Science topic

# Electrical Power Engineering - Science topic

Electrical Power Engineering is an infrastructure of bulk electrical energy transfer.
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It is a network of 30 earth pits. 3 sets of10 pits.
I have disconnected all the 3 sets. However, when I check for the resistance between the network of first 10 and that of the second set, I get 45ohms. Should it not show in k or M ohms as they are not galvanically coupled. One thing is for sure that they are not shorted as the resistance is as high as 40+
If I disconnected one pit from the remaining 9 in the first set, I get around 250ohms with multimeter.
I am trying to decouple all the 3 sets from each other but to no avail.
is it due to the high conductive compound that has gone into these pits?
Meanwhile, I'll try to explore more on this
try to measure[1], if possible, the AC-resistances[2] (impedances, at 1kHz), also.
1. "8. Method for the Earth measurement of a large earthing system" https://www.kew-ltd.co.in/2019/05/02/a-guide-to-earthground-resistance-test/
2. "What is the resistance of Earth Pit?" https://www.quora.com/What-is-the-resistance-of-Earth-Pit
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Voltage collapse in power systems
Dear all fellows ,
I'm trying to understand the role of excitation current.
If the load in parallel grid increases then armature current increases which increases torque and reduces the grid frequency. But the increment in load current will increase stator magnetic field which further increase the load angle keeping excitation constant (If constant) . (Am i right so far??)
But as rpm decreases the voltage will decrease but the voltage is fixed by grid (I don't understand this i mean there is clear cut formula that voltage depends on flux which is constant and rpm which is now decreased so why does terminal voltage remain constant) .
How does this effects the VARs then? Does VARs will also remain same if excitation is constant.
I've observed that frequency varies continously between 49.5 to 50.5 and 51 hz but voltage remains at 128kv level. Tap changers remain at fix level.
Generator voltage remains at 11.5 kv (Ge generator) .
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Is it just in order to eliminate the circulating currents among DGs by maintaining    same voltage and angle ? Also how does it improve the stability of the system?
In essence, a virtual impedance is a way of altering the control of an inverter so that it appears as though an additional impedance was inserted between the inverter and the load in the physical circuit. In other words, the control designer is able to change the effective impedance between the inverter and the load.
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Which research area in Power Electronics will make for a good Master thesis in the field of Power Electronics? Would be obliged if someone can inform me about the ongoing scope of such research projects. I am searching for a good research proposal for my Master thesis in the domain of Power Electronics.
Would be obliged, for your help.
Regards
One of the main topics of the power electronics is the power flow control from the renewable electricity sources such as solar and wind to the grid where one has to maximize the power transfer and deliver pure waveforms to the grid. Such transfer needs global control to control also the power delivered to the grid.
Also ramping up the power is required.
Best wishes
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I am simulating a power converter circuit on Simulink platform. This also include a 400 V AC grid. I am not sure about a generic thumb rule to define the impedance of the cables for this 3ph 400V Grid system. Any suggestions?
As an alternative, you can measure the grid impedance for the 400 V AC system directly. Please check our below publications for in-circuit impedance measurement:
[1] Z. Zhao, "Measurement setup consideration and implementation for inductively coupled online impedance extraction," Ph.D. thesis, Nanyang Technological University, advised by Prof. Kye Yak See, Mar. 2021.
[2] Z. Zhao, K. Y. See, E. K. Chua, A. S. Narayanan, W. Chen, and A. Weerasinghe, "Time-variant in-circuit impedance monitoring based on the inductive coupling method," IEEE Transactions on Instrumentation and Measurement., vol. 68, no. 1, pp. 169-176, Jan. 2019.
[3] Z. Zhao, K. Y. See, W. Wang, E. K. Chua, A. Weerasinghe, Z. Yang, and W. Chen, "Voltage-dependent capacitance extraction of SiC power MOSFETs using inductively coupled in-circuit impedance measurement technique," IEEE Transactions on Instrumentation and Measurement, vol. 61, no. 4, pp. 1322-1328, Aug. 2019.
[4] Z. Zhao, A. Weerasinghe, Q. Sun, F. Fan, K. Y. See, "Improved calibration technique for two-probe setup to enhance its in-circuit impedance measurement accuracy," Measurement, 2021, vol. 185, Art no. 110007.
[5] A. Weerasinghe, Z. Zhao, N. Narampanawe, Z. Yang, T. Svimonishvili, K. Y. See, "Single-probe inductively coupled in-circuit impedance measurement," IEEE Transactions on Electromagnetic Compatibility, 2021, doi: 10.1109/TEMC.2021.3091761.
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Normally, for a forward fault, phase difference between voltage and current of relay (theta) lies between -90 and +90; and for a reverse fault, theta is outside of this range. Some works, however, use negative components of voltage and current of relay to identify fault direction. I want to know that what is the criterion for a forward/reverse fault in this condition? In my simulation studies, phase difference between negative components of voltage and current lies between -90 and +90 for a reverse fault.
The negative- and zero-sequence networks are passive, no "source" behind the relay. The fault (unbalance, in general) acts as a source that excites the V2 and I2 quantities at the relay location. So for a forward fault (the Thevenin source in front of the relay), V2 = -I2*Z2SYS_LOC, and for a reverse fault (the Thevenin source behind the relay) V2 = +I2*(Z2LINE+Z2SYS_REM). Similarly for the zero-sequence and incremental-quantity directional elements. More details in this primer (paper and presentation): Sequence Component Applications in Protective Relays - Advantages, Limitations, and Solutions
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When I study about inductors I found that inductors have a constant value and value of inductance depends upon the permeability of core. And when I see the hysteresis curve then found that permeability depends on magnetising current and initial state of core(if it has retained some magnetism earlier). So I think inductor is non-linear in pure sense but approximated to linear. And in capacitors also due to analogous nature we can predict that it also nonlinear and capacitance is also not fixed due to variable permittivity.
