This paper presents a design of an Integrated Modular Motor Driver (IMMD) for an openwinding permanent magnet synchronous motor (OW-PMSM). A losses calculation method to validate both electrical and thermal design is proposed. Loss calculation method takes account of losses in both transistors and conductors. Obtained calculation results are compared with experimental results to validate the proposed losses calculation method. Observed losses discrepancy between the proposed method and experimental measurements is 3.6 %. Maximum efficiency of IMMD prototype is measured at 97 % for an output power of 1.63 kW.