Digitally controlled three-phase high power switch-mode AC-DC converter

Switch-mode, high power AC-DC converters have recently been proposed as a power source for applications such as DC arc furnaces and electrolytic production of aluminum, where they offer significant advantages over conventionally used thyristor rectifiers in terms of size and cost. In this thesis, the description of the operation, steady state and dynamic analyses for a switch-mode high power AC-DC converter, featuring digital control, is presented.; In the thesis, an original digital control strategy for the high power switch-mode AC-DC converter configuration is proposed and analyzed. The strategy provides a fast transient response to disturbances and achieves equal current sharing between the buck converter modules paralleled inside the high power switch-mode converter. Equal current sharing is maintained in the steady state as well as in transient operation. The control principle is verified on the 2 kW scaled-down model of the switch-mode converter, controlled by a DSP/FPGA based digital controller.; As part of the thesis, analysis of the converter's operation in the steady state under the proposed control is carried out to determine the steady-state operating point and the resulting current/voltage ratings of the semiconductor switches of the converter. Sampled-data small signal dynamic analysis of the system under the proposed digital control scheme is carried out to determine its small signal stability characteristics. A system design procedure based on the results of the steady state and dynamic analysis is presented. Steady-state and dynamic behavior of the rectifier is experimentally verified.