IEEE Electrification Magazine - December 2017 - 17

For a simple mechanical integration, the TMs are
mounted on the landing gear close to the wheels. The acto-dc converter and the WACU are installed in the fuselage
of the aircraft for a better environment. The distance
between the power electronics component and the TMs is
substantial, leading to the logical step of increasing the
voltage of the electrical machine. Then, the inverter and TM
currents are reduced, leading to a lighter interface cable.
The smaller-size cable leads to easier routing around the
landing gear during deployment and retraction. This step
requires the ac-to-dc converter to perform a boosting function. Two 40-kW continuous and 60-kW peak ATRUs feeding both the WACUs were used for the PAS demonstration.

Wheel Actuation and Control Unit
WACU Major Requirements
The major function of the WACU is to receive dc power
from the ATRU and convert it to a VF and amplitude ac
voltage to drive the TM. The WACU receives a torque command from the system controller over the serial data bus.
The TM current is regulated by the WACU to provide the
commanded torque.
The WACU also performs a built-in test (BIT) to protect
itself and the other components in the EDS. The WACU is
responsible for measuring and detecting
xx
overheating conditions in the WACU, ATRU, and TM
xx
overcurrent and/or open circuit conditions in the
WACU, TM, and connecting cables
xx
ground fault conditions in the TM and cabling
xx
overspeed of the TM
xx
any failed sensor feedback, including temperature,
voltage, current, and motor position
xx
loss of communication with the system controller
xx
health monitoring of the ATRU.

WACU Block Diagram
Figure 7 illustrates the main functional blocks within the
WACU. The DSP controller handles the operating mode
transitions, inrush current limiting, control regulation, BIT,
and communication with the system controller. The DSP
and control electronics are powered from the aircraft's
28-V power bus through an EMI filter and multiple output
voltage power supplies.
The ±270-Vdc input power from the ATRU is EMI filtered
and fed to the inverter. The switching devices in the
inverter are controlled by gate drivers featuring galvanic
isolation from the control circuitry. The inverter threephase output is measured by current sensors for control
and protection. An ac output EMI filter limits the conducted
and radiated emissions from the WACU. The ac output
drives the TM.
The rotor position feedback and temperature feedback
from the TM are conditioned and measured by the DSP for
control and protection.

WACU Power Topology
The WACU power stage consists of an active threephase bridge, two-level inverter. To prevent large inrush
currents upon application of ±270-Vdc power to the
WACU, the ATRU includes inrush-current-limiting
resistors on the three-input power phases. Once the
WACU power stage is fully charged and near full dc bus
voltage is reached, the WACU commands an ac contactor located in the ATRU to close. The contactor is connected across the three inrush-limiting resistors. After
this, the main contactor is closed, and the WACU is
ready to draw full power from the ATRU.
The inverter integrated-gate bipolar transistor
switches are sized to handle the two corner conditions
of operation: the highest motor currents, which are

dc
dc Link
EMI
Filter

Current
Sense

ac
EMI
Filter

PMSM
Motor

Gate Driver
28 v
+28 V
EMI
Filter

Power
Supply

Resolver/
RTDs
DSP Controller

Torque
Command

Figure 7. The WACU architecture block diagram.

IEEE Elec trific ation Magazine / D EC EM BE R 2 0 1 7

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2017