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This paper proposes a new power-assist control in pushing task as an intelligent function of wheelchair by repulsive compliance control. In this strategy, the reaction force of human input into object is estimated without torque/force sensor and is utilized to generate the power-assist torque for wheel driving. The proposed approach brings a sophisticated function that makes it easy to carry out pushing task by wheelchair rider. First, human acceleration estimation observer (HAOB) and workspace disturbance observer (WDOB) are employed. HAOB can abstract human input as equivalent acceleration without torque/force sensor. WDOB guarantees robustness of the whole control system against disturbances. Second, HAOB-based compliance control is constructed to generate the motion command of pushing task for power-assist control. The generated motion command is determined so that the wheelchair accelerates according to human input. From this point of view, the proposed control is called repulsive compliance control. The compliance control itself is passive control, and stable and flexible responses are expected. Simulations and experiments are conducted to confirm the validity of the proposed approach.