Impedance measurement is an effective solution for evaluating stability of a power system with high penetration of renewable sources.In this paper,the impedance measurement is achieved by a typical high-power impedanc...Impedance measurement is an effective solution for evaluating stability of a power system with high penetration of renewable sources.In this paper,the impedance measurement is achieved by a typical high-power impedance measuring converter(HPIM-converter)with chirp signal injection.The modulation saturation phenomenon of the HPIM-converter is revealed,and the frequency sweep boundary is analyzed in detail.To expand the rated frequency range of the HPIM-converter,a spread frequency band control scheme based on an over-modulation technique is proposed in this paper.The proposed control method enlarges the rated frequency band and can inject a disturbance voltage into the system under test with consistent amplitude in the rated frequency band.Also,a smooth transition strategy between linear modulation mode and over-modulation mode is proposed for suppressing signal fluctuation.Finally,the effectiveness of the proposed method is verified by simulation tests.展开更多
The negative impact on communication performance in wireless multi-hop communication net-work caused by limited bandwidth,high bit eror rate （BER）,fading,noise and interference is alleviated by an adaptive filtering...The negative impact on communication performance in wireless multi-hop communication net-work caused by limited bandwidth,high bit eror rate （BER）,fading,noise and interference is alleviated by an adaptive filtering game based on frequency subbands selection and predetemined threshold.Such threshold is being obtained in Gaussian and multipath fading channel according to the frequency-matching principle and BER performance.The dynamic selection of subbands will obtain high use efficiency without the help of frequency hopping,and propound a new thought to improve band limited communication for wireless multi-hop communication network.The effectiveness of the adaptive filtering method has been verified by interleaving spread spectrum orthogonal frequency division multiplexing （ISS-OFDM） in different interference conditions,and the simulating results based on network simulator 2 （NS2） indicate that system BER can be improved greatly.展开更多
Using the Hefei Light Source phase Ⅱ project （HLS- Ⅱ） as an example, a theoretical analysis of shortening the bunch lengths using a higher harmonic cavity （HHC） is given. The threshold voltage of an active HHC a...Using the Hefei Light Source phase Ⅱ project （HLS- Ⅱ） as an example, a theoretical analysis of shortening the bunch lengths using a higher harmonic cavity （HHC） is given. The threshold voltage of an active HHC and the threshold tuning angle of a passive HHC are first analysed. The optimum tuning angle for the constant detuning scenario and the optimum harmonic voltage for the constant voltage scenario are presented. The calculated results show that the reduced bunch length is about half that of the nominal bunch. The bunch lengths vary from 11 mm at 0.1 A to 7 mm at 0.4 A for the constant detuning scenario, while the bunch lengths are around 7 mm over the beam current range for the constant voltage scenario. In addition, the synchrotron frequency spread is increased. It indicates that HHC may be used to reduce the bunch length and increase the Landau damping of synchrotron oscillations in a storage ring.展开更多
文摘Impedance measurement is an effective solution for evaluating stability of a power system with high penetration of renewable sources.In this paper,the impedance measurement is achieved by a typical high-power impedance measuring converter(HPIM-converter)with chirp signal injection.The modulation saturation phenomenon of the HPIM-converter is revealed,and the frequency sweep boundary is analyzed in detail.To expand the rated frequency range of the HPIM-converter,a spread frequency band control scheme based on an over-modulation technique is proposed in this paper.The proposed control method enlarges the rated frequency band and can inject a disturbance voltage into the system under test with consistent amplitude in the rated frequency band.Also,a smooth transition strategy between linear modulation mode and over-modulation mode is proposed for suppressing signal fluctuation.Finally,the effectiveness of the proposed method is verified by simulation tests.
基金Supported by the National Nature Science Foundation of China(No.61302074)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20122301120004)+1 种基金the Natural Science Foundation of Heilongjiang Province(No.QC2013C061)Research Foundation of Education Bureau of Heilongjiang Province(No.12531480)
文摘The negative impact on communication performance in wireless multi-hop communication net-work caused by limited bandwidth,high bit eror rate （BER）,fading,noise and interference is alleviated by an adaptive filtering game based on frequency subbands selection and predetemined threshold.Such threshold is being obtained in Gaussian and multipath fading channel according to the frequency-matching principle and BER performance.The dynamic selection of subbands will obtain high use efficiency without the help of frequency hopping,and propound a new thought to improve band limited communication for wireless multi-hop communication network.The effectiveness of the adaptive filtering method has been verified by interleaving spread spectrum orthogonal frequency division multiplexing （ISS-OFDM） in different interference conditions,and the simulating results based on network simulator 2 （NS2） indicate that system BER can be improved greatly.
基金Supported by National Nature Science Foundation of China(10675116)Major State Basic Research Development Programme of China(2011CB808301)
文摘Using the Hefei Light Source phase Ⅱ project （HLS- Ⅱ） as an example, a theoretical analysis of shortening the bunch lengths using a higher harmonic cavity （HHC） is given. The threshold voltage of an active HHC and the threshold tuning angle of a passive HHC are first analysed. The optimum tuning angle for the constant detuning scenario and the optimum harmonic voltage for the constant voltage scenario are presented. The calculated results show that the reduced bunch length is about half that of the nominal bunch. The bunch lengths vary from 11 mm at 0.1 A to 7 mm at 0.4 A for the constant detuning scenario, while the bunch lengths are around 7 mm over the beam current range for the constant voltage scenario. In addition, the synchrotron frequency spread is increased. It indicates that HHC may be used to reduce the bunch length and increase the Landau damping of synchrotron oscillations in a storage ring.
