Showing papers on "Proportional control published in 2019"

A Generalized Droop Control for Grid-Supporting Inverter Based on Comparison Between Traditional Droop Control and Virtual Synchronous Generator Control

Abstract: In this paper, a generalized droop control (GDC) is proposed for a grid-supporting inverter based on a comparison between traditional droop control and virtual synchronous generator (VSG) control Both the traditional droop control and VSG control have their own advantages, but neither traditional droop control nor VSG control can meet the demand for different dynamic characteristics in grid-connected (GC) and stand-alone (SA) modes at the same time Rather than using a proportional controller with a low-pass filter, as in a traditional droop control, or fully mimicking the conventional synchronous generator parameters in a VSG control, the active power control loop of the GDC can be designed flexibly to adapt to different requirements With a well-designed controller, the GDC can achieve satisfactory control performance; unlike a traditional droop control, it can provide virtual inertia and damping properties in SA mode; unlike a VSG control, the output active power of an inverter with GDC can follow changing references quickly and accurately, without large overshoot or oscillation in the GC mode Moreover, given specific controller parameters, the GDC can function as both a traditional droop control and a VSG control The GDC's controller parameter design is more intuitive and flexible, and this paper provides a distinct design process Finally, the effectiveness of the proposed control method is validated by the simulation and experimental results

Mixed stepping/scanning mode control of stick-slip SEM-integrated nano-robotic systems

Abstract: The ability to do dexterous automated and semi-automated tasks at the micro- and nano-meter scales inside a Scanning Electron Microscope (SEM) is a critical issue for nanotechnologies. SEM-integrated nano-robotic systems with several Degrees Of Freedom (DOF) and one or several end-effectors have therefore widely emerged in research laboratories and industry. The Piezoelectric Stick-Slip (PSS) is one of the best actuation principle for SEM-integrated nano-robotic systems as it has two operating modes, namely a coarse positioning mode with long travel range, and a fine positioning mode with a resolution of the order of the nanometer. The main contribution of this paper is the design of a switch control strategy to deal efficiently and in a transparent way from the user's point of view, with the transition between the coarse and the fine operating modes of PSS actuators. The aim is to be able to perform positioning tasks with a millimeter displacement range and a nanometer resolution without worrying about the mode of operation of the actuator. The coarse mode and the fine mode are respectively controlled with a frequency/voltage proportional control and a H∞ control. The switch control is based on an internal model of the actuator. Experimental results show the effectiveness of the new mixed coarse/fine mode control strategy to satisfy closed-loop stability and bumpless specifications at the switching time. For the best knowledge of the authors, this result is the first demonstration of such a control capability for PSS actuators.

Adaptive Auto-Regressive Proportional Myoelectric Control

Abstract: In proportional myographic control, one can control either position or velocity of movement. Here, we propose to use adaptive auto-regressive filters, so as to gradually adjust between the two. We implemented this in an adaptive system with closed-loop feedback, where both the user and the machine simultaneously attempt to follow a cursor on a 2-D arena. We tested this on 15 able-bodied and three limb-deficient participants using an eight-channel myoelectric armband. The human–machine pairs learn to perform smoother cursor movements with a larger range of motion when using the auto-regressive filters, as compared with our previous effortswithmoving-average filters. Importantly, the human–machine system converges to an approximate velocity control strategy resulting in faster and more accuratemovements with lessmuscle effort. The method is not specific tomyoelectriccontroland could be used equally well for motion control using high-dimensional signals from reinnervatedmuscles or direct brain recordings.

Parameters identification and trajectory control for a hydraulic system.

