A novel transformerless three-phase unidirectional bridgeless flying capacitor (UBFC) rectifier for medium-voltage and high-voltage applications is presented by this paper. The rectifier consists of three single-phase rectifiers in wye connection, the DC outputs of the three single-phase rectifiers are connected in parallel to provide a high common DC-link bus which makes it convenient to connect with NPC or FC multilevel inverters. To avoid phase to phase current circulation, an additional inductor and diode are added to each single-phase rectifier. Compared with conventional bidirectional multilevel converters, only half IGBTs are employed with lower voltage stress, line-frequency transformers are no longer be required, which makes the proposed rectifier has a series of advantages such as reduced cost, simplified control complexity, increased reliability and improved overall efficiency. The basic operating principle of the proposed rectifier in continuous conduction mode is discussed, an improved carrier-based level-shifted PWM modulation method integrated with voltage balancing and the double closed-loop control strategy are proposed to achieve more voltage levels and keep the flying capacitors in balance. The feasibility of proposed rectifier is verified by the simulation as well as experimental results.