What is the difference between variable frequency starting and soft starting of motors?

Motor variable frequency starting and soft starting are two different starting methods. They have obvious differences in the control method, starting performance, energy consumption, etc. of the motor during the starting process. The following is a detailed comparison of the two starting methods:

1. The difference in starting principles

1. Principle of variable frequency starting

Variable frequency starting means changing the motor's power supply frequency, thereby changing the motor's speed and torque, to achieve smooth starting of the motor. During the starting process, the frequency converter first converts the input AC power into DC power, and then converts the DC power into adjustable frequency AC power through the inverter to supply the motor. By adjusting the frequency, the motor's speed and torque can be controlled to achieve a smooth transition during the starting process.

1. Soft start principle

Soft start means that during the motor starting process, the motor's supply voltage and current are controlled so that the motor's starting current and torque gradually increase within a certain range, thereby achieving a smooth start of the motor. Soft starters usually use power electronic devices such as thyristors or IGBTs to control the motor's supply voltage and current by adjusting the device's conduction angle to achieve a smooth transition in the starting process.

2. Difference in startup performance

1. Starting current

The starting current of variable frequency starting is usually lower, because the frequency converter can keep the current of the motor at a lower level during the starting process by adjusting the frequency. Although the starting current of soft starting is also lower, it is still higher than that of variable frequency starting.

1. Starting torque

Variable frequency starting can achieve constant torque starting, that is, during the starting process, the torque of the motor remains unchanged. However, the starting torque of soft starting will gradually increase with the increase of current, and constant torque starting cannot be achieved.

1. Startup time

The start time of variable frequency starting can be adjusted as needed, and fast start or slow start can be achieved. However, the start time of soft starting is usually longer because the current and torque need to be gradually increased to achieve the purpose of smooth starting.

1. Smoothness of the startup process

Variable frequency starting can achieve a very smooth starting process, because by adjusting the frequency, the speed and torque of the motor can be controlled to achieve a smooth transition of the starting process. Although soft starting can also achieve smooth starting, its smoothness is slightly less than that of variable frequency starting.

3. The difference between energy consumption and efficiency

1. Energy consumption

The energy consumption of variable frequency starting is relatively low, because the inverter can adjust the power supply frequency according to the actual needs of the motor, so that the energy consumption of the motor during the starting process is kept at a low level. The energy consumption of soft starting is relatively high, because it is necessary to gradually increase the current and torque to achieve the purpose of smooth starting.

1. efficiency

The efficiency of variable frequency starting is higher because the inverter can adjust the power supply frequency according to the actual needs of the motor, so that the efficiency of the motor during the starting process is maintained at a high level. The efficiency of soft starting is relatively low because it requires additional energy to gradually increase the current and torque.

4. Differences in applicable occasions

1. Frequency conversion start

Frequency conversion starting is suitable for occasions that require frequent starting, stopping or speed regulation, such as fans, pumps, etc. In addition, frequency conversion starting is also suitable for occasions with high requirements for starting performance, such as high-precision equipment, large equipment, etc.

1. Soft Start

Soft start is suitable for occasions with large starting current and high starting torque requirements, such as large motors, heavy equipment, etc. In addition, soft start is also suitable for occasions with high requirements for the smoothness of the starting process, such as conveyor belts, elevators, etc.

5. The difference between cost and maintenance

1. cost

The cost of variable frequency starting is relatively high because it requires the use of devices such as frequency converters. The cost of soft starting is relatively low because it only requires the use of devices such as soft starters.

1. maintain

The maintenance of variable frequency starting is relatively complicated because it involves the commissioning and maintenance of the frequency converter. The maintenance of soft starting is relatively simple because it only requires regular inspection and maintenance of the soft starter.

VI. Conclusion

The variable frequency starting and soft starting of the motor each have their own advantages and disadvantages. The choice of which starting method should be based on the specific application, equipment performance requirements, cost budget and other factors. Variable frequency starting has the advantages of low starting current, constant starting torque, smooth starting process, low energy consumption, high efficiency, etc., and is suitable for occasions that require frequent starting, stopping or speed regulation. Soft starting has the advantages of low starting current, gradually increasing starting torque, good starting process smoothness, and low cost, and is suitable for occasions with large starting current and high starting torque requirements.