How can I configure the Specialized Power Systems block "Three-Phase Parallel RLC Load" to behave as a constant power load during simulation in Simulink R2022b?

I have an electrical power network supplied with a three-phase voltage source, for which RMS voltage varies over time. This system is implemented in Simulink R2022b using blocks from the Simscape Specialized Power Systems library. The model includes the block "Three-Phase Parallel RLC Load", and I have selected the option "constant PQ" in the "Load Flow" tab in the Properties window to emulate a constant-power load. After a few seconds upon simulation start, the RMS voltage of the source increases, and the power in the load also increases. I was expecting the power in the load to remain constant.

How can I setup a constant-power load with a variable voltage supply?

Answer 1

[MathWorks Support Team]

This workflow involves an ongoing change in the voltage upon simulation start, which requires the load impedance change over time. The setting of “Load type” in the 'Load Flow' tab (i.e., 'constant Z', 'constant PQ', and 'constant I') are used by the “Load Flow” tool of the “Powergui” block (Environment block for Simscape Electrical Specialized Power Systems models). They are used for model initialization only, and they have no impact on the block model and on the simulation performance. When the simulation is running, the load block keeps set as a combination of passive components (R, L, and C). Please refer to the documentation page of the “Three-Phase Parallel RLC Load” block (sent in my previous email and also below) for more details:

https://www.mathworks.com/help/releases/R2022b/sps/powersys/ref/threephaseparallelrlcload.html#bsxmed0-2

Then, the “Three-Phase Dynamic Load” block is recommended for this workflow. More information about this block, including an example with a power network is provided in the following documentation page:

https://www.mathworks.com/help/releases/R2022b/sps/powersys/ref/threephasedynamicload.html