Dear Sarvesh Singh sir,
Ist part : Permittivity and permeability can be a complex quantity in different mediums if we go further into details. For example, in homogeneous medium, they are constant while for isotropic medium they are scalar constant.
2nd part : Capacitors and inductors can be linear or non-linear which depends upon many factors. Ex- using iron core will show a non-linear behaviour for inductor whereas using air-core will show linear behaviour for inductor. Linearity of these elements also depends upon various factors like medium, material used in the fabrication etc
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Hi,
I am working on tracing current unbalance in HV systems. All papers study unbalance based on simulations which may fail in practical conditions. I'd like to know whether there is any standard for CT/CVT accuracy class used for current/voltage unbalance measurement or not. I have read IEC60044-1 and IEC60044-5 for CT/CVT standards. There is also IEC 61000-4-30 which defines unbalance measurement classes and it is indicated that CT/CVT accuracy may affect measured current/voltage unbalance ratio in practice (which is obviously correct), but no numerical analysis is provided and here my problem arises. Let's say maximum accepted voltage unbalance in HV systems is 1%. A low-accuracy CVT (say 3% class) may cause a voltage unbalance of <1% be measured >1%. In other words a BALANCE system look UNBALANCE or vice versa. Is there any standard that provide unbalance limit + measurement instrument's accuracy class?
Something like:
If you are using a CVT of 3% accuracy class, maximum acceptable voltage unbalance is 2%.
If you are using a CVT of 1% accuracy class, maximum acceptable voltage unbalance is 1%.
(I know IEC61000-3-13 is another standard related to unbalance, but unfortunately I don't have access to it)
Regards
Please take a look at this paper
regards
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Respected Prof. Dr. XXXXXXX;
Omar H. Abdalla
Dear i have sent an email with my Cv and Cover letter to the provided email, but no reply.
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Is there a real dataset (meansurements) that recorded the daily values of load profiles (Residential, Commercial and Industrial Consumers)? I am trying to test an algoirthm in machine learning that will cluster the different loads automatically. But for that I need a dataset as input.
Commercial and Residential Hourly Load Profiles for all TMY3 Locations in the United States
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I have dataset which shows the length of power lines. I need to classify the lines based on the line length. Is there a rule to classify the High voltage (HV) and low voltage (LV) lines based on line length? For instance, can we say lines below 500m (meters) are considered as LV lines and lines above this length are HV lines?
You were about to hit the target but missed for just a little bit. Here is the answer to your question in brief.
Transmission lines are classified into two standards.
• Voltage Rating
• Length of Line
As per voltage rating, there are 5 types of transmission existing
1. Low Voltage (LV) < 1000V
2. Medium Voltage (MV) 1000V < V < 69kV
3. High Voltage (HV) < 138kV
4. Extra High Voltage (EHV) 345kV < V < 800kV
5. Ultra High Voltage (UHV) > 800kV
As per the length of the line, there are 3 types of transmission existing
1. Short Transmission Line < 50km
2. Medium Transmission Line 50km < L < 150km
3. Long Transmission Line > 150km
Once again these standards can vary in different countries. Hope that information will be helpful for you. Good Luck!
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This ques is used my research
New Topology Three Phase Multilevel Inverter for Grid-Connected Photovoltaic System
• May 2014 DOI: 10.1109/ISIE.2014.6864679
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.
For more details ,we have these articles:
1- Optimal distributed generation allocation in distribution systems for loss minimization
Authors Karar Mahmoud, Naoto Yorino, Abdella Ahmed
2- Advanced Pareto Front Non-Dominated Sorting Multi-Objective Particle Swarm Optimization for Optimal Placement and Sizing of Distributed Generation
DOI: 10.3390/en9120982
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Dear researchers,
I have the following questions:
1. I want to know how I can read a number of TABLES and PARAMETERS from excel?
2. How can I make GAMS show the zero values as "0" in the results? Obviously, the program drops them...
I know how to convert one table or parameter from GAMS to excel. When I use 'xls2gms' or 'gdxxrw', it is ok but just for one table, for example.
However, in my case study, there is a sheet that contains many tables, and I don't know how to convert them to the assigned table names in GAMS. The ide shows an error with this regard!
Data Exchange with Microsoft Excel
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What is fire? Causes? Prevention?
Causes
For a fire to start it needs a source of ignition, a source of fuel and a source of oxygen. For example, if a smoker falls asleep with a cigarette still lit, and sets fire to the sofa, the cigarette is the source of ignition, the material on the sofa is the source of fuel and the air is the source of oxygen.
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I use a piezoelectric sensor, a humidifier electronic circuit and a 32-volt power supply to generate high-frequency ultrasound waves. I use these waves to atomize the liquid.
the problem is that the viscosity of the liquid is high, so the generated ultrasonic waves cannot atomize the liquid well.
any idea for this problem?
for example, can i use two circuit with two supply power and connect their output to the sensor to higher the sensor power? or ...
welcome!
I think the problem is not only in the power of the ultrasound waves.
As the ultrasound generator invokes harmonic waves then
P= pm sin wt where p is the pressure, Pm is the peak value of the pressure w is the angular frequency.
Assume that the speed of the pressure waves is v,
Then the wavelength lambda= v/f,
The division of the material is the matter of lambda.
You have to decrease lambda to the about double the interatomic distance.
So you have to concentrate your effort to see t5he effect of decreasing lambda oo your liquid.
Best wishes
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I'd like to know the common FACT devices in distribution systems.
D-STATCOM,SSSC,,TCSC,IPFC,SVC and UPFC.
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I want to simulate nonlinear state space equations, I need it for stability analysis.
