Dear Dr Zimmerman, I am trying to solve an ac opf with the mips solver (560) in a lightly meshed 6.6 kV distribution system of 32 branches. The range for the reactances is [0.05-1.9 pu], whereas some of them have almost negligible values. When I am solving the simple ac power flow the problem converges with no problems to be appeared. However, when I am trying to solve the same problem with optimal power flow, assigning some costs to the generators, the ac opf fails numerically or the message ' the matrix is singular to working precision, the results may be inaccurate' appears.
I suspect that the problem is the solver. Could you recommend me another solver to use? Any guidance would be appreciated. Kind Regards, Angelina
