The Experts below are selected from a list of 14262 Experts worldwide ranked by ideXlab platform
Xin Zhang - One of the best experts on this subject based on the ideXlab platform.
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source side series virtual impedance control to improve the Cascaded System stability and the dynamic performance of its source converter
IEEE Transactions on Power Electronics, 2019Co-Authors: Xin Zhang, Qingchang Zhong, Visakan Kadirkamanathan, Jinsong He, Jingjing HuangAbstract:Instability problem is an important issue for dc/dc conversion Cascaded Systems (Cascaded System in short). Though most of the existing stabilization methods can stabilize the whole System very well, they may ignore their impacts on the dynamic performance of the original Cascaded System. Unfortunately, these impacts are negative to some extent. Recently, an adaptive-series-virtual-impedance (ASVI) control strategy has been reported to address the above problem. It not only can stabilize the Cascaded System via shaping the load input impedance, but also can reduce its impact on the original load converter. However, though the ASVI control strategy has already greatly reduced its impact on the load converter, its remaining impact is negative. To solve this problem, this paper moves the ASVI from the load side to the source side via a proposed source-side series-virtual-impedance (SSVI) control strategy for the source converter. This SSVI control strategy not only has the same stabilization function and adaptive characteristics as the ASVI control strategy, but also improves the performance of the source converter. In addition, since the SSVI control strategy is realized by changing the control block of the source converter, the performance of the load converter is not affected. Therefore, the SSVI control strategy can be treated as a supplement and expansion of the ASVI control strategy. Moreover, depending on the method of realization, the SSVI control strategy can be divided into the source stabilization methods of the Cascaded System. Finally, a 100 W 48 V–32 V–24 V Cascaded System has been fabricated to validate the proposed control strategy.
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stabilization of a Cascaded dc converter System via adding a virtual adaptive parallel impedance to the input of the load converter
IEEE Transactions on Power Electronics, 2016Co-Authors: Xin Zhang, Qingchang Zhong, Wenlong MingAbstract:Connecting converters in cascade is a basic configuration of dc distributed power Systems (DPS). The impedance interaction between individually designed converters may make the Cascaded System become unstable. The previous presented stabilization approaches not only need to know the information of the regulated converter, but also have to know the characteristics of the other converters in the System, which are contradictory to the modularization characteristic of dc DPS. This letter proposes an adaptive-input-impedance-regulation (AIIR) method, which connects an adaptive virtual impedance in parallel with the input impedance of the load converter, to stabilize the Cascaded System. This virtual impedance can adaptively regulate its characteristic for different source converters. Therefore, with the AIIR method, all the load converters can be designed to a fixed standard module to stably adapt various source converters. In addition, at any cases, the AIIR approach only changes the load converter's input impedance in a very small frequency range to keep the load converter's original dynamic performance. The requirements on the AIIR method are derived and the control strategies to achieve the AIIR method are proposed. Finally, considering the worst stability problem that often occurs at the System whose source converter is an LC filter, a load converter Cascaded with two different LC input filters is fabricated and tested to validate the effectiveness of the proposed AIIR control method.
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stabilization of Cascaded dc dc converters via adaptive series virtual impedance control of the load converter
IEEE Transactions on Power Electronics, 2016Co-Authors: Xin Zhang, Qingchang Zhong, Wenlong MingAbstract:It has been shown recently that a Cascaded dc/dc converter System can be stabilized via amplitude compensation (SAC) or phase compensation (SPC) for the input impedance of the load converter. In this letter, it is shown that the Cascaded System when adopting the SAC is unconditionally stable but conditionally stable when adopting the SPC, that is, SAC is more stable than SPC. Then, the comparison is carried out for the parallel-virtual-impedance (PVI) and series-virtual-impedance (SVI) control strategies that are adopted to implement the SAC, and it is found that only the SVI control strategy can achieve the SAC for the whole load and input voltage range of the load converter without limitation. Therefore, SVI is in general better than PVI when realizing SAC. Following on this, an adaptive mechanism is introduced to improve the traditional SVI control strategy so that the load converter can be stably connected to different source converters such as $LC$ input filters and traditional dc/dc converters. Finally, a load converter Cascaded with three different source converters is fabricated to validate the effectiveness of the proposed adaptive SVI control strategy.
