The purpose of this paper is to present an assessment of the negative impedance instability concept of the constant power loads in the More Electric Aircraft (MEA) power systems. We address the fundamental problems faced in the stability studies of these multi-converter power electronic systems. An approach to the design of sliding-mode controllers for PWM DC/DC converters with constant power loads is presented. Because of the negative impedance destabilizing characteristics of constant power loads, conventional linear control methods have stability limitations around the operating points. However, the proposed controllers improve large-signal stability and dynamic responses. The proposed controllers are simulated and their responses under different operations are discussed. Finally, we verify the stability of the controllers using the second theorem of Lyapunov.