Why do I receive an error when I connect a source block in a loop with only capacitors or inductors in SimPowerSystems?

I have created a simple circuit which contains a voltage source and a Parallel RLC branch. When I try to simulate the system, I receive the following error:

 Error using ==> d:/matlab6p5p1/toolbox/powersys/powersys/private/psb2sys (getAPQ)

 Voltage source 'U_AC Voltage Source' is in a loop containing capacitors only 

 (branch 'Parallel RLC Branch' among others).

You will receive a similar error if you connect a current source in a loop with only inductors:

 Error using ==> d:/matlab6p5p1/toolbox/powersys/powersys/private/psb2sys (getAPQ)

 Inductive branch 'Parallel RLC Branch' is in series with current source or nonlinear element

 modeled as current source (branch 'AC Current Source')

Answer 1

[MathWorks Support Team]

This is an expected error message. It is not possible to simulate a system with an ideal voltage source when it is in a loop with only capacitors, or an ideal current source in a loop with only inductors.

For a capacitor, this is due to the fact that the voltage across a capacitor can not change instantaneously. An ideal voltage source could supply an infinite amount of current to maintain its voltage when the circuit is switched on. A real voltage source has an internal resistance associated with it, which would cause the voltage to drop when the circuit is switched on.

For an inductor, this is due to the fact that the current flowing through an inductor can not change instantaneously.

Currently, to work around this problem, connect a small series resistance in the loop.