Figure 7.13 shows a simple model of the PM motor driving a mechanical load.The equivalent circuit of the motor is a series circuit consisting of an inductance (LA)from the armature windings, a resistance (RA) to account for wire and commutatorresistance, and a voltage source CEMF. Recall that the CEMF is an internally gener- ated voltage that increases with motor speed. The polarity of the CEMF is such that it subtracts from the line voltage (Vln), creating an effective armature voltage. Theinductance (LA) limits how fast the armature current can change but doesn’t affect thesteady-state operation. Writing Kirchhoff’s equation around the loop of Figure 7.13(for steady state), we get
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