A novel control concept for reliable operation of a three-phase three-switch buck-type unity-power-factor rectifier with integrated boost output stage under heavily unbalanced mains condition

In this paper the reliable operation of a three-phase three-switch buck-type pulsewidth-modulation unity-power-factor rectifier with integrated boost output stage under heavily unbalanced mains, i.e., mains voltage unbalance, loss of one phase, short circuit of two phases, or earth fault of one phase is investigated theoretically and experimentally. A brief description of the principle of operation and the most advantageous modulation method are given. The analytical calculation of the relative on-times of the active switching states and of the dc-link current reference value is treated in detail for active and deactivated boost output stage. Based on the theoretical considerations a control scheme which allows for controlling the system for any mains condition without changeover of the control structure is described. Furthermore, digital simulations as well as experimental results are shown which confirm the proposed control concept for different mains failure conditions and for the transition from balanced mains to a failure condition and vice versa. The experimental results are derived from a 5-kW prototype (input voltage range (280...480) V_rms line-to-line, output voltage 400 V_DC) of the rectifier system, where the control is realized by a 32-bit digital signal processor.