Voltage sag is one of the most common power quality disturbances in industry,which causes huge inrush currents in stator windings of induction motors,and adversely impacts the motor secure operation.This paper firstly...Voltage sag is one of the most common power quality disturbances in industry,which causes huge inrush currents in stator windings of induction motors,and adversely impacts the motor secure operation.This paper firstly introduces a 2D Time-Stepping multi-slice finite element method(2D T-S multi-slice FEM)which is used for calculating the magnetic field distribution in induction motors under different sag events.Then the paper deduces the transient analytical expression of stator inrush current based on the classical theory of AC motors and presents a separation method for the positive,negative and zero sequence values based on instantaneous currents.With this method,the paper studies the influences of voltage sag amplitude,phase-angle jump and initial phase angle on the stator positive-and negative-sequence peak currents of 5.5 kW and 55 kW induction motors.This paper further proposes a motor protection method under voltage sag condition with the stator negative-sequence peak currents as the protection threshold,so that the protection false trip can be avoided effectively.Finally,the calculation and analysis results are validated by the comparison of calculated and measured stator peak value of the 5.5 kW induction motor.展开更多
The N3 power plant of Taipower is located in the southern tip of Taiwan and connected to the power pool by four out-linking 345-kV overhead transmission circuits. There are two 951-MW generators. Each generator occupi...The N3 power plant of Taipower is located in the southern tip of Taiwan and connected to the power pool by four out-linking 345-kV overhead transmission circuits. There are two 951-MW generators. Each generator occupied 11% of the system peak load in 1985 when the generator was in commercial operation. Since Taipower is an isolated system, at the N-2 conditions, those generators were reduced to 75% loading to protect the power system. By the way, to avoid damage of negative sequence current (NSC), the limits of the N3 power plant are stricter than those in the IEEE Standard. However, in 2010, the capacity ratio of each generator in the plant to the system peak load has been reduced to 3% only. To increase the economic benefit of those generators, it is required to reassess the operation limits of NSC. EMTP was used to calculate the levels of NSC from the out-linking transmission circuits. From the results of this study, the effects of NSC could be ignored when the four out-linking circuits are in N-0, N-1, and N-2 conditions. The generators can be operated in full loading under these conditions. The modifications to the NSC limits of the N3 power plant are also suggested.展开更多
To improve the accuracy of the stator winding fault diagnosis in induction motor,a new diagnostic method based on the Hilbert-Huang transform(HHT)was proposed.The ratio of fundamental zero sequence voltage to positive...To improve the accuracy of the stator winding fault diagnosis in induction motor,a new diagnostic method based on the Hilbert-Huang transform(HHT)was proposed.The ratio of fundamental zero sequence voltage to positive sequence voltage after switch-off was selected as the stator fault characteristic,which could effectively avoid the influence of the supply unbalance and the load fluctuation,and directly represent the asymmetry in the stator.Using the empirical mode decomposition(EMD)based on HHT,the zero sequence voltage after switch-off was decomposed and the fundamental component was extracted.Then,the fault characteristic can be acquired.Experimental results on a 4-kW induction motor demonstrate the feasibility and effectiveness of this method.展开更多
高压直挂电池储能系统(battery energy storage system,BESS)采用H桥电路串联的方法升高电压后接入电网,将电池簇分散接入级联H桥变换器的直流侧,具有高度模块化的结构,对比低压方案具有单机容量大、效率高、响应速度快等明显优势。高...高压直挂电池储能系统(battery energy storage system,BESS)采用H桥电路串联的方法升高电压后接入电网,将电池簇分散接入级联H桥变换器的直流侧,具有高度模块化的结构,对比低压方案具有单机容量大、效率高、响应速度快等明显优势。高压直挂BESS若能兼具无功补偿能力,实现系统四象限运行,将具有更大的成本优势和经济效益。电池簇接单相H桥变换器的结构,使得系统运行在高比例无功补偿工况时,电池簇电流在一个二倍基频的周期中会出现两次反向,导致电池运行在高频充放电的工况,这会对电池寿命和电池状态监测造成较大的影响。为解决这一问题,提出一种基于零序电压注入的高比例无功补偿控制方法,避免了二倍基频脉动电流对电池进行高频充放电,再通过优化零序电压的幅值和相位,最大程度上降低对电池的影响。展开更多
