There are many ways to classify frequency converters, which can be divided into voltage-source frequency converters and current-source frequency converters according to the working mode of the main circuit. According to the switching mode, it can be divided into PAM controlled inverter, PWM controlled inverter and high carrier frequency PWM controlled inverter; According to the working principle, it can be divided into V/f control inverter, slip frequency control inverter and vector control inverter. According to the classification of uses, it can be divided into general frequency converters, high-performance special frequency converters, high-frequency converters, single-phase converters and three-phase converters.
Simply put, frequency converters are divided into general frequency converters, high-performance frequency converters and special frequency converters according to their uses. The special inverter can only use fans and pumps.
The selection of frequency converter needs to be matched with the rated input voltage, rated output power and frequency adjustment range according to the series of technical parameters of the load motor it drives.
The selection of inverter should first be considered from the evaluation of performance-price ratio. When choosing a frequency converter, don’t think that the higher the grade, the better. Instead, choose a suitable frequency converter according to the characteristics of the drag load to meet the use requirements, so as to use it in quantity and be economical. If the general frequency converter can meet the use requirements, it is not necessary to adopt a high-performance frequency converter. However, for some very important occasions where downtime is not allowed, even if the price is higher, you should choose a frequency converter with good performance, high reliability and difficulty in failure.
The selection of frequency converter should be based on the drive motor capacity and load characteristics.
The general frequency converter sets the driving motor capacity according to the 4-pole motor. Therefore, with different motor poles and different load characteristics, the selected inverter model and capacity are also different. If the motor is not a 4-pole motor, check whether the selected frequency converter is suitable according to the current.
The capacity selection of frequency converter is closely related to whether the capacity of motor can be fully utilized. If the capacity of the inverter is too small, the power of the motor will not be fully exerted; On the contrary, if the capacity of the inverter is too large, the margin of the inverter becomes meaningless and unnecessary investment is increased.
Correct selection of inverter working system. Inverter is composed of semiconductor devices, etc. The heating time constant of semiconductor devices is small (usually measured in minutes), and overload and overtemperature have a serious impact on them. Therefore, strict load conditions, basic load current, overload current, duration and frequency (interval time to allow overcurrent reproduction) are usually stipulated for semiconductor power electronic devices.
The working level of frequency converter is divided into 6 levels according to the different operating conditions and load conditions.
Level 1: Rated output current, no possibility of overload.
Level 2: Allow the output of basic load current, and on this basis, there can be 150%.
The load characteristics and load torque characteristics of mechanical equipment should be considered when selecting frequency converter; For example, load characteristics are divided into: friction load, gravity load, fluid load and inertia load; Load torque characteristics are divided into: constant torque, constant power, torque reduction, power reduction and square torque. The above table is an example of selecting a frequency converter according to the load torque characteristics.