Optimal emplacement of capacitors or svc !.?

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Hi friends, i'm working in a transmission power network, for the base case i used QV curves to identify the critical buses in voltage and their reactive requirements , but for some contingency cas (N-1) of lines the solution doesn't converge (blown up ), so i can't use qv curves cause of solutions divergence caused by voltage collapse phenomena (maybe ) . So do you know any tools or method to do,in purpose to solve the problem and to know the optimal Compensator emplacement and requirements. Regards