A new single-pole switching technique for suppressing turbine-generator torsional vibrations and enhancing power stability and continuity

The author presents a new single-pole switching technique for reducing torsional torques in turbine blades and shafts and enhancing power system stability and transmission continuity. During the dead time between single-pole tripping and line reclosing, the significant negative-sequence current flowing into the nearby turbine-generator may cause supersynchronous resonance effect on low pressure turbine blades and even results in fatigue damage. Thus, during this time, the proposed grounding capacitor set up at the neutral of the wye transformer is inserted not only to eliminate this negative current but also to recover the prefault power transmission in advance. The induced adverse effect on turbine blades can be precluded. Adaptive reclosing is then applied to reclose the tripped phase and the grounding capacitor is switched off. This effectively improves the power system stability again and prevents further torque amplifications. This scheme is suitable for a single-circuit transmission line and can improve system reliability.     

Solid-state AC breaker with parallel switched capacitor circuits for microgrid system

ABSTRACT

In this paper, a novel solid-state AC breaker, based on double-paralleled switched capacitors controlled with complementary pulse width modulation technique, is proposed for transition of microgrid due to its advantages of low di/dt stress to power devices and controllable resistance features. The circuit topology of the breaker is based on parallel switched capacitors, its operating and control theory are analyzed in detail to show its advantage in theory. The equivalent impedance of proposed parallel switched capacitor circuits is up to the switching frequencies, and the proposed switch is suitable for seamless transition between the island mode and grid-connected mode to reduce the current shock by changing the switching frequencies. Simulation and experimental results verify the effectiveness and feasibility of the new AC breaker.     

一种新型的基于数据平面共享环的IP over ASTN机制

提出了一种重叠模型下新型的基于数据平面共享环的IP over ASTN机制,其优点是利用IP网络中路由器自身具备的能力和在ASTN边缘节点引入基于以太网的二层交换能力,以较低的环路带宽代价实现各IP网间可达性信息传达,同时避免了对路由器的基本运行机制的较复杂修改。分析了相应的组网形式、边缘节点结构和网络运行机制,并对其中具有关键意义的带宽限制参数提出两种参数确定算法。     

Capacitor voltage balancing in multilevel flying capacitor inverters by rule-based switching pattern selection

A rule-based scheme is investigated for capacitor voltage balancing in a multilevel flying capacitor inverter (MFCI). Without using voltage feedback, the scheme determines the best switching pattern for maintaining nil mean current in all capacitors, hence minimising the capacitor voltage fluctuation. The method is developed to work with the selective harmonic elimination (SHE) technique for sinusoidal voltage generation applied to control static VAR compensators. The method has been designed using a four-cell five-level MFCI as an example. The selected pattern has been shown to give superior performance in load-voltage total-harmonies distortion level and mean capacitor voltage fluctuation. The method is validated experimentally for this form of MFCI     

Some observations on the switching and memory phenomena in ZnTe-Si

The I-V characteristics of p-ZnTe films deposited on -Si using different growth conditions have been studied. The devices fabricated at substrate temperatures above 473 K possess bistable impedance states: switching from high-to-low impedance occurs when ZnTe film is positive biased, while switching from low-to-high impedance state occurs when ZnTe film is negative biased. It is observed that zero-based capacitance, open circuit photovoltage and short circuit current density are increased when the device is switched to the low impedance state and revert to their initial values when switched back to the high-impedance state. It is believed that an electronic switching mechanism is responsible, most probably the filling and the emptying of traps in the wide band gap ZnTe films.     

Restoration strategy for secondary power network with grey relational analysis

An operational strategy for secondary power system restoration using grey relational analysis (GRA) is presented. The restoration scheme can be divided into three steps involving fault section determination, recovering process and voltage correction process. Three GRAs are incorporated to design the overall restoration scheme. The first GRA uses the network-switching status to identify the fault. The second GRA combines the switching states and load levels for network recovery. The third GRA uses capacitor bank control (CBC) to support bus voltages. Optimal power flow (OPF) is also used to verify the proposed scheme by off-line analysis to confirm a secure overall network operation including load-power balance, power generation limits, voltage limits and power flow limits. Computer simulations were conducted with an IEEE 30-bus power system to show the effectiveness of the proposed restoration scheme.     

Voltage and frequency control of parallel operated synchronous generator and induction generator with STATCOM in micro hydro scheme

Parallel operation of synchronous and induction generators in micro hydro scheme is presented. The synchronous generator has an exciter, which provides a fixed excitation to produce normal rated terminal voltage at full resistive load. On the other hand, the induction generator has neither exciter nor speed controller. Static compensator (STATCOM) is connected to the common bus for terminal voltage and frequency control. A resistive dump load is connected across the DC link capacitor of STATCOM through a chopper to control active power. Simulink model is developed to perform transient analysis of the proposed scheme. Experimental results are presented to compare with the simulation results. It is found that connection of an induction generator in parallel with the synchronous is much simpler than connecting two synchronous generators in parallel.     

