Four-leg current source inverter (4L-CSI) has  abilities of zero-sequence current handling, voltage boosting, and  output short-circuit protection, but it also has the drawbacks of  bulkiness and low efficiency. To address these drawbacks, a  three-level buck 4L-CSI (3L-Buck-4L-CSI) topology and a simple  and high-efficiency modulation scheme are proposed. Due to the  multilevel characteristics of 3L-Buck-4L-CSI, the volume of its  DC inductor can be reduced greatly and the DC-link current  could respond quickly. The proposed modulation scheme is an  algebraic modulation scheme, in which the duty cycles are  obtained by solving algebraic equations simply and directly. In  addition, it reduces the DC-link current and the switching times  compared with the conventional modulation schemes, which  greatly improves the efficiency of the converter. The  experimental results validate the effectiveness of the proposed  topology and modulation scheme.