Losses Analysis of a Three-Phase Bidirectional Active Split Source Inverter for Traction Applications

Abstract

In automotive applications, industrials use dc-dc boosting stages interfaced upstream of the voltage source inverter (VSI) to increase the dc-bus voltage. These topologies enable the motors to be driven with higher dc-bus voltage than that delivered by the battery. Apparently, the use of extra dc-dc converter decreases the efficiency of the whole system. Recently, a single-stage topology called the split source inverter (SSI) was derived. This topology enables the boosting function. Unfortunately, it exhibits very poor utilization of the dc-bus voltage, thus preventing its use for traction applications. In previous work, the authors introduced a new single-stage topology called the bidirectional active SSI (B-ASSI). It enables the boosting function with bidirectional power flow capability and a large utilization of the dc-bus voltage. However, its efficiency was not thoroughly studied and compared with conventional two-stage solution not conducted. This article proposes an in-depth losses analysis of the B-ASSI. Analytical expression of the currents is proposed and validated by simulation. The extensive experimental validations are carry out on a permanent magnet synchronous machine (PMSM) testbench. The derived expressions and proposed approach enable a theoretical comparison of the B-ASSI to two-stage solutions and to the SSI but also giving insights about the design of the converter. This theoretical comparison is performed on a normalized driving cycle. It demonstrates that for the given design constraints, the B-ASSI exhibits lower losses than the classical two-stage solution and the SSI for low-speed operating conditions corresponding to urban drive profiles.