Texas Tech University System

Yeqin Wang

Beibei Ren

Qing-Chang Zhong

A unified control scheme to achieve seamless mode change between grid-connected mode and islanded mode for photovoltaic (PV) systems includes two decoupled control units: a DC-DC converter control unit and a DC-AC converter control unit. The DC-bus voltage is controlled through the DC-DC converter control unit, which supplies a 'stiff DC source' to the DC-AC converter. The seamless mode change is implemented in the DC-AC converter control module via three digital switches between power flow control for grid-connected mode (or MPPT mode), and droop control for islanded mode (or droop mode), while preserving the continuity of control signals in all control units with the configurations of digital switches.

Seamless mode change between grid-connected mode and islanded mode for pv systems

A control system and method include a control strategy and a UDE (Uncertainty and Disturbance Estimator)-based controller incorporated into the control strategy to achieve proportional load sharing for parallel-operated inverters. The UDE-based controller regulates the reactive power against the output generated by a reactive power reference unit according to the load voltage to generate the amplitude of the control voltage. The conventional droop method regulates real power to generate the phase of the control voltage. As a result, the model uncertainties (e.g., parameter drifts and uncertain output impedance), and system disturbances (e.g., fluctuating DC-link voltage and load change) can be estimated and compensated for accurate load sharing.

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Lubbock, TX, United States of America

Yeqin Wang