Operation Analysis and Verification of H-Bridge Modular Cascaded Linear Amplifier to Improve Efficiency by Increasing the Number of Cells

The harmonic and electromagnetic noise issues by switching operations are becoming more serious due to the enhancement of the fast-switching capability of power devices. A modular cascaded linear amplifier (MCLA) has been proposed as a power conversion circuit that does not generate electromagnetic interference without any output filter by utilizing partial linear operation. An H-bridge MCLA can improve efficiency by increasing the number of cascaded H-bridge cells and applying unequal DC capacitor voltages. In this study, the operating modes of the MCLA are analyzed to increase the number of H-bridge cells and enhance the efficiency. Based on the analysis, an extended control scheme including capacitor voltage balancing for the MCLA with four H-bridge cells is developed utilizing a regularity of the operation, and an experiment was conducted using a laboratory prototype. It is verified that the prototype MCLA realizes sinusoidal voltage output with balanced capacitor voltages, and achieves the efficiencies of 88.8% and 92.1% under equal and unequal DC capacitor voltages, respectively, even in a linear amplifier.