The difference between frequency converters and soft starters
Definition: A frequency converter is a device that transforms alternating current with fixed voltage and frequency into alternating current with variable voltage and frequency.
Function: To reduce the impact load during motor startup, control motor speed, lengthen startup time, and smooth out the current flow, achieving soft starting. It also improves the efficiency of the power grid and the motor. In practice, frequency converters are mainly used for energy saving by adjusting and changing the output voltage, current, and frequency. Generally, speed-regulating motors use frequency converters .
shortcoming:
1. It is expensive to manufacture and costs much more than microcomputer protection.
2. Since most current frequency converters use PWM control, this pulse modulation method causes high-order harmonic currents to be generated on the power supply side during operation, resulting in voltage waveform distortion. When the power system is polluted by harmonics, it will affect the operating efficiency of the system at best, and damage the equipment or even endanger the safe operation of the power system at worst.
3. Overload causes the frequency converter to trip more frequently. When an overload occurs, the motor generally has a strong overload capacity, and as long as the motor parameters in the frequency converter's parameter table are set properly, the motor is unlikely to overload. However, the frequency converter itself has a poor overload capacity and is prone to overload alarms.
Soft starter
Definition and Function: Connected in series between the power supply and the controlled motor, this system uses a microcomputer to control the conduction angle of its internal thyristors to achieve AC voltage regulation. This allows the motor input voltage to gradually increase from zero according to a preset function until the start-up is complete, providing the motor with full voltage – this is called soft start. During soft start, the motor's starting torque and speed gradually increase until the thyristors are fully conducting, and the motor operates at its rated voltage mechanical characteristics, achieving smooth starting and reducing starting current. This avoids overcurrent tripping during startup. The starting process ends when the motor reaches its rated speed, providing the rated voltage for normal motor operation.
shortcoming:
1. The power supply frequency cannot be adjusted, so the motor cannot be started from zero voltage and zero frequency, and zero-impact start cannot be achieved.
2. Speed cannot be adjusted.
3. The soft starter exits the system after starting the motor and loses its protection function.
A frequency converter is used in applications where speed regulation is required. The output of a frequency converter can change not only the voltage but also the frequency.
A soft starter is actually a voltage regulator that protects the motor. When used for reduced-voltage starting of a motor, the output of the soft starter only changes the voltage and does not change the frequency.
Inverters have all the functions of soft starters, but they are more complex in structure and much more expensive.
A frequency converter controls electrical equipment by adjusting the frequency, enabling speed regulation and starting, such as variable frequency pumps used in industry. Soft starting essentially involves changing the resistance connected in series in the circuit, gradually increasing the current. This method is used to start high-power motors, reducing the fluctuations in the power grid caused by directly starting a high-power motor, or the inconvenience of unloading some unimportant loads.
