# Electrical Engineering

What will happen if the feature dataset has been scaled in the range of 0.1 to 1 for linear classifier rather than using the scaling range 0 to 1?

In general the dataset used for classification using Lilinear classifier is scaled in the range 0 to 1. now if the scaling range  of 0.1 to 1 is feeded to the same classifier, would it effect the result?

Chia-Hsiang Yang · Technical University Darmstadt

It seems that you just need a union scale range for all features. Is it correct? I'm not 100% sure. But anyway I think the result should be a least a bit different among cases with different united scale ranges.

What is the relationship between speed and time in designing the systems?

I plan to investigate the system behavior and the factors influencing them, and I have a model with a circuit design system. In this model, we have tried to design a new plan for the proposed system.

Paul Howard Riley · University of Nottingham

Where is the figure?

I have simulated I-V curve at 1000w/m^2. Now, I want to simulate I-V curves for different illumination levels. How can I simulate?

I have used following equations to simulate the curves at different illumination levels

L1=1000 w/m^2;
L2=700 w/m^2;
delIL=IL1*(L1-L2)/L1;       // IL1= photocurrent at 1000 w/m^2
I2=x-delIL;                        // I2 and V2 are current &voltage values at 700
V2=v-delIL*Rs;                // Rs= resistance of pv cell

// x & v are current &voltage values at 1000

Am I right or wrong ? I have some doubts

Ashraful Haider Chowdhury · Military Institute of Science and Technology

Thank you sir for your wise advise.I will follow your approach.If I face any problem surely I will knock You.Once again thank you sir

How do I calculate statistical sampling error and confidence limits as my sample approaches the entire population?

My understanding of the statistical sampling error is derived from the binomial distribution where the variance, which is the square of the standard deviation, is simply N, the size of the sample. I believe that I know, or once knew, that the confidence limit is calculated from this distribution using an error function integral, Erf(x). In my physics career, we always worked with samples that were small compared with the whole population, and one got used to calculating the statistical component of the total error from sigma = SQRT(N). Estimating systematic errors was where most of the error analysis effort was spent.

Now I am doing social science research where one has access, on some occasions, to entire populations, for example, the number of women graduating with Electrical Engineering degrees from U.S. institutions year-by-year. When I propagate the sampling errors through a calculation of the ratio of women to women and men graduates, I get an enormous error, larger than and comparable to the ratio itself.

Clearly, I am doing something wrong. For example:

1.) Elementary calculus or algebraic errors (see attached)
2.) Violating assumption(s) of the simple propagation of errors scheme:
a.) the component errors are small compared with the measured quantities.
b.) the component errors are uncorrelated with one another.
3.) Applying sigma = SQRT(N) when I have the entire sample
4.) <strike> Something else I remain blind to. </strike> My main mistake was adding the central value to the error before graphing the main value with error bars. Merely graphing the main value with error bars works as expected. (Edit made 27 August 2014.)

For what it is worth, another physicist kindly checked (1.) and (2.) for me and said they were correct.

It seems to me that it should be possible to calculate the sampling error as the sample approaches 100% of the population and the confidence limit approaches 100%. In this case, the sampling error should approach zero, smoothly, I would imagine.

If the sampling error is simply zero when one has the entire sample, this formula should tell me. If I had this formula, and understand how to derive it, it seems that the sampling error being zero when one has the entire sample would be easier to accept.

It seems to me that there would still be systematic errors. But these are hard to estimate, particularly where self-reported data is aggregated nationwide.

It also seems to me that there may still be errors related to the population size, but I have no understanding or intuition for that, other than the fact that the data look "naked" to me without their error bars and that to the naked eye, smaller populations (e.g. astronomy) appear to have more year-to-year statistical fluctuation that larger populations (e.g. biology)

If one of you could get me back on the statistical path, I would greatly appreciate that.

Thanks,

Mark Frautschi

James R Knaub · Energy Information Administration

PS - Actually not sure what you meant by "error bars" being the same, and would be curious as to the standard error of the regression coefficient for time for each field, if you have them available.

At present, is there any practical implementation of six phase transmission lines around the world?

If so please mention the exact location and where it is implemented.

Babak Porkar · NSERC/Hydro-Quebec/UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE)

Dear Raghu,

Yes, for example see the attached paper and its refs. 1 and 2.

Good Luck

How we can improve the power factor of an induction generator?

Different configurations of Induction Generators are being used for the generation of power. When IG is operated as a self excited mode, then it have poor voltage & frequency regulation and lower power factor. How we can improve the power factor of Self Excited Induction Generator.

