Showing papers on "Proportional control published in 2009"

Optimized Design of Stationary Frame Three Phase AC Current Regulators

Abstract: Current regulation plays an important role in modern power electronic AC conversion systems The most direct strategy to regulate such currents is to use a simple closed loop proportional-integral (PI) regulator, which has no theoretical stability limits as the proportional and integral gains are increased, since it is only a second order system However, pulsewidth modulation (PWM) transport and controller sampling delays limit the gain values that can be achieved in practical systems Taking these limitations into account, this paper presents an analytical method to determine the best possible gains that can be achieved for any class of practical linear AC current controller The analysis shows that the maximum possible proportional gain is determined by the plant series inductance, the DC bus voltage and the transport and sampling delays, while the maximum possible integral gain is determined primarily by the transport and sampling delays The work is applicable to stationary frame PI regulators, stationary frame controllers with back electromotive force compensation, stationary frame P+ resonant (PR) controllers, and synchronous d- q frame controllers, since they all have identical proportional and integral gains that must be optimized for any particular application

Extracting Simultaneous and Proportional Neural Control Information for Multiple-DOF Prostheses From the Surface Electromyographic Signal

Abstract: A novel signal processing algorithm for the surface electromyogram (EMG) is proposed to extract simultaneous and proportional control information for multiple DOFs. The algorithm is based on a generative model for the surface EMG. The model assumes that synergistic muscles share spinal neural drives, which correspond to the intended activations of different DOFs of natural movements and are embedded within the surface EMG. A DOF-wise nonnegative matrix factorization (NMF) is developed to estimate neural control information from the multichannel surface EMG. It is shown, both by simulation and experimental studies, that the proposed algorithm is able to extract the multidimensional control information simultaneously. A direct application of the proposed method would be providing simultaneous and proportional control of multifunction myoelectric prostheses.

Improved Control of DFIG Systems During Network Unbalance Using PI–R Current Regulators

Abstract: This paper presents a new control strategy for a doubly fed induction generator (DFIG) under unbalanced network voltage conditions. Coordinated control of the grid- and rotor-side converters (GSC and RSC, respectively) during voltage unbalance is proposed. Under an unbalanced supply voltage, the RSC is controlled to eliminate the torque pulsation at double supply frequency. The oscillation of the stator output active power is then compensated by the active power output from the GSC, to ensure constant active power output from the overall DFIG generation system. In order to provide precise control of the positive- and negative-sequence currents of the GSC and RSC, a current control scheme consisting of a proportional integral (PI) controller and a resonant (R) compensator is presented. The PI plus R current regulator is implemented in the positive synchronous reference frame without the need to decompose the positive- and negative-sequence components. Simulations on a 1.5-MW DFIG system and experimental tests on a 1.5-kW prototype validate the proposed strategy. Precise control of both positive- and negative-sequence currents and simultaneous elimination of torque and total active power oscillations have been achieved.

Delay-dependent stability for load frequency control with constant and time-varying delays

Abstract: Load frequency control (LFC) requires transmission of remote measurements to the control center and of control signals from the control center to the plant. Constant delays exist in the dedicated communication channel and an open communication network introduces time-varying delays. Those delays would degrade the dynamic performance of LFC and even cause instability. This paper investigates the delay-dependent stability of the LFC scheme by adopting a delay-dependent criterion and linear matrix inequalities (LMIs). The maximal delay time which allows a power system with a LFC scheme embedded to retain stable is defined as the delay margin for stability analysis. A proportional-integral (PI) controller using the area control error (ACE) as input signal is employed in the LFC scheme. Special attention is paid to the relationship between the gains of PI controller and the delay margin. Case studies are carried out based on one-area and two-area LFC schemes to demonstrate the effectiveness of the criterion. Both constant and time-varying delays are considered. Moreover, the accuracy of the criterion used is also verified by simulation studies.

