Over modulation method and system for three level space vector

Abstract

The invention provides a method and a system for over-modulating three-level space vectors. The method comprises the following steps: calculating the modulation ratio and angle of a reference voltage; dividing the modulation ratio into a first setting interval and a second setting interval; positioning the modulation ratio in the first setting interval and calculating the duty cycle of a short vector, a long vector and a medium vector by intervals according to the angle of the reference voltage; correcting the duty cycle of the short vector, the long vector and the medium vector respectively according to the magnitude of the short-vector duty cycle; calculating the N-action duty cycle and the P-action duty cycle of each phase according to the corrected duty cycle; positioning the modulation ratio in the second setting interval and calculating the keeping angle of the reference voltage; calculating the N-action duty cycle and the P-action duty cycle of each phase by intervals accordingto the resulting of comparing the keeping angle with the angle of the reference voltage; and conversing the N-action duty cycle and the P-action duty cycle of each phase into action time and mapping the action time back to the prior sector. The method and the system have the advantage of ensuring that SVPWM over-modulation is simple in calculation steps and higher in modulation precision.

Description

technical field [0001] The invention relates to the technical field of AC drives, in particular to an overmodulation method and system for a three-level space vector. Background technique [0002] Pulse Width Modulation (PWM: Pulse Width Modulation) is an important part of the AC drive control system. Its function is to adjust the width of the pulse signal that controls the on-off of the main circuit power semiconductor device according to the input reference voltage vector and the current DC bus voltage, so that the fundamental wave voltage output by the main circuit is equal to the input reference voltage vector. [0003] Space Vector Pulse Width Modulation (SVPWM: Space Vector Pulse Width Modulation) is a PWM method based on the control idea of ​​motor flux trajectory tracking. [0004] According to the different modulation ratios, SVPWM can be divided into linear modulation and over modulation. see figure 1 , is a schematic diagram of three-level space vector pulse wi...

AI Technical Summary

Problems solved by technology

[0016] In the overmodulation algorithm of the prior art, it is necessary to calculate the reference angle or holding angle according to the modulation ratio first, and then correct the amplitude and phase of the reference voltage vector according to the reference angle or holding angle, and also judge and correct the vector action time. The implementation steps are cumbersome and take up a lot of system resources

At the same time, in the prior art, there is a nonlinear relationship between the reference angle, hold angle and modulation ratio that cannot be expressed analytically. In practical applications, the functional relationship between them can only be described by curve fitting or tables, which severely limits the accuracy of the algorithm

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