Nonlinear adaptive MIMO controller for high performance DC motor field weakening

This paper investigates a novel field weakening technique for a separately excited DC motor that exhibits considerable nonlinearities. Using the transformed motor system with uncertainties in both parameters and load torque, a constant power field weakening controller is developed by nonlinear adaptive multi-input multi-output (MIMO) backstepping combined with variable structure control. Due to the decoupling effect, this controller achieves speed tracking at any desired set point of operation. To demonstrate the effectiveness of the proposed controller, the results of computer tests are presented for a specific motor. It has been shown that the controller provides globally robust speed control performance, while the motor system is operated over a wide dynamic regime of field weakening, even under the presence of mismatched parameters and load uncertainties.