The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
K Gopakumar - One of the best experts on this subject based on the ideXlab platform.
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timing calculations for a general n level dodecagonal space vector structure using only Reference Phase voltages
IEEE Transactions on Industrial Electronics, 2016Co-Authors: Sudharshan R Kaarthik, K Gopakumar, Carlo Cecati, I NagyAbstract:Multilevel inverters with dodecagonal (12-sided polygon) voltage space vector (SV) structures have advantages like extension of linear modulation range, elimination of fifth and seventh harmonics in Phase voltages and currents for the full modulation range including extreme 12-step operation, reduced device voltage ratings, lesser dv/dt stresses on devices and motor Phase windings resulting in lower EMI/EMC problems, and lower switching frequency—making it more suitable for high-power drive applications. This paper proposes a simple method to obtain pulsewidth modulation (PWM) timings for a dodecagonal voltage SV structure using only sampled Reference voltages. In addition to this, a carrier-based method for obtaining the PWM timings for a general N-level dodecagonal structure is proposed in this paper for the first time. The algorithm outputs the triangle information and the PWM timing values which can be set as the compare values for any carrier-based hardware PWM module to obtain SV PWM like switching sequences. The proposed method eliminates the need for angle estimation, computation of modulation indices, and iterative search algorithms that are typical in multilevel dodecagonal SV systems. The proposed PWM scheme was implemented on a five-level dodecagonal SV structure. Exhaustive simulation and experimental results for steady-state and transient conditions are presented to validate the proposed method.
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a medium voltage inverter fed im drive using multilevel 12 sided polygonal vectors with nearly constant switching frequency current hysteresis controller
IEEE Transactions on Industrial Electronics, 2014Co-Authors: Najath Abdul Azeez, K Gopakumar, Anubrata Dey, K Mathew, Jaison Mathew, Marian P KazmierkowskiAbstract:In this paper, a current error space vector (CESV)-based hysteresis current controller for a multilevel 12-sided voltage space vector-based inverter-fed induction motor (IM) drive is proposed. The proposed controller gives a nearly constant switching frequency operation throughout different speeds in the linear modulation region. It achieves the elimination of 6n ±1, n = odd harmonics from the Phase voltages and currents in the entire modulation range, with an increase in the linear modulation range. It also exhibits fast dynamic behavior under different transient conditions and has a simple controller implementation. Nearly constant switching frequency is obtained by matching the steady-state CESV boundaries of the proposed controller with that of a constant switching frequency SVPWM-based drive. In the proposed controller, the CESV Reference boundaries are computed online, using the switching dwell time and voltage error vector of each applied vector. These quantities are calculated from estimated sampled Reference Phase voltages. Vector change is decided by projecting the actual current error along the computed hysteresis space vector boundary of the presently applied vector. The estimated Reference Phase voltages are found from the stator current error ripple and the parameters of the IM.
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space vector pwm signal generation for multilevel inverters using only the sampled amplitudes of Reference Phase voltages
IEE Proceedings - Electric Power Applications, 2005Co-Authors: R S Kanchan, K K Mohapatra, M R Baiju, P P Ouseph, K GopakumarAbstract:A pulse width modulation (PWM) scheme for multilevel inverters is proposed. The proposed PWM scheme generates the inverter leg switching times, from the sampled Reference Phase voltage amplitudes and centres the switching times for the middle vectors, in a sampling interval, as in the case of conventional space vector PWM (SVPWM). The SVPWM scheme, presented for multilevel inverters, can also work in the overmodulation range, using only the sampled amplitudes of Reference Phase voltages. The present PWM technique does not involve any sector identification and considerably reduces the computation time when compared to the conventional space vector PWM technique. The present PWM signal generation scheme can be used for any multilevel inverter configuration. A five-level inverter configuration, using an open-ended winding induction motor drive, is used to verify the SVPWM generation scheme experimentally.
