Delta source, wye resistive load

[Tomex]

Hi there,

I’m out of ideas what’s going on here. I have delta connected sinewave sources, wye connected resistive loads. I might be overlooking some basics but it really bugs me why:

1. The currents are in phase although there’s no reactive load.
2. The currents are distorted and of a different amplitude.
3. I’m getting warnings in the output window

Thanks!
Tomas

[KSKelvin]

Add series resistance to each source. Right click on V1, V2 and V2, add attribute, Rser=1u.
Do you think the result is good with this?

[lpoma]

@Tomex ,

I redrew your schematic (Attached). I received your same results.
User_Motor_test.qsch (7.4 KB)

I’ve done some 3-phase motor sims in the past. Your wiring scheme seems “strange”.

I’ve attached a similar 3-phase motor sim design. Check it out.
User_Motor_test1.qsch (8.7 KB)

Len

[KSKelvin]

I ran this circuit in LTspice, it also won’t work if you don’t add a series resistor.

If you take closer look of 3 voltage sources connect in delta, with only V1 and V2, it already defined the voltage different between node L1 and L3.
For example, by disable V3, you can still see V(L1,L3) is following exactly how V3 should be.
In short, when you add V3 without a series resistor, you are equivalent to connect two parallel voltage source to each other : (V1+V2 in series) parallel to a single V3. That why you get an error in LTspice or Singular matrix warning from Qspice. Qspice is trying to have Gmin stepping and adding gshunt to force simulation to run.
But adding a series resistance should do this trick. Just like how you handle two parallel voltage sources.

[Tomex]

Thanks @KSKelvin that was the remedy I was looking for.
The reason is exactly like you describe:
Connecting ideal independent voltage sources - even though they have the same voltage - makes the solution matrix singular
this results in unpredictable behavior. Similarly to this:

Thanks all!
Tomas