The inverter achieves the purpose of step-down startup by changing the frequency.
Supplementary knowledge comparison 1: Soft starter and inverter Inverter and soft start device belong to the category of buck start. The inverter achieves the purpose of step-down start by changing the frequency. The soft start is to start the process from voltage 0 to full voltage by changing the conduction angle of the thyristor.
The inverter is fully controlled, and the motor speed can be controlled by the instrument signal at any time. The soft starter can only be used for step-down when the motor starts and stops. 2: Motor starting mode Large analogy motor starting method: full pressure direct start, auto-decompression start, Y-Δ start, soft start, variable frequency start, etc. In the case where both the grid and the load are allowed, the motor is preferably started directly because the steering control is convenient and economical. Auto-coupling decompression is often used to start larger-capacity squirrel-cage asynchronous motors. Although auto-coupling decompression is an old-fashioned starting device, multi-tap decompression using autotransformers can accommodate multiple loads. The need for starting, but also to get a larger starting torque, coupled with the installation of thermal relays and low voltage trips with perfect overload and loss of pressure protection is widely used. The star-delta starting mode has good current characteristics and poor torque characteristics, so it is only suitable for occasions with no load or light load starting, but this method is the simplest and the cheapest, and can save power consumption in light load operation. All of the above starting methods belong to the staged decompression starting, and there are obvious disadvantages, that is, secondary inrush current occurs during starting. 3: Comparison between soft start and traditional decompression start mode
1. No inrush current. When the soft starter starts the motor, the motor starting current is linearly increased from zero to a set value by gradually increasing the conduction angle of the thyristor. No impact on the motor, improve the reliability of power supply, start smoothly, reduce the impact torque on the load machine, and extend the service life of the machine. 2, there is a soft parking function, that is, smooth deceleration, and gradually stop, it can overcome the shortcomings of instantaneous power failure, reduce the impact on heavy-duty machinery, avoid the water hammer effect of the elevation water supply system, and reduce equipment damage. 3. The starting parameters are adjustable. According to the load condition and the power relay protection characteristics, it can be adjusted steplessly to the optimal starting current.
Soft starters and frequency converters are two completely different applications. The frequency converter is used for speed adjustment. The output not only changes the voltage but also changes the frequency. The soft starter is actually a voltage regulator for motor starting. At the time, the output only changes the voltage and does not change the frequency.
The frequency converter has all the soft starter functions, but it is much more expensive than the soft starter and the structure is much more complicated.