非线性扰动的切换系统的异步控制：模态依赖的平均驻留时间方法

研究了一类具有非线性扰动的切换系统的异步控制问题,异步是指控制器的切换相对于子系统的切换经历时间延迟。利用异步切换系统状态方程的解析解直接研究系统动力学,无需构造任何李雅普诺夫函数。提出了保证闭环系统在模态依赖平均驻留时间(MDADT)方案下指数稳定的充分条件。MDADT意味着每个子系统都有自己的平均驻留时间(ADT),这比ADT更具一般性。此外,利用线性矩阵不等式方法设计了异步切换控制器。最后,通过数值算例说明了该方法的有效性。     

开关电流高阶椭圆低通滤波器的设计(英文)

提出了一种新的开关电流高阶椭圆低通滤波器通用综合方法,该法遵循从RLC滤波器到有源RC滤波器,再到开关电容滤波器,最后到开关电流滤波器的顺序进行设计,方法简单易行.文中给出了5阶开关电流椭圆低通滤波器的设计实例,ASIZ仿真频率响应满足所需的频率技术要求.     

基于ATP-EMTP的500kV断路器三相合闸过电压分析

针对500kV系统的断路器三相合闸操作过电压,建立了基于ATP-EMTP的仿真模型,对合闸电阻对断路器三相合闸过电压的影响进行了仿真分析。分析了合闸电阻对三相合闸最大过电压、姒统计过电压的影响,操作过电压的仿真计算对于断路器的参数选择和电网的绝缘配合计算具有一定的实际价值。     

New multifrequency method for the determination of the dissipation factor of capacitors and of the time constant of resistors

A new method for the simultaneous determination of the dissipation factor of capacitors and of the time constant of resistors by a multifrequency method is presented. This method is based on the measurement of impedance ratios at two or more frequencies. A bridge is set up with a programmable two-channel ac voltage source and the impedances to be compared. The impedance ratios are determined by synchronous sampling procedures and application of discrete Fourier transform. In a first experiment, a high-grade gas-filled 1 nF standard capacitor was compared with a stable 1 M/spl Omega/ ac resistor at frequencies between 31 Hz and 666 Hz. The estimated standard uncertainties (k=1) are 0.6/spl middot/10/sup -6/ for the dissipation factor of the capacitor and 0.4 ns for the time constant of the ac resistor.     

异步切换下切换系统的动态输出反馈保成本控制

作为一类重要的混杂系统,切换系统由若干个子系统以及一个协调各子系统之间切换的切换信号构成,在自然科学、工程控制和社会系统等方面有着广泛的应用。在对切换系统的控制问题进行研究时,一般假设子系统和控制器同步运行。然而,在实际工程控制中,控制器的切换相对于子系统的切换存在切换时延,从而产生异步切换。因此,对异步切换下的切换系统研究是十分必要的。针对一类异步切换下切换系统的动态输出反馈保成本控制问题进行了研究。报告了切换系统的研究现状以及异步切换下切换系统的最新研究成果。利用分段李雅普诺夫函数法和平均驻留时间法,得到了使得异步切换下的闭环切换系统稳定的动态输出反馈控制器存在的充分条件。从线性矩阵不等式的角度,提出了异步切换动态输出反馈保成本控制器设计方案,并给出成本上界的优化方法。最后,通过一个数值算例说明了提出的方法的有效性。     

A survey of behavioral modeling of ferroelectric capacitors

Six different behavioral models for ferroelectric capacitors are surveyed with an emphasis on their usefulness in the transient circuit simulation of integrated nonvolatile memories. These models can be broadly classified into two categories, namely, those that rely on the hysteresis loop and those that rely on the switching current of a ferroelectric capacitor. The former often involves a continuous cycling of a ferroelectric capacitor with a sinusoidal waveform. The latter employs a pulse measurement technique to capture the switching current of the capacitor. The pulse waveform applied to the ferroelectric capacitor in the latter approach resembles the actual waveform encountered in a typical ferroelectric memory access. This resemblance makes switching-current based models more suitable for use in high-speed-memory circuit simulations     

Synchronous Demodulator for Autonomous Sensors

In this paper, a novel differential synchronous demodulator is presented that uses the on-off switching characteristic of the power supply in autonomous systems as the control signal for demodulation. The proposed circuit, which uses only an op amp and a double-pole double-throw switch, can be useful in sensor nodes for sensor networks or distributed data-acquisition systems involving ac sensors or impedance measurements. Three prototype demodulators have been implemented using op amps with different power-bandwidth characteristics, and their common-mode rejection ratio (CMRR), nonlinearity, and initial transient were characterized. The working of the circuit when supplied by a piezoelectric energy converter is also verified.     

