The voltage source converter based high voltage direct current(VSC-HVDC)system is based on voltage source converter,and its control system is more complex.Also affected by the fast control of power electronics,oscilla...The voltage source converter based high voltage direct current(VSC-HVDC)system is based on voltage source converter,and its control system is more complex.Also affected by the fast control of power electronics,oscillation phenomenon in wide frequency domain may occur.To address the problem of small signal stability of the VSCHVDC system,a converter control strategy is designed to improve its small signal stability,and the risk of system oscillation is reduced by attaching a damping controller and optimizing the control parameters.Based on the modeling of the VSC-HVDC system,the general architecture of the inner and outer loop control of the VSCHVDC converter is established;and the damping controllers for DC control and AC control are designed in the phase-locked loop and the inner and outer loop control parts respectively;the state-space statemodel of the control system is established to analyze its performance.And the electromagnetic transient simulation model is built on the PSCAD/EMTDC simulation platform to verify the accuracy of the small signal model.The influence of the parameters of each control part on the stability of the system is summarized.The main control parts affecting stability are optimized for the phenomenon of oscillation due to changes in operation mode occurring on the AC side due to faults and other reasons,which effectively eliminates system oscillation and improves system small signal stability,providing a certain reference for engineering design.展开更多
Objective： To evaluate the clinical efficacy of Shenqi Fuzheng injection combined with gemcitabine plus cisplatin（GP） in the treatment of advanced non-small cell lung cancer （NSCLC）. Methods： we performed a syst...Objective： To evaluate the clinical efficacy of Shenqi Fuzheng injection combined with gemcitabine plus cisplatin（GP） in the treatment of advanced non-small cell lung cancer （NSCLC）. Methods： we performed a systematicsearch in the electronic databases such as Cochrane Library, Pubmed, Embase, Chinese Journal Full-text Database,Chinese Biomedical Literature Database, Chinese Science and Technology Periodical Full-text Database andWanfang Database up to 30 January 2017. Randomized controlled trials （RCT） of Shenqi Fuzheng Injectioncombined with GP chemotherapy in the treatment of advanced NSCLC were searched, and all the RCTs wereconducted on methodological quality assessment. Data extraction and data analysis were according to standards ofCochrane systematic review. Results： Eight trials were included including a total of 701 patients. Meta-analysisresults： Shenqi Fuzheng injection combined with GP chemotherapy could significantly improve the functionalstatus of patients with NSCLC （OR = 3.44, 95% CI [2.26, 5.25], P 〈 0.0001） and clinical treatment efficacy （OR =（OR = 0.31, 95%CI [0.20, 0.47], P 〈 0.0001. The rate of leukopenia （OR = .31, 95%CI [0.20,0.47], P 〈 0.0001）,thrombocytopenia （OR = 0.58, 95%CI [0.37, 0.91], P = 0.020）, hemoglobin decline （（OR = 0.31, 95%CI [0.16,0.59], P = 0.0004） and incidence of gastrointestinal reactions （OR = 0.58,P 〈 0.05） could be reduced. Conclusion：Shenqi Fuzheng injection combined with GP chemotherapy in the treatment of advanced NSCLC obtainedsignificantly clinical efficacy. The quality of the literature incorporated is low, the conclusion requires high-qualityresearch to further prove.展开更多
Two-dimensional DC and small-signal analysis of gate-to-source scaling effects in SiC-based high-power field-effect transistors have been performed in this paper. The simulation results show that a downscaling of gate...Two-dimensional DC and small-signal analysis of gate-to-source scaling effects in SiC-based high-power field-effect transistors have been performed in this paper. The simulation results show that a downscaling of gate-to-source distance can improve device performance, i.e. enhancing drain current, transconductance, and maximum oscillation frequency. This is associated with the peculiar dynamic of electrons in SiC MESFETs, which lead to a linear velocity regime in the source access region. The variations of gate-to-source capacitance, gate-to-drain capacitance, and cut-off frequency with respect to the change in gate-to-source length have also been studied in detail.展开更多
