RuntimeWarning: invalid value encountered in sqrt

[JunejaAmmy]

Hi Dr. Cui,

I'm facing below issue while running TDS. Can you please help me?

I have followed below steps with use case: ieee14_dgprct.xlsx

1. Ran the simulation for 1500 seconds with tstep = 0.33 and shrinkt = 0
2. Altered the value of tm0 of GENROU_1 to 1.55
3. Continued the simulation to 1800 seconds and faced below issue.

C:\Users\AmrinderS\.andes\pycode\ESST3A.py:21: RuntimeWarning: invalid value encountered in sqrt
  return ((-v + vbus, LAW2_y*VB_y*ue - vout, -UEL + UEL0, ue*(-IN*VE + KC*XadIfd), -FEX_y + select([less_equal(IN, 0),less_equal(IN, 0.433),less_equal(IN, 0.75),less_equal(IN, 1),greater(IN, 1),__trues], [__ones,1 - 0.577*IN,sqrt(0.75 - IN**2),1.732 - 1.732*IN,__zeros,__zeros], default=nan), FEX_y*VE - VB_x, VBMAX*VB_lim_zu + VB_lim_zi*VB_x - VB_y, KG*vout - VG_x, VGMAX*VG_lim_zu + VG_lim_zi*VG_x - VG_y, LAW1_y - VG_y - vrs, -vref + vref0, -LG_y - vi + vref, HLI_zi*vi + HLI_zl*VIMIN + HLI_zu*VIMAX - vil, HG_lt_z0*UEL + HG_lt_z1*vil - HG_y, LL_LT1_z1*LL_LT2_z1*(-LL_x + LL_y) + LL_x*TB - LL_y*TB + TC*(HG_y - LL_x), ue*(-vf0 + vout), 0, 0, 0, 0, 0, 0, 0))
Time step reduced to zero. Convergence is not likely.
Simulation terminated at t=1502.6400 s.

[cuihantao]

You disabled automatic step size shrinking. The numerical integration could not converge after some disturbance.

What you can do is enable shrinkt and see if it converged. If yes, you can manually interpolate the data at needed timestamps.

[cuihantao]

Altering tm0 of generators will trigger electromechanical transient response that is unlikely to solve using a large step size of 0.33 s.