Do you think that with increasing the penetration level of renewable energy power plants, synchronous generators can be removed from the power system? Is the system inertia not lost?
Hi, Mahdi Saadatmand
As the penetration of renewable energy sources (solar energy and wind energy) increases, the amount of conventional synchronous generator (SG) powered by coal, oil and gas will be phased out. The static converter of solar and wind power system doesn't exhibit any rotational inertia/ rotating mass, unlike a SG. Hence, a virtual inertia-based converter (e.g. virtual synchronous machine (VSM), virtual synchronous generator (VSG) and synchronverter) is invented to emulate the dynamic behaviour of a SG.
By synthesizing virtual inertia, it enables the droop controls by controlling the converter via PWM. Hence, for frequency droop control, whenever there is frequency (f) drop, the converter will inject active power (P) to balance the power generation and consumption, or vice versa. For voltage droop control, whenever there is a voltage drop, the converter will inject reactive power (Q) or vice versa.
By doing this, the power grid will view the renewable energy sources as a conventional SG and the grid frequency and voltage will not be deteriorated even under the intermittency of solar/ wind, overloading fault or voltage sag. You may have a look on the research papers on this topic:
[1] https://www.researchgate.net/publication/340768747
[2] https://www.researchgate.net/publication/334828362
[3] https://www.researchgate.net/publication/339922363
[4] https://www.researchgate.net/publication/339857994
[5] https://www.researchgate.net/publication/337776242
Hope these information helps!
Dear Saadatmand
The main power generation sources, i.e. large power plants are not expected to be removed forever. The renewable resources will not be enough for supporting the customers with high reliability as provided by the strong current power plants. The large units are supposed to exist in power systems (may be feed by new fuels). Also, some renewables can exist with large power production capacity (for example, the hydro units) to add larger inertia to the power grid. On the other hand, the control loops of power converters can provide considerable virtual inertia.Thus, the power system inertia won't be removed at all.maybe
The whole modern electricity net is based on alternative current and has its origin in the works of Nikola Tesla toward end of 19th century. If you take the synchronous generators out you come to the DC supply which cannot be send over big distances. More than that DC generators and motors have collectors which make them wear sensitive.
The advantage of synchronous current are multiple and it is not the place to make the list.
Interesting is but the reason of your question : why take them out?
Dear Nick Hamburger
Thank you.
This is a question to start the discussion.
Can renewable energy power plants completely replace synchronous generators? In other words, can a power system produce electrical energy only through renewable energy power plants without the need for the synchronous generators?
The inertia cann't be lost as we progress and proceed towards zero - carbon power generation. If zero carbon energy by renewables must be accomplished then power providers must rethink diesel generators and begin retrofit schemes that could make them run cleaner and or reduced carbon content
We can look at it as a theoretical question. Practically I am not able to imagine whether we will at all go ahead completely to renewable energy source like Solar. I agree with other experts with reference to inertia.
Many researchers assume that the systems that have 70% renewable generation are fully renewable systems. Synchronous generators are very important for power system flexibility and for the inertia of power systems. Many recent researches discuss the virtual inertia in power systems with fully renewable systems.
Well the issue of inertia has cropped up again, in the context of more static generation and then dc gradually increasing and leaving reduced ac hitherto continuing since the days of Tesla as an alternative to Edison's dc. Like any other system to match the demand we have supply and carrier or transporter (of electricity) in between. In our case it is wire-based circuits. Necessarily the latter may have to be switched on or off when supply to demand is to be maintained or not required. Besides that, it may be on account of protecting the system against violation of limit of variables, like, excessive current (due to fault), excessive voltage (for open-circuited or lightly loaded high voltage line). So that the system doesn't attain such excess value, obviously there are ways and means. But taking circuit off means making the system structurally weak. Issue, therefore, comes, in whatever form it may be on stability of the system. In an all ac system or a hybrid system (of ac and dc) due to mis-match of supply and demand by approaching gradually, even if momentary it is inertia that slows down the change to adjust to the new point of operation. If it is not there at all (in case of all dc system), or low in case of hybrid system with mostly renewable (predominantly solar-based generation), power electronic based system has to play a great role in terms of adequate delay instead of making it fast-acting effectively to create something like virtual inertia. Further as it is known in the usual ac system inertia plays a significant role in keeping the system synchronized through slowing down the effect of change, damping of system (something like effect of resistance) helps in early settling to reach changed point of operation. In all dc system the latter would be more dominant in fact in comparison to inertia, whether to limit variable or transients to die down.
