Note: Descriptions are shown in the official language in which they were submitted.
2027292
- VOLTAGE REGULATION/CONVERSION DEVICE AND METHOD
The present invention relates to a voltage
regulation/conversion device and method, and in particular to a
device and method for regulating an a.c. single phase supply
voltage wherein load variations are liable to fluctuate to a
relatively large extent, the regulation being achieved by means
of the conversion to a d.c. supply for energy storage thereof
during low load levels.
The present invention is particularly applicable to
electric railways, wherein loads fluctuate as trains move over
the railway on constantly changing grades, as they slow for
speed restrictions and crossings with other trains, as they
slow or stop for signals, and as they accelerate after slowing
or stopping. In order to improve the voltage regulation and
load factor of electric railway distribution systems, a number
of proposals have previously been put forward and implemented.
These include reducing the distance between the high voltage
supply substations, providing switching stations between the
substations, providing series or shunt connected capacitors to
reduce reactive power along the distribution system, and
- providing transformer type regulators to provide voltage
regulation. Each of these have drawbacks, such as high cost,
or adverse effects due to the high consumption of power, etc.
In normal a.c. traction systems, each substation feeds
radially to an open midpoint between substations. For trains
near the midpoint, there is no contribution from the adjacent
substation.
AMD/0205a - 2 -
2027292
- Even when the nominal voltages are identical, the
paralleling of adjacent busbars usually causes undesirable
reactive power flows between the busbars. When the three phase
high voltage supplies to adjacent substations are essentially
in phase, and fast protection is installed, the voltage
regulation on the typically 25 kV railway distribution system
can be halved, by paralleling the adjacent substations. Such a
system is, for example, extensively used by the French national
railways, however, the circumstances which would cause adjacent
substations on the three phase high voltage system to be
sufficiently in phase are unlikely to occur in Australia.
The present invention seeks to provide a voltage
regulation system whereby a single phase a.c. supply, such as a
railway distribution system can be regulated cost-effectively,
by utilising a pair of rectifier/converters and an energy
storage means for the storage and later supply of excess energy
back to the single phase a.c. distribution system.
In one broad form the present invention provides a
voltage regulation system, comprising:
a single phase a.c. supply;
an a.c. busbar, connected to said single phase a.c.
supply, having at least one variable load connected thereto;
a pair of rectifier/converters adapted to convert a.c.
power to d.c. power and vice versa;
an energy storage means connected to said d.c. busbar;
whereby in periods of low load, excess energy supplied to
said a.c. busbar from said a.c. suppiy is transferred via a
first of said pair of rectifier/converters to said d.c. busbar
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and stored in said energy storage means, and, in
periods of high load, the energy previously stored
in said energy storage means is transferred via a
second of said rectifier/converters to said a.c.
busbar, supplementing the energy supply to said
load.
In a preferred embodiment, the voltage
regulation system further comprises a transformer
supply between a.c. busbar and said pair of
rectifier/converters.
Also preferably, the voltage regulation
system is implemented wherein said energy storage
means is either a d.c. capacitor or a chemical
storage battery.
Preferably also, said voltage regulation
system is implemented wherein said transformer is
configured as an auto transformer.
In accordance with a particular embodiment
of the invention there is provided a voltage
regulation apparatus for use in a power distribution
system including an a.c. busbar having at least
first and second a.c. busbar sections, each said
a.c. busbar section being capable of having at least
one variable load operably connected thereto, said
first a.c. busbar section being electrically
isolated from said second a.c. busbar section by an
open circuit, said first a.c. busbar section having
a first single phase a.c. power supply connected
thereto and said second a.c. busbar section having a
second single phase a.c. power supply connected
thereto, said voltage regulation apparatus
comprising:
a d.c. busbar;
an a.c. to d.c. power conversion means
having an input operably connected to said first
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202729~
_
a.c. busbar section, and having an output operably
connected to said d.c. busbar;
a d.c. to a.c. power conversion means
having an input operably connected to said d.c.
busbar and having an output operably connected to
said second a.c. busbar section;
energy storage means operably connected to
said d.c. busbar for storing energy produced from
the output of said a.c. to d.c. power conversion
means, and for supplying said energy to said d.c. to
a.c. power conversion means; and
control means for controlling the
operation of said a.c. to d.c. power conversion
means so as to either generate or absorb power
between said first a.c. busbar section and said a.c.
to d.c. power conversion means, and for controlling
the operation of said d.c. to a.c. power conversion
means so as to either generate or absorb power
between said second a.c. busbar section and said
d.c. to a.c. power conversion means, whereby, in
periods of low load, excess power supplied from said
a.c. busbar is transferred to said d.c. busbar, and,
in periods of high load, the energy stored in said
energy storage means is transferred to said a.c.
busbar, supplementing the energy to said load,
thereby facilitating voltage regulation along said
first and second a.c. busbar sections.
In accordance with a further specific
embodiment of the invention there is provided a
power distribution system comprising:
an a.c. busbar having at least ~irst and
second a.c. busbar sections, each said a.c. busbar
section being capable of having at least one
variable load operably connected thereto, said first
a.c. busbar section being electrically isolated from
said second a.c. busbar section by an open circuit;
,~
,, .
