Capacitor current imbalance and its suppression method between phase legs for three‐phase inverter

This paper proposes a method to suppress the capacitor current imbalance between the phase legs of a three‐phase inverter circuit. This circuit consists of half‐bridge modules and DC‐link capacitors closely connected to each module. It can be designed for low stray inductance between power semiconductor devices and DC‐link capacitors in each module. However, in the conventional structure, the stray inductance between the phase legs may lead to an imbalance in the capacitor current due to the DC‐side resonance phenomenon under a higher switching frequency condition by using a SiC MOSFET. This paper presents the analyses of the equivalent circuit considering the circuit configuration, which suggests that capacitor current imbalance occurs depending on the stray inductance between phase legs. To suppress the capacitor current imbalance, a delta‐type bus bar connecting phase legs is proposed. The experiment results at 300 V and 4.6 A demonstrate the suppression effectiveness of the proposed method.     

A simplified design-oriented analysis of switched-capacitor active filters

The method presented in this paper provides a simplified approach to obtain the z-domain equivalent circuit of an SC active filter by one-for-one substitution of each basic SC element with its z-domain equivalent admittance, if a specific terminal condition is met. Then, traditional circuit analysis techniques can be used to derive the z-domain transfer function of the filter. This method makes the analysis and the design of the SC active filter simple and similar to the S-domain method. Two application examples are given.     

Realization of a general all‐pole current transfer function by using CBTA

In this article, a general all‐pole current transfer function synthesis procedure using current backward transconductance amplifiers (CBTAs) is proposed. The proposed configuration uses n current backward transconductance amplifiers and n grounded capacitors as the only type of passive elements. The circuit is eligible to realize any all‐pole transfer characteristics with a given strictly Hurwitz (stable) denominator polynomial. Further, it is straightforward to find the values of the passive elements from the coefficients of this polynomial by using the Routh–Hurwitz algorithm as in the realization of a two‐element kind passive network synthesis. In this sense and as far as the author's knowledge, it is the only active structure that can be synthesized like a passive two‐element kind Cauer circuit. The simulations that are performed using PSPICE exhibit satisfactory results coherent with the theory. Copyright © 2011 John Wiley & Sons, Ltd.     

采用高耦合度分裂电抗器的并联型断路器均流过程研究

为了研究基于高耦合度分裂电抗器(high coupled split reactor,HCSR)的并联型断路器的并联均流效果,推导了简单并联及基于HCSR的并联型断路器并联支路间不平衡电流的表达式,通过分析得出结论:HCSR单臂限流电感、双臂间耦合度、选用的断路器弧阻大小等因素是影响并联型断路器均流效果的主要因素。为验证上述结论,建立了HCSR、真空灭弧室、SF6灭弧室的电路仿真模型,开展了相关仿真分析,并采用合成回路进行了对应断路器并联开断实验。仿真、实验结果与理论分析结果相符合。基于上述研究结果,最终给出了针对不同类型并联断路器的HCSR单臂电感的选取原则,以用于指导新型并联断路器的设计。     

Modeling a rectilinearly channeled negative surface discharge

This study presents a new theoretical model for describing a rectilinearly channeled negative discharge generated on PET film (δ = 50 μm) under atmospheric conditions. The channel is modeled using an RC distributed constant circuit with front potential V_t and moving at propagation speed v_t. A conduction equation (∂U/∂t=μ√U∂²U/∂²z), U = V², with V the potential and μ the electron mobility is introduced under the assumption that the generated current consists of only electrons. This equation can be solved using the boundary conditions and the speed condition in which the speed is considered as being proportional to the gradient of U [, β const]. Although it is difficult to solve the conduction equation analytically under the boundary condition and speed condition, using the simplified boundary condition and the length l(t) instead of the speed condition, the conduction equation is solved numerically. The U(z, t) are calculated and compared with the experimental results. I proposed that one of the best approaches to the discussion of the conduction equation is using the solution of the Stefan problem which corresponds to the fusion phenomenon occurring in a column of ice. The solution of the Stefan problem is also compared with the above numerical solution. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 7–13, 1997     

