特高压变压器空载直流偏磁计算精度分析

针对特高压变压器直流偏磁计算问题,提出一种空载简化电路模型下的分段解析法,为直流偏磁数值计算奠定基础。根据特高压变压器简化电路模型,推导励磁电流解析式。电感随着电流的变化,分两段取值;电感的取值通过比较电流计算值与临界电流值的大小来判断。设置临界电流误差判据来判别电流计算值是否达到临界电流。分析计算表明,当电阻为实际电阻时,临界电流误差判据严格,可获得直流分量的准确解,临界电流误差判据宽松时,直流分量与准确解出现较大误差,甚至计算错误;通过人为增大串联电阻值,临界电流误差判据可相对宽松,从而获得直流分量近似准确解。在此基础上,以解析解的计算结果为基准,对比分析四阶龙格库塔法数值解。结果表明,步长较大相当于临界电流误差判据宽松,必须加大电阻,直流分量才可与准确解接近;步长较小相当于临界电流误差判据严格,电阻可不必太大。在特高压变压器直流偏磁数值计算中,可通过人为增大串联电阻值和适当减小计算步长来获得较为准确的直流偏磁特性。     

Quasi‐active power factor correction on flyback‐based dc/dc converter

This paper presents a novel input current shaper based on a quasi‐active power factor correction (PFC) scheme. In this method, high power factor and low harmonic content are achieved by providing an auxiliary PFC circuit with a driving voltage which is derived from a third winding of the transformer of a cascaded dc/dc flyback converter. It eliminates the use of active switch and control circuit for PFC. The auxiliary winding provides a controlled voltage‐boost function for bulk capacitor without inducing a dead angle in the line current. Since the dc/dc converter operates at high switching frequency, the driving voltage is also of high switching frequency, which results in reducing the size of the magnetic components. Operating principles, analysis and experimental results of the proposed method are presented. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation of harmonic currents and power factor on power rectifier circuits with nonequi-PWM and equi-PWM control (inductive load)

Lately, on the power rectifier circuit with semiconductor switching device, PWM control is generally employed for the purposes of reducing the harmonic currents on the dc side and improving the power factor of fundamental wave. In this case, the analysis of the current waveform becomes fairly complex. However, we express the PWM controlled voltage waveform by the step function, and can easily analyze the current waveform. We reported formerly some results of analysis about the waveform and harmonics of the current. In this paper, on the power rectifier circuit to which the nonequi-PWM and equi-PWM control are applied, we exactly calculate the harmonic currents on the dc and ac side, and the power factor by the use of the above analytical results. The characteristics of both control methods are compared on condition that each controlled factor of the load voltage is equal. These results are shown in the calculated charts. The following items can be seen from these charts on the power rectifier circuit: (1) The nonequi-PWM control can let the harmonic currents on the dc side decrease more than the equi-PWM control. But on the contrary, the harmonic currents on the ac side increase. Consequently, when the nonequi-PWM control is applied, the total power factor decreases by the increase of distortion factor of the current on the ac side. (2) The difference between the harmonic currents on the dc and ac side to both of the nonequi-PWM and equi-PWM control increases with the increase of controlled factor of the load voltage. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 117–125, 1999     

A simplified method of calculating busbar inductance and its application for stray resonance analysis in an inverter dc link

Sinusoidal PWM control is widely applied to power electronic converters. The carrier frequency of recent converter products is gradually being raised in order to decrease current harmonics as much as possible. However, in the dc filter circuits of large capacity converters, the capacitance of a unit capacitor is relatively large, and the busbars are relatively long. Therefore, the resonant frequency is lower than those of small capacity converters. Consequently, there is a concern that the carrier frequency will become close to the resonant frequency, which will cause trouble. On the other hand, it is often necessary to decrease the inductance of the loop circuit consisting of a switching device and its by‐pass circuit, in order to suppress the switching surge voltage. In both cases described above, it is important to be sure of the exact busbar inductance for reliable design. In this paper, a simplified method of calculating busbar inductance is proposed. This method is based on the partial inductance theory. In particular, the characteristics of a pair of busbars, and the use of the method are described. Finally, an application to stray resonance analysis in the dc filter circuit of a three level inverter is described in comparison with experimental data. From these results, we confirmed that the proposed method is usable to estimate busbar inductance quickly and accurately. © 1999 Scripta Technica, Electr Eng Jpn, 126(3): 49–63, 1999     

Fundamental operation of direct linked frequency changer with bilateral switching circuits

