Standalone power-supply systems become a key solution to effectively address load demand in remote locations wherein the voltage asymmetry raises as a particular concern in view of the large number of single phase household and communities loads. Over these loading conditions, the use of Four-Leg Voltage Source Inverters (FL-VSIs) appears as a suitable topology to provide clean power with symmetrical voltage waveforms. The reported work employs the differential flatness theory associated with Grey Wolf optimization in order to guarantee proper operations of the FL-VSIs in different loading conditions. In fact, the differential flatness theory is applied to check the flatness of the FL-VSIs, which allows implementing a reduced control model. Then, a Grey Wolf algorithm which acts as a tracking controller (GWC) is developed. The GWC generates an optimal control signal used by the differentially flat model so as to ensure adequate control performance, even under severe load disturbances and model inaccuracies. A comprehensive experimental test is carried out to validate the effectiveness of the proposed flatness based grey wolf controller (FB-GWC).