Selecting the right frequency converter is a frequent question for our technicians and sales quoting personnel. Below, we summarize some methods and approaches based on practical experience.
The primary factors to consider include: brand, power, current, voltage, load (i.e., the equipment driven by the motor), and application. Additionally, some optional accessories should be considered during selection, such as whether the control panel needs to be purchased separately, and whether filters, reactors, braking resistors, and braking units are required. Some specialized equipment requires dedicated frequency converters. For example, injection molding machines, elevators, and textile mills often benefit from using dedicated frequency converters.
Brand selection is crucial, whether considering business or technical aspects. There are hundreds of brands on the market, with ABB, Siemens, and Schneider being the most popular imported brands. I'll briefly introduce some inverter brands: European and American brands include ABB, Siemens, Schneider, VK, SEW, AB, Danfoss, Emerson, Eaton, and Lenze; Japanese and Korean brands include Fuji, Yaskawa, Mitsubishi, Omron, Toshiba, Sanken, Hitachi, Panasonic, Samsung, Delta Electronics (Taiwan), Teco; and domestic brands include Huichuan, Invt, Leadway, Puchuan, Sanjing, Orui, Siasun, Kangwo, Blue Ocean Huateng, Panier, Senlan, and Zhengxian, among others.
Common power ratings for frequency inverters are 0.75KW, 1.5KW, 2.2KW, 3.7KW, 5.5KW, 7.5KW, 11KW, 15KW, 18.5KW, 22KW, 37KW, 45KW, 55KW, 75KW, 90KW, 110KW, 132KW, 160KW, 185KW, 200KW, 220KW, 250KW, 285KW, and 312KW. 55kW inverter models are generally defined by power rating, such as Siemens 6SE6430-2UD33-0DB0, which is a 30kW inverter. However, ABB models are defined by current rating, such as ACS510-01-046A-4, which is a 46A 22kW inverter. It's worth noting that control panels for imported brands need to be purchased separately; the inverter price does not include the control panel, while domestic inverters generally include it. Generally, the motor's power is the basis for selecting the inverter's power rating. However, it's important to note that the actual motor current should be the primary factor in inverter selection; the motor 's rated power is only a reference. For applications involving fans and pumps with relatively small loads, inverter manufacturers typically offer dedicated series. Domestic manufacturers generally use the P series, while imported brands like ABB typically use ACS510, Siemens 430, Schneider ATV61, etc. For special applications with large loads, a higher-rated inverter is usually required.
Here are some selection principles:
1. Select the frequency converter according to the load characteristics. For example, if the load is a constant torque load, you can choose Siemens MM440 frequency converter, ABB ACS800 series frequency converter, etc.; if the load is a fan or pump type load, you can choose Siemens MM430 frequency converter, ABB ACS510 series frequency converter, etc.
2. When selecting a frequency converter, the actual motor current value should be used as the basis for selection; the motor's rated power should only be used as a reference. Secondly, it should be fully considered that the frequency converter's output contains high-order harmonics, which will degrade the motor's power factor and efficiency.
3. If the frequency converter is to be operated with a long cable, the frequency converter should be selected with a larger range or an output reactor should be installed at the output end of the frequency converter.
4. When a frequency converter is used to control several motors connected in parallel, the total length of the cables from the frequency converter to the motors must be within the allowable range of the frequency converter.
5. For some special applications, such as high ambient temperature, high switching frequency, and high altitude, the inverter's capacity may be reduced, and the inverter needs to be selected with a larger capacity.
6. When selecting a frequency converter for a high-speed motor, it should be slightly larger than that for a regular motor.
7. When using a frequency converter for a pole-changing motor, careful attention should be paid to selecting the capacity of the frequency converter so that its maximum rated current is below the rated output current of the frequency converter.
8. When driving an explosion-proof motor, if the frequency converter does not have an explosion-proof structure, the frequency converter should be installed outside the hazardous area.
9. When using a frequency converter to drive a geared motor, the operating range is limited by the lubrication method of the rotating gear parts. Do not exceed the maximum permissible speed.
10. When a frequency converter drives a wound-rotor asynchronous motor, it often utilizes an existing motor. Overcurrent tripping due to ripple current is prone to occur, so a frequency converter with a slightly larger capacity than usual should be selected.
11. When a frequency converter drives a synchronous motor, the output capacity is reduced by 10% to 20% compared with a power frequency power supply.
12. For loads with large torque fluctuations, such as compressors and vibratory machines, and for loads with peak loads, such as hydraulic pumps, the operating frequency should be understood, and a frequency converter with a rated output current greater than its maximum current should be selected.
13. When a frequency converter controls a Roots blower, the starting current is very large, so when selecting a frequency converter, it is important to ensure that the capacity of the frequency converter is large enough.
14. When selecting a frequency converter, be sure to pay attention to whether its protection level matches the site conditions.
15. Single-phase motors are not suitable for inverter drives. Even with a high-reliability inverter itself, if the inverter selection and capacity are not properly matched, the resulting variable frequency speed control system cannot achieve high reliability and may even fail to operate. So how can we ensure the normal and efficient operation of the variable frequency control system? We must ensure the inverter's capacity is matched. First, select the correct inverter type based on the load characteristics.
The general principle is to match the frequency converter with the appropriate characteristics for the load.
(1) Constant torque production equipment – Within the speed regulation range, the load torque remains essentially constant. A frequency converter with constant torque performance should be selected. Its overload capacity is 150% of the rated current for 1 minute.
(2) Square torque production equipment - within the speed regulation range, the load torque is proportional to the square of the speed, i.e., M∝n2. Centrifugal fans and water pumps are typical examples. Inverters with the M∝n2 characteristic have a relatively small overload capacity, capable of withstanding 110%-120% of the rated current for 1 minute.
(3) Constant power load production equipment - within the speed regulation range, the speed is low and the torque is high; the speed is high and the torque is low. Typical equipment includes machine tools and winding mechanisms.
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