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Chapter 6: Electric Motors 141• Brushless• UniversalThe last three motor types are just variations of the first three, fabricated withdifferent construction techniques. The compound motor is a combination of the seriesand shunt motors. For the first three motor types we’ll look at the circuit showing howthe motor circuit field windings are connected, and then look at the characteristics ofthe torque and speed versus armature current and shaft horsepower curves that describetheir operation (Figure 6-3).Each of the motor types will be examined for its torque, speed, reversal, andregenerative braking capabilities—the factors important to EV users. The motor typeswill all be compared at full load shaft horsepower—the only way to compare differentmotor types of equal rating. Efficiency is a little harder to determine since it also dependson the external resistance of the circuit to which the motor is connected. So efficiencyhas to be calculated for each individual case.Series DC MotorsThe most well-known of the DC motors, and the one which comes to mind for tractionapplications (like propelling EVs), is the series DC motor. It’s so named because its fieldwinding is connected in series with the armature (Figure 6-3). Because the same currentFi g u r e 6-3 Summary of DC motor types—windings and characteristics.