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improving the stability of Cascaded dc dc converter Systems via shaping the input impedance of the load converter with a parallel or series virtual impedance
IEEE Transactions on Industrial Electronics, 2015Co-Authors: Xin Zhang, Xinbo Ruan, Qingchang ZhongAbstract:Interactions between individually designed power subSystems in a Cascaded System may cause instability. This paper proposes an approach, which connects a virtual impedance in parallel or series with the input impedance of the load converter so that the magnitude or phase of the load converter's input impedance is modified in a small range of frequency, to solve the instability problem of a Cascaded System. The requirements on the parallel virtual impedance (PVI) and series virtual impedance (SVI) are derived, and the control strategies to implement the PVI and SVI are proposed. The comparison and general design procedure of the PVI and SVI control strategies are also discussed. Finally, considering the worst stability problem that often occurs at the System whose source converter is an $LC$ filter, two Cascaded Systems consisting of a source converter with an $LC$ input filter and a load converter, which is either a buck converter or a boost converter, are fabricated and tested to validate the effectiveness of the proposed control methods.
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adaptive active capacitor converter for improving stability of Cascaded dc power supply System
IEEE Transactions on Power Electronics, 2013Co-Authors: Xin Zhang, Xinbo RuanAbstract:Connecting converters in cascade is a basic configuration of dc distributed power Systems (DPS). The impedance interaction between individually designed converters may make the Cascaded System unstable. The previous presented approaches of stabilizing the Cascaded Systems need to modify the source and/or load converter's internal structure such as the topology and control circuit that are contradictory to the modularization characteristic of dc DPS. In this paper, an adaptive active capacitor converter (AACC) is introduced to stabilize the Cascaded System. The AACC is connected in parallel with the Cascaded System's intermediate bus and only needs to detect the bus voltage without any change of the existing subSystems. Hence, it can be designed as a standard module for dc DPS. The AACC serves as an equivalent bus capacitor to reduce the output impedance of the source converter, thus avoiding the intersection with the load converter's input impedance, and as a result, the Cascaded System becomes stable. The equivalent bus capacitor emulated by the AACC is adaptive according to the output power of the Cascaded System, and thus, the power loss of AACC is minimized and the dynamic response of the System is better than that of the System using a passive capacitor. Furthermore, since no electrolytic capacitor is needed in the AACC, the Cascaded System's lifetime is prolonged. The operation principle, control, and design consideration of the AACC are discussed in this paper, and a 480 W Cascaded System comprising two phase-shifted full-bridge converters has been built and evaluated. The experimental results verify the validity of the proposed AACC.
Jerzy Kanicki - One of the best experts on this subject based on the ideXlab platform.
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three dimensional Cascaded System analysis of a 50 µm pixel pitch wafer scale cmos active pixel sensor x ray detector for digital breast tomosynthesis
Physics in Medicine and Biology, 2017Co-Authors: Chumi Zhao, Anastasios Konstantinidis, R D Spelle, Nikita Vassiljev, Jerzy KanickiAbstract:High-resolution, low-noise x-ray detectors based on the complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) technology have been developed and proposed for digital breast tomosynthesis (DBT). In this study, we evaluated the three-dimensional (3D) imaging performance of a 50 ��m pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). The two-dimensional (2D) angle-dependent modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) were experimentally characterized and modeled using the Cascaded System analysis at oblique incident angles up to 30��. The Cascaded System model was extended to the 3D spatial frequency space in combination with the filtered back-projection (FBP) reconstruction method to calculate the 3D and in-plane MTF, NNPS and DQE parameters. The results demonstrate that the beam obliquity blurs the 2D MTF and DQE in the high spatial frequency range. However, this effect can be eliminated after FBP image reconstruction. In addition, impacts of the image acquisition geometry and detector parameters were evaluated using the 3D Cascaded System analysis for DBT. The result shows that a wider projection angle range (e.g. ��30��) improves the low spatial frequency (below 5 mm-1) performance of the CMOS APS detector. In addition, to maintain a high spatial resolution for DBT, a focal spot size of smaller than 0.3 mm should be used. Theoretical analysis suggests that a pixelated scintillator in combination with the 50 ��m pixel pitch CMOS APS detector could further improve the 3D image resolution. Finally, the 3D imaging performance of the CMOS APS and an indirect amorphous silicon (a-Si:H) thin-film transistor (TFT) passive pixel sensor (PPS) detector was simulated and compared.
