Synchronous Motors

Synchronous Motors







So-called synchronous motors are the most suitable motors for hybrid applications. In contrast to asynchronous motors, the impeller/rotor speed of synchronous motors is identical to the rotary field speed. This is achieved through a slight modification in the coil design and the position of the magnetic poles. The rotor speed is determined exclusively by the number of pole pairs and the frequency (slip =0).

The disadvantage of synchronous motors is their low resistance to overloading. If the mechanical load is too high, the rotor speed falls below the rotary field speed. As a consequence, the motor falls out of synchronization and stops. Therefore, a synchronous motor does not start autonomously.

The engine control has to compensate for this behaviour. In the Porsche Cayenne S Hybrid, the power electronics adapt the frequency accordingly. The frequency is increased from 0 Hz to the required speed in order that the motor can start. Consequently, a synchronous motor cannot operate without control electronics.

The advantages of the synchronous motor include the extremely compact design and simultaneous use as a generator. The illustration shows the complete hybrid module on the Porsche Cayenne S Hybrid, consisting of a dry clutch and electric motor/generator between the combustion engine and transmission. The complete module is almost 150 mm in length and generates a total electrical power of 38 kW.

The three-phase alternators used in Porsche vehicles are also synchronous generators.