See these articles:
1-Nonlinear dynamic analysis of a single-machine infinite-bus power system
Article Nonlinear dynamic analysis of a single-machine infinite-bus ... 2- PSDAT: Power System Dynamic Analysis Toolbox
Code PSDAT: Power System Dynamic Analysis Toolbox
Best regards
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Hello,
I am comparing different techniques (Current Injection (Already calculated), Newton Raphson (Already Done), and Backward-Forward Sweep (facing problem)) for load flow analysis for three phase unbalanced system though Matlab.
From couple of weeks, I have tried to develop matlab code for Backward-Forward sweep but failed. It will be great help if I get code (even general/conventional method will be very helpful for me) for backward-forward sweep for three-phase (not single phase).
Looking forward for your help. Thanx.
Cheers,
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I need ETAP software. Can anyone please share the link? As I am new user of ETAP, I also need a user guide please.
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I am interested to simulate distribution networks with distributed generation utilizing custom controls. Simulink is quite versatile in control system design and is friendly for people preferring visual approach to programming. But I am not always satisfied with how it solves power flow for detailed network models.
Lets say that I am looking for more reliable power flow solvers, but with control system design versatility of Simulink (preferably with visual programming). Any suggestions?
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How to measure power factor in a single phase connection?
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I am designing a control for bi-directional LLC-SRC DC-DC converter. The converter charges a battery from the grid. But during reverse operation, i.e when the current flows from battery towards the grid, what may be the impacts of current on the resonant capacitor (Cs as attached)? Do I need to wait for the discharge of DC link capacitors (fast/slow anyhow) on both sides? I cannot see any abnormal change or fluctuations during simulations. For practical approach, I am not sure. Any suggestions?
Good question, follow
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I am currently designing a BMS for a 48 V Battery pack of an electric vehicle. One of the major challenges regarding the BMS is to equalize the voltages of the cells (as different cell have different ageing) of the battery pack. How can one address this issue??
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As we have seen that most powerful and expensive quadcopters being swept away by prevailing wind gusts and losing connection with the controller, and even that “fail-safe” GPS-enabled Return To Home feature will struggle and oftentimes fail when flying into a strong headwind.
How to make it reliable and robust for sever weather conditions?
First basic step is to define "strong wind" speed, and then compare that with the quadcopter's maximum speed. No Return To Home (RTH) feature can be effective as long as wind speed > quadcopter maximum speed so "speed" has to be first defense. Once quadcopter max speed is exceeded, it is just be a matter of time before the quadcopter is out of ground control range; options then are to land, and wait for input, (maybe not a great option in heavily wooded areas, or over water), or switch to an autonomous mode which will attempt return to base GPS location as long as power allows.
Next consideration would be turbulent response; in strong winds, particularly in urban areas, where wind gusting around buildings will make control response times critical.
Note also that GPS-enabled RTH features will struggle with tall obstacles, be they trees or high rise buildings, that block the (most direct) return path.
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I want to use multiple DSTATCOM in my project,thus it's price is very important to be minimum.This device is the same with single phase inverter, but it injects reactive current only to the connected node in parallel to the 1-phase load.could anyone please inform me./thanks/
Yes, if possible u can also contact to Semikcron, they will share you exact price list of STATCOM.
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Is it possible to estimate eletrical load based on statistics and geographic population?
I want to estimates load profiles of houses based on available statitics like total population, avergae energy consumption per year by that area, average persons livining per house, size of building etc.
Is there way a way to estimate load based on these statistics? some of the availble statistics are attached.
Now, unders the Corona situation, the load study will be different since the average estimation of consumed energy will be greater than usual, everybody is supposed to be at home, good luck @ Muhammad Ali
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I am trying to estimate load profile for different houses based on occupancy profiles, number of people, total rooms, and age factor. Is there a way to estimate energy consumption based on the data of these parameters? Any ideas would be highly appreciated.
All programs Calculating loads are guesswork calculations and not very accurate, I advise assuming the data if you could not get it, even electrical loads are predictive and not accurate so what you consume today may not be as much as you consume tomorrow, more importantly, the selection and development of optimization technology, available energy sources and modeling of electric power elements.
Best regards
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Resistances in transmission system are negligible, so 1.0pu voltage assumption holds. However, in distribution system, resistances are not negligible. Please provide information about some simple ACOPF relaxation method. Thanks.
In distrib. systems u cant neglect resistances of lines, so I think u should use full AC OPF not just the linearized DC OPF.
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Consider a sinusoidal supply at fundamental frequency as shown, with a series inductive reactance leading to a bus. Let a diode rectifier load be connected to the bus. The switch Sw for resistive load be open. In this condition, the diode rectifier draws fundamental current from the source and also sends back harmonic current to it. Thus, the voltage drop in series reactance is distorted by the harmonic and so bus voltage is also correspondingly distorted. Now if switch Sw is closed, the resistive load draws both fundamental current as well as harmonic current from the distorted bus voltage. Both current components will lead to power dissipation in resistance as bus voltage contains both the corresponding voltage components. The question is from where is the harmonic power supplied to the resistor ? The sinusoidal source by basic understanding, cannot deliver any power corresponding to harmonic currents as its voltage remains sinusoidal, even though its current contains harmonics.
Dear Sujit,
Now i will give a conceptual answer and after that i may return again to share in the analysis of the give circuit.
The conceptual answer is that there is no ideal voltage source. A real voltage source has a resistance and may be also and inductance because of the wiring.
The ideal source voltage will remain sinusoidal. But assume that you have a voltage source Vs with a source resistance Rs,
A current i is passing through it, then its terminal voltage will be
v= Vs- iRs.
If i is distorted then v will be distorted.
In order to prevent the distortion you must make
either Rs=0
or I is pure sinusoidal.
