Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1043810
K. Kondo, K. Yuki
For railway vehicle traction purpose, slip frequency of induction traction motors are controlled with detecting rotor frequency by pulse generators or PGs as the speed sensors. Applying the speed sensor less control method to the railway vehicle traction to eliminate the PGs, we expect to improve cost efficiency and reliability of the traction control system. Though speed sensor-less control methods are popular in general industrial application purpose, some novel control functions may be added and its compatibility is verified to cope with the problem particular in railway vehicle traction application. In this paper, we present the result of the application to railway vehicle traction control with theoretical study and tests.
{"title":"An application of the induction motor speed sensor less control to railway vehicle traction system","authors":"K. Kondo, K. Yuki","doi":"10.1109/IAS.2002.1043810","DOIUrl":"https://doi.org/10.1109/IAS.2002.1043810","url":null,"abstract":"For railway vehicle traction purpose, slip frequency of induction traction motors are controlled with detecting rotor frequency by pulse generators or PGs as the speed sensors. Applying the speed sensor less control method to the railway vehicle traction to eliminate the PGs, we expect to improve cost efficiency and reliability of the traction control system. Though speed sensor-less control methods are popular in general industrial application purpose, some novel control functions may be added and its compatibility is verified to cope with the problem particular in railway vehicle traction application. In this paper, we present the result of the application to railway vehicle traction control with theoretical study and tests.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"346 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124272423","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1042736
J. Keradec
Two studies related to losses in ferrite core transformers are presented. They both aim to check the accuracy of transformer equivalent circuits. First, a 3 kW-two winding transformer is used in a converter which works at 25 kHz. In order to compare the losses forecasted using electronic circuit simulation together with the transformer electrical model, to those deduced from oscilloscopic electrical power measurements a lot of experimental precautions have been taken. Because the transformer have a power efficiency of 92%, knowing the lost part of the power within 10% needs input and output powers to be acquired within 0.4%. Second, to validate the copper losses electrical representation of a smaller transformer, calorimetric measurements have been carried out. Although in both cases high performance equipment is required, the most expensive is the time required to control it. As long as measurement is not considered as an unavoidable subject of investigation, no reliable result can be expected.
{"title":"Validating the power loss model of a transformer by measurement: the price to pay","authors":"J. Keradec","doi":"10.1109/IAS.2002.1042736","DOIUrl":"https://doi.org/10.1109/IAS.2002.1042736","url":null,"abstract":"Two studies related to losses in ferrite core transformers are presented. They both aim to check the accuracy of transformer equivalent circuits. First, a 3 kW-two winding transformer is used in a converter which works at 25 kHz. In order to compare the losses forecasted using electronic circuit simulation together with the transformer electrical model, to those deduced from oscilloscopic electrical power measurements a lot of experimental precautions have been taken. Because the transformer have a power efficiency of 92%, knowing the lost part of the power within 10% needs input and output powers to be acquired within 0.4%. Second, to validate the copper losses electrical representation of a smaller transformer, calorimetric measurements have been carried out. Although in both cases high performance equipment is required, the most expensive is the time required to control it. As long as measurement is not considered as an unavoidable subject of investigation, no reliable result can be expected.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"314 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124291154","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1042785
G. Verneau, L. Aubard, J. Crebier, C. Schaeffer, J. Schanen
This study deals with power MOSFET models. Parasitic capacitors are one of the main parameters for dynamic models, and have a critical influence on switching waveforms and switching losses. Most of classical models consider that these capacitors are one-voltage dependent. The aim of this paper is to present a new insight based on a physical structure analysis of charge locations and moves and electrical waveforms, both during switching transitions. Establishment of the model with respect to critical voltage changes is presented, and results are compared with experimental curves. This model appears to be more accurate and more reliable than PSPICE or manufacturer original models.