Abstract: In order to improve the tracking accuracy of a hydraulic system, an improved ant colony optimization algorithm (IACO) is proposed to optimize the values of proportional-integral-derivative (PID) controller. In addition, this paper presents an experimental study on the parameters identification to deduce accurate numerical values of the hydraulic system, which also determines the relationship between control signal and output displacement. Firstly, the basic principle of the hydraulic system and the mathematical model of the electro-hydraulic proportional control system are analyzed. Based on the theoretical models, the transfer function of the control system is obtained by recursive least square identification method (RLS). Then, the key parameters of the control system model are obtained. Some improvements are proposed to avoid premature convergence and slow convergence rate of ACO: the transition probability is revised based adjacent search mechanism, dynamic pheromone evaporation coefficient adjustment strategy is adopted, pheromone update rule and parameters optimization range are also improved. Then the proposed IACO tuning based PID controller and the identification parameters are modeled and simulated using MATLAB/Simulink and AMESim co-simulation platform. Comparisons of IACO, standard ACO and Ziegler-Nichols (Z-N)PID controllers are carried out with different references as step signal and sinusoidal wave using the co-simulation platform. The simulation results of the bucket system using the proposed controller demonstrates improved settling time, rise time and the convergence speed with a new objective function J. Finally, experiments with leveling operations are performed on a 23 ton robotic excavator. The experimental results show that the proposed controller improves the trajectory accuracy of the leveling operation by 28% in comparison to the standard ACO-PID controller.

Cascaded Proportional Control With Algebraic Estimators for PFC AC/DC Converters

Abstract: Conventionally, a proportional-integral (PI)-based dual-loop control strategy, in which both the dc-bus voltage and the inductor current are regulated, is utilized to control ac/dc converters with power factor correction (PFC). Due to the characteristics of the PI controller, converters experience poor control performance such as current distortion and slow dynamic response. This paper proposes a novel cascaded proportional control in conjunction with algebraic estimation method for PFC ac/dc converters. Different from the conventional control system, the average dc-bus energy and the instantaneous input power of the converter are regulated. Moreover, system nonlinearity, load power and uncertainties are estimated by incorporating algebraic estimators. A holistic design of controller parameters and stability analysis are presented based on the z -domain transfer functions. A 1 kW PFC ac/dc prototype is designed and experimental results demonstrate the effectiveness of the proposed control scheme.

An adaptive ball-head positioning visual servoing method for aircraft digital assembly

Abstract: To gain accurate support for large aircraft structures by ball joints in aircraft digital assembly, this paper aims to propose a novel approach based on visual servoing such that the positioner’s ball-socket can automatically and adaptively approach the ball-head fixed on the aircraft structures.,Image moments of circular marker labeled on the ball-head are selected as visual features to control the three translational degrees of freedom (DOFs) of the positioner, where the composite Jacobian matrix is full rank. Kalman–Bucy filter is adopted for its online estimation, which makes the control scheme more flexible without system calibration. A combination of proportional control with sliding mode control is proposed to improve the system stability and compensate uncertainties of the system.,The ball-socket can accurately and smoothly reach its desired position in a finite time (50 s). Positional deviations between the spherical centers of ball-head and ball-socket in the X-Y plane can be controlled within 0.05 mm which meets the design requirement.,The proposed approach has been integrated into the pose alignment system. It has shown great potential to be widely applied in the leading support for large aircraft structures in aircraft digital assembly.,An adaptive approach for accurate support of large aircraft structures is proposed, which possesses characteristics of high precision, high efficiency and excellent stability.

Improving Handling Stability Performance of Four-Wheel Steering Vehicle Based on the H2/H∞ Robust Control

Abstract: Considering the demand for vehicle stability control and the existence of uncertainties in the four-wheel steering (4WS) system, the mixed H2/H∞ robust control methodology of the 4WS system is proposed. Firstly, the linear 2DOF vehicle model, the nonlinear 8DOF vehicle model, the driver model, and the rear wheel electrohydraulic system model were constructed. Secondly, based on the yaw rate tracking strategy, the mixed H2/H∞ controller was designed with the optimized weighting functions to guarantee system performance, robustness, and the robust stability of the 4WS vehicle stability control system. The H∞ method was applied to minimize the effects of modeling uncertainties, sensor noise, and external disturbances on the system outputs, and the H2 method was used to ensure system performance. Finally, numerical simulations based on Matlab/Simulink and hardware-in-the-loop experiments were performed with the proposed control strategy to identify its performance. The simulation and experimental results indicate that the handling stability of the 4WS vehicle is improved by the H2/H∞ controller and that the 4WS system with the H2/H∞ controller has better handling stability and robustness than those of the H∞ controller and the proportional controller.

