The difference between a soft starter and a inverter

- Jul 16, 2019-

Frequency Inverter:


The ac current converter that transforms the voltage and the frequency fixed into the voltage, and the AC with variable frequency is called the inverter. Function: reduce the impact load caused by the motor start, control the motor speed, extend the start-up time, flatten the current, to achieve the purpose of soft start, but also improve the efficiency of the power grid and motor. In fact, the inverter is mainly used in energy saving, through regulation, change the output voltage, current, frequency. The motor of the general speed control calculation uses the inverter.


1. High cost, the price is much more expensive than the protection of microcomputers.

2. Because the current inverter almost all use PWM control mode, such a pulse modulation form makes the drive running in the power supply side to produce a high harmonic flow, and cause voltage waveform distortion, the power system by harmonic pollution, light affect the operating efficiency of the system, heavy damage to the equipment and even endanger the safe operation of the power system. 3. Overload makes the inverter beat more frequently, usually there has been a load phenomenon, generally speaking, the motor due to overload capacity is strong, as long as the inverter parametertable motor parameters set properly, generally not likely to appear motor overload, and the inverter itself due to poor overload capacity is easy to have an alarm. 

Soft starter:

Definition and role

Interlink between the power supply and the charged motor, through the micro-computer control its internal thyristor trigger through the on-angle to achieve AC voltage control, so that the motor incoming voltage from zero to preset function relationship gradually rise, until the end of the start, give the motor full voltage, that is, soft start, in the soft start ingress process, the motor starting torque gradually increased, The speed is gradually increased until the thyristor is fully on and the motor is operated on the mechanical properties of the rated voltage, enabling smooth start-up and reducing the start-up current. Avoid starting overcurrent tripping. The start-up process is completed when the motor reaches the rated number of revolutions, providing the rated voltage for the normal operation of the motor.


1. Can not adjust the power frequency, so can not start the motor from zero pressure zero frequency, can not achieve zero impact start.

2. Cannot speed up. 3. The soft starter exits the system after starting the motor and loses its protection function.



1. The inverter is used where the speed adjustment is needed, and the output of the drive not only changes the voltage but also changes the frequency at the same time.

2. Soft starter is actually a regulator, the motor plays a protective role, for the motor buck start-up soft starter output only changes the voltage does not change the frequency.

3. The drive has all the functions of the soft starter, but its structure is complex and the price is much more expensive than the soft starter.

4. The inverter is used to control the use of electrical equipment by adjusting the frequency, which can be adjusted and started, such as the inverter pump for industrial use. The basic principle of soft start is to change the resistance of the thread in the circuit, so that the current from small to large, such a way to start the high-power motor, used to reduce the high-power motor direct start-up to the grid caused fluctuations, or cause some unimportant load unloading trouble.