Improved overmodulation method for diode clamped three-level inverter

Abstract

The invention relates to an improved overmodulation method for a diode clamped three-level inverter. The method comprises the following steps: 1, obtaining a synthesized reference voltage vector V*ref according to the diode clamped three-level inverter; 2, defining a modulation degree function of the synthesized reference voltage vector V*ref, and determining a modulation region in which the synthesized reference voltage vector V*ref of the three-level inverter is positioned according to a value range of the modulation degree function; 3, correcting amplitudes of the synthesized reference voltage vector in a first overmodulation region and a second overmodulation region where the synthesized reference voltage vector of the inverter is positioned, and a phase angle of the synthesized reference voltage vector; and 4, modulating corrected voltage vectors Vref in the first and second overmodulation regions by using a virtual space vector-based nearest three vector (NTV) method. By the method, neutral-point voltage fluctuation of a capacitor on the direct-current side can be adjusted, output level is prevented from directly jumping between positive level and negative level without passing zero level, and the inverter is guaranteed to stably work in an overmodulation region.

Description

technical field [0001] The invention relates to the technical field of three-level inverters, in particular to an improved diode-clamped three-level inverter overmodulation method. Background technique [0002] Compared with the two-level inverter, the existing diode-clamped three-level inverter has the advantages of reducing the withstand voltage requirements of the switching devices, improving the system operating voltage level, reducing the harmonic content, and improving the output voltage waveform quality And other advantages, are widely used in medium and high power occasions. In such occasions, in order to make full use of the DC bus voltage, the inverter is often required to operate in the over-modulation region, such as increasing the maximum torque of the motor on the load side of the inverter through over-modulation operation, and extending the field-weakening operating range of the motor. [0003] There are two kinds of space vector modulation methods commonly u...

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Problems solved by technology

[0004] What the present invention aims to solve is that the traditional three-level inverter space vector modulation method is difficult to adjust the midpoint voltage fluctuation of the DC side capacitor during the overmodulation operation, and at the same time, the output level exists between positive and negative voltages without passing through zero potential. The problem of jumping directly between levels, aiming to provide an improved overmodulation method for diode-clamped three-level inverters

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