Download REDUCING SWITCHING LOSSES IN BLDC MOTOR DRIVES BY

REDUCING SWITCHING LOSSES IN BLDC MOTOR DRIVES BY REDUCING BODY
DIODE CONDUCTION OF MOSFETS
ABSTRACT
This project proposes a new power electronic topology that aims to reduce switching losses in
hard-switched inverters for brushless dc (BLDC) motor drives. This is achieved by extending the
benefits of synchronous rectification used in low-voltage switch-mode dc–dc conversion to highvoltage motor drive applications and by minimizing the reverse conduction behaviour of the
intrinsic body diode of the synchronous rectifier MOSFET. The proposed topology for reducing
body diode conduction includes the addition of a MOSFET in series with the rectifying switch
and a SiC Schottky diode around the series switch combination.
A new power electronic circuit has been applied to a BLDC motor drive that consists of an
additional MOSFET in series with the synchronous MOSFET in a driver bridge, along with a
SiC diode placed anti parallel with the MOSFET pair. The goal of the additional circuit was to
eliminate the reverse recovery current of the synchronous rectifier MOSFET to reduce switching
losses and increase overall efficiency. Test data taken using a prototype that contains both a
traditional bridge and a bridge with the proposed pinch-off MOSFET show efficiency
improvements in the circuit containing the pinch-off MOSFET.
A nearly 33% reduction in the power dissipation was measured with the pinch-off MOSFET
configuration. This shows very good agreement with the simulation results, which achieve a
reduction of power dissipation in the bridge by more than 40%. Thermal measurement
comparisons show a 42 ◦C reduction in the temperature of the top MOSFET of the bridge
containing the pinch-off circuit.
The proposed circuit presents many advantages over the traditional synchronous rectifier. With
lower peak ringing voltage on the switch node, the component voltage stresses are lower.
Because there is no reverse recovery current spike, top MOSFET turn-on stress is reduced.
Higher frequency operation is possible in applications where the dead time would otherwise need
to be increased to allow the current to leave the body diode and transfer into the parallel Schottky
rectifier.