Source current harmonic analysis of adjustable speed drives under input voltage unbalance and sag conditions

Adjustable Speed Drives (ASDs) have become the primary choice for most new and retrofit precision motor-control applications, offering major improvements in system efficiency. The significant increase in the use of ASDs makes it important to understand the compatibility issues between ASDs and their electrical environment in order to appropriately design the electrical systems. Even though there have been numerous studies addressing ASD effects on power systems, models for predicting the effect of the source voltage sags or unbalance have been limited. This paper is devoted to the analysis of utility-side input current harmonics under input voltage unbalance and sag conditions and the effects of these harmonics on the distribution transformer K-factor for practical ASD systems. The relationships between the unbalanced input voltages, the resulting input current harmonics, the input inductance, and the required transformer K-factor are explored for 5 hp, 100 hp, and 600 hp power distribution systems with ASDs. The results can be used as a design guide for power distribution system design with ASDs. Theoretical derivations are accompanied by both simulations and experimental results to provide verification of key conclusions.     

基于谐波分析法的高速变频电机铁耗计算方法

提出了一种计算非正弦供电时的高速变频电机铁耗的简单而有效的方法。该方法以谐波分析法为基础，能够综合考虑电源谐波、电机铁芯饱和以及集肤效应的影响，具有较高的精度。与有限元法计算结果的比较表明，该方法具有较高的精度。     

Converter-connected distributed generation units with integrated harmonic voltage damping and harmonic current compensation function

The steadily growing share of converter-connected distributed generators, combined with a large amount of nonlinear and unbalanced loads connected to the electric power system, has led to a degraded power quality. Both harmonic voltage and harmonic current distortion may cause many unfavourable effects on the power system. However, the converter-connected distributed generators can be redesigned to have a positive effect on the distortion of the grid voltage. Two different approaches can be discerned. At the one hand, distributed generation units can be controlled to synthesize a resistive load for harmonic voltage components. This approach is called harmonic voltage damping. At the other hand, if the polluting current of an adjacent nonlinear load is measured and added to the control loop, the converter-connected distributed generator is able to compensate all harmonic current components of the nonlinear load. This approach is referred to as harmonic current compensation. In this paper, a control strategy for a converter-connected distributed generator is extended with a harmonic voltage damping function and a harmonic current compensation function. Experimental tests show that the voltage distortion of the grid voltage can be significantly improved.     

An investigation of voltage instability problems

The authors investigate the voltage stability problem based on singular perturbation theory. Possible voltage instability patterns are classified into four types (I, II-1, II-2S, and II-2D) according to the mechanism causing voltage instability. Several features of each type of instability are studied as well as their analysis methods. Voltage instability tends to begin with type I and then leads to one of the remaining types. The load flow Jacobian can be an effective index to approximately assess type I and II-2S instabilities, while types II-1 and II-2D require direct nonlinear analyses and eigenvalue analyses, respectively. The validity of the classification proposed has been verified through numerical simulations and theoretical analyses which take into account dynamic characteristics of generating units, loads, and tap-changing transformers     

伪火花开关自放电电压特性与电压跌落过程实验研究

设计了典型参数下的伪火花放电开关,进行了空气介质下的电压特性实验,详细研究了气体压力,电极间隙距离,电极孔径和电极材料对伪火花开关耐受电压的影响;给出了伪火花开关放电电压与气压变化的关系曲线;测量了产生伪火花放电的气压范围和单间隙伪火花开关耐受电压的最大值,测得了伪火花放电与辉光放电的转折点气压,并对实验结果进行了理论分析。研究了伪火花开关电压跌落时间与放电电压的关系,首次将开关电压跌落过程分为暂态阶段和稳态阶段,讨论了放电电路参数,气体压力,开关结构和放电电压对电压跌落时间的影响。实验表明,在气压和开关结构不变的条件下,暂态过程时间由放电电压决定,电压越高,则所需时间就越短;稳态过程时间由放电电路参数决定,而与放电电压无关。最后讨论了真空洁净程度和开关加工与装配工艺对伪火花开关耐受电压的影响。     

Computer method of direct synthesis of nonlinear two-poles under time characteristics of current and voltage

The method of synthesis of nonlinear two-poles under the time characteristics of a current and voltage on its terminals. The algorithm is proved, and the parameters of the two-pole modeling influence of currents of converting electric locomotives of the next feeding zones on the external characteristics of traction substation of an alternating current are determined.     

