“双高”电力系统对实时仿真算法的计算效率提出了更高的要求,采用单一的仿真算法往往难以兼顾计算效率与仿真精度。为解决这一问题,提出了一种混合使用移频分析(shifted frequency analysis,SFA)与传统电磁暂态(electromagnetic transi...“双高”电力系统对实时仿真算法的计算效率提出了更高的要求,采用单一的仿真算法往往难以兼顾计算效率与仿真精度。为解决这一问题,提出了一种混合使用移频分析(shifted frequency analysis,SFA)与传统电磁暂态(electromagnetic transients program,EMTP)方法的多速率实时仿真方案,并对子系统的接口算法进行了改进。首先,充分发挥SFA方法的高效性优势,建立了在移频相量下联立子系统诺顿等效电路的SFA-EMTP混合仿真框架。随后,从减少计算量的角度出发,提出了一种滑窗离散傅里叶变换与三相坐标变换相结合的解析信号构造方法。进而,为兼顾计算的实时性与仿真精度,提出了一种开关状态更新时刻与仿真节点错位的多速率仿真计算时序。最后,对含分布式电源接入的配电网算例采用所提算法与其他多种算法进行仿真,并将仿真结果与PSCAD(Power Systems Computer Aided Design)的离线仿真结果进行对比,验证了所提算法的正确性和有效性。展开更多
针对基于电压源转换器的高压直流(high voltage direct current based voltage source converter,VSC-HVDC)输电系统,该文提出电磁暂态–机电暂态多尺度建模方法并验证多尺度仿真算法的准确、快速和灵活性。该模型采用频移分析(shifted-...针对基于电压源转换器的高压直流(high voltage direct current based voltage source converter,VSC-HVDC)输电系统,该文提出电磁暂态–机电暂态多尺度建模方法并验证多尺度仿真算法的准确、快速和灵活性。该模型采用频移分析(shifted-frequency analysis,SFA)等多尺度建模方法。首先推导移频(shifted frequency,SF)域和dq域之间的解析变换关系,并提出用于系统特性分析的VSC移频多尺度模型;其次,选择性插入π模型获得直流输电线的多尺度暂态模型;最后,通过调整仿真参数,如仿真时间步长和移动频率,使得建立的模型能够灵活仿真具有多个时间尺度和不同网络位置的各种暂态。采用两端和五端VSC-HVDC输电系统作为算例,仿真结果对比表明,提出的模型和算法能够精确模拟高频暂态,快速仿真慢变化暂态,降低计算成本。此外,多尺度模型还可提高VSC-HVDC输电系统电磁–机电暂态混合仿真的灵活性。展开更多
The Autoregressive Moving Average （ARMA） model for whispered speech is proposed. with normal speech, whispered speech has no fundamental frequency because of the glottis being semi-opened and turbulent flow being cr...The Autoregressive Moving Average （ARMA） model for whispered speech is proposed. with normal speech, whispered speech has no fundamental frequency because of the glottis being semi-opened and turbulent flow being created, and formant shifting exists in the lower frequency region due to the narrowing of the tract in the false vocal fold regions and weak acoustic coupling with the aubglottal system. Analysis shows that the effect of the subglottal system is to introduce additional pole-zero pairs into the vocal tract transfer function. Theoretically, the method based on an ARMA process is superior to that based on an AR process in the spectral analysis of the whispered speech. Two methods, the least squared modified Yule-Walker likelihood estimate （LSMY） algorithm and the Frequency-Domain Steiglitz-Mcbide （FDSM） algorithm, are applied to the ARMA mfldel for the whispered speech. The performance evaluation shows that the ARMA model is much more appropriate for representing the whispered speech than the AR model, and the FDSM algorithm provides a name acorate estimation of the whispered speech spectral envelope than the LSMY algorithm with higher conputational complexity.展开更多
Objective： To evaluate the comparative therapeutic efficacy of radiofrequency ablation （RFA） and hepatic resection （HR） for breast cancer liver metastases （BCLMs）. Methods： Studies that had examined the outcom...Objective： To evaluate the comparative therapeutic efficacy of radiofrequency ablation （RFA） and hepatic resection （HR） for breast cancer liver metastases （BCLMs）. Methods： Studies that had examined the outcomes for both RFA and HR for BCLM were identified by searching the electronic databases PubMed, EMBASE, and the Cochrane Library. Pooled analyzes of the overall survival （OS）, disease-free survival （DFS）, and short-term outcomes of BCLM were performed. Results： Patients with BCLM gained many more survival benefits from HR than from RFA with regard to the 3-year OS rate （combined odds ratio （OR） 0.41, 95% confidence interval （CI） 0.29-0.59, P〈0.001）, 5-year OS rate （combined OR 0.38, 95% CI 0.32-0.46, P〈0.001）, 3-year DFS （combined OR 0.36, 95% CI 0.27-0.49, P〈0.001）, and 5-year DFS （combined OR 0.51, 95% CI 0.40-0.66, P〈0.001）. RFA had fewer postoperative compli- cations （combined OR 0.30, 95% CI 0.20-0.44, P〈0.001） and shorter hospital stays （combined OR -9.01, 95% CI -13.49-4.54, P〈0.001） than HR. Conclusions： HR takes precedence over RFA in the treatment of patients with BCLM, considering the better survival rate. RFA gives rise to fewer complications and can be carried out with a shorter hos- pital stay, compared to HR. RFA should be reserved for patients who are not optimum candidates for resection.展开更多
