A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency wav...A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency waves mostly is maximal height of topography and topographic slope. The former makes frequency of topographic Rossby waves decrease, the latter makes Rossby waves instable. Moreover, when topographic slope is appropriate, it can also make Rossby waves turn into low-frequency waves.展开更多
Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrati...Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.展开更多
The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diamet...The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing isdeduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domainvelocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various pointssuffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence ofvibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point main-ly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors af-fecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that thelarger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The leasthigh-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increaseof pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modu-lus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width andlarger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geomet-rical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditionssuch as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on theexternal conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some externalmeasures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adoptingsuitable receiving point.展开更多
A novel structure for a charge pump circuit is proposed, in which the charge-pump (CP) current can adaptively regulated according to phase-locked loops (PLL) frequency synthesis demand. The current follow technolo...A novel structure for a charge pump circuit is proposed, in which the charge-pump (CP) current can adaptively regulated according to phase-locked loops (PLL) frequency synthesis demand. The current follow technology is used to make perfect current matching characteristics, and the two differential inverters are implanted to increase the speed of charge pump and decrease output spur due to theory of low voltage difference signal. Simulation results, with 1st silicon 0. 25μm 2. 5 V complementary metal-oxide-semiconductor (CMOS) mixed-signal process, show the good current matching characteristics regardless of the charge pump output voltages.展开更多
This paper investigates the propagation of linear dust acoustic waves in inhomogeneous dusty plasmas due to spatial gradients of dust charge, plasma densities. A linear dispersion relation is obtained with the non-adi...This paper investigates the propagation of linear dust acoustic waves in inhomogeneous dusty plasmas due to spatial gradients of dust charge, plasma densities. A linear dispersion relation is obtained with the non-adiabatic dust charge iguctuation and the non-thermally distributed ions. The numerical results show that the inhomogeneity, nonthermal ions and non-adlabatic dust charge iguctuatlon have strong iniguence on the frequency and the damping rate of waves.展开更多
为了实现“双碳”战略目标,推动我国能源转型,实现海上风电等大规模新能源的安全可靠送出成为研究关键。柔性低频输电系统通过降低输电频率来提高输送能力并节省经济成本,逐渐成为“新型电力系统”中除传统工频输电和直流输电方式之外...为了实现“双碳”战略目标,推动我国能源转型,实现海上风电等大规模新能源的安全可靠送出成为研究关键。柔性低频输电系统通过降低输电频率来提高输送能力并节省经济成本,逐渐成为“新型电力系统”中除传统工频输电和直流输电方式之外的有益补充。但是,柔性低频输电系统的稳定性问题,尤其是大信号稳定性问题仍是工程实践中的难题。为此,采用Lyapunov直接法对基于模块化多电平矩阵换流器(modular multilevel matrix converter,M3C)的柔性低频输电系统进行了大信号稳定性分析。首先针对系统非线性状态方程阶数较高,导致难以通过经验或者线性系统Jacobian矩阵方法直接构造能量函数的难题,通过扇区非线性方法建立了模糊模型,简洁快速地构建了系统能量函数并计算了大信号稳定吸引域(large signal domain of attraction,LS-DOA)。其次引入多维空间吸引域的映射方法,从频率差异的角度更加直观地揭示了主电路和控制系统等参数对系统大信号稳定性的影响。然后结合线性矩阵不等式(linear matrix inequality,LMI)凸优化理论,分析了系统大信号不稳定的相关机理并给出了高效的镇定策略。最后通过MATLAB/Simulink建立了系统模型,实现了对理论分析的仿真验证,研究结果对柔性低频输电系统的工程实践有一定的参考作用。展开更多
