A Novel DC-Power Control Method for Cascaded H-Bridge Multilevel Inverter

The cascaded H-bridge converter has been widely used in industry. The ability of dealing with unequal power generation among dc links is necessarily required in many applications, such as large-scale photovoltaic power plants and electric vehicles. In this paper, a novel dc-power control method (PCM) is proposed to keep the ac-current balance and maintain power generation ratios of each dc source at their expected values. A simplified modulation strategy is introduced to implement the proposed method, in which the duration times are modified directly by the correction value derived from the PCM method. To calculate and adjust the power generation ratios, a method based on first-in first-out (FIFO) data queue is utilized. The limitation and ranges of power generation ratio are analyzed in detail. DC power per phase can be controlled accurately by the proposed method in variable-frequency condition, even under larger power generation ratios. Results obtained from simulations and experiments are presented to verify the feasibilities and superiorities of the proposed method.