Objective:To compare the efficacy of platinum-and non-platinum-based regimens as first-line treatment for advanced triple-negative breast cancer(TNBC)and analyze the relationship between their efficacy and BRCA gene s...Objective:To compare the efficacy of platinum-and non-platinum-based regimens as first-line treatment for advanced triple-negative breast cancer(TNBC)and analyze the relationship between their efficacy and BRCA gene status.Methods:Retrospectively analyze clinical data of 220 patients diagnosed pathologically with advanced TNBC and treated at the Department of Breast Oncology,Peking University Cancer Hospital from 2013 to 2018 and evaluate the efficacy of chemotherapy.A total of 114 patients had BRCA1/2 gene tested by next generation sequencing(NGS)using peripheral blood,and we analyzed the correlation between their efficacy and BRCA1/2 gene status.Results:Non-platinum-based chemotherapy(NPCT)was administered to 129 and platinum-based chemotherapy(PBCT)to 91 study patients.The clinical benefit rate(CBR)and median progression-free survival(PFS)were not statistically different between NPCT and PBCT groups.The median overall survival(OS)was 30.0 and 22.5 months for PBCT and NPCT group,respectively[P=0.090,hazard ratios(HR)=0.703].BRCA status was assessed in 114 patients,14 of whom had deleterious germline BRCA1/2(g BRCA)mutations(seven in each group).In PBCT group,the CBR was 85.7%and 35.1%for patients with and without deleterious g BRCA mutations,respectively(P=0.039).The median PFS were 14.9 and 5.3 months and median OS were 26.5 and 15.5 months for patients with and without deleterious g BRCA mutations,respectively(P=0.001,P=0.161,respectively).Patients in PBCT group had significantly greater rates of grade 3-4 anemia(5.5%vs.0%)and thrombocytopenia(8.8%vs.0%),whereas palmar-plantar erythrodysesthesia(12.4%vs.0%)and peripheral neuropathy(8.6%vs.1.1%)occurred more frequently in NPCT group.Conclusions:Platinum-based regimens are more effective in patients with deleterious g BRCA mutations,but no difference in patients without BRCA gene mutations,so non-platinum is an option in patients without BRCA gene mutations considering the toxicity and side effect.And we recommend that patients with advanced TNBC should have BRCA gene test.展开更多
this study provided the strong evidence that L2 learner's development patterns in syntactic structure is very similar to the pattern of L1 learners.L2 and L1 learner pass the similar gradual route to get the TL ne...this study provided the strong evidence that L2 learner's development patterns in syntactic structure is very similar to the pattern of L1 learners.L2 and L1 learner pass the similar gradual route to get the TL negative structure.But L2 learners' acquisitional sequences are not completely rigid.Individual learners may be interfered by other social or psychological factors en route and they may take longer than two years and some never travel the whole distance.展开更多
A novel control strategy for three-phase shunt active power filter (SAPF) was proposed to improve its performance under non-ideal mains voltages. The approach was inspired by our finding that the classic instantaneous...A novel control strategy for three-phase shunt active power filter (SAPF) was proposed to improve its performance under non-ideal mains voltages. The approach was inspired by our finding that the classic instantaneous reactive power theory based algorithm was unsatisfactory in terms of isolating positive sequence fundamental active components exactly under non-ideal mains voltages. So, a modified ip-iq reference current calculation method was presented. With usage of the new method, not only the positive sequence but also the fundamental active current components can be accurately isolated from load current. A deadbeat closed-loop control model is built in order to eliminate both delay error and tracking error between reference voltages and compensation voltages under unbalanced and distorted mains voltages. Computer simulation results show that the proposed strategy is effective with better tracking ability and lower total harmonic distortion (THD). The strategy is also applied to a 10 kV substation with a local electrolysis manganese plant injecting a large amount of harmonics into the power system, and is proved to be more practical and efficient.展开更多
