Current Command Research Articles

Improved Control of Linear Motors for Broadband Transducer Calibration

To achieve accuracy in measuring vibrations, the sensors must be calibrated over an entire amplitude and frequency range. The linear motor with the advantage of long strokes has great potential in transducer calibration. In order to provide motion over a broad frequency range, the improved control of the linear motor is investigated. The Luenberger observer is designed for broadband state estimation by data fusion of the current command and the displacement measurement. The high bandwidth position loop is constructed to avoid drift move, outside of which the vibration control is employed to compensate the frequency response variation. The improved control of the linear motor is powerful in reducing harmonic distortion and maintaining amplitude stability over the frequency range from 0.1 to 160 Hz. Calibration of the MEMS accelerometer using the controlled linear motor is conducted to show its effectiveness in determining the sensitivity curve and the standard deviation.

Research on MMC-HVDC multi-objective model predictive control strategy under asymmetric faults

When an asymmetric fault occurs on the AC side of the MMC-HVDC system, a large number of non-characteristic harmonics will be generated on both sides of the system, which will affect the operation of the system. Model predictive control has the advantages of intuitive modeling and fast dynamic response. And considering its advantages in MMC application and the ability of multi-objective control, this paper proposes a multi-objective model predictive control strategy based on a two-phase stationary coordinate system as the MMC-HCDC system control strategy when an asymmetric fault occurs. This strategy, which combines classic vector control and adds weight coefficients, divides the control system into three parts: current command prediction, multi-objective control and voltage output control based on the idea of functional equivalence. In addition, the strategy avoids the complicated coordinate transformation and enhances the control ability of MMC-HVDC under asymmetric faults. Finally, a 21-level MMC-HVDC system is built based on PSCAD/EMTDC, which verifies the control effect of the control strategy.

A Hybrid BCI Based on SSVEP and EOG for Robotic Arm Control.

Brain-computer interface (BCI) for robotic arm control has been studied to improve the life quality of people with severe motor disabilities. There are still challenges for robotic arm control in accomplishing a complex task with a series of actions. An efficient switch and a timely cancel command are helpful in the application of robotic arm. Based on the above, we proposed an asynchronous hybrid BCI in this study. The basic control of a robotic arm with six degrees of freedom was a steady-state visual evoked potential (SSVEP) based BCI with fifteen target classes. We designed an EOG-based switch which used a triple blink to either activate or deactivate the flash of SSVEP-based BCI. Stopping flash in the idle state can help to reduce visual fatigue and false activation rate (FAR). Additionally, users were allowed to cancel the current command simply by a wink in the feedback phase to avoid executing the incorrect command. Fifteen subjects participated and completed the experiments. The cue-based experiment obtained an average accuracy of 92.09%, and the information transfer rates (ITR) resulted in 35.98 bits/min. The mean FAR of the switch was 0.01/min. Furthermore, all subjects succeeded in asynchronously operating the robotic arm to grasp, lift, and move a target object from the initial position to a specific location. The results indicated the feasibility of the combination of EOG and SSVEP signals and the flexibility of EOG signal in BCI to complete a complicated task of robotic arm control.

Adaptive Control for Torque Ripple Minimization in PM Synchronous Motor (Dept.E)

paper presents two methods for designing special purpose controllers for permanent magnet synchronous motor. The main target of the designed controllers is to reduce torque ripples of this type of motors. The first proposed adaptive method is based on two loop controllers (current controller and speed controller) in addition to using space vector pulse width modulation to maximize fundamental component of torque. The second proposed method is based on PI current controllers enabling tracking of quadrature current command values. Simulation results of the suggested adaptive controller are compared with that of the PI controller. Comparative analysis proves the effectiveness of the suggested adaptive controller than the classical PI one according to ripple reduction as well as dynamic response. Moreover, the suggested adaptive controller when compared with other controllers shows great success in torque ripples reduction, enabling speed tracking while minimizing the torque ripple. Keywordsreference adaptive system, PM synchronous motor, torque control.

