U2T1、In general, the outstanding advantage of DCmachines lies in their flexibility and versatility. Before the widespreadedavailability of AC motor drives, DC machines were essentially the only choiceavailable for many applications requiring a high degree of control. Theirprincipal disadvantages stem from the complexity associated complexity increasethe cost over competing AC machines, it also increases the need for maintenanceand reduces the potential reliability of these machines.