Accurate output power control of inverters for microgrids based on local measurement

Abstract

The precise control of the output power of micro-source inverters (MSI) is of great significance for the stability of voltage and power flow control in a microgrid. Wireless droop control method (WDCM) is one of the effective methods for multi-inverters to share loads dynamically and automatically, provided that the line impedance between the inverter output terminal and the point of common couple at the bus is negligible. However, in the multi-inverter microgrid system, the line equivalent impedance cannot be ignored, and the voltage drop introduced by the impedance will cause output power control error of MSIs. This paper investigates the effect of the line impedance, virtual impedance and droop coefficient on the errors of output power of inverters to find out that the droop coefficient and line impedance instead of the inner virtual impedance will cause the error following the reference command (EFC), while droop coefficient, the characteristics and values of virtual output impedance and line impedance will be related to the error of the proportional sharing load (EPSL). To solve the problems above, the equivalent grid voltage method is proposed to improve the control accuracy of output power tracking the command in grid-connect mode, meanwhile a power compensation conductance is proposed to improve accuracy of proportional sharing load. Finally, the effectiveness of the theoretical analysis and improvement of the control scheme is verified by simulation in MATLAB / Simulink.