In this paper,a synchronized control strategy of double fed induction generator that can provide reserve capability and primary frequency support for microgrid is firstly developed.The microgrid based small signal sta...In this paper,a synchronized control strategy of double fed induction generator that can provide reserve capability and primary frequency support for microgrid is firstly developed.The microgrid based small signal stability performance is investigated under multiple operating conditions.The effect of three categories of key controller parameters on dominant eigenvalues is studied by sensitivity analysis,including:1)active power drooping coefficient;2)reactive power drooping coefficient;3)parameters of outer loop excitation current control.Finally,some constructive suggestions on how to tune controller parameters to improve microgrid’s small signal stability performance are discussed.展开更多
A small-signal model of photovoltaic(PV)generation connected to weak AC grid is established based on a detailed model of the structure and connection of a PV generation system. An eigenvalue analysis is then employed ...A small-signal model of photovoltaic(PV)generation connected to weak AC grid is established based on a detailed model of the structure and connection of a PV generation system. An eigenvalue analysis is then employed to study the stability of PV generation for different grid strengths and control parameters in a phaselocked loop(PLL) controller in the voltage source converter. The transfer function of the power control loop in the dq rotation frame is developed to reveal the influence mechanism of PLL gains on the small-signal stability of PV generation. The results can be summarized as follows:(1)oscillation phenomena at a frequency of about 5 Hz may occur when the grid strength is low;(2) the tuning control parameters of the PLL have a noticeable effect on the damping characteristics of the system, and larger proportional gain can improve the system damping;(3)within a frequency range of 4-5 Hz,the PLL controller has positive feedback on the power loop of PV generation. A virtual inductance control strategy is proposed to improve the operational stability of PV generation. Finally, a simulation model of PV generation connected to weak AC grid is built in PSCAD/EMTDC and the simulation results are used to validate the analysis.展开更多
双馈风电场经柔性直流输电并网或经串补线路送出时均发生过次同步振荡(subsynchronous oscillation,SSO),而双馈风电场经电网换相高压直流输电(line-commutatedconverter based high voltage direct current,LCC-HVDC)送出时是否会出现...双馈风电场经柔性直流输电并网或经串补线路送出时均发生过次同步振荡(subsynchronous oscillation,SSO),而双馈风电场经电网换相高压直流输电(line-commutatedconverter based high voltage direct current,LCC-HVDC)送出时是否会出现SSO尚不明确,亟需开展相关研究。该文采用模块化建模方法建立研究系统的小信号模型,并将其与PSCAD/EMTDC中的电磁暂态模型进行阶跃响应对比,验证小信号模型的正确性。然后,通过特征值分析及参与因子分析研究双馈风电场和LCC-HVDC间的相互作用,并分析系统参数改变对稳定性的影响。结果显示,不存在双馈风电场和LCC-HVDC的状态变量共同参与的振荡模式,表明双馈风电场和LCC-HVDC间的相互作用不明显,不会由此导致SSO;当并网风电机组台数或输电线路长度增加时,发电机模式阻尼增强,锁相环-直流电压外环模式阻尼减弱。展开更多
柔性直流输电换流站控制器的性能对系统的安全稳定运行有重要意义。基于二阶线性自抗扰控制（linearactive disturbancerejectioncontrol,LADRC）设计了电压源换流器高压直流输电（或柔性直流输电）（voltagesourceconverter based high...柔性直流输电换流站控制器的性能对系统的安全稳定运行有重要意义。基于二阶线性自抗扰控制（linearactive disturbancerejectioncontrol,LADRC）设计了电压源换流器高压直流输电（或柔性直流输电）（voltagesourceconverter based high voltage direct current,VSC-HVDC）换流站控制器,实现了有功、无功的快速独立调节并发挥了自抗扰控制动态特性好、鲁棒性高、抗扰能力强的优势。提出了结合小信号分析法和频域法的优势整定LADRC控制器参数的具体方法,利用频域法精简控制器参数个数,建立系统全局小信号模型,从小信号稳定性的角度定量确定控制器参数,分析了小信号法与传统复频域法整定控制器参数的优劣。考虑外部交流系统对VSC-HVDC控制器参数整定的影响,通过算例验证了控制器的控制效果以及参数整定结果的正确性和有效性,最后给出了在工程上整定换流站线性自抗扰控制器参数的方法,为柔性直流输电换流站控制器的设计和LADRC参数整定提供了新思路。展开更多
基金supported by Research on the Oscillation Mechanism and Suppression Strategy of Yu-E MMC-HVDC Equipment and System(2021Yudian Technology 33#).
