How to Choose a Suitable Inverter for Asynchronous Motors?

For the inverter with higher frequency of asynchronous motor, it should be considered according to the type of control object, speed regulation range, static speed accuracy, starting torque, etc., so that it is easy to use and economical while meeting the process and production requirements. For asynchronous motors, the first thing to consider when choosing a suitable inverter is the type of load. The types of loads are mainly divided into three types:

1. Constant torque load conditions: such as conveyor belts and mixers; when the inverter drives a constant torque load, the torque at low speed should be large enough and the overload capacity is large enough. If stable operation at low speed is required, the standard asynchrony of the heat dissipation capacity of the motor should be considered to prevent the motor temperature from rising too high.

2. Constant power load and fan: machine tool spindle, rolling mill, paper machine; if the constant torque of the motor matches the constant power speed regulation range, that is, in the case of so-called "matching", the capacity of the motor and the capacity of the inverter are both minimum.

3. Water pump capacity: fan, water pump, oil pump. When the required air volume and flow rate are reduced, the use of the frequency converter to adjust the wind power and flow rate by means of speed regulation can greatly save electricity. Knowing the type of load, the selection of frequency conversion should be based on the following points:

(1) The number of poles of the motor. Generally, the number of motor poles should not be less than 4, otherwise the capacity of the inverter will be appropriately increased.

(2) When selecting the inverter, the current value of the actual motor should be used as the basis for selection, and its rated power should be used as a reference.

(3) Each inverter manufacturer has fan, water pump inverters, such as Siemens, ABB, Fuji, etc. If the specification and model of the motor are determined, the specification and model of the inverter can be basically determined (brand comparison).

(4) When the frequency converter drives the submersible pump motor, since the rated current of the submersible pump motor is greater than the rated current of the usual motor, when the frequency converter is selected, its rated current should be greater than the rated current of the submersible pump motor.

(5) When the frequency converter controls the Roots blower, because its starting current is very large, it is necessary to pay attention to whether the capacity of the frequency converter is large enough when selecting the frequency converter.

(6) If the long-line cable of the inverter is required to run, measures should be taken to suppress the influence of the long-line cable on the ground connection, so as to avoid insufficient output of the inverter. Therefore, the inverter should be enlarged by a grade, and an output reactor should be selected or installed at the output end of the inverter. (7) When the inverter is used to control several motors in parallel, it must be considered that the cable length from the inverter to the motor and the capacity of the inverter are within the easy range. If it exceeds the specified value, enlarge the first and second gears to select the inverter. In addition, in this case, the control mode of the inverter can only be V/F control mode (fan, water pump load), and the inverter cannot protect the overcurrent and overload protection of the motor. fuse for protection.

(8) When selecting an inverter, be sure to pay attention to whether its protection level matches the situation on site. Otherwise, on-site dust, water vapor, etc. will affect the long-term operation of the inverter.

(9) If it is used for vector closed-loop control, the inverter and the motor must be matched, neither too large nor too small. For heavy loads, the heavy-duty type can be selected.