上面这幅 3D 动画较大，可能需要等一段时间才会显示。如果看不到，可以按 F5 刷新一下页面，或者重新打开这个网页。 下方投影是电路图， Z 轴表示电位大小。电阻用倾斜板表示，垂直板描述了 PN 结的电位差，长方体支架描述了电容间的电位差以及 PN 结导通所需要的电位差。三极管分成了 c 、 b 、 e 三块， b 在 c 、 e 之间，很窄， c 、 e 的高度表示 Ucb 和 Ube 。 Ube 也是 PN 结，需要达到 0.7V 左右才导通。 电路中 LED 亮灯时间很短，但电流是 mA 级别的，其他支路电流是 μA 级别的，两者大小相差太大，所以没有在图中画出其他支路的电流。 两次突变间隔较短是因为电容充电时间或者说LED亮灯时间较短。 灭灯时间较长，这段时间内 LED的 长方体支架比较明显，意味着电压不够亮灯。两个三极管发射极的 长方体支架灭灯时也能看到，意味着电压不够打开发射结。 这两个电路图显然是一样的。我觉得画成矩形框更方便连线，每个元件位于一条边，中间再插两个三极管就可以了。电路里很多字母都有特别的含义，随便给电位点标字母很容易引起误解，例如： B 、 C 、 E代表了三极管的三个极， L、C代表电感， D代表二极管， P 、N 代表PN结，这些 字母最好不要用。 电位分析： 以 G 为地。 A 点电位最高，由于 LED 亮灯时两端电压会超过 1.5V ，所以电路取两节电池， A 点电位 3V 。 M 电位可变，由于 M 与 A 之间有 PN 结， A 电位为 3V ， PN 结带来 0V-1V 的压降，所以 M 电位应在 2V-3V 之间。实际数据下限有可能更低。 F 电位可变，电位越高 LED 越亮。一般的红 LED 导通电压 1.8V ，所以可以估计亮灯时 F 比 G 点高 1.8V ，电位太低则灭灯， F 的电位估计在 1V-2V 之间。 H 电位可变，由于与 G 之间有 PN 结，所以 H 电位应在 0V-1V 之间，实际数据下限有可能更低。 F 电位比 H 高，使用电解电容时，正极需放在在 F 处。 仿真波形 用 2H2222A 和 2SA1015 仿真，充电时间约 0.8ms ，放电时间约 4ms 。相差约 5 倍。但闪得太快了，真实的模型里肉眼应该分辨不出是否有闪烁。仿真时结合现实的模型考虑了 2Ω 的电池内阻。 绿色波形为 F ，黄色为 H ， F 电位较高时 LED 亮灯，此时 H 电位也较高，但逐渐下降，说明电容在充电。 F 电位较低时 LED 灭灯，此时 H 电位也较低，但逐渐上升，说明电容在放电。 F 的电位变化不大的原因在于 LED 的伏安特性是非线性的，电流越小电阻越大。电容放电时的电流很小，波形中 H 的电位从 0.2V 上升至 0.4V ，利用位于 H 与 3V 之间的 200kΩ 电阻可算出，所以，电容放电电流在 4ms 内从 14μA 降到了 13μA 。 紫色波形为 A ，蓝色为 M ， LED 亮灯电流较大， A 的电位下降至了 2.6V ，利用 2Ω 的内阻可以估算出亮灯时电流达到了 200mA 。至于 M 的电位为什么下降这么多，可能与三极管的型号有关，也可能是 PNP 进入饱和状态了。 详细的分析下篇博文再说。 参考文献： 分析一个简单好玩儿的闪烁灯电路 2017.8.6 张先森的馆藏 http://www.360doc.cH/mip/677081176.htmF3
上面3幅3D动画较大，可能需要等一段时间才会显示。如果看不到，可以按F5刷新一下页面，或者重新打开这个网页。 下方投影是电路图，Z轴表示电位大小。电阻用倾斜板表示，电场用垂直板表示，电容间的电场用透明垂直长方体表示，三极管分成了c、b、e三块，b在c、e之间，很窄，c、e的高度表示Ucb和Ube。 蓝色和绿色电位高度接近时电路会出现突变，只能这么展示，并不是动画卡顿。 电路中LED亮灯时，回路电流是mA级别的，其他支路电流是 μA 级别的，两者大小相差约50-500倍，所以没有在图中画出其他支路的电流。 用3D图可以很方便的分析节点电位的变化以及电容的充放电。 电路图 电路中电阻为 50kΩ ，电容为 1.0μF ，电源为 3.0V ，红LED亮灯电压 1.8V 左右，绿LED亮灯电压 2.0V 左右。三极管为 2N2222A 。 电位分析： 以 G 为地。 E 点电位最高，由于 LED 亮灯时两端电压会超过 1.5V ，所以电路至少需要两节电池。两节电池时 E 点电位一般为 3V ，但如果电流太大，考虑电池内阻， E 点电位会略有下降。例如：内阻 2Ω ，总电流 50mA 时，内阻分压 0.1V ， E 点电位将降为 2.9V 。如果没考虑这一点，模拟的数据有可能和实际的数据不符。 K 、 L 电位可变，电位越低 LED 越亮。一般的红、绿 LED 导通电压在 2V 左右，所以可以估计亮灯时 K 、 L 电位比 E 点电位低 2V ，电位太高则灭灯。若 E 点电位 3V ， K 、 L 的电位估计在 1V-2V 之间，若 E 点电位为 6V ， K 、 L 电位估计在 4V-5V 之间。电位有下限的原因可以通过分析电容的充放电来解释。 M 、 N 电位可变，电位较低时，与之相连的三极管截止，电位较高时三极管导通。因为发射极有 PN 结， M 、 N 电位应在 0V-1V 之间。该范围与电池数量无关。 K 、 L 电位较高，使用电解电容时，正极需放在在 K 、 L 处。 电容充放电分析： 电容充电时，充电回路包括 LED 、电容、电容斜下方三极管的发射极。由于 PN 结均为正向，电阻较小，所以时间常数较小，充电时间较短。 电容放电时，放电回路包括与电容相连的电阻、电容、电容下方三级管的集电极 - 发射极。电阻较大时，时间常数较大，完全放电所需时间较长。 由于充电时间短，完全放电时间长，所以电容正极板电位即 K 、 L 电位有可能不会下降太多，就又开始上升了。这就是 K 、 L 电位有下限的原因。充放电转换的瞬间，电容两端的电位会突变，但电容电压不变。例如：突变前 U L =2V ， U M =1V ，突变后 U L =1V ， U M =0V ，虽然 U L 、 U M 发生了突变，但两者的差值即电容电压保持 1V 不变。 上面两点分析都可以结合3D动画来理解。 上图显示了充电回路 ( 左 ) 和放电回路 ( 右 ) 。但只是标注出了回路，没有显示电流大小。电流的分析下篇博文再说。 参考文献： Astable Multivibrator (Oscillator) Dec 7 2016 http://www.falstad.com/circuit/e-multivib-a.html 双闪灯电路 2014-08-02 老白说模电 https://v.youku.com/v_show/id_XNzQ5ODQwMTcy.html?spm=a2hzp.8253869.0.0
这几天在 Power Globe 上看到对无功功率的一些讨论，把一些比较好的解释放到这里。正如Charles A. Gross 所说，这些解释都（部分地）正确地揭示或说明了无功功率，但也都不是一个完美或根本的解释，其中的一个原因是我们在尝试为一个非物理或抽象的量提供物理解释。 It’s been fun reading all the explanations. One of my favorites is “Q is the foam on the beer…”.They all have elements of truth, but never the whole truth and nothing but the truth. Hence, none really explain what Q is.The reason that we are having so much trouble coming up with a physical explanation for Q is that Q is non-physical, as are many concepts in engineering. --Charles A. Gross, PE, PhD, FIEEE Reactive power is a measure of the back and forth flow between energy in magnetic and electric fields in components. The reactive power value measures the magnitude of the instantaneous flow between these fields. ---B.Ross ------------------------------------------------------------------------------------------------------------- The answer to your question requires some understanding of ac circuits. Ac voltages (V) and currents(I) vary sinusoidally in time and have three basic properties: strength (RMS magnitude, V in volts, I in amperes); frequency (e.g. 60 Hz); and phase. Phase involves