Xerographic properties of a-Se:Te photoconductors

It is shown that the dark decay of the electrostatic surface potential on a corona-charged a-Se:Te alloy photoreceptor occurs via electric field-enhanced xerographic depletion discharge (FEXDD) in which Poole-Frenkel-assisted thermal emission of holes from deep mobility-gap states and their subsequent sweep out generates a negative bulk space charge. The theoretical model development is applied to explain the observed experimental dark discharge data over a wide range of charging (initial) voltages. It is shown that although the time required for the surface potential to decay to its half value t_1/2 initially increases with the charging voltage V₀ at the highest charging voltage, t_1/2 actually decreases with V₀. Results obtained from cycled-up xerographic experiments on single and double-layer photoreceptors are also reviewed and discussed in conjunction with transient photoconductivity experiments     

Fully digital, vector-controlled PWM VSI-fed AC drives with aninverter dead-time compensation strategy

A dead-time compensation method in vector-controlled pulse width modulator (PWM) voltage source inverters (VSIs) is proposed. The method is based on a feedforward approach that produces compensating signals obtained from the I_d-I_q current and inverter output angular frequency references in the rotating reference (d-q) frame. It provides excellent inverter output voltage distortion correction for both fundamental and harmonic components. The correction is not affected by the magnitude of the inverter output voltage or current distortions. Since this dead-time compensation method allows current loop calculations in the d- q frame at a slower sampling rate, with a conventional microprocessor than calculations in the stationary reference frame, a fully digital. vector-controlled speed regulator with just a component current control loop is realized for PWM VSIs. Simulations and test results obtained for the compensation method are also described     

A stator flux-oriented voltage source variable-speed drive based onDC link measurement

The authors present a new control strategy for variable speed drives, which is aimed at improving or even replacing existing volts per hertz (V/f) open loop variable-speed drives. This strategy uses only the DC link current and voltage, which are readily available in a V/f drive for protection purposes, to implement closed loop flux and torque control. Stator flux and electromagnetic torque feedback signals are derived from the DC link voltage, the DC link current, and inverter switching states. Digital implementation is seen to be possible with slight modification on existing V/f drives. Practical considerations in implementing such a system are emphasized, and experimental results are presented to show the feasibility of the scheme     

Theory for finite-phase traveling-wave boundary-guided transport oftriboelectrified particles

Numerical simulations are used to picture synchronous and asynchronous domains of traveling-wave pumping of charge-conserving particles (having mass m, charge q, radius a, and mobility b) in terms of the dimensionless frequency Ω=(ω/k)/(bE₀), mass M=(m/q) (kb) (bE₀), and gravitational acceleration G=mg/qE₀, where k and ω are the wavenumber and angular frequency of the imposed wave and E₀=kV, where V is the peak voltage. The effects of having a finite number of phases consisting of discrete electrodes covered by a semi-insulating layer are highlighted. The time-average velocity in the direction of wave travel is found to be synchronous (have velocity ω/k) for 0<Ω<Ω*<1, where Ω* is reduced by having finite phases. Because the discrete electrodes result in hops of higher magnitude, they tend to result in a conversion to asynchronous hopping and `certain' modes at a lower frequency than with a sinusoidal wave. At low M, they can also result in the stalling of particle pumping as the frequency is raised. Predicted effects of image forces, dielectric layer thickness, bulk conductivity, and surface conductivity as well as particle sticking and slipping are discussed     

Dynamic equalization during charging of serial energy storageelements

A technique is described that equalizes the amount of charge in a serial string of energy-storage cells during charging by using DC-to-DC converters to divert portions of the charging current past selected cells (or groups of cells). When no converters are operating, the charging current through the string is equal to that of the charging source. As the string charges, one cell eventually reaches a threshold voltage V_A. At threshold, a shunt converter is activated to divert current around the cell, thus maintaining it at V_A. The diverted current extracts energy, which is returned to the charging bus and appears as an additional charging current to the source. This positive feedback increases the current available for charging the string and allows the least charged cells, or cells of larger capacity, to be charged at higher rates than available directly from the source. During discharging, the converters across the remaining cells supply energy to the bus, while the converter across the open cell maintains a constant terminal voltage. The maximum current gain of the system is equal to the number of converters used in the system     

Influence of an insulating spacer on the V-tcharacteristics of a coaxial gas-insulated cable. II. Tests on EHV buses

For pt.I see ibid., vol.3, no.1, p.16-25 (1988). The V- t characteristics of EHV buses were evaluated for two configurations with rated voltages of 550 and 800 kV. The bus dimensions were 6 m in length and 17.8/53.3 cm and 20.3-61 cm in diameter, respectively. They were each fitted with two tripod-type epoxy spacers. The results show a pronounced influence of the supporting spacers on the V-t characteristic, corresponding to a reduced withstand voltage and less dispersion in the measured breakdown voltages. A statistical method is presented for deriving the V- t characteristics of a gas-insulated system from those of the individual components     

On the definition of power factor and apparent power in unbalancedpolyphase circuits with sinusoidal voltage and currents

