VFT （variable frequency transformer） has been recently used as art alternative to HVDC （high voltage direct current） to control power flow between asynchronous networks. VFT consumes less reactive power than a bac...VFT （variable frequency transformer） has been recently used as art alternative to HVDC （high voltage direct current） to control power flow between asynchronous networks. VFT consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery, and has better natural damping capability. VFT is simply a DFIM （doubly-fed induction machine） where the machine torque controls the power flow from stator to rotor and vice versa. The main disadvantage of this VFT is the slip rings and brushes required for the rotor circuit, especially in bulk power transmission. The BDFM （brushless doubly-fed machine） with nested cage rotor machine is proved to be a comparable alternative to conventional DFIM in many applications with the advantage that all windings being in the stator frame with fixed output terminals. In this paper, the BDFM is used as a BVFT （brushless variable frequency transformer）. A prototype machine is designed and simulated to verify the system validity.展开更多
This paper introduces the design and implementation of 1 D variable cutoff frequency (VCF) digital filters. A lowpass to highpass transformation and a lowpass to bandpass transformation for VCF infinite impulse r...This paper introduces the design and implementation of 1 D variable cutoff frequency (VCF) digital filters. A lowpass to highpass transformation and a lowpass to bandpass transformation for VCF infinite impulse response (IIR) filter are presented. The transformed highpass and bandpass filters are implemented in a network structure in which the cutoff frequencies are variable by adjusting single parameter.展开更多
To establish the algorithm of SAT-TMD system with the wavelet transform(WT),the modal mass participation ratio is proposed to distinguish if the high-rising structure has the characteristic of closely distributed freq...To establish the algorithm of SAT-TMD system with the wavelet transform(WT),the modal mass participation ratio is proposed to distinguish if the high-rising structure has the characteristic of closely distributed frequencies.A time varying analytical model of high-rising structure such as TV-tower with the SAT-TMD is developed.The proposed new idea is to use WT to identify the dominant frequency of structural response in a segment time,and track its variation as a function of time to retune the SAT-TMD.The effectiveness of SAT-TMD is investigated and it is more robust to change in building stiffness and damping than that of the TMD with a fixed frequency corresponding to a fixed mode frequency of the building.It is proved that SAT-TMD is particularly effective in reducing the response even when the building stiffness is changed by ±15%;whereas the TMD loses its effectiveness under such building stiffness variations.展开更多
The invariant, propagator, and wavefunction for a variable frequency harmonic oscillator in an electromagnetic field are obtained by making a specific coordinate transformation and by using the method of phase space p...The invariant, propagator, and wavefunction for a variable frequency harmonic oscillator in an electromagnetic field are obtained by making a specific coordinate transformation and by using the method of phase space path integral method. The probability amplitudes for a dissipative harmonic oscillator in the time varying electric field are obtained.展开更多
Early detection of sudden cardiac death may be used for surviving the life of cardiac patients. In this paper we have investigated an algorithm to detect and predict sudden cardiac death, by processing of heart rate v...Early detection of sudden cardiac death may be used for surviving the life of cardiac patients. In this paper we have investigated an algorithm to detect and predict sudden cardiac death, by processing of heart rate variability signal through the classical and time-frequency methods. At first, one minute of ECG signals, just before the cardiac death event are extracted and used to compute heart rate variability (HRV) signal. Five features in time domain and four features in frequency domain are extracted from the HRV signal and used as classical linear features. Then the Wigner Ville transform is applied to the HRV signal, and 11 extra features in the time-frequency (TF) domain are obtained. In order to improve the performance of classification, the principal component analysis (PCA) is applied to the obtained features vector. Finally a neural network classifier is applied to the reduced features. The obtained results show that the TF method can classify normal and SCD subjects, more efficiently than the classical methods. A MIT-BIH ECG database was used to evaluate the proposed method. The proposed method was implemented using MLP classifier and had 74.36% and 99.16% correct detection rate (accuracy) for classical features and TF method, respectively. Also, the accuracy of the KNN classifier were 73.87% and 96.04%.展开更多
A kind of novel nonlinear digital filter,2 D variable coutoff boundary (VCB) IIR low pass filter, is presented in this paper. Based on 1 D variable IIR low pass filter, two types of 2 D VCB IIR low pass filter a...A kind of novel nonlinear digital filter,2 D variable coutoff boundary (VCB) IIR low pass filter, is presented in this paper. Based on 1 D variable IIR low pass filter, two types of 2 D VCB IIR low pass filter are designed via spectral transformation. One is a separable 2 D VCB IIR low pass filter; the other is designed via all pass transformation. The cutoff boundary of such a kind of filter can be changed automatically according to the characteristics of input signals by adjusting the location of poles through error signals obtained lately.展开更多
变频变压器(variable frequency transformer,VFT)是一种能够联接异步电网的新型灵活交流输电系统设备。介绍了变频变压器的基本结构和主要功能,重点分析如何利用变频变压器抑制电力系统低频功率振荡,开发了基于变频变压器和普罗尼(Pro...变频变压器(variable frequency transformer,VFT)是一种能够联接异步电网的新型灵活交流输电系统设备。介绍了变频变压器的基本结构和主要功能,重点分析如何利用变频变压器抑制电力系统低频功率振荡,开发了基于变频变压器和普罗尼(Prony)方法的电力系统低频功率振荡自适应阻尼控制器的系统模型和计算程序。利用电力系统综合分析程序建立了包括变频变压器在内的典型4机电力系统和大型实际复杂电力系统的仿真模型,对不同系统规模、不同结构情况下阻尼控制器抑制低频振荡的效果进行大量仿真研究,验证了自适应阻尼控制器的适应性和有效性。展开更多
文摘VFT （variable frequency transformer） has been recently used as art alternative to HVDC （high voltage direct current） to control power flow between asynchronous networks. VFT consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery, and has better natural damping capability. VFT is simply a DFIM （doubly-fed induction machine） where the machine torque controls the power flow from stator to rotor and vice versa. The main disadvantage of this VFT is the slip rings and brushes required for the rotor circuit, especially in bulk power transmission. The BDFM （brushless doubly-fed machine） with nested cage rotor machine is proved to be a comparable alternative to conventional DFIM in many applications with the advantage that all windings being in the stator frame with fixed output terminals. In this paper, the BDFM is used as a BVFT （brushless variable frequency transformer）. A prototype machine is designed and simulated to verify the system validity.
