Synchronous motor

Figure 5.38 shows a model of the two poles of an AC synchronous motor. It shows a model of the rotating magnetic field-type motor that has the armature coils for rotating the magnetic field in the stator and the coil for the magnet in the rotor. The other one is the rotating armature-type that has the coils for controlling the magnetic field in the rotor and the field coils in the stator. Generally, the stator coils are simpler than the rotor, and the voltage and the current required for the stator are lower than those for the rotor. For this reason, rotating magnetic field motors are very popular. As this figure shows, the magnetic poles of the rotor is induced by the field coil, and the rotor is actuated synchronously with the rotating magnetic field induced by the three-phase alternating current through the stator coils.

Figure 5.38 also shows a motor that has a coil in the rotor. This type of motor needs the brush or slip rings feeding the current to the rotor coil to induce the magnetic poles. The permanent magnet motor (PM motor) uses permanent magnets instead of electrically induced magnets to produce the magnetic moment of the rotor. The permanent magnet-type one does not need electricity or a slipping contact point, so it should be structurally durable and efficient in terms of energy consumption since it saves electricity for inducting.

Application to electric vehicles

Table 5.6 shows examples of how these synchronous motors are used on passenger-carrying electric vehicles. Almost all the electric vehicles use the permanent magnet-type synchronous motors as the traction motor.

These examples in Table 5.6 are rare-earth permanent magnet-type motors. The compact passenger-type electric vehicle weighs over 1.5 t and requires a 50-70 kW traction motor. It is equipped with a compact drive unit motor that has one-stage reduction gears.

Smaller 'city-EVs', such as Toyota's e-com or Nissan's Hypermini, have been introduced recently. Carrying two passengers, they weigh under 1.0 t. The number of applications of these smaller PM motor is increasing. Another trend is the introduction of hybrid electric vehicles (HEVs), such as the Toyota Prius and Honda Insite. HEVs use a motor and weigh less than PEVs because they have smaller batteries, as their motors require less power. As a result, demand for the smaller PM motors are growing.