{"title":"Empirical power MOSFET modeling: practical characterization and simulation implantation","authors":"G. Verneau, L. Aubard, J. Crebier, C. Schaeffer, J. Schanen","doi":"10.1109/IAS.2002.1042785","DOIUrl":"https://doi.org/10.1109/IAS.2002.1042785","url":null,"abstract":"This study deals with power MOSFET models. Parasitic capacitors are one of the main parameters for dynamic models, and have a critical influence on switching waveforms and switching losses. Most of classical models consider that these capacitors are one-voltage dependent. The aim of this paper is to present a new insight based on a physical structure analysis of charge locations and moves and electrical waveforms, both during switching transitions. Establishment of the model with respect to critical voltage changes is presented, and results are compared with experimental curves. This model appears to be more accurate and more reliable than PSPICE or manufacturer original models.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114804423","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1042702
C. Grabner, E. Schmidt
The mechanical displacement of Roebel bars inlaid in slots of synchronous machines is caused by forces of electromagnetic and mechanical origin. In each occurring operational state, the mechanical behaviour is affected not only by the forces but also by nonlinear magnetic and mechanical material properties. The presented analytical calculations take into account for this influence appropriate boundary conditions and introduce correction coefficients in dependence of the bar currents. The analytical method for calculating the bar displacement is compared with fully coupled electromagnetic-mechanical finite element analyses whereby the sufficient high accuracy of the analytical results is confirmed.
{"title":"Analytical approximation of the displacement process of Roebel bars","authors":"C. Grabner, E. Schmidt","doi":"10.1109/IAS.2002.1042702","DOIUrl":"https://doi.org/10.1109/IAS.2002.1042702","url":null,"abstract":"The mechanical displacement of Roebel bars inlaid in slots of synchronous machines is caused by forces of electromagnetic and mechanical origin. In each occurring operational state, the mechanical behaviour is affected not only by the forces but also by nonlinear magnetic and mechanical material properties. The presented analytical calculations take into account for this influence appropriate boundary conditions and introduce correction coefficients in dependence of the bar currents. The analytical method for calculating the bar displacement is compared with fully coupled electromagnetic-mechanical finite element analyses whereby the sufficient high accuracy of the analytical results is confirmed.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115129407","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1042697
Yaping Du, John Burnett, S. M. Chan
Reliable emergency power supply is essential to fire services installations. However, the extent of reliability and availability of standby generators in Hong Kong buildings are a query so far. This paper presents a generator reliability survey in Hong Kong. The results regarding fault events, reliability and availability of standby generators are showed by a means of analysis on their fault/failure records. Recommendations on reliable operation of standby generators are provided also in the paper.
{"title":"Reliability of standby generators in Hong Kong buildings","authors":"Yaping Du, John Burnett, S. M. Chan","doi":"10.1109/IAS.2002.1042697","DOIUrl":"https://doi.org/10.1109/IAS.2002.1042697","url":null,"abstract":"Reliable emergency power supply is essential to fire services installations. However, the extent of reliability and availability of standby generators in Hong Kong buildings are a query so far. This paper presents a generator reliability survey in Hong Kong. The results regarding fault events, reliability and availability of standby generators are showed by a means of analysis on their fault/failure records. Recommendations on reliable operation of standby generators are provided also in the paper.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114504492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1042722
R. Hill-Cottingham, P. C. Coles, J. Eastham, F. Profumo, A. Tenconi, G. Gianolio, M. Cerchio
High efficiency at full load as well as at partial load and high torque density are the challenging characteristics required by the propulsion system for a solar aircraft. The proposed solution is a multi-disc axial flux PM motor with a mechanical structure made of plastic materials: (a) the multi-disc geometry allows high torque density by increasing the number of air-gap surfaces; (b) the PMs and the (almost) ironless magnetic circuit, cutting the no load losses, allow very high efficiency over the complete working range; (c) the motor structure made of plastic materials, with high thermal and mechanical characteristics, allows further increases in the torque density. The paper presents the motor design and performances.