Apurva Kulkarni · Indian Institute of Science

Even doubly excited Induction Generator gives good pf

To have the qualified research center, I'd like to design a robotics research Lab based on MATLAB/SIMULINK software. this Lab is a project based Lab and all students should to do a research project and extract at least 4 papers from projects. So which method do you recommended?

Farzin Piltan · IRANIAN CENTER OF ADVANCED SCIENCE AND TECHNOLOGY

Dear Prof,

Thank you very much.

Kind Regards

What is the typical cost of laying XLPE and MI HVDC marine cable in dollar per kilometer?

How much does it cost to lay XLPE and MI HVDC marine cable in USD/km? A rough guess will suffice.

Detlef Wald · Institute of Electrical and Electronics Engineers

How deep, what type?

Multilayer Background subtraction?

I am working on Multilayer background subtraction paper published by Yao Jian. In this paper I didn't understand how modes and layers are making for background subtraction. Can someone kindly help me?

Khizar Saleem · University of Surrey

sorry for late response. Actually i am confused with background modelling. In this paper he described that background model for each pixel consist of k modes lets k=3, then each pixel is modelled by three modes. each mode consist of LBP, weight and layer number. I am confused how he assigned weight to each mode like in MOG we can assign weight by EM algorithm but in this case how? second point how he assigned layer number to each mode, thirdly k=3 means three histogram of LBP codes how we can compute three histogram at one pixel by LBP?

How to calculate sub-threshold leakage current of comparator in microwind 3.1 at layout level?

Leakage current

Mani Kandan · Sri Krishna College of Engineering and Technology

yes

Can we formulate Kirchhoff’s laws for resistances (KRL) and conductances (KGL) based on KVL and KCL?

In the question below, we have been discussing if voltage sources possess negative resistance:

https://www.researchgate.net/post/Are_electrical_sources_elements_with_static_negative_impedance_If_so_is_there_any_benefit_from_this_concept

This idea is proposed in a series of reputable sources cited in the Wikipedia work below:

https://en.wikipedia.org/wiki/User:Chetvorno/work6#Negative_static_or_.22absolute.22_resistance

It actually means to extend the scope of Ohm's law by applying it to the two kinds of electrical sources - voltage and current source.

Considering the ratio V/I = R as a static negative resistance. In the basic Ohm’s arrangement, a voltage source is connected to a load (a resistor). The voltage V across and the current I through them are the same as magnitudes. As a result, the ratio V/I (the resistance) for each element is the same what is known as Ohm’s law - R = V/I. However, while the voltage across and the current through the load have the same signs, in the case of the source they are opposite. Therefore, the resistor has a “positive” resistance R while the voltage source can be considered as having a negative “resistance" -R, and the sum of the two resistances is zero.

Considering the ratio I/V = G as a static negative conductance. In this dual Ohm’s arrangement, a current source is connected to a load (a resistor). The current I through and the voltage V across them are the same as magnitudes. As a result, the ratio I/V (the conductance) for each element is the same what is a dual form of the Ohm’s law - G = I/V. However, while the current I through and the voltage across the load have the same signs, in the case of the source they are opposite. Therefore, the resistor has a “positive” conductance G while the voltage source can be considered as having a negative “conductance " -G, and the sum of the two conductances is zero.

Here, I propose to develop this idea further as Kirchhoff done with Ohm's law in the distant 1845. Here are my speculations...

Converting the Kirchhoff’s law for voltages (KVL) to a law for resistances (KRL). KVL says that the sum of the voltages E (emfs) and the voltage drops V is equal to zero:

-E1 + -E2 + -E3 + ... V1 + V2 +V3 + ... = 0

If we formally divide this “voltage” equation by the current I

-E1/I + -E2/I + -E3/I + ... V1/I + V2/I +V3/I + ... = 0

and apply the Ohm's law for emfs and voltage drops, we will obtain

-R1 + -R2 + -R3 + ... R1 + R2 +R3 + ... = 0

where the voltages E are represented by the negative “resistances” -R1, -R2, -R3..., and the voltage drops V1, V2, V3... – by the “positive” resistances R1, R2, R3. So, we can name this “resistance” equation Kirchhoff’s law for resistances (KRL):

The sum of voltage-type negative resistances connected in series in a closed loop is equal to the sum of  positive resistances.