This paper describes a direct linked‐type frequency changer (DLT‐FC) proposed by the authors. The DLT‐FC is a converter circuit with a new configuration for direct frequency change. The DLT‐FC does not require a dc link circuit, nor bilateral switches. In addition, dc snubber circuits can be applied without the need for a regenerative circuit of snubber energy. Therefore, the DLT‐FC can be designed to be compact and light, and has a long life. The authors manufactured a prototype of the DLT‐FC and experimentally checked its CVCF and VVVF operation. The results indicate that the performance of the DLT‐FC makes it suitable for industrial use. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 53–61, 1999     

Design of Sensitivity Function of Multirate VCM Control System

A method for designing a sensitivity function for a multiple‐input single‐output servo system is proposed. The method does not require weighting or weighting functions, unlike linear‐quadratic (LQ) or H_∞ design. First, a controller candidate is derived by taking into consideration the robustness specification for the plant system. Then, the sensitivity function is derived from the gain specification of the sensitivity function. As the design of a multirate controller can be shown to be equivalent to a multiple‐input single‐output system, the method is employed to design a multirate VCM position control system. The multirate controller is designed such that at frequencies higher than the Nyquist frequency, the desired robustness is achieved. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 53–59, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22296     

A single-phase PWM current source type converter coupled with an ac chopper

A current source type converter can easily generate a sinusoidal current on the ac side by employing a PWM strategy. In the converter system for a single-phase supply, however, the dc current pulsates because the dc output voltage of the converter contains an ac component with twice the ac supply frequency. The dc current pulsations cause the ac current waveform to be distorted. Although the use of a dc reactor with large inductance reduces the dc current pulsations, the size and the weight of converter equipment including a dc reactor is large. Two-phase rectification using two full-bridge converters and a converter system with an ac chopper circuit has been proposed for elimination of the dc pulsations. In these converters, the number of switching devices comprising the circuit will unavoidably increase. To solve this problem, we propose a novel single-phase current source type converter coupled with an ac chopper circuit and the PWM method. In this circuit, two switching devices in the main bridge are used to form an ac chopper bridge with two added devices and a capacitor. This paper gives the experimental and theoretical waveforms and the steady-state characteristics. The results prove that a smooth dc current and a sinusoidal ac current are obtained, and that a great reduction of the dc inductance can be achieved by using the proposed converter. © 1998 Scripta Technica. Electr Eng Jpn, 123(3): 36–45, 1998     

用于有源滤波器谐波检测的一种新的自适应算法

提出了一种新的变步长最小均方(least-mean-square,LMS)自适应谐波检测算法,并将其应用于有源电力滤波器中。以一种时变步长迭代方法取代传统的定步长迭代法,旨在提高算法在求取均方差最小值的过程中方向估值的精度,从而达到提高算法收敛速度的目的。文中详细推导了2阶步长迭代公式,并导出了扩展的N阶步长迭代公式的递归表达式。通过仿真将所提出的新算法与传统的定步长算法进行了比较,证明新算法的收敛特性明显优于传统算法。     

A non‐isolated high step‐up DC‐DC converter with integrated 3 winding coupled inductor and reduced switch voltage stress

In this paper, a non‐isolated high step‐up dc‐dc converter based on coupled inductor is proposed. The proposed converter can be used in renewable energy applications. In suggested converter, the high voltage is achieved using 3‐winding coupled inductor, which leads to low voltage rate of the switch. A clamp circuit is used to recycle the leakage inductance energy. Also, the clamp circuit prevents the creation of voltage spikes on semiconductor devices and causes the voltage stress of elements are limited to less than the output voltage. The presented theoretical analyses show that the operation of suggested converter in continuous conduction mode needs to small magnetic inductor. Therefore, the size of coupled inductor's core is reduced, and so the size and cost of presented converter will be decreased. Analysis of the proposed converter is provided with laboratory results to verify its performance.     

Modeling and numerical simulation of a brushless permanent-magnet DC motor in dynamic conditions by time-stepping technique

A method of modeling and numerical simulation of a brushless permanent-magnet dc motor using time-stepping finite-element technique is presented. In the proposed model, the electromagnetic field equations, the stator circuit equation, and the motion equation are solved simultaneously at each time step; thus, the eddy-current effect, the saturation effect, the rotor movement, and the nonsinusoidal quantities can all be taken into account directly in the system of equations. Dynamic conditions of the motor at starting, step voltage variation, and load torque changes are investigated using the proposed dynamic model.     

