Five-stage discrete frequency-conversion soft-start device based on power factor angle closed-loop control

Abstract

The name of the invention is a 5-stage discrete frequency conversion soft starter based on power factor angle closed-loop control, which is applied in the motor starting process. The main circuit adopts the traditional thyristor soft starter main circuit, including the main circuit three-phase AC contactor K1, bypass One-way three-phase AC contactor K2, three-phase six-way anti-parallel thyristor, motor. The synchronous signal acquisition circuit and the current detection circuit collect the voltage and current signals in the main circuit and output them to the single-chip microcomputer, and the single-chip microcomputer sends instructions to the trigger circuit after calculation, and the trigger circuit receives the single-chip microcomputer signal and sends a trigger pulse to the thyristor. The control method of this device adopts the 5-stage discrete frequency conversion soft-start control method. During the process of voltage rise, the frequency is discretely increased in 5 stages. f / 7→ f / 4 → f / 3→ f / 2→ f (50Hz). The device can reduce the starting current of the motor and increase the starting torque of the motor, and is especially suitable for the occasion of heavy-load starting of the motor.

Description

technical field [0001] The invention belongs to the technical field of motor starting, and in particular relates to a five-stage discrete frequency conversion soft starting device based on power factor angle closed-loop control, in particular to a soft starting device suitable for motor heavy-load starting occasions. Background technique [0002] Three-phase asynchronous motors have been widely used in production and life, but due to excessive starting current, it will have adverse effects on the power grid and the entire transmission system. Traditional starting devices include star-delta starters, self-dual step-down starters, stator series resistance starting devices, etc., but due to their respective shortcomings, they are gradually eliminated. Frequency converters can also be used for motor starting, but more for speed regulation Occasionally, if it is only used for the start of the motor, it will cause a waste of resources. The new thyristor soft starter is a device s...

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Problems solved by technology

[0002] Three-phase asynchronous motors have been widely used in production and life, but due to excessive starting current, it will have adverse effects on the power grid and the entire transmission system

However, it is essentially a step-down start, and the starting torque of the motor is proportional to the square of the voltage, so the starting torque of the motor will be reduced, making it difficult to start the motor with a heavy load, and reducing the scope of application of the soft starter

[0003] In the prior art, "Varactor-based Hierarchical Variable Frequency Heavy-Load Soft Starter" (Application No.: 201020590402.9) discloses a variable reactor-based hierarchical variable-frequency heavy-duty soft-starter, which can The main winding of the varactor is connected in series between the contactor and the stator of the AC motor, the secondary winding of the varactor is connected to three opposite parallel thyristors, and the starting contactor is connected in series between the power supply and the varactor. The starting contactor is connected in series with the variable reactor and then connected in parallel with the running contactor. This device inherits the advantages of the soft start device composed of variable reactors and realizes the current limiting function during the motor starting process; The voltage at each frequency division level cannot be kept constant during the motor starting process, which makes the vibration obvious during the motor starting process

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