Converting the Kirchhoff’s law for currents (KCL) to a law for conductances (KGL). KCL says that the sum of the currents entering/exiting a node is equal to zero:
-I1 + -I2 + -I3 + ... I4 + I5 +I6 + ... = 0

(here I suppose the currents I1, I2 and I3 are produced by current sources while I4, I5 and  I6 are consumed by resistor loads)

If we formally divide this “current” equation by the voltage V

-I1/V + -I2/V + -I3/V + ... I4/V + I5/V +I6/V + ... = 0

and apply the dual Ohm's law, we will obtain

-G1 + -G2 + -G3 + ... G4 + G5 +G6 + ... = 0

where the source's currents are represented by the negative “conductances” -G1, -G2, -G3..., and the load's currents – by the “positive” conductances G4, G5, G6. So, we can name this “conductance” equation Kirchhoff’s law for conductances (KGL):

The sum of current-type negative conductances connected in parallel to a node is equal to the sum of positive conductances.

Converting the Kirchhoff’s laws to a law for powers (KPL). Finally, we can extend this modifying idea to powers. If we formally multiply the “voltage” equation above by the current I

-E1*I + -E2*I + -E3*I + ... V1*I + V2*I +V3*I + ... = 0

or, if we multiply thе “current” equation above by the voltage V

-I1*V + -I2*V + -I3*V + ... I4*V + I5*V +I6*V + ... = 0

we will obtain

-P1 + -P2 + -P3 + ... P4 + P5 +P6 + ... = 0

We can name this derivative “power” equation Kirchhoff’s law for powers (KPL)... and actually this is the well-known power balance:

The sum of negative powers (in a loop or at a node) is equal to the sum of positive powers.

I would like to inform that the idea to modify Kirchhoff’s laws in such a way was born during heated discussions mainly between Prof. Lutz von Wangenheim and me.

Cyril Mechkov · Technical University of Sofia

There is a contradiction in Researchgate that I still can not figure out - on the one hand, there is a very large number of members in a given group; on the other hand, there is a lack of interest in the most basic concepts in this area...

In this case, only in Electrical Engineering section there are 108,746 members, and in Physics - 61,784 members... and none of them responded to my challenge to the most fundamental laws of physics and electrical engineering...

I would be happy if there is at least one negative response:)

Is cycloconverter a matrix converter?

Can we call cycloconverter a matrix converter?

Basically yes, it have the same configuration but switches are transistors instead of thyristors, but that small change give the matrix converter a lot of flexibility, transistors switch at high frequency and it can produce any voltage waveforms, and then many control strategies are investigated.

The cycloconverter is usually used to drive a huge motor s at low speed, it can only reduce the frequency at the output, but thyristors can be made for very high power, and at low speed (low output frequency) the thd can be low, for diving a big motor to low speed cycloconverter is the cheapest solution in this moment. The matrix converter haven´t found many industrial applications jet but it is a very promising technology.

Is there a way to transpose paralleled foil windings in HF transformers?

High current high frequency transformers and inductors are wound with copper foil. Sometimes, foils also have to be paralleled to handle the rms current. Thus, the inner foil always carries the highest current since it has the smallest resistance and inductance. Transposing will balance the currents, but how to do it with foils.

Michael Meisser · Karlsruhe Institute of Technology

Dear Sujit, dear Jacob,

experimental evaluation seems to be a very comfortable solution since it provides you with real data. However, it may turn out that it is impossible to fit the experimental results with the assumptions and hard to identify the real physical soucres of either higher or lower losses. Hence, it may be advisable to run simulations of limited accuracy first in order to get an idea about the interplay of proximity and skin losses in your intended design. A 2D-Simulation of the core cross-section with the windings represented as circular stripes may be sufficient. I suggest COMSOL to build and simulate such an model.

How to evaluate PV systems' performance?
By the efficiency or the field?
Mehdi Hedayatpoor · University of Yazd

This paper focuses on the modeling of solar photovoltaic (PV) cell and the performance of typical solar PV panels in selected areas in the Sultanate of Oman. An accurate solar PV cell electrical model is based on the junction diode equations. The model consists of a photo-current current source, a single diode junction and a series resistance, and takes into account temperature and solar irradiation dependence. The model is developed using MATLAB/Simulink and is used to investigate the variation of the maximum power point for different temperatures and solar irradiation levels. Finally, the model is experimentally validated for a typical 30 Watt solar module connected to a variable load.

What is a 'cycloconverter'?
What is a 'cycloconverter'?
Mehdi Hedayatpoor · University of Yazd

hi dear friend

if you search on power electronic book,you can find information.

