Influence of the overlap time on the AC grid current of CSR and its restraining method

To avoid large overvoltage when the current of the dc-link inductor is interrupted, overlap time is added to the drive signals in current source converters, which results in the extra harmonic in grid current. Waveforms of AC side current before and after added overlap time are achieved from analysis of the current commutation process. The expression of overlap current is given according to the pulse equivalent principle and the quantitative relationship between the extra harmonic of AC side current and overlap time is also given on the basis of the Fourier analysis. In addition, a method of restraining the overlap current is proposed. Finally, simulation and experiment results demonstrate the effectiveness of the proposed analysis and restraining method.