Method for tracing motor rotation speed by frequency transformer and device thereof

Abstract

The invention relates to a method used for tracking the rotating speed of an electric motor through a frequency converter. The method comprises the following steps: firstly, the frequency converter is controlled to output currents with the set frequency, and the amplitude of the output current is fixed; secondly, according to the output frequency of the frequency converter, the voltage value of the V/F curve of the electric motor is calculated; thirdly, whether the output voltage of the frequency converter is larger than or equal to the voltage value of the V/F curve of the electric motor is judged, if yes, the step four is carried out, and if no, the step five is carried out; fourthly, the output voltage and the output frequency of the frequency converter are maintained to be unchanged, and the search is finished; and fifthly, the set frequency is changed, and the step one is executed. The invention also provides a corresponding device. The invention cuts the cost of a rotating speed tracking circuit out, improves the reliability of a system, and enables the system to have obvious advantages in cost and reliability.

Description

technical field [0001] The invention relates to a speed tracking method, more specifically, to a method and device for a frequency converter to track a motor speed. Background technique [0002] Inverter is a device for driving AC motors, and it has been widely used in the industrial field in recent years. The wide application of frequency converters can not only improve the level of my country's equipment manufacturing industry, but also achieve obvious energy-saving effects in certain industries. [0003] Before the inverter drives the motor to run, the motor may be in a rotating state. For example, the fan may rotate at a high speed under the action of the ambient wind; The control of the motor is lost, so that the motor rotates at a high speed under the action of inertia. If the motor is in a rotating state, the frequency converter must obtain the motor speed first, and then it can control the motor normally, otherwise the frequency converter will cause over-current an...

AI Technical Summary

Problems solved by technology

[0010] 1. There is a large current ripple on the DC bus current of the inverter, which makes it a very difficult technology to judge whether the DC bus current is 0

2. In the frequency converter, there is generally only three-phase output current detection, and there is no current detection device on the DC bus. To realize this method, a set of current detection device needs to be added, which increases the cost and reduces the reliability of the product.

[0013] The main disadvantage of this method is that it requires a special hardware circuit, which not only increases the cost in the productization, but also reduces the reliability of the system

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