Analysis of the advantages and disadvantages of the inverter and soft starter
Definition: A converter that converts alternating current with constant voltage and frequency into alternating voltage with variable voltage and frequency is called inverter.
Function: Reduce the impact load caused by the motor starting, control the motor speed, lengthen the starting time, smooth the current, achieve the purpose of soft start, and improve the efficiency of the grid and motor. In fact, the frequency converter is mainly used in energy saving, and the output voltage, current and frequency are changed by adjustment. The general speed calculation motor uses a frequency converter.
Disadvantages:
1. The cost is high, and the price is much more expensive than the microcomputer protection.
2. Since the current inverter almost adopts the PWM control mode, such a pulse modulation form causes the high-order harmonic current to be generated on the power supply side when the inverter is running, and the voltage waveform is distorted, and the power system is subjected to harmonic pollution. Affect the operating efficiency of the system, and damage the equipment and even the safe operation of the power system.
3. Overload makes the inverter jump more frequently. When the overload occurs normally, the motor is generally overloaded. As long as the motor parameters of the inverter parameter table are set properly, the motor overload is generally not present. The inverter itself is overloaded. Poor capacity is prone to overload alarms.
Soft starter
Definition and function: serially connected between the power supply and the controlled motor, the micro-computer controls the internal thyristor to trigger the conduction angle to realize AC voltage regulation, so that the motor input voltage gradually rises from zero with a preset function relationship until the end of the start, The full voltage of the motor is soft start. During the soft start process, the starting torque of the motor is gradually increased, and the rotational speed is gradually increased until the thyristor is fully turned on. The motor works on the mechanical characteristics of the rated voltage to achieve smooth start and reduce the starting current. . Avoid starting overcurrent trips. When the motor reaches the rated number of revolutions, the starting process ends and the rated voltage is supplied for the normal operation of the motor.
Disadvantages:
1. The power frequency cannot be adjusted, so the motor cannot be started from zero voltage and zero frequency, and zero impact start cannot be achieved.
2. Can not adjust speed.
3. The soft starter exits the system after starting the motor and loses its protection function.
The frequency converter is used for speed adjustment. The output of the inverter not only changes the voltage but also changes the frequency at the same time.
The soft starter is actually a voltage regulator that protects the motor. When the motor is stepped down, the soft starter output only changes the voltage without changing the frequency.
The frequency converter has all the functions of a soft starter, but its structure is complicated and the price is much more expensive than the soft starter.
The frequency converter controls the electrical equipment by adjusting the frequency, and can be adjusted and started, such as the industrial variable frequency pump. The soft start is basically far away by changing the resistance connected in the circuit to make the current from small to large. This way is used to start a high-power motor, which is used to reduce the fluctuation of the high-power motor directly to the grid, or cause some The trouble of important load unloading.
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