Electrical transmission or interconnection systems – With current collection or transfer
Reexamination Certificate
2000-08-14
2003-09-16
Leja, Ronald W. (Department: 2836)
Electrical transmission or interconnection systems
With current collection or transfer
Reexamination Certificate
active
06621183
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to the supply of power to the trackway conductors forming the primary circuit of an inductive power supply system; in particular this invention relates to the supply of power to the trackway conductors connected in a series resonant circuit which comprises the primary circuit of an inductive power supply system capable of distributing inductive power over a distance.
BACKGROUND
An inductive power transfer system generally comprises (a) a generator of alternating current, (b) one or more conductors carrying the alternating current as tracks (the “primary inductive pathway”) to one or more consumers, (c) a space carrying an alternating magnetic flux as a consequence of current flow within the conductor(s), (d) a pickup means (the “secondary winding”), which intercepts a part of the magnetic flux, and (e) power consuming means. Systems originating from our developments have been characterised by inclusion of: (f) an operating frequency generally above 10 kHz, (g) a tuned, resonant primary and a tuned, resonant secondary, (h) loose coupling between primary and secondary, and (i) provide power control by means of partial decoupling of the secondary without significantly affecting other consumers sharing the same primary conductors.
We first developed parallel tuned primary inductive pathways for inductive power transfer. When inductive power transfer is to be applied to systems including relatively long primary inductive pathways or tracks, high-frequency alternating currents at the high voltage that is required to drive parallel-tuned tracks become rather difficult to generate in a practicable manner. The high voltage is required in order to insert sufficient current into the track, given an unavoidable track inductance. It is difficult to drive a long, parallel-tuned track because (apart from safety and insulation considerations) there are finite limits to the voltage that can be switched, and handled, using known technology. Furthermore, safety is a real issue. Track extension methods are not suitable for parallel tuned tracks because when the track length is increased the “group velocity” of the track tends to zero while the characteristic impedance at the required frequency tends to infinity. In contrast, series compensated tracks can be extended using “modules” including lumped series capacitors, without adding to the number of system poles.
Previous techniques for generating AC resonant currents in inductive power transfer have generally been optimised for the case of parallel-tuned circuits. An example high-frequency converter (see
FIG. 1
) has a half-bridge configuration. The action of the switches can be regarded simply as adding boosts to the resonating current, like maintaining a child's movements on a swing. Usefully, the switches generally change state at or very close to a zero-voltage condition and switching losses are thereby minimised. In our preferred version, the resonating capacitance is generally a lumped capacitance within or close to the power supply, and the track inductance comprises most of the resonating inductance. The current in the track is a relatively pure sine wave. This type of converter is described for example in our Application No: PCT/GB92/01463. It can be regarded as a “half-bridge” converter, where a centre-tapped inductor having a high reactance forms a passive half of a bridge and provides a DC return path. This type of converter is generally used in a “slave” mode in that its switching frequency is determined by the actual resonant frequency of the system. The particular converter that we have selected is quite efficient, has low switching losses, and the switches themselves do not carry the magnetising current of the track. However it does have a propensity to detuning and having an unstable frequency under heavy loads, and the energy stored in the DC inductor may cause a voltage and/or current overshoot if the load is reduced suddenly.
Now that the advantages of series compensated tracks (as defined later) are becoming evident, and series compensated tracks are seen as being more relevant to commercialisation of inductive power transfer, other types of power supply may be preferable.
Furthermore, for possible applications such as the provision of inductive power to rail vehicles, there is a need to raise the amount of current that can be fed into a given track, and to raise the distance over which that current can be effective, and in general there is a need for reduction of the capital costs associated with an installation.
DEFINITION
A series compensated track for use in inductive power transfer systems may be described as an elongated conductive loop wherein the outgoing and return conductors are parallel and spaced apart. During installation the inductive reactance is maintained at or near a relatively small value despite extensions of length, by inserting sets of discrete capacitors in series with the conductors at one or more evenly spaced sites. One example “small value” of inductance is 620 &mgr;H—in relation to a track energised at 15 kHz, resistance 0.4 ohms, circulating current 250 A, at 1 kV rms.
OBJECT
It is an object of this invention to provide improved means for energising an inductive power transfer system, or at least to provide the public with a useful choice.
STATEMENT OF INVENTION
In a first broad aspect the invention provides apparatus for the supply of power from an alternating power source to the primary conductors of an inductive power transfer system having at least one tuned primary trackway; each primary trackway having an inherent resonant frequency, wherein the apparatus includes at least one reactive network having an input and an output; the network being capable of being connected between the power source and at least one primary trackway, said network including at least one inductance having a selected value and connected to at least one capacitance having a selected value, said network being capable of affecting a transfer of power between the supply of power and the at least one primary trackway.
Preferably the tuned primary trackway includes one or more series compensating capacitors along its length
In a related aspect the invention provides apparatus as previously described, wherein the network comprises a transconductance pi network (as herein defined) including one or more inductors and one or more capacitors, the transconductance pi network having an input and an output; the network being capable of being connected at the input to the power source and at the output to at least one primary trackway, wherein the network is capable of providing a deliberately mismatched coupling between the source of alternating power and the primary trackway so that the source appears to present a substantially infinite impedance and the primary trackway appears to present a substantially zero impedance; and so that the voltage at the output of the transconductance pi network may in use be substantially greater than that provided to the input of the transconductance pi network.
In another related aspect the invention provides apparatus as previously described, wherein the component values within any one transconductance pi network are selected so that the network is capable of determining the proportion of circulating current to be fed from the output of the network into the primary trackway and so that the amount of circulating current within the primary trackway can be controlled.
In a further related aspect the invention provides apparatus as previously described, wherein the apparatus comprises at least one transconductance pi network, each network being connected to a corresponding primary trackway, the network or networks being capable by means of a selection of suitable component values of determining the proportion of circulating current that may be fed from the network into each primary trackway so that the amount of circulating current within the primary trackway can be controlled.
In yet another related aspect the invention provides apparatu
Auckland Uniservices Ltd.
Leja Ronald W.
Saliwanchik Lloyd & Saliwanchik
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