Best wishes
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As a part of Industry 4.0, IoT also enjoys a vital position in smart technologies. However, with respect to power electronics, I have read that privacy over the internet could be a concern. Does this technology benefit us in power electronics /power systems domain? Are there any applications available?
The Internet of Things (IoT) is a concept that refers to a digital interconnection of everyday objects with the Internet. It is, in short, the internet connection more with objects than with people. This fact. constitutes a radical change in the quality of life of people in society, offers a large number of new opportunities for access to data, specific services in education, security, healthcare and transportation, among other fields. Power electronics plays a fundamental role in this process. Give an example. Heating, Ventilation and Air Conditioning (HVAC) systems. The power electronics supports the drive and control hardware of these thermal machines. Allowing the intelligent control of these machines that are responsible for 40% to 60% of the energy consumption of a building. This strategy is a great opportunity to save energy.
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How to integrate the harmonic power flow with the power flow in MATPOWER?
Dear friend
Hi!
I think the below reference helps you to model harmonic power flow.
Baghzouz, Y. (1991). Effects of nonlinear loads on optimal capacitor placement in radial feeders. IEEE Transactions on Power Delivery, 6(1), 245-251.
best regards.
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Are there any standards regarding islanded micro grids applicable in terms of general operation, especially regarding AC/DC converters with battery, PV or other sources.
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How can I solve this PV modeling equation: I=Iph-Io*(exp((V+Rs*I)/Vt*n)-1)-((V+Rs*I)/Rp), knowing that all the parameters are known except I and V? I'm trying to develop a circuit PV model to simulate a real PV module from the datasheet parameters. Thank you
The i-v characteristic equation of the solar cell has an independent parameter which is V and a dependent parameters which is I. If the physical and technological parameters are known which are called the model parameters then this equation will be a single equation in two unknowns the I and V. So one has to assume V and calculate I. So, understanding this fact your problem will be straight forward. It is a matter of direct calculation of I given V.
As for the equivalent circuit parameters please follow the method given in our book chapter:
Best wishes
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The increase in the trend of distributed generation has led to the formation of community microgrids. What is the best possible solution to connect single-phase loads to a microgrid with 2 level voltage source converter?
I feel one possible solution to connect single-phase loads is to use a 3-phase 4 -wire transformer.
You can use the split DC link which includes two series capacitor in parallel with a large balancing resistor for each of them . This a simple way to provide a neutral point which its voltage clamped at half of the DC link voltage .
Special PWM generating schemes can be used for balancing of the capacitors voltages. But where the neutral current is large, it flows through the capacitors and, hence, bulky capacitors are needed to make the voltage ripple on the capacitors. Also the neutral point usually drifts and becomes unbalanced when it includes DC component. So different strategies for neutral point balancing are reported, usually using the Space Vector Pulse Width Modulation or MPC control.
A better way to provide a neutral line is to add an additional fourth leg, called a neutral leg, to the conventional three-leg converter. The neutral current can be controlled to flow through the inductor so that the neutral point is maintained at the mid-point of the DC link. This allows the phase legs and the neutral leg to be controlled independently, which means the three phases can be controlled independently as well.
Ref :
Control of Power Inverters in Renewable Energy and Smart Grid Integration https://ieeexplore.ieee.org/book/6381785
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For example, if I want to find the stochastic OPF of a system, shift factors can provide a way to find shifted power for different scenarios. Therefore, OPF for each scenario is not required but only for base case. This will reduce simulation time. Please share relevant code if possible. Thanks.
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Hello everyone,
I have three questions about connecting onshore wind farms to substations:
1) I know, that larger onshore wind farms are connected to higher voltage levels (110 kV or 132 kV). But which voltage level would I choose, if I only have one wind turbine? does a rule of thumb exist depending of the wind turbine / farms capacity (MW)? A reference to cite would also be nice.
2) I have a wind farm which is already connected to a substation. Another wind farm is newly built and is nearer to the first wind farm than to the substation. Is it also possible to connect the wind farms, instead of the connecting line to the substation?
3) Do you have references for costs to connect wind farms to substations for UK? For example costs per km.
Thank you very much!
Jann
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I need to design a 11Kv distribution line for a rural area. which software will be good for this purpose
Dear Sirs,
How to select a Diameter of Conductor(ACSR) For 11KV Line? (Which Parameters include to select Dia of Conductor) and also suggest me IS Codes to check.
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I am studying the effects of FACTS devices on power oscillations in a system.For this purpose I have used an IEEE 9 bus system and created a three phase fault on bus 5.The UPFC should provide damping to clear the fault and hence decrease the fault clearing time.But I am not getting the usual results. The load angle versus time curves are attached. Can someone help me to figure out where I am going wrong?
Dear friend
Mihalic, R., Zunko, P., & Povh, D. (1996). Improvement of transient stability using unified power flow controller. IEEE Transactions on Power Delivery, 11(1), 485-492.
Best regards.
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I have done a theoretical analysis to find out the rating power that need to be produced from PV panels depends on the datasheet given below at 7222W.
I have calculated the sizing design of PV arrays for 4 panels connected in series and 7 in parallel to get total at 28 panels at rate 120V and 60A that need to meet the demand.
Note Xsys=0.09 ohm at 25KA current fault level from IET datasheet.
the issue is how to implement this demand of power from the PV using matalb codes or simulink by demonstrates parallel and series connection of solar panels to get the rate at 120V and 60A?
the attached files shows schmatic of proposed system
Regards
Did you completed the series parallel connection in simulink?
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when temprature ar radiation change , value of series , shunt rsistance change also
How can we counter the effects of small variations in the resistance with temperature changes (throughout the day) in solar pv cell?
