A Voltage Modulated Direct Power Controlled Fuel Cell - Battery System Connected to a Weak AC Grid

Abstract

A fuel cell can be integrated into an AC grid using a Voltage Source Inverter (VSI). The conventional vector current control can be effectively used to control the VSI when the grid is strong. However, the interactions between the inner current controller and the Phase Locked Loop (PLL) may make the system unstable when the grid is weak. In this paper a Voltage Modulated Direct Power Control (VMDPC) is used to control the VSI. The VMDPC technique does not need a PLL for its operation. The simulations were carried out in MATLAB/Simulink. The performance of the controller against step changes in fuel flow rate, active and reactive power references, fuel composition and temperature are analysed. The effect of sag in grid voltage on the performance of the controller is also evaluated. The total harmonic distortion of the current injected into the grid is found to be within acceptable limits.