What is the difference between soft start and variable frequency start?

Soft start and variable frequency start are two different ways of starting motors. They are widely used in industrial automation and power systems. This article will introduce the concepts, principles, characteristics, application scenarios and differences between soft start and variable frequency start in detail.

1. The concept and principle of soft start

1. The concept of soft start

Soft start, as the name implies, is a starting method that enables the motor to smoothly and gradually accelerate to the rated speed during the starting process. It controls the input voltage of the motor so that it gradually increases during the starting process, thereby reducing the starting current, reducing the starting impact, and extending the service life of the motor and equipment.

1. Principle of soft start

A soft starter is a device that implements the soft start function. It usually consists of three main parts: thyristor, control circuit and protection circuit. Thyristor is the core component of the soft starter, which can control the input voltage of the motor. The control circuit is responsible for receiving the start signal and controlling the conduction angle of the thyristor according to the preset start curve, so as to achieve smooth start of the motor. The protection circuit is responsible for monitoring the running status of the motor. Once an abnormal situation is found, the power supply is immediately cut off to protect the safety of the motor and the equipment.

2. Concept and principle of variable frequency starting

1. The concept of variable frequency starting

Frequency conversion starting is a starting method that achieves smooth starting and speed regulation of the motor by changing the power supply frequency of the motor. It converts the industrial frequency power supply into variable frequency power supply through the inverter and supplies it to the motor, thereby achieving the starting and speed regulation of the motor.

1. The principle of variable frequency starting

The frequency converter is the core device for variable frequency starting. It is mainly composed of three parts: rectifier, intermediate circuit and inverter. The rectifier converts the industrial frequency power supply into DC power supply, the intermediate circuit is responsible for energy storage and filtering, and the inverter converts the DC power supply into variable frequency AC power supply to the motor. By controlling the output frequency of the inverter, the motor can be started and the speed can be adjusted.

3. Characteristics of soft start and variable frequency start

1. Soft start characteristics

(1) Small starting current: The soft starter controls the input voltage of the motor so that it gradually increases during the starting process, thereby reducing the starting current and reducing the starting impact.

(2) Smooth starting process: The soft starter can achieve smooth starting of the motor, reduce mechanical shock and vibration during the starting process, and extend the service life of the equipment.

(3) Simple operation: The operation of the soft starter is relatively simple. You only need to set the starting time and starting curve to start the motor.

(4) Wide range of applications: Soft starters are suitable for various types of motors, such as squirrel cage type, winding type, etc., and do not have high requirements on the capacity and power of the motor.

1. Characteristics of variable frequency starting

(1) The starting process is controllable: variable frequency starting can realize the starting and speed regulation of the motor. By controlling the output frequency of the inverter, smooth starting and precise speed regulation of the motor can be achieved.

(2) Significant energy-saving effect: Variable frequency starting can adjust the running speed of the motor according to actual needs, thereby reducing energy consumption and achieving energy saving.

(3) Wide range of applications: Variable frequency starting is suitable for various types of motors, such as squirrel cage type, winding type, synchronous motor, etc., and does not have high requirements on the capacity and power of the motor.

(4) High control accuracy: Variable frequency starting can achieve precise control of the motor and meet the needs of high-precision control.

4. Application scenarios of soft start and variable frequency start

1. Application scenarios of soft start

Soft start is mainly used in occasions with large starting current and large starting impact, such as fans, pumps, conveyor belts and other equipment. Soft start can effectively reduce starting current, reduce starting impact and extend the service life of equipment.

1. Application scenarios of variable frequency starting

Variable frequency starting is mainly used in occasions that require speed control, such as conveyor belts, elevators, air conditioning systems, etc. Variable frequency starting can achieve smooth starting and precise speed regulation of the motor to meet the needs of different working conditions.

5. The difference between soft start and variable frequency start

1. Different startup methods

Soft starting is to achieve smooth starting of the motor by controlling the input voltage of the motor so that it gradually increases during the starting process; while variable frequency starting is to achieve starting and speed regulation of the motor by changing the power supply frequency of the motor.

1. Different control methods

The control method of the soft starter is relatively simple. You only need to set the starting time and starting curve to start the motor. The control method of the frequency converter is more complicated. It is necessary to adjust the output frequency according to actual needs to start and regulate the speed of the motor.

1. Different scope of application

Soft starters are suitable for situations where the starting current is large and the starting impact is large, while frequency converters are suitable for situations where speed control is required.

1. Different energy saving effects

Variable frequency starting can achieve precise speed regulation of the motor, thereby reducing energy consumption and achieving energy saving; while the energy saving effect of the soft starter is relatively small.

1. Different control accuracy

Variable frequency starting can achieve precise control of the motor and meet the needs of high-precision control; while the control accuracy of the soft starter is relatively low.

VI. Conclusion

Soft start and variable frequency start are two different motor starting methods, each with its own characteristics and applicable scope. Soft start is suitable for occasions with large starting current and large starting impact, which can achieve smooth starting of the motor, reduce starting impact and extend the service life of the equipment; while variable frequency start is suitable for occasions that require speed control, which can achieve smooth starting and precise speed regulation of the motor, meet the needs of different working conditions, and have significant energy-saving effects.