Showing papers on "Proportional control published in 2016"

High-Density Electromyography and Motor Skill Learning for Robust Long-Term Control of a 7-DoF Robot Arm

Abstract: Myoelectric control offers a direct interface between human intent and various robotic applications through recorded muscle activity. Traditional control schemes realize this interface through direct mapping or pattern recognition techniques. The former approach provides reliable control at the expense of functionality, while the latter increases functionality at the expense of long-term reliability. An alternative approach, using concepts of motor learning, provides session-independent simultaneous control, but previously relied on consistent electrode placement over biomechanically independent muscles. This paper extends the functionality and practicality of the motor learning-based approach, using high-density electrode grids and muscle synergy-inspired decomposition to generate control inputs with reduced constraints on electrode placement. The method is demonstrated via real-time simultaneous and proportional control of a 4-DoF myoelectric interface over multiple days. Subjects showed learning trends consistent with typical motor skill learning without requiring any retraining or recalibration between sessions. Moreover, they adjusted to physical constraints of a robot arm after learning the control in a constraint-free virtual interface, demonstrating robust control as they performed precision tasks. The results demonstrate the efficacy of the proposed man–machine interface as a viable alternative to conventional control schemes for myoelectric interfaces designed for long-term use.

Modeling, Modulation, and Control of the Three-Phase Four-Switch PWM Rectifier Under Balanced Voltage

Abstract: The modeling, modulation, and control of the three-phase four-switch (TPFS) PWM rectifier are investigated in this paper. Three space vector pulse width modulation methods using different equivalent zero vectors are developed, where sector identification and the trigonometric function are not required. Then, the high-frequency model for the current ripple analysis is proposed, and the effects of three SVM approaches on the ac current ripple are investigated. According to the analytical results, the method introducing the smallest current ripple is selected. With the optimized SVM approach, a control-oriented model, considering the capacitor voltage oscillation and deviation, is built in the dq synchronous frame to facilitate the controller design. Furthermore, a control strategy implementing the proportional controller is developed to eliminate the capacitor voltage deviation. Meanwhile, the dual-loop control of the TPFS is not affected by the proposed strategy as the capacitor voltage deviation is eliminated. Finally, a novel linear modulation index function is defined to reject the low-frequency harmonic current introduced by the overmodulation. Experimental results demonstrate that excellent current performance is achieved with comprehensive considerations of the modeling, modulation, and control strategy.

Active control of vortex-induced vibrations of a circular cylinder using windward-suction- leeward-blowing actuation

Abstract: This paper studies the control of two-dimensional vortex-induced vibrations (VIVs) of a single circular cylinder at a Reynolds number of 100 using a novel windward-suction-leeward-blowing (WSLB) concept. A lattice Boltzmann method based numerical framework is adopted for this study. Both open-loop and closed-loop controls are implemented. In the open-loop control, three types of actuation arrangements, including the pure suction on the windward side of the cylinder, the pure blowing on the leeward side, and the general WSLB on both sides, are implemented and compared. It is found that the general WSLB is the most effective, whereas the pure suction is the least effective. In the closed-loop control, the proportional (P), integral (I), and proportional-integral (PI) control schemes are applied to adjust the WSLB velocities according to the flow information obtained from a sensor. The effects of four key control parameters including the proportional gain constant, the integral gain constant, the length of data history used for the feedback, and the location of the sensor are investigated. It is found that the use of only P control fails to completely suppress the VIV, the use of only I control can achieve the complete suppression, and the PI control performs the best in terms of both the control effectiveness and efficiency. In the PI control, there exists an optimal length of data history for the feedback, at which the VIV control is the most efficient. There also exist the minimum required WSLB velocities for the VIV suppression, independent of the control schemes. Moreover, it is found that the VIV control is independent of the sensor location.

Closed-loop step response for tuning PID-fractional-order-filter controllers.

