To suppress peak voltage on rectifier diodes in a full bridge( FB) converter,the mechanism of peak voltage was analyzed and an improved FB converter was proposed. One reason for peak voltage is the resonance of the tr...To suppress peak voltage on rectifier diodes in a full bridge( FB) converter,the mechanism of peak voltage was analyzed and an improved FB converter was proposed. One reason for peak voltage is the resonance of the transformer's leakage inductance and the rectifier diodes' junction capacitances. The other reason is that the fast reverse recovery current of the rectifier diodes flows through the transformer's leakage inductance. An H bridge composed of four diodes,an auxiliary inductance, and a clamping winding were adopted in the proposed converter,and peak voltage was suppressed by varying the equivalent inductance, principally in different operating modes. Experimental results demonstrate that the peak voltage of rectifier diodes decreases by 43%,the auxiliary circuit does not lead to additional loss, and the rising rate, resonant frequency,and amplitude of the rectifier diodes' voltage decrease.Peak voltage and electromagnetic interference( EMI) of rectifier diodes are suppressed.展开更多
The effects of initial oxygen concentration on the reverse leakage current of PIN rectifier diodes were studied.We fabricated the PIN rectifier diodes with different initial oxygen concentrations,and analyzed the elec...The effects of initial oxygen concentration on the reverse leakage current of PIN rectifier diodes were studied.We fabricated the PIN rectifier diodes with different initial oxygen concentrations,and analyzed the electrical properties,anisotropic preferred etching by means of optical microscopy,Fourier transform infrared spectroscopy and transmission electron microscopy.It is pointed out that the reverse leakage current increases exponentially with the increasing initial oxygen concentration.Furtherly,we researched and analyzed the mechanism of the effects of initial oxygen concentration on the reverse leakage current of PIN rectifier diode.It is shown that the oxygen precipitations present in an "S" curve with increasing initial oxygen concentration after high temperature diffusion.The main reason is that the nucleation and growth of oxygen precipitation at high temperature induce bulk oxidation-induced defects (B-OSF),which are mainly dislocations,and a small amount of rod stacking faults.The density of B-OSF increases with the increasing initial oxygen concentration.The existence of B-OSF has great effects on the reverse leakage current of PIN rectifier diode.展开更多
Due to low investment cost and high reliability,a new scheme called DR-HVDC(Diode Rectifier based HVDC)transmission was recently proposed for grid integration of large offshore wind farms.However,in this scheme,the ap...Due to low investment cost and high reliability,a new scheme called DR-HVDC(Diode Rectifier based HVDC)transmission was recently proposed for grid integration of large offshore wind farms.However,in this scheme,the application of conventional control strategies for stability operation face several challenges due to the uncontrollability of the DR.In this paper,a coordinated control strategy of offshore wind farms using the DR-HVDC transmission technology to connect with the onshore grid,is investigated.A novel coordinated control strategy for DR-HVDC is proposed based on the analysis of the DC current control ability of the full-bridge-based modular multilevel converter(FB-MMC)at the onshore station and the input and output characteristics of the diode rectifier at the offshore.Considering the characteristics of operation stability and decoupling between reactive power and active power,a simplified design based on double-loop droop control for offshore AC voltage is proposed after power flow and voltage–current(I–V)characteristics of the offshore wind farm being analyzed.Furthermore,the impact of onshore AC fault to offshore wind farm is analyzed,and a fast fault detection and protection strategy without relying on communication is proposed.Case studies carried out by PSCAD/EMTDC verify the effectiveness of the proposed control strategy for the start up,power fluctuation,and onshore and offshore fault conditions.展开更多
The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with car...The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with carbon atoms in one of the electrodes acts as a high performance nanoribbon rectifier. It is interesting to find that there exists a particular bias-polarity-dependent matching band between two electrodes,leading to a similar current-voltage(I-V) behavior as conventional P-N diodes. The I-V behavior presents a linear positive-bias I-V characteristic,an absolutely negligible leakage current,and a stable rectifying property under a large bias region. The results suggest that C doping might be an effective way to raise ABNNRs devices' rectifying performance.展开更多
One of the strategies to tune current-voltage behaviors in organic diodes is to combine field-induced charge transfer processes with schottky barrier.According to this principle,a rectifying diode with hysteresis effe...One of the strategies to tune current-voltage behaviors in organic diodes is to combine field-induced charge transfer processes with schottky barrier.According to this principle,a rectifying diode with hysteresis effect was fabricated utilizing a hybrid of electroactive polystyrene derivative covalently tethered with electron-donor carbazole moieties and electrostatic linked with electron-acceptor CdTe nanocrystals.Current-voltage characteristics show an electrical switching behavior with some hysteresis is only observed under a negative bias,with three orders of On/Off current ratio.The hybrid material based rectifier exhibits a rectification ratio of six and its maximum rectified output current is about 5 × 10-5 A.The asymmetric switching is interpreted as the result of both field induced charge transfer and schottky barrier,capable of reducing the misreading of cross-bar memory.Meanwhile,chemical doping of CdTe nanocrystals instead of physical blend favor their uniform dispersion in matrix and stable operation of device.展开更多
基金National Natural Science Foundation of China(No.41004027)Cooperation Innovation Projects of Ministry of Education,China(No.OSR-02-01)
文摘To suppress peak voltage on rectifier diodes in a full bridge( FB) converter,the mechanism of peak voltage was analyzed and an improved FB converter was proposed. One reason for peak voltage is the resonance of the transformer's leakage inductance and the rectifier diodes' junction capacitances. The other reason is that the fast reverse recovery current of the rectifier diodes flows through the transformer's leakage inductance. An H bridge composed of four diodes,an auxiliary inductance, and a clamping winding were adopted in the proposed converter,and peak voltage was suppressed by varying the equivalent inductance, principally in different operating modes. Experimental results demonstrate that the peak voltage of rectifier diodes decreases by 43%,the auxiliary circuit does not lead to additional loss, and the rising rate, resonant frequency,and amplitude of the rectifier diodes' voltage decrease.Peak voltage and electromagnetic interference( EMI) of rectifier diodes are suppressed.
