A Logic-Combined Modulation Strategy for Hybrid Cascade H-Bridges With Partial DC Power Supply Replacement With Capacitors

The multiunit hybrid cascaded H-bridge (CHB) inverters with a 1:2 voltage ratio on the dc side have the disadvantage of requiring multiple dc power supplies. Therefore, a capacitor can be used as a substitute for the power supply with the dc side in the cascaded inverter. First, a three-cell hybrid CHB with a voltage ratio of 1:1:2 on the dc side is regulated by an improved hybrid modulation method used in this article. The switching tube operating state generated by the strategy is screened and combined to obtain two sets of switching modes, and the control circuit alternately works in two sets of modes to achieve dc capacitor voltage regulation. Second, the operating conditions and voltage regulation principle of the capacitor are analyzed. According to the relationship between the working state of the capacitor and the inverter output, the minimum value of the dc capacitor is calculated by the formula under the parameter requirements of the capacitor voltage ripple. Then, the expansion of the inverter scheme and the adjustment method of the modulation strategy are given. Finally, experiments and simulations are used to verify the proposed strategy.