30-03-2012, 11:35 AM
High-Performance Direct Torque Control of an Induction Motor
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INTRODUCTION
HI GH DYNAMIC performance of servo motor drives is indispensable in many applications of today’s
automatically controlled machines. AC servo motor control
has attracted much attention recently in the power electronics
field. Field-oriented control has been developed, enabling an
ac motor to attain dynamic responses as rapid as for a dc
motor. The principle of field-oriented control is based on
Fleming’s law, which describes the interaction force between
fluxes and currents.
INDUCTIOMONT OR DRIVEB Y A DOUBLTEH REE-PHASE
INVERTER
a schematic diagram of the power circuit,
which is composed of two sets of three-phase inverters, a
reactor L for suppressing the zero phase sequence current, and
an open-delta connection induction motor (IM). Since neutral
points of the induction motor are not isolated, zero phase
sequence current, expressed as io = i, + ib + ic, exists. The
current io increases the copper losses as well as the required
inverter capacity.