文摘The voltage source converter based high voltage direct current(VSC-HVDC)system is based on voltage source converter,and its control system is more complex.Also affected by the fast control of power electronics,oscillation phenomenon in wide frequency domain may occur.To address the problem of small signal stability of the VSCHVDC system,a converter control strategy is designed to improve its small signal stability,and the risk of system oscillation is reduced by attaching a damping controller and optimizing the control parameters.Based on the modeling of the VSC-HVDC system,the general architecture of the inner and outer loop control of the VSCHVDC converter is established;and the damping controllers for DC control and AC control are designed in the phase-locked loop and the inner and outer loop control parts respectively;the state-space statemodel of the control system is established to analyze its performance.And the electromagnetic transient simulation model is built on the PSCAD/EMTDC simulation platform to verify the accuracy of the small signal model.The influence of the parameters of each control part on the stability of the system is summarized.The main control parts affecting stability are optimized for the phenomenon of oscillation due to changes in operation mode occurring on the AC side due to faults and other reasons,which effectively eliminates system oscillation and improves system small signal stability,providing a certain reference for engineering design.
文摘Objective： To evaluate the clinical efficacy of Shenqi Fuzheng injection combined with gemcitabine plus cisplatin（GP） in the treatment of advanced non-small cell lung cancer （NSCLC）. Methods： we performed a systematicsearch in the electronic databases such as Cochrane Library, Pubmed, Embase, Chinese Journal Full-text Database,Chinese Biomedical Literature Database, Chinese Science and Technology Periodical Full-text Database andWanfang Database up to 30 January 2017. Randomized controlled trials （RCT） of Shenqi Fuzheng Injectioncombined with GP chemotherapy in the treatment of advanced NSCLC were searched, and all the RCTs wereconducted on methodological quality assessment. Data extraction and data analysis were according to standards ofCochrane systematic review. Results： Eight trials were included including a total of 701 patients. Meta-analysisresults： Shenqi Fuzheng injection combined with GP chemotherapy could significantly improve the functionalstatus of patients with NSCLC （OR = 3.44, 95% CI [2.26, 5.25], P 〈 0.0001） and clinical treatment efficacy （OR =（OR = 0.31, 95%CI [0.20, 0.47], P 〈 0.0001. The rate of leukopenia （OR = .31, 95%CI [0.20,0.47], P 〈 0.0001）,thrombocytopenia （OR = 0.58, 95%CI [0.37, 0.91], P = 0.020）, hemoglobin decline （（OR = 0.31, 95%CI [0.16,0.59], P = 0.0004） and incidence of gastrointestinal reactions （OR = 0.58,P 〈 0.05） could be reduced. Conclusion：Shenqi Fuzheng injection combined with GP chemotherapy in the treatment of advanced NSCLC obtainedsignificantly clinical efficacy. The quality of the literature incorporated is low, the conclusion requires high-qualityresearch to further prove.
基金This work was supported by the Major State Basic Research Development Program of China, under Contract 51327010101.
文摘Two-dimensional DC and small-signal analysis of gate-to-source scaling effects in SiC-based high-power field-effect transistors have been performed in this paper. The simulation results show that a downscaling of gate-to-source distance can improve device performance, i.e. enhancing drain current, transconductance, and maximum oscillation frequency. This is associated with the peculiar dynamic of electrons in SiC MESFETs, which lead to a linear velocity regime in the source access region. The variations of gate-to-source capacitance, gate-to-drain capacitance, and cut-off frequency with respect to the change in gate-to-source length have also been studied in detail.
