Abstract: The three-unit hybrid cascaded multi-level inverter can use fewer switching devices to achieve high-quality voltage output, but its low-voltage units switching loss under the mixed frequency traditional modulation strategy and the power imbalance problems between cascaded units. Aiming at the above problems, an improved hybrid modulation strategy was proposed, and on the basis of the improved hybrid modulation strategy, the expression of the fundamental wave of the output voltage of the cascade units was derived, and the average output power expressions of the cascade units were obtained. Then the power balance was optimized for the improved hybrid modulation strategy. Under the premise that the improved hybrid modulation strategy has good output voltage harmonic performance, the triangular carrier position of the PD modulation strategy was modified to effectively balance the switching loss of the low-voltage unit and control the output of the high-voltage unit's pulse width to effectively realizes the power self-equalization between the cascaded units under the full amplitude modulation factor. The correctness of the theoretical analysis and validity of the proposed power balance modulation strategy are confirmed by simulation and experimental results.