How To Correctly Select A Frequency Inverter

The correct selection of a frequency converter should be based on load characteristics and current matching, while also taking into account operating conditions and the environment. Proper frequency converter selection directly affects the equipment's operating performance, stability, and lifespan. Choosing the wrong model can not only affect performance but also potentially damage the equipment.

Step 1: Determine Load Type and Control Requirements

1. Fans and Pumps: Load torque is proportional to the square of the speed. Requirements for speed regulation accuracy and dynamic response are usually not high.

A dedicated fan/pump inverter or a general-purpose inverter can be selected, typically matched to the motor power in a 1:1 ratio.

2. Constant Torque Loads: At any speed, the torque required by the load is essentially constant. The inverter must output sufficient torque even at low frequencies.

A heavy-duty or vector control inverter must be selected, and the capacity may need to be increased by one level.

3. Constant Power Loads: The power required by the load is essentially constant, and torque is inversely proportional to speed.

A vector control inverter capable of field weakening speed regulation must be selected, often combined with a braking unit and braking resistor to dissipate regenerative energy.

Step 2: Determine Motor Parameters

1. Rated Power: The rated power of the inverter should be ≥ the rated power of the motor. For heavy loads, special loads, or applications requiring high overload capacity, it is recommended to increase the capacity by one level.

2. Rated Voltage: 380V (commonly used in domestic industry), 220V (single-phase/low power), 660V/1140V (medium/high voltage). The inverter's input and output voltage ratings must match the motor.

3. Rated Current: The inverter's rated output current must be greater than or equal to the motor's rated current. Motors have poor heat dissipation at low speeds, and the current may be higher; therefore, ensure the inverter has a certain current margin.

4. Number of Poles/Rated Frequency: Typically 50Hz or 60Hz.

Step 3: Consider Special Applications and Operating Conditions

1. High Altitude (>1000m) or High Temperature (>40℃)
Thin air/high temperature reduces heat dissipation, requiring the inverter to be derated. Select an inverter with a capacity one level higher.

2. Long Distance Between Motor and Inverter (>50 meters)
Long cables may cause overcurrent and insufficient output due to ground capacitance. Increase the inverter capacity one level or add an output reactor on the output side.

3. High Load Inertia or Frequent Braking
Large amounts of regenerative energy are generated during deceleration, potentially causing overvoltage faults in the inverter. Add a braking unit and braking resistor to the inverter.

4. Poor Power Quality
Large voltage fluctuations may damage the inverter's rectifier unit. Add an input reactor or AC reactor on the inverter's input side.

Step 4: Assess the Installation Environment and Peripheral Configuration

1. Installation Environment: Ensure that ambient temperature, humidity, dust, corrosive gases, vibration, etc., meet the specifications in the user manual. In harsh environments, select a cabinet with a higher protection rating.

2. Peripheral equipment: To ensure system reliability, circuit breakers, contactors, filters, etc. are often required.