Soft starters and frequency inverters are two completely different products with different purposes.
A frequency inverter is used in applications that require speed control, where its output not only changes the voltage but also the frequency.
On the other hand, a soft starter is essentially a voltage regulator used during motor starting, modifying its output voltage without changing the frequency.
While a frequency inverter includes all the functions of a soft starter, it is significantly more expensive and structurally more complex.
WORKING PRINCIPLE OF SOFT STARTERS
Typical soft starters use six thyristors or controllable silicon rectifiers arranged in a reversed parallel connection to start the motor smoothly by controlling the firing angle of the three-phase reversed parallel connection.
The thyristor consists of three parts: a gate (control electrode), a cathode, and an anode. When an internal pulse is applied to the gate, it allows current flow from the anode to the cathode, then supplying the current to the motor.
When no internal pulse is applied to the gate, the thyristor is in the off state, limiting the current flow to the motor. These internal pulses limit the voltage applied to the motor, gradually slowing down the starting current. The pulses are sent according to the ramp-up time, so that the current is gradually applied to the motor. The motor connected to the soft starter starts smoothly with a constant current and reaches maximum speed. The motor maintains that speed. The stopping process is similar to the starting process.
Vergleich zwischen Frequenzumrichtern und Softstartern
Characteristics of soft starters:
- Enables smooth motor starting and deceleration.
- Minimizes impact on the power grid.
- Smaller and easier to install compared to star-delta starters.
Characteristics of frequency inverters:
- Includes most functions of soft starters.
- Provides more protection and control features.
- Used in applications that require speed control and constant voltage variation.
WHAT TO CHOOSE: SOFT STARTER OR FREQUENCY INVERTER?
How can we determine which device our application requires? The choice depends on how you want to control your application. If your application requires smooth starting but no speed control, then a soft starter is the best choice. If speed control is required, a frequency inverter must be used.
In addition, price can be a deciding factor in many practical applications. Due to the fewer control functions, soft starters are priced lower than frequency inverters. Finally, a soft starter is typically smaller than most frequency inverters if equipment size is a critical factor.
Further information on frequency converters can be found on our frequency converter page.
Discover our 230V frequency converter and 400V frequency converter for specific applications
