The Experts below are selected from a list of 24759 Experts worldwide ranked by ideXlab platform
Yongchang Zhang - One of the best experts on this subject based on the ideXlab platform.
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Performance Improvement of Direct Power Control of PWM Rectifier Under Unbalanced Network
IEEE Transactions on Power Electronics, 2017Co-Authors: Yongchang Zhang, Jihao GaoAbstract:Direct power control (DPC) has attracted wide attention due to its advantages of simple structure, quick response, strong robustness, and elimination of current regulation/pulse width modulation blocks. However, Conventional Table-based DPC cannot work well when the grid voltages are unbalanced. Some work has been done on DPC to mitigate the influence of grid unbalance by adding power compensations to the original power references. However, they are usually complicated due to the positive/negative-sequence extraction of grid voltage and/or currents. Furthermore, applying only one voltage vector during one control period leads to high steady-state power ripples. This paper proposes an improved DPC by using a new definition of instantaneous reactive power. As a result, the distortion in grid current is eliminated, and constant active power and new reactive power are obtained. Neither complicated calculation of power compensation nor positive/negative-sequence extraction of grid voltage/current is required. The corresponding switching Table suiTable to regulate both active power and the new reactive power is established. Furthermore, the concept of duty cycle control is introduced to further improve the steady-state performance. Both simulation and experimental results are presented to confirm the theoretical study and the effectiveness of the proposed method.
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Direct power control of doubly fed induction generator based on extended power theory under unbalanced grid condition
2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia (IFEEC 2017 - ECCE Asia), 2017Co-Authors: Yongchang ZhangAbstract:Conventional Table-based direct power control (DPC) achieves quick dynamic response with very simple structure, which has been widely studied for power control of doubly fed induction generator (DFIG) system. However, DPC presents high steady power ripples and rich current harmonics with variable switching frequency. Furthermore, it would produce highly distorted stator current and power oscillations under unbalanced grid voltage conditions if no special measure is taken. This paper proposes a novel DPC method to solve the problems above. On one hand, it uses space vector modulation (SVM) to synthesis the rotor voltage reference, which is obtained based on the principle of deadbeat power control. As a result, the switching frequency is constant and the power ripples as well as current harmonics are significantly reduced. On the other hand, it uses extended power theory to replace the Conventional instantaneous power theory, which can achieve autonomous active power ripple elimination in the stator side with sinusoidal stator currents even under unbalanced grid voltage condition. The positive/negative sequence extraction of stator voltages and currents are not required, which further simplifies the structure of system. The effectiveness of the proposed method is validated by the presented simulation results from a 15 kW DFIG system.
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direct power control of a pulse width modulation rectifier using space vector modulation under unbalanced grid voltages
IEEE Transactions on Power Electronics, 2015Co-Authors: Yongchang Zhang, Changqi QuAbstract:Compared with Conventional Table-based direct power control (DPC), DPC using space vector modulation (DPC-SVM) exhibits several specific features, such as a constant switching frequency and small ripples in both active power and reactive power. However, Conventional DPC-SVM exhibits highly distorted grid currents when the grid voltages are unbalanced. In this study, we propose a novel and simple DPC-SVM that is effective under both ideal and unbalanced grid voltage conditions by using an extension of original instantaneous power theory. After deducing the power slopes of both active power and reactive power, the suiTable converter voltage reference to nullify the errors of active power and reactive power is analytically derived, which is subsequently synthesized by SVM. The proposed DPC-SVM does not require the extraction of complex positive/negative sequence from the grid voltage/current or power compensation. Compared to prior DPC-SVM using original imaginary power, the proposed method exhibits much better performance by obtaining highly sinusoidal line currents and eliminating twice grid-frequency ripples in both active power and the reactive power under unbalanced conditions. Simulations and experimental results supported the theoretical study and confirmed the effectiveness of the proposed method.
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Direct power control of PWM rectifier with optimal duty ratio under unbalanced network
2015 9th International Conference on Power Electronics and ECCE Asia (ICPE-ECCE Asia), 2015Co-Authors: Yongchang Zhang, Yingchao Zhang, Longhan CaoAbstract:Direct power control (DPC) attracted wide attention due to its advantages of simple structure, quick response, strong robustness and elimination of current regulation/PWM blocks. However, Conventional Table-based DPC cannot work well when grid voltage is unbalanced. This paper proposes an improved DPC by using a new definition of instantaneous reactive power. As a result, the distortion in grid current is eliminated and constant active power and new reactive power are obtained. Neither complicated calculation of power compensation nor positive/negative sequence extraction of grid voltage/current is required. The corresponding switching Table suiTable to regulate both active power and the new reactive power is established. Furthermore, the concept of duty cycle control is introduced to further improve the steady state performance of Conventional DPC. Experimental results are presented to confirm the theoretical study and the effectiveness of the proposed method.