A cycloconverter is a device that converts alternating current, or AC, power at one frequency into AC power of an adjustable but lower frequency without any direct current, or DC, stage in between. It can also be considered as a static frequency changer and typically contains silicon-controlled rectifiers. The device consists of an array containing back-to-back, parallel, connected switches, which are used to fabricate the desired output AC waveforms. It's possible to control the frequency of these output AC waveforms by opening and closing the switches in a controlled fashion.

This converter converts single-phase or three-phase AC power to single-phase or three-phase power having a variable frequency and magnitude. Typically, the output frequency of the AC power is lower than the input frequency. A cycloconverter has the capacity to operate with loads of variable power factors and also allows bidirectional power flow. They can be broadly classified into two types — phase-controlled cycloconverters and envelope cycloconverters. In the former, control of the firing angle is accomplished through adjustable gate impulses, while in the latter, the switches remain in an on state and conduct in consecutive half cycles.

They are mostly used to control the speed of drives and for converting variable input frequency power into constant frequency output, such as in very high-power applications, including driving synchronous motors and induction motors. Some of the places where cycloconverters are employed include cement mill drives, mine winders, and ore grinding mills. They are also utilized in ship propulsion drives, scherbius drives, and rolling mill drives.

Offering many advantages, a cycloconverter can be used in quite a few low-speed applications and is also a compact system. Its ability to directly affect the frequency conversion of power without any intermediate stage involving DC power is another huge advantage. If the cycloconverter experiences a commutation failure, the results are minimal, such as the blowing off of individual fuses.

It also has the capacity of regeneration, covering the total range of speeds. Another huge advantage of the cycloconverter is its ability to deliver a sinusoidal waveform at a lower output frequency. This advantage comes from its ability synthesize the output waveform using a large number of segments of the input waveform.

This technology does have some disadvantages, though. Firstly, the frequency of the output power is around one third or less of the input frequency. It's possible to improve the quality of the output waveform if a larger number of switching devices are employed. A cycloconverter requires quite a complex control mechanism and also uses a large quantity of thyristors. Its use is also limited by severe harmonics and the low-output frequency range.

What you think about the application of the resonant inverters for PV leads to improved overall efficiency of the energy conversion?

Is it an area on which one can work now?

Alex Van den Bossche · Ghent University

Converters cost 200-500 euro/kW peak installed, whereas PV panels cost about 800 euro/kW peak to the customer now   (zonnepanelen.nl)

So for 1% less efficiency you have to pay 8 euro more/kWp in panels, but the converters last some 10 years and the panels 30years, so one rather can invest only 3 euro to gain an average 1% efficiency. So, it is difficult to have a return on investment of the higher efficiency if the converter costs more. The main advantage of a high efficiency for the manufacturer is to be able to do advertising with high efficiency and to be able to use a smaller heatsink (cost).

Does the amplifier in negative feedback systems possess negative impedance?

Negative feedback systems compensate disturbances in the feedback loop by adding extra power equal to the power dissipated in disturbing elements. So they can be considered as negative impedance elements.

In electronics, this arrangement can be observed in op-amp circuits with voltage type negative feedback (voltage followers, amplifiers, stabilizers...) where the op-amp adds extra voltage equal to the voltage drop across the positive element connected in the feedback loop. Thus the op-amp output acts as an element with negative impedance that neutralizes the positive impedance of the element in the feedback loop. As a result, the combination of both the (positive and negative) elements has zero total impedance.

We have already discovered two dual implementations of this general arrangement - inverting and non-inverting.

In op-amp inverting circuits, the op-amp output acts as a pure negative impedance element that neutralizes the positive impedance of the element connected between the output and the inverting input. As a result, the combination of both the (positive and negative) elements has zero total impedance (a virtual ground):

https://www.researchgate.net/post/Does_the_op-amp_in_all_the_inverting_circuits_with_negative_feedback_behave_as_a_negative_impedance_element_negative_resistor_capacitor_etc

In op-amp non-inverting circuits, the op-amp output acts as a voltage source with voltage equal to the input voltage and an internal negative impedance  that neutralizes the positive impedance of the element connected between the output and the non-inverting input. As a result, the combination of both the (positive and negative) elements has zero total impedance, and the whole input voltage appears across the other positive element connected between the non-inverting input and ground:

https://www.researchgate.net/post/Does_the_op-amp_in_non-inverting_circuits_with_negative_feedback_behave_as_a_voltage_source_with_negative_internal_impedance?

The attached picture is conceptual; it presents the most elementary system with negative feedback - a follower. The amplifier A (supplied by the energy source E) acts as an element with negative impedance -Z that compensates the positive impedance Z of the disturbing element. So, the output quantity Y is always equal to the input quantity X (Y = X).

