High-frequency isolated DC/DC converter for input voltage conditioning of a linear power amplifier

Conventional linear power amplifiers show a high output voltage quality but are characterized by high power losses and/or low power density. Therefore, there is a growing interest in increasing the efficiency of linear power amplifiers, e.g. for the realization of high power testing voltage sources. In this paper a high-frequency isolated DC/DC converter system for the conditioning of the input voltage of a linear power amplifier. The output voltage of the DC/DC converter is varied according to the output voltage to be formed by the linear power amplifier so that the voltage drop occurring across the power amplifier output transistors is reduced to low values which results in a significant increase of the total system efficiency. The control design of the DC/DC converter is for fast output voltage response according to the high large signal bandwidth of the linear power amplifier. The three-level input stage of the proposed system does allow a direct connection to the output of a three-phase three-level PWM rectifier ensuring low effects on the supplying mains. The operating principle of the proposed system is described and the design of the output voltage control is treated in detail. The resulting dynamic behavior of the system is analyzed by digital simulation. Finally, the theoretical considerations are verified by measurements on a 1.5 kW laboratory prototype.