Abstract: Analytical methods are usually applied for tuning fractional controllers. The present paper proposes an empirical method for tuning a new type of fractional controller known as PID-Fractional-Order-Filter (FOF-PID). Indeed, the setpoint overshoot method, initially introduced by Shamsuzzoha and Skogestad, has been adapted for tuning FOF-PID controller. Based on simulations for a range of first order with time delay processes, correlations have been derived to obtain PID-FOF controller parameters similar to those obtained by the Internal Model Control (IMC) tuning rule. The setpoint overshoot method requires only one closed-loop step response experiment using a proportional controller (P-controller). To highlight the potential of this method, simulation results have been compared with those obtained with the IMC method as well as other pertinent techniques. Various case studies have also been considered. The comparison has revealed that the proposed tuning method performs as good as the IMC. Moreover, it might offer a number of advantages over the IMC tuning rule. For instance, the parameters of the fractional controller are directly obtained from the setpoint closed-loop response data without the need of any model of the plant to be controlled.

Multichannel electrotactile feedback for simultaneous and proportional myoelectric control

Abstract: Objective. Closing the loop in myoelectric prostheses by providing artificial somatosensory feedback to the user is an important need for prosthetic users. Previous studies investigated feedback strategies in combination with the control of one degree of freedom of simple grippers. Modern hands, however, are sophisticated multifunction systems. In this study, we assessed multichannel electrotactile feedback integrated with an advanced method for the simultaneous and proportional control of individual fingers of a dexterous hand. Approach. The feedback used spatial and frequency coding to provide information on the finger positions (normalized flexion angles). A comprehensive set of conditions have been investigated in 28 able-bodied subjects, including feedback modalities (visual, electrotactile and no feedback), control tasks (fingers and grasps), systems (virtual and real hand), control methods (ideal and realistic) and range of motion (low and high). The task for the subjects was to operate the hand using closed-loop myoelectric control and generate the desired movement (e.g., selected finger or grasp at a specific level of closure). Main results. The subjects could perceive the multichannel and multivariable electrotactile feedback and effectively exploit it to improve the control performance with respect to open-loop grasping. The improvement however depended on the reliability of the feedforward control, with less consistent control exhibiting performance trends that were more complex across the conditions. Significance. The results are promising for the potential application of advanced feedback to close the control loop in sophisticated prosthetic systems.

Bayesian Filtering of Surface EMG for Accurate Simultaneous and Proportional Prosthetic Control

Abstract: The amplitude of the surface EMG (sEMG) is commonly estimated by rectification or other nonlinear transformations, followed by smoothing (low-pass linear filtering). Although computationally efficient, this approach leads to an estimation accuracy with a limited theoretical signal-to-noise ratio (SNR). Since sEMG amplitude is one of the most relevant features for myoelectric control, its estimate has become one of the limiting factors for the performance of myoelectric control applications, such as powered prostheses. In this study, we present a recursive nonlinear estimator of sEMG amplitude based on Bayesian filtering. Furthermore, we validate the advantage of the proposed Bayesian filter over the conventional linear filters through an online simultaneous and proportional control (SPC) task, performed by eight able-bodied subjects and three below-elbow limb deficient subjects. The results demonstrated that the proposed Bayesian filter provides significantly more accurate SPC, particularly for the patients, when compared with conventional linear filters. This result presents a major step toward accurate prosthetic control for advanced multi-function prostheses.

Control Strategy of Flyback Microinverter With Hybrid Mode for PV AC Modules

Abstract: This paper presents a control strategy of a flyback microinverter with hybrid operation mode for photovoltaic ac modules. The proposed control strategy consists of two components: the proportional-resonant (PR) controller with the harmonic compensator (HC) and the hybrid nominal duty ratio. Compared to the conventional control strategy using the proportional-integral controller, the PR controller with HC provides a higher system gain at the fundamental and harmonic frequencies of the grid without using a high proportional gain in both operation modes. Then, it enhances the tracking speed and disturbance rejection performances satisfying the desired stability. Moreover, by applying the hybrid nominal duty ratio yielded from the proposed operation mode selection, the disturbance rejection is achieved more effectively, and the control burden is reduced. Finally, the simulation and experimental results were shown to verify the tracking speed and disturbance rejection performances of the proposed control strategy.