Four-quadrant instantaneous torque control of switched reluctance machine at low speed based on co-energy control

An instantaneous torque control scheme of switched reluctance machines for four-quadrant operation at low speed based on co-energy considerations is presented. The co-energy is estimated online with a co-energy estimator, which only requires easily obtainable parameters such as the machine terminal quantities and the machine characteristics at low current. By regulating the co-energy while tracking a one-dimensional co-energy profile, the torque contribution of each phase of the switched reluctance machine can be controlled and optimised. Thus, the requirement of pre-measured data is reduced when compared to current-profiling methods. The closed-loop control system is analysed and then designed based on internal model control. The excitation sequence and torque sharing function for four-quadrant operation to produce smooth torque output are also presented. The operation limits of the scheme are examined. Computer simulation and experimental results confirm that the proposed scheme can be exploited to reduce the high-frequency torque ripples significantly.     

A ferroelectric capacitor macromodel and parameterization algorithmfor SPICE simulation

A compact equivalent circuit model, or macromodel, is presented which reproduces both the DC charge storage and transient switching current responses of a ferroelectric capacitor. The macromodel circuit element values are rigorously linked to physical quantities which are readily characterized with simple electrical measurements. A software package is described which both parameterizes and optimizes the model to measured data and outputs a SPICE input file. Together, the macromodel and parameterization software form a complete linkage between material characterization and circuit design which is largely transparent to the design engineer. Optimization results lend insight into the underlying theory of ferroelectric switching and the sources of nonideal charge storage. SPICE simulations demonstrate the utility of the macromodel for VLSI circuit simulation     

Flux‐difference splitting scheme with modified multidimensional dissipation on unstructured meshes

Abstract

A flux‐difference splitting scheme with a modified multidimensional dissipation for high‐speed compressible flow analysis on unstructured meshes is presented. The scheme eliminates unphysical flow behaviors such as a spurious bump of the carbuncle phenomenon that occurs on the bow shock from flow over a blunt body, and the expansion shock generated from flow over a forward facing step. The switching function suggested by Quirk is implemented as a choice to detect the vicinity of strong shock. The proposed scheme is further extended to obtain higher‐order spatial and temporal solution accuracy. The scheme is, in addition, combined with an adaptive meshing technique that generates unstructured triangular meshes to resemble the flow phenomena for reducing computational effort. The entire procedure is evaluated by solving several benchmarks as well as steady‐state and transient high‐speed compressible flow problems.     

Analysis and implementation of a soft switching interleaved forward converter with current doubler rectifier

A soft switching interleaved forward converter with current doubler rectifier is presented. Active clamp circuit is used in the primary winding of transformers to recycle the energy stored in the leakage inductor and the magnetising inductor so that the voltage stresses of switches are reduced. The leakage inductance of transformers, the magnetising inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of clamp switches. The resonance between the leakage inductance of transformers and output capacitance of switch will achieve ZVS operation for the main switches in the proposed converter. The interleaved operation can reduce the current ripple on the output capacitor. Two current doubler rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of the transformer. All these features make the proposed converter suitable for the DC-DC converter with high output current. The operation principle and system analysis of the proposed converter are provided in detail. Finally, experimental results, taken from a laboratory prototype rated at 125 W, are presented to verify the feasibility of the proposed converter.     

Zero voltage switching active clamp buck-boost stage Cuk converter

The paper presents an active clamp buck-boost stage Cuk converter to achieve soft switching commutation. An auxiliary switch and a clamp capacitor are connected in parallel with the primary side of the transformer to absorb all the energy stored in the transformer leakage inductance. The resonant inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of the auxiliary switch. On the other hand, the resonance between the resonant inductance and output capacitance of the main switch will achieve ZVS of the main switch in the proposed converter. The principle of operation and system analysis are presented. Design considerations of the proposed converter are also provided. Experimental results for a 170 W prototype circuit operating at 70 kHz are given to demonstrate the effectiveness of the proposed converter     

四端对标准电容器频率特性的校验理论及测定方法

对四端对阻抗测量仪在其使用频段内进行校准,须确定四端对标准电容器的频率特性。空气介质四端对标准电容器频率特性的校验理论,是从四端对标准器阻抗矩阵出发,按四端对导纳定义进行简化后,再用网络分析仪在较高频率对有关参数进行测定,分析计算后将确定的频率特性曲线回归到100kHz～13MHz范围内。给出标准电寄器1000pF、100pF、10pF、1pF的频率特性曲线及不确定度分析,它将作为阻抗高频段计量的溯源依据。