Page 425 - Power Electronics Handbook

414 Power semiconductor circuit applications
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wheel

Control - Toque ’ 44
logic sensor
and
power

Steering
column

Figure 14.63 An electrically power assisted steering system

feature. Traditionally power assisted steering systems used hydraulic servo
systems, which can be quite large and unsuitable for use in smaller vehicles.
Electrical power assisted steering, on the other hand, uses an electric motor,
rather than a hydraulic ram, to turn the wheels, so it can be made to fit into
a relatively small area. Figure 14.63 shows the principle behind an EPAS
system. The torque sensor measures the force applied by the driver on the
steering wheel, and feeds this into the central control system. The speed of
the vehicle on the road is also sensed and fed into the same control system,
which then calculates the level of drive, and its direction, which need to be
applied to the drive motor.
It is important to note that this is a power assisted steering system and that
the mechanical link between the steering wheel and the wheels still exists. So
if the EPAS system were to fail the driver still has control of the vehicle,
which is a safety requirement.

14.6 Electrochemical

There are many electrochemical applications for power semiconductors
although only electroplating, electrolysis and electrochemical forming are
considered here. In electroplating a layer of metal is deposited from a
metal anode onto the target, both of these being immersed in a bath of a
suitable electrolyte. The current densities required for the process are low,
the amount of metal deposited being directly proportional to the