PM Synchronous Motor Speed Control Using Hybrid Fuzzy-PI With Novel Switching Functions

Abstract: Vector control is one of the standard techniques used for the control of a permanent magnet synchronous motor (PMSM). The outer speed loop in vector controlled PMSM drive greatly affects the drive performance. In order to combine the advantages of proportional plus integral (PI) and fuzzy controllers, hybrid fuzzy-PI controllers are used in which the output can either be the outputs of the two, i.e. the PI or fuzzy units being switched as per the predetermined speed errors or be a combination of the two outputs with separate weights assigned to them with online calculations for the weights from the speed errors. The former method based on switching often causes chattering effects, and later method demands larger execution time because of inclusion of separate switching algorithms. This paper reports the vector control of PMSM with hybrid fuzzy-PI speed controller with switching functions calculated based on the weights for both the controller outputs using the output of (a) only the fuzzy controller, (b) only the PI controller and (c) a combination of the outputs of both the controllers. These switching functions are very simple and effective and do not demand any extra computations to arrive at the hybrid fuzzy-PI controller outputs. These control algorithms have been simulated and also implemented on hardware with TMS320F2812 digital signal processor, and it is observed that the performance of the vector controlled PMSM drive with these hybrid fuzzy-PI speed controllers in terms of the response and torque ripples is very promising.

Design of a Data-Driven PID Controller

Abstract: Since most processes have nonlinearities, controller design schemes to deal with such systems are required. On the other hand, proportional-integral-derivative (PID) controllers have been widely used for process systems. Therefore, in this paper, a new design scheme of PID controllers based on a data-driven (DD) technique is proposed for nonlinear systems. According to the DD technique, a suitable set of PID parameters is automatically generated based on input/output data pairs of the controlled object stored in the database. This scheme can adjust the PID parameters in an online manner even if the system has nonlinear properties and/or time-variant system parameters. Finally, the effectiveness of the newly proposed control scheme is evaluated on some simulation examples, and a pilot-scale temperature control system.

Design and control of Proportional-Resonant controller based Photovoltaic power conditioning system

Abstract: This paper presents a current control technique for a single-phase grid-connected DC/AC inverter which is used in Photovoltaic power conditioning system (PV PCS). A Proportional - Resonant (PR) controller is used for replacing the conventional Proportional - Integral (PI) controller in this system. By comparison with the conventional PI control method, the PR control can introduce an infinite gain at the fundamental frequency and hence can achieve zero steady-state error. A theoretical analysis of the PR controller is presented and verified by experiment. Furthermore, a pseudo synchronous d-q transformation is employed in current control scheme and an all-pass filter based single-phase digital phase-locked loop (PLL) is introduced to detect the phase of grid voltage. Based on the theoretical analysis, the control strategy is implemented on a 32-bit fixed-point TMS320F2812 DSP and tested in a 3kW prototype PV PCS. Simulation and experimental verify the high performance of the implemented control scheme.

Direct Virtual Torque Control for Doubly Fed Induction Generator Grid Connection

Abstract: This paper presents a grid-connection control strategy of doubly fed induction generator wind system based on the direct control of both a virtual torque and rotor flux of the generator. This control is achieved with no proportional-integral regulator and requires the measurement of only grid voltages, rotor currents, and rotor position. The same switching table is used for grid synchronization and for running process. A field-programmable-gate-array-based design of the proposed control is developed and tested on a 4-kW experimental prototype. Experimental results are provided to show the effectiveness of the fast and soft grid-connection method developed.

Design and Analysis of Precision Active Disturbance Rejection Control for Noncircular Turning Process

Abstract: In this paper, a new fast tool servocontrol method for noncircular turning process (NCTP) is presented. Based on the tracking and disturbance rejection requirements for NCTP, the controller is designed through a combined active disturbance rejection control and feedforward arrangement by exploiting the unique disturbance estimation and compensation concept and the known reference acceleration signals. In such a design framework, an extended state observer is applied to estimate and compensate for the variant dynamics of the system, nonlinearly variable cutting load, and other uncertainties. Then, a simple proportional integral controller and the acceleration feedforward design produce the control law. To quantify the controller performances, the transfer function description of the controller is derived, and the dynamic stiffness and tracking have been analyzed. By defining the vector margin variation rate, the effects of the plant parameter variations on closed-loop stability are also addressed. Experimental results of machining the first- and second-order oval profiles demonstrate that the tracking error is less than 3 mum for different cutting parameters.