I recommend this article:
Bevrani, H. & Raisch, Jӧrg. (2017). On Virtual inertia Application in Power Grid Frequency Control. Energy Procedia. 141. 681-688. 10.1016/j.egypro.2017.11.093.
Article On Virtual inertia Application in Power Grid Frequency Control
The loss of synchronous machine cases a decrease of the inertia of the power system and there is a directly impact in the rate of change of frequency of system ROCOF. If the system is isolated with max RES penetration the stability of the power system can be affected seriously!???
Choophong Lairat, Adnene Haj Hamida
It seems that, with reduced the penetration level of synchronous generators, the application of virtual inertia is necessary.
Yes !!! But
with a high penetration of renewable energies in weakly interconnected or isolated systems, the knowledge of the minimum must-run units to ensure the frequency stability and voltage stability too. The virtual inertia is a solution to "reduce" the frequency stability constraints and minimize the ROCOF of the system. however, you must pay attention to the voltage stability too.
Hi, Mahdi Saadatmand
As the penetration of renewable energy sources (solar energy and wind energy) increases, the amount of conventional synchronous generator (SG) powered by coal, oil and gas will be phased out. The static converter of solar and wind power system doesn't exhibit any rotational inertia/ rotating mass, unlike a SG. Hence, a virtual inertia-based converter (e.g. virtual synchronous machine (VSM), virtual synchronous generator (VSG) and synchronverter) is invented to emulate the dynamic behaviour of a SG.
By synthesizing virtual inertia, it enables the droop controls by controlling the converter via PWM. Hence, for frequency droop control, whenever there is frequency (f) drop, the converter will inject active power (P) to balance the power generation and consumption, or vice versa. For voltage droop control, whenever there is a voltage drop, the converter will inject reactive power (Q) or vice versa.
By doing this, the power grid will view the renewable energy sources as a conventional SG and the grid frequency and voltage will not be deteriorated even under the intermittency of solar/ wind, overloading fault or voltage sag. You may have a look on the research papers on this topic:
[1] https://www.researchgate.net/publication/340768747
[2] https://www.researchgate.net/publication/334828362
[3] https://www.researchgate.net/publication/339922363
[4] https://www.researchgate.net/publication/339857994
[5] https://www.researchgate.net/publication/337776242
Hope these information helps!
I agree with virtual inertia as the answer and expect it to become more common especially with HVDC links. I am also a proponent of nuclear power which would contribute to the grid and, given waste is stored safely, would have less carbon in the manufacturing phase.
Hi Mahdi!
As wind and solar generation increases in a power system tne inertia of the whole system decreases. In addition this type of renewable generation resources are replacing conventional generation (carbon, gas,..) the lost of the system inertia increases. As a result of this, the inertial response of the system following an disturbance is negatively affected. So the increase od wind and solar generation must be accompanied by an increase on the operating reserves and additional infrastructure (energy storage systems) to face the operation challenges imposed by a large incorporation of wind and solar generation in a power system.
https://www.nerc.com/comm/Other/essntlrlbltysrvcstskfrcDL/ERSTF%20Framework%20Report%20-%20Final.pdf
Dear Jorge Calderon
Great. Thank you very much. I agree with your comment. Many auxiliary devices and supplementary controllers of renewable energy power plants can increase the power system inertia.
https://www.researchgate.net/project/Damping-of-Low-Frequency-Oscillation-Using-PV-Farms
I would add that this increase in power system inertia for renewables is the same as on a HVdc link and what has been referred to here as virtual inertia. The difference with this "virtual inertia" is there is no actual mass moving with an angular velocity as there would be in a synchronous condenser (no real inertia) but the power is modulated so the end result is the same. The drawback of these virtual inertial solutions is that if the controls do not work for whatever reason (maybe because of the disturbance itself on the system) then there is no virtual inertia , whereas, with a synchronous condenser the mass will always keep rotating resisting frequency change and providing inertia regardless of the disturbance.