Reference‐free approach for mitigating human–machine conflicts in shared control of automated vehicles

Shared control is a promising approach that can facilitate the mutual understanding and cooperative control between human and machine. In this study, a novel reference-free framework for shared control of automated vehicles is proposed with the aim of mitigating conflicts between the human driver and the automatic system during their interactions. Position constraint and time to collision are deployed to prevent collision and guarantee stability by limiting the yaw rate and sideslip angle of the vehicle. The design of the shared controller is formulated as a model predictive control problem. It determines vehicle state based on the current driver command and implements control actions only if the vehicle state induced by the human driver violates the pre-defined constraints. The system models, safety constraints and the proposed shared controller are then integrated. The algorithm is validated through computer simulation under two different driving scenarios. The simulation results show that the proposed reference-free approach can offer the human driver more degrees of freedom during shared control, effectively mitigating human–machine conflicts, compared to the previous work. In addition, the algorithm ensures the safety and stability of the system under risky driving conditions, validating its feasibility and effectiveness.

Luenberger Position Observer Based on Deadbeat-Current Predictive Control for Sensorless PMSM

Two problems can cause control performance degradation on permanent magnet synchronous motor (PMSM) systems, namely, fluctuation of PMSM parameters and the time delay between current sampling and command value update. In order to reduce the influence of these problems, a new current-predictive control strategy is proposed in this article for medium- and high-speed PMSM. This strategy is based on the discrete mathematical model of PMSM. This new control strategy consists of two main steps: First, an integrator is applied to calculate current compensation value; second, the predictive current value is obtained through deadbeat-current predictive method. The stability of predictive control system is also proved in the article. With this deadbeat-current predictive control scheme, the real current can reach the desired value within one control-step. Based on this new current control method, Luenberger observer and phase-locked loop position tracker is applied in this article. Experimental results for 0.4 kW surface-mounted PMSM confirm the validity and excellent performance for parameters fluctuation of new current predictive control.

Intelligent Maximum Power Factor Searching Control Using Recurrent Chebyshev Fuzzy Neural Network Current Angle Controller for SynRM Drive System

To develop a high-performance synchronous reluctance motor (SynRM) drive system, a novel maximum power factor control (MPFC) using a current angle controller with stator resistance and stator flux estimators is proposed. First, a traditional maximum power factor control system using a saliency ratio of the SynRM to generate a fixed current angle command is described. Since the saliency ratio requires offline prepreparation and cannot be adjusted automatically, it is difficult to improve the performance of the MPFC in different operating regions because of the increasing of manufacturing cost and time-consumption. Therefore, an intelligent-maximum power factor searching control (MPFSC) using a recurrent Chebyshev fuzzy neural network (RCFNN) current angle controller is developed for the speed control of a SynRM. In order to search the online optimal power factor (PF) points of the SynRM under different operating conditions, the RCFNN current angle controller is designed to produce the compensated current angle command. Moreover, a proportional-integral speed controller is adopted to generate the stator current magnitude command, and the proposed intelligent-MPFSC is employed to generate the current angle command. Furthermore, the proposed intelligent-MPFSC system is implemented in a 32-bit floating-point TMS320F28075 digital signal processor. Finally, from the experimental results, the current angle commands of the optimal PF can be effectively obtained online at different speed operating commands with varied load torque.

Robust model predictive current control without dead‐zone compensation

To solve the problems of large steady-state errors, high harmonic components and poor robustness of traditional current model prediction, a novel three-vector model predictive current control for permanent magnet synchronous motor is presented in this study. The vectors operating time is calculated with the combination of current increment and the unconventional modulation method is adopted to generate duty cycle containing dead zone. Adopting the current command correction link, the current deviation caused by inaccuracy parameter is reduced. Proved by experiment, novel control system not only the current steady-state error and current harmonic component are reduced, but also the parameter robustness is enhanced.