A study of the loss characteristics of the amorphous magnetic material under nonsinusoidal wave magnetic flux

This paper presents a study on iron loss characteristics of an amorphous magnetic material under nonsinusoidal wave magnetic flux. The iron loss characteristics of the amorphous magnetic material have been compared to those of grain‐oriented magnetic steel sheets. Measurements of the iron loss have been carried out by means of an SST. It was found that the ratio of the iron loss increase of the amorphous magnetic material under the excitation by distorted waveforms and symmetric PWM waveforms is lower than that of grain‐oriented magnetic steel sheets. On the other hand, the ratio of the iron loss increase of the amorphous magnetic material under the excitation by asymmetric PWM waveforms is higher than that of grain‐oriented magnetic steel sheets. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 11–18, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20004     

Development of high voltage harmonic measuring instruments for distribution systems using optical voltage sensor and current sensor

Application of an optical measuring technique was attempted in order to develop harmonic voltage and current measuring instruments for distribution systems. To develop the harmonic voltage measuring system using a Bi₁₂GeO₂₀ crystal as a sensing Pockels cell for high‐voltage distribution lines, zinc oxide elements were adopted as a voltage divider. Also, an optical current sensor system was improved on the harmonic current measuring system using an R₃Fe₅O₁₂ film as a Faraday device. In practical three‐phase distribution systems, the developed high voltage harmonic measuring devices using the optical voltage sensor and current sensor were compared with conventional harmonic analyzers for low voltage. As a result, it was confirmed that the developed high voltage harmonic measuring devices had satisfactory characteristics for practical use. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 84–93, 1999     

Performance optimization of BiCMOS circuits under reduced supply voltage

As the supply voltage is reduced, the speed superiority of BiCMOS over CMOS may be diminished, but BiCMOS still has the advantage of inducing relatively smaller characteristic degradation in nMOS transistors by suppressing the drain voltage in the gate. Introducing a new quantitative methodology to evaluate hot electron-induced degradation of nMOS transistor characteristics, this report finds that both BiNMOS gates and CBiMOS gates will have a considerable superiority over CMOS gates in the voltage range from 2.5 V to 3.3 V, even with the same nMOS transistor characteristics. BiNMOS is 30% faster than CMOS owing to amplification of the pMOS drain current by an npn transistor. CBiCMOS is 40% faster and has a sevenfold longer life than CMOS. The speed improvement comes from amplification of both pMOS and nMOS drain currents by npn and pnp transistors, respectively, and the lifetime improvement is due to the effect of the voltage drop through the pnp transistors on the drain terminal of the nMOS transistors. The analytical methodology was also utilized to choose an optimum drain structure, although CMOS necessitates the LDD (lightly doped drain), SD (single drain) structure. Thus, the speed of the gates can be further improved, and the speed of CBiCMOS is expected to be 45% faster than that of CMOS gates. Even in the case of SD structure, the lifetime of CBiCMOS was estimated to be two orders of magnitude longer than that of CMOS with LDD structure. © 1998 Scripta Technica. Electr Eng Jpn, 121(4): 56–64, 1997     

谐波对电容式电压互感器运行特性的影响研究

针对电容式电压互感器（Capacitor Voltage Transformers,CVT）在谐波干扰下二次侧产生畸变的问题,阐述了CVT的结构特性和工作原理,从系统传递函数角度分析了杂散电容和耦合电容对CVT高频特性的影响以及谐波干扰使CVT的测量误差发生的变化.为了进一步了解谐波对CVT运行特性的影响,运用仿真软件Matlab搭建包含杂散电容和耦合电容的CVT高频等效电路模型对其进行仿真试验,以获得CVT的幅频特性曲线.仿真结果表明,电网中的谐波电压会使CVT的测量误差产生变化,并不适宜直接用来测量谐波电压.     

Effect of interactions between voltage and current harmonics on the net harmonic current produced by single phase non-linear loads

The effect of the interaction between both load voltage and current harmonics on the net harmonic current produced by different types of single phase non-linear loads is investigated. Two types of loads are considered: the fluorescent lamps' load and single phase diode bridge rectifiers' load. Studies are done on each load alone and then on the combination of both. The electromagnetic transient program has been used to model these loads. The computer simulations are supported by laboratory testing. The main conclusion of this work is that neglecting the interactions between both voltage and current harmonics will result in incorrect estimation of the harmonic current produced by these loads. Also it is concluded that using a combination of different types of loads can result in a reduction of the current and voltage distortions.     

一种基于改进控制的模拟电压暂降电源控制方法

电压暂降问题已成为影响工业发展的主要电能质量问题,模拟电压暂降已成为验证电能质量优化装置有效性的重要手段,同时也是验证工业装置电压暂降耐受特性的重要措施.重点分析了模拟电压暂降电源装置与传统逆变电源相比的独特运行特性,即输出可控性与可重复性、控制器增益可变性及无源谐振抑制需求特性.同时针对其运行特性,提出了基于变比例增...     