A low noise phase locked loop (PLL) frequency synthesizer implemented in 65 nm CMOS technology is introduced. A VCO noise reduction method suited for short channel design is proposed to minimize PLL output phase noi...A low noise phase locked loop (PLL) frequency synthesizer implemented in 65 nm CMOS technology is introduced. A VCO noise reduction method suited for short channel design is proposed to minimize PLL output phase noise. A self-calibrated voltage controlled oscillator is proposed in cooperation with the automatic frequency calibration circuit, whose accurate binary search algorithm helps reduce the VCO tuning curve coverage, which reduces the VCO noise contribution at PLL output phase noise. A low noise, charge pump is also introduced to extend the tuning voltage range of the proposed VCO, which further reduces its phase noise contribution. The frequency synthesizer generates 9.75-11.5 GHz high frequency wide band local oscillator (LO) carriers. Tested 11.5 GHz LO bears a phase noise of-104 dBc/Hz at 1 MHz frequency offset. The total power dissipation of the proposed frequency synthesizer is 48 mW. The area of the proposed frequency synthesizer is 0.3 mm^2, including bias circuits and buffers.展开更多
[目的]虚拟惯性阻尼控制(Virtual Inertia and Damping Control,VIDC)潜在的正反馈可能加剧控制环路内部的相互作用进而引起母线电压低频振荡,破坏电动汽车直流充电站(Electric Vehicle DC Charging Station,EVCS)的稳定性。虽然已有多...[目的]虚拟惯性阻尼控制(Virtual Inertia and Damping Control,VIDC)潜在的正反馈可能加剧控制环路内部的相互作用进而引起母线电压低频振荡,破坏电动汽车直流充电站(Electric Vehicle DC Charging Station,EVCS)的稳定性。虽然已有多时间尺度阻抗模型解释VIDC的稳定机制和VIDC控制下EVCS的低频振荡机理,但其本质上是一个高阶传递函数,获取阻尼控制策略的解析表达式。[方法]针对这一问题,文章对环路虚拟阻抗进行了详细的阻抗分析,直观地揭示了每个控制环路阻抗高阶属性的根本原因。[结果]通过伯德图近似提出了控制环路闭环增益的降阶拟合方法,建立了低阶阻抗电路模型。[结论]通过Matlab/Simulation仿真结果验证了所提出的多时间尺度低阶阻抗电路模型的有效性。展开更多
大规模风电并网系统在受到大功率缺额扰动后,电网会出现频率骤降,而低频减载(Under Frequency Load Shedding,UFLS)控制是防止频率失稳的有效手段。首先,基于含UFLS的改进系统频率响应模型(System Frequency Model,SFR),研究了新型电力...大规模风电并网系统在受到大功率缺额扰动后,电网会出现频率骤降,而低频减载(Under Frequency Load Shedding,UFLS)控制是防止频率失稳的有效手段。首先,基于含UFLS的改进系统频率响应模型(System Frequency Model,SFR),研究了新型电力系统受到大功率扰动下的频率特征,基于经典频率响应模型建立改进的系统频率响应模型,考虑火电、风电联合调频控制策略,并引入UFLS频率控制;然后,根据所建立的系统频率响应模型对大规模风电并网系统参数进行整定,并建立多资源参与调频下的大规模风电并网系统频率特征表达式;最后,通过Matlab/Simulink仿真平台,验证UFLS控制策略参与调频的可行性及UFLS控制参数对频率调制效果的影响。展开更多
This paper presents a low phase-noise fractional-N frequency synthesizer which provides an inphase/quadrature-phase(I/Q) signal over a frequency range of 220–1100 MHz for wireless networks of industrial automation...This paper presents a low phase-noise fractional-N frequency synthesizer which provides an inphase/quadrature-phase(I/Q) signal over a frequency range of 220–1100 MHz for wireless networks of industrial automation(WIA) applications. Two techniques are proposed to achieve the wide range. First, a 1.4–2.2 GHz ultralow gain voltage-controlled oscillator(VCO) is adopted by using 128 tuning curves. Second, a selectable I/Q divider is employed to divide the VCO frequency by 2 or 3 or 4 or 6. Besides, a phase-switching prescaler is proposed to lower PLL phase noise, a self-calibrated charge pump is used to suppress spur, and a detect-boosting phase frequency detector is adopted to shorten settling time. With a 200 k Hz loop bandwidth, lowest measured phase noise is 106 dBc/Hz at a 10 k Hz offset and 131 dBc/Hz at a 1 MHz offset. Fabricated in the TSMC 0.18 μm CMOS process, the synthesizer occupies a chip area of 1.2 mm^2, consumes only 15 m W from the 1.8 V power supply,and settles within 13.2 s. The synthesizer is optimized for the WIA applications, but can also be used for other short-range wireless communications, such as 433, 868, 916 MHz ISM band applications.展开更多
文摘A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency waves mostly is maximal height of topography and topographic slope. The former makes frequency of topographic Rossby waves decrease, the latter makes Rossby waves instable. Moreover, when topographic slope is appropriate, it can also make Rossby waves turn into low-frequency waves.
