<p>To address the issue of the relatively low DC voltage utilization rate in traditional multi-level cascaded H bridges, a single DC source inverter with a dual capacitor unit and DC-side voltage ratio of 1:1:1 is constructed using floating capacitors to replace some of the DC-side voltage sources. The modulation schemes designed for cascaded H-bridge inverters with a single capacitor are no longer applicable to the proposed inverter topology. Therefore, this paper proposes an improved modulation strategy, from which four distinct modulation modes are derived. The charge and discharge of the capacitors are controlled by sampling the capacitor voltage and output current to control the inverter to work alternately in four modes. Furthermore, the capacitor charging and discharging conditions are thoroughly analyzed, along with variations of the capacitor charge under different modulation regimes. To determine the optimal capacitance value, the minimum required capacitance is calculated based on both the capacitor voltage ripple specification and the maximum discharge interval. Finally, to verify the accuracy of the theoretical analysis, the effectiveness of the modulation strategy on the performance optimization of the inverter is verified by experiments and simulations.</p>