The protection for the failure o f the inver ter with supply in the thyristor inver ter source to be used for battary formation and as charge/ discharg e is studied. T he aux iliary cir cuit to sw itch off the thyr istor in t he inverter is added in order to improve the propert ies of battary char ge/ discharge source. The signal sensing for power- off and the implement of t he control sourcetd be used for the pro tection is analysised in this paper .