Automated electrified transportation - Propulsion Systems for Hybrid Vehicles - page 550

communications, control and power delivery and management. The topics of
command, communications and control are beyond the scope of this topic. Also,
other than citing references such as Anderson on the merits of elevated versus
surface guideways, the most relevant issue is power delivery. The preceding
chapters in this topic discuss in considerable depth the concerns and issues of
propulsion power and how aerodynamic loading dominates the power equation,
P ( V ), at high vehicle speeds (see Q2 in 'Exercises' section).
Because of aerodynamic loading, it may be necessary for guideway vehicles at
high speed inter-city to platoon to minimize total road load. Even in that case, the
lead vehicle will experience the brunt of aerodynamic loading and need on the order
of 100 kW of propulsion power. Some discussions on this topic have considered the
use of mechanical linkage so that all the vehicles in a platoon would contribute to the
propulsion load, but the details of such connection at high speed are daunting.
In the following subsections, we treat the topic of power coupling and some
details of the actuators and inductive pick-up arrangements to implement this.

12.3.1 Inductive coupling technology
The most direct means of non-contact power delivery is via some form of inductive
power transfer where the primary conductor consists of a long energized cable mounted
directly on the guideway wall and sufficiently rigid to permit a vehicle mounted CWT to
follow it at high speed. Klontz et al. [13] describe just such a unit to be used to deliver
power to mining carts. To minimize the mass of the CWT and its stabilizing actuators,
the primary conductor should be excited at relatively high frequency such as 5-50 kHz.
It is known [13] that such inductive coupling can exhibit power density of 25 kW/kg
with sufficiently small airgaps in the structure. However, maintaining stability at
high speeds and holding a desired small physical airgap in the CWT to primary rail
structure will be very demanding on the positioning actuators and their control. The
CWT is essentially a current transformer with a single-pass primary current carrying
conductor and single, or multiple, secondary turns on a toroidal magnetic core with small
gap once on the primary rail. Because of the circumferential flux in the CWT core and
the necessity for a very small physical airgap, it is necessary to have magnetic material in
the guideway rail support arm to complete the magnetic circuit [14]. An example will
help to clarify the case of a CWT for vehicle mobile power delivery.

Example 1: A coaxial winding transformer on a toroidal core is shown schemati-
cally in this example. Use a simplified magnetic circuit analysis to derive the CWT
secondary voltage and compute its magnitude for two cases of primary excitation
frequency, f p 1 ¼ 15 kHz and f p 2 ¼ 50 kHz.

For the CWT in Figure 12.6, the following dimensions apply:

Primary frequency, f p 15 or 50 kHz CWT core width, W 18 mm

Primary current peak, I 0 500 A Physical airgap, 2 g 1.4 mm

CWT core length, l L 280 mm Secondary turns, N s 1