Implementation of PSO MPPT Technique for Wind Energy Conversion Systems

One major advantage of renewable energy is that it is sustainable and will never run out. They provide clean energy because they are non-pollutant and non-contributor to greenhouse effects and global warming. Renewable energy facilities generally require less maintenance than traditional generators. Their fuel being derived from natural and available resources reduces the costs of operation. The proposed PSO algorithm uses the dc current as the perturbing variable. The algorithm detects sudden wind speed changes indirectly through the dc-link voltage slope. The voltage slope is also used to enhance the tracking speed of the algorithm and to prevent the generator from stalling under rapid wind speed slow down conditions. The proposed method uses two modes of operation: A PSO mode with adaptive step size under slow wind speed fluctuation conditions, and a prediction mode employed under fast wind speed change conditions. The dc-link capacitor voltage slope reflects the acceleration information of the generator, which is then used to predict the next step size and direction of the current command.

Control of Rotor Field-Oriented Induction Motor Drive During Input Supply Voltage Sag

This article proposes a speed control strategy for rotor field-oriented induction motor (RFO-IM) drive during input supply voltage sag (VS). The purpose of this control technique is to maintain the torque and speed constant during VS condition. In the control technique, reference d-axis and q-axis current commands are obtained by solving the voltage, current, and torque constraints in the current plane. In the event of VS beyond a limit, the control is made such that the motor delivers the load torque with reduced speed. Traversal of operating points of the motor during input supply VS for constant load torque and rated reference speed are analyzed, and the limit of reduction in d-axis current reference is also obtained. Mathematical equations explaining the current trajectory to be followed during VS, VS limit, and the settling speed are derived. The proposed control is simulated in MATLAB/Simulink and experimental validation is conducted on a 3-hp IM.

Continuous Control Set Model Predictive Control of a Switch Reluctance Drive Using Lookup Tables

A problem of the switched reluctance drive is its natural torque pulsations, which are partially solved with finite control set model predictive control strategies. However, the continuous control set model predictive control, required for precise torque stabilization and predictable power converter behavior, needs sufficient computation resources, thus limiting its practical implementation. The proposed model predictive control strategy utilizes offline processing of the magnetization surface of the switched reluctance motor. This helps to obtain precalculated current references for each torque command and rotor angular position in the offline mode. In online mode, the model predictive control strategy implements the current commands using the magnetization surface for fast evaluation of the required voltage command for the power converter. The proposed strategy needs only two lookup table operations requiring very small computation time, making instant execution of the whole control system possible and thereby minimizing the control delay. The proposed solution was examined using a simulation model, which showed precise and rapid torque stabilization below rated speed.

Design and Implementation of Torque Control and Estimation for an Electric Hand-Tool

<p>This paper proposes the design and implementation of torque control and torque estimation for an electric hand-tool. This hand-tool does not require any torque transducer or any Hall-effect sensor. Only some low-cost resistances are used to measure the stator currents of a brushless DC motor, which is used to drive the hand-tool. Novel 3-phase current commands are proposed here to obtain greater torque than traditional 3-phase, square-wave current commands. The output torque of the hand-tool can be estimated and displayed by an LED display. A PI controller is used to achieve the current-loop control. A digital signal processor, TMS-320-F2808 that was manufactured by Texas Instruments, is used to execute the control and estimation algorithms. Experimental results show the correctness and feasibility of the proposed methods.</p>

Current-Scaling Gain Compensation of Motor Drives Under Locked-Rotor Condition Considering Inequality of Phase Resistances

This article proposes a current-scaling gain-compensation algorithm for motor drive applications under the locked-rotor condition. In heavy industrial applications, such as elevators and cranes, initial commissioning tests are performed with the rotor locked. To compensate for errors in the current-scaling gain, the proposed method controls the current in the d-q axis using two-phase current-sensing methods in a stationary reference frame. The three-phase scaling gains are then estimated using the resulting d-axis current command and output voltage and are compensated for using these estimations. The proposed method delivers accurate compensations by considering the inequality between phase resistances. The effectiveness of the proposed algorithm is verified through simulations and experiments.

