AC motor gear variable or frequency conversion good?What are the disadvantages?
Each has its advantages and disadvantages.The gear case, can only be very variable, only a few or dozens of fixed speed, cost, is not very high, but when the gear there is the problem of the transmission gear must be stopped, otherwise it will damage the gear structure. But one of the great advantages of gear reduction is that the power is small and the value is very small. Only mechanical structural friction losses. That is, great torque can be gained after slowing down.
The advantages of variable frequency speed control is that a wide range of stepless speed regulation can be achieved within a range of any speed, at the time of transmission, the motor does not need to stop. Now the price of converter is not very high. But there are disadvantages, the reliability of electronic products is much worse than the reliability of mechanical products, even the normal operation is also prone to problems. And when there is a problem that the speed of the speed in the rated speed is a constant torque speed regulation process, that is to say its speed down, while torque did not change, the output power is motor becomes small. The device will not work on certain load characteristics. At this time, it is necessary to use the gear change structure to speed down at a high speed, then decelerate under the gear change mechanism to obtain large power.
Frequency converter selection:When choosing the frequency converter, we should make sure the following points:1) adopt the purpose of frequency conversion, constant voltage control or constant current control, etc..2) the load type of frequency converter, such as vane pump or displacement pump, etc. pay particular attention to the performance curve of the load, and the performance curve determines the mode and method of application.3) matching of frequency converter and load;I. voltage matching; the rated voltage of the converter is in line with the rated voltage of the load.II. current matching; the ordinary centrifugal pump, the rated current of the converter is in line with the rated current of the motor. For special loads, such as deep water pumps, it is necessary to refer to the motor performance parameters and determine the current and overload capacity of the inverter with maximum current.III. torque matching; this may occur when a constant torque load or a deceleration device is applied.4) when the high speed motor is driven by a transducer, the higher the higher harmonic is, the higher the output current value is due to the small reactance of the high speed motor. Therefore, the type selection of frequency converter used in high speed motor is slightly larger than the selection of ordinary motor.5) if you want a long cable converter operation, this time to take measures to curb the influence of long cable on the coupling capacitor, to avoid the shortage of inverter output, so in this case, the frequency converter to enlarge the capacity of a file or install the output reactor in the inverter output.6) for some special applications, such as high temperature, high altitude, at this time will cause the inverter to reduce capacity, frequency converter capacity to enlarge a block.
The frequency converter is the electric energy control device that transforms the power frequency power to another frequency by the on-off function of the power semiconductor device. We now use the converter mainly adopts the AC-DC-AC mode (VVVF inverter or variable frequency vector control), the first AC power into DC power supply through the rectifier, then the AC power into DC power supply frequency and voltage can be controlled by the supply of electric motive. The frequency converter circuit is usually composed of rectifier, intermediate DC link, inverter and control of 4 parts. The rectifier is a three-phase bridge controlled rectifier, and the inverter is IGBT three-phase bridge inverter, and the output is PWM waveform. The intermediate DC link is filter, DC energy storage and buffer reactive power.