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Table-Based Direct Power Control for Three-Phase AC/DC Converters Under Unbalanced Grid Voltages
IEEE Transactions on Power Electronics, 2015Co-Authors: Yongchang ZhangAbstract:This paper proposes a simple but effective direct power control (DPC) strategy for three-phase ac/dc converters operating under unbalanced grid voltage conditions. An extended instantaneous power theory is adapted and applied in the proposed DPC, where the reactive power is expressed in the form of dot product of grid currents and delayed grid voltages. Neither complicated positive/negative sequence extraction of grid voltage/current nor power compensation is required. The switching Table suiTable to control both active power and reactive power is constructed by analyzing the influence of each converter voltage vector on power slopes. Compared to Conventional Table-based DPC using original pq theory, the proposed DPC achieves constant active power and reactive power as well as sinusoidal grid currents, while maintaining the simplicity and robustness as much as possible. The presented simulation and experimental results confirm the theoretical study and the effectiveness of the proposed method.
J E Bobrow - One of the best experts on this subject based on the ideXlab platform.
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comparison of three dimensional assist as needed robotic arm hand movement training provided with pneu wrex to Conventional Tabletop therapy after chronic stroke
American Journal of Physical Medicine & Rehabilitation, 2012Co-Authors: David J Reinkensmeyer, Eric T Wolbrecht, Vicky Chan, Cathy Chou, Steven C Cramer, J E BobrowAbstract:ObjectiveRobot-assisted movement training can help individuals with stroke reduce arm and hand impairment, but robot therapy is typically only about as effective as Conventional therapy. Refining the way that robots assist during training may make them more effective than Conventional therapy. Here we measured the therapeutic effect of a robot that required individuals with a stroke to achieve virtual tasks in three dimensions against gravity.DesignThe robot continuously estimated how much assistance patients needed to perform the tasks and provided slightly less assistance than needed in order to reduce patient slacking. Individuals with a chronic stroke (n = 26, baseline upper extremity Fugl-Meyer score = 23 ± 8) were randomized into two groups and underwent 24 one hour training sessions over 2 months. One group received the assist-as-needed robot training and the other received Conventional Table top therapy with the supervision of a physical therapist.ResultsTraining helped both groups significantly reduce their motor impairment, as measured by the primary outcome measure, the Fugl-Meyer score, but the improvement was small (3.0 ± 4.9 points for robot therapy, versus 0.9 ± 1.7 for Conventional therapy). There was a trend for greater reduction for the robot trained group (p = 0.07). The robot group largely sustained this gain at the three-month follow-up. The robot-trained group also experienced significant improvements in Box and Blocks score and hand grip strength, while the control group did not, but these improvements were not sustained at follow-up. In addition, the robot-trained group showed a trend toward greater improvement in sensory function, as measured by the Nottingham Sensory Test (p = 0.06).ConclusionsThese results suggest that, in patients with chronic stroke and moderate-severe deficits, assisting in three dimensional virtual tasks with an assist-as-needed controller may make robotic training more effective than Conventional Table top training.
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Comparison of three-dimensional, assist-as-needed robotic arm/hand movement training provided with Pneu-WREX to Conventional Tabletop therapy after chronic stroke.
American Journal of Physical Medicine & Rehabilitation, 2012Co-Authors: David J Reinkensmeyer, Eric T Wolbrecht, Vicky Chan, Cathy Chou, Steven C Cramer, J E BobrowAbstract:ObjectiveRobot-assisted movement training can help individuals with stroke reduce arm and hand impairment, but robot therapy is typically only about as effective as Conventional therapy. Refining the way that robots assist during training may make them more effective than Conventional therapy. Here we measured the therapeutic effect of a robot that required individuals with a stroke to achieve virtual tasks in three dimensions against gravity.DesignThe robot continuously estimated how much assistance patients needed to perform the tasks and provided slightly less assistance than needed in order to reduce patient slacking. Individuals with a chronic stroke (n = 26, baseline upper extremity Fugl-Meyer score = 23 ± 8) were randomized into two groups and underwent 24 one hour training sessions over 2 months. One group received the assist-as-needed robot training and the other received Conventional Table top therapy with the supervision of a physical therapist.ResultsTraining helped both groups significantly reduce their motor impairment, as measured by the primary outcome measure, the Fugl-Meyer score, but the improvement was small (3.0 ± 4.9 points for robot therapy, versus 0.9 ± 1.7 for Conventional therapy). There was a trend for greater reduction for the robot trained group (p = 0.07). The robot group largely sustained this gain at the three-month follow-up. The robot-trained group also experienced significant improvements in Box and Blocks score and hand grip strength, while the control group did not, but these improvements were not sustained at follow-up. In addition, the robot-trained group showed a trend toward greater improvement in sensory function, as measured by the Nottingham Sensory Test (p = 0.06).ConclusionsThese results suggest that, in patients with chronic stroke and moderate-severe deficits, assisting in three dimensional virtual tasks with an assist-as-needed controller may make robotic training more effective than Conventional Table top training.