{"title":"Plastic structure multi-disc axial flux PM motor","authors":"R. Hill-Cottingham, P. C. Coles, J. Eastham, F. Profumo, A. Tenconi, G. Gianolio, M. Cerchio","doi":"10.1109/IAS.2002.1042722","DOIUrl":"https://doi.org/10.1109/IAS.2002.1042722","url":null,"abstract":"High efficiency at full load as well as at partial load and high torque density are the challenging characteristics required by the propulsion system for a solar aircraft. The proposed solution is a multi-disc axial flux PM motor with a mechanical structure made of plastic materials: (a) the multi-disc geometry allows high torque density by increasing the number of air-gap surfaces; (b) the PMs and the (almost) ironless magnetic circuit, cutting the no load losses, allow very high efficiency over the complete working range; (c) the motor structure made of plastic materials, with high thermal and mechanical characteristics, allows further increases in the torque density. The paper presents the motor design and performances.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114717791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1043808
A. Trzynadlowski, Zhiqiang Wang, J. Nagashima, C. Stancu
Results of a comparative investigation of deterministic and random PWM techniques to be employed in a new AC drive system for electric vehicles, currently under development at General Motors Company, are presented. The study, employing the advanced simulation package SABER from Avant! Corp., was focused on the reduction of electromagnetic interference (EMI) when a deterministic PWM strategy is replaced with a random PWM (RPWM) method. To assess the impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were also investigated. Two RPWM techniques with randomly varied switching frequency of the inverter were considered: one with the sampling frequency of the modulator varying in step with the switching frequency, and one with a fixed sampling frequency equal to the average switching frequency. The study has demonstrated good potentials of RPWM techniques, whose use results in EMI reduction by 10 dB and more, while the drive performance is barely affected.
{"title":"Comparative investigation of PWM techniques for general motors' new drive for electric vehicles","authors":"A. Trzynadlowski, Zhiqiang Wang, J. Nagashima, C. Stancu","doi":"10.1109/IAS.2002.1043808","DOIUrl":"https://doi.org/10.1109/IAS.2002.1043808","url":null,"abstract":"Results of a comparative investigation of deterministic and random PWM techniques to be employed in a new AC drive system for electric vehicles, currently under development at General Motors Company, are presented. The study, employing the advanced simulation package SABER from Avant! Corp., was focused on the reduction of electromagnetic interference (EMI) when a deterministic PWM strategy is replaced with a random PWM (RPWM) method. To assess the impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were also investigated. Two RPWM techniques with randomly varied switching frequency of the inverter were considered: one with the sampling frequency of the modulator varying in step with the switching frequency, and one with a fixed sampling frequency equal to the average switching frequency. The study has demonstrated good potentials of RPWM techniques, whose use results in EMI reduction by 10 dB and more, while the drive performance is barely affected.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117347339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1043769
D. Katsis, J. D. van Wyk
Power cycling in operating power semiconductors creates stresses in the device package. These stresses cause cracks to grow in the solder die-attach layer, leading to voids between the silicon and the heat spreader. The thermal performance of power semiconductor devices is eventually compromised by these voids. This study compares the thermal impedance of modules with varying void area at a constant power dissipation level in order to develop a relationship between thermal impedance and void area. The effect of aging on thermal transient behavior is then correlated to finite element thermal simulations. Conclusions about the impact of thermal performance changes due to aging are created to help designers accommodate for the growth of age-related defects and their effects on operating temperature of power semiconductor devices.
{"title":"Experimental measurement and simulation of thermal performance due to aging in power semiconductor devices","authors":"D. Katsis, J. D. van Wyk","doi":"10.1109/IAS.2002.1043769","DOIUrl":"https://doi.org/10.1109/IAS.2002.1043769","url":null,"abstract":"Power cycling in operating power semiconductors creates stresses in the device package. These stresses cause cracks to grow in the solder die-attach layer, leading to voids between the silicon and the heat spreader. The thermal performance of power semiconductor devices is eventually compromised by these voids. This study compares the thermal impedance of modules with varying void area at a constant power dissipation level in order to develop a relationship between thermal impedance and void area. The effect of aging on thermal transient behavior is then correlated to finite element thermal simulations. Conclusions about the impact of thermal performance changes due to aging are created to help designers accommodate for the growth of age-related defects and their effects on operating temperature of power semiconductor devices.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123479957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1044154
A. Rubaai
This paper suggests a control strategy of coordinating multiple dynamic-braking units during the transients ensuing major disturbances. The control strategy considered in this study is a two-level hierarchy. The proposed two-level structure results from the decomposition of the overall problem into parallel sub-problems. This allows the retention of the closed-loop controls associated with each subsystem, which together constitute the lower level (Level I). The central coordinating controller forms the upper level (Level II). The coordination of the local controllers by the central controller, accounts for nonlinear terms and interconnections, and yields the global optimization of the overall system transient performance. The local controllers are not dependent on one another and are robust to any changes in the network configuration, due to the feedback or closed-loop control formulation inherent in the proposed strategy. To ensure physical realizability of the local controllers, the input was restricted to locally measurable signals. The methodology was implemented into a prototype software program, which was tested on a single machine connected to a very large network approximated by an infinite bus, and then on the IEEE four-generator test system. These studies considered fault clearing times greater that the critical, assuring an unstable condition. The well-damped optimal state and control trajectories illustrate the successful solution of the problem, indicating that the technique is a valuable tool dealing with transient control problems for large-scale systems.
