Grid Integration - Science topic

Of course. I hope it can help you https://www.comsol.com/model/vanadium-redox-flow-battery-14153

For LVRT you could have a look at the European RfG https://www.entsoe.eu/network_codes/rfg/

Unfortunately the HVRT requierments are not yet reflected in this document.

For HVRT you could use the German or Italian HV or MV grid code. For Germany you could find it here https://www.vde.com/en/fnn/topics/technical-connection-rules/tar-for-high-voltage

But it's not free.

Markus Pöller Thank you Markus. Current loops are there to limit current through the converter. is there any role played by this current loop in synchronizing the DSTATCOM at PCC?

Surajit Chattopadhyay A standard topology would be based on the physical difference of technical properties, which is my informed guess only.

For immediate infrastructure creation, all Fuel filling stations should also have EV charging stations.

Dear Sanchit Saran Agarwal

These investigations can provide you with a very comprehensive overview.

Savings (Dollar) = [ Export Energy * ExportTariff ] + [ ImportTariff * (alternating current Load - Grid Import Energy) ]

Basic savings (Dollar) = ImportTariff * (alternating current Load - Grid Import Energy) + [ Export Energy * ExportTariff - System payment ]

! you can consider one parameter such as Z as any payment or extra cost of systems.

Dear Kah Yung Yap ,

Please see my road map for the transformation from conventional to PV generation in the paper at the link:

Best wishes

Hi Mohammad Ashhar ,

Maybe you would like to take a look at the following paper:

Codes to reproduce results are available and robust stable PI controllers were successfully tuned.

Best

Yes, it is possible. All starts with what you want to control. For the best of my knowledge, in dq-frame we may want to control:

1. Fundamental component. In this case we just need a PI controller. The dq-frame rotates at the fundamental frequency.

2. Harmonic components. We have some options here.

(a) We can use PR tuned at 6th in order to compensate 5th and 7th. The dq-frame rotates at the fundamental frequency.

(b) We can tune PR at 5th and 7th. We need to have dq-frames rotating not at the fundamental frequency, but at -5th and +7th frequencies.

(c) we can use PR tuned at 5th and 7th and make the dq-frame rotates at -6th and +6th frequencies.

3. Oscillation compensation. There is also an option to compensate double-frequency oscillation that arises in dq-frame due to unbalanced grid voltage conditions. In this case, a notch filter is used, which similar to the resonant part of the PR controller. The notch filter is tuned at 2sd harmonic.

One good book that covers these issues is the Grid Converters for Photovoltaic and Wind Power Systems by Remus Teodorescu, Marco Liserre and Pedro Rodriguez.

Yes, it is possible to do, but you need to clearly understand dq algebra and trigonometry. For a given initial torque and flux in the machine, you back-calculate what would be the dq set points, by assuming then you find the initial values for sine and cosine, get the trigonometric identity to calculate the initial possible values for the angle. It is algebra + physics + electrical engineering, plus really know what you are doing.

Please take a look at these attached sites

Good luck

https://www.researchgate.net/publication/334817993_Optimized_Placement_of_Onshore_Wind_Farms_Considering_Topography

Hi Nathalie,

working through pages 10 to 12 of the following paper seems to provide the answer to the question why VPE doesn't have a switching frequency component during bipolar switching:

I still did not complete the reading myself but by providing the link I intend to give you the chance to overtake my slow reading. ;-)

Hope this helps.

OK. The subject belongs to the measurement based electromechanical equivalents. You will find sufficient literature including those (articles, conferences papers, and book chapters) authored by me and available within my RG profile.

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

Unlike conventional generators (i.e. large thermal, and hydro), the dynamic properties of solar-PV (and wind as well as most of the new power generation technologies) are significantly different due to the characteristics of their components, electronic interface with the grid, inertia, operation mode ... etc. The following papers focus on the maximum penetration level (MPL) of solar-PV generators hosted by a grid. The small-signal stability, and FRT requirements are considered as constraints in the determination of the MPL. In addition, the impacts various modes of operation on the MPL are considered.

Mathematically, the commonly used PR controller is not equivalent to PI controller. It can be deduced using the theory presented in the appendix of [1] that the controller in stationary frame shown in the attached figure is equivalent to a PI controller in synchronous frame.

