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.