` - 4b - 20?72~2
a first single phase a.c. power supply
operably connected to said first a.c. busbar
section;
a second single phase a.c. power supply
operably connected to said second a.c. busbar
section;
a d.c. busbar;
an a.c. to d.c. power conversion means
having an input operably connected to said first
a.c. busbar section, and having an output operably
connected to said d.c. busbar;
a d.c. to a.c. power conversion means
having an input operably connected to said d.c.
busbar and having an output operably connected to
said second a.c. busbar section;
energy storage means operably connected to
said d.c. busbar for storing energy produced from
the output of said a.c. to d.c. power conversion
means, and for supplying said stored energy to said
d.c. to a.c. power conversion means; and
control means for controlling the
operation of said a.c. to d.c. power conversion
means so as to either generate or absorb power
between said first a.c. busbar section and said a.c.
to d.c. power conversion means, and for controlling
the operation of said d.c. to a.c. power conversion
means so as to either generate or absorb reactive
power between said second a.c. busbar section and
said d.c. to a.c. power conversion means, whereby,
in periods of low load, excess power supplied from
said a.c. busbar is transferred to said d.c. busbar,
and, in periods of high load, the energy stored in
said energy storage means is transferred to said
a.c. busbar, supplementing the energy to said load,
thereby facilitating voltage regulation along said
first and second a.c. busbar sections.
.h
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2027292
The present invention will become more
fully understood from the following detailed
description thereof, in connection with the
accompanying drawings, wherein:
Fig. 1 shows an implementation of a
voltage regulation system in accordance with the
present invention; and
Fig. 2 illustrates an alternative
embodiment of a voltage regulation system, also in
accordance with the present invention.
In Fig. 1 is shown an a.c. distribution
system, designated 1, connected to an a.c. supply
voltage. Connected to the a.c. distribution system
are a pair of rectifier/converters 2 and 3, the
rectifier/converters 2 and 3 also being connected to
a d.c. busbar 4. Also connected the d.c. busbar 4,
are shown energy storage means 5 and 6, being
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20272~2
chemical batteries and capacitors respectively. Intermediate
each of the components are circuit breakers 7.
In operation, during a high voltage period being present
on the a.c. busbar 1, excess energy is transferred via a first
rectifier/converter 2, or a.c. to d.c. converter, via the d.c.
busbar 4, to one or both of the energy storage devices 5 and
6. Then, during a low voltage period being present on the a.c.
busbar 1, extra energy can be supplied from the energy storage
device 5 and 6, via the second rectifier converter 3, or d.c.
to a.c. converter back to the a.c. distribution line 1. This
then supplements the previously low a.c. supply voltage being
present on the a.c. busbar 1.
To control the operation of the rectifier/converters 2
and 3, control buses 8 may be utilised, which may be controlled
from a single or separate remote control points or from the
instantaneous system voltage on the a.c. or d.c. line,
responding to bring in the operation of the a.c. to d.c.
converter 2 and also the d.c. to a.c. converter 3.
Power electronic converters, such as shown in Fig. 1, as
items 2 and 3, are known to be used on mine winders, in steel
works, and in links between power systems of different
frequencies. It is not however known to use such converters to
interchange power between the adjacent but out of phase feeders
across the open circuit breaker at the mid point switching
station, for instance in electric railways. A force
commutating inverter, such as herein described, has the added
advantage of being able to control the reactive power
generation.
In Fig. 2 is illustrated an alternative embodiment of the
AMD/0205a - 5 -
20272q2
invention, the features of Fig. 2 similar to those shown in
Fig. 1 being designated by like numerals to Fig. 1. The extra
feature shown in Fig. 2 is the provision of a transformer 9.
The transformer, having two separate secondary windings 11,
consequently has minimal coupling between the secondary
windings. By controlling the commutation of the converter, the
phase angle of the inverter output can be regulated so that the
inverter either generates or absorbs reactive power from the
single phase railway distribution system. This generation or
absorption of reactive power modifies the quantity of reactive
power transmitted from the source substation and hence the
voltage regulation throughout the single phase a.c.
distribution system.
The two secondary windings 11 required for this device
may be constructed on a common core of a transformer which
serves other functions, for example, on the core of an auto
transformer.
As with the device of Fig. 1, the device of Fig. 2 may be
arranged to function automatically, controlled by the system
voltage at the point of installation only, or it may be
controlled by common signals from remote control points to
produce changes in the performance of the single phase
distribution system at locations remote from the point of
installation. Such changes may include levelling of the demand
of the single phase railway system of the three phase supply,
voltage regulation of the single phase a.c. distribution system
and power factor control of the single phase a.c. railway
distribution system.
AMD/0205a - 6 -
20272q2
-. It will be understood that the present invention provides
a novel voltage regulation system, which will reduce the
operating costs of railway systems, and provides a more
regulated supply than the currently available weak radially
feed power systems.
It will be understood to persons skilled in the art that
numerous variations and modifications are envisaged to the
present invention. Such variations and modifications should
however be considered to fall within the spirit and the scope
of the present invention as hereinbefore described.
AMD/0205a - 7 -