3/2接线中断路器合闸后电流不平衡问题分析

3/2接线为500kV变电站的主要接线形式。针对某500kV变电站第2串中间的断路器在合闸运行后该串3组电流互感器(TA)均产生电流不平衡的问题,构建了电路模型并结合实际回路电阻的情况进行了分析,指出产生三相电流不平衡的原因为站内或电源至站内的三相阻抗不平衡所致,针对不平衡电流造成的影响等因素,提出了运维措施和建议。     

低压配电用浪涌保护器试验中的几个问题分析

介绍了以拥有大通流容量的开关型SPD为代表的Ⅰ级试验品进行动作负载试验预处理试验时,IEC 61643-1:2005规定应用8/20μs电流波进行触发续流试验,是因为RLC结构的10/350μs冲击装置的电容量相对8/20μs很大,容抗相对试品导通阻抗较小,续流发生时,试验回路可等效成容抗和试品导通阻抗的并联结构,工频电源产生的续流更容易从阻抗小的支路中流过,且此时主电路开关会发生严重的拉弧现象,严重影响开关的使用寿命,试验论证了上述观点。对氧化锌压敏电阻(MOV)残压测试时,流过MOV的电流为零时,测得的残压仍会维持一段时间后归零,可能是受电容器上的残余电荷的影响所导致的,利用试验并结合二阶电路理论,对测试时电路的工作状态分析了该问题。     

碳化硅金属氧化物半导体场效应晶体管短路特性

器件的短路能力对整流器及其故障保护具有极其重要的意义。当器件故障运行时,为避免器件损坏,须在最短的时间内将故障予以切除,而此时器件的最大短路运行时间为系统保护装置提供了有力的时间支持。主要研究了碳化硅金属氧化物半导体场效应晶体管(Si C MOSFET)在短路条件下的运行能力,以Cree公司的1 200 V/19 A Si C MOSFET为模型,设计了硬件电路,测试其不同电压等级下的短路电流;并在直流电压等级为600 V的条件下,测试了不同栅极电压、不同温度工况下的短路电流。研究结果表明器件的短路峰值电流随着栅极电压的升高而增大,而其短路运行时间却大幅降低;温度对短路运行时间的影响则相对不甚明显;同时还给出了器件在不同工况下的最大短路运行时间Tsc(max)。     

剩余电流动作断路器电路优化设计

针对剩余电流保护可靠性和安全性的广泛需求,通过分析传统剩余电流动作断路器电路的设计缺陷,提出了解决方案。该方案采用三相桥式整流电路,并将脱扣器放置在压敏电阻和整流桥之后,能有效保证断路器在三相系统中一相断电的情况下,剩余电流保护功能正常;采用以稳压管稳压电路为基础的串联型稳压电路,实现宽电压范围的工作需求;采用高性价比的晶闸管组成双晶闸管串联脱扣电路,耐压值增加1倍。设计更符合电磁兼容特性和剩余电流动作断路器可靠性和安全性的要求。     

Development and design of wave SC filters

A direct z-domain simulation of LC ladder and unit-element filters by means of wave SC circuits is presented. the development of a wave SC circuit is achieved by interconnecting a limited number of basic SC building blocks. the derived circuits are fully parasitic-free, symmetric and can be optimally designed for dynamic range maximization and capacitance area minimization. the number of operational amplifiers in the simulated unit-element filters is essentially low in comparison to earlier presented parasitic-insensitive wave SC filters and to leap-frog-type SC filters. Four- and two-phase multiplexed simulated LCR filters can be developed. Bilinear s-z transformation applies for all the circuits; thus the design is exact and there is no requirement for a high clock frequency. Filters with transmission zeros can be developed. the simulated responses of various types of filters are in good agreement with the theory. Detailed examples of different designs are given.     

