With a car, we still have to ride a motorcycle electric car or bicycle; with air conditioning, we still have to blow the fan, and occasionally find a fan to do it yourself twice. There are so many examples of this, and one product may not be able to meet all application needs. Although the inverter is powerful, but the soft starter also has its strengths, even on many occasions, is currently using the traditional star triangle start-up.
The main purpose of the design of the inverter is to adjust the speed of the AC asynchronous motor, that is, the so-called speed control use, so that the motor works in different speed segments, to meet the work requirements of the equipment, the factory to buy the inverter, mainly for this. Because the inverter to adjust the speed, this process needs to fm and pressure, so the need to use expensive IGBT and other power devices to achieve, and the chopping inverter output control is more complex, the requirements of the componentisis is very high, but also involves complex calculation algorithms. These factors determine that the price of the inverter is bound to be much more expensive than other products.
In addition to the speed control function, of course, can also achieve the so-called soft start function, the white is to allow the motor to gradually increase the speed according to a certain curve, this time period can be artificially set, the process is focused on bucking start, because the motor start-up current will be much larger than normal current, If a very high voltage is applied at once, the current is too big, not only will impact the grid, affect the transformer, but also may have adverse effects on motor bearings and other components, so the start time to let the voltage a little lower, can slowly go up, you can avoid these problems.
And soft starter, even contactors to achieve the star triangle start, only designed the function of buck start, they do not have the so-called speed control function, so the structure is simple, the requirements of the component is not high, the soft starter is a SCR silicon regulator, no FM function, but sometimes simple is also a force.
Many equipment just need the motor start-up current small point, and after the start-up is completed, switch to frequency, this occasion the use of inverters to cause waste, completely unnecessary, the use of cheap soft starter, even if broken, also easy to repair, the overall maintenance costs are low, in addition to Theu-Hao, who will not care about "money" it. For example, 160KW soft starter, about 3000 yuan, and the same 160KW inverter, the price of about 13,000, is 4 times the price, of course, small power inverter and soft starter price is not much difference, which is why rarely meet the root cause of small power soft starter.
Some occasions should not use inverters: the inverter is not the output of real sine waves, but through the PWM chopping inversion output of a series of square waves, the power grid and equipment interference is relatively large. And the use of SCR pressure-regulating soft starter, start-up time does not bring interference, the operation of the motor in the frequency, will not produce any adverse effects. If the motor is just to start a bit, and the scene has a lot of expensive instruments, the use of inverters may affect the operation of these instruments, so-called money and not flatter.
Inverter generally should not be in the output contactors and other devices to switch, mainly the inverter control is too complex, when the motor switch, may cause the motor idling time phase and the phase of the inverter output is very different, switching time to produce a relatively large impact, the inverter's IGBT life will have an impact. And the soft starter itself design is to consider switching, will pay attention to these details, the use of some phase-locking ring technology to track, etc. , is no such function, because scrare is cheap and reliable, can use high pressure-resistant silicon to make up, and IGBT is too expensive, the inverter generally does not consider switching to the application of frequency, Therefore, these sites may be more ideal for soft starters than inverters.