Power Quality Enhancement Using Cascaded Current-Voltage Controller

The cascaded current–voltage control strategy has been proposed for inverters in micro grids. It consists of an inner voltage loop and an outer current loop and offers excellent performance in terms of THD for both the inverter local load voltage and the grid current. In particular, when nonlinear and/or unbalanced loads are connected to the inverter in the grid-connected mode, the proposed strategy significantly improves the THD of the inverter local load voltage and the grid current at the same time. The controllers are designed using the H∞ repetitive control in this paper but can be designed using other approaches as well. The proposed strategy also achieves seamless transfer between the stand-alone and the grid-connected modes. The strategy can be used for single-phase systems or three-phase systems. As a result, the nonlinear harmonic currents and unbalanced local load currents are all contained locally and do not affect the grid. Simulation  results under various scenarios have demonstrated the excellent performance of the proposed strategy.

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