[en] Stable and reproducible generation of a photon beam at Free Electron Lasers (FELs) necessitates a low energy spread of the electron beam. A low level radio frequency (LLRF) control system stabilizes the RF field inside accelerating modules. An electron beam passing through the cavity induces a voltage proportional to the charge and the cavity shunt impedance. The feedback loop tries to compensate for the perturbation after the accelerating gradient drops. The delay and high gain result in an overshoot or oscillations during transients. A feed forward signal can be applied to act on the plant simultaneously with the RF feedback. It can be generated off-line based on system characteristics and beam parameters or on-line using information obtained from the beam diagnostic systems. In the latter scheme fluctuations of the beam current are accounted for in real-time using an open-loop (feedforward) controller. The bunch charge detection scheme and its implementation is described. This paper describes results of the tests performed on the ELBE (Electron Linac for beams with high Brilliance and low Emittance) radiation source at the HZDR (Helmholtz-Zentrum Dresden-Rossendorf) facility using a MTCA.4-based LLRF control system. (author)