With this general and two specific questions I make an effort to show the connection between two seemingly different phenomena - negative feedback and negative impedance.

Cyril Mechkov · Technical University of Sofia

IMO the negative resistance phenomenon is a special case of the more general phenomenon named amplification. In the classic analog electronics, we implement it in a quite silly wasteful way:) - by controlling the electrical energy with active elements (variable resistors). They can be externally-controlled (as in conventional 2-port amplifiers) or self-controlled (as in exotic 1-port amplifiers). In the first case, there is no negative resistance; we can observe it only in the second case... An example is the tunnel-diode amplifier...

Maybe, for your goals it is enough to say that the voltage and current change in different directions when the resistance varies... without mentioning negative resistance...

What is "negative differential resistance"? How is it implemented? How does it operate? What is its relationship with the true negative resistance?
When we see somewhere written "negative resistance", we are never sure what exactly it is, just because it has two varieties - "true" and "differential"... and the former is not a resistance:) We have already started a discussion about the true (absolute) negative resistance
https://www.researchgate.net/post/What_is_negative_impedance_Does_can_it_exist_If_so_how_can_elements_with_negative_impedance_be_implemented_Are_they_passive_or_active

and its op-amp implementation (NIC)
https://www.researchgate.net/post/What_is_the_basic_idea_behind_the_negative_impedance_converter_How_is_it_implemented_How_does_it_operate_What_does_the_op-amp_do_in_this_circuit

Now it remains only to clarify what the negative differential resistance is. To help the discussion, here are my speculations about the amazing phenomenon.

If we increase the voltage across an ordinary ohmic resistor, the current flowing through it increases proportionally according to Ohm's law (Iout = Vin/R). Also, if we increase the current through the resistor, the voltage across it increases as well (Vout = Iin.R). Thus the voltage and the current change in the same directions. But there are mysterious two-terminal electronic components (negative differential resistors, shortly NDR), having just the opposite behavior in the middle part of their IV curves - the voltage across and the current through them change in opposite directions. Some of them - neon lamps, thyristors, have an S-shaped IV curve while other - tunnel, Gunn and lambda diode, have an N-shaped IV curve (see the attached picture).

Although the negative differential resistance seems to be a mystic phenomenon, it is actually based on an extremely simple, clear and intuitive trick - the powerful "dynamizing" idea that is brought here to the utmost degree. IMO a differential negative resistor is nothing more than a kind of "self-varying", dynamic resistor that changes extremely its instant (ohmic, chordal) resistance depending on the current passing through the resistor or on the voltage applied across it... the differential negative resistor is actually an "over-dynamic" resistor.

Negative differential resistors are dynamic but still positive resistors. They have different kinds of resistance in the three parts of their IV curves (located in the 1st or the 3th quadrant) - "positive" in the end parts and negative in the middle part. The three parts form the whole IV curve that, depending on the NDR behavior in the middle part, can be S- or N-shaped. When the input quantity (no matter current or voltage) increases, the S-shaped NDR decreases while the N-shaped NDR increases its instant resistance.

Each of the two NDR can be driven both by voltage and current. To operate in a linear mode, an S-shaped NDR has to be driven by current while an N-shaped NDR - by voltage (the attached picture); v.v., to operate in a bi-stable mode, an S-shaped NDR has to be driven by voltage while an N-shaped NDR - by current. So, in contrast to the widespread but misleading viewpoint, there are no particular current controlled (CCNR) and voltage controlled (VCNR) negative resistors - there are only S-shaped and N-shaped NDR, and each of them can be controlled both by a current and voltage.

In the middle negative resistance region, negative differential resistors behave as two-terminal active elements (such as transistors). They cannot be used independently; they need an additional power supply to be connected. Thus the combination of the negative differential resistor and the power supply can be considered as another kind of a true negative resistor (the other kind of a true negative resistor is a combination of a constant "positive" resistor and a varying voltage source - this is the case in a NIC). From another viewpoint, this combination can be thought as of an electrical source with negative internal resistance. It is a usual practice to think of a negative differential resistor as of a true negative resistor implicitly assuming the existence of a power supply...