Design of PI Controller in Pitch Control of Wind Turbine: A Comparison of PSO and PS Algorithm

Abstract: In wind energy conversion system (WECS) at wind speed above rated, the pitch angle is controlled to keep the generated output fixed so also the speed and the frequency. The model is built as a discrete model of WECS connected to Grid including a Line to Ground (LG) fault in Grid. A Proportional-Integral (PI) controller with gain K p and K i is used in pitch angle control loop. The proportional gain K p and integral gain K i are tuned through Particle Swarm Optimization (PSO) and Pattern Search (PS) algorithms. A comparison of two different objective functions with its weight adjustment is presented. The performances of the algorithms in designing the optimal controller are compared. The analysis indicates the superiority of PSO over PS and takes less time to achieve the minimum error criteria. The controller designed using PSO minimizing the proposed objective function has better settling time as regards wind turbine speed response, compared to the other. The control action is validated in real time using OPAL-RT taking different cases of random wind speed, gust and gust with random wind speed and Line to Ground fault.

Flatness-based control for a quadrotor camera helicopter using model predictive control trajectory generation

Abstract: This paper addresses a flatness-based controller and a Model Predictive Control (MPC) trajectory generation for a quadrotor camera helicopter. Applications like aerial videography can highly benefit from an automation of the pilot's tasks, enabling the camera operator to solely focus on camera motion control. The coupled nonlinear system dynamics of a quadrotor pose difficulties precisely controlling several channels simultaneously for agile maneuvering using conventional controllers. A flatness-based approach is employed to obtain linear input-output dynamics, even for large attitude angles. The associated state feedback equations are explicitly derived. The resulting linear system dynamics are controlled using a cascaded proportional control structure. Feasible reference trajectories are generated using a linear MPC, which translates operator commands for camera motions — e.g. relative to a point-of-interest — into quadrotor trajectories complying with operational constraints. Flatness-based controller and MPC trajectory generation show tracking errors below 1% in simulation tests. Accurate and smooth positioning is achieved in first indoor test flights. The gained results motivate adoptions of the proposed control approach to other UAV applications with similar demands for pilot automation and accuracy.

Design approach of discrete-time resonant controllers for uninterruptible power supply applications through frequency response analysis

Abstract: A new methodology to design discrete-time multiple resonant controllers for single-phase uninterruptible power supply inverters is proposed in this study. This methodology is based on classical linear tools and consists on the synthesis of the inverter output impedance according to standard specifications. This synthesis is performed using a multi-loop control strategy composed of an inner current control loop using a proportional controller, and an outer voltage control loop using the multiple resonant controller. A prototype was built to demonstrate the practical feasibility of the theoretical proposal. A significant reduction of the output impedance at determined harmonic frequencies resulted in a low-voltage total harmonic distortion of the output voltage of about 1.76%, for IEC 62040-3 reference non-linear load.

Sliding-Mode-Based Missile-Integrated Attitude Control Schemes Considering Velocity Change

Abstract: A sliding-mode-based control scheme is proposed for integrated roll–pitch–yaw attitude control of a fin-controlled skid-to-turn missile during the boost phase. The missile aerodynamics accompany nonlinear, partially unstable, and cross-coupling effects among input channels so that integrated control is required. A mathematical model of the attitude dynamics and aerodynamics is constructed regarding the inertial property variations. Two possible architectures (the single-loop control scheme employing the higher-order sliding mode controller and the separated control scheme based on the traditional sliding mode controller) are proposed. For the integrated attitude control of the missile, multiple sliding surfaces are chosen for simultaneous tracking of the attitude commands. To demonstrate the performance of the proposed control scheme, numerical simulations are performed using a nonlinear six degrees-of-freedom missile model in the presence of uncertainties.

A robust current control based on proportional-integral observers for permanent magnet synchronous machines

Abstract: This paper deals with a novel robust current control scheme for Permanent Magnet Synchronous Machine based on the conventional cascade structure. The main idea is to substitute the commonly used decoupling network, which requires the precise knowledge of the system parameters in any working condition, with a more flexible and robust scheme. In particular, the traditional configuration is improved by mean of two proportional-integral observers which allow the preservation of the drive performances under the effects of disturbance. The improved robustness is achieved maintaining the reliable basic scheme with a pure proportional controller in the forward path with advantages in terms of design and tuning. A genetic algorithm is used to optimize the controller and the observer parameters. This multi-objective optimization leads to a good stability and an overall improved performance of the drive above all the operative range. The choice of the optimal solution is based on a novel fitness function which takes into account both dynamical features and disturbance rejection capabilities of the system. The effectiveness of the proposed control scheme is verified by mean of numerical simulations and experiments as well.