Consensus of Heterogeneous Nonlinear Multiagent Systems With Duplex Control Laws

Abstract: This note addresses the consensus of heterogeneous nonlinear multiagent systems with duplex control laws including the integral control law and the proportional control law. Sufficient conditions are derived to ascertain the consensus of multiagent systems under directed communication graphs. It is shown herein that the connectivity of the communication graph underlying the integral control law is more important than that of proportional one for consensus and that the graph underlying the proportional control law does not need to be connected. It is also shown that the heterogeneous nonlinear multiagent systems are applicable for distributed optimization. In particular, simulation results on the nonlinear multiagent system for distributed parameter estimation in a wireless sensor network are provided to substantiate the theoretical results.

Adaptive super-twisting sliding mode control of three-phase power rectifiers in active front end applications

Abstract: A robust control approach for three-phase two-level grid-connected power converters using an adaptive super-twisting algorithm (ASTA) is studied. A cascaded structure of the proposed control method is employed, which consists of two control loops, the dc-link capacitor voltage regulation loop (outer loop) and the grid phase current tracking loop (inner loop). In the outer control loop, a proportional controller using H ∞ technique is considered, which is designed to regulate the dc-link capacitor voltage to some desired value. An extended state observer used to asymptotically estimate the external disturbance is integrated into the outer control loop. For the inner control loop, two ASTA-based controllers are implemented that force the grid phase currents to their desired values in finite time. Lyapunov analysis is provided to show the finite time convergence of the closed-loop system. With the help of ASTA, a priori knowledge of the upper bounds of the derivative of the disturbances is not required. Illustrative simulation results in comparison with the linear proportional-integral control method are provided to demonstrate the effectiveness and robustness of the proposed ASTA, in the presence of load variation and parametric uncertainty.

Frequency Regulation using Data-Driven Controllers in Power Grids with Variable Inertia due to Renewable Energy

Abstract: With the increasing penetration of non-synchronous variable renewable energy sources (RES) in power grids, the system's inertia decreases and varies over time, affecting the capability of current control schemes to handle frequency regulation. Providing virtual inertia to power systems has become an interesting topic of research, since it may provide a reasonable solution to address this new issue. However, power dynamics are usually modeled as time-invariant, without including the effect of varying inertia due to the presence of RES. This paper presents a framework to design a fixed learned controller based on datasets of optimal time-varying LQR controllers. In our scheme, we model power dynamics as a hybrid system with discrete modes representing different rotational inertia regimes of the grid. We test the performance of our controller in a twelve-bus system using different fixed inertia modes. We also study our learned controller as the inertia changes over time. By adding virtual inertia we can guarantee stability of high-renewable (low-inertia) modes. The novelty of our work is to propose a design framework for a stable controller with fixed gains for time-varying power dynamics. This is relevant because it would be simpler to implement a proportional controller with fixed gains compared to a time-varying control.

Modeling and Design of a Fuzzy Logic Based PID Controller for DC Motor Speed Control in Different Loading Condition for Enhanced Performance

Abstract: This paper proposes the design and simulation of a Fuzzy Logic based PID controller for DC motor speed control. The speed of a DC motor depends on armature voltage, field current and torque. In this paper, the armature voltage is changed in order to have the required speed output. The armature voltage is firstly controlled by a simple proportional controller and then controlled by PID constants and tuned by a Fuzzy Logic Controller (FLC). The FLC tunes the values of PID parameters based on the fuzzy rules fed into it and gives a satisfactory output wave shape for wide range of motor speed variation. Constant output voltage is maintained in the proposed system though changes are done in input voltage. Hence, significant amount of reduction in overshoot is observed which improves the efficiency of the motor. MATLAB-Simulink environment is used to achieve the results of the simulation and carry out the analysis.