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A Space Vector based PWM Switching Scheme for the reduction of Common-Mode Voltages for a Dual Inverter fed Open-end Winding Induction motor Drive
IEEE 36th Conference on Power Electronics Specialists 2005., 2005Co-Authors: V T Somasekhar, S. Srinivas, K GopakumarAbstract:It has been demonstrated that two two-level inverters connected at each end of an open end winding induction motor are capable of achieving the functionality of a three-level inverter. In this paper, a space vector based PWM switching scheme for the dual inverter fed open end winding induction motor drive is proposed. The common-mode voltages associated with such a drive are significantly reduced with the proposed PWM strategy., compared to the work reported earlier. In this work, the redundancy of the space vector combinations at a particular location is exploited, to reduce the common-mode voltages at lower indices of modulation. In the work reported earlier, the common mode voltages were enhanced with the decrement of modulation index. On the contrary, the common-mode voltages are reduced with the decrement of the modulation index with the PWM strategy presented in this paper. This PWM scheme for open-end winding induction motor drives may be suitable for applications, which call for frequent starting and run at low speeds. This scheme employs only the instantaneous Reference Phase voltages for the implementation. The time consuming task of sector identification is avoided with the proposed switching scheme. Another advantage with this scheme is that it does not require any look-up tables for its implementation. The scheme ensures a smooth switching all through, ensuring equal switching duty for both the inverters
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a space vector based pwm method using only the instantaneous amplitudes of Reference Phase voltages for three level inverters
Epe Journal, 2003Co-Authors: K Gopakumar, V T Somasekhar, K K Mohapatra, L UmamandAbstract:This paper presents a space vector based PWM method for the 3-level inverter. The three level inverter space phasors are located in 19 locations forming 24 sectors. The instantaneous Reference space phasor is generated by switching between the three vectors forming the sector in which the tip of the Reference vector lies. The proposed PWM method does not require the sector identification and look up tables to select the appropriate vectors. The inverter leg switching times are directly obtained from the instantaneous Reference Phase voltage amplitudes and the inverter switching vectors are automatically generated . The inverter leg switching times and the appropriate vectors are obtained using an algorithm, which does not involve computations like square root or coordinate transformations. The proposed method is implemented on a 1hp induction motor drive and the experiment results are presented.
J Wang - One of the best experts on this subject based on the ideXlab platform.
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tu ab 202 05 gpu based 4d deformable image registration using adaptive tetrahedral mesh modeling
Medical Physics, 2016Co-Authors: Zichun Zhong, L Zhuang, J Wang, Haibin Chen, Xin ZhenAbstract:Purpose: Deformable image registration (DIR) has been employed today as an automated and effective segmentation method to transfer tumor or organ contours from the planning image to daily images, instead of manual segmentation. However, the computational time and accuracy of current DIR approaches are still insufficient for online adaptive radiation therapy (ART), which requires real-time and high-quality image segmentation, especially in a large datasets of 4D-CT images. The objective of this work is to propose a new DIR algorithm, with fast computational speed and high accuracy, by using adaptive feature-based tetrahedral meshing and GPU-based parallelization. Methods: The first step is to generate the adaptive tetrahedral mesh based on the image features of a Reference Phase of 4D-CT, so that the deformation can be well captured and accurately diffused from the mesh vertices to voxels of the image volume. Subsequently, the deformation vector fields (DVF) and other Phases of 4D-CT can be obtained by matching each Phase of the target 4D-CT images with the corresponding deformed Reference Phase. The proposed 4D DIR method is implemented on GPU, resulting in significantly increasing the computational efficiency due to its parallel computing ability. Results: A 4D NCAT digital phantom was used to test the efficiency and accuracy of our method. Both the image and DVF results show that the fine structures and shapes of lung are well preserved, and the tumor position is well captured, i.e., 3D distance error is 1.14 mm. Compared to the previous voxel-based CPU implementation of DIR, such as demons, the proposed method is about 160x faster for registering a 10-Phase 4D-CT with a Phase dimension of 256×256×150. Conclusion: The proposed 4D DIR method uses feature-based mesh and GPU-based parallelism, which demonstrates the capability to compute both high-quality image and motion results, with significant improvement on the computational speed.
