convergence error simulating driver circuit for one stage of three phase inverter

[joconno]

hello,

I was trying to test a circuit idea for driving one stage of a three phase inverter from a microcontroller. I used a digital square wave to trigger the logic level MOSFETs, but was getting a 'convergence error'

Does anybody know what this means?

Have attached cct diagram.

Many thanks

J

[johnsold]

I ran into a similar problem recently using a generic SPICE simulator. I learned that the discontinuities at the transitions of a square wave can cause convergence problems.  In particular the circuit you show has no base resistor for Q3 so the base currents might get quite large if the voltage at U2 is several volts.

A small R-C circuit (R in series, C to ground) with a time constant of ~ time step might smooth the signal enough to eliminate the convergence problem.  Since you are using a fairly low frequency another idea is to drive Q3 with a large amplitude sine wave through a series resistor and clamp diodes to limit the base voltages at Q3.

Lynn