基金supported by National Natural Science Foundation of China (No.50475112)National Hi-Tech Research and Development Program of China (863 Program,No.2006AA110112).
文摘Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.
基金supported by the National Natural Science Foundation of China(Grant No.51008115)the Provincial Science Foundation of Jiangsu(Grant No.BK2008040)
文摘The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing isdeduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domainvelocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various pointssuffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence ofvibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point main-ly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors af-fecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that thelarger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The leasthigh-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increaseof pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modu-lus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width andlarger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geomet-rical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditionssuch as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on theexternal conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some externalmeasures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adoptingsuitable receiving point.
文摘A novel structure for a charge pump circuit is proposed, in which the charge-pump (CP) current can adaptively regulated according to phase-locked loops (PLL) frequency synthesis demand. The current follow technology is used to make perfect current matching characteristics, and the two differential inverters are implanted to increase the speed of charge pump and decrease output spur due to theory of low voltage difference signal. Simulation results, with 1st silicon 0. 25μm 2. 5 V complementary metal-oxide-semiconductor (CMOS) mixed-signal process, show the good current matching characteristics regardless of the charge pump output voltages.
基金supported by the National Natural Foundation of China (Grant Nos 10475066 and 10347006)
文摘This paper investigates the propagation of linear dust acoustic waves in inhomogeneous dusty plasmas due to spatial gradients of dust charge, plasma densities. A linear dispersion relation is obtained with the non-adiabatic dust charge iguctuation and the non-thermally distributed ions. The numerical results show that the inhomogeneity, nonthermal ions and non-adlabatic dust charge iguctuatlon have strong iniguence on the frequency and the damping rate of waves.
文摘为了实现“双碳”战略目标,推动我国能源转型,实现海上风电等大规模新能源的安全可靠送出成为研究关键。柔性低频输电系统通过降低输电频率来提高输送能力并节省经济成本,逐渐成为“新型电力系统”中除传统工频输电和直流输电方式之外的有益补充。但是,柔性低频输电系统的稳定性问题,尤其是大信号稳定性问题仍是工程实践中的难题。为此,采用Lyapunov直接法对基于模块化多电平矩阵换流器(modular multilevel matrix converter,M3C)的柔性低频输电系统进行了大信号稳定性分析。首先针对系统非线性状态方程阶数较高,导致难以通过经验或者线性系统Jacobian矩阵方法直接构造能量函数的难题,通过扇区非线性方法建立了模糊模型,简洁快速地构建了系统能量函数并计算了大信号稳定吸引域(large signal domain of attraction,LS-DOA)。其次引入多维空间吸引域的映射方法,从频率差异的角度更加直观地揭示了主电路和控制系统等参数对系统大信号稳定性的影响。然后结合线性矩阵不等式(linear matrix inequality,LMI)凸优化理论,分析了系统大信号不稳定的相关机理并给出了高效的镇定策略。最后通过MATLAB/Simulink建立了系统模型,实现了对理论分析的仿真验证,研究结果对柔性低频输电系统的工程实践有一定的参考作用。
文摘A low noise phase locked loop (PLL) frequency synthesizer implemented in 65 nm CMOS technology is introduced. A VCO noise reduction method suited for short channel design is proposed to minimize PLL output phase noise. A self-calibrated voltage controlled oscillator is proposed in cooperation with the automatic frequency calibration circuit, whose accurate binary search algorithm helps reduce the VCO tuning curve coverage, which reduces the VCO noise contribution at PLL output phase noise. A low noise, charge pump is also introduced to extend the tuning voltage range of the proposed VCO, which further reduces its phase noise contribution. The frequency synthesizer generates 9.75-11.5 GHz high frequency wide band local oscillator (LO) carriers. Tested 11.5 GHz LO bears a phase noise of-104 dBc/Hz at 1 MHz frequency offset. The total power dissipation of the proposed frequency synthesizer is 48 mW. The area of the proposed frequency synthesizer is 0.3 mm^2, including bias circuits and buffers.