A Control Strategy for Four-Switch Three-Phase Brushless DC Motor Using Single Current Sensor

Abstract: A control strategy based on single current sensor is proposed for a four-switch three-phase brushless DC (BLDC) motor system to lower cost and improve performance. The system's whole working process is divided into two groups. In modes 2, 3, 5, and 6, where phase c works, phase-c current is sensed to control phases a and b, and phase-c current is consequently regulated. In modes 1 and 4, the combination of four suboperating modes for controlling phase-c current is proposed based on detailed analysis on the different rules that these operating modes have on phase-c current. Phase-c current is maintained at nearly zero level first, and phase- a and phase-b currents are regulated by speed circle. To improve control performance, a single-neuron adaptive proportional-integral (PI) algorithm is adopted to realize the speed regulator. Simulation and experimental systems are set up to verify the proposed strategy. According to simulation and experimental results, the proposed strategy shows good self-adapted track ability with low current ripple and strong robustness to the given speed reference model. Also, the structure of the drive is simplified.

Nonlinear Tracking Control of 3-D Overhead Cranes Against the Initial Swing Angle and the Variation of Payload Weight

Abstract: In this brief, we propose a nonlinear tracking control method of 3-D overhead crane systems which works well even in the presence of the initial swing angle and the variation of payload weight. Besides the practical importance of the overhead cranes, this study is also theoretically interesting because four variables (trolley and girder positions, two swing angles) should be controlled using two control inputs (trolley and girder forces). To control such an underactuated system as cranes, a simple proportional-derivative (PD) controller has been normally used. Unlike the conventional regulation control, the newly proposed nonlinear tracking control law further improves the performance and robustness, which is based on the feedback linearizing control by using the swing angular rate as well as the swing angle. The proposed nonlinear tracking control law eliminates the nonlinear characteristics of the system and achieves the satisfactory position control and swing suppression, even when the initial swing angle and the variation of payload weight exist. We present the stability analysis and simulation results to demonstrate the practical application of our scheme.

Tuning fractional order proportional integral controllers for fractional order systems

Abstract: In this paper, two fractional order proportional integral controllers are designed to improve the performance and robustness for a class of fractional order systems which can better model many real systems such as bioengineering systems. For comparison between the fractional order proportional integral controllers and the traditional integer order PID (IOPID) controller, the IOPID controller is also designed following the same proposed tuning specifications. Unfortunately, the designed IOPID controller can not meet the required spcification. However, the designed fractional order proportional integral (FOPI) and fractional order [proportional integral] (FO[PI]) controllers both can satisfy all the three specifications proposed. From the simulation results presented, it can be seen that both the FOPI and FO[PI] controllers designed work efficiently. Furthermore, we can observe that the FO[PI] controller outperforms the FOPI controller following the proposed design schemes for the fractional order systems considered.

A Systematic Method for Gain Selection of Robust PID Control for Nonlinear Plants of Second-Order Controller Canonical Form

Abstract: A systematic method to select gains of a discrete proportional-integral-derivative (PID) controller is presented. The PID controller with the gains obtained by the proposed method can robustly control nonlinear multiple-input-multiple-output (MIMO) plants in a second-order controller canonical form, such as robot dynamics. This method has been made possible by the finding that the discrete PID control is equivalent to the discrete form of time-delay control (TDC), a robust control method for nonlinear plants with uncertainty. By using this equivalence relationships are obtained between PID gains and parameters of TDC, which enable a systematic method for the select PID gains. In addition, based on the systematic method, a simple and effective method is proposed to tune PID gains applicable to nonlinear plants with inaccurate models. This method incorporates a set of independent tuning parameters that is far less than those for conventional methods for PID gain selection. The usefulness of the proposed methods is verified through the ease and simplicity of determining PID gains for six degrees-of-freedom (DOF) programmable universal machine for assembly (PUMA)-type robot manipulator; the effectiveness of these PID gains is confirmed by the adequate and robust performance through experimentation on the robot.

