The difference between soft starter and frequency converter

Soft starters and frequency converters are two widely used devices in the industrial control field. The following will explain the differences between soft starters and frequency converters:1. The control principles of soft starters and frequency converters are differentThe soft starter is actually an excessive control device, which is an industrial control product between the star triangle starting device and the frequency converter. Its functions are more than those of the star triangle starting device, but less than those of the frequency converter. From the perspective of the main circuit of the soft starter, it is a three-phase anti parallel thyristor connected in series between the power supply and the controlled motor. Then, the internal digital circuit controls the moment when the thyristor conducts within a complete sine waveform of AC power. If the thyristor is allowed to conduct at the beginning of an AC cycle, the output voltage of the soft starter is high. If the thyristor is allowed to conduct at a certain position in an AC cycle, So the voltage output by the soft starter is low. We use this method to gradually increase the voltage at the motor end during the starting process, thereby controlling the starting current and torque of the motor to achieve a smooth start. It can be seen that the soft starter can only change the voltage of the power supply, not the frequency of the power supply.The principle of the frequency converter is relatively complicated. Its function is to change the power supply with voltage of 380V/220V and frequency of 50HZ into an AC power conversion device with adjustable voltage and frequency. The torque and speed of the AC motor can be adjusted by adjusting the frequency and voltage of the power supply. We can see from the main circuit that its main circuit is composed of another six Field-effect transistor, Under the precise control of the control circuit, six Field-effect transistor are turned on in turn. In a unit time, the more times the tubes are turned on, the higher the output voltage and frequency will be. Therefore, this main circuit realizes the frequency regulation and voltage regulation of the output power supply under the control of the digital control circuit.2. The purpose of soft starters and frequency converters is differentThe main problem that soft starters solve is to reduce the starting current of large loads and reduce the impact on the power grid. The startup of large equipment will generate a very large starting current, which will cause a significant voltage drop. If traditional step-down methods such as star delta are used, it will not only cause a significant current impact on the power grid, but also cause a significant mechanical impact on the load. In this case, a soft starter is often used for startup to achieve a smooth start of the motor and reduce the power supply capacity.The frequency converter is mainly used in places with speed regulation. It can control the speed of three-phase motors. For example, it can be used in the speed regulation of spindle motors of CNC machine tools, the transmission control of mechanical conveyor belts, large fans, and applications of heavy machinery. In general, its function is far more practical than the soft starter3. The control functions of the frequency converter of the soft starter are differentThe main function of a soft starter is to adjust the starting voltage of the motor, achieve smooth starting of the motor, and reduce the impact of the motor on the machinery and power grid. However, because it controls the voltage by controlling the conduction angle for chopping, and the output is an incomplete sine wave, this leads to low starting torque, high noise, and high harmonics, which can pollute the power grid. Although the soft starter also has various functions such as limited flow function setting and startup time setting, compared to the hundreds of functional command parameters of the frequency converter, the functional parameters of the soft starter are relatively monotonous. Overall, the functions of a soft starter are not as extensive as those of a frequency converter.4. The position of the soft starter is different from that of the frequency converterIn the field of industrial control, most active frequency converters with soft starters are capable, so soft starters are in an awkward position in the field of industrial control. Therefore, these two control devices are priced higher than soft starters at the same power.Overall, soft starters are mostly used as starting devices for high-power devices, while frequency converters are mostly used to regulate various powers.