The main purpose of the electrical power system is to transport and distribute energy generated by the central power plants in a safe and reliable manner to the customer premises. Most of the electrical equipment is e...The main purpose of the electrical power system is to transport and distribute energy generated by the central power plants in a safe and reliable manner to the customer premises. Most of the electrical equipment is exposed within the open which suggests they can be vulnerable to lightning strikes, road dwindling, windstorms, and a few engineering activities with the potential of causing different degrees of damage to the electrical equipment. One of the ways to guard the equipment is to deploy switching devices. However, the operations of most of these switching devices produce oscillatory transient in the electrical transmission and distribution systems which result in voltage, current, and frequency fluctuations in the load. This paper investigates the effect of switching devices on power quality and proposes a positive sequence voltage power transient suppression technique that can spontaneously improve the distorted voltage at the instant of capacitor switching using the capacitor line model as a case study. MATLAB/Simulink software was utilized for the analysis on an electrical network model with bus voltages of 69 kV/12.47 kV and 480 V. The results showed that, during switching operations, the positive sequence voltage power detector block produces ripple-free accurate results.展开更多
基金This work was supported in part by the National Natural Science Foundation of China under Grant51307050。
文摘Voltage sag is one of the most common power quality disturbances in industry,which causes huge inrush currents in stator windings of induction motors,and adversely impacts the motor secure operation.This paper firstly introduces a 2D Time-Stepping multi-slice finite element method(2D T-S multi-slice FEM)which is used for calculating the magnetic field distribution in induction motors under different sag events.Then the paper deduces the transient analytical expression of stator inrush current based on the classical theory of AC motors and presents a separation method for the positive,negative and zero sequence values based on instantaneous currents.With this method,the paper studies the influences of voltage sag amplitude,phase-angle jump and initial phase angle on the stator positive-and negative-sequence peak currents of 5.5 kW and 55 kW induction motors.This paper further proposes a motor protection method under voltage sag condition with the stator negative-sequence peak currents as the protection threshold,so that the protection false trip can be avoided effectively.Finally,the calculation and analysis results are validated by the comparison of calculated and measured stator peak value of the 5.5 kW induction motor.
文摘The N3 power plant of Taipower is located in the southern tip of Taiwan and connected to the power pool by four out-linking 345-kV overhead transmission circuits. There are two 951-MW generators. Each generator occupied 11% of the system peak load in 1985 when the generator was in commercial operation. Since Taipower is an isolated system, at the N-2 conditions, those generators were reduced to 75% loading to protect the power system. By the way, to avoid damage of negative sequence current (NSC), the limits of the N3 power plant are stricter than those in the IEEE Standard. However, in 2010, the capacity ratio of each generator in the plant to the system peak load has been reduced to 3% only. To increase the economic benefit of those generators, it is required to reassess the operation limits of NSC. EMTP was used to calculate the levels of NSC from the out-linking transmission circuits. From the results of this study, the effects of NSC could be ignored when the four out-linking circuits are in N-0, N-1, and N-2 conditions. The generators can be operated in full loading under these conditions. The modifications to the NSC limits of the N3 power plant are also suggested.
基金Project (No. 50677060) supported by the National Natural ScienceFoundation of China
文摘To improve the accuracy of the stator winding fault diagnosis in induction motor,a new diagnostic method based on the Hilbert-Huang transform(HHT)was proposed.The ratio of fundamental zero sequence voltage to positive sequence voltage after switch-off was selected as the stator fault characteristic,which could effectively avoid the influence of the supply unbalance and the load fluctuation,and directly represent the asymmetry in the stator.Using the empirical mode decomposition(EMD)based on HHT,the zero sequence voltage after switch-off was decomposed and the fundamental component was extracted.Then,the fault characteristic can be acquired.Experimental results on a 4-kW induction motor demonstrate the feasibility and effectiveness of this method.