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su d 207 04 gpu based 4d cone beam ct reconstruction using adaptive meshing method
Medical Physics, 2015Co-Authors: Zichun Zhong, J Wang, P Iyengar, W Mao, Xiaohu GuoAbstract:Purpose: Due to the limited number of projections at each Phase, the image quality of a four-dimensional cone-beam CT (4D-CBCT) is often degraded, which decreases the accuracy of subsequent motion modeling. One of the promising methods is the simultaneous motion estimation and image reconstruction (SMEIR) approach. The objective of this work is to enhance the computational speed of the SMEIR algorithm using adaptive feature-based tetrahedral meshing and GPU-based parallelization. Methods: The first step is to generate the tetrahedral mesh based on the features of a Reference Phase 4D-CBCT, so that the deformation can be well captured and accurately diffused from the mesh vertices to voxels of the image volume. After the mesh generation, the updated motion model and other Phases of 4D-CBCT can be obtained by matching the 4D-CBCT projection images at each Phase with the corresponding forward projections of the deformed Reference Phase of 4D-CBCT. The entire process of this 4D-CBCT reconstruction method is implemented on GPU, resulting in significantly increasing the computational efficiency due to its tremendous parallel computing ability. Results: A 4D XCAT digital phantom was used to test the proposed mesh-based image reconstruction algorithm. The image Result shows both bone structures and inside of the lungmore » are well-preserved and the tumor position can be well captured. Compared to the previous voxel-based CPU implementation of SMEIR, the proposed method is about 157 times faster for reconstructing a 10 -Phase 4D-CBCT with dimension 256×256×150. Conclusion: The GPU-based parallel 4D CBCT reconstruction method uses the feature-based mesh for estimating motion model and demonstrates equivalent image Result with previous voxel-based SMEIR approach, with significantly improved computational speed.« less
Zichun Zhong - One of the best experts on this subject based on the ideXlab platform.
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tu ab 202 05 gpu based 4d deformable image registration using adaptive tetrahedral mesh modeling
Medical Physics, 2016Co-Authors: Zichun Zhong, L Zhuang, J Wang, Haibin Chen, Xin ZhenAbstract:Purpose: Deformable image registration (DIR) has been employed today as an automated and effective segmentation method to transfer tumor or organ contours from the planning image to daily images, instead of manual segmentation. However, the computational time and accuracy of current DIR approaches are still insufficient for online adaptive radiation therapy (ART), which requires real-time and high-quality image segmentation, especially in a large datasets of 4D-CT images. The objective of this work is to propose a new DIR algorithm, with fast computational speed and high accuracy, by using adaptive feature-based tetrahedral meshing and GPU-based parallelization. Methods: The first step is to generate the adaptive tetrahedral mesh based on the image features of a Reference Phase of 4D-CT, so that the deformation can be well captured and accurately diffused from the mesh vertices to voxels of the image volume. Subsequently, the deformation vector fields (DVF) and other Phases of 4D-CT can be obtained by matching each Phase of the target 4D-CT images with the corresponding deformed Reference Phase. The proposed 4D DIR method is implemented on GPU, resulting in significantly increasing the computational efficiency due to its parallel computing ability. Results: A 4D NCAT digital phantom was used to test the efficiency and accuracy of our method. Both the image and DVF results show that the fine structures and shapes of lung are well preserved, and the tumor position is well captured, i.e., 3D distance error is 1.14 mm. Compared to the previous voxel-based CPU implementation of DIR, such as demons, the proposed method is about 160x faster for registering a 10-Phase 4D-CT with a Phase dimension of 256×256×150. Conclusion: The proposed 4D DIR method uses feature-based mesh and GPU-based parallelism, which demonstrates the capability to compute both high-quality image and motion results, with significant improvement on the computational speed.
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su d 207 04 gpu based 4d cone beam ct reconstruction using adaptive meshing method
Medical Physics, 2015Co-Authors: Zichun Zhong, J Wang, P Iyengar, W Mao, Xiaohu GuoAbstract:Purpose: Due to the limited number of projections at each Phase, the image quality of a four-dimensional cone-beam CT (4D-CBCT) is often degraded, which decreases the accuracy of subsequent motion modeling. One of the promising methods is the simultaneous motion estimation and image reconstruction (SMEIR) approach. The objective of this work is to enhance the computational speed of the SMEIR algorithm using adaptive feature-based tetrahedral meshing and GPU-based parallelization. Methods: The first step is to generate the tetrahedral mesh based on the features of a Reference Phase 4D-CBCT, so that the deformation can be well captured and accurately diffused from the mesh vertices to voxels of the image volume. After the mesh generation, the updated motion model and other Phases of 4D-CBCT can be obtained by matching the 4D-CBCT projection images at each Phase with the corresponding forward projections of the deformed Reference Phase of 4D-CBCT. The entire process of this 4D-CBCT reconstruction method is implemented on GPU, resulting in significantly increasing the computational efficiency due to its tremendous parallel computing ability. Results: A 4D XCAT digital phantom was used to test the proposed mesh-based image reconstruction algorithm. The image Result shows both bone structures and inside of the lungmore » are well-preserved and the tumor position can be well captured. Compared to the previous voxel-based CPU implementation of SMEIR, the proposed method is about 157 times faster for reconstructing a 10 -Phase 4D-CBCT with dimension 256×256×150. Conclusion: The GPU-based parallel 4D CBCT reconstruction method uses the feature-based mesh for estimating motion model and demonstrates equivalent image Result with previous voxel-based SMEIR approach, with significantly improved computational speed.« less
V T Somasekhar - One of the best experts on this subject based on the ideXlab platform.
