Method for switching different carrier wave ratios in frequency-division synchronous modulation

Abstract

The invention relates to a method for switching different carrier wave ratios in frequency-division synchronous modulation. At least two frequency bands are adopted and the number of sampling points is set to be N, a first frequency band is entered when the speed of an asynchronous motor changes and a frequency signal changes, in the first frequency band, corresponding to a certain carrier wave ratio and modulation degree, the state in which the motor is when running in the first frequency band is observed, when frequency changes, whether the frequency belongs to the first frequency band is judged, if the frequency belongs to the first frequency band, the motor returns to the state of the first frequency band to run, if the frequency does not belong to the first frequency band, whether the number of the sampling points N is equal to 0 is judged at this time, if the number of the sampling points N is equal to 0, after certain phase compensation is performed, the following second frequency band is entered, and if N is not equal to 0, the motor returns to the state of the first frequency band to run. According to the method provided by the invention, switching of different carrier wave ratios can be performed in frequency-division synchronous modulation, motor current, torque and rotating speed pulsation can be greatly reduced, and the method is of great significance to improving speed control performance of the alternating current asynchronous motor.

Description

technical field [0001] The invention relates to the technical field of asynchronous motor control, in particular to a method for switching different carrier ratios in segmental synchronous modulation. Background technique [0002] Since the main magnetic flux of the asynchronous motor is designed and operated according to the sinusoidal law, in order to make the asynchronous motor operate well, the sinusoidal pulse width modulation and space vector control are usually used; in the segmental synchronous modulation, due to the switching of the carrier ratio, A voltage phase mutation is generated, which causes a large-scale disturbance of the motor current, torque and speed, which impacts the motor and the load and generates noise; in low-frequency situations, asynchronous modulation is usually used, and in high-frequency situations, synchronous modulation is used. The asynchronous motor has a wide range of speed regulation. In the synchronous modulation mode, due to the influe...

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Problems solved by technology

[0003] However, in the segmental synchronous modulation, in the process of switching from one carrier ratio to another carrier ratio, at the switching moment and the following several modulation wave cycles, due to the sudden change in the width of the stator pulse voltage, the width of the stator voltage is not according to The sine law changes, and the motor current, torque and speed are disturbed in a large range during the switching process

[0004] At present, in segmental synchronous modulation, when switching between different carrier ratios, two methods are mainly used: one is to switch when the sampling point N is equal to 0, so theoretically speaking, there is no phase when switching between the previous frequency band and the next frequency band Poor, but in fact, due to time differences in software execution, random phase deviations are generated when switching between different frequency bands, resulting in torque ripple; the second is directly based on the carrier ratio of the previous frequency band and the next frequency band , calculate the current phase deviation, and compensate according to the phase deviation when switching between different frequency bands; the defect of this method is that the calculation of the phase deviation is not necessarily an integer, and the error of the compensated phase deviation is greater when the low frequency and the carrier are smaller. Larger, the greater the vibration generated by the motor

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