  This paper proposes a drive train topology with a dynamically reconfigurable
dc battery, which breaks hard-wired batteries into smaller subunits. It can
rapidly control the output voltage and even contribute to voltage shaping of
the inverter. Based upon the rapid development of low-voltage transistors and
modular circuit topologies in the recent years, the proposed technology uses
recent 48 V power electronics to achieve higher-voltage output and reduce
losses in electric vehicle (EV) drive trains. The fast switching capability and
low loss of low-voltage field effect transistors (FET) allow sharing the
modulation with the main drive inverter. As such, the slower insulated-gate
bipolar transistors (IGBT) of the inverter can operate at ideal duty cycle and
aggressively reduced switching, while the adaptive dc battery provides an
adjustable voltage and all common-mode contributions at the dc link with lower
loss. Up to 2/3 of the switching of the main inverter is avoided. At high drive
speeds and thus large modulation indices, the proposed converter halves the
total loss compared to using the inverter alone; at lower speeds and thus
smaller modulation indices, the advantage is even more prominent because of the
dynamically lowered dc-link voltage. Furthermore, it can substantially reduce
the distortion, particularly at lower modulation indices, e.g., down to 1/2
compared to conventional space-vector modulation and even 1/3 for discontinuous
pulse-width modulation with hard-wired battery. Other benefits include
alleviated insulation stress for motor windings, active battery balancing, and
eliminating the vulnerability of large hard-wired battery packs to weak cells.
We demonstrate the proposed motor drive on a 3-kW setup with eight battery
modules.