An investigation into the OLTC effects on voltage collapse

It is known that following disturbances, on-load tap changers act to restore the load bus voltage and thus restore the load power to near pre-disturbance level. As the system is probably weakened by the contingencies, this will often over-tax existing supplies due to increased losses and reduction in power plant ability, and thus voltage collapse may result. This paper discusses the less emphasized effect of on-load tap changers from another point of view, i.e., how the maximum power transfer limit is affected by on-load tap changers. In addition to restoring the load, on-load tap changers also extend the power transfer ability. Whether the overall effect is beneficial or counter-productive depends on the system ability to balance the amount of extended power transfer limit and the amount of restored load by the same tap changers     

多组变压器在低压大电流开关电源中应用的研究

本文介绍了一种低压大电流开关电源采用的变压器结构，并与传统的一组变压器结构进行了比较。以12V／1000A移相全桥ZVS开关电源的PSPICE仿真验证了这种结构的优点。     

Analysis of the voltage phasors characteristics for motor unbalanced supplies under constant voltage level

This article presents an analytical and graphical study of the supply characteristics of a three-phase induction motor operating under constant average voltage in unbalanced conditions. Till now, researchers have addressed the unbalance analysis of induction motors without paying attention to the accuracy on the voltage level issue. This work develops the loci of voltage phasors and their symmetrical components, and calculates the variation ranges of voltages and voltage unbalance factor (IEC) for an induction motor operating under constant line average voltage and constant percent voltage unbalance (NEMA). The results are applied to the variation limits established in the electrotechnical standards.     

Parameter determination of a nonsinusoidal periodic signal harmonic based on the modified sine transform

An algorithm is presented for determining the amplitude and the initial phase of the oscillations of the kth harmonic included in the structure of the nonsinusoidal periodic signal. The algorithm differs from the well-known Euler–Fourier method based on sine and cosine transforms. The qualitative difference of the proposed method consists in the use of the cosine function, which is an analytic solution of a modified sine transform, the structure of which includes a sinusoidal factor with a complex argument that contains a variable phase angle. The coordinates of the maximum of this functional dependence, which is raised to a positive integer power to improve the accuracy of determining the parameters, are uniquely associated with the amplitude and the initial phase of oscillations of the kth harmonic of the nonsinusoidal signal. The considered method minimizes the use of nonlinear operations and at its core has the element inherent in the selective filter. The possibility of obtaining information on the parameters of the first voltage and current harmonics with the required accuracy enhances the reliability of the evaluation of processes occurring in the power system in the conditions of interference in the form of higher harmonics. An example problem is solved in the MS Excel environment.     

Snubber用高频高压隔离偏置电源研究

一般来说,托卡马克(EAST)装置中的NBI加热系统都是利用Snubber来实现保护的.为了优化Snubber的结构,通常都给其添加一个偏置直流源,将Snubber的性能维持在BH曲线的负饱和点附近,这样能使Snubber的质量减小一半.而目前普遍使用的偏置直流源是将50/60 Hz的交流电经过高压隔离变压器变压后整流直接得到.50/60 Hz的高压隔离变压器体积大、质量重,将带来移动不便和占用大量空间等缺点,如将50/60 Hz变为高频后经高频高压隔离变压器处理,这一问题就能得到解决.基于高频高压技术进行了EAST Snubber高压隔离偏置电源的设计与实验研究.     

高压输电线路电流差动保护特性分析

用电磁暂态仿真软件PSCAD（Power Systems Computer Aided Design）进行仿真,在界面上可设置系统参数、故障距离、故障类型等相关参数,启动一次仿真计算;然后利用MATLAB（Matrix Laboratory矩阵实验室）程序读取仿真得到的数据进行判据的计算,画出差流和制动电流的波形。分析了不同运行条件下保护判据的灵敏度、可靠性以及线路电容和大过渡电阻的影响。     

DC voltage control and harmonic current suppression in a single‐phase PFC converter

This paper presents a DC voltage control scheme for a single‐phase PFC converter which can realize both the harmonic suppression of the input current and the fast dynamic response to the DC voltage. Instead of using a constant DC voltage reference, the controller calculates a fluctuating DC voltage reference, having the frequency at twice the source frequency. In the calculation of the DC voltage reference, the circuit parameters are used. Since the parameter errors may cause an error in the DC voltage reference, parameter identification is also described. The effectiveness of the proposed control algorithm has been verified experimentally. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(1): 54–64, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10060