What are the differences and links between the soft starters and the frequency converters, and their respective principles and uses?
The soft starter is activated by adjusting the voltage and current, and the frequency converter starts the motor by changing the frequency of the power supply. The soft starter can theoretically smooth and gradually start the motor to the maximum speed. No impact current (ordinary start-up current is 6-7 times the rated current) The inverter is best suited for tap water and fans, etc. The soft starter is not suitable for everything except for heavy load start.
The frequency changer mainly consists of rectifying (alternating current direct current), filtering, re-rectifying (direct current alternating current), braking unit, driving unit, detecting unit micro-processing unit and so on. Motor asynchronous speed expression bit:
N = 60 f (1-s) / p (1)
Where n --- the speed of asynchronous motor; f --- the frequency of asynchronous motor; s --- motor slip; p --- motor pole pairs.
From the formula (1) we can see that the output speed of the motor is related to the input power frequency, slip rate and the number of pole pairs of the motor. Therefore, the direct speed regulation mode of AC motor mainly has variable speed (adjustment P), rotor Resistance speed control or cascade speed or internal feedback motor (adjust s) and frequency control (adjust f) and so on.
And we now use the most widely used is the frequency control, from the speed n is proportional to the frequency f, as long as the change in frequency f can change the motor speed, when the frequency f in the range of 0 ~ 50Hz, the motor speed adjustment range is very width. The inverter is to change the motor power frequency to achieve speed adjustment, is an ideal high efficiency, high performance speed control means.
Soft starters and frequency converters are two completely different uses of the product. The frequency converter is used for the need for speed control where the output not only changes the voltage but also changes the frequency; the soft starter is actually a voltage regulator for the motor to start when the output only changes the voltage and does not change the frequency. The frequency converter has all the soft starter functions, but its price is much more expensive than the soft starter, the structure is much more complex. Soft starter (soft starter) is a set of motor soft start, soft stop, light load energy saving and a variety of protection functions in one of the new motor control device, known as the Soft Starter abroad. The softener uses a three-phase anti-parallel thyristor as a voltage regulator, which connects it between the power supply and the motor stator. This circuit, such as three-phase full-bridge rectifier circuit. When using the soft starter to start the motor, the output voltage of the thyristor gradually increases, the motor gradually accelerates until the thyristor is fully conductive, the motor works at the mechanical characteristics of the rated voltage, smooth start, reduce the starting current and avoid starting the overcurrent trip. When the motor reaches the rated speed, the start-up process ends, the soft starter automatically uses the bypass contactor to replace the completed thyristor, providing the rated voltage for the normal operation of the motor to reduce the heat loss of the thyristor and prolong the service life of the soft starter , To improve its efficiency, but also to avoid the harmonic pollution to the grid. Soft starter also provides soft stop function, soft stop and soft start the process of reverse, the voltage gradually reduced, the number of revolutions gradually reduced to zero, to avoid free-wheeling caused by the impact of torque. How the frequency converter works
