Comparison of Power Control Methods for Renewable Energy Resources Operating in a Weak Grid

Abstract

A Renewable Energy Resource (RER) based power grid should be capable to deliver active power $(\boldsymbol{P}_{{GRID}})$ and reactive power $(\boldsymbol{Q}_{{GRID}})$ to fulfill the customer load demand and maintain stability during a weak grid condition. A Voltage Source Inverter (VSI) can provide the demand $\boldsymbol{P}_{{GRID}}$ and $\boldsymbol{Q}_{{GRID}}$ to the grid to maintain a stable power system. Traditionally adopted PI control-based Indirect Power Control (IPC) scheme controls VSI to inject required grid power but as the control is nonlinear, the time to reach the steady-state is longer than the desired. In this paper, we have discussed and compared Direct Power Control (DPC) and the inverter Flux Power Control (FPC) approach with the IPC approach to control the transients caused by the varying RERs and load throughout the day. Besides, due to the transmission line parameters and operations of power, current oscillations are common in a weak grid. In this comparative study, the concept for improving transient response is validated by MATLAB/Simulink for a 100KW 100KVAR grid-tied VSI system. Finally, the comparative performances of the controllers for a weak grid have been discussed.