Changqi Qu - One of the best experts on this subject based on the ideXlab platform.
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direct power control of a pulse width modulation rectifier using space vector modulation under unbalanced grid voltages
IEEE Transactions on Power Electronics, 2015Co-Authors: Yongchang Zhang, Changqi QuAbstract:Compared with Conventional Table-based direct power control (DPC), DPC using space vector modulation (DPC-SVM) exhibits several specific features, such as a constant switching frequency and small ripples in both active power and reactive power. However, Conventional DPC-SVM exhibits highly distorted grid currents when the grid voltages are unbalanced. In this study, we propose a novel and simple DPC-SVM that is effective under both ideal and unbalanced grid voltage conditions by using an extension of original instantaneous power theory. After deducing the power slopes of both active power and reactive power, the suiTable converter voltage reference to nullify the errors of active power and reactive power is analytically derived, which is subsequently synthesized by SVM. The proposed DPC-SVM does not require the extraction of complex positive/negative sequence from the grid voltage/current or power compensation. Compared to prior DPC-SVM using original imaginary power, the proposed method exhibits much better performance by obtaining highly sinusoidal line currents and eliminating twice grid-frequency ripples in both active power and the reactive power under unbalanced conditions. Simulations and experimental results supported the theoretical study and confirmed the effectiveness of the proposed method.
David J Reinkensmeyer - One of the best experts on this subject based on the ideXlab platform.
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comparison of three dimensional assist as needed robotic arm hand movement training provided with pneu wrex to Conventional Tabletop therapy after chronic stroke
American Journal of Physical Medicine & Rehabilitation, 2012Co-Authors: David J Reinkensmeyer, Eric T Wolbrecht, Vicky Chan, Cathy Chou, Steven C Cramer, J E BobrowAbstract:ObjectiveRobot-assisted movement training can help individuals with stroke reduce arm and hand impairment, but robot therapy is typically only about as effective as Conventional therapy. Refining the way that robots assist during training may make them more effective than Conventional therapy. Here we measured the therapeutic effect of a robot that required individuals with a stroke to achieve virtual tasks in three dimensions against gravity.DesignThe robot continuously estimated how much assistance patients needed to perform the tasks and provided slightly less assistance than needed in order to reduce patient slacking. Individuals with a chronic stroke (n = 26, baseline upper extremity Fugl-Meyer score = 23 ± 8) were randomized into two groups and underwent 24 one hour training sessions over 2 months. One group received the assist-as-needed robot training and the other received Conventional Table top therapy with the supervision of a physical therapist.ResultsTraining helped both groups significantly reduce their motor impairment, as measured by the primary outcome measure, the Fugl-Meyer score, but the improvement was small (3.0 ± 4.9 points for robot therapy, versus 0.9 ± 1.7 for Conventional therapy). There was a trend for greater reduction for the robot trained group (p = 0.07). The robot group largely sustained this gain at the three-month follow-up. The robot-trained group also experienced significant improvements in Box and Blocks score and hand grip strength, while the control group did not, but these improvements were not sustained at follow-up. In addition, the robot-trained group showed a trend toward greater improvement in sensory function, as measured by the Nottingham Sensory Test (p = 0.06).ConclusionsThese results suggest that, in patients with chronic stroke and moderate-severe deficits, assisting in three dimensional virtual tasks with an assist-as-needed controller may make robotic training more effective than Conventional Table top training.
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Comparison of three-dimensional, assist-as-needed robotic arm/hand movement training provided with Pneu-WREX to Conventional Tabletop therapy after chronic stroke.
American Journal of Physical Medicine & Rehabilitation, 2012Co-Authors: David J Reinkensmeyer, Eric T Wolbrecht, Vicky Chan, Cathy Chou, Steven C Cramer, J E BobrowAbstract:ObjectiveRobot-assisted movement training can help individuals with stroke reduce arm and hand impairment, but robot therapy is typically only about as effective as Conventional therapy. Refining the way that robots assist during training may make them more effective than Conventional therapy. Here we measured the therapeutic effect of a robot that required individuals with a stroke to achieve virtual tasks in three dimensions against gravity.DesignThe robot continuously estimated how much assistance patients needed to perform the tasks and provided slightly less assistance than needed in order to reduce patient slacking. Individuals with a chronic stroke (n = 26, baseline upper extremity Fugl-Meyer score = 23 ± 8) were randomized into two groups and underwent 24 one hour training sessions over 2 months. One group received the assist-as-needed robot training and the other received Conventional Table top therapy with the supervision of a physical therapist.ResultsTraining helped both groups significantly reduce their motor impairment, as measured by the primary outcome measure, the Fugl-Meyer score, but the improvement was small (3.0 ± 4.9 points for robot therapy, versus 0.9 ± 1.7 for Conventional therapy). There was a trend for greater reduction for the robot trained group (p = 0.07). The robot group largely sustained this gain at the three-month follow-up. The robot-trained group also experienced significant improvements in Box and Blocks score and hand grip strength, while the control group did not, but these improvements were not sustained at follow-up. In addition, the robot-trained group showed a trend toward greater improvement in sensory function, as measured by the Nottingham Sensory Test (p = 0.06).ConclusionsThese results suggest that, in patients with chronic stroke and moderate-severe deficits, assisting in three dimensional virtual tasks with an assist-as-needed controller may make robotic training more effective than Conventional Table top training.
