How to converge when simulating the power system with negative resistance and positive inductance?

I find that the current can't converge when I use there-phase serials RLC branch whose type is RL with negative resistance and positive inductance, and this RL is connected to there-phase voltage source.

When R and L parameter are both positive or negative, the result converges.

I am confused.

Figure 1. Simulation

Figure 2. Simulation with negative resistance and negative inductance

Figure 3. Simulation with negative resistance and positive inductance

Answer 1

[Sabin]

Negative values are allowed for resistance, inductance, and capacitance. The system can simulate with negative resistance and positive inductance. However, certain combinations of parameters may run into potential unstable systems. But this can be the case with positive parameterization as well. We must pay attention to parameterization and think if they make sense. Then running the system in discrete time can also pose challenges as we have to discretize according to the smallest time constant in the system.