Fractional-order [proportional derivative] controller for robust motion control: Tuning procedure and validation

Abstract: A fractional-order [proportional derivative] (FO-[PD]) controller is proposed for robust motion control systems. Focusing on a class of simplified models for motion control systems, a practical and systematic tuning procedure has been developed for the proposed FO-[PD] controller synthesis. The fairness issue in comparing with other controllers such as the traditional integer order PID (IO-PID) controller and the fractional order proportional derivative (FO-PD) controller has been for the first time addressed under the same number of design parameters and the same specifications. Side-to-side fair comparisons of the three controllers (i.e., IO-PID, FO-PD and FO-[PD]) via both simulation and experimental tests have revealed some interesting facts: 1) IO-PID controller designed may not always be stabilizing to achieve flat-phase specification while both FO-PD and FO-[PD] controllers designed are always stabilizing; 2) Both FO-PD and FO-[PD] controllers outperform IO-PID controller designed in this paper; 3) FO-[PD] controller outperforms FO-PD controller more when the time constant of the motion control system increases. Extensive validation tests on our real-time experimental test-bench illustrate the same.

Adaptive Controller for Single-Link Flexible Manipulators Based on Algebraic Identification and Generalized Proportional Integral Control

Abstract: In this paper, we propose a fast online closed-loop identification method combined with an output-feedback controller of the generalized proportional integral (GPI) type for the control of an uncertain flexible robotic arm with unknown mass at the tip, including a Coulomb friction term in the motor dynamics. A fast nonasymptotic algebraic identification method developed in continuous time is used to identify the unknown system parameter and update the designed certainty equivalence GPI controller. In order to verify this method, several informative simulations and experiments are shown.

Robust Control of PM Spherical Stepper Motor Based on Neural Networks

Abstract: There are many uncertainties and disturbances in the real dynamic system of a spherical stepper motor that make traditional control methods with lower precision, such as uncertain changes of magnetic field, load, and friction that generate speed ripple and deteriorate the 3-D tracking performance of the spherical motor system. In this paper, an available method is proposed to solve them by using neural networks (NNs) and a robust control scheme for improving the performance. First, a simplified torque calculation model based on finite-element method results can guarantee quick prediction of electromagnetic torque with lower error. Thus, the system model considering the friction, load, and disturbances is developed. Second, a robust NN (RNN) control scheme is presented to eliminate uncertainties to improve the tracking robust stability and overcome the undesired influence of uncertainties based on the nonlinear system dynamic model under continuous-trajectory tracking mode. Finally, as an example, the step-response and continuous-tracking processes of the motor using an RNN controller are simulated, and experiments, including the tracking using RNN proportional-differential control, are carried out to confirm the usefulness of the proposed control scheme. The simulation and experimental results of the proposed control scheme on the spherical stepper motor system demonstrate the effectiveness on satisfactory tracking performance.

Sliding-Mode Control With Double Boundary Layer for Robust Compensation of Payload Mass and Friction in Linear Motors

Abstract: Direct drives with linear motors have been recently attracting the attention of both industry and academia. The main peculiarity of these systems is the lack of mechanical reduction and transmission devices, which makes the influence of some uncertain electromechanical phenomena (e.g., friction, cogging forces, etc.) and load disturbances much more significant than in the case of conventional rotary actuators. This paper describes a control system for a tubular synchronous linear motor based on a sliding-mode control (SMC) and a proportional-integral (PI)-based equivalent disturbance observer. The distinctive peculiarities of the proposed scheme are the use of a control law that guarantees the stability of the system regardless of the payload mass, the adoption of a double boundary layer addressing effectively the harmful effects of static friction, and the introduction of a simple PI-based equivalent disturbance observer that avoids steady-state errors regardless of model uncertainties and external disturbances. The reduced computational cost of the control law, alongside with the introduction of the effective design criteria for the SMC and the disturbance observer, makes the implementation of the proposed approach as simple as standard cascaded linear control schemes using industrial microcontrollers. The aforementioned considerations are validated by extensive experiments.

Designing optimal controllers for doubly fed induction generators using a genetic algorithm

Abstract: This work presents a design procedure based on evolutionary computation, more specifically on a genetic algorithm combined with the formal pole placement project, to obtain optimal controllers to the rotor-side converter of doubly fed induction generators (DFIGs), in variable-speed wind generation systems connected to the electrical grid. With this procedure it is intended to improve the global system dynamic behaviour during and after the fault period, also increasing the transient stability margin of the power system and the fault ride-through capability. The control action of the DFIG converters is accomplished by proportional and integral controllers, whose gains' adjustment is not a trivial task, because of the high complexity of the system. The results obtained confirm the efficiency of the proposed control design procedure.

Discrete-Time Sliding Mode Control With Time-Varying Surface for Hard Disk Drives

Abstract: A time optimal-based discrete-time sliding mode control (DSMC) scheme with application to hard disk drives (HDDs) is developed in this study. In this approach, an approximate time optimal switching curve is adopted for the time-varying sliding mode design and the controller, which consists of an equivalent part and a discontinuous one, is designed such that the trajectory from any initial point is driven into a sliding region in the vicinity of the switching surface without chattering and thereafter remains inside it. By using the time-varying switching surface, one unified framework for both track seeking and following control is provided and smooth transition from seeking control to track following control is achieved as well. Simulation and experimental studies on the design of controller in HDDs were conducted to illustrate its feasibility and effectiveness. The simulation/experimental results demonstrate that the proposed scheme provides better performance during track seeking than the commonly used discrete-time proximate time-optimal servomechanism (PTOS) and sliding mode proximate time optimal servomechanism (SMPTOS). Moreover, the unified controller achieves better disturbance suppression in track-following than the proportional-integral-differential (PID) control.

Fractional order proportional integral (FOPI) and [proportional integral] (FO[PI]) controller designs for first order plus time delay (FOPTD) systems

Abstract: In this paper, systematic design schemes of fractional order proportional integral (FOPI) controller and fractional order [proportional integral] (FO[PI]) controller for the first order plus time delay (FOPTD) system are presented, respectively. For comparison between the fractional order and the integer order controllers, the integer order proportional integral derivative (IOPID) controller is also designed following the same proposed tuning specifications to achieve the robustness requirement. It is found that the three controllers designed by the proposed tuning methods not only make the system stable, but also improve the performance and robustness for the first order plus time delay (FOPTD) systems. Simulation results are presented to validate the proposed tuning schemes. Furthermore, from the simulation results, it can be seen that the FOPI controller outperforms the other two controllers.

Modeling and control of the single-phase photovoltaic grid-connected cascaded H-bridge multilevel inverter

Abstract: This paper presents the modeling and control of the single-phase photovoltaic grid-connected five-level cascaded H-bridge multilevel inverter. For the unity power factor, the proportional and integral current controller with the duty ratio feed-forward compensation method is used. And in order to track the maximum power point and to reduce the partial shading due to stacked photovoltaic modules, each DC voltage is stably controlled to their maximum power points by dedicated voltage controllers of each H-bridge module. The modeling approach and the control loop design method are provided in this paper. The proposed control schemes are validated from experimental results of the 2-kW prototype hardware.

