Cannot specify per-phase P and Q in Simscape Wye-Connected Load

Hello ,

I am using the Wye-Connected Load block in Simscape Electrical and I get dimension errors when I try to specify P and Q as vectors (per-phase values), e.g. [Pa Pb Pc]. In contrast, the Three-Phase Parallel RLC Load block allows per-phase specification without issues.Is it possible to define unbalanced per-phase powers in the Simscape Wye-Connected Load, or is this block limited to balanced (scalar) P and Q only?

Answer 1

[Umar]

Hi @Prosper, Thanks for reaching out about the Wye-Connected Load block issue. I went through your question carefully, looked at both screenshots you provided, and did a thorough search through the MathWorks Simulink documentation to give you a clear answer. You're absolutely right about what you're seeing. The Simscape Wye-Connected Load block really is limited to balanced loads only. When you set it to parameterize by rated power and voltage, it only accepts single scalar values for real power, inductive reactive power, and capacitive reactive power. These represent the total three-phase power, not individual per-phase values. So no, you cannot specify unbalanced per-phase powers like [Pa Pb Pc] in this block, even though that would be really useful for many applications. The Three-Phase Parallel RLC Load block you showed in your second image does exactly what you want. It has that checkbox option called "Specify PQ powers for each phase" and when you enable it, you can enter three-element vectors like [10e3 9e3 11e3] for the active powers, and similarly for the reactive powers. This gives you full control over unbalanced loads with different power values for each phase. Here's the thing though. The Three-Phase Parallel RLC Load block is part of the Specialized Power Systems library, which MathWorks has officially marked for removal in R2026a. They're transitioning everything over to the newer Simscape Electrical blocks. The problem is that the modern Simscape blocks don't have this per-phase power specification capability yet. The Wye-Connected Load only does balanced loads, and the RLC Three-Phase block doesn't even have power-based parameterization at all, just direct R, L, C values, and those values are identical across all three phases. So for your current work, I'd say stick with the Three-Phase Parallel RLC Load block. It does exactly what you need and there's no point fighting against it. Just be aware that when R2026a comes around, you might need to rethink your approach. You could either convert your power specifications to component values and use three separate impedance blocks for each phase, or you could submit a feature request to MathWorks asking them to add per-phase power specification to the modern Simscape Wye-Connected Load block. Given that they're deprecating the old library, it would make sense for them to carry over all the useful features. Hope this helps.

[Prosper Diyani]

Hello, indeed, with MATLAB R2026a I will no longer be able to use the Specialized Power Systems library. For now, I need these unbalanced conditions, so I will continue using the Specialized blocks and follow your advice by submitting a feature request to MathWorks regarding this functionality. Thank you.