Steven C Cramer - One of the best experts on this subject based on the ideXlab platform.
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comparison of three dimensional assist as needed robotic arm hand movement training provided with pneu wrex to Conventional Tabletop therapy after chronic stroke
American Journal of Physical Medicine & Rehabilitation, 2012Co-Authors: David J Reinkensmeyer, Eric T Wolbrecht, Vicky Chan, Cathy Chou, Steven C Cramer, J E BobrowAbstract:ObjectiveRobot-assisted movement training can help individuals with stroke reduce arm and hand impairment, but robot therapy is typically only about as effective as Conventional therapy. Refining the way that robots assist during training may make them more effective than Conventional therapy. Here we measured the therapeutic effect of a robot that required individuals with a stroke to achieve virtual tasks in three dimensions against gravity.DesignThe robot continuously estimated how much assistance patients needed to perform the tasks and provided slightly less assistance than needed in order to reduce patient slacking. Individuals with a chronic stroke (n = 26, baseline upper extremity Fugl-Meyer score = 23 ± 8) were randomized into two groups and underwent 24 one hour training sessions over 2 months. One group received the assist-as-needed robot training and the other received Conventional Table top therapy with the supervision of a physical therapist.ResultsTraining helped both groups significantly reduce their motor impairment, as measured by the primary outcome measure, the Fugl-Meyer score, but the improvement was small (3.0 ± 4.9 points for robot therapy, versus 0.9 ± 1.7 for Conventional therapy). There was a trend for greater reduction for the robot trained group (p = 0.07). The robot group largely sustained this gain at the three-month follow-up. The robot-trained group also experienced significant improvements in Box and Blocks score and hand grip strength, while the control group did not, but these improvements were not sustained at follow-up. In addition, the robot-trained group showed a trend toward greater improvement in sensory function, as measured by the Nottingham Sensory Test (p = 0.06).ConclusionsThese results suggest that, in patients with chronic stroke and moderate-severe deficits, assisting in three dimensional virtual tasks with an assist-as-needed controller may make robotic training more effective than Conventional Table top training.
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Comparison of three-dimensional, assist-as-needed robotic arm/hand movement training provided with Pneu-WREX to Conventional Tabletop therapy after chronic stroke.
American Journal of Physical Medicine & Rehabilitation, 2012Co-Authors: David J Reinkensmeyer, Eric T Wolbrecht, Vicky Chan, Cathy Chou, Steven C Cramer, J E BobrowAbstract:ObjectiveRobot-assisted movement training can help individuals with stroke reduce arm and hand impairment, but robot therapy is typically only about as effective as Conventional therapy. Refining the way that robots assist during training may make them more effective than Conventional therapy. Here we measured the therapeutic effect of a robot that required individuals with a stroke to achieve virtual tasks in three dimensions against gravity.DesignThe robot continuously estimated how much assistance patients needed to perform the tasks and provided slightly less assistance than needed in order to reduce patient slacking. Individuals with a chronic stroke (n = 26, baseline upper extremity Fugl-Meyer score = 23 ± 8) were randomized into two groups and underwent 24 one hour training sessions over 2 months. One group received the assist-as-needed robot training and the other received Conventional Table top therapy with the supervision of a physical therapist.ResultsTraining helped both groups significantly reduce their motor impairment, as measured by the primary outcome measure, the Fugl-Meyer score, but the improvement was small (3.0 ± 4.9 points for robot therapy, versus 0.9 ± 1.7 for Conventional therapy). There was a trend for greater reduction for the robot trained group (p = 0.07). The robot group largely sustained this gain at the three-month follow-up. The robot-trained group also experienced significant improvements in Box and Blocks score and hand grip strength, while the control group did not, but these improvements were not sustained at follow-up. In addition, the robot-trained group showed a trend toward greater improvement in sensory function, as measured by the Nottingham Sensory Test (p = 0.06).ConclusionsThese results suggest that, in patients with chronic stroke and moderate-severe deficits, assisting in three dimensional virtual tasks with an assist-as-needed controller may make robotic training more effective than Conventional Table top training.