基金This work is jointly supported by National High Technology R&D Program of China(No.2011AA050204)the 2014 Endeavour Research Fellowship and 2014 Research Collaborative Award of University of Western Australia,the project of the State Grid(Off-shore wind farm plan in Zhejiang province).
文摘In this paper,a synchronized control strategy of double fed induction generator that can provide reserve capability and primary frequency support for microgrid is firstly developed.The microgrid based small signal stability performance is investigated under multiple operating conditions.The effect of three categories of key controller parameters on dominant eigenvalues is studied by sensitivity analysis,including:1)active power drooping coefficient;2)reactive power drooping coefficient;3)parameters of outer loop excitation current control.Finally,some constructive suggestions on how to tune controller parameters to improve microgrid’s small signal stability performance are discussed.
基金supported by State Grid Corporation of China ‘‘Study on active frequency and voltage control technologies for second level power disturbance in photovoltaic power plant’’National Natural Science Foundation of China (No. 51277024)
文摘A small-signal model of photovoltaic(PV)generation connected to weak AC grid is established based on a detailed model of the structure and connection of a PV generation system. An eigenvalue analysis is then employed to study the stability of PV generation for different grid strengths and control parameters in a phaselocked loop(PLL) controller in the voltage source converter. The transfer function of the power control loop in the dq rotation frame is developed to reveal the influence mechanism of PLL gains on the small-signal stability of PV generation. The results can be summarized as follows:(1)oscillation phenomena at a frequency of about 5 Hz may occur when the grid strength is low;(2) the tuning control parameters of the PLL have a noticeable effect on the damping characteristics of the system, and larger proportional gain can improve the system damping;(3)within a frequency range of 4-5 Hz,the PLL controller has positive feedback on the power loop of PV generation. A virtual inductance control strategy is proposed to improve the operational stability of PV generation. Finally, a simulation model of PV generation connected to weak AC grid is built in PSCAD/EMTDC and the simulation results are used to validate the analysis.
文摘双馈风电场经柔性直流输电并网或经串补线路送出时均发生过次同步振荡(subsynchronous oscillation,SSO),而双馈风电场经电网换相高压直流输电(line-commutatedconverter based high voltage direct current,LCC-HVDC)送出时是否会出现SSO尚不明确,亟需开展相关研究。该文采用模块化建模方法建立研究系统的小信号模型,并将其与PSCAD/EMTDC中的电磁暂态模型进行阶跃响应对比,验证小信号模型的正确性。然后,通过特征值分析及参与因子分析研究双馈风电场和LCC-HVDC间的相互作用,并分析系统参数改变对稳定性的影响。结果显示,不存在双馈风电场和LCC-HVDC的状态变量共同参与的振荡模式,表明双馈风电场和LCC-HVDC间的相互作用不明显,不会由此导致SSO;当并网风电机组台数或输电线路长度增加时,发电机模式阻尼增强,锁相环-直流电压外环模式阻尼减弱。
文摘柔性直流输电换流站控制器的性能对系统的安全稳定运行有重要意义。基于二阶线性自抗扰控制（linearactive disturbancerejectioncontrol,LADRC）设计了电压源换流器高压直流输电（或柔性直流输电）（voltagesourceconverter based high voltage direct current,VSC-HVDC）换流站控制器,实现了有功、无功的快速独立调节并发挥了自抗扰控制动态特性好、鲁棒性高、抗扰能力强的优势。提出了结合小信号分析法和频域法的优势整定LADRC控制器参数的具体方法,利用频域法精简控制器参数个数,建立系统全局小信号模型,从小信号稳定性的角度定量确定控制器参数,分析了小信号法与传统复频域法整定控制器参数的优劣。考虑外部交流系统对VSC-HVDC控制器参数整定的影响,通过算例验证了控制器的控制效果以及参数整定结果的正确性和有效性,最后给出了在工程上整定换流站线性自抗扰控制器参数的方法,为柔性直流输电换流站控制器的设计和LADRC参数整定提供了新思路。
