A soft starter with continuous frequency conversion and its control method

Abstract

The invention discloses a continuously variable frequency soft starter and a control method thereof, and belongs to the field of AC asynchronous motor starting devices. The main feature of this invention is to realize frequency conversion and bypass by combining pulse width modulation technology and space vector control algorithm: when adjusting speed below the power frequency, the pulse width modulation algorithm is used to realize continuous frequency conversion of the soft starter; the motor succeeds Change the adjustment when starting and reaching the frequency of the power grid. In the control mode, the space vector control algorithm is used to realize bypass switching control, thereby realizing the function that the soft starter can exit on its own after the motor is started, so as to solve the problem that the inverter cannot be bypassed when used in soft starters, and make up for the existing existing problems. The shortcoming of level frequency conversion soft starter is that it cannot continuously convert frequency.

Description

【Technical field】 [0001] The invention belongs to the field of starting devices for AC asynchronous motors, in particular to a soft starter with continuous frequency conversion and a control method thereof. 【Background technique】 [0002] AC asynchronous motor has many advantages, so it is widely used in the fields of industrial and agricultural production and national defense. However, when starting directly, the starting current can reach 5-8 times the rated current, or even higher. Such a large starting current will have adverse effects on the motor itself, the power grid, and the load. In order to overcome the disadvantages of large starting current, we usually use step-down The starting mode starts. [0003] Traditional soft start methods, such as the star-delta conversion step-down soft start used in the 1960s, the stator circuit series reactor (or resistor) step-down start, the frequency-sensitive rheostat soft start, and the autotransformer step-down Methods such a...

AI Technical Summary

Problems solved by technology

This method has two important disadvantages: first, the starting torque is small; second, the speed of the stator magnetic field cannot be changed, and the starting slip is too large, causing the motor to reverse and vibrate violently when starting

Its motor transmission control system using frequency conversion control has excellent dynamic and static performance, wide range of speed regulation, and good smoothness. It can meet the requirements in terms of starting performance, but it has the disadvantage that it is not easy to exit after the motor is started.

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