电网电压不平衡下燃料电池并网逆变器功率控制

基于参考指令变更的三相并网逆变器功率控制方法,通过调节影响功率波动的参考指令内的谐波分量可以实现逆变器电流质量和功率波动间协调控制,但不能实现三相电压不平衡下负序交流分量的无静差调整。针对此问题,提出了三相电压不平衡下燃料电池三相并网逆变器功率控制方法,构建了燃料电池三相并网逆变器电路拓扑结构。在此基础上采用无锁相环直接功率控制方法,采用全通滤波器对并网逆变器电路中的电压和电流基波分量进行90°相移,消除2倍频的负序交流分量,实现并网逆变器有功功率和无功功率的有效控制。仿真结果证明,所提方法控制的并网逆变器进网电流谐波含量为0.33%,输出电流正弦度较高,电网电压不平衡状态下仍能坚持对电流进行控制。该方法功率控制效果好,具有较强的安全性。     

Self-rehealing characteristics of a sodium current limiter and its overcurrent coordination for low-voltage distribution system

The sodium current limiter developed and applied for low voltage use is not a current limiting fuse but a new type of reusable current limiting device that utilizes metallic sodium as a fusible element. Excellent current limiting performance and quick self-rehealing properties of the sodium limiter allowed highly reliable electric power systems to be obtained economically and compactly. Here we examine experimentally the rehealing properties of the sodium limiter after current limiting operation and discuss the overcurrent coordination of the sodium limiter for a low-voltage distribution system. The results are summarized here:

• 1 (1) The resistance of the sodium limiter, being between about one thousand and several thousand times its normal resistance r₀ at room temperature during a current limiting operation of short circuit fault currents, changes abruptly to 30 to 40 times its r_o value just after the disappearance of the fault current and falls steadily to r_o.
• 2 (2) The sodium limiter can recover current-carrying capability for an overload current even immediately after a current limiting operation and maintain its capability for the following normal load current. The upper limit of the recovery of the sodium limiter is given by its overcurrent against the time characteristics under the normal condition.
• 3 (3) The self-rehealing characteristics of the sodium limiter presented here give the ability to design a low-voltage motor control center using the sodium limiter which maintains maximum service continuity up to high fault currents.

     

Current‐mode dual‐output ICCII‐based tunable universal biquadratic filter with low‐input and high‐output impedances

A new tunable current‐mode (CM) biquadratic filter with three inputs and three outputs using three dual‐output inverting second‐generation current conveyors, three grounded resistors and two grounded capacitors is proposed. The proposed circuit exhibits low‐input impedance and high‐output impedance which is important for easy cascading in the CM operations. It can realize lowpass, bandpass, highpass, bandreject and allpass biquadratic filtering responses from the same topology. The circuit permits orthogonal controllability of the quality factor Q and resonance angular frequency ω_o, and no component matching conditions or inverting‐type input current signals are imposed. All the passive and active sensitivities are low. Hspice simulation results are based on using TSMC 0.18 µm 1P6M process complementary metal oxide semiconductor technology and supply voltages ±0.9 V to verify the theoretical analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

基于电压、电流不平衡度差值的干式变压器匝间短路故障识别方法

干式变压器绕组发生轻微匝间短路时,相电压、相电流等电气量变化甚微,不能作为表征匝间短路故障的敏感特征量,导致相应保护措施缺失,运行过程中设备烧毁事故时有发生。通过建立干式变压器“场-路”耦合仿真模型,利用实际试验和工程计算获取的状态参数,验证模型的准确性。通过建立和分析其绕组匝间短路故障数学模型,提取相电压、相电流不平衡度标幺值的差值,作为判断匝间短路故障的特征量。通过仿真分析不同工况下其绕组发生匝间短路故障时不同电气量的变化情况,论证了所提新故障特征量不仅能提前感知绕组匝间短路故障,而且能够克服固有的三相不对称及不平衡运行带来的影响,有效性、灵敏性兼顾,为实时监测干式变压器绕组匝间绝缘状态提供一种新方法。     

Analyses and techniques for phase noise reduction in CMOS Hartley oscillator topology

