I.M. Nejdawi, S.R. Alwash, and I.A. Smadi (Jordan)

DC motors, DC drives, Fuzzy logic, speed control

Therefore, it is difficult to apply linear control techniques by linearizing about a nominal operating point of the nonlinear system. A novel variable structure fuzzy logic controller applied to a separately excited DC motor (SEDCM) is presented. This approach is based on the nonlinear differential equations model of a SEDCM with the effect of magnetic saturation and armature reaction taken into consideration. The controller is based on fuzzy theory to design different fuzzy logic controllers (FLC) to achieve high-performance speed tracking through rejecting load disturbance. Two types of fuzzy controllers are proposed, classical PI Fuzzy logic controller (CPIFLC), and Variable structure fuzzy logic controller (VSFLC). Numerical simulations are presented to illustrate the method and to demonstrate the effectiveness of the proposed controllers in comparison with traditional PI controllers. Figure 1. Equivalent circuit of SEDCM Figure 1 shows the equivalent circuit of SEDCM where ia is the current in the armature circuit, the armature inductance is denoted by La and φf is the airgap flux due to the field winding and ω is the motor angular speed. The field flux φf is related to the field current if by φf(if)=f(if), where f(.) is the magnetization curve, φf may be modeled as a linear function of if , i.e. φf(if)=Lf if , where Lf denotes the field inductance [8,9]. Ra and Rf denote the resistance of the armature and field windings, respectively. Therefore, to model the electrical dynamics for both armature and field circuits and the mechanical dynamics, the SEDCM is described by the three interconnected differential equations below [5]:

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