Distributed Predictive Control Scheme for Grid-Tied Cascaded Multilevel Impedance Source Inverter with LVRT Capability
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This paper presents a decoupled power control scheme for grid-tied single-phase quasi-impedance-source cascaded multilevel inverter (qZS-CMI) for photovoltaic (PV) applications. The proposed control scheme for the grid-tied qZSI-CMI is based on finite-set model predictive control (MPC) to harvest the desired active power from PV modules with ability to provide ancillary services for the grid. The proposed control scheme has two modes of operation: normal grid mode and low voltage ride through (LVRT) mode. In normal grid mode, the controller commands the qZS-CMI to operate at global maximum power point (MPP). The proposed technique regulates the impedance network elements' voltage and current according to the MPP of PV panels and grid voltage/current requirements. In LVRT mode, the controller commands the qZS-CMI to provide the required reactive power for grid during voltage sag as an ancillary service from the inverter as imposed by grid codes. The main features of the proposed system include: global MPP operation during normal grid condition, LVRT capability during grid voltage sag, mitigation of the PV modules mismatch on overall energy harvesting, and seamless transition between normal grid and LVRT modes of operation. Several real-time experiments are conducted to verfiy the system performance with transients in both solar irradiance and the grid voltage.