文摘“双高”电力系统对实时仿真算法的计算效率提出了更高的要求,采用单一的仿真算法往往难以兼顾计算效率与仿真精度。为解决这一问题,提出了一种混合使用移频分析(shifted frequency analysis,SFA)与传统电磁暂态(electromagnetic transients program,EMTP)方法的多速率实时仿真方案,并对子系统的接口算法进行了改进。首先,充分发挥SFA方法的高效性优势,建立了在移频相量下联立子系统诺顿等效电路的SFA-EMTP混合仿真框架。随后,从减少计算量的角度出发,提出了一种滑窗离散傅里叶变换与三相坐标变换相结合的解析信号构造方法。进而,为兼顾计算的实时性与仿真精度,提出了一种开关状态更新时刻与仿真节点错位的多速率仿真计算时序。最后,对含分布式电源接入的配电网算例采用所提算法与其他多种算法进行仿真,并将仿真结果与PSCAD(Power Systems Computer Aided Design)的离线仿真结果进行对比,验证了所提算法的正确性和有效性。
文摘针对基于电压源转换器的高压直流(high voltage direct current based voltage source converter,VSC-HVDC)输电系统,该文提出电磁暂态–机电暂态多尺度建模方法并验证多尺度仿真算法的准确、快速和灵活性。该模型采用频移分析(shifted-frequency analysis,SFA)等多尺度建模方法。首先推导移频(shifted frequency,SF)域和dq域之间的解析变换关系,并提出用于系统特性分析的VSC移频多尺度模型;其次,选择性插入π模型获得直流输电线的多尺度暂态模型;最后,通过调整仿真参数,如仿真时间步长和移动频率,使得建立的模型能够灵活仿真具有多个时间尺度和不同网络位置的各种暂态。采用两端和五端VSC-HVDC输电系统作为算例,仿真结果对比表明,提出的模型和算法能够精确模拟高频暂态,快速仿真慢变化暂态,降低计算成本。此外,多尺度模型还可提高VSC-HVDC输电系统电磁–机电暂态混合仿真的灵活性。
基金supported by the Independent Innovation Foundation of Shandong University(No.2009JC004)the Natural Science Foundation of Shandong Province(No.Y2007G31)
文摘The Autoregressive Moving Average （ARMA） model for whispered speech is proposed. with normal speech, whispered speech has no fundamental frequency because of the glottis being semi-opened and turbulent flow being created, and formant shifting exists in the lower frequency region due to the narrowing of the tract in the false vocal fold regions and weak acoustic coupling with the aubglottal system. Analysis shows that the effect of the subglottal system is to introduce additional pole-zero pairs into the vocal tract transfer function. Theoretically, the method based on an ARMA process is superior to that based on an AR process in the spectral analysis of the whispered speech. Two methods, the least squared modified Yule-Walker likelihood estimate （LSMY） algorithm and the Frequency-Domain Steiglitz-Mcbide （FDSM） algorithm, are applied to the ARMA mfldel for the whispered speech. The performance evaluation shows that the ARMA model is much more appropriate for representing the whispered speech than the AR model, and the FDSM algorithm provides a name acorate estimation of the whispered speech spectral envelope than the LSMY algorithm with higher conputational complexity.
文摘Objective： To evaluate the comparative therapeutic efficacy of radiofrequency ablation （RFA） and hepatic resection （HR） for breast cancer liver metastases （BCLMs）. Methods： Studies that had examined the outcomes for both RFA and HR for BCLM were identified by searching the electronic databases PubMed, EMBASE, and the Cochrane Library. Pooled analyzes of the overall survival （OS）, disease-free survival （DFS）, and short-term outcomes of BCLM were performed. Results： Patients with BCLM gained many more survival benefits from HR than from RFA with regard to the 3-year OS rate （combined odds ratio （OR） 0.41, 95% confidence interval （CI） 0.29-0.59, P〈0.001）, 5-year OS rate （combined OR 0.38, 95% CI 0.32-0.46, P〈0.001）, 3-year DFS （combined OR 0.36, 95% CI 0.27-0.49, P〈0.001）, and 5-year DFS （combined OR 0.51, 95% CI 0.40-0.66, P〈0.001）. RFA had fewer postoperative compli- cations （combined OR 0.30, 95% CI 0.20-0.44, P〈0.001） and shorter hospital stays （combined OR -9.01, 95% CI -13.49-4.54, P〈0.001） than HR. Conclusions： HR takes precedence over RFA in the treatment of patients with BCLM, considering the better survival rate. RFA gives rise to fewer complications and can be carried out with a shorter hos- pital stay, compared to HR. RFA should be reserved for patients who are not optimum candidates for resection.