文摘[目的]虚拟惯性阻尼控制(Virtual Inertia and Damping Control,VIDC)潜在的正反馈可能加剧控制环路内部的相互作用进而引起母线电压低频振荡,破坏电动汽车直流充电站(Electric Vehicle DC Charging Station,EVCS)的稳定性。虽然已有多时间尺度阻抗模型解释VIDC的稳定机制和VIDC控制下EVCS的低频振荡机理,但其本质上是一个高阶传递函数,获取阻尼控制策略的解析表达式。[方法]针对这一问题,文章对环路虚拟阻抗进行了详细的阻抗分析,直观地揭示了每个控制环路阻抗高阶属性的根本原因。[结果]通过伯德图近似提出了控制环路闭环增益的降阶拟合方法,建立了低阶阻抗电路模型。[结论]通过Matlab/Simulation仿真结果验证了所提出的多时间尺度低阶阻抗电路模型的有效性。
文摘大规模风电并网系统在受到大功率缺额扰动后,电网会出现频率骤降,而低频减载(Under Frequency Load Shedding,UFLS)控制是防止频率失稳的有效手段。首先,基于含UFLS的改进系统频率响应模型(System Frequency Model,SFR),研究了新型电力系统受到大功率扰动下的频率特征,基于经典频率响应模型建立改进的系统频率响应模型,考虑火电、风电联合调频控制策略,并引入UFLS频率控制;然后,根据所建立的系统频率响应模型对大规模风电并网系统参数进行整定,并建立多资源参与调频下的大规模风电并网系统频率特征表达式;最后,通过Matlab/Simulink仿真平台,验证UFLS控制策略参与调频的可行性及UFLS控制参数对频率调制效果的影响。
基金supported by the National High Technology Research and Development Program of China(No.2011AA040102)
文摘This paper presents a low phase-noise fractional-N frequency synthesizer which provides an inphase/quadrature-phase(I/Q) signal over a frequency range of 220–1100 MHz for wireless networks of industrial automation(WIA) applications. Two techniques are proposed to achieve the wide range. First, a 1.4–2.2 GHz ultralow gain voltage-controlled oscillator(VCO) is adopted by using 128 tuning curves. Second, a selectable I/Q divider is employed to divide the VCO frequency by 2 or 3 or 4 or 6. Besides, a phase-switching prescaler is proposed to lower PLL phase noise, a self-calibrated charge pump is used to suppress spur, and a detect-boosting phase frequency detector is adopted to shorten settling time. With a 200 k Hz loop bandwidth, lowest measured phase noise is 106 dBc/Hz at a 10 k Hz offset and 131 dBc/Hz at a 1 MHz offset. Fabricated in the TSMC 0.18 μm CMOS process, the synthesizer occupies a chip area of 1.2 mm^2, consumes only 15 m W from the 1.8 V power supply,and settles within 13.2 s. The synthesizer is optimized for the WIA applications, but can also be used for other short-range wireless communications, such as 433, 868, 916 MHz ISM band applications.