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Hi everyone,
It's known that the cutting process of electrical steel introduce additional iron loss. Research articles indicate that the increase of iron loss when steel is cut with CO2 laser is much higher than the case where the steel is cut by punching. I was wondering, if the trend is the same for Nd:YAG laser cutting ?
Bekka Nassim Yes It will lost less than tool cutting
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Kindly, provide some references for the same.
You can also check the IEC - 60076-5 which talks about the ability to withstand short circuit . in page 14 an 15 of this IEC standard, you can find the " Short-circuit apparent power of the system ", both for European and North American Networks. It's valid and you can apply it to your calculations.
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Through Simulink 'Powergui FFT Analysis Tool', we can directly obtain the plots of different harmonics in Bar or List display style. However, I am looking for ways to plot these harmonic contents with respect to time and to show their decaying nature during transformer energization (as stated in the literature).
Thanks
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I've simulated a simple three-phase four-wire distribution system and I've use a DSTATCOM for load compensation. Its control algorithm is based on the PQ theory. I have a problem in compensator block. When I run my simulation, a error appears. Can anybody ti help me?
Here,I've attached my simulation and PDF files,Please check it.
Kindly mention the error u r getting
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I want to inquire about any advantage or disadvantage of using boundary power over boundary bus angles when two areas coordinating
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I have a hard form of the book with me. I am looking to have a .pdf version of it. Please share any link where I can have it.
Thank you
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Suppose we have capacitors in the line towards the load end to compensate for lagging Kvar...At night time some of the load might be switched off leading to a leading power factor condition in the circuit....Can anyone tell me some ways to work out a circuit in which I can bring v and i in phase when the loads are suddenly switched off and prevent leading pf condition?This has to be at minimum cost...
Dibyajyoti Chowdhury please can you share the solution which finally worked for you.
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Here is the formula for 3L and LG fault :
I= Vf/(Z1) I=3Vf/(Z0+Z1+Z2)
By analyzing the formula, one can come to conclusion that LG fault is more severe (assuming Z0<Z1=Z2, which is the usual case). But are we forgetting the fact that in 3L fault, there is a major role played by sub-transient reactance (Zst) which is much smaller that Z1. So the formula gets modified to I=Vf/(Zst) for LLL fault (applicable for first 2 3 cycles). But I have no clue whether same phenomenon occurs in LG fault as well or not and I am similarly confused with this. Can anyone help?
Single phase to ground fault is the most sever fault at the terminals of a generator. However, if the generator is grounded through a resistor (impedance), the fault current would be limited. In this case, it is important to analyse and compare 3 phase and single phase fault. The best way is to use DIgSILENT or ETAP.
Regards, Arash
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Nominal power and frequency: 55 MVA, 50 Hz
Number of windings on left side: 1 (Nominal voltage: 230.94 kVA)
Number of windings on right side: 2 (Nominal voltages: 41.86 kVA, 20.25 kVA)
Hello Asghar,
If you are modellign an ideal transformer, you can set the turns on each winding equal to the voltage of the respective winding.
If the transformer is not ideal, you have to limit the transformer core flux to the maximum of the core material you are using. The following equation can be used to calculate the number of turns in the primary:
E(rms) = 4.44fNAB(peak)
Then use the secondary to primary voltage ratio times the primary turns to calculate the turns of each winding on the secondary.
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For my new design of Hydroelectric system that can be built and operates efficiently and reliably in oceans and seas.
If you have invented something of importance, you might try patenting it first, before sharing the ideas. Otherwise I would discuss with experienced professor or researcher who knows how to obtain grants, publish findings, etc., or other funding source might be energy companies. You assume also that you might be allowed to install a prototype in ocean, but likely need permission, permits, etc. for that, and how to move electricity to land for storage or transmission. Also assess how safe is system to marine life, people? How susceptible to storm damage? A sponsor/investor is going to want many of these questions answered first. If developed on University time as an employee or student, it may also have some rights to invention. You may need some legal advice. If University or another agency has a dedicated marine experiment station, that may be a good option for trial installation, monitor results, etc. A licensed engineer may need to review or certify plans for safety, consistency with laws and liability issues.
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Normally, multi area in power system means areas are at same voltage level. But my opinion is that TSO DSO coordination also come under umbrella of multi area. Please correct me if i am wrong.
Thanks for clarification Aamir. Your problem statement is clear, but there is still a point of ambiguity while taking the multi-area approach. The traditional multi-area systems involve weak coherency (loose coupling) due to large electrical distances. In contrast, the transmission and distribution systems are strongly coupled via substation transformers. Thus, due to a rather strong coherency, the transmission and distribution systems are taken as a single area.
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As we know that any MILP/MINLP problem is feasible only on some points in its search space. Consequently, it is not possible get its JACOBIAN as well as HESSIAN matrices, as I think. As a result, for MILP/MINLP problems it is not important to know its convexity. Further, as MILP/MINLP problems are having their feasible search space in form of a set of some discrete points so these problems are NON-CONVEX.
How can you justify my observations? Am I right? or Am I missing something very important?
With sincere regards,
M. N. Alam
Hi everyone. I want just to make some comments regarding this issue, hoping it is still relevant for those involved in the conversation and for those who will look for a reference in it. As noted above, the fact that at least one of the variables is constrained to have discrete values makes any Mixed-integer problem by definition non-convex. Usually the way to deal with these kind of non-convex problems is through enumeration, which requires us to explore all the different possible values of those discrete variables. Since the number of combinations of the possible discrete solutions grows exponentially (e.g. with n binary variables you have 2^n possible combinations) one needs to rely on tools to avoid exploring all these combinations. Among these tools, we can solve the continuous relaxation of the original problem (defining the discrete variables as continuous variables bounded by the original discrete bounds) which can inform us on bounds for the original problem. Each time we find a solution that satisfies the original integrality constraints, i.e. that all the variables originally discrete have a discrete value and satisfy all the constraints, we find a feasible solution to the original problem which also provides a primal bound (upper bound in case you are minimizing). Every other solution of the continuous relaxation, that is solving a problem in a larger feasible region compared to the original, provides a dual bound (lower bound if minimizing) to the original problem. Using these bounds we can reduce the search space for our enumeration algorithms resulting in the famous Branch and Bound methods.