{"title":"Design and analysis of nonlinear hierarchical controllers for electric utility industry","authors":"A. Rubaai","doi":"10.1109/IAS.2002.1044154","DOIUrl":"https://doi.org/10.1109/IAS.2002.1044154","url":null,"abstract":"This paper suggests a control strategy of coordinating multiple dynamic-braking units during the transients ensuing major disturbances. The control strategy considered in this study is a two-level hierarchy. The proposed two-level structure results from the decomposition of the overall problem into parallel sub-problems. This allows the retention of the closed-loop controls associated with each subsystem, which together constitute the lower level (Level I). The central coordinating controller forms the upper level (Level II). The coordination of the local controllers by the central controller, accounts for nonlinear terms and interconnections, and yields the global optimization of the overall system transient performance. The local controllers are not dependent on one another and are robust to any changes in the network configuration, due to the feedback or closed-loop control formulation inherent in the proposed strategy. To ensure physical realizability of the local controllers, the input was restricted to locally measurable signals. The methodology was implemented into a prototype software program, which was tested on a single machine connected to a very large network approximated by an infinite bus, and then on the IEEE four-generator test system. These studies considered fault clearing times greater that the critical, assuring an unstable condition. The well-damped optimal state and control trajectories illustrate the successful solution of the problem, indicating that the technique is a valuable tool dealing with transient control problems for large-scale systems.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122135151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2002-12-10DOI: 10.1109/IAS.2002.1043747
B. Gerhard, M. Manjrekar, J. Daniel, P. Maibach
The result of several control schemes, applied to three-phase line-connected PWM converters under unbalanced input voltage conditions, is to further reduce the utility supply voltages due to the drawn currents. The proposed method, named equal resistance control (ERC), considers the health of the phases during unbalanced conditions in order to minimize the effects of the drawn power on the network voltages. The control philosophy is to make the current drawn from a particular phase proportional to the amplitude of remaining voltage on that phase and in-synchronism with its phase angle. The power transfer to the load is therefore optimal since no reactive power is drawn from the network. The ERC philosophy uses a feedforward per-phase control structure, where the voltage drop across the input impedance is estimated. An application example is included where this scheme is applied to a power quality device designed to mitigate voltage disturbances. Theoretical analysis, computer simulations and experimental measurements are included.
{"title":"Equal resistance control-a control methodology for line-connected converters that offers balanced resistive load under unbalanced input voltage conditions","authors":"B. Gerhard, M. Manjrekar, J. Daniel, P. Maibach","doi":"10.1109/IAS.2002.1043747","DOIUrl":"https://doi.org/10.1109/IAS.2002.1043747","url":null,"abstract":"The result of several control schemes, applied to three-phase line-connected PWM converters under unbalanced input voltage conditions, is to further reduce the utility supply voltages due to the drawn currents. The proposed method, named equal resistance control (ERC), considers the health of the phases during unbalanced conditions in order to minimize the effects of the drawn power on the network voltages. The control philosophy is to make the current drawn from a particular phase proportional to the amplitude of remaining voltage on that phase and in-synchronism with its phase angle. The power transfer to the load is therefore optimal since no reactive power is drawn from the network. The ERC philosophy uses a feedforward per-phase control structure, where the voltage drop across the input impedance is estimated. An application example is included where this scheme is applied to a power quality device designed to mitigate voltage disturbances. Theoretical analysis, computer simulations and experimental measurements are included.","PeriodicalId":202482,"journal":{"name":"Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344)","volume":"48 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120818237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：