Issue link: https://resources.mouser.com/i/1525523
11 | AC induction motors offer a cheap, reliable design widely used for both industrial and domestic use cases. For example, single-phase motors can usually be found in smaller applications, such as compressors, fans, mixers, toys, and drilling machines. Three- phase designs are mainly used in more demanding roles, including cranes, crushers, and lifts. AC Synchronous Motors As the name suggests, in a synchronous motor, the rotor speed and the stator magnetic field speed of rotation are the same. One of the downsides of induction motors is that the slip necessary for them to operate makes them unsuitable for precisely timed applications because if the load changes, the rotation speed will also change. AC synchronous motors eliminate slip and are, therefore, ideal for these roles. As the rotation speed is not affected by the load, synchronous motors are often used in applications where a constant speed is required (e.g., a pipeline pump, where the flow speed needs to remain constant regardless of pressure). For the motor to operate properly, the rotor needs to generate its own magnetic field. The reason for this, especially in larger motors, is the rotor's inertia, which stops it from self-starting and synchronizing with the stator magnetic field. Generating the magnetic field can usually be achieved in two ways: by supplying windings with a DC current (excited) or by using permanent magnets (non- excited). Differences in load will cause a lag in the phase, but the motor will be at a constant rotation governed by the supply frequency. Excited Rotors The rotor of an excited synchronous motor has windings that match those in the stator. A DC power supply is used to energize the windings in the rotor to produce a constant magnetic field, allowing the rotor to interact and sync with the rotating magnetic field from the stator. DC excited motors are normally used for applications that require less than 1kW of power. Non-Excited Rotors Non-exited synchronous rotors use ferromagnetic materials instead of current to provide the magnetic field in the rotor. There are three main types of non- excited rotor designs: hysteresis, synchronous reluctance, and permanent magnet synchronous. Hysteresis Motors The hysteresis motor rotor is fabricated from layers of material that exhibit a wide hysteresis loop fixed around a solid non-magnetic (usually aluminum) core. The rotor exhibits high retentivity, making it difficult to change the magnetic polarities caused by the stator's revolving magnetic field. The stator magnetic field produces eddy currents in the rotor, providing the starting torque. As the rotor accelerates, hysteresis torque becomes more prevalent until the rotor reaches synchronous speed, where the eddy current torque is reduced to zero, and hysteresis is responsible for all the torque. Hysteresis motors are simple, silent, and reliable. They require no excitation to start and synchronize smoothly. They also do not draw large amounts of current during startup and operation. They are often used in equipment that needs constant speed and where noise is detrimental to the operation of the application (e.g., in turntables). Synchronous Reluctance Motors The rotor of a synchronous reluctance motor is fabricated from a soft magnetic material with properties that create areas of high and low magnetic permeability. Both the rotor and stator are constructed with salient poles. This type of construction can cause a high torque ripple, so the rotor is often built with fewer poles than the stator to minimize that effect. Reluctance is lowest when the salient poles on the rotor and stator are aligned and highest when they are at maximum misalignment. The rotor always moves from high reluctance to low reluctance, producing torque. This torque will pull the rotor to the nearest salient stator pole on the stator and cause rotation. The system can be controlled using equipment to provide a continuous, rotational output. Synchronous reluctance motors have grown in popularity recently as electronics have made motor control easier. The design is also simple, cost-effective, rugged, and easy to manufacture. However, the sophisticated drive system required can increase its overall cost. Its high efficiency, ability to be controlled easily, and reliability make it ideal for