Modeling and Position Tracking Control of a Novel Circular Hydraulic Actuator With Uncertain Parameters

Abstract: In order to realize precise position tracking of a novel circular hydraulic actuator with parameter uncertainties and bounded disturbances, an adaptive sliding mode controller (ASMC) that incorporates a fuzzy tuning technique is proposed in this paper. The mechanical structure and basic principle of the actuator are first introduced, and the mathematical model of its corresponding valve-controlled hydraulic servo system is constructed. Based on Lyapunov stability theory, online parameter estimation and sliding mode controller design are effectively integrated to approximate the equivalent control of sliding mode. To mitigate the undesired chattering phenomenon and further improve system performance, a fuzzy tuning scheme is employed to regulate the proportional gain of the approaching control term. In addition, a real-time control platform is established, and the controllers parameter identification and position tracking are verified by preliminary experiments. Finally, the traditional PID controller and the exponent approaching sliding controller are also conduced to further evaluate the control performances of the designed controller, and the comparative results demonstrate that the proposed control scheme has better control performance in reducing errors for trajectory tracking.

Evaluation of Voltage Regulators for Dual-Loop Control of Voltage-Controlled VSCs

Abstract: This paper presents an evaluation for the voltage regulators adopted in the digital dual-loop voltage-controlled, LC-filtered voltage-source converters. Given the proportional control on the filter inductor current, four different capacitor voltage regulators implemented in the αβ frame are compared. The analysis elaborates that the basic proportional and resonant voltage regulator limits the control bandwidth of the voltage loop, and also results in a large non-passive impedance region, which can lead to harmonic instability. Four enhanced voltage controls are then presented, aiming to improve the transient performance of the voltage loop and the passivity of the output impedance of the converter. Experimental tests corroborate the theoretical analysis.

Comparison of Flow-Dependent Controllers for Remote Real-Time Pressure Control in a Water Distribution System with Stochastic Consumption

Abstract: The control of pressure at a remote critical node using a pressure control valve is a highly effective way to attain pressure management. To perform real-time control, various kinds of controllers can be used, including flow-dependent controllers. These controllers calculate valve setting adjustment based both on the deviation of the pressure from the set-point and on the flow rate at the valve site. After putting all the flow-dependent controllers present in the scientific literature within the same framework, this paper presents a numerical comparison of their performance under realistic conditions of stochastic demand. Two controllers were selected for the comparison, namely the simple LCF (parameter-less proportional controller with known constant pressure control valve flow); and LVF (parameter-less controller with known variable pressure control valve flow), which uses a flow rate forecast. Indeed, this study considered an upgrade of LVF, in which the flow rate forecast was tailored to the conditions of stochastic demand. The application in a specific example network proved the performance of these controllers to be quite similar, although LCF was preferable due to its simple structure. For LCF, the average pressure at the critical node had a clear relationship to the consumption pattern. LVF outperformed when the hourly variation dominates the fluctuations in the flow. The conditions under which this out-performance occurred are comprehensively discussed.

Passivity-based attitude control with input quantization:

Abstract: A passivity-based controller with quantization for spacecraft attitude control is developed. This passive control scheme includes two parts which are a proportional controller for quaternion feedba...

Mathematical modeling and analysis of the electrohydraulic actuator with the throttle control

Abstract: High demands to modern electrohydraulic actuators are placed. This applies to the static and dynamic characteristics of the drives, which is achieved by using different correcting devices (controllers). In the article analysis of the most effective regulator for an electro-hydraulic actuator is conducted during the comparison of its dynamic characteristics at introduction of various types of correcting devices: the introduction of state controller, the introduction of additional pressure feedback and a proportional controller. Block diagrams of the electrohydraulic actuator are constructed according to the corresponding mathematical models. The optimization of the control parameters was carried out to improve the static characteristics of the actuator.

