Modified Modulation Strategy With Balanced Power and Switching Losses Distributed for Seven-Level Cascaded H-Bridge Inverters

In this paper, the problems existing in common modulation methods are analyzed, and an optimized modulation strategy is proposed. Firstly, the single-pole frequency doubling modulation technique is adopted to reduce the maximum switching frequency to 1/2 of the original switching frequency, and the equivalent switching frequency of inverters remain constant. On this basis, the trigger signal of each unit is rotated in units of 1/4 cycle, so the output power of each cell is balanced after 3/4 cycles. The method is simple in control, and the Total Harmonic Distortion (THD) of line voltage is better than the carrier phase shift technique. The working stress of all the unit switching tubes is the same, the heat dissipation distribution is uniform, the switching loss is effectively reduced, and the service life and system reliability are improved. Finally, simulation and experimental results verify the correctness and feasibility of the optimized modulation strategy.