Parallel circulating current suppression method for three-phase four-leg inverters based on third harmonic injection

Abstract

The invention discloses a control strategy for restraining circulating currents of three-phase four-leg inverters on the basis of third-harmonic injection, and provides a method for restraining circulating currents of three-phase four-leg inverters on the basis of third-harmonic injection. The method includes that three-phase current reference signals outputted by voltage loops are synthesized into a zero-sequence current reference signal (4) on the basis (1) of parallel-connection voltage and current double-loop control of the three-phase four-leg inverters for a parallel-connection topology of two three-phase four-leg inverter modules (2) and (3), and error amplifiers track the zero-sequence current reference signal for a mid-line inductive current in a fourth leg of each module, so that mid-line currents of the two three-phase four-leg inverters are shared, and purposes of restraining the circulating currents of the mid-line currents, protecting power tubes and improving the efficiency of each inverter are achieved; and output signals of current loops of the two modules are synthesized to form two third-harmonic signals (5), the two third-harmonic signals (5) are added to obtain a sum (6), an average value (7) of the sum is used as a common third-harmonic signal (8) for being injected into three-phase and mid-line modulation signals of the two inverter modules, zero-sequence modulation components in the third-harmonic signals are eliminated, and the instantaneous zero-sequence circulating currents caused by factors such as inconsistency of parameters of a main circuit filter and inconsistency of switching time of switching tubes are restrained. The method has the outstanding advantages that the circulating currents of the mid-line currents are effectively restrained; control loops are simple; and third-harmonic injection of the parallel-connection inverters is unaffected, and the direct-current voltage utilization rate is increased.

Description

Technical field: [0001] The invention relates to a method for suppressing parallel circulation of three-phase four-bridge inverters based on third harmonic injection, which belongs to the control technology in electric energy conversion devices. Background technique: [0002] At present, in distributed power generation systems such as new energy, aircraft and electric vehicles, three-phase four-leg inverters controlled by SPWM are widely used for their advantages of three-phase decoupling, asymmetric load capacity, and short-circuit current limiting. With the continuous improvement of the power level of power electronic equipment, the inverter parallel technology stacks multiple inverter modules to jointly provide power to the load, which has become the preferred choice for inverter expansion and reduction of switch tube current stress. [0003] Because the parallel connection of inverters is different from the parallel connection of traditional DC-DC converters, when multip...

AI Technical Summary

Problems solved by technology

In practice, the main circuit parameters of each module and the switching time of the main power tube cannot be consistent, and the asymmetry of the third harmonic caused by these factors will inevitably lead to the aggravation of the circulation problem

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