[1] D. N. Zmood; D. G. Holmes. "Stationary frame current regulation of PWM inverters with zero steady-state error," IEEE Transactions on Power Electronics, 2003, 18(3): 814 - 822.

You can find in the attached figure that there exist coupling terms between the alpha axis-controller and the beta-axis controller. The commonly used PR controller in stationary frame does't include such coupling terms. The coupling terms come from the controller itself, not from the plant. If completely decoupled controller is required, the coupling terms generated by the plant model (e.g. the typical R-L model) should also be included.

I have done some test in matlab/simulink some time ago that such a controller performs exactly the same with the PI controller in stationary frame, if the parameters Kp and Ki have the same values.

However, in practice, the performance difference between the commonly used PR controller and PI controller may not be so obvious.

In addition, I would like to recommend the an advanced resonant controller, i.e. the vector-proportional-integral (VPI) controller. Its expression is s(Kps+Ki)/(s^2+w^2). Its numerator could be used to cancel the pole of the R-L plant. VPI controller could eliminate undesired peaks in the bode plot. According to my experience, it performs really better than the common PR controller. More information about the VPI controller could be found in [2] and other literature.

[2] Alejandro G. Yepes; Francisco D. Freijedo; Jesús Doval-Gandoy; Óscar López; Jano Malvar; Pablo Fernandez-Comesaña. " Effects of Discretization Methods on the Performance of ResonantControllers," IEEE Transactions on Power Electronics, 2010, 25(7): 1692 - 1712.

Hello Dear, Read this

No, it is not essentially required. In addition, transmitting power over large distances may cause many operational problems. You may read the following

A more practical solution that also can contribute in reducing the adverse impacts of the intense variability of wind power is the conversion of wind power to hydrogen, then transferring it to the design locations via pipelines. The hydrogen may be used in fueling thermal loads, or may be converted to electricity in either an electrochemical process, or a thermal process. You may read

Chapter 1 to 3 in

and

Sanjoy Roy

What you propose is what is typically done nowadays, and for simple systems it works, skilled people do it even without simulation.

But if 5 parameters, P, I, D, low pass in D and saturation have to be chosen, there is a big chance that trial and error does not converge to the right solution. If there are resonances in filters or a DC-link with small film capacitors that add to the problem, the chances to find a solution by trial and error get very low. In practice also noise, disturbances and non-linearities can be present.

A typical non-linearity is the saturation of a controller (wind-up) but also that a control jumps from 95% duty to 100% duty ratio.

The Nyquist (or Bode) is an independent way to know if one is far away or not from what could be obtained.

My experience is that even a lot of systems get unstable at half of the switching frequency rather than the resonance frequencies.

A typical problem is that Matlab implements PWM without delay, which is true for a pure analog PWM. Most of people use that model for a digital system where there is definitely a delay between sampling and PWM compare levels.

In drives, the wind-up is eliminated by resetting the speed integrator when the torque is limiting during acceleration. If this is not done a lot of error is cumulated and will result in a big overshoot in speed.

Wind-up is one aspect, but there are many reasons why simulations do not correspond to the reality.

In theory the practice is equal to the theory, however, in practice it is not.

Alex

You should should measure the grid voltage (point of common coupling) using voltage sensors. Then, you should design a phase locked loop (PLL) to obtain the grid voltage angle.Using this angle you can apply the voltage oriented control and achieve the synchronization with the grid.

Hi Sara

Sorry for the delay in getting back to you. The last couple of weeks have been somewhat fraught.

Anyway, my interest lies in all aspects of cloud, whatever the flavour. My initial focus was on key management issues, followed by technical vulnerabilities and forensic issues, which can be problematic. I have tagged IoT into the mix along the way, and will then move on to the the Threat Environment itself. By tackling the problem from different angles, my hope is that a better all round solution can be found. And there remain other issues yet to be properly addressed. This might take some time. Often, companies do not exactly help themselves as much as they could. It will be some time before all the holes can be properly identified, and properly mitigated.

Regards

Bob

Yes, SURFER: you could ask to MM and HP.

maybe i can help you but need more explanation what you want exactly!