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50 μm pixel pitch wafer scale cmos active pixel sensor x ray detector for digital breast tomosynthesis
Physics in Medicine and Biology, 2015Co-Authors: Chumi Zhao, Anastasios Konstantinidis, Thalis Anaxagoras, R D Spelle, Yi Zheng, Jerzy KanickiAbstract:Wafer-scale CMOS active pixel sensors (APSs) have been developed recently for x-ray imaging applications. The small pixel pitch and low noise are very promising properties for medical imaging applications such as digital breast tomosynthesis (DBT). In this work, we evaluated experimentally and through modeling the imaging properties of a 50 μm pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). A modified Cascaded System model was developed for CMOS APS x-ray detectors by taking into account the device nonlinear signal and noise properties. The imaging properties such as modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) were extracted from both measurements and the nonlinear Cascaded System analysis. The results show that the DynAMITe x-ray detector achieves a high spatial resolution of 10 mm(-1) and a DQE of around 0.5 at spatial frequencies <1 mm(-1). In addition, the modeling results were used to calculate the image signal-to-noise ratio (SNRi) of microcalcifications at various mean glandular dose (MGD). For an average breast (5 cm thickness, 50% glandular fraction), 165 μm microcalcifications can be distinguished at a MGD of 27% lower than the clinical value (~1.3 mGy). To detect 100 μm microcalcifications, further optimizations of the CMOS APS x-ray detector, image aquisition geometry and image reconstruction techniques should be considered.
Qingchang Zhong - One of the best experts on this subject based on the ideXlab platform.
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source side series virtual impedance control to improve the Cascaded System stability and the dynamic performance of its source converter
IEEE Transactions on Power Electronics, 2019Co-Authors: Xin Zhang, Qingchang Zhong, Visakan Kadirkamanathan, Jinsong He, Jingjing HuangAbstract:Instability problem is an important issue for dc/dc conversion Cascaded Systems (Cascaded System in short). Though most of the existing stabilization methods can stabilize the whole System very well, they may ignore their impacts on the dynamic performance of the original Cascaded System. Unfortunately, these impacts are negative to some extent. Recently, an adaptive-series-virtual-impedance (ASVI) control strategy has been reported to address the above problem. It not only can stabilize the Cascaded System via shaping the load input impedance, but also can reduce its impact on the original load converter. However, though the ASVI control strategy has already greatly reduced its impact on the load converter, its remaining impact is negative. To solve this problem, this paper moves the ASVI from the load side to the source side via a proposed source-side series-virtual-impedance (SSVI) control strategy for the source converter. This SSVI control strategy not only has the same stabilization function and adaptive characteristics as the ASVI control strategy, but also improves the performance of the source converter. In addition, since the SSVI control strategy is realized by changing the control block of the source converter, the performance of the load converter is not affected. Therefore, the SSVI control strategy can be treated as a supplement and expansion of the ASVI control strategy. Moreover, depending on the method of realization, the SSVI control strategy can be divided into the source stabilization methods of the Cascaded System. Finally, a 100 W 48 V–32 V–24 V Cascaded System has been fabricated to validate the proposed control strategy.
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stabilization of a Cascaded dc converter System via adding a virtual adaptive parallel impedance to the input of the load converter
IEEE Transactions on Power Electronics, 2016Co-Authors: Xin Zhang, Qingchang Zhong, Wenlong MingAbstract:Connecting converters in cascade is a basic configuration of dc distributed power Systems (DPS). The impedance interaction between individually designed converters may make the Cascaded System become unstable. The previous presented stabilization approaches not only need to know the information of the regulated converter, but also have to know the characteristics of the other converters in the System, which are contradictory to the modularization characteristic of dc DPS. This letter proposes an adaptive-input-impedance-regulation (AIIR) method, which connects an adaptive virtual impedance in parallel with the input impedance of the load converter, to stabilize the Cascaded System. This virtual impedance can adaptively regulate its characteristic for different source converters. Therefore, with the AIIR method, all the load converters can be designed to a fixed standard module to stably adapt various source converters. In addition, at any cases, the AIIR approach only changes the load converter's input impedance in a very small frequency range to keep the load converter's original dynamic performance. The requirements on the AIIR method are derived and the control strategies to achieve the AIIR method are proposed. Finally, considering the worst stability problem that often occurs at the System whose source converter is an LC filter, a load converter Cascaded with two different LC input filters is fabricated and tested to validate the effectiveness of the proposed AIIR control method.