Discussion of thyristor characteristic optimization for HVDC valves

We have been developing thyristor valves for high‐voltage dc transmission systems for more than 20 years. During this period, the size, power loss, and reliability have been dramatically improved and one of the technical advances which support the improvements is to increase the voltage and current rating of thyristors. However, when thyristor voltage rating exceeds 6 kV, increasing the voltage rating does not lead to size and power loss reduction of the valve because of turn‐off characteristic deteriorations. This paper describes a method which can optimize the thyristor characteristics in such a way that the size and power loss of valves are minimized. Two different approaches for HVDC and back‐to‐back systems are presented. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 43–52, 1999     

Measurement of the inductance of a coil with core at different currents by a dc chopper

Contents This paper describes a new method for the measurements of the dynamic inductance of a coil with a saturable core. A formula for dynamic inductance is obtained by analyzing the proposed measurement circuit. In this method, a controllable dc voltage source, a dc chopper and a measurement system based on a PC, Lab-VIEW data acquisition card are used. The duty cycle of the dc copper is equal to the half pulse cycle and, the coil current at which the inductance is to be measured, is obtained by changing the input voltage V _d . The peak-to-peak ripple current in the formula is determined by the measuring system.

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übersicht Es wird ein neues Verfahren zur Messung der dynamischen Induktivit?t einer Spule mit s?ttigbarem Kern vorgestellt. Ausgehend von der Analyse des vorgeschlagenen Me?kreises wird eine Formel für die Induktivit?t hergeleitet. Das Verfahren benutzt eine steuerbare Gleichstromquelle, einen Gleichstromsteller und eine Me?einrichtung aus PC und Datenerfassungskarte. Als Einschaltzeit des Stellers wurde die halbe Pulsperiode gew?hlt. Die Einstellung des Stroms für die Me?punkte erfolgt durch ?nderung der Eingangsspannung. Die gemessene Stromschwankung geht in die Formel zur Bestimmung der Induktivit?t ein.

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Received: 25 November 1999     

Determination of equivalent circuit constants of synchronous machines from the extended Dalton‐Cameron method

This paper presents a method of determining the equivalent circuit constants which accord with the physical construction of synchronous machines, using the dc decay testing method with the rotor in arbitrary position (proposed by the authors and called the extended Dalton–Cameron method). The conventional Dalton–Cameron method calculates the direct‐ and quadrature‐axis subtransient reactance from a standstill response test in any arbitrary rotor position using a single‐phase power supply. The extended Dalton–Cameron method determines the direct‐ and quadrature‐axis operational impedances for each slip from a standstill response test using a small‐capacity dc power supply. The direct‐ and quadrature‐axis operational impedance loci thus obtained synchronous machine constants (subtransient, transient, and synchronous reactances) are used to estimate the direct‐ and quadrature‐axis equivalent circuit constants which accord with the physical construction of synchronous machines. As an example, equivalent circuit constants are determined for a 10‐kW laminated salient‐pole‐type synchronous machine with damper winding. The validity of the equivalent circuit constants is confirmed by comparing the calculated resistance and leakage reactance of the field winding determined from the operational impedance when the terminals are short‐circuited, to those when the terminals are connected to an external resistance. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 56–67, 2002     

低频方波金卤灯电子镇流器及其控制策略研究

该文提出了一种两级低频方波输出的高性能电子镇流器，作为MH灯工作电源。PFC级用于功率因数校正，DC／AC级结合了BUCKDC／DC变换器和全桥DC／AC逆变器的特点，负载侧输出为低频方波，可有效克服MH灯声共振现象。采用分段控制方法实现镇流器与灯特性的配合，给出了其相应的控制策略。详细分析了它的工作原理和控制方法，给出了主要参数的计算方法。与传统三级低频方波电子镇流器相比，结构简单、所用器件少、可靠性高。电路仿真和实验结果验证了该方案是可行的。     

Research on Maximizing Power Transfer Efficiency of Wireless In‐Wheel Motor by Primary and Load‐Side Voltage Control

The authors have developed a wireless power transfer (WPT) system for an in‐wheel motor (IWM). It is called a wireless in‐wheel motor (W‐IWM). This paper presents a method that enhances the WPT efficiency in this system. Some methods that maximize the power transfer efficiency by power converter control have been proposed in the past WPT research. In this research, a dc‐dc converter is inserted on the receiver side to vary the load state. However, the space on the receiver side is very small for the W‐IWM; therefore, it is preferable to make the secondary circuit small. Therefore, a full bridge converter is used instead of a dc‐dc converter in the W‐IWM. In this paper, the authors propose a theoretical formula for the transfer efficiency of the IW‐IWM. From an analysis of this formula, there is a combination of a primary voltage and load voltage that maximize the efficiency. The feasibility is validated by an experiment using a motor bench set.     

