Think of the frequency converter as a power supply. In some rigidly connected systems, the motor that runs slightly faster will have a heavier load; while the motor that runs slightly slower will have a lighter load. However, because the same inverter is driven, the slip of the load is increased, and the slip of the load becomes smaller. This will have a certain automatic correction capability, which will eventually keep the motors running synchronously, but the load distribution. It is not uniform. Generally, the motor power should be amplified by one level when selecting the motor.
Pay attention to the following problems when one inverter supplies multiple motors at the same time.
The power of the motor can not be too different, generally do not differ by more than two power levels.
The motor is preferably manufactured by the same manufacturer. If it is a motor of the same power, it is better to use the same batch to ensure the consistency of the motor characteristics, and to maximize the slip of the motor (the difference between the rotating magnetic field speed of the stator and the rotor speed). ) Consistent to ensure good synchronization performance.
Full consideration of the length of the motor cable, the longer the cable, the greater the capacitance between the cables or between the cable and the ground, the output voltage of the inverter is rich in high-order harmonics, so the high-frequency capacitor ground current will be formed, the inverter The impact of the operation.The length of the cable is calculated as the total length of all cables connected to the frequency converter. Ensure that the total length of the cable is within the range allowed by the drive. If necessary, an output reactor or output filter should be installed at the output of the inverter.
The inverter can only work in V/F control mode (relative to vector control mode) and select the appropriate V/F curve. The rated operating current of the inverter should be greater than 1.2 times the sum of the rated currents of all motors.
In order to protect the motor, a thermal relay should be installed in front of each motor. It is not recommended to install an air switch. In this way, the main circuit can be disconnected when the motor is overloaded, and the influence on the inverter itself when the main circuit is disconnected during the operation of the inverter can be avoided.
For applications requiring fast braking, in order to prevent overvoltage when stopping, the brake unit and braking resistor should be added; some low-power inverters have a built-in braking unit, so only the braking resistor can be connected.