With the rapid development of power electronics technology and new semiconductor devices, AC speed regulation technology has been continuously improved and enhanced. The gradually improved frequency converter, with its good output waveform and excellent performance-price ratio, has been widely applied in AC motors. For example, large motors used for steel rolling in steel plants, medium and small roller table motors, traction motors for railways and urban rail transit, elevator motors, crane motors for container lifting equipment, motors for pumps and fans, compressors, and motors for household appliances have all successively adopted AC variable frequency speed regulation motors and achieved good results. The axial and radial dimensions of a motor basically determine its overall shape. Slender motors and short, stout motors may present some technical difficulties in the manufacturing process, and relative errors may have a greater impact on motor performance. For variable frequency motors, resonance factors must also be considered for their impact on motor operating performance. Compared with power frequency motors, the rotor balance quality of variable frequency motors must be high, and the machining precision of mechanical components must be high to ensure that vibration performance meets requirements under high-speed operation. The axial length of variable frequency motors should be controlled to prevent objective factors of high-speed vibration caused by excessive axial dimensions. Customers who have used variable frequency motors may know that, especially when the frequency regulation range is wide, severe vibration often occurs in a certain frequency band in most cases. This is what we call resonance, also known as "resonance." It is a phenomenon where the amplitude increases sharply when the frequency of an external periodic force is the same as or very close to the natural oscillation frequency of the system. The function of current transformers The frequency at which resonance occurs is called the "resonance frequency." Considering the facts that variable frequency motors have resonance and a wide speed regulation range, the magnetic field design of variable frequency motors should be further optimized to suppress higher harmonic magnetic fields and maximally meet the requirements for wide frequency, energy saving, and low noise. Especially for the selection of frequency converters, it should be combined with the actual operating conditions and matched with suitable high-quality frequency converters.