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stabilization of Cascaded dc dc converters via adaptive series virtual impedance control of the load converter
IEEE Transactions on Power Electronics, 2016Co-Authors: Xin Zhang, Qingchang Zhong, Wenlong MingAbstract:It has been shown recently that a Cascaded dc/dc converter System can be stabilized via amplitude compensation (SAC) or phase compensation (SPC) for the input impedance of the load converter. In this letter, it is shown that the Cascaded System when adopting the SAC is unconditionally stable but conditionally stable when adopting the SPC, that is, SAC is more stable than SPC. Then, the comparison is carried out for the parallel-virtual-impedance (PVI) and series-virtual-impedance (SVI) control strategies that are adopted to implement the SAC, and it is found that only the SVI control strategy can achieve the SAC for the whole load and input voltage range of the load converter without limitation. Therefore, SVI is in general better than PVI when realizing SAC. Following on this, an adaptive mechanism is introduced to improve the traditional SVI control strategy so that the load converter can be stably connected to different source converters such as $LC$ input filters and traditional dc/dc converters. Finally, a load converter Cascaded with three different source converters is fabricated to validate the effectiveness of the proposed adaptive SVI control strategy.
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improving the stability of Cascaded dc dc converter Systems via shaping the input impedance of the load converter with a parallel or series virtual impedance
IEEE Transactions on Industrial Electronics, 2015Co-Authors: Xin Zhang, Xinbo Ruan, Qingchang ZhongAbstract:Interactions between individually designed power subSystems in a Cascaded System may cause instability. This paper proposes an approach, which connects a virtual impedance in parallel or series with the input impedance of the load converter so that the magnitude or phase of the load converter's input impedance is modified in a small range of frequency, to solve the instability problem of a Cascaded System. The requirements on the parallel virtual impedance (PVI) and series virtual impedance (SVI) are derived, and the control strategies to implement the PVI and SVI are proposed. The comparison and general design procedure of the PVI and SVI control strategies are also discussed. Finally, considering the worst stability problem that often occurs at the System whose source converter is an $LC$ filter, two Cascaded Systems consisting of a source converter with an $LC$ input filter and a load converter, which is either a buck converter or a boost converter, are fabricated and tested to validate the effectiveness of the proposed control methods.
Chumi Zhao - One of the best experts on this subject based on the ideXlab platform.
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three dimensional Cascaded System analysis of a 50 µm pixel pitch wafer scale cmos active pixel sensor x ray detector for digital breast tomosynthesis
Physics in Medicine and Biology, 2017Co-Authors: Chumi Zhao, Anastasios Konstantinidis, R D Spelle, Nikita Vassiljev, Jerzy KanickiAbstract:High-resolution, low-noise x-ray detectors based on the complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) technology have been developed and proposed for digital breast tomosynthesis (DBT). In this study, we evaluated the three-dimensional (3D) imaging performance of a 50 ��m pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). The two-dimensional (2D) angle-dependent modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) were experimentally characterized and modeled using the Cascaded System analysis at oblique incident angles up to 30��. The Cascaded System model was extended to the 3D spatial frequency space in combination with the filtered back-projection (FBP) reconstruction method to calculate the 3D and in-plane MTF, NNPS and DQE parameters. The results demonstrate that the beam obliquity blurs the 2D MTF and DQE in the high spatial frequency range. However, this effect can be eliminated after FBP image reconstruction. In addition, impacts of the image acquisition geometry and detector parameters were evaluated using the 3D Cascaded System analysis for DBT. The result shows that a wider projection angle range (e.g. ��30��) improves the low spatial frequency (below 5 mm-1) performance of the CMOS APS detector. In addition, to maintain a high spatial resolution for DBT, a focal spot size of smaller than 0.3 mm should be used. Theoretical analysis suggests that a pixelated scintillator in combination with the 50 ��m pixel pitch CMOS APS detector could further improve the 3D image resolution. Finally, the 3D imaging performance of the CMOS APS and an indirect amorphous silicon (a-Si:H) thin-film transistor (TFT) passive pixel sensor (PPS) detector was simulated and compared.
