Guide: A soft starter is an advanced motor control device that offers smooth start-up, gentle shutdown, energy savings during light load, and multiple protection features. Let’s explore how a soft starter works.
1. Soft Starter Working Principle – Introduction
A soft starter is a modern motor control system that integrates functions such as soft starting, soft stopping, energy saving under light load, and various protective measures. Known internationally as a "Soft Starter," it mainly consists of three-phase parallel thyristors connected in series between the power source and the motor, along with its electronic control circuit. By controlling the conduction angle of these thyristors, the input voltage to the motor can be adjusted according to different requirements, enabling a range of operational functions.
2. The Working Principle of the Soft Starter – Startup Modes
The soft starter is designed to manage motor operations efficiently by offering several startup methods. It combines soft start, soft stop, energy efficiency, and protection into one compact unit. One of the most well-known domestic models is the HPS2 series. Its main components include three-phase parallel thyristors connected between the power supply and the motor, along with an electronic control system. Common startup modes include:
- (1) Ramp constant current soft start
- (2) Ramp boost soft start
- (3) Step start
- (4) Pulse shock start
3. The Working Principle of the Soft Starter
The soft starter uses three-phase parallel thyristors as regulators, connected between the power supply and the motor's stator. This forms a three-phase fully controlled bridge rectifier circuit. When the motor starts, the thyristor output voltage gradually increases, allowing the motor to accelerate smoothly until it reaches full speed. This reduces the starting current and prevents overcurrent tripping.
Once the motor reaches its rated speed, the soft starter automatically bypasses the thyristor using a contactor, providing full voltage for normal operation. This reduces heat loss and extends the lifespan of the soft starter, improving overall efficiency and minimizing harmonic distortion in the power grid.
Additionally, the soft starter offers a soft stop function, which is the reverse of the soft start. The voltage decreases gradually, allowing the motor to slow down smoothly and come to a complete stop without causing mechanical stress or torque shock. The voltage curves for both soft start and soft stop are illustrated below.
Further Reading:
- 1. Single-chip AT89C51 motor soft starter
- 2. Principles of soft start and application examples
- 3. Application of motor soft starters in prospecting engineering
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