Soon after developing these methods for Mixed Integer linear programs (which by definition have a convex continuous relaxation), it was identified that the actual boundary between Polynomial solvable and Non-polynomial solvable was not in the linear/nonlinear boundary but in the convex/non convex boundary; meaning that there are polynomial algorithms to solve nonlinear convex programs. This allowed that one could solve the convex MINLP problems using the same Branch and Bound techniques with each node being Polynomial solvable. Finally, other methods relying on the decomposition of the MINLP in MILP and NLP problems were developed. The decomposition of the original problem was done though the gradient based approximation of the nonlinear functions (outer approximation), which produces a supporting hyperplane, i.e. an inequality that won't cut off any part of the feasible region, if the constraints defined a convex feasible region.
So, to the original question, whether if it is necessary to test convexity of the MILP/MINLP problems we have:
• By definition the problem is nonconvex.
• If we used the convention of naming these problems convex based on continuous relaxation for MILP it is not necessary, they are convex in this definition, for MINLP it depends on which solver/algorithm are you using.
• In case you know it is convex, you can apply an algorithm which is guaranteed to return you the global optimal solution (e.g. Outer approximation). These algorithms are not even guaranteed to return a feasible solution in case you have a nonconvex MINLP, but are considerably efficient.
• There are algorithms available to return the global optimal solution of nonconvex MINLP problems. These rely on convexification of the nonconvex terms in your problem, and you end up paying a cost in terms of computational time for these kind of guarantees.
Together with some colleagues we have recently published a paper comparing solvers for convex MINLP. It is open access and you can find it here . Please let us know if you have any other question regarding this topic.
Cheers!
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What is the most important topic to work on now a days on electrical network? Energy storage system, distributed system (Microgrid) operation and control, or Demand response of an electrical grid ?
For energy storage -- name some modern storage system other than battery storage.
Demand response -- ways to predict the demand (probability).
Grid operation and control-- design strategy (appropriate circuit and challenges)
Currently, the major research trends in electrical power engineering include handling of issues related to instantaneous power and energy balance considering stochastic generation, power loss reduction in T&D subsystems, demand response and energy engagement, and energy efficiency. Under these big themes, you will find many numerous focused topics.
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What is the function of line traps other than communication?
If power line carrier communication is used for signal transmission through the power conductor itself then only wave trap is required to filter out the noises.
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High-penetration of renewable power generation throughout the network might increase transmission/distribution congestion. What are the effective tools in both transmission and distribution level for managing congestion due to renewable penetration?
Pena, I., Martinez-Anido, C. B., & Hodge, B. M. (2018). An extended IEEE 118-bus test system with high renewable penetration. IEEE Transactions on Power Systems, 33(1), 281-289.
Burchett, S. M., Chow, J., Kar, K., Zimmerman, R., Swider, M., Marwali, M., & Zhang, G. (2018, June). Investigation of Generator Ramp Rates in High Renewable Penetration Systems using an Academic New York Network Model. In 2018 IEEE International Conference on Probabilistic Methods Applied to Power Systems (PMAPS) (pp. 1-6). IEEE.
Schermeyer, H., Vergara, C., & Fichtner, W. (2018). Renewable energy curtailment: A case study on today's and tomorrow's congestion management. Energy Policy, 112, 427-436.
Zakeri, B., Price, J., Zeyringer, M., Keppo, I., Mathiesen, B. V., & Syri, S. (2018). The direct interconnection of the UK and Nordic power market–Impact on social welfare and renewable energy integration. Energy.
Thanks,
Sobhan
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The estimated angle (x_est) in linear(DC) State Estimation using WLS criteria is calucted as follows:
x_est= [ Inverse {Transpose (H) * W * H } *Transpose (H) * W ] * z
Here z= Matrix Real Power Injections into the buses
W = diagonal matrix
Question: How to extract   H matrixusing matpower
Hi
Can you help me for find H and Z matrix for case 118?
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I need some help to calculate a fault distance in a H.V transmission line. I used a simulink(Matlab) model with a programing code for a simple transmission line with 2 sources.
The result simulation gives me an error in fault distance value. I can send a code and the model. Please some helps.
Thank you for consideration.
There are lots of papers with simple and effective technique which elaborate the method to calculate the distance of fault with respect to relaying point.
Consider some of the technical papers
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We would like to buy a new Battery Test Station (Battery Cycler) for testing 150Ah LFP Batteries in Crate (0.1-2C). Apart from the Max Voltage and Current range of the test system, what else has to be considered while buying a test system?
It would be very helpful if anyone can suggest some good test systems suppliers for this test (>300A)?
Dear Raam Kasinathan
the following attachment will give good idea about
Battery Test System
Regards
Alkathy
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I'm working on "Proper Placement of DG(Renewable Resources) and Reliable Protection Scheme for Power System "
I need help in placement of Inductor in Power system to minimize the Fault Circuit current, without DG and with DG.
I have attached Simulink Model bellow.
I performed a similar study for a refinary you can find some useful information in the following paper.
Benefits assessment of fault current limiters in a refinery power plant: a case study
A Cali, S Conti, F Santonoceto, G Tina
Power System Technology, 2000. Proceedings. PowerCon 2000. International
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I want to do switching overvoltage simulation in power system. What are the recommended practices to do the job? Can we do it without any commercial software (e.g build own algorithm in Python)? Thank you in advance.
I recommend EMTP (ATP) software. This is very good software for studying power system transients.
