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Harmonics generated from large-scale grid-connected photovoltaic plant (GCPV) has the characteristics of high frequency and wide frequency range. So the adverse impact of distributed parameter of high-voltage cables becomes more significant. Based on an actual GCPV, harmonic output particularities were discussed according to its operating mechanism. Step-up transformer, reactive power compensation device, distributed capacitance of transmission line and the loads were considered, the passive multiport network model was established, and the transmission mechanism of harmonics in this network was analysed by the definition of resonance amplification factors. Double resonance curves of harmonic current were discovered, that is, the transmission line of different distance may amplify a harmonic current twice. The simulation and data measurement in the field were carried out based on a large-scale GCPV in Qinghai province. The proposed scheme was verified by the comparison of simulation data and measurements.

This study presents an improved dead-beat control method for three-phase pulse-width modulation rectifier of the switching power supply under source-voltage harmonics and unbalance disturbances. First, a reference currents extraction method and an active negative sequence currents injection method for the dead-beat control are presented to suppress the input harmonic currents and the second harmonic voltage of the DC-link voltage in the rectifier. Then, active disturbance rejection control is presented to substitute for the PI control, which can improve the transient response and strengthen the antidisturbance ability of the rectifier. Finally, to improve the efficiency of the power supply, two auxiliary inductors are introduced to realise soft switching of the DC/DC converter, which is an idea of taking the rectifier and the DC/DC converter as a whole. The feasibility and superior performances of the presented control methods and topology have been validated by the experimental results.

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