Mode Switching Stability Analysis and Step-down Operation Strategy of Photovoltaic Cascaded DC/DC Converters

doi:10.3969/j.issn.1000-7229.2020.01.012

Abstract

Abstract: In the photovoltaic DC boost collection system, DC/DC converters on the photovoltaic side realize power transmission through the cascaded topology. However, when the input photovoltaic power is different greatly, the cascaded converter switches between the maximum power point tracking (MPPT) mode and the constant voltage mode, and the mode switching control causes the system stability change. In this paper, the isolated boosting full-bridge converter is taken as the research object, and the small-signal model of the converter output impedance under the control of incremental conductivity method-MPPT and constant voltage is established, and then the equivalent impedance model of cascaded system is deduced. According to the impedance stability criterion, the difference of system stability under control mode switching is evaluated. The results show that the stability of the system is reduced when the converter is switched from the MPPT mode to the constant voltage mode, and the stability is significantly deteriorated as the number of switching control mode modules increases. Therefore this paper proposes to decrease the bus voltage to maintain PV-side DC/DC converter within the MPPT control mode. Finally, a simulation model of the cascaded system is built in Matlab/Simulink to verify the correctness of the theoretical analysis.

Key words: isolated boosting full-bridge converter, multi-mode control, small signal modeling, equivalent impedance model, stability analysis

CLC Number:

TM 615

TIAN Yanjun,CHEN Yingfei, WANG Hui, WANG Yi, GAO Haonan. Mode Switching Stability Analysis and Step-down Operation Strategy of Photovoltaic Cascaded DC/DC Converters[J]. Electric Power Construction, 2020, 41(1): 97-105.

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