G series YVP/YVF variable-frequency variable-speed three-phase asynchronous motor is a special asynchronous motor applicable to the operation of variable-frequency variable-speed system powered by frequency converter. It can realize stepless speed regulation of cage-type three-phase asynchronous motor. It has the mechanical characteristics of low-speed constant torque output and high-speed constant power output. It has the advantages of compact structure, good speed regulation performance and obvious energy-saving effect, and can be widely used in machinery, building materials Beverage and other industries generally need power machinery matching occasions with speed regulation. It can be used for open-loop or closed-loop control, and can also be interfaced with computer control to realize automatic control. It is an ideal product for stepless speed regulation of AC motors.
The electromagnetic design of the characteristics of the permanent variable frequency motor:
For ordinary asynchronous motors, the main performance parameters to be considered during redesign are overload capacity, starting performance, efficiency and power factor. As the critical slip is inversely proportional to the power frequency, the variable-frequency motor can be started directly when the critical slip is close to 1. Therefore, the overload capacity and starting performance need not be considered too much. The key problem to be solved is how to improve the adaptability of the motor to non-sinusoidal power supply.
The methods are generally as follows:
1) Reduce stator and rotor resistance as much as possible.
Reducing the stator resistance can reduce the fundamental copper loss to compensate for the increase of copper loss caused by higher harmonics
2) In order to suppress the high order harmonics in the current, it is necessary to properly increase the inductance of the motor. However, the rotor slot leakage reactance is large and its skin effect is also large, and the copper loss of higher harmonic is also increased. Therefore, the size of motor leakage reactance should take into account the rationality of impedance matching in the entire speed range.
3) The main magnetic circuit of the variable-frequency motor is generally designed to be in an unsaturated state. One is to consider that higher harmonics will deepen the magnetic circuit saturation, and the other is to consider that at low frequency, the output voltage of the converter is appropriately increased in order to improve the output torque.
2. Structural design
In the structural design, the influence of non-sinusoidal power supply characteristics on the insulation structure, vibration, noise cooling mode and other aspects of the variable frequency motor is also mainly considered, and the following issues are generally noted:
1) The insulation grade is generally F or higher, and the strength of ground insulation and wire turn insulation should be strengthened, especially the ability of insulation to withstand impulse voltage.
2) For the vibration and noise of the motor, the rigidity of the motor components and the whole shall be fully considered, and its natural frequency shall be increased as much as possible to avoid resonance with each force wave.
3) Cooling mode: forced ventilation cooling is generally adopted, that is, the cooling fan of the main motor is driven by an independent motor.
4) Measures to prevent shaft current: bearing insulation measures shall be taken for motors with capacity more than 160KW. The main reason is that it is easy to produce magnetic circuit asymmetry and shaft current. When the current generated by other high-frequency components acts together, the shaft current will increase greatly, resulting in bearing damage. Therefore, insulation measures should be taken generally.
5) For constant power variable frequency motors, when the speed exceeds 3000/min, special grease with high temperature resistance shall be used to compensate for the temperature rise of bearings.