two quantities (V and I, in this case) . V and I are said to be “in phase”, if they both peak at the same instant; are zero at the same instant; reverse polarity/direction at same instant; etc. V and I are said to be “out of phase”, if when V peaks, I is zero, and vice versa. More precisely we really should say “V and I are 90 degrees out of phase”. . Now general, V and I are not in phase or 90 degrees out of phase but somewhere in between. It is possible to divide the current (I) into two components: the in-phase component or “active current” (IA) and the (90 deg) out-of-phase component or “reactive current” (IR) Correspondingly, there are two kinds of power: Active Power (P) = V*IA, which we say is measured in watts Reactive Power (Q) = V*IR, which we say is measured in volt-amperes reactive, or “vars” There is also a third kind of power in ac circuits: Apparent Power (S) = V*I, which we say is measured in volt-amperes , or “VA”. These three are related: S = sqrt as are the currents. I = sqrt How much of “I” is “IA” is communicated thru something called the power factor (pf), such that IA = I*pf and P = S*pf An Example: A 120 V ac source supplies 10 A at a pf = 0.8 lagging. The term lagging means that the current trails the voltage in time. Find S, P, and Q. S = V*I = 120(10) = 1200 VA P = S*pf = 1200(0.8) = 960 W Q= sqrt(1200^2-960^2)= 720 var I = 10 A IA = I*pf = 10(0.8) = 8 A IR = sqrt(10^2-80^2)= 6 A Now that we know what Q is, at least in terms of V, I, and phase, what is it physically? There are three passive circuit elements: R,L,C R, and only R, dissipates active power (P). L and C are called “reactive elements” in that they do not dissipate energy, but they do store it an internal magnetic field (L), or electric field (C). This field energy” is constantly flowing into and out of L and C and the source, and over an ac cycle, averages to zero. This energy exchange requires a current component that is necessarily 90 deg out of phase with the voltage (IR), and hence a corresponding power component Q = V*IR. --- Charles A. Gross, PE, PhD, FIEEE ---------------------------------------------------------------------------------------------------------------------------------------------------- Reactive power is a myth and a delusion. It is no more than a mathematical coincidence. It can be extremely useful, but it is without foundation. You know the math: it is just a matter of using a sine or a cosine term to switch between real and reactive power. It is just the difference between the one side or the other of a right-angle triangle. But think! That right triangle does not represent a phasor. The 90-degree rotation business of phasors does not apply because power is not a phasor. A few years ago, NIST did a survey of the way this thing called reactive power was being measured, and found there were at least nine different methods that would give nine different results, depending on how far the waveform was from sinusoidal. It became a NEMA report: NEMA C12.24 TR-2011, Definitions for Calculations of VA, VAh, VAR, and VARh for Poly-Phase Electricity Meters, registered with ANSI May 2011. Over a hundred years ago, we engineers were asking whether it was possible to measure something that was not real, and whether the fact that you could measure something meant that it was real. The digital revolution in measurements has firmly answered that it is possible to measure something that is not real, because the number-crunching part of measurement is no more than data compression. The ways we measure reactive power underlines that. Today, you can buy equipment that will let you choose whose definition you use in the measurement. That is not to say the idea of reactive power is not useful. It has simplified thinking about voltage management in the power system. It has led to some interesting solutions in that area: SVCs for example. But once you get away from the simplified notion of a perfect sine-wave, you enter undefined territory, the realm of imagination. Power factor is in the same boat. Another calculation of very great value and usefulness, and yet not defined for waves that are not sinusoidal. We will, of course, continue to use these terms: they are much too useful to abandon. But we should be aware of their limited meaning, and sometimes we are not. See, for example, Berrisford, A.J., “Smart Meters should be smarter”, presented at the IEEE PES General Meeting, San Diego, CA July 2012. DOI 10.1109/PESGM.2012.6345146 --- Harold Kirkham,Staff Scientist,Pacific Northwest National Laboratory.