As I have told in the question about the true negative impedance, I wasted a few years of my life to struggle with orthodox wikipedians inhabiting the electronics Wikipedia with the idea to tell the truth about the negative (differential) resistance in the respective Wikipedia article... but I could not... All my edits and imagine finally - the whole article about the negative differential resistance, were removed! Here is a short history of this "epic battle" (I was writing under the user names Circuit-fantasist and Circuit dreamer):
https://en.wikipedia.org/wiki/User:Circuit-fantasist/Negative_resistance#Some_history_in_retrospective,

and some my insights shared with wikipedians
https://en.wikibooks.org/wiki/Talk:Circuit_Idea/Negative_Differential_Resistance#How_to_create_negative_resistance

But I did not give up and after a year, I told the truth about the negative differential resistance in Wikibooks:
https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance
https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Resistance
Erik Lindberg · Technical University of Denmark

Hi Cyril,

concerning:
"BTW what does "general nonlinear resistor" mean ?"

The voltage V is an arbitrary function R of the current I i.e. we have an arbitrary curve in the IV-plane. This may include sources and problems with multiple solutions.

What are the best signal processing methods to determine differences between signals with different lengths?

I have some signals with different lengths (from 1 to 129 ) and I need to compare them and find their similarities and differences. Actually, I need to extract features for the signals regardless the origin of them. (I do not know the origin, I just have the samples). What methods can be applied to analyze signals with different lengths and find their differences?

Narasim Ramesh · Sri Jagadguru Chandrasekaranathaswamiji Institute of Technology

Try using DFT . This should help in identifying similar characteristics based on the components. The time signals of same lengths can also be obtained by inversion

Cheers

What's the meaning of the limitation of the temperature of the capacitors?

Usually, the datasheet of capacitors will give a limitation of temperature where the capacitors could apply, like -40℃~85℃.
I thought 85℃ meant ambient temperature in the past several years. But today someone I know who works in a capacitor company tells me that 85℃ means the core temperature, where core means the center of capacitor.

Then which one is right? Is it related to some standard?

Narasim Ramesh · Sri Jagadguru Chandrasekaranathaswamiji Institute of Technology

For design / test purposes the explanations of Pisupati Sadasiva Subramanyam

and Nebi Caka  are apt and eminently suitable. Perhaps if the Rseries and thermal

impedance from surface of capacitor(forced/ natural cooled and upright / horizontal) to

ambient is known along with current profile one can estimate the core temperature.

Cheers

Are electrical sources elements with "static negative impedance"? If so, is there any benefit from this concept?

The negative impedance concept is so attractive that some authors try to bring it on even the most basic electrical elements as voltage and current sources. See as an example the work of this Wikipedian (although it seems his own creation, it is assembled entirely by else's thoughts extracted from reputable sources):
https://en.wikipedia.org/wiki/User:Chetvorno/work6#Negative_static_or_.22absolute.22_resistance

Also, this viewpoint was presented by Simone Orcioni in the question below:
https://www.researchgate.net/post/Does_the_op-amp_in_all_the_inverting_circuits_with_negative_feedback_behave_as_a_negative_impedance_element_negative_resistor_capacitor_etc

As far as I understand, this "negative resistance viewpoint at voltage sources" is the following. A voltage source is connected to a load (a resistor)... so the voltage V (VG in he  Simone's figure) across them and the current I through them are the same... and therefore the ratio V/I (the resistance) for each element is the same (see the first attached picture below)... Thus the resistor has a resistance RL = V/I and the voltage source has a "negative resistance" RS = V/-I = -RL... so the sum of the two resistances (voltages, according to KVL) is zero... It sounds temptingly simple but...

In this arrangement, there is only one "main" voltage source and one resistor (the load)... and this is the possibly simplest electric circuit still from 19-th century - a source driving a load. But the popular belief is that "negative resistance" is a "supplemental" concept... It implies another (supplemental, "helping") voltage source (BH in the second attached picture)... and this is not an ordinary constant but "dynamic" voltage source whose voltage is proportional to the current flowing through it (a 2-terminal current-to voltage converter)... and so it will act as a negative resistor with resistance -Ri. This negative resistance compensates another positive resistance Ri (e.g., the source internal resistance or the line resistance) thus giving as a result zero total resistance between the main source VIN and the load RL... and this 4-component circuit is reduced to the Simone's initial 2-component circuit (source and load)... The sense of this "trick" is that the unwanted resistance Ri (the voltage drop across it) is neutralized by an equivalent voltage:

http://www.circuit-fantasia.com/circuit_stories/inventing_circuits/ser_nr_comp/ser_neg_res_comp.htm

If this supplemental voltage source was an ordinary constant voltage source, it would still compensate the voltage drop across Ri... but only for one value of the current; maybe because of that they name this kind of "negative resistance" with the name "static negative resistance". Really, it can compensate also the relatively steady voltage drop across a constant-voltage nonlinear resistor (diode, LED, Zener diode, etc)... but this is just another special case...