Regards.
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Say we got a solar array which supply power to battery through a DCDC converter. We want to design two control loops for the converter.
One is the inner(fast) loop which regulates the converter output voltage or current. This loop can be analysis by the traditional converter small signal model.
Another one is outter(slow) loop which is regulate the converter input voltage or current  (solar array output voltage or current). How can we analysis the stability for this loop? Do we need to include the small signal module of solar array? If the voltage or current is regulated by some algorithms, how to model the algorithm?
Any tips would be very helpful, thank you
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F. Blaabjerg, ph.d. Professor (Full), Aalborg University, Aalborg · Department of Energy Technology.
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This parameter is used for recognition of islanded networks.
For islanding detection, sometimes RMS rate of change of voltage is used. We have used in one of our publications.
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Dear All,
I am currently working on thesis on Reduced switch count inverter for driving three phase BLDC motor. However I am not clear abut how to calculate the DC link capacitor values so that it works good with load(impedance).
I understand that there is a relationship between the Capacitor reactance (Xc) and the impedance(Xl) reactance that is feeding the DC capacitors mid point. Suppose if I know the impedance, rated speed, DC voltage How d I get the Capaciotrs value?
What abut the Capacitor value calculation when the DC link mid point in unbalanced?
I would be really thankful if anyone of you could guide me or help me through this.
Regards,
SM
Primarily , the amount of capacitance in the dc link should gives minimum voltage ripple (i.e >5%) to provide stiff voltage . then you should consider the worst operating point of the drive cycle (which is the speed that yields maximum current ripple) because the ripple contents affected by the motor speed.
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Dear All
Can you provide me with maximum allowable currents of branches in IEEE 33 bus distribution system?
Thank you
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OpenDSS is a wonderful package, but it is not suitable for simulating some special features of railway traction network, it would be fantastic to have something similar related to Railway power systems. What do you think?
I totally agree with you in that
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Assume two wind generators are connected in parallel to a bus and supply power to a load demand. The rated power of the first generator is 2 MW, and the rated power of the second generator is 2.5 MW.  You need to build the overall system model including the wind turbines, wind driven generators, and load demand. To maintain the power balance in the simulation, the load demand is the sum of the wind power outputs. Demonstrate the active power output curve with respect to the wind speed in the steady state. You can specify different wind speeds to get the curve.
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When we use less surface area of solar chimney with using a geothermal process - what is the efficency and what is effect of the project?
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Why do we use clock circuit when we are designing certain micro controller onto PCB? What it is usage?
What other circuits do we need in order to proceed?
Would you be able to give some advice when you are start from the beginning designing the whole PCB boards?
Oscillating Options
Every microcontroller needs a clock source. The CPU, the memory bus, the peripherals—clock signals are everywhere inside a microcontroller. They govern the speed at which the processor executes instructions, the baud rate of serial-communication signals, the amount of time needed to perform an analog-to-digital conversion, and so much more.
All of this clocking action goes back to the source of the clock signal, namely the oscillator. Therefore, you need to make sure that your oscillator can support whatever performance you expect from your microcontroller. At the same time, though, some oscillator options are more complex or expensive than others, so your choice of oscillator should also reflect the importance of reducing cost and complexity whenever possible.
There are quite a few ways to generate a clock signal for a microcontroller. The datasheet for your particular device should provide a good deal of information about what types of oscillators you can use and how to implement them in a way that is compatible with the device’s hardware. This article will focus on the advantages and disadvantages of various clock sources so that you can better choose among the oscillator options discussed in your microcontroller’s datasheet.
So let’s start with a list, followed by a discussion of each option:
• Internal
• Usually (as far as I know, always) a resistor–capacitor circuit
• Phase-locked loop for frequency multiplication
• External
• CMOS clock
• Crystal
• Ceramic resonator
• Resistor–capacitor
• Capacitor only
Internal Oscillators: The KIS Option
I’m an advocate of the Keep It Simple principle; consequently, I have a special appreciation for internal oscillators, and I encourage you to avail yourself of the internal oscillator whenever possible. No external components are required: You can safely assume that the frequency is well chosen since the oscillator was designed by the same people who designed the rest of the microcontroller. Also, the salient performance specs—e.g., initial accuracy, duty cycle, temperature dependency—are (hopefully) right there in the datasheet.
The dominant disadvantage with internal oscillators is the lack of precision and frequency stability. The baseline frequency depends on the values of the passive components that make up the oscillator circuit, and the tolerances for the values of these passive components are not particularly tight. Furthermore, capacitance and resistance are influenced by ambient temperature, so internal RC oscillators experience temperature “drift”—i.e., changes in temperature lead to changes in frequency.
In my experience, many applications can tolerate the shortcomings of an internal oscillator, especially when the frequency has been calibrated at the factory. With older microcontrollers, the internal oscillator might have tolerance as bad as ±20%. However, a newer device can give you ±1.5% (or better), which is accurate enough for RS-232 communication and even (in conjunction with clock-recovery circuitry) for USB.
Another way to expand the capabilities of an internal oscillator is manual “trimming”—if your microcontroller includes a trimming/calibration register, you can adjust the frequency by modifying the value in this register. This is a perfectly practical technique for low-quantity designs: Simply measure the clock frequency with an oscilloscope or frequency counter and then trim the oscillator accordingly.
A variation on the internal-oscillator theme is the phase-locked loop (PLL). A PLL allows a low-quality, high-speed internal oscillator to benefit from the stability and precision of an external oscillator. In general, a PLL doesn’t help you to avoid external components because it requires a reference clock that is usually derived from a crystal. An exception, though, is when you have a high-quality clock somewhere on the PCB but don’t want to use it for the microcontroller because it’s too slow—you could use a PLL to multiply this clock up to an acceptable frequency.
