate the appropriate pulse width modulation switching time instants. The proposed controller possesses many advantages not demonstrated by a single controller in the previous literature. For example, unlike many previously proposed time-optimal digital controllers, the proposed controller provides an excellent transient response as it is capable of reacting asynchronously to a load transient event. In addition, it is demonstrated that the proposed controller can operate without requiring information pertaining to the Buck converter's output inductor. Furthermore, the proposed controller can be extended to applications that require load-line regulation. Lastly, unlike all previous digital time-optimal controllers, the proposed controller does not require digital multiplier or divider blocks nor does it require 2-D lookup tables. Thus, the controller can be implemented through the use of low-cost field programmable gate arrays or complex programmable logic devices.

Inverse neuro-fuzzy MR damper model and its application in vibration control of vehicle suspension system

Abstract: In this paper, a magneto-rheological (MR) damper-based semi-active controller for vehicle suspension is developed. This system consists of a linear quadratic Gauss (LQG) controller as the system controller and an adaptive neuro-fuzzy inference system (ANFIS) inverse model as the damper controller. First, a modified Bouc-Wen model is proposed to characterise the forward dynamic characteristics of the MR damper based on the experimental data. Then, an inverse MR damper model is built using ANFIS technique to determine the input current so as to gain the desired damping force. Finally, a quarter-car suspension model together with the MR damper is set up, and a semi-active controller composed of the LQG controller and the ANFIS inverse model is designed. Simulation results demonstrate that the desired force can be accurately tracked using the ANFIS technique and the semi-active controller can achieve competitive performance as that of active suspension.