我们从 Wiley 出版的电气工程、控制系统、电路理论和通信技术类期刊中，选取了过去三个月 内下载量最高的 25 篇文章，推荐给大家免费阅读，时间有限，大家抓住机会。 Analysis of possible introduction of PV systems considering output power fluctuations and battery technology, employing an optimal power generation mix model Electrical Engineering in Japan Semi-Global Output Feedback Stabilization for a Class of Uncertain Nonlinear Systems Asian Journal of Control A signal processing adaptive algorithm for nonstationary power signal parameter estimation International Journal of Adaptive Control and Signal Processing A novel design of compact wideband hexagonal antenna Microwave and Optical Technology Letters Distributed Tracking Control for Networked Mechanical Systems Asian Journal of Control Robust stability of nonlinear model predictive control with extended Kalman filter and target setting International Journal of Robust and Nonlinear Control Globally decentralized adaptive backstepping neural network tracking control for unknown nonlinear interconnected systems. Asian Journal of Control Planar UWB monopole antenna with dual band-notched characteristics for UWB applications Microwave and Optical Technology Letters Multiobjective particle swarm optimization for a novel fuzzy portfolio selection problem IEEJ Transactions on Electrical and Electronic Engineering Low-power, low-area preamplifier for ultra high-speed multi-channel optical communication system International Journal of Circuit Theory and Applications Composite adaptive disturbance observer?based control for a class of nonlinear systems with multisource disturbance International Journal of Adaptive Control and Signal Processing Consensus of multi-agent systems with nonlinear dynamics and sampled-data information: a delayed-input approach International Journal of Robust and Nonlinear Control A model-driven development method for Management Information Systems Electronics and Communications in Japan Microlens for uncooled infrared array sensor Electronics and Communications in Japan Distributed output regulation of leader–follower multi-agent systems International Journal of Robust and Nonlinear Control Bounded Consensus Algorithms for Multi-Agent Systems in Directed Networks Asian Journal of Control RC models of a constant phase element International Journal of Circuit Theory and Applications Robust control of robot manipulators based on uncertainty and disturbance estimation International Journal of Robust and Nonlinear Control A 5-GHz energy-efficient tunable pulse generator for ultra-wideband applications using a variable attenuator for pulse shaping International Journal of Circuit Theory and Applications Inactivation property of microorganisms in water irradiated by atmospheric-pressure plasma using dielectric barrier discharge IEEJ Transactions on Electrical and Electronic Engineering Nonlinear convex and concave relaxations for the solutions of parametric ODEs Optimal Control Applications and Methods A CCII-based wide frequency range square waveform generator International Journal of Circuit Theory and Applications Hybrid modelling and emulation of mem-systems International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1 x 8 MEMS Flexible integrated optical device for optical fiber-based networking applications Microwave and Optical Technology Letters Decoupled WWAN/LTE antennas with an isolation ring strip embedded therebetween for smartphone application Microwave and Optical Technology Letters
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