Dynamic Approximation with Feedback Control for Energy-Efficient Recurrent Neural Network Hardware

Abstract: This paper presents methodology of feedback-controlled dynamic approximation to enable energy-accuracy trade-off in digital recurrent neural network (RNN). A low-power digital RNN engine is presented that employs the proposed dynamic approximation. The on-chip feedback controller is realized by utilizing hysteretic or proportional controller. The dynamic adaptation of bit-precisions during the RNN computation is selected as approximation approach. Considering various applications, the digital RNN engine designed in 28nm CMOS shows ~36% average energy saving compared to the baseline case, with only ~4% of accuracy degradation on average.

Myoelectric Control System and Task-Specific Characteristics Affect Voluntary Use of Simultaneous Control

Abstract: Clinically available myoelectric control does not enable simultaneous proportional control of prosthetic degrees of freedom. Multiple studies have proposed systems that provide simultaneous control, though few have investigated whether subjects voluntarily use simultaneous control or how they implement it. Additionally, few studies have explicitly evaluated the effect of providing proportional velocity control. The objective of this study was to evaluate factors influencing when and how subjects use simultaneous myoelectric control, including the ability to proportionally control the velocity and the required task precision. Five able-bodied subjects used simultaneous myoelectric control systems with and without proportional velocity control in a virtual Fitts' Law task. Though subjects used simultaneous control to a substantial degree when proportional velocity control was present, they used very little simultaneous control when using constant-velocity control. Furthermore, use of simultaneous control varied significantly with target distance and width, reflecting a strategy of using simultaneous control for gross cursor positioning and sequential control for fine corrective movements. These results provide insight into how users take advantage of simultaneous control and highlight the need for real-time evaluation of simultaneous control algorithms, as the potential benefit of providing simultaneous control may be affected by other characteristics of the myoelectric control system.

DC-Link Voltage Coordinated-Proportional Control for Cascaded Converter With Zero Steady-State Error and Reduced System Type

Abstract: Cascaded converter is formed by connecting two subconverters together, sharing a common intermediate dc-link voltage. Regulation of this dc-link voltage is frequently realized with a proportional-integral (PI) controller, whose high gain at dc helps to force a zero steady-state tracking error. Such precise tracking is, however, at the expense of increasing the system type, caused by the extra pole at the origin introduced by the PI controller. The overall system may, hence, be tougher to control. To reduce the system type while preserving precise dc-link voltage tracking, this paper proposes a coordinated control scheme for the cascaded converter, which uses only a proportional dc-link voltage regulator. The resulting converter is thus dynamically faster, and when compared with the conventional PI-controlled converter, it is less affected by impedance interaction between its two subconverters. The proposed scheme can be used with either unidirectional or bidirectional power flow, and has been verified by simulation and experimental results presented in this paper.

Augmented −1 adaptive control of an actuated knee joint exoskeleton: From design to real-time experiments

Abstract: This paper deals with the control of a lower limb exoskeleton acting at the knee joint level. Classical −1 adaptive control law is proposed to ensure assistance-as-needed and resistive rehabilitation following a desired trajectory that is defined by a therapeutic doctor. This control law introduces a time lag within the desired trajectory tracking due to the presence of a filter in its structure. In order to mitigate this drawback, the classical −1 adaptive control is augmented by a nonlinear proportional control. The classical and augmented −1 adaptive control laws are tested in real-time using the Exoskeleton Intelligently COmmunicating and Sensitive to Intention (EICOSI) of LISSI-lab. Real-time experimental results highlight the utility of these control laws in assistance-as-needed and resistive rehabilitation paradigms.

Improved indirect field-oriented control of induction motor drive based pso algorithm

Abstract: Optimization techniques are increasingly used in research to improve the control of three-phase induction motor (TIM). Indirect field-oriented control (IFOC) scheme is employed to improve the efficiency and enhance the performance of variable speed control of TIM drives. The space vector pulse width modulation (SVPWM) technique is used for switching signals in a three-phase bridge inverter to minimize harmonics in the output signals of the inverter. In this paper, a novel scheme based on particle swarm optimization (PSO) algorithm is proposed to improve the variable speed control of IFOC in TIM. The PSO algorithm is used to search the best values of parameters of proportional-integral (PI) controller (proportional gain (kp) and integral gain (ki)) for each speed controller and voltage controller to improve the speed response for TIM. An optimal PI controller-based objective function is also used to tune and minimize the mean square error (MSE). Results of all tests verified the robustness of the PSO-PI controller for speed response in terms of damping capability, fast settling time, steady state error, and transient responses under different conditions of mechanical load and speed.

