How does the PQ configuration work in a power flow study?

[kalinathk]

Hello everyone,

I have been conducting voltage stability studies on a transmission network and have been using the 'System.PQ.config' method (as shown below) to convert the loads in the network from a constant PQ configuration to a constant impedance configuration:

system.PQ.config.p2p = 0.0
system.PQ.config.p2i = 0.0
system.PQ.config.p2z = 1.0
system.PQ.config.q2q = 0.0
system.PQ.config.q2i = 0.0
system.PQ.config.q2z = 1.0

However, when I compare the results, I do not observe any noticeable difference in the voltage profile. I am trying to understand how this configuration is applied during a power flow study and whether there is a more reliable method other than comparing voltage profiles, like showed below here.

Thank you in advance,

[cuihantao]

These settings are used when initializing time domain simulation. It will not affect the power flow calculation as PQ is meant to be constant PQ in power flow. The exception is the pq2z option, which will convert the PQ load to Z load when the voltage is excessively low during power flow iterations. This is somewhat uncommon.

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On Thu, May 8, 2025, 2:35 PM Kali-Nath ***@***.***> wrote: Hello everyone, I have been studying the voltage stability studies in a transmission network and following 'System.PQ.config' (as follows) method to convert the loads in the network from PQ configuration to Constant Impedance configuration. system.PQ.config.p2p = 0.0 system.PQ.config.p2i = 0.0 system.PQ.config.p2z = 1.0 system.PQ.config.q2q = 0.0 system.PQ.config.q2i = 0.0 system.PQ.config.q2z = 1.0 But when I compared the results, I do not see any difference in the voltage profile. I am just wondering how this configuration works in the power flow study scenario and how to validate other than the voltage measurement method to verify that? Thank you in advance, image_2025-05-08_143205051.png (view on web) <https://github.com/user-attachments/assets/3a549760-82d2-4170-981f-99a9aab9032d> — Reply to this email directly, view it on GitHub <#610>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABSNZA6RSU6DOGEAUTFBSN325OPYFAVCNFSM6AAAAAB4XGGFV6VHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZYGI4TMMZWGY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[kalinathk]

Thank you very much for your reply, Dr. Cui.
I replaced the PFlow.run() with the TDS approach as follows,

system.PQ.config.p2p = 0.0
system.PQ.config.p2i = 0.0
system.PQ.config.p2z = 1.0
system.PQ.config.q2q = 0.0
system.PQ.config.q2i = 0.0
system.PQ.config.q2z = 1.0

system.PFlow.run()
system.TDS.init()
system.TDS.config.tf = 2.0
system.TDS.config.tstep = 1/200
system.TDS.run()

And run this in a for loop for the P-V analysis, when I changed the load configuration from p2p -> p2i -> p2z and compared, the voltage profile still looks very identical like below,

Could you please advice me on how to debug the load conversion approach in TDS?
I really appreciate your help in answering my questions.
Thank you very much.

[kalinathk]

Hello Dr. Cui,
I have been going through my code step by step, I am confused on this particular part, when I replaced the PFlow.run() approach with TDS.run(), I did not changed the way I am retrieving the data at the end of the simulation. I am still using the following approach,

system.StaticLoad.get(src='Ppf', idx=pq_loads_idx, attr='v')
system.StaticLoad.get(src='Qpf', idx=pq_loads_idx, attr='v')
system.PV.get(src='a', idx=pv_gens_idx, attr='e')
system.Bus.get(src='v', idx=bus_to_monitor, attr='v')
system.Bus.get(src='a', idx=bus_to_monitor, attr='v')

Does it mean, I might be retrieving the power flow data, instead of the time series information even after running TDS.
From observing the examples, I noticed that there is a way plot the TDS data after the simulation. But do you have any method (or example) to retrieve the P,Q consumption of the loads and gen at particular time step of the simulation, instead of using the 'plotter' function?

Thank you very much for your help in advance.

[cuihantao]

Hi Kali-Nath,

I replaced the PFlow.run() with the TDS approach as follows,

system.PQ.config.p2p = 0.0
system.PQ.config.p2i = 0.0
system.PQ.config.p2z = 1.0
system.PQ.config.q2q = 0.0
system.PQ.config.q2i = 0.0
system.PQ.config.q2z = 1.0

system.PFlow.run()
system.TDS.init()
system.TDS.config.tf = 2.0
system.TDS.config.tstep = 1/200
system.TDS.run()

And run this in a for loop for the P-V analysis, when I changed the load configuration from p2p -> p2i -> p2z and compared, the voltage profile still looks very identical like below,

The PQ load model is converted to three different models but all based on their power flow solution. If there is no disturbance, the three time-domain simulations are the same flat runs. That's why you see identical voltages (across three settings) and flat voltages (over time).

system.StaticLoad.get(src='Ppf', idx=pq_loads_idx, attr='v')
system.StaticLoad.get(src='Qpf', idx=pq_loads_idx, attr='v')
system.PV.get(src='a', idx=pv_gens_idx, attr='e')
system.Bus.get(src='v', idx=bus_to_monitor, attr='v')
system.Bus.get(src='a', idx=bus_to_monitor, attr='v')

Check this out: https://docs.andes.app/en/latest/_examples/ex2.html#variables

[kalinathk]

Hello Dr. Cui,

Thank you for clarifying my questions. I went through the documentation link you have shared and understood that I can access the variables listed in the '.lst' file.
However, when I inspected, I noticed that the .lst file I have stores voltages, angles of the buses in addition to the q output form PV and Slack buses and it does not have any load data related indices.
I uploaded the TDS results as csv and cross checked too. I couldn't find any P & Q values of the load.
If the TDS plotter function doesn't store these values by default, is there an option to add them to monitor during the simulation?

Apologies for the long thread of questions, thank you very much for your patience in answering my questions.

Thank you.