Offset problem in simulating current and voltage phase relation of parallel rlc circuit, Is it a bug ?

tested multisim for Parallel RLC Circuit with voltage source as in
http://www.electronics-tutorials.ws/accircuits/parallel-circuit.html
But the current flows through the inductance L has DC component as in the picture attached (the red sine wave). Is it a bug ?, please tell me how to correct it.
Attachments:
phasor.jpg ‏183 KB

Hi there,
As strange as this may sound, this is not a bug. OK, this sounds really funny, but I am totally serious, and I am going to explain why:
In a circuit energy must be conserved.
An inductor is a purely reactive component, that is, it does not dissipate any power.
When simulation starts, Multisim assumes the inductor current to be 0, which may seem reasonable. The voltage across the inductor is also 0 at this point. This is the initial condition.
The voltage across the inductor increases, and thus, the current increases. The current keeps increasing during the first 2 quadrants of the sinusoidal phase output.
The current never decreases until the voltage drop is negative.
But by the time an entire cycle is over, the current is back to 0. This makes sense as energy is conserved and the inductor is not absorbing any energy.
OK. Now look at what happened. During the whole cycle, the current was positive only! The current increased during the first half of the cycle and returned to 0 during the second half. This is because of the fluke of initial conditions! In fact, a good circuit simulator will maintain the DC offset for a long duration. The DC offset may drift because of rounding errors and the like.
This will never be observed in real life as real inductors have winding resistance and other problems.
OK, so, if you would like to see no DC offset, do the following:
Run your simulation
Record the DC offset that you want to eliminate
Stop your simulation
Double click the offending inductor in the Multisim schematic
Click on the Value tab
Check the Initial conditions box under Additional SPICE simulation parameters
Enter the negative of the DC offset that you recorded in step 2 into the box right next to it
Start your simulation. Did your offset go away? Or did it double?
If your offset doubled, take away the sign from the DC offset that you entered in step 7. I bet you know why.
It took me a while to figure this one out. Hope that helps!
Yi
Software Developer
National Instruments - Electronics Workbench Group

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