CMOS Clock
Another straightforward clocking option is the so-called “CMOS clock,” which falls into the for-lack-of-a-better-term category. “CMOS clock” is a vague (though convenient) way of referring to any clock signal driven by some other component on the board. The CMOS clock is a great option if your design already includes a clock signal with 1) a workable frequency and 2) electrical characteristics that are compatible with the microcontroller’s CMOS-clock-input circuitry. Often, though, this is not the case, so let’s look at two options for generating a CMOS clock.
First is the “crystal oscillator.” This is a good time to point out that a quartz crystal is not an oscillator; rather, a quartz crystal is the central component in a quartz-crystal oscillator circuit.
Crystal oscillators are handy devices that consist of a quartz crystal and the additional circuitry needed to generate a standard digital clock signal. Thus, you get the stability and precision of a crystal without worrying about load capacitance and the careful PCB layout needed to ensure robust operation with a standalone crystal.
The second option is a “silicon oscillator”. This term refers to oscillator ICs that are not based on quartz crystals or ceramic resonators. These devices are versatile and easy to use, and they can be quite accurate. For example, the LTC6930 series from Linear Tech requires only one bypass capacitor, and the vast majority of the parts are within .05% of the nominal frequency: Silicon oscillators are more reliable than crystals and ceramic resonators, especially in harsh environments subject to shock or vibration. But they’re also more expensive.
Quartz and Ceramic
When you need seriously high precision and stability without the additional cost of a crystal-based oscillator IC, opt for the standalone-crystal approach. Parts with tolerance below 20 parts per million (i.e., 0.002%) are readily available. The oscillator circuit shown above is partially integrated into microcontrollers that support the standalone-crystal configuration; you will need to provide the correct load capacitors. The total load capacitance (CLTOTAL) is specified in the crystal’s datasheet, and the load capacitors are chosen as follows:
CLTOTAL=CL1×CL2CL1+CL2+CPCLTOTAL=CL1×CL2CL1+CL2+CP
where CP represents whatever parasitic capacitance is present. This calculation is pretty simple in practice: Choose a reasonable value for CP (say, 5 pF), subtract this from CLTOTAL, then multiply by two. So if the datasheet gives a load capacitance of 18 pF, we have
CL1=CL2=(18 pF−5 pF)×2=26 pFCL1=CL2=(18 pF−5 pF)×2=26 pF
Ceramic resonators are less accurate than crystals; common tolerances are 1000 to 5000 parts per million. They may save you a few cents if you don’t need the accuracy of quartz, but in my mind, the main advantage is that you can get ceramic resonators with integrated load capacitors.
Last, and Least . . .
There aren’t many situations that call for an external resistor–capacitor or capacitor-only oscillator. If for some reason you are opposed to the external-oscillator options discussed thus far, choose a microcontroller with an internal oscillator and use that. If, however, you are determined to dig out a passive or two from your box of spare parts, refer to the microcontroller’s datasheet for guidance on how to connect and design the oscillator circuit. Here is an example of how to connect the components, taken from the datasheet for the C8051F12x–13x (PDF) microcontrollers from Silicon Labs:
And you can refer to page 190 (PDF) of this same datasheet for an example of information on choosing component values.
I hope you now know enough to make an informed, confident decision next time you need to choose an oscillator for your microcontroller. Here are my recommendations in a nutshell:
• Internal oscillator whenever possible
• Silicon oscillator if the accuracy is adequate and the cost is acceptable—otherwise, quartz crystal
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Does magnetic field can heat the human body?
According to the International Commission on Non-Ionizing Radiation protection (ICNIRP), there is a maximum allowable magnetic field exposure to our body. I don't understand why magnetic field can be harmful to our body. I understand that electric field can heat our body by ionic polarization and dipole rotation of an atom or molecules. Whereas, magnetic field can only heat magnetic materials.
Most organs have almost the same relative permeability value as that of the free space (Ping-Ping Ding et al, IEEE Transactions on Magnetics, 2014; J. Malmivuo and R. Plonsey, Bioelectromagnetism, 1995). One factor influence the magnetic filed is the magnetic volume susceptibility of the tissue, but it is often very small although non-zero (Schenck JF, Progress in biophysics and molecular biology, 2005). Some non-zero susceptibility tissues have the thermal effect in alternative field. It also depends on the frequency of the field.
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Hello,
I have a question on PWM Technique for Power Electronics Inverter.
For 3-level inverter and sine PWM, modulation index is evaluated by
m=(V(line-lineRMS)/sqrt(3))*sqrt(2))/(Vdc/2)
Now, when I change the technique to Third Harmonic Injection PWM (THIPWM), the DC bus utilization increased by 15.5% which is evident.
Can anyone tell, how the equation to find modulation index will change in THIPWM? How one can calculate analytically the modulation index in THIPWM technique?
as a simple logic, for THIPWM, I reduce modulation index by 15.5% of value which I obtained for SPWM. I am not sure is it the engineering way or not.
Regards
Aalok
Try to study chapter 3 from the following book for the best knowledge in PWM techniques:
HIGH PERFORMANCE CONTROL OF AC DRIVES WITH MATLAB/SIMULINK MODELS
Prof. Haitham Abu-Rub, Texas A&M University at Qatar, Qatar
Prof. Atif Iqbal, Qatar University, Qatar and Aligarh Muslim University, India
Prof. Jaroslaw Guzinski, Gdansk University of Technology, Poland
attached is the THI derivation
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Can anyone help me in finding the optimal cost function in model predictive control of machines. How are the 6 voltage vectors calculated from the 2 level vsi and used in finding the optimal cost function?
I am trying to implement Model predictive torque control of pmsm, but not able to implement it successfully. can anyone help me out with the matlab code for the torque control part.
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