I would not recommend dq control on single-phase converters. You will loose "information" during transients. You may find relevant information and references on this paper:

NREL has archived historical PV and wind output. Out of them, you can create your own shape files. If you have trouble getting those data, send an email to me; Jeremy.Lin@pjm.com

Best,

Jeremy

Hello Mr. Joshi,

the first question you asked. I would answer with yes.

The second question is more complex. Connecting decentralized systems as microgrid being able to operate in grid connected and in island mode is possible but expensive. Therefore you will have a higher security of supply. It depends on what customers want.

Regards

Grid failure can occur due to a variety of causes such as: continued over-stressing, low frequency operation, increased load demand, peaking characteristics of the demand, ineffective load control, reduced level of security due to opening of interstate lines and violation of grid discipline. Separating healthy part in the system during fault at pre-determined points is called as islanding. To ensure supply of power, in a complex system, intentional islanding becomes necessary to save healthy part to recover from the blackout.

Thanks for your valuable answers

Thanks for your valuable answers

There are indeed many possibilities. However, the question is not what it should be but what you pay for.   In low voltage, if you reduce the rms in your own conductors you will need less power. But while using a PFC, you may introduce may be 3% loss and pay for it, it is probably more than the losses in your wires.

In industrial cases one pays for real power and reactive power, in the way the meters measure it, so by 15 minutes averaged.

In fact if you inject harmonic power into the grid, it reduces your energy bill, if you absorb harmonic power you pay for it, it is a shame...

I discussed the problem of harmonics in that paper:

In fact one rather should pay for the fundamental power, not for the total power you receive....

Also the power factor gets a strange definition when you look at how the electricity is tariffed...

Actually there are two types of efficiiency calculated at PV grid connected system, the first one depend on the PV module efficiency, which range between 10 to 20 % for the best conditions. The second one depend on the converter and inverter used in the grid system, which arrange between 90 to 98 for both of them.

you can control the reactive power injected from PV in the control loops of the voltage source converter.

Solar generator does not produce at night but it does not consume any energy. So if you neglect its depreciation, then at night it makes zero profit.

Since demand and supply should be balanced in any point in time, normally PV devices are embedded in network and production should be balanced with other sources (like hydro and thermal).

In liberalized energy markets there is hourly price that is calculated to balance demand and supply. Then the revenue of PV system should be the sum of its output in certain hour multiplied by the price during this hour. However, most of PV owners enjoy feed-in tariff (fixed price to sell to network) and this is a kind of subsidy. Without it PV system working in market conditions would be even less profitable.

Many thanks to all for your input and suggestions.

All the above comments are relevant. Just to add more, before you add any generator to the system, you need to check the capacity of the lines, thermal limit, short circuit capacity and for control purposes, the damping limit is another important criteria. Another important aspect is that of protection. You cannot just connect a remote plant to your system without properly protecting your generator through relay protection and circuit breakers.  

Dear Tej,

We also faced same problem of even order harmonics.

they are mainly introduced because of the offsets in the sensor.

make sure that all the offsets given by the current sensors are removed properly.

you can try this small procedure

1. keep power reference to zero.

2. connect to grid.

3. check the current on the output of the inverter

 if it is not near to zero or having some offset then problem is surely because of sensor

Dear Akhilesh,

I recommend you study the following manuscripts. They may be helpful for your research especially the MATLAB codes and Simulink schematics.

Regards,

Morteza

Dear Umid,

There was a European project, Meta-PV, that looked into the possibility of injecting reactive power for voltage control purposes. The outcome was that the proposed solution was not effective due to the high R/X value of low voltage cables. 

We are currently coordinating an FP7-project, INCREASE (www.project-increase.eu) where we are developing control strategies to use active power to do voltage control. The results already look promising. I will be presenting our project on the 2nd public workshop of the iGreengrid project in Paris this Thursday.