Unity-power-factor PWM converter with DC ripple compensation

The generation of harmonics and their subsequent propagation into power lines is a topic of increasing concern to power-supply authorities. To prevent obstacles in the power system, a unity-power-factor PWM converter will be applied at ac-dc power conversion plants. However, the PWM converter, especially at single-phase circuit, has some serious defects, including low-frequency ripple current that flows into the dc line and gives rise to a low-frequency ripple voltage that appears on the dc output. In usual cases, it is necessary to connect a very large capacitor or a passive L-C resonant circuit to the dc line for reduction of low-frequency ripple voltage. However, when batteries are connected to the dc output, most of the dc ripple current flows into the battery even if the above circuits are used, because the impedance of the battery is very low compared to that of the circuits. The low-frequency ripple current causes power loss on the battery and the temperature rises. It is well known that the life of a battery is deeply influenced by the temperature. The ripple current, therefore, should be reduced as low as possible. To accomplish reduction of the low-frequency ripple current, a novel topology for the PWM rectifier is presented in this paper. The main circuit is constituted by adding only a pair of switching devices to the conventional PWM converter circuit. With a simple control technique, the ripple energy on the dc line is converted into stored energy on the input ac capacitors through additional switches. The theoretical characteristics are obtained by using the state-space averaging method. The effect of ripple reduction is confirmed by experiments using a breadboard setup. © 1998 Scripta Technica, Electr Eng Jpn, 123(1): 51–62, 1998     

A three-terminal piecewise-linear modelling approach to dc analysis of transistor circuits

The simulation of electronic circuits by computer has become an important part of present-day circuit analysis and design, especially in the area of integrated circuit design. One of the goals in computer simulation of integrated circuits is to have a program ‘package’ for which the input consists of chip fabrication data (mask dimensions, impurity profiles, material data such as carrier lifetimes) and the output displays the complete circuit response. This requires both an efficient modelling approach and a fast circuit analysis method. In this paper a simulation method is described which generates dc responses (in the form of operating points or transfer characteristics) of transistor circuits directly from physical parameter data. The basis of the method is a two-dimensional piecewise-linear approach to the dc modelling of bipolar transistors. The model is directly used in a piecewise-linear circuit analysis program to simulate the dc response of a given circuit.     

A suitable single-phase pulse width modulation current source inverter for utility interactive photovoltaic generation system

A suitable single-phase inverter for the utility interactive photovoltaic generation system is proposed. The single-phase Pulse Width Modulation (PWM) current source inverter has a novel circuit configuration in which an auxiliary branch is added to the normal single-phase bridge circuit. To reduce the size and weight of the dc reactor, a double frequency parallel resonance circuit (LC tank circuit) is inserted in the dc side of the inverter. As a result, the double frequency voltage appearing in the dc side of the inverter due to the pulsation of the single-phase instantaneous power is perfectly suppressed by the tank circuit. The constant dc current without pulsation is supplied from PV array to the inverter. The inverter provides a sinusoidal ac current for domestic loads and the utility line with unity power factor. The virtual maximum power of the PV array can be obtained without any feedback control. In the system, the PV array can play an important role as a current-limiter due to its V-I characteristics. Computed waveforms by simulation are shown. Excellent inverter equipment will be realized that is smaller in size and lighter in weight than is usual for a conventional inverter.     

Theoretical analysis of transient recovery voltages when clearing a transformer secondary fault

An analytical formula for the transient recovery voltage and its derivative dv/dt across a circuit breaker has been derived for the case of a transformer secondary fault. A comparison of the calculated results with field test and EMTP simulation results has demonstrated it to have satisfactory accuracy. By applying the formula, the effects of various circuit parameters on the transient recovery voltage and its derivative dv/dt are elucidated. The derivative dv/dt, defined conventionally as the ratio of the crest value and the time to the crest, is found to be about two‐thirds of the maximum value of dv/dt given as a function of time. In addition, a formula for the critical circuit parameters at which dv/dt across a vacuum circuit breaker reaches the critical condition, that is, the circuit breaker fails to interrupt a fault current, is derived. © 2000 Scripta Technica, Electr Eng Jpn, 134(3): 44–52, 2001     

直流系统中空气断路器和熔断器级差配合试验研究

直流系统中空气断路器和熔断器级差配合试验研究模拟变电所直流电源系统断路器和熔断器级差配合的实际使用环境,编制了多种试验方案,对蓄电池直流系统的两段保护和三段保护直流断路器及熔断器级差配合的选择性进行了上下级配合的实际分短路分断试验,取得了大量有价值的数据和波形,提出了试验结论和验证了直流系统直流断路器级差配合的原则.该项研究还针对目前浙江电网直流系统中存在的问题提出了提高直流系统可靠性的改进措施,为今后直流系统断路器和熔断器的设计选型和技术改造提供了依据.