Three-level SHEPWM method of inhibiting common mode voltages

Abstract

The invention relates to a three-level SHEPWM method of inhibiting common mode voltages, comprising the steps of: calculating a switching angle, and drafting a three phase output oscillogram; regarding SHEPWM three phase output as a space vector set consistent with SVPWM, and respectively calculating common mode voltages corresponding to a large vector, a middle vector, a positive small vector, a negative small vector and a zero vector; according to three phase voltage output waveforms, calculating an output vector change and effect section of a period within 360 DEG; determining the type of a three phase output vector at a current time; when the type of the three phase output vector is a positive small vector, switching a three phase switching state into a same position negative small vector which is paired with the positive small vector; and when the type of the three phase output vector belongs to the other four types, a three phase SHEPWM switching state is outputted normally. The method can maintain midpoint voltage self-balance characteristics and effectively reduce inverter output common mode voltages under the condition of not eliminating line voltage specific harmonic waves.

Description

technical field [0001] The invention relates to a three-level converter modulation method, in particular to a three-level specific harmonic elimination pulse width modulation (SHEPWM) method for suppressing common-mode voltage. Background technique [0002] With the advancement of science and technology and the improvement of living standards, people's requirements for power quality are also constantly improving. Multi-level converters such as three-level converters are more and more used in industries and social life to provide better quality. of electric energy. [0003] SHEPWM makes certain low-order harmonics not exist in the output voltage by setting a "gap" at a specific position of the output voltage waveform. Since the phase voltage waveform satisfies odd symmetry and symmetry. The basic principle is to expand the inverter output voltage waveform into the form of Fourier series, make the Fourier coefficients of the low-order harmonics zero, obtain a set of nonlin...

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Problems solved by technology

[0004] The existing three-level SHEPWM method cannot effectively suppress the common-mode voltage

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