Dear all
It seems that, the solution is virtual inertia. Do you think virtual inertia is enough?
I think virtual inertia is a tep in the right direction, but just virtual inertia may be not enough, A combitation of virtual inertia and energy storage systems is better than just virtual inertia
Hydro electric is what we use in Manitoba and it is renewable and green but you cannot put it anywhere ( need the natural resource and can only dam the river so many times).
Wind always has to be backed up by our Hydro ( cannot count on it in low wind or high wind or extreme cold).
Conversely, you can add a synchronous condenser anywhere. Also , as mentioned before , nuclear power has physical inertia in the form of fission that continues to supply. Lastly, the DC links are already there ( nothing needs to be built) and vrtual inertia can be added.
power even when not needed.
Dear Omar H. Abdalla
Thank you for your comment. Wind turbine generators are inverter based so they have not inherent inertia. Also, hydroelectric power plants don't have continuous performance therefore they aren't suitable for inertia compensation.
Dear all
Please send your comment about inherent inertia. Do you think the inverter based generators have inherent inertia?
Yes, with the replacement of synchronous generators, system inertia will be reduced. But inertial response (IR) and primary frequency response (PFR) of synchronous generators can be replicated using fast frequency response devices.
For instance, energy storage with very low response time can provide inertial support after a large disturbance. Energy storage which can provide high amount of power for a fairly long time can be used for primary frequency response when system inertia is very low.
An HVDC link is an inverter based generator and there is no inherent inertia since if the commutating voltage is distorted any virtual inertia that may have been there is lost.
This paper below suggests my comment is only true for line commutated converter HVDC inverters. VSC s should be able to supply some inherent inertia depending on the controls ( paper does not use conventional PLL).
www.irjet.net/archives/V2/i6/IRJET-V2I6104.pdf
Mahdi Saadatmand, can you please develop your reasoning around " hydroelectric power plants don't have continuous performance therefore they aren't suitable for inertia compensation"? I think I did not follow you on that...
Virtual inertia is the way to go, but can a power system work fine without a rotating mass inertia? I mean can it work fine with strictly virtual inertia?
Dear Erick F. Alves
Thank you for your comment. I meant that it is possible that in the case of hydropower plants there are not always nominal operating conditions given the amount of water stored in the dam.
Of course, this is my opinion. Mention it if you have more information.
It should be noted that the main question of this discussion was whether the power system without synchronous generators can (this includes the hydropower plant) provide enough inertia?
Dear Adeyemi Alabi
This is exactly what we are discussing here. Due to the rapid growth of renewable energy power plants and the lack of inherent inertia and except rotation in this type of power plants, please comment.
Most networks have motor loads (fans, pumps etc) that have their own inertia. It could be an interesting topic for an academic project to study how a network behaves if the frequency is not as stable as today. In principle most lighting and power electronic loads or inverters should still work.
Dear Tom Berry
Thank you for your comment. Please note that this discussion is about power swing damping and frequency control in power systems based on inherent inertia of synchronous generators.
Dear Mahdi Saadatmand to the best of my knowledge, there are two aspects to the traditional inertia; the inertia time constant, which determines the speed at which the system responds to the frequency change, and the inertia constant that determines how much energy is stored to control the frequency. In a hypothetical network with no synchronous generations (and no rotating mass inertia), The later of the two aspects of traditional inertia can be taken care of with energy storage devices. The energy storage can act as loads or sources depending on the state of the network frequency and inject or absorb active power from the network to control the frequency. I think the penetration of EVs can play a role in such a network.
The other aspect of traditional inertia; the inertia time constant seems to be more difficult to replace. However, with proper control strategy of the power electronic devices on the system, the inertia time constant can be reconfigured to achieve the desired speed of frequency response.
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