Current-limit control method to prevent subsequent commutation failure of LCC-HVDC based on adaptive trigger voltage

With the wide construction of the line-commuted converter-based high-voltage direct current (LCC-HVDC), a large-scale AC/DC hybrid grid pattern has gradually formed. LCC-HVDC is prone to subsequent commutation failure (SCF) during the recovery process of first commutation failure (FCF). This phenomenon poses a great threat to the safe and stable operation of the power grid. LCC-HVDC is equipped with several controllers to prevent SCF. However, these controllers adopt preset fixed parameters and ignore the fault severity and LCC-HVDC self-regulation. The controller effect may not match the dynamic demand of the FCF recovery and even become the driving force of SCF. Accordingly, a new method is proposed on the basis of the quantification of the FCF recovery consequence, and it can avoid SCF by dynamically adjusting the DC current command according to a variable slope of Ud--Id - ord curve. First, the causes and influencing factors of SCF are presented by analyzing the recovery process of CF under the AC grid fault. Second, the correlation factors of the FCF recovery path are analyzed, and the idea of adaptive control against SCF based on the critical slope is proposed. Third, the critical slope of the Ud-Id - ord curve is derived with considering the influence of the initial state of the fault and constant extinction angle control. Then, a current-limit control method to prevent SCF based on the adaptive trigger voltage is proposed with considering the influence of the DC current variation on power angle stability. Finally, simulation results verify the effectiveness of the proposed method in preventing SCF.

Maximum Torque per Ampere Control for IPMSM Traction System Based on Current Angle Signal Injection Method

Rail transportation interior permanent magnet synchronous motor traction control system (IPMSM TCS) requires high torque output capability. Traditional algorithms used to find the maximum torque per ampere (MTPA) operating point in TCS have strong dependence on motor parameters. Because the algorithm is less robust to motor parameters, there will be deviation between the MTPA operating point and the actual value when the parameters change, so that it is difficult to guarantee the torque output capability of the traction system under different working conditions. This paper introduces a current angle signal injection control method (CASIM) to solve this problem. The proposed method tracks the MTPA operating point and generates d-axis current command according injecting an angle signal to current and making the partial derivative of torque to current angle equal to zero. At the same time, less motor parameters are needed to calculate the torque in this method. Consequently, in the process of looking for MTPA operating point, the accuracy is less affected by the variation of motor parameters. And also it does not inject any real signal to IPMSM, so that it does not increase copper and iron losses. Moreover, it is robust to speed mutation and torque disturbances. The effectiveness of CASIM proposed in this paper is proved by simulation and experiment results on an IPMSM TCS platform.

Analysis and compensation of circulating currents errors in modular multilevel converters in low‐frequency operation

Errors in the injected high-frequency circulating currents are originally investigated for modular multilevel converters (MMCs) in low-speed drive operation. The mathematical analysis reveals that the magnitude and phase errors in the injected circulating currents cause serious energy imbalance in the MMC arms, resulting in large voltage fluctuations in the submodules. Furthermore, these fluctuations get larger when the circulating currents are injected at higher frequencies, which reduces the drive system stability and damages the submodule capacitors. A remedy approach is proposed to minimise the error effects by adjusting the circulating current command. A full-scale system comprising a 1 MVA MMC and a 1 MW induction machine is simulated to verify the theoretical analysis. The experimental investigation of a down-scale MMC feeding an inductor is also conducted to validate the theoretical results.

A Novel Method for Implementing Harmonic Compensation with Multi-Inverters in a Micro-Grid

This paper presents a new multi-inverter-based compensation scheme for the harmonic and reactive influences in a micro-grid, which not only realizes the integration of renewable energy, but also combines the functions of improving power quality at the point of common coupling (PCC) simultaneously. The proposed method uses the remaining power energy in the inverter to implement local harmonic compensation, which achieves the flexible customization of power quality and economics. Specifically, an accurate and stable modulated hopping Discrete Fourier Transform (mHDFT) algorithm with merits of computation of a sparse DFT result is applied to measure the harmonic current. In addition, a proportional resonant (PR) controller selected to track the command current due to its infinite gain for a specific point ensures there is no steady-state error (ess). Besides, delay compensation and discretization by pre-swapping bilinear transformation are performed to improve the stability of the current loop and enable the controller for digital implementation respectively. The simulation results based on Matlab/Simulink are given to verify the performance of the proposed method.

