This paper presents a simplified iterative maximum power point tracking (MPPT) algorithm for single-stage grid-connected PV systems. The single-stage topology is adopted as it reduces power losses and simplifies the system configuration. The proposal is based on the fact that the derivative of the output power with respect to the panel voltage is null at the maximum power point. The designed MPPT generates the appropriate reference d-axis duty cycle component to be applied to the inverter. In order to evaluate the proposal effectiveness, simulation tests are carried out under variable irradiance profiles. Obtained results show that the proposed method allows reaching unity efficiency and greatly attenuates oscillations in transient and stationary states. In addition, despite the irradiance variation, the injected grid currents maintain a sinusoidal waveform.