Variable frequency speed regulation can be applied to most motor driving occasions, because it can provide accurate speed control, so it can easily control the lifting, lowering and variable speed operation of mechanical transmission. The application of frequency conversion can greatly improve the efficiency of the process (speed change does not depend on mechanical parts), and at the same time it is more energy-saving than the original fixed-speed motor. The following are the reasons why 10 uses variable frequency speed regulation to illustrate the basic understanding of the increasingly popular application of frequency converters:
(1) controls the starting current of the motor. When the motor is started directly through the power frequency, it will generate 7 to 8 times the rated current of the motor. This current value will greatly increase the electrical stress of the motor winding and generate heat, thus reducing the life of the motor. Variable frequency speed regulation can start at zero speed and zero voltage (or increase the torque appropriately). Once the relationship between frequency and voltage is established, the inverter can drive the load according to V/F or vector control mode. Adopting frequency conversion speed regulation can fully reduce starting current and improve winding durability. The most direct benefit to users is that the maintenance cost of the motor will be further reduced and the life of the motor will be correspondingly improved.
(2) Reduce the voltage fluctuation of power lines. When the motor starts at power frequency, the current will increase sharply and the voltage will fluctuate greatly. The degree of voltage drop will depend on the power of starting motor and the capacity of distribution network. Voltage drop will cause voltage sensitive equipment in the same power supply network to trip or work abnormally, such as PC, sensor, proximity switch and contactor. After adopting variable frequency speed regulation, the voltage drop can be eliminated to the greatest extent because it can be started step by step with zero frequency and zero voltage.
(3) The power required for starting is low. The power of the motor is directly proportional to the product of current and voltage, so the power consumed by the motor directly started at power frequency will be much higher than the power required for variable frequency starting. Under some working conditions, the power distribution system has reached the highest limit, and the surge generated by starting the motor directly at the power frequency will have a serious impact on other users in the same network, and will be warned or even fined by the power grid operator. If the inverter is used to start and stop the motor, similar problems will not occur.
(4) controllable acceleration function. Variable frequency speed regulation can start from zero speed and accelerate evenly according to the needs of users, and its acceleration curve can also be selected (linear acceleration, S-shaped acceleration or automatic acceleration). However, when it is started by power frequency, it will cause severe vibration to the shaft or gear of the motor or the connected mechanical part. This kind of vibration will further aggravate the mechanical wear and loss and reduce the life of mechanical parts and motors. In addition, frequency conversion start-up can also be applied to similar filling lines to prevent bottles from falling over or being damaged. (5) The running speed is adjustable. The application of frequency conversion speed regulation can optimize the process. According to the rapid change of the process, the speed change can be realized by remote control PLC or other controllers.
(6) Adjustable torque limit. After variable frequency speed regulation, the corresponding torque limit can be set to protect the machinery from damage, thus ensuring the continuity of the process and the reliability of the product. The current frequency conversion technology not only makes the torque limit adjustable, but also the torque control accuracy can reach about 3% ~ 5%. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, and it cannot be operated by setting an accurate torque value like frequency conversion control.
(7) Controlled stop mode. Just like controllable acceleration, in variable frequency speed regulation, the stop mode can be controlled, and there are different stop modes to choose from (deceleration parking, free parking, deceleration parking +DC braking). Similarly, it can reduce the impact on mechanical parts and motors, thus making the whole system more reliable and prolonging its service life accordingly.
(8) Energy-saving centrifugal fan or water pump can greatly reduce energy consumption after adopting frequency converter, which has been reflected in more than ten years of engineering experience. Because the final energy consumption is faster than the motor speed after frequency conversion.
(9) Reversible operation control In inverter control, no additional reversible control device is needed to realize reversible operation control, only the phase sequence of output voltage needs to be changed, which can reduce maintenance cost and save installation space.
(10) Reduce mechanical transmission parts.