Incremental Checkpointing for Fault-Tolerant Stream Processing Systems: A Data Structure Approach

As the demand of high-speed stream processing grows, in-memory databases are widely used to analyze streaming data. It is challenging for in-memory systems to meet the requirements of high throughput and data persistence at the same time since data are not stored in disks. ARIES logging and command logging are two popular logging methods. In current applications, both ARIES logging and command logging are necessary. However, no checkpointing mechanism includes both the functions of ARIES logging method and command logging method. Besides, adopting ARIES logging method in an in-memory database creates high overhead. Command logging records redundant commands and has high storage cost. To address the above issues, we utilize order-irrelevant characteristics of data structure and incremental checkpointing concepts to devise a data structure based incremental checkpointing (DSIC) mechanism. DSIC mechanism is a very low overhead checkpointing approach while retaining the features of ARIES logging and command logging. DSIC mechanism reduces more than 70 percent logging time of the existing logging scheme and saves 40 percent storage costs of the existing logging scheme.

Individual adaptive performance in computer-mediated work: a migration perspective

PurposeIn dynamic environments, employees should respond to changing demands carrying out actions to achieve proper knowledge of the information systems (IS) that they use (individual adaptation). However, few studies have investigated the determinants of this behaviour. This study proposes and empirically evaluates a cognitive-attitudinal model grounded in migration theory, which considers push, pull and mooring factors.Design/methodology/approachData collected from ERP users were analysed using partial least squares.FindingsCoherent with migration theory, the results show that the individual adapts influenced by push factors (dissatisfaction with their current command of the IS), pull factors (expected benefits from improving their command) and mooring factors (attitude to the adaptation process). Also, inertia and cost of adaption impact on attitude.Research limitations/implicationsThis study introduces migration theory to the IS literature as a basis for comprehensively explaining adaptation in organisational settings.Practical implicationsThe results suggest that management should: exhibit the instrumental benefits of a solid command of the IS; show the current gap in employee knowledge to revert it and, introduce changes to move employees out of their comfort zone to encourage ongoing learning and reduce resistance.Originality/valueWhile previous studies have focused on the implementation stage and the emotional factors to explain adaptation, this study intends to bridge this gap by investigating cognitive-attitudinal factors that trigger the intention to adapt in the post-adoption stage. The findings of this study are useful to researchers in adaptation behaviour, and to managers to promote IS learning for their staff.

Fuzzy Logic Speed Control of Permanent Magnet Synchronous Machine and Feedback Voltage Ripple Reduction in Flux-Weakening Operation Region

Voltage feedback flux-weakening control has the advantages of simplicity and robustness against parameter variation. However, due to less voltage control margin in the flux-weakening region, the increased feedback voltage ripple could deteriorate the system performance in the flux-weakening region and may even cause oscillation. In this article, based on a nonsalient permanent magnet synchronous machine, the steady-state feedback voltage ripple in the flux-weakening region are analyzed first. It shows that the feedback voltage ripple caused by the current command ripple could dominate in some flux-weakening regions. Consequently, the speed bandwidth based on the conventional speed proportional-integral (PI) controller in the flux-weakening region can be hardly increased, which leads to poor dynamic performance. In order to obtain both fast speed dynamics and less steady-state ripple, especially in the flux-weakening region, an adaptive fuzzy logic (FLC) speed controller is designed and compared with the conventional speed PI controller. With the adaptive FLC, the dc-link voltage utilization can be increased and better flux-weakening capability can be obtained. Finally, the improved performances are verified by the experimental results.