IEEE Electrification Magazine - September 2013 - 25

Generator Inverter

Motor Inverter

dc-dc Converter
IPM
Filter
Capacitors

Motor

Battery

Inductor

Generator

+
-

Figure 6. A block diagram of the Toyota Prius e-motor drive system [5].

machine level, during motoring, the goal is to provide the
generated taking into consideration cross--coupling terms,
terminals with the proper voltages to meet the torque comwhich arise from the aforementioned coupled electrical
mands that the driver is imposing through the action of the
interaction, and then converted back to the three-phase
pedal. Additionally, many vehicles employ regenerative
quantities. Pulse-width modulation is used to generate a
breaking, which uses the electric machine as a generator to
gate signal for the power electronic switches to create the
convert the energy produced by the action of slowing the
required voltage waveforms (Figure 8).
vehicle and using it to charge the battery pack. With hybrid
To meet the advanced requirements of fast dynamics,
vehicles, a supervisory control is necessary to determine
field-oriented vector or direct-torque control is also the
the power flow through the system as there are multiple
solution for induction machines. With rotor-flux-oriented
energy sources, the battery, and ICE that work differently
control in a squirrel cage induction motor, the unstable
during various modes.
portion of the natural speed-torque characteristics vanishTo control any machine, a relationship must be estabes, and hence, there is no chance of instability due to cerlished between the input excitation and the resulting
tain types of load torques. The additional advantage is the
torque. The torque in an electric machine arises from the
fact that the maximum torque-producing capability of the
interaction of magnetic fields in the stator and rotor, and
machine is dictated by thermal considerations only. The
the generation of these fields depends on a coupled and
electromagnetic torque response becomes as fast as a sepcomplicated interaction of the current and flux linkage of
arately excited dc machine of identical torque rating but
the internal windings. The most commonly adopted ac
with a reduced size and weight. The only disadvantage
electric motor control in EVs is the vector-control technique,
in a field-oriented controlled induction motor drive is the
which is capable of mathematically
separating the component of current directly responsible for torque
Current
Powertrain
EV Battery
ac Motor
-generation (Figure 7). This is done by
Sensors
projecting all the three-phase quantities along two axes: the direct (d)
axis, which is in line with the field,
and the quadrature (q) axis, which is
perpendicular to it. To find these
axes, it is necessary to determine
the position of the rotor online.
In a PM motor drive, when the
Encoder/
ia ib ic
motor operates under base speed,
Resolver
T 1 - T6
the controller calculates the referid
ence d- and q-axis current using a
Te
Position/Speed
maximum torque-per-ampere techiq
Tabcodq
Calculation
Hysteresis
nique to ensure the efficiency and
Current/Sine
torque production of the motor.

PWM
Ze
id
Power
Over base speed, a field-weakening
Voltage

Signal
MTPA/FW
Te
method is used to estimate the curiq
rent reference and ensure the
power limit is not exceeded. The
Figure 7. Overall schematic of three-phase ac traction motor drive.
reference d- and q-axis voltage is

IEEE Elec trific ation Magazine / s ep t em be r 2 0 1 3

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2013