This study considers the problem of controlling the voltage of a microgrid using the reactive power capabilities of inverters. On a simulated grid, we implemented the Feedback Optimization algorithm in two cases. The proposed FO controller satisfies the constraints and requires no load measurements nor any grid state estimation. The only model knowledge needed by this technique is the sensitivity of the voltages with respect to reactive power, which can be obtained from the reactance bus. An approximation to these sensitivities is also sufficient, thus making this approach model-free, easy to tune, and markedly robust to measurement noise.