Definition for the apparent power S and for the power factor PF in unbalanced polyphase circuits with sinusoidal waveforms are presented. It is proved that the definition S²=(V_a²+V _b²+V_c²) (I _a²+I_b²+I _c²) has a definite physical meaning, leading itself to a convenient resolution in positive, negative and zero sequence, nonactive and active power. It is suggested that the power factor be represented with the help of the ratio P⁺/ S, where P⁺ is the positive sequence active powers     

An approach for the regularization of a power flow solution aroundthe maximum loading point

A method which is capable of greatly widening the range where the power flow solution is regular is presented. This is achieved by giving some modifications to the conventional power flow solution method and eliminating the singular point or shifting it to region where the voltage is lower than that of the maximum loading point. Then, the continuous execution of V-P curves including the maximum loading point is realized. The efficiency and effectiveness of the method were tested in a practical 598-node system are compared with the conventional method     

一种新颖的三相四桥臂逆变器解耦控制的建模与仿真

三相四桥臂逆变器是针对三相不平衡或非线性负载的供电提出来的。该文提出了1种采用内环空间矢量电流调节器和外环同步坐标比例积分控制器相级联的三相四桥臂逆变器的控制方案，实现了对三相四桥臂逆变器的解耦控制。建立了三相四桥臂逆变器在αβγ空间的电路模型，分析了其在αβγ空间的三维电压矢量分布并由此提出了1种采用2个三电平滞环比较器和1个两电平滞环比较器相结合的内环电流调节方案。外环采用了同步坐标电压控制器，使用1个简单的比例调节器就可实现输出电压跟踪的零稳态误差，保证了良好的稳态性能。建立了整个系统在dqo坐标系下的控制模型，实现了对d,q,o3个分量的独立解耦控制。仿真结果验证了该控制方案的正确性与可行性。     

Optimal pulse patterns of a nine-phase voltage source PWM inverter for use with a triple three-phase wound ac motor

The authors have already described the nine-phase inverter driving system providing both the triple three-phase voltage source inverter with 180-deg conducting period and the ac motor windings with triple three-phase construction. The nine-pulse inverter driving system used three small-capacity three-phase coupling reactors having special windings for current balance and reduction of higher harmonics. In addition, for voltage control, current balance, and waveform improvement, optimal PWM pulse patterns were applied to the six-phase inverter driving system using a three-phase coupling reactor to provide double three-phase construction. In the system based on the mode in the title, the PWM control was applied to the nine-phase inverter driving system described in the foregoing. The coupling reactors in the system balance the fundamental currents of three sets of three-phase inverters and also absorb higher harmonic voltages other than 18p±1 (p = 1, 2, …) orders. The optimal pulse patterns found by the approach to make the performance index minimum using the Lagrange multiplier method can be applied to the PWM to reduce the higher harmonic currents greater than those calculated by the modulation method comparing the sinusoidal signal wave with triangular carrier signal. This system can have a larger capacity than the six-phase PWM inverter driving system in which coupling reactors absorb higher harmonic voltages other than the 12p±1 orders and also improve output current waveforms. In addition, the system includes the capacity of coupling reactors slightly larger than the six-phase PWM inverter driving system but enables operation with smaller torque ripples and electromagnetic noises in low- to high-frequency ranges.     

基于SVPWM控制的三相逆变电源装置的研制

介绍了基于空间电压矢量脉宽调制(SVPWM)控制的船用三相逆变电源装置的设计方法。SVPWM控制利用逆变器输出电压矢量的正多边形运动轨迹去逼近正弦电压的圆形运动轨迹,构造的正多边形边数越多,逆变器输出电压就越逼近基频正弦波。实验结果表明,该电源装置解决了船舶供电网络中电压波动范围大、频率不稳的问题,提高了船舶电源的供电可靠性。该装置不仅可满足使用恒频恒压正弦交流电船舶的电气设备的要求,还可满足使用变频变压正弦交流电的调速电机的要求。此外,该装置具有体积小、效率较高、直流电压利用率较高等特点。     

不平衡工况下电网电压序分量快速提取方法

快速准确地获取三相不平衡电网电压的序分量(即正、负、零序分量)是实现高性能并网逆变器控制的基本要求。文中提出了一种实用的瞬时序分量提取方法,可提高不平衡电网电压序分量的提取速度。首先,使用虚拟正交信号构建法和单相锁相运算获得虚拟三相电压相量,之后利用对称分量法和单相锁相逆运算,即可快速获得序分量的幅值和实时相位。该方法仅需电网电压及其虚拟正交信号,即可直接获得瞬时电压序分量,无需闭环检测方法中的参数设计和调试过程,且计算精度能够满足工程要求。通过MATLAB/Simulink实时仿真平台验证了该方法的正确性。     

A performance comparison of full- and half-bridge series resonantinverters in high-frequency high-power applications

