Synchronous carrier modulation method and device for three-level inverter

Abstract

The invention discloses a synchronous carrier modulation method for a three-level inverter, and the method comprises the steps: carrying out the negation of a three-phase sine wave, and injecting a specific offset, and obtaining three groups of three-phase initial modulation waves; respectively selecting specific initial modulation waves for three phases in different space angle regions to obtain three-phase actual modulation waves; obtaining two groups of carriers with opposite initial directions by setting the triangular carrier frequency to be the even number times of three of the fundamental wave frequency; selecting specific initial direction carriers in different space angle areas to obtain actual carriers; and formulating a comparison rule of the actual modulation wave and the actual carrier wave, and obtaining a control signal of the three-level inverter based on comparison of the actual modulation wave and the actual carrier wave, thereby realizing synchronous carrier wave modulation for reducing the common-mode voltage. According to the method, the amplitude of the common-mode voltage can be reduced by one half while harmonic waves of multiple of three and even harmonic waves in the line voltage are eliminated, the change frequency of the common-mode voltage can be reduced by two thirds, and the method has the advantages of being simple in calculation and convenient to implement.

Description

technical field [0001] The invention relates to a PWM control method, in particular to a three-level inverter synchronous carrier modulation method and device. Background technique [0002] A typical three-level inverter such as a three-level neutral point clamped (Neutral Point Clamped, NPC) inverter, its main circuit topology is as follows figure 1 . Due to the advantages of low device voltage stress, high output voltage and current quality, simple structure, and bidirectional flow of energy, three-level inverters have been widely used in fields such as motor drive, new energy power generation, and mining shields. [0003] Define the three level states of the three-level inverter output from high to low as P, O and N, and the DC side voltage is 2E, then the space vector of the three-level inverter can be summarized in figure 2 . figure 2 Each space vector in can be classified into zero vector, small vector, medium vector and large vector according to the magnitude. Th...

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Problems solved by technology

[0010] The above studies only focus on the synchronous modulation or the suppression of common-mode voltage modulation of the three-level inverter, but do not combine the two, and fail to optimize the output voltage harmonic performance and common-mode voltage performance at the same time.

In addition, the above modulation methods are all realized based on space vector synthetic reference voltage, and all need to calculate the action time of each space vector and preset the switching action mode in each space angle area. The steps are cumbersome and the calculation is complicated, which is not conducive to engineering popularization and application.

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