This study proposes a robust technique for accurate estimation of single-phase grid voltage fundamental amplitude and frequency. The technique relies on a quadrature signal generator (QSG) based on a fixed frequency tuned second-order generalised integrator (SOGI) and an infinite-impulse-response differentiation filter (DF). The DF is used to estimate the fundamental frequency from the instantaneous phase angle obtained from the generated orthogonal voltage waveforms. The estimation technique is robust and offers an easy tuning process as there is no interdependent loop between the orthogonal voltage system and the frequency estimation. Additionally, the technique is computationally efficient and can also reject the negative effects caused by the direct current offset and harmonics. Furthermore, the frequency estimation is less sensitive to harmonics when compared with a similar technique relying on the QSG based on the fixed frequency tuned SOGI and leastsquares method. Simulation and real-time experimental results are provided to validate the robustness of the proposed technique.