Note that, in contrast with an ordinary source, this exotic voltage source will not independently produce voltage if there is no input voltage VIN; it starts acting after the main (input) voltage source begins increasing its voltage from zero.

IMO the word "resistor"/"negative resistor" has the meaning of something that resists/"helps" the current flowing through it... so it implies some initial current produced by another (main, input) voltage source... Therefore, this main source is simply a source, not a negative resistor... and maybe this viewpoint is just a misconseption as many others in the field of negative impedance phenomena?

I would add here also the questions asked by Lutz Wangenheim: "Does it make sense to interpret this scenario as a connection of a positive and a negative resistance of the same value? More than that, are voltage and current directions of the voltage source in accordance with the DEFINIONS of a negative resistance? If this would be true, we could treat each voltage source in each circuit as a negative resistance, couldn´t we?"

Cyril Mechkov · Technical University of Sofia

Dear Lutz and other colleagues,

I spent a week in a small village in the center of the country, away from the city noise and without an internet... i.e., almost in the conditions in which Kirchoff formulated his famous laws nearly two centuries ago:) Temperatures were unusually high (almost 40 degrees) and during the hot afternoons I hid in a tightly closed room with a big fan and I wrote these lines on my laptop (only this gadget broke the illusion of the Kirchoff's time:)...

Lutz, I decided it is time to inform the scientific community about our idea to modify the Kirchhoff's laws that was born in the process of heated discussions. I suggest you do it in the form of an "imaginary article" that to write together as an open project... and then offer it in a proper magazine (at least, we can place it in our profiles as raw data)...

Such an open project can be a web page (module) in Wikibooks but the problem there is that every casual visitor can edit it. So I preferred to upload it in my Google cloud storage, where we can edit it together... and even it can be available to other RG members... Here is the link to the initial (uncompleted, raw) version that can be edited by anyone who wishes to do so:

I suggest you we continue to comment here, in our discussions, of what we can write in the article. This can serve as a good certificate of our personal contributions as well...

As regards the authorship, I think the idea is mainly the result of discussions between you and me here... but if someone else has a claim to authorship, we can include him/her. I think the order of writing the author names corresponds to their contributions at the moment... but we can change it dynamically...

After these organizational issues only remains for us to see if the idea is still true and if it is worth:) I suggest to do it in a separate question:

https://www.researchgate.net/post/Can_we_formulate_Kirchhoffs_laws_for_resistances_KRL_and_conductances_KGL_based_on_KVL_and_KCL

Regards, Cyril

Laboratory Equipment for NBTI measure in Logic Circuits?

I need to analyze experimentally the degradation due to NBTI of the delay of a digital circuit (e.g: a Ring Oscillator). Can anyone suggest which lab equipment I may need?

Harish kumar Selvaraj · KGiSL Institute of Technology

Hi,

I think a simple CRO or a DSO with DMM will serve your purpose.

You can measure the impact of NBTI at a lower accuracy by the following method.

1. Transistor parameter monitoring: This technique is based on monitoring the selected transistors to measure NBTI impact on the circuit. Monitor the transistor drain current, threshold voltage, and transconductance to quantify the impact. And monitor the transistor leakage current to characterize NBTI.
2. Circuit parameter monitoring: This technique is based on monitoring the circuit parameters to measure NBTI impact. Monitored the beat frequency of two ring oscillators one stressed and the other unstressed, to characterize the impact. Characterize NBTI in termsof the control voltage of the two delay locked loops.

What does a negative voltage in fuel cell v-i curve mean?

Recently I was analyzing various v-i curves of different types of fuel cell. While simulating a fuel cell stack I could figure out an v-i curve (whose .jpg file is attached) which is bit different from the conventional v-i curves of fuel cell. I find the voltage is going to negative value, but generally we do not find a v-i cuve of fuel cell whose voltage goes to negative, v-i cuve with positive voltages are generally seen in books, or research papers.

Can any one tell me whats is happening exactly in the fuel cell so that the voltage is shown negative?

Mingtian Fan · China Electric Power Research Institute

In fact, there exists no negative voltage in the physical power system. The reason is that the MATLAB didn't set limits for voltage calculation algorithm.

How can I control a governor to synchronize two diesel generators with the pll method?
I cant synchronize it with an external oscillator and must synchronize it with a line.
Christian E. Jacob · Max Planck Institute for Plasma Physics

For the speed control you can use a servo-controller. Normally the outputs of the servo-controller are two currents. You need a governor set-signal. This is your speciall development task!

