frequency converter
Definition: A converter that transforms alternating current with fixed voltage and frequency into alternating current with variable voltage and frequency.
Function: Reduces the impact load caused by motor startup, controls motor speed, lengthens startup time, smooths out current, achieves soft start, and also improves the efficiency of power grid and motor.
In practice, frequency converters are mainly used for energy saving by adjusting and changing the output voltage, current, and frequency. Frequency converters are generally used for motors requiring speed regulation.
Disadvantages: 1. High cost, much more expensive 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
Inverters fluctuate frequently. When an overload occurs, the motor, due to its strong overload capacity, is unlikely to overload as long as the motor parameters in the inverter's parameter table are set correctly. However, the inverter itself, due to its poor overload capacity, is prone to overload alarms.
Soft starter
Definition: Connected in series between the power supply and the controlled motor, the AC voltage is regulated by the thyristor triggering angle controlled by the microcomputer, so that the motor input voltage gradually rises from zero according to a preset function relationship until the start-up ends, and the motor is given full voltage, which is called soft start.
Function: During soft starting, the motor's starting torque and speed gradually increase until the thyristors are fully conducting. The motor operates at its rated voltage mechanical characteristics, achieving smooth starting and reducing starting current. This prevents 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.
The difference between the two
1. 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.
2. A soft starter is actually a voltage regulator that protects the motor. When used for reduced-voltage starting of the motor, the output of the soft starter only changes the voltage and does not change the frequency.
3. Variable frequency drives have all the functions of soft starters, but their structure is complex and their price is much higher than that of soft starters.
4. A frequency converter controls electrical equipment by adjusting the frequency, allowing for 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 causing problems with unloading some unimportant loads.
