A permanent magnet synchronous motor (PMSM) uses permanent magnets embedded in the steel rotor to create a constant magnetic field. The stator carries windings connected to an AC supply to produce a rotating magnetic field. At synchronous speed the rotor poles lock to the rotating magnetic field. Permanent magnet synchronous motors are similar to brushless DC motors. Because of the constant magnetic field in the rotor these cannot use induction windings for starting. These motors require a variable-frequency power source to start. The main difference between a permanent magnet synchronous motor and an asynchronous motor is the rotor. Some studies seem to indicate that NdFeB permanent magnet synchronous motors are around 2 percent more efficient than the highest-efficiency (IE3) asynchronous motors—using the same stator laminations and similar variable-frequency speed controllers. Permanent magnet motors have been used as gearless elevator motors since 2000. Ningbo Guanghan Solar Pump Industry is a factory specialized in manufacturing solar submersible pumps and solar surface pumps. The head office was established in 1989 in Daxi Town, Wenling City, the hometown of water pumps in China, and a branch factory was established in Jiangshan Town, Ningbo City in 2019. It is located near the highway intersection, very close to Ningbo Port and Shanghai Port, and the transportation is very convenient.