Why does the current fault level reduce significantly when the microgrid changes from grid-connected to an islanded mode of operation?
I need the explanation in order to understand the key aspects of designing a protection system for a microgrid so that it becomes easy to design the same.
Barnali Motling · Somaiya Vidyavihar

Dear Mr. Mehdi ,

Thanks a lot for your response and explanation.

Warm wishes

What are your thoughts on renewable ocean energy, such as wave, wind and tidal energy?
For example, Marine Renewables off the coast of Ireland has the potential to produce over 70GW of energy, more than 14 times the country’s current energy demand. There are many such examples speaking about the viability of ocean energy. A floating windfarm off Coos Bay in Oregon was approved! Are there such attempts in your country, maybe realized projects?
John Fleming · University of Strathclyde

All large-scale methods of electricity generation and distribution have undesirable effects. Those who benefit from the electricity should compensate those who suffer. Given that modern societies are not possible without an electricity supply, compensation for the bad effects should be fair, adequate and routine, indeed guaranteed in the laws of the land concerned.

What do you think about the complement between lab courses and industrial needs for electrical engineering students?

Hello everybody. What is the most important tasks to do, as academics, in order to prepare the electrical engineering students to be involved in a fast way in the industry?

Albert Manfredi · The Boeing Company

I think that in a university setting, teaching theory is going to remain of primary importance. It is far more difficult to learn theory on the job, in industry, than it is to get practical knowledge on the job. I do think that lab courses are important, however university is not meant to be technical school. A university is supposed to produce individuals who can get beyond what is practice today, and for that, the graduate needs a broader perspective than what a lab course teaches. So, my point is, let's not over-emphasize the importance of making a good solder joint.

As to focusing on narrow subject matter, that's a two-edged sword. Most students have no idea what they will be working on after they graduate, so it's best to expose them to as many disciplines as possible. At the same time, the more knowledge is accrued over the centuries, the harder it will be to cram that in a four or five year curriculum.

By the way, I do not deny that industries these days seem to be looking for new hires that are well versed in certain very well defined areas. The "ideal" candidate seems to be the person with 5 years of experience in precisely the subject matter of that new job opening. I find that near-sighted and a good way of never hiring the best people. Hopefully the HR departments, and managers, will get past this self-defeating mindset.

We need universities to produce creative thinkers first and foremost.

Are there any good papers on the substitution method used in the design of oscillators?
I want to learn the basics of the substitution method. I guess it is used for optimizing oscillator designs. I've read the concept in Michal Odyniec's book on designing RF/MW oscillators. However I am still not clear. Hoping to gain some clarity here. Thanks!
Anuraag Misra · Variable Energy Cyclotron Centre

Poornashree, it will be a good idea to tell here what type of oscillator you are designing , as the line of attack changes depending on specs.

Can high power DC linear voltage regulators be made with IGBTs ?
High power DC linear power supplies are needed for application like testing of aircraft equipment, high stability power supplies etc. They are made using bipolar transistors or MOSFETs operating in linear mode. Can they be practically replaced by IGBTs operating in linear mode ?
Francesc Casanellas · ALP, S.C.

If you need a LINEAR regulator (I suppose to get very low noise) with high current and high voltage, I would use IGBTs as you suggest.  I do not see a better option. Only problem: your current control has to be very good.

To control any nonlinear system; what is the difference between fuzzy sliding mode controller and sliding mode fuzzy controller?

To design a controller for nonlinear and uncertain systems we have two choice: the first one is fuzzy sliding mode controller and the second one is sliding mode fuzzy controller. I'd like to know that which one is better and why?

Farzin Piltan · IRANIAN CENTER OF ADVANCED SCIENCE AND TECHNOLOGY

Dear Researchers;

I think:

Fuzzy sliding mode controller (FSMC) is a nonlinear controller based on sliding mode method when fuzzy logic methodology applied to sliding mode controller to reduce the high frequency oscillation (chattering) and compensate the dynamic model of uncertainty based on nonlinear dynamic model.

Sliding mode fuzzy controller (SMFC) is an artificial intelligence controller based on fuzzy logic methodology when, sliding mode controller is applied to fuzzy logic controller to reduce the fuzzy rules and refine the stability of close loop system in fuzzy logic controller.
However the SMFC has a good condition but the main drawback compared to FSMC is calculation the value of sliding surface slope coefficient pri-defined very carefully and FSMC is more suitable for implementation.

Regards