基金Funded by the National Natural Science Foundation of China (No. 62004154)。
文摘The effects of initial oxygen concentration on the reverse leakage current of PIN rectifier diodes were studied.We fabricated the PIN rectifier diodes with different initial oxygen concentrations,and analyzed the electrical properties,anisotropic preferred etching by means of optical microscopy,Fourier transform infrared spectroscopy and transmission electron microscopy.It is pointed out that the reverse leakage current increases exponentially with the increasing initial oxygen concentration.Furtherly,we researched and analyzed the mechanism of the effects of initial oxygen concentration on the reverse leakage current of PIN rectifier diode.It is shown that the oxygen precipitations present in an "S" curve with increasing initial oxygen concentration after high temperature diffusion.The main reason is that the nucleation and growth of oxygen precipitation at high temperature induce bulk oxidation-induced defects (B-OSF),which are mainly dislocations,and a small amount of rod stacking faults.The density of B-OSF increases with the increasing initial oxygen concentration.The existence of B-OSF has great effects on the reverse leakage current of PIN rectifier diode.
基金supported by State Grid Science and Technology Project“Study on Key Technologies of Large Scale Offshore Wind Power Integrating with Onshore Grid”(4000-202055045A-0-0-00)
文摘Due to low investment cost and high reliability,a new scheme called DR-HVDC(Diode Rectifier based HVDC)transmission was recently proposed for grid integration of large offshore wind farms.However,in this scheme,the application of conventional control strategies for stability operation face several challenges due to the uncontrollability of the DR.In this paper,a coordinated control strategy of offshore wind farms using the DR-HVDC transmission technology to connect with the onshore grid,is investigated.A novel coordinated control strategy for DR-HVDC is proposed based on the analysis of the DC current control ability of the full-bridge-based modular multilevel converter(FB-MMC)at the onshore station and the input and output characteristics of the diode rectifier at the offshore.Considering the characteristics of operation stability and decoupling between reactive power and active power,a simplified design based on double-loop droop control for offshore AC voltage is proposed after power flow and voltage–current(I–V)characteristics of the offshore wind farm being analyzed.Furthermore,the impact of onshore AC fault to offshore wind farm is analyzed,and a fast fault detection and protection strategy without relying on communication is proposed.Case studies carried out by PSCAD/EMTDC verify the effectiveness of the proposed control strategy for the start up,power fluctuation,and onshore and offshore fault conditions.
基金supported by the National Natural Science Foundation of China(21401023 and 21374017)Cultivating Fund for Excellent Young Scholar of Fujian Normal University(FJSDJK2012063)Program for Innovative Research Team in Science and Technology in Fujian Province University(IRTSTFJ)
文摘The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with carbon atoms in one of the electrodes acts as a high performance nanoribbon rectifier. It is interesting to find that there exists a particular bias-polarity-dependent matching band between two electrodes,leading to a similar current-voltage(I-V) behavior as conventional P-N diodes. The I-V behavior presents a linear positive-bias I-V characteristic,an absolutely negligible leakage current,and a stable rectifying property under a large bias region. The results suggest that C doping might be an effective way to raise ABNNRs devices' rectifying performance.
基金supported by the National Basic Research Pro-gram of China (973 projeet) (2009CB930600)National Natural Science Foundation of China (Grants 90406021,20704023,60876010,60706017,and 20774043)+3 种基金the Key Project of Chinese Ministry of Education (No. 104246, 208050, 707032, NCET-07-0446)the NSF of Jiangsu Province (Grants BK2008053, 08KJB510013, SJ209003and TJ207035)Research Fund for Postgraduate Innovation Project of Jiangsu Province (No. CX08B_083Z)STITP (No. 2009120)
文摘One of the strategies to tune current-voltage behaviors in organic diodes is to combine field-induced charge transfer processes with schottky barrier.According to this principle,a rectifying diode with hysteresis effect was fabricated utilizing a hybrid of electroactive polystyrene derivative covalently tethered with electron-donor carbazole moieties and electrostatic linked with electron-acceptor CdTe nanocrystals.Current-voltage characteristics show an electrical switching behavior with some hysteresis is only observed under a negative bias,with three orders of On/Off current ratio.The hybrid material based rectifier exhibits a rectification ratio of six and its maximum rectified output current is about 5 × 10-5 A.The asymmetric switching is interpreted as the result of both field induced charge transfer and schottky barrier,capable of reducing the misreading of cross-bar memory.Meanwhile,chemical doping of CdTe nanocrystals instead of physical blend favor their uniform dispersion in matrix and stable operation of device.