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50 μm pixel pitch wafer scale cmos active pixel sensor x ray detector for digital breast tomosynthesis
Physics in Medicine and Biology, 2015Co-Authors: Chumi Zhao, Anastasios Konstantinidis, Thalis Anaxagoras, R D Spelle, Yi Zheng, Jerzy KanickiAbstract:Wafer-scale CMOS active pixel sensors (APSs) have been developed recently for x-ray imaging applications. The small pixel pitch and low noise are very promising properties for medical imaging applications such as digital breast tomosynthesis (DBT). In this work, we evaluated experimentally and through modeling the imaging properties of a 50 μm pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). A modified Cascaded System model was developed for CMOS APS x-ray detectors by taking into account the device nonlinear signal and noise properties. The imaging properties such as modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) were extracted from both measurements and the nonlinear Cascaded System analysis. The results show that the DynAMITe x-ray detector achieves a high spatial resolution of 10 mm(-1) and a DQE of around 0.5 at spatial frequencies <1 mm(-1). In addition, the modeling results were used to calculate the image signal-to-noise ratio (SNRi) of microcalcifications at various mean glandular dose (MGD). For an average breast (5 cm thickness, 50% glandular fraction), 165 μm microcalcifications can be distinguished at a MGD of 27% lower than the clinical value (~1.3 mGy). To detect 100 μm microcalcifications, further optimizations of the CMOS APS x-ray detector, image aquisition geometry and image reconstruction techniques should be considered.
R D Spelle - One of the best experts on this subject based on the ideXlab platform.
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three dimensional Cascaded System analysis of a 50 µm pixel pitch wafer scale cmos active pixel sensor x ray detector for digital breast tomosynthesis
Physics in Medicine and Biology, 2017Co-Authors: Chumi Zhao, Anastasios Konstantinidis, R D Spelle, Nikita Vassiljev, Jerzy KanickiAbstract:High-resolution, low-noise x-ray detectors based on the complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) technology have been developed and proposed for digital breast tomosynthesis (DBT). In this study, we evaluated the three-dimensional (3D) imaging performance of a 50 ��m pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). The two-dimensional (2D) angle-dependent modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) were experimentally characterized and modeled using the Cascaded System analysis at oblique incident angles up to 30��. The Cascaded System model was extended to the 3D spatial frequency space in combination with the filtered back-projection (FBP) reconstruction method to calculate the 3D and in-plane MTF, NNPS and DQE parameters. The results demonstrate that the beam obliquity blurs the 2D MTF and DQE in the high spatial frequency range. However, this effect can be eliminated after FBP image reconstruction. In addition, impacts of the image acquisition geometry and detector parameters were evaluated using the 3D Cascaded System analysis for DBT. The result shows that a wider projection angle range (e.g. ��30��) improves the low spatial frequency (below 5 mm-1) performance of the CMOS APS detector. In addition, to maintain a high spatial resolution for DBT, a focal spot size of smaller than 0.3 mm should be used. Theoretical analysis suggests that a pixelated scintillator in combination with the 50 ��m pixel pitch CMOS APS detector could further improve the 3D image resolution. Finally, the 3D imaging performance of the CMOS APS and an indirect amorphous silicon (a-Si:H) thin-film transistor (TFT) passive pixel sensor (PPS) detector was simulated and compared.
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50 μm pixel pitch wafer scale cmos active pixel sensor x ray detector for digital breast tomosynthesis
Physics in Medicine and Biology, 2015Co-Authors: Chumi Zhao, Anastasios Konstantinidis, Thalis Anaxagoras, R D Spelle, Yi Zheng, Jerzy KanickiAbstract:Wafer-scale CMOS active pixel sensors (APSs) have been developed recently for x-ray imaging applications. The small pixel pitch and low noise are very promising properties for medical imaging applications such as digital breast tomosynthesis (DBT). In this work, we evaluated experimentally and through modeling the imaging properties of a 50 μm pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). A modified Cascaded System model was developed for CMOS APS x-ray detectors by taking into account the device nonlinear signal and noise properties. The imaging properties such as modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) were extracted from both measurements and the nonlinear Cascaded System analysis. The results show that the DynAMITe x-ray detector achieves a high spatial resolution of 10 mm(-1) and a DQE of around 0.5 at spatial frequencies <1 mm(-1). In addition, the modeling results were used to calculate the image signal-to-noise ratio (SNRi) of microcalcifications at various mean glandular dose (MGD). For an average breast (5 cm thickness, 50% glandular fraction), 165 μm microcalcifications can be distinguished at a MGD of 27% lower than the clinical value (~1.3 mGy). To detect 100 μm microcalcifications, further optimizations of the CMOS APS x-ray detector, image aquisition geometry and image reconstruction techniques should be considered.