Control Strategy for Dynamic Voltage Restorer Under Distorted and Unbalanced Voltage Conditions

Abstract: Under the condition where power grid voltage is unbalanced and distorted, dynamic voltage restorer (DVR) is used to compensate the negative sequence voltage and harmonic voltage. In this paper, a novel double closed-loop control strategy is presented. The outer voltage loop of the controller is based on proportional multi-resonant (PMR) controller, while the inner current loop is based on proportional controller. Parameter tuning of inner current loop is investigated and the optimal gain is obtained through root locus curve. This method can maximize the stability of current loop and effectively suppress LC resonance at the same time. Simulation and experimental tests show that the proposed control strategy significantly improves the output voltage quality of DVR.

Effects on oscillation mechanism and design of grid-voltage feedforward in grid-tied converter under weak grid

Abstract: Grid-voltage feedforward control is widely used in grid-tied converters. The reported studies show that the grid-voltage feedforward may reduce the system stability margin, and may lead to oscillation problem in renewable power generation system. This study revisits the effect of voltage feedforward control on system stability and especially focuses on low frequency oscillation with impedance-based method. The low frequency oscillation usually happens in industry around 100 Hz and shows frequency coupling characteristics. A converter equivalent impedance which includes the effects of voltage feedforward and also covers the frequency coupling introduced by phase locked loop (PLL) is established. Based on the built impedance, the effect on oscillation mechanism with voltage feedforward and PLL is revealed. The results show that the voltage feedforward could increase the system stability margin and may be employed to improve the system stability. Then how to design an optimal proportional voltage feedforward control is demonstrated. Experimental results verify the theoretical analysis and the design of the proportional grid-voltage feedforward control.

Point-actuated feedback control of multidimensional interfaces

Abstract: We consider the application of feedback control strategies with point actuators to stabilise desired interface shapes. We take a multidimensional Kuramoto--Sivashinsky equation as a test case; this equation arises in the study of thin liquid films, exhibiting a wide range of dynamics in different parameter regimes, including unbounded growth and full spatiotemporal chaos. In the case of limited observability, we utilise a proportional control strategy where forcing at a point depends only on the local observation. We find that point-actuated controls may inhibit unbounded growth of a solution, if they are sufficient in number and in strength, and can exponentially stabilise the desired state. We investigate actuator arrangements, and find that the equidistant case is optimal, with heavy penalties for poorly arranged actuators. We additionally consider the problem of synchronising two chaotic solutions using proportional controls. In the case when the full interface is observable, we construct feedback gain matrices using the linearised dynamics. Such controls improve on the proportional case, and are applied to stabilise non-trivial steady and travelling wave solutions.

Permanent-Magnet Synchronous Motor Sensorless Control Using Proportional-Integral Linear Observer with Virtual Variables: A Comparative Study with a Sliding Mode Observer

Abstract: Quick convergence, simple implementation, and accurate estimation are essential features of realizing permanent-magnet synchronous motor (PMSM) position estimation for sensorless control using microcontrollers. A linear observer is often designed on real plant variables and is more sensitive to parameter uncertainty/variations. Thus, conventionally, a sliding mode observer (SMO)-based technique is widely used for its simplicity and convergence ability against parameter uncertainty. Although SMO has been improved for switching chattering and phase delay, it provides purely proportional gain, which leads to steady-state error and chattering in observation results. Different from conventional linear observer using real plant variables or SMO with proportional gain, a simple proportional-integral linear observer (PILO) using virtual variables is proposed in this paper. This paper also provides a comparative study with SMO. By introducing virtual variables without physical meaning, the PILO is able to simplify observer relations, get smaller phase shifts, adapt mismatched parameters, and obtain a fixed phase-shift relation. The PILO is not only simple, but also improves the estimation precision by solving the controversy between chattering and phase-delay, steady-state error. Moreover, the PILO is less sensitive to parameters mismatching. Simulation and experimental results indicate the merits of the PILO technique.

