What is the main advantage of a single-phase synchronous motor over a single-phase induction motor?

The main advantage of a single-phase synchronous motor is that it operates at a constant speed that is independent of the load. This characteristic is primarily due to the design of synchronous motors, which require the rotor to lock in with the rotating magnetic field produced by the stator. As a result, the speed of the rotor synchronizes with the frequency of the supply current, making the motor very reliable for applications where maintaining a steady speed is critical.

This constant speed behavior contrasts with single-phase induction motors, where the speed can vary depending on the load conditions. Induction motors experience slip, which means that as the load increases, the rotor speed decreases from the synchronous speed. In applications requiring precise timing, such as in clocks or synchronous drives, the ability of synchronous motors to maintain a fixed speed provides significant advantages in performance and efficiency.

While other options may present certain benefits in their respective contexts—such as torque at startup or efficiency at low loads—those aspects do not match the consistent operational speed benefit offered by synchronous motors.