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A Space Vector based PWM Switching Scheme for the reduction of Common-Mode Voltages for a Dual Inverter fed Open-end Winding Induction motor Drive
IEEE 36th Conference on Power Electronics Specialists 2005., 2005Co-Authors: V T Somasekhar, S. Srinivas, K GopakumarAbstract:It has been demonstrated that two two-level inverters connected at each end of an open end winding induction motor are capable of achieving the functionality of a three-level inverter. In this paper, a space vector based PWM switching scheme for the dual inverter fed open end winding induction motor drive is proposed. The common-mode voltages associated with such a drive are significantly reduced with the proposed PWM strategy., compared to the work reported earlier. In this work, the redundancy of the space vector combinations at a particular location is exploited, to reduce the common-mode voltages at lower indices of modulation. In the work reported earlier, the common mode voltages were enhanced with the decrement of modulation index. On the contrary, the common-mode voltages are reduced with the decrement of the modulation index with the PWM strategy presented in this paper. This PWM scheme for open-end winding induction motor drives may be suitable for applications, which call for frequent starting and run at low speeds. This scheme employs only the instantaneous Reference Phase voltages for the implementation. The time consuming task of sector identification is avoided with the proposed switching scheme. Another advantage with this scheme is that it does not require any look-up tables for its implementation. The scheme ensures a smooth switching all through, ensuring equal switching duty for both the inverters
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a space vector based pwm method using only the instantaneous amplitudes of Reference Phase voltages for three level inverters
Epe Journal, 2003Co-Authors: K Gopakumar, V T Somasekhar, K K Mohapatra, L UmamandAbstract:This paper presents a space vector based PWM method for the 3-level inverter. The three level inverter space phasors are located in 19 locations forming 24 sectors. The instantaneous Reference space phasor is generated by switching between the three vectors forming the sector in which the tip of the Reference vector lies. The proposed PWM method does not require the sector identification and look up tables to select the appropriate vectors. The inverter leg switching times are directly obtained from the instantaneous Reference Phase voltage amplitudes and the inverter switching vectors are automatically generated . The inverter leg switching times and the appropriate vectors are obtained using an algorithm, which does not involve computations like square root or coordinate transformations. The proposed method is implemented on a 1hp induction motor drive and the experiment results are presented.
I Nagy - One of the best experts on this subject based on the ideXlab platform.
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timing calculations for a general n level dodecagonal space vector structure using only Reference Phase voltages
IEEE Transactions on Industrial Electronics, 2016Co-Authors: Sudharshan R Kaarthik, K Gopakumar, Carlo Cecati, I NagyAbstract:Multilevel inverters with dodecagonal (12-sided polygon) voltage space vector (SV) structures have advantages like extension of linear modulation range, elimination of fifth and seventh harmonics in Phase voltages and currents for the full modulation range including extreme 12-step operation, reduced device voltage ratings, lesser dv/dt stresses on devices and motor Phase windings resulting in lower EMI/EMC problems, and lower switching frequency—making it more suitable for high-power drive applications. This paper proposes a simple method to obtain pulsewidth modulation (PWM) timings for a dodecagonal voltage SV structure using only sampled Reference voltages. In addition to this, a carrier-based method for obtaining the PWM timings for a general N-level dodecagonal structure is proposed in this paper for the first time. The algorithm outputs the triangle information and the PWM timing values which can be set as the compare values for any carrier-based hardware PWM module to obtain SV PWM like switching sequences. The proposed method eliminates the need for angle estimation, computation of modulation indices, and iterative search algorithms that are typical in multilevel dodecagonal SV systems. The proposed PWM scheme was implemented on a five-level dodecagonal SV structure. Exhaustive simulation and experimental results for steady-state and transient conditions are presented to validate the proposed method.