Servomechanism for periodic reference input: Discrete wavelet transform-based repetitive controller

Abstract: The presented work explored the possibility of developing a discrete wavelet transform-based repetitive control (DWTRC) strategy along with a proportional controller for a liquid level system (LLS)...

Model Predictive Control of Polymer Electrolyte Membrane fuel cell with dead-end anode and periodic purging

Abstract: This paper proposes a model predictive control structure to attain performance requirements and to meet with actuator constraints. The goal is to maintain the differential pressure between the anode and cathode sides of a polymer electrolyte membrane fuel cell (PEMFC), at the inlet side of the stack, known as fuel overpressure, in a desired region. The effects of dynamic purging, nitrogen crossover, and load are included as disturbances. A proportional control valve is used as an actuator. Applying the pneumatic modeling technique, the behavior of a Ballard 3kW test station in a dead-end anode configuration is replicated and experimentally validated. To achieve a linear model, a nonlinear transformation is used to decompose the valve dynamic behavior. To evaluate the controller performance, numerical simulation is conducted using data from the experimental model. The results show the ability of the controller to compensate for all disturbances.

A dead-band model and its online detection for the pilot stage of a two-stage directional flow control valve

Abstract: The dead-band in the electro-hydraulic proportional control valve is one of the main factors that affect its dynamic performance. Especially in the pilot stages of two-stage directional flow control valves, the insistent dead-band will result in a conservative valve controller design. In this paper, a detailed dead-band model describing the relationship between pilot valve spool and the flow rate of the pilot control valve is proposed. And an improved dead-band description involved with the housing clearance of the valve spool is developed to prove the dead-band uncertainty for a single valve system. Then a simple and effective method is proposed to detect the varying dead-band values in the pilot stage. This method is specially designed with a limited main spool displacement and short time interval so that it can be used for online detection without affecting the hydraulic system where the two-stage valve is involved. With the regular dead-band inverse function, comparative experimental results show that...

Tunning PID controller using particle swarm optimization algorithm on automatic voltage regulator system

Abstract: PID Controller (Proportional Integral Derivative) was invented since 1910, but till today still is used in industries, even though there are many kind of modern controllers like fuzz controller and neural network controller are being developed. Performance of PID controller is depend on on Proportional Gain (Kp), Integral Gain (Ki) and Derivative Gain (Kd). These gains can be got by using method Ziegler-Nichols (ZN), gain-phase margin, Root Locus, Minimum Variance dan Gain Scheduling however these methods are not optimal to control systems that nonlinear and have high-orde, in addition, some methods relative hard. To solve those obstacles, particle swarm optimization (PSO) algorithm is proposed to get optimal Kp, Ki and Kd. PSO is proposed because PSO has convergent result and not require many iterations. On this research, PID controller is applied on AVR (Automatic Voltage Regulator). Based on result of analyzing transient, stability Root Locus and frequency response, performance of PID controller is better than Ziegler-Nichols.

A hybrid NDI control method for the high-alpha super-maneuver flight control

Abstract: This paper proposes a hybrid Nonlinear Dynamic Inversion (NDI) control method for the high angle of attack super-maneuverable flight control. In the post-stall flight regime, the problems of nonlinearity, time varying, coupling and uncertainties would arise, which is a big challenge for the flight control method. A hybrid NDI control method based on the angular acceleration feedback control is proposed to increase system robustness and performance. It is inspired by the idea of the NDI and the Increment NDI (INDI) control methods, and contains three parts: feedforward control, proportional control, and logical integral control. The hybrid NDI control method can not only increase system robustness, but also improve the system dynamic performance. To demonstrate the effectiveness of the method in the post-stall flight control, numerical simulations are conducted to evaluate its ability to handle system uncertainties, time-varying problems, and nonlinear factors. Simulation results show that the system responses are almost not affected by these complex, troublesome factors and have good performance and robustness.