The harmonic wavelet transform（HWT） and its fast realization based on fast Fourier transform（FFT） are introduced. Its ability to maintain the same amplitude-frequency feature is revealed. A new method to construct...The harmonic wavelet transform（HWT） and its fast realization based on fast Fourier transform（FFT） are introduced. Its ability to maintain the same amplitude-frequency feature is revealed. A new method to construct the time-frequency（TF） spectrum of HWT is proposed, which makes the HWT TF spectrum able to correctly reflect the time-frequency-amplitude distribution of the signal. A new way to calculate the HWT coefficients is proposed. By zero padding the data taken out, the non-decimated coefficients of HWT are obtained. Theoretical analysis shows that the modulus of the coefficients obtained by the new calculation way and living at a certain scale are the envelope of the component in the corresponding frequency band. By taking the cross section of the new TF spectrum, the demodulation for the component at a certain frequency band can be realized. A comparison with the Hilbert demodulation combined with band-pass filtering is done, which indicates for multi-components, the method proposed here is more suitable since it realizes ideal band-pass filtering and avoids pass band selecting. In the end, it is applied to bearing and gearbox fault diagnosis, and the results reflect that it can effectively extract the fault features in the signal.展开更多
A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported.The dual resonator consists of a rectilinear oscillator(R_LO)performing mag...A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported.The dual resonator consists of a rectilinear oscillator(R_LO)performing magnetic levitation and a rotary oscillator(R_TO)performing electromagnetic coupling through a stator and a rotor.Both oscillators,coupled by magnetic forces generated by a set of arc permanent magnets,radially magnetized and centro-symmetrically fixed onto the R_LO and the rotor of the R_TO achieve the reciprocating-to-rotary motion conversion and frequency up-conversion.Specifically,the dual resonator is able to convert stochastic reciprocating motion into controllable rotation,provide intrinsic frequency up-conversion,use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy harvesting.While solely focusing on developing a dual resonator provides substantial benefits,its dynamic behavior is unclear,thus electromagnetic-dynamic governing equations are derived,and a curve fitting model of restoring torque of R_TO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical system.Power analysis is carried out for providing aquantitative guidance of customizing the harvester to achieve an optimal power density.展开更多
随着出力具有随机波动性特征的分布式电源渗透率的不断攀升以及城市电缆化率的进程加速,有源配电网线路中无功过剩和过电压的现象日益明显,对动态无功补偿装置的经济性、可靠性和精准调控能力提出更高要求。在电流源型静止同步补偿器的...随着出力具有随机波动性特征的分布式电源渗透率的不断攀升以及城市电缆化率的进程加速,有源配电网线路中无功过剩和过电压的现象日益明显,对动态无功补偿装置的经济性、可靠性和精准调控能力提出更高要求。在电流源型静止同步补偿器的基础上,该文结合双旋转移相变压器的连续调节特性,提出一种新型旋转式无功补偿器(novel rotary var compensator,NRVC)拓扑电路。通过构建NRVC稳态数学模型,深入分析得到NRVC补偿调控机理及其补偿容量约束关系。针对NRVC结构特点,提出基于瞬时无功理论的无功补偿控制策略,其中功率外环可对功率因数进行精确控制,电流内环加入限幅环节有效限流,提高装置运行可靠性。通过仿真及动模实验验证所提拓扑及其控制策略的有效性,结果验证了NRVC具备双向、连续调节补偿无功的能力,具有调节精度高、谐波畸变率低的优点。展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50575233)National Hi-tech Research and Development Program of China (Grant No. 2008AA042408)
文摘The harmonic wavelet transform（HWT） and its fast realization based on fast Fourier transform（FFT） are introduced. Its ability to maintain the same amplitude-frequency feature is revealed. A new method to construct the time-frequency（TF） spectrum of HWT is proposed, which makes the HWT TF spectrum able to correctly reflect the time-frequency-amplitude distribution of the signal. A new way to calculate the HWT coefficients is proposed. By zero padding the data taken out, the non-decimated coefficients of HWT are obtained. Theoretical analysis shows that the modulus of the coefficients obtained by the new calculation way and living at a certain scale are the envelope of the component in the corresponding frequency band. By taking the cross section of the new TF spectrum, the demodulation for the component at a certain frequency band can be realized. A comparison with the Hilbert demodulation combined with band-pass filtering is done, which indicates for multi-components, the method proposed here is more suitable since it realizes ideal band-pass filtering and avoids pass band selecting. In the end, it is applied to bearing and gearbox fault diagnosis, and the results reflect that it can effectively extract the fault features in the signal.
基金partially supported by the U.S.Office of Navy Research (No.N000141410230)partially supported by the Department of Energy ARPA-E (No. DOE-AR0000531)
文摘A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported.The dual resonator consists of a rectilinear oscillator(R_LO)performing magnetic levitation and a rotary oscillator(R_TO)performing electromagnetic coupling through a stator and a rotor.Both oscillators,coupled by magnetic forces generated by a set of arc permanent magnets,radially magnetized and centro-symmetrically fixed onto the R_LO and the rotor of the R_TO achieve the reciprocating-to-rotary motion conversion and frequency up-conversion.Specifically,the dual resonator is able to convert stochastic reciprocating motion into controllable rotation,provide intrinsic frequency up-conversion,use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy harvesting.While solely focusing on developing a dual resonator provides substantial benefits,its dynamic behavior is unclear,thus electromagnetic-dynamic governing equations are derived,and a curve fitting model of restoring torque of R_TO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical system.Power analysis is carried out for providing aquantitative guidance of customizing the harvester to achieve an optimal power density.
文摘随着出力具有随机波动性特征的分布式电源渗透率的不断攀升以及城市电缆化率的进程加速,有源配电网线路中无功过剩和过电压的现象日益明显,对动态无功补偿装置的经济性、可靠性和精准调控能力提出更高要求。在电流源型静止同步补偿器的基础上,该文结合双旋转移相变压器的连续调节特性,提出一种新型旋转式无功补偿器(novel rotary var compensator,NRVC)拓扑电路。通过构建NRVC稳态数学模型,深入分析得到NRVC补偿调控机理及其补偿容量约束关系。针对NRVC结构特点,提出基于瞬时无功理论的无功补偿控制策略,其中功率外环可对功率因数进行精确控制,电流内环加入限幅环节有效限流,提高装置运行可靠性。通过仿真及动模实验验证所提拓扑及其控制策略的有效性,结果验证了NRVC具备双向、连续调节补偿无功的能力,具有调节精度高、谐波畸变率低的优点。