Best regards,

Bart 

Hi,

I'm not sure I fully understood what you're trying to do but the following code does the steps you've requested. You may however adapt some of them for your intended purpose. The code 1) creates a 512*512 array, 2) selects a bit of it, 3) rescales it to have more array elements, 4) Passes the gaussian filter over it, 5) and finally views all results (with matplotlib).

from __future__ import division

import numpy as np

import scipy.ndimage as im

import matplotlib.pyplot as plt

# 1) CREATING SOME TEST DATA

X = np.linspace(-5, 5,512)

Y = np.linspace(-5, 5,512)

X, Y = np.meshgrid(X, Y)

R = np.sqrt(X**2 + Y**2)

Z = np.sin(R)

# 2) SELECTING A BIT OF MY DATA

x0,x1 = 200,400 # X COORDINATES OF PARCEL

y0,y1 = 400,512 # Y COORDINATES OF PARCEL

Z2 = Z[x0:x1,y0:y1].copy() # CREATING TE PARCEL FROM COORDINATES

# 3) RESCALING THE BIT OF DATA

nx = int(1/((x1-x0)/512)) # APROX. NUMBER OF REPEATABLES FOR X

ny = int(1/((y1-y0)/512)) # APROX. NUMBER OF REPEATABLES FOR Y

Z3 = Z2.repeat(nx,axis=1).repeat(ny,axis=0) # BUILDING A RESCALE FOR Z2

# 4) PASSING A GAUSSIAN FILTER OVER IT.

Z4 = im.filters.gaussian_filter(Z3,3) # SIGMA 3 (PUT WHATEVER YOU WANT)

# VIEW ALL RESULTS

plt.imshow(Z.T,origin='lower',interpolation='nearest')

plt.title('Original')

plt.show()

plt.imshow(Z2.T,origin='lower',interpolation='nearest')

plt.title('Parcel')

plt.show()

plt.imshow(Z3.T,origin='lower',interpolation='nearest')

plt.title('Rescaled parcel')

plt.show()

plt.imshow(Z4.T,origin='lower',interpolation='nearest')

plt.title('Gaussian convoluted rescaled parcel')

plt.show()

One of the important features of the smart grid is the integration of renewable energy sources (such as wind and solar). Each micro-grid provides electricity to the customers as the combination of renewable and non-renewable energy sources. Therefore, the micro-grids first use the renewable energy produced by itself, and then, take remaining required energy from the main grid. Consequently, if there is any problem with the main grid, still, the micro-grids can provide electricity to the customers, and thus, supports the distributed architecture of the smart grid instead of the centralized one. Additionally, with the availability of renewable energy sources, micro-grids can provide electricity in a cost-effective and reliable manner.

There are several existing works related to the renewable energy and smart grid. Some of them address the following issues:

1. Dealing with the intermittent behavior of the renewable energy sources, while integrating it with the smart grid.

2. Impact of self-generated energy sources in the smart grid - load shifting, minimization of energy cost, providing uninterrupted energy service etc.

I would suggest to go through some papers related to integrating renewable energy sources in smart grid published in IEEE Trans. on Smart Grid.

You can also refer to the book entitled "Design of Smart Power Grid Renewable Energy Systems", Wiley Publication, 2011

See the TWENTIES project. It describes most of the issues, along with some exciting new solutions

This paper may be helpful

Check out thee links for details about a large grid reliability and stability analysis:

Generally the challenges will be in producing the output power with high quality and reliability to be synchronized with the local grid connection. Harmonics issue generated from inverters sometime need an extra equipments before connecting to grid. Power lossses during transmission before busbar connection point however not an issue due to infinite busbar will absorb the differences hence from commercial point of view, the local grid utility company somehow is absorbing the losses especially from solar side during night.

OpenStack is one of the best available option for now....as it open source and freeware we can do all the type of R&D upon it. Its implementation is little bit hard but we can try to understand it .. here is the refrence link ...http://www.openstack.org/

Globus toolkit is widely used Grid middleware for implementing Grid computing concepts. You should visit http://www.globus.org/

Could you please clarify, whether you want to know about instabilities in smart grids that occurs due to microgrids or instabilities in microgrids??? Although MGs are having lots of advantages, the higher penetration of MGs in a power grids can invite lots of instability issues...like voltage and frequency instabilities, low frequency power oscillations...etc. There is no well developed operational code for MGs. Independent control of MGs willtake the powergrids to instability, if MG penetration is more. In case of distributed generations (DGs), it can support grid stability with proper synchronous control.