Zero-sequence voltage optimal control method for multilevel converters in stretched αβ coordinate system

Abstract

The invention relates to an optimal control method for zero-sequence voltage of a stretched αβ coordinate system multilevel converter. This control method first uses the feature that the difference between the vertical and horizontal relative coordinate values ​​of each level vector in the αβ coordinate system is 1 / 3 and an integer multiple, and proposes a method to stretch the α coordinate value of the αβ coordinate system to the original value. 3 times, and the β coordinate value is stretched to the times of the original value to construct a new mn coordinate system. Based on the mn coordinate system, and on the basis of introducing zero-sequence voltage constraints, a fast zero-speed zero-sequence system that is independent of the number of multi-level levels and can ensure that the zero-sequence voltage is within 1 / 3 of the single-level level is designed. Sequence voltage optimization control method. The zero-sequence voltage optimization control method of the multi-level converter disclosed by the present invention makes the positioning of the sector where the reference voltage vector is located, the calculation of the action time of the space vector and the solution of the output state of the multi-level circuit very simple, only need to carry out Simple four arithmetic operations and comparison operations, the method is fast and suitable for online digital realization.

Description

technical field [0001] The invention mainly relates to a zero-sequence voltage optimization control method, in particular to a zero-sequence voltage optimization control method of a multilevel converter based on a stretched αβ coordinate system. Background technique [0002] Multi-level converters have the unique advantage of realizing high-voltage and large-capacity converters. The use of multi-level conversion technology has become an important way and method to realize high-voltage and large-capacity converters. However, since the output voltage of each phase of the multi-level converter is an integral multiple of the single-level level E, it is impossible for the multi-level converter to avoid the generation of zero-sequence components, and the zero-sequence voltage components will be in the motor. A common-mode voltage is formed in a similar load, and the common-mode current generated by the internal parasitic loop of the motor will cause damage to the motor bearings an...

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Problems solved by technology

This method can reduce the peak value of the zero-sequence voltage output by the inverter, but it destroys the independence between the two control indicators of the two-phase space vector and the zero-sequence voltage component in the SVPWM control method, and is not suitable for high-level data inverter system

In addition, this method will cause the two power devices to switch at the same time, resulting in a voltage pulse of opposite polarity in the half cycle of the line voltage, causing torque ripple

[0005] (3) Based on the 45° coordinate system, the zero-sequence voltage output by the multilevel converter is suppressed by using the modulation method, but in the process of implementing the method, it is necessary to multiply a rotation matrix whose coefficient is an irrational number in each calculation process, And it is cumbersome to calculate the output state of the multilevel converter in the abc coordinate system in this coordinate system

[0006] In summary, in the existing multi-level zero-sequence voltage optimization control scheme, it is necessary to invest a large amount of hardware equipment and destroy the independence between the two control indicators of the two-phase space vector and zero-sequence voltage components in the SVPWM control method. Both cannot well avoid the generation of zero-sequence voltage components of multi-level converters and suppress the common-mode current caused by the zero-sequence voltage amplitude of multi-level converters

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