Load-commutated full- and half-bridge series resonant inverters are dual at lower operating frequencies where the di/dt inductance L_s has negligible effect on their performance. At higher frequencies, however, the effect of inductor L_s dominates the ratings of components, and their performance is significantly different. The difference in their performance is a function of the operating frequency and is more pronounced at higher frequencies. To study the behavior of inverters at higher frequencies, a detailed analysis is presented which includes the effect of the di/dt inductance. Finally, the performance of two inverters is compared in terms of inverter kVA rating, and the kVA rating of the compensating capacitor     

Influence of an insulating spacer on the V-tcharacteristics of a coaxial gas-insulated cable. I. Study on areduced-scale coaxial conductor

Two different spacer designs, a disc spacer and a composite-profile cone, were evaluated in a coaxial conductor 2.5/7 cm in diameter to study their influence on the V-t characteristic of the conductor when it is subjected to repeated applications of impulse voltages of constant waveshape and increasing magnitude. The results show that an insulating spacer can reduce the critical withstand voltage and yield smaller dispersion in the breakdown voltages. These effects can be minimized by adopting a design that favors breakdown in the gas rather than along the spacer interface     

一种新的三相4桥臂逆变器及其控制策略

三相4桥臂逆变器与传统三相逆变器不同。第4桥臂的引入,加上负载的不确定性,使得空间矢量调制控制变得非常复杂,从分析对称三相逆变器每相能独立工作出发,通过引入一特定结构的三相变压器并视其为负载,通过控制第4桥臂来控制负载中点电压,既实现了三相负载的解耦,又能使输出相电压达到220 V。仿真实验证明,该结构与方法对不同性质负载都有很好的适应性,并且容易实现。     

Performance of a High-Speed Motor Drive System Using a Novel Multilevel Inverter Topology

The performance of a novel multilevel six-switch (SS) three-phase inverter drive is examined for low-voltage high-speed motor applications. The switching losses of hard-switched voltage-source-inverter topologies place limits on the maximum feasible switching frequency. When operating at higher fundamental frequencies, this results in low-frequency modulation ratios and either high load harmonic currents that cause excessive rotor heating or larger than desired output reactors with a large fundamental voltage drop. The multilevel inverter structure examined offers an increased number of output pulsewidth-modulated (PWM) voltage levels, higher frequency PWM output waveforms, reduced dead-time effects, and a significant reduction in harmonic content. These features reduce the total losses in the motor load when compared to the standard SS three-phase inverter. The harmonic reduction provided by the multilevel topology relative to the standard inverter is experimentally demonstrated with a 15-hp 18 000-r/min induction machine.     

基波电流瞬时值检测及同步电流相量测量方法

为了能够实时有效地测量出系统在各种状态下的基波电流相量的频率、幅值和相角,给出了一种基波电流瞬时值检测及同步电流相量测量算法。把系统的零序电压和电流瞬时值看作三相系统中的a相分量,按照正序对称原则无延迟地构造出b相和c相电流和电压。利用同步坐标变换的方法准确检测出零序、负序和正序基波电流瞬时值,给出了基波电流相量的频率、相角和幅值测量算法。该方法提高了多种动态条件下的测量精度和动态响应特性,仿真结果表明了该方法的正确性和有效性。     

一种新型三相电流型逆变器的研究

提出了一种基于导抗变换器的新型三相电流型逆变器,并对其控制策略作了理论分析、仿真和实验研究.本系统利用导抗变换器的电压源-电流源变换特性,将输入直流电压变换为高频正弦电流,经高频变压器隔离及电流等级变换后进行裂相调制,输出为三相正弦电流.相比于传统的电流型逆变器,采用此方法不仅省去了直流侧电抗器,而且采用高频变压器替代了工频变压器,减小了隔离变压器及输出滤波器的体积,有利于装置的小型化和降低成本.仿真和实验结果证明了该方案的可行性及有效性.     

Expansion of operating limits for permanent magnet motor by currentvector control considering inverter capacity

The current vector control method of PM (permanent magnet) motors is examined to expand the operating limits associated with inverter capacity. This control method is optimum in the sense of deriving maximum output torque within the voltage and current constraints. The effects of motor parameters are examined by computer simulation. The operating limits are greatly expanded by controlling the d- and q-axis components of the armature current according to the rotor speed. The operating limits are examined considering the demagnetization of the permanent magnet. If the permanent magnet has a straight demagnetization curve, like a rare-earth permanent magnet, the PM motor can be safely operated until the demagnetizing coefficient becomes 1.0. If wide speed range or constant power operation is desirable, a permanent magnetic with a high coercivity and a linear demagnetization curve must be used for the PM motor     

单相与三相输入兼容的特定消谐式变频器研究

设计了一种新型单相与三相输入兼容的特定消谐式变频器.提出了一种单相与三相输入兼容的变频器主电路,深入研究了离线计算与在线计算相结合实现特定消谐的方法.实验结果表明,该变频器具有消除谐波次数多,残余谐波含量小,电压利用率高,直流母线电压高,输出稳压特性好,开关角数据存储空间小的特点,有很好的应用前景.