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Very recently, an adaptive synergetic controller (ASC) has been proposed in order to solve the problem of the design of a synergetic controller (SC) when the parameters and dynamics of the controller system are unknown. The ASC algorithm was designed based on the Simple Adaptive Control (SAC) Technique.  Although the ASC has been successfully validated through Quadrotor experimental test bench, the integral time-varying control gains could cause divergence if a sequence of disturbances is introduced to the controlled system. This is because the recently proposed ASC does not include any preventive parameter that can bound the adaptive gain dynamics, and then prevent them from divergence. Also, the stability analysis of the ASC is given without considering disturbance. In this paper, a sigma modification method is introduced which consists in introducing an additional term to the ASC algorithm. Taking into account the external disturbances, the stability analysis of the adaptive system with the sigma modification method is formally established. Simulation and experimental validation through Quadrotor test-bench are given in order to confirm the theoretical results.