Understanding Simscape Electrical - Specialized Power Systems - Load Flow Generator Type

I am trying to understand the setting "Generator type" of the "Load flow tab" of elements from the Specialized Power Systems Library. In the example "power_simplealt" that is given in the Simplified Sync. Machine Model Documentation, a "Simplified Synchronous Machine" is used as a generator on a grid represented by the "Three-Phase Programmable Voltage Source". The former is set to "PV" in the Load Flow Tab/Generator type, the latter to "swing". When I now open the Load Flow Analyzer App via the powergui block and click "Compute", an error warning appears and tells me, the the current combination of "PV" and "swing" is not allowed (this is the official Matlab example though!). Apparently only swing + PQ is okay.

Furthermore, when I click powergui block > "Tools" tab > "Machine Initialization", I am able to "Compute and Apply" the correct initial values for steady state operation (the app warns me that it is no longer maintained, so that might explain why it works and the load flow analyzer app does not). However, the computed settings lead to a perfectly executable model with results that appear correct.

Can somebody explain

• what is the state of these various Apps
• which can be used and which should not
• why is the official model giving an "error" when using the Load Flow Analyzer
• what exactly does PV and PQ do, can you explain with regard to the operation of a real generator supplying energy to the grid? The documentation is very short and simplified, I am a mechanical engineer so I need a bit more info on that to understand and apply it.

Thanks!

Edit: A lot of the documentation of this library seems to be deprecated. Check out this documentation on initial states. It talks about an "Initial state" option in the Tools tab of the powergui. There is none ...

Answer 1

[Riya]

Hi Felix

According to my understanding, It seems that the error message is expected. Touse this model for load flow analysis, you have to change the bus type to "PQ."

In the model "power_simplealt", the machine is connected with the voltage source in series directly and there is no other component (e.g.,resistor and/or inductor) between them. So there is only one bus which is the interconnection between the machine and the voltage source.

In load flow analysis, it is not allowed to define a bus as both swing bus and PV bus. By changing the bus type of the machine to be 'PQ' busand specifying reasonable active and reactive power generation in the 'Load Flow' tab, the load flow analysis will work.

When using Machine Initialization, the restriction above does not apply, which is why you are able to compute. But strictly speaking, when using the machine initialization, the bus type in the App should be selected as 'P & Q generator', not 'P & V generator'.

Generally, for a simple circuit, using either load flow analysis or machine initialization is applicable. However, for a complicated circuit (e.g.the shipped example model 'power_LFnetwork_5bus' ), the load flow analysis should be used.

I hope it helps.