From GridLAB-D Wiki
The iteration_limit global variable determines that maximum number of iterations of the main synchronization loop permitted before the clock must advanced. If the main loop reaches the iteration limit and the clock has not advanced, GridLAB-D will terminate the simulation with a convergence error.
GLM
To set the iteration in a GLM file, use the syntax:
#set iteration_limit=100
Command line
To set the iteration at the command line, use the syntax:
host% gridlabd -D iteration_limit=100