文摘This paper introduces the design and implementation of 1 D variable cutoff frequency (VCF) digital filters. A lowpass to highpass transformation and a lowpass to bandpass transformation for VCF infinite impulse response (IIR) filter are presented. The transformed highpass and bandpass filters are implemented in a network structure in which the cutoff frequencies are variable by adjusting single parameter.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50478031)China Postdoctoral Science Foundation(Grant No.2006040240)
文摘To establish the algorithm of SAT-TMD system with the wavelet transform(WT),the modal mass participation ratio is proposed to distinguish if the high-rising structure has the characteristic of closely distributed frequencies.A time varying analytical model of high-rising structure such as TV-tower with the SAT-TMD is developed.The proposed new idea is to use WT to identify the dominant frequency of structural response in a segment time,and track its variation as a function of time to retune the SAT-TMD.The effectiveness of SAT-TMD is investigated and it is more robust to change in building stiffness and damping than that of the TMD with a fixed frequency corresponding to a fixed mode frequency of the building.It is proved that SAT-TMD is particularly effective in reducing the response even when the building stiffness is changed by ±15%;whereas the TMD loses its effectiveness under such building stiffness variations.
文摘The invariant, propagator, and wavefunction for a variable frequency harmonic oscillator in an electromagnetic field are obtained by making a specific coordinate transformation and by using the method of phase space path integral method. The probability amplitudes for a dissipative harmonic oscillator in the time varying electric field are obtained.
文摘Early detection of sudden cardiac death may be used for surviving the life of cardiac patients. In this paper we have investigated an algorithm to detect and predict sudden cardiac death, by processing of heart rate variability signal through the classical and time-frequency methods. At first, one minute of ECG signals, just before the cardiac death event are extracted and used to compute heart rate variability (HRV) signal. Five features in time domain and four features in frequency domain are extracted from the HRV signal and used as classical linear features. Then the Wigner Ville transform is applied to the HRV signal, and 11 extra features in the time-frequency (TF) domain are obtained. In order to improve the performance of classification, the principal component analysis (PCA) is applied to the obtained features vector. Finally a neural network classifier is applied to the reduced features. The obtained results show that the TF method can classify normal and SCD subjects, more efficiently than the classical methods. A MIT-BIH ECG database was used to evaluate the proposed method. The proposed method was implemented using MLP classifier and had 74.36% and 99.16% correct detection rate (accuracy) for classical features and TF method, respectively. Also, the accuracy of the KNN classifier were 73.87% and 96.04%.
文摘A kind of novel nonlinear digital filter,2 D variable coutoff boundary (VCB) IIR low pass filter, is presented in this paper. Based on 1 D variable IIR low pass filter, two types of 2 D VCB IIR low pass filter are designed via spectral transformation. One is a separable 2 D VCB IIR low pass filter; the other is designed via all pass transformation. The cutoff boundary of such a kind of filter can be changed automatically according to the characteristics of input signals by adjusting the location of poles through error signals obtained lately.
文摘依据FFT→优化窗→IFFT思路,突破线性时频变换的窗函数积分性能桎梏,实现高性能优化窗函数的线性时频变换应用,建立新型时频变换算法——K-S变换.对信号x(t)的FFT频谱向量进行频移处理后,与该频移点下Kaiser优化窗的频谱向量进行Hadamard乘积,再将乘积结果进行FFT逆变换(IFFT),构造出K-S变换复时频矩阵,由此获得x(t)的时间-频率-幅值、时间-频率-相位三维信息;给出逆变换的数学推导与局部性质、线性性质和变分辨率特性;0~150 kHz电网的稳态与时变超谐波信号仿真实验表明,K-S变换的时域、频域分辨能力均优于流行的短时傅里叶变换、S变换,具有优良的变分辨率性能;0~40 kHz超谐波信号的实测证明,基于K-S变换的超谐波电压幅值测量绝对误差均小于0.032 3 V.
文摘变频变压器(variable frequency transformer,VFT)是一种能够联接异步电网的新型灵活交流输电系统设备。介绍了变频变压器的基本结构和主要功能,重点分析如何利用变频变压器抑制电力系统低频功率振荡,开发了基于变频变压器和普罗尼(Prony)方法的电力系统低频功率振荡自适应阻尼控制器的系统模型和计算程序。利用电力系统综合分析程序建立了包括变频变压器在内的典型4机电力系统和大型实际复杂电力系统的仿真模型,对不同系统规模、不同结构情况下阻尼控制器抑制低频振荡的效果进行大量仿真研究,验证了自适应阻尼控制器的适应性和有效性。