Minimum-variance Brownian motion control of an optically trapped probe

Abstract: This paper presents a theoretical and experimental investigation of the Brownian motion control of an optically trapped probe. The Langevin equation is employed to describe the motion of the probe experiencing random thermal force and optical trapping force. Since active feedback control is applied to suppress the probe's Brownian motion, actuator dynamics and measurement delay are included in the equation. The equation of motion is simplified to a first-order linear differential equation and transformed to a discrete model for the purpose of controller design and data analysis. The derived model is experimentally verified by comparing the model prediction to the measured response of a 1.87 microm trapped probe subject to proportional control. It is then employed to design the optimal controller that minimizes the variance of the probe's Brownian motion. Theoretical analysis is derived to evaluate the control performance of a specific optical trap. Both experiment and simulation are used to validate the design as well as theoretical analysis, and to illustrate the performance envelope of the active control. Moreover, adaptive minimum variance control is implemented to maintain the optimal performance in the case in which the system is time varying when operating the actively controlled optical trap in a complex environment.

Novel Expressions of Equations of Relative Motion and Control in Keplerian Orbits

Abstract: : In this Note, the relative motion between two spacecraft is studied with emphasis on physical insights. The full equations of relative motion in Keplerian orbits are converted into the general form of a second-order differential equation, and then feedback control laws are proposed for different control objectives. Besides the control laws presented in this Note, other various control design methods, which have already been developed for other applications (such as robot manipulator or spacecraft control), can also be easily applied for the relative motion control, thanks to the use of the generic form.

Self-tuning-parameter fuzzy PID temperature control in a large hydraulic system

Abstract: Oil temperature control in a large hydraulic system is dealt with using the fuzzy logic control algorithm. Mathematic model of the control system characterized by large time delay is created based on law of thermodynamics. A self-tuning-parameter fuzzy PID controller is designed to regulate the cooling water flow rate through the triple proportional valve in order to control the oil temperature. The simulations and experiments are carried out, making a comparison with conventional PID control. The results suggest that fuzzy PID strategy can efficiently improve the performance of the hydraulic temperature control system, irrespective of time delay problem and parameter variations. It achieves higher control accuracy of temperature, faster response and stronger robustness than conventional PID control system.

A New Current Feedback PR Control Strategy for Grid-Connected VSI with an LCL Filter

Abstract: Proportional Resonant (PR) controller with harmonic compensators has extremely higher gain at the desired frequencies to reduce the harmonic distortions in the alternative voltage or current waves. However, the harmonic compensators of the PR controller are limited to several low-order current harmonics, due to the system instability when the compensated frequency is out of the bandwidth of the system control loop, especially for the grid-connected converters with the use of an LCL-filter and conventional current feedback methods. In this paper, a new current feedback method and PR control strategy for grid-connected voltage source inverters (VSI) with an LCL-filter is proposed. The weighted average value of the currents flowing through the two inductors of the LCL-filter is used as the feedback to the current PR regulator. Consequently, the control system with the LCL-filter is degraded from a third-order function to a first-order one. In this way, a large proportional control loop gain can be chose to obtain a wide control loop bandwidth that is required by the harmonics compensations of the PR controller, the system can be optimized easily for minimum current harmonic distortions as well as the system stability. The characteristics of the inverter system with the proposed controller are investigated and compared with those using traditional control methods. Experimental results on a 5kW fuel cell inverter are provided, and the new current control strategy has been verified.

Adaptive PID with sliding mode control for the rotary inverted pendulum system

Abstract: In this paper, a novel adaptive PID with sliding mode control for the rotary inverted pendulum is proposed. The goal is to achieve system robustness against parameter variations and external disturbances. In this study, the three parameters of PID controller, proportional gain, integral gain, and derivative gain can be systematically obtained according to the adaptive law. Further reduction of the high frequency chattering in the controller is achieved by using the boundary layer technique. The proposed control method is applied to a rotary inverted pendulum control system. By using Lyapunov theorem, the stability and convergence of the proposed scheme is proven. Simulation results show that the chattering and the steady state error are eliminated and trajectory tracking is achieved effectively.