A Proportional Plus a Hysteretic Term Control Design: A Throttle Experimental Emulation to Wind Turbines Pitch Control

Abstract: Pitch control is a relevant issue in wind turbines to properly operate the angle of the blades. Therefore, this control system pitches the blades usually a few degrees every time the wind changes in order to keep the rotor blades at the required angle thus controlling the rotational speed of the turbine. All the same time, the control of the pitch angle is not easy due to the system behavior being highly nonlinear. Consequently, the main objective of this paper is to depict an easy to implement control design based on a proportional controller and a hysteretic term to an emulator pitch control system in wind turbines. This emulator is just an automotive throttle device. This mechanical body dynamically captures some hard non-linearities presented in pitch wind turbine mechanisms, such as backlash, asymmetrical non-lineal effects, friction, and load variations. Even under strong non-linear effects that are difficult to model, a proportional controller and a hysteretic term may satisfy the main control design objective. Hence, a recent control design is developed and applied to a throttle system. We invoke the Lyapunov theory to confirm stability of the resultant closed-loop system. In addition, the proposed control approach is completely implemented by using operational amplifiers. Hence, no digital units are required at all. Moreover, the cost of the developed experimental platform and its outcomes are inexpensive. According to the experimental results, the controller performance seems acceptable, and validating of the control contribution too. For instance, a settling-time of about 0.03 s to a unit step-response is obtained.

Mitigating Line Frequency Instability of Boost PFC Converter Under Proportional Outer-Voltage Loop With Additional Third Current-Harmonic Feedforward Compensation

Abstract: For the average current mode (ACM)-controlled boost power factor correction (PFC) converter, there is line frequency instability under light load and small output capacitor conditions. The line frequency instability is characterized as self-oscillation in the form of period-doubling, which drastically increases the total harmonic distortion (THD) and additional losses. Regarding this line frequency instability, this paper proposes a stability control scheme incorporating an outer-voltage proportional controller and an additional third current-harmonic feedforward compensation (TCFC). Specifically, the outer-voltage proportional controller replaces the traditional low-pass filter (LPF) to mitigate the line frequency instability, and the TCFC aims to ensure an acceptable THD. Moreover, the dynamic response of the proposed current-feedforward-based stability control scheme outperforms the existing voltage-feedback-based schemes. Furthermore, the control parameters are determined by the harmonic averaged model, and the feasibility of the proposed scheme is verified by experiments based on IC UC3854BN. The experimental results demonstrate that the THD with the line frequency instability is 56.60%, while it is improved to 15.58% by using the proposed scheme.

The Voltage Control Strategy of a DC-Link Bus Integrated Photovoltaic Charging Module in a Unified Power Quality Conditioner

Abstract: In order to improve the functionality and efficiency of a unified power quality conditioner (UPQC), a DC-link bus integrated photovoltaic charging module is proposed in a UPQC. It can generate power for essential loads apart from providing energy to a DC-link bus. A conventional proportional integral (PI) controller fails to run smoothly in dynamic conditions of the micro-grid, since it has poor capabilities in determining suitable values of proportional gain and integral gain. So, the optimization algorithm for a PI controller based on chaos particle swarm optimization based on a multi-agent system (CPSO-MAS) algorithm was developed in this paper to overcome properties such as intermittent instability in the micro-grid. Through verification by simulation and experiment of UPQC harmonic compensation, it showed that the proposed DC link bus voltage control strategy can be effectively applied to UPQC towards various conditions related to voltage and current distortion. In addition, it proved that the proposed strategy has faster convergence than other algorithms, which enhances the stability of DC-link bus voltage. Hence, the contribution presented in this paper is to provide a novel approach for the power quality improvement of UPQC.