This paper reports the analyses of the inductive degeneration , noise filter , and optimum current density techniques for phase noise reduction in the CMOS Hartley oscillator circuit topology. The design of the circuit topology is carried out in 28 nm bulk CMOS technology in a range of common conditions adopted also for a previous study on the Colpitts topology, so complementing the previous study on Colpitts topology and allowing a direct comparison between the Hartley and Colpitts topologies. The theoretical analyses of the three techniques are carried out and verified by means of circuit simulations. The results obtained for the inductive degeneration and noise filter show the existence of an optimum inductance for minimum phase noise. Moreover, the results obtained for the optimum bias current density technique applied to a Hartley oscillator circuit topology incorporating either inductive degeneration or noise filter provide the demonstration of the existence of an optimum bias current density for minimum phase noise. Moreover, we will go beyond this important result, by investigating for the first time the relationship with the optimum current density for transistor minimum noise figure and other general results reported in the literature. Overall, the analyses show that the adoption of these techniques may lead to a potential phase noise reduction up to 16 dB at a 1 MHz frequency offset for an oscillation frequency of 10 GHz, with respect to the traditional Hartley topology. Lastly, we report a comparison under common conditions between Colpitts and Hartley topologies implementing the aforementioned techniques, which could, from a designer perspective, be useful to acquiring a few key insights about the circuit design opportunities and focus the design efforts toward specific directions for performance optimizations. Copyright © 2017 John Wiley & Sons, Ltd.     

Modified CFOA,its transpose,and applications

It is shown that the recently‐proposed modified current feedback operational amplifier (MCFOA) is quite a versatile element in that given a realization for a system function using MCFOAs, we can obtain three alternate realizations using the same MCFOA but by appropriately connecting the y, x, w, and z terminals of the MCFOA to the remaining part of the original realization. Using the results concerning the transpose of a multi‐terminal element, it is further shown that the transpose of an MCFOA is another MCFOA. Thus, using the results of transposition, given a voltage‐mode circuit using MCFOAs, we can directly obtain four current‐mode circuits using the same MCFOAs or vice versa. Copyright © 2015 John Wiley & Sons, Ltd.     

基于非周期分量衰减速率的变压器励磁涌流鉴别方法

提出一种基于非周期分量与基波分量比值(简称k0)衰减速率的励磁涌流鉴别方法。首先利用变压器仅一侧有电流还是多侧都有电流的特点,实现变压器空充与非空充状态的初步划分。判出空充状态后,利用三相差流中k0衰减速率的差异进一步判别励磁涌流与故障电流。基于k0衰减速率的励磁涌流鉴别方法原理简单可靠、计算量小,易于工程实现,对传统的二次谐波判据是个有益的补充。Matlab仿真和现场误动数据表明该方法不仅能够在变压器剩磁较大时确保空载合闸的成功率,当变压器空充到轻微匝间故障时亦能大大缩短保护的闭锁时限。     

Current mode filters using two output inverting CCII

Current mode Tow Thomas filter using two‐output inverting second‐generation current conveyor is given, the circuit has low input impedance, employs two grounded capacitors and three grounded resistors and has independent control on Q. A universal current mode filter capable of realizing the five filter functions is also given. Both circuits have low sensitivities to all circuit components. Spice simulation results are included. Copyright © 2007 John Wiley & Sons, Ltd.     

Switched capacitor circuit for 1/f noise generation using a power-law circuit

A simple switched capacitor (SC) circuit is given which realizes a one-dimensional discrete dynamical system X_n+1 = X_n + ux^z generating intermittent chaos with a 1/f-shaped power spectrum. an integrated circuit with a pair of logarithmic and antilogarithmic amplifiters can easily realize the power-law term x^z which plays a key role in generating l/fnoise. an inevitable small offset voltage ? in the SC circuit governs the cut-off frequency of 1/f noise, and when the dynamical system is modified by introducing an effective ?, the ‘indirect method’ enables us to get the precise power spectrum in the modified system.     

电力电容器噪声测试中电流注入方式的研究

高压直流换流站内的电力电容器在实际工况下具有很强的工频成分和丰富的谐频成分.为了模拟实际工况,在研究现有电流注入电路的基础上,设计了一种针对电容器单元噪声试验的桥式全工况电流注入电路.电路的两个桥端用于注入工频电流,并且采用并联谐振补偿电感减小工频电源电流;在电路的另两个桥端用于注入谐波电流,谐波电流电源由谐频信号发生器和功率放大器组成,可以实现同时施加48次以下任意谐波的组合,以模拟实际工况的各种应用场合.试验表明,在50 ～2 500 Hz频率范围内实现了工频与12个谐波电流同时注入电容器单元的试验工作,试验结果完全符合模拟高压直流换流站中电容器单元的可听噪声要求.