文摘高压直挂电池储能系统(battery energy storage system,BESS)采用H桥电路串联的方法升高电压后接入电网,将电池簇分散接入级联H桥变换器的直流侧,具有高度模块化的结构,对比低压方案具有单机容量大、效率高、响应速度快等明显优势。高压直挂BESS若能兼具无功补偿能力,实现系统四象限运行,将具有更大的成本优势和经济效益。电池簇接单相H桥变换器的结构,使得系统运行在高比例无功补偿工况时,电池簇电流在一个二倍基频的周期中会出现两次反向,导致电池运行在高频充放电的工况,这会对电池寿命和电池状态监测造成较大的影响。为解决这一问题,提出一种基于零序电压注入的高比例无功补偿控制方法,避免了二倍基频脉动电流对电池进行高频充放电,再通过优化零序电压的幅值和相位,最大程度上降低对电池的影响。
文摘Objective:To compare the efficacy of platinum-and non-platinum-based regimens as first-line treatment for advanced triple-negative breast cancer(TNBC)and analyze the relationship between their efficacy and BRCA gene status.Methods:Retrospectively analyze clinical data of 220 patients diagnosed pathologically with advanced TNBC and treated at the Department of Breast Oncology,Peking University Cancer Hospital from 2013 to 2018 and evaluate the efficacy of chemotherapy.A total of 114 patients had BRCA1/2 gene tested by next generation sequencing(NGS)using peripheral blood,and we analyzed the correlation between their efficacy and BRCA1/2 gene status.Results:Non-platinum-based chemotherapy(NPCT)was administered to 129 and platinum-based chemotherapy(PBCT)to 91 study patients.The clinical benefit rate(CBR)and median progression-free survival(PFS)were not statistically different between NPCT and PBCT groups.The median overall survival(OS)was 30.0 and 22.5 months for PBCT and NPCT group,respectively[P=0.090,hazard ratios(HR)=0.703].BRCA status was assessed in 114 patients,14 of whom had deleterious germline BRCA1/2(g BRCA)mutations(seven in each group).In PBCT group,the CBR was 85.7%and 35.1%for patients with and without deleterious g BRCA mutations,respectively(P=0.039).The median PFS were 14.9 and 5.3 months and median OS were 26.5 and 15.5 months for patients with and without deleterious g BRCA mutations,respectively(P=0.001,P=0.161,respectively).Patients in PBCT group had significantly greater rates of grade 3-4 anemia(5.5%vs.0%)and thrombocytopenia(8.8%vs.0%),whereas palmar-plantar erythrodysesthesia(12.4%vs.0%)and peripheral neuropathy(8.6%vs.1.1%)occurred more frequently in NPCT group.Conclusions:Platinum-based regimens are more effective in patients with deleterious g BRCA mutations,but no difference in patients without BRCA gene mutations,so non-platinum is an option in patients without BRCA gene mutations considering the toxicity and side effect.And we recommend that patients with advanced TNBC should have BRCA gene test.
文摘this study provided the strong evidence that L2 learner's development patterns in syntactic structure is very similar to the pattern of L1 learners.L2 and L1 learner pass the similar gradual route to get the TL negative structure.But L2 learners' acquisitional sequences are not completely rigid.Individual learners may be interfered by other social or psychological factors en route and they may take longer than two years and some never travel the whole distance.
基金Project(JC200903180555A) supported by Shenzhen City Science and Technology Plan, China
文摘A novel control strategy for three-phase shunt active power filter (SAPF) was proposed to improve its performance under non-ideal mains voltages. The approach was inspired by our finding that the classic instantaneous reactive power theory based algorithm was unsatisfactory in terms of isolating positive sequence fundamental active components exactly under non-ideal mains voltages. So, a modified ip-iq reference current calculation method was presented. With usage of the new method, not only the positive sequence but also the fundamental active current components can be accurately isolated from load current. A deadbeat closed-loop control model is built in order to eliminate both delay error and tracking error between reference voltages and compensation voltages under unbalanced and distorted mains voltages. Computer simulation results show that the proposed strategy is effective with better tracking ability and lower total harmonic distortion (THD). The strategy is also applied to a 10 kV substation with a local electrolysis manganese plant injecting a large amount of harmonics into the power system, and is proved to be more practical and efficient.
文摘The main purpose of the electrical power system is to transport and distribute energy generated by the central power plants in a safe and reliable manner to the customer premises. Most of the electrical equipment is exposed within the open which suggests they can be vulnerable to lightning strikes, road dwindling, windstorms, and a few engineering activities with the potential of causing different degrees of damage to the electrical equipment. One of the ways to guard the equipment is to deploy switching devices. However, the operations of most of these switching devices produce oscillatory transient in the electrical transmission and distribution systems which result in voltage, current, and frequency fluctuations in the load. This paper investigates the effect of switching devices on power quality and proposes a positive sequence voltage power transient suppression technique that can spontaneously improve the distorted voltage at the instant of capacitor switching using the capacitor line model as a case study. MATLAB/Simulink software was utilized for the analysis on an electrical network model with bus voltages of 69 kV/12.47 kV and 480 V. The results showed that, during switching operations, the positive sequence voltage power detector block produces ripple-free accurate results.
