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This paper proposes a robust vibration controller design for active suspension system of in-wheel-motor-driven electric vehicles based on unified µ-synthesis framework. First, multiple parameter uncertainties and unmodelled high-order dynamics of the suspension are analyzed and discussed. By applying the mixed uncertainties and linear fraction transformation, model perturbations are separated from the suspension system and their perturbation bounds can be also limited. Then the uncertain quarter-vehicle active suspension model with dynamic damping in-wheel motor driven system is established, in which in-wheel motor is suspended as a dynamic vibration absorber. The resulting robust µ-synthesis feedback controller of generalized closed-loop active suspension system is designed with the concept of structured singular value µ and µ-synthesis theoretics, and solved via comprehensive solution of the D-G-K iteration. The µ analysis results show that the µ controller possesses less conservative stability and performance margins as compared to the H8 method against system uncertainties. Furthermore, simulations of nominal and perturbed suspension systems are implemented and the corresponding frequency and time-domain responses are compared, and then simulations results confirm that the developed µ controller is capable of attenuating the negative vibration of the active suspension system compared with H8 controller and passive suspension.