Fuzzy PI controllers are using in the place of linear PI controller with success in process control, assuring better control quality criteria. The paper presents some methods, with a higher grade of generality, to design PI fuzzy controllers, to assure internal and external stability to control systems and better control quality criteria. Families of input-output transfer characteristics and gain characteristics of fuzzy blocks are used in the design procedures. An equivalence of PI fuzzy controller with linear PID controllers is done in a first approximation. Then, the fuzzy controller is design to assure absolute global internal stability and external BIBO stability of control systems. Ail application is presented with modeling and simulations. Results of simulation demonstrate the advantages of these design methods, assuring better quality control criteria and robustness at error in parameter estimation and at disturbance influence for the control systems.