The instability of a vehicle in a state of spin is explained by the notion of saddle-node bifurcation, the characteristic of which has a close connection with perturbations of cornering force. The control law for a direct yaw moment control system to protect a vehicle from spin is designed through LMI (Linear Matrix Inequality) approach. The designed controller satisfies a constant scaling H^∞ norm condition for an arbitrary velocity in some specified range; this guarantees that the control robustly stabilizes the vehicle and protects it from spin in the presence of perturbations of cornering force. The result is examined through computer simulations.
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