DC Motors:
- Brushed DC Motor
- Brushless DC Motor
AC Motors:
- Synchronous AC Motors
- Induction (Non-Synchronous AC Motors)
Electric motors are machines that convert electrical energy—from either stored power or a direct electrical connection—into mechanical energy through the production of rotational force. The two major types of electric motors are:
- AC motors, which are powered by alternating current
- DC motors, which are powered by direct current
Both AC and DC motors use electrical current to produce rotating magnetic fields that, in turn, generate rotational mechanical force in the armature—located on the rotor or stator—around the shaft.
See the below image for the advantages of AC vs. DC motors:
Looking beyond the two broad categories, this is where there are sub-sets of types of AC & DC Motors.
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Brushed DC Motors: The brushes and commutator inside a brushed motor mechanically commutate the motor windings and it continues rotation as long as its power supply is connected. Brushed motors are easy to control, but require periodic maintenance and replacement of brushes, and therefore have an estimated lifespan of 1000~1500 hours (more or less due to operating conditions)
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Brushless DC Motors: Brushless motor systems offer better performance than brushed motors due to electrical commutation and closed-loop feedback but require drivers to electrically commutate the motor windings.
- **Synchronous AC Motor **: The synchronous motor rotates at the same rate as the frequency of the supply current, a fact that gives the motor its name. Synchronous motors are constructed of a stator, rotor and Synchronous motors are used in a wide range of applications.
- Induction AC Motor: Induction motors are the simplest and most rugged electric motor available. These AC electric motors consist of two electrical assemblies: the wound stator and the rotor assembly. The electric current needed to turn the rotor is created by electromagnetic induction created by the stator winding. Induction motors are among the most commonly used type of motor in the world.
AC Motors are less common for consumer applications, and more common for industrial, automotive applications. AC motors are capable of providing much higher torque through AC voltage (either single or three-phase AC).
One of the main differences between AC and DC motors is speed control. An AC motor runs at the frequency of the AC supply and resists changes to the speed even when the load changes. To change the speed of the motor, it’s necessary to use a Variable Frequency Drive (VFD) which converts the AC supply to DC and back again at a different frequency. However, besides adding to the motor’s cost, VFDs have inherent inefficiencies that may create problems such as shaft and bearing currents that can shorten the motor’s lifespan if not managed properly. Additionally, AC motors tend to lose torque at higher speeds.
Stepper Motors: Stepper motors are brushless DC motors that move in discrete steps. They have multiple coils that are organized in groups called “phases”. By energizing each phase in sequence, the motor will rotate, one step at a time.
Servo Motors: A servo motor is any motor coupled with a feedback sensor to facilitate positioning; thus, servo motors are the backbone of robotics. Both rotary and linear actuators are used. Low-cost brushed DC motors are common, but are being superseded by brushless AC motors for high-performance applications.
Useful Reference Material: