Start-up techniques of three-phase AC/DC PWM converter with diode rectifier under full load in DC distribution systems

This paper proposes a new circuit of AC/DC PWM converter by adding a diode rectifier to control three-phase AC/DC PWM converter under full load stably. Also, wiring method of LCL filter according to the connecting type of low-frequency transformer is proposed to solve the problem of floating state occurring from the circuit in case of considering the low-frequency transformer. Most of the DC loads have electrically sensitive properties to the input voltage. Therefore, in this system, in order to minimize the overshoot of DC link that may occur when power conversion device is connected with load, control should be started in the state of connection with DC load. However, since the constant current flows continuously into switches of AC/DC PWM converter and load, boost is practically impossible due to the saturation of the boost inductors. In this paper, the proposed techniques let power converter control the DC link while power converter maintains stable condition under full load. The proposed circuit is applied to 50kW DC distribution system and this paper verifies the feasibility of the proposed method through simulations.