Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-11-08
2001-11-13
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C307S104000
Reexamination Certificate
active
06317338
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a power supply for an electroluminescent display, and to the use of inductive power transfer to provide power across an extended gap between a primary inductive trackway and a secondary pickup device, for a range of purposes including motive power, battery charging and lighting, including lighting using electroluminescent panels.
BACKGROUND
Inductive power transfer, although contactless, has in most applications in the prior art using primary pathways required that the configurations shall include ferromagnetic cores and that the secondary or pickup shall be quite closely placed in proximity to, or about the primary conductor. For example, Kelley in U.S. Pat. No. 4,833,337 uses elongated ferrite inverted “U” cores and a ferrite member fixed to the primary pathway as well. BOYS& Green (WO92/17929) use “E” cores with one primary conductor located inside each space between the three limbs of the “E”. Bolger (U.S. Pat. No. 3,914,562) teaches a 120 Hz primary inductive cable along a roadway, the cable having iron laminations along its entire length. These laminations face corresponding laminations within the moving vehicles that draw power from the tracks. These are expensive, heavy constructions which will exhibit magnetic attraction forces and any magnetostrictive effects within the cores will tend to cause noise. For transferring power to moving road vehicles, avoidance of core structures (at least in the primary pathway) and a wider tolerance in positioning is clearly useful.
Inductive power transfer systems in which various portions of the system are tuned to resonance are somewhat liable to instability should one or more resonant circuits assume a different resonant frequency to that of the system mean. Means to enhance stability are always useful, given that resonance is in most cases the preferred way to optimise the transfer of inductive power.
There are many applications in attention-gathering fields (i.e. advertising) in which it will be useful to extend the gap over which a useful field can be transmitted under inductive power transfer principles. Advantages of doing this include the concealment of the power sources so that panels appear to magically light up without a visible connection. Hence the use of inductive power transfer, which itself may involve higher frequencies, as a way of driving electroluminescent panels across a gap and without bare wires or contacts is a useful venture.
Electroluminescent panels have been available since at least 1957 as a source of lighting or of display and advertising material, yet they have proven to be difficult to drive at an acceptable level of brightness and at the same time retain a reasonably long life. Panels require a relatively high frequency (well above mains frequency) in order to glow at a useful level. Prior-art driving circuits such as dedicated chips rely on inverters to develop AC power at typically 800-1200 Hz, and up to typically 50 V peak-to-peak. Because the output of those inverters is substantially a square-wave waveform the phosphors of the panels are not excited optimally and brightness is not remarkable. Attempts to get more light with higher driving voltage usually results in breakdown of the dielectric and a failure of the panel, or a markedly curtailed life. There may be thermal runaway effects involved.
OBJECT
It is an object of this invention to provide an improved way to drive loads such as (but not limited to) electroluminescent panels across a gap using inductively transferred electric power, or at least to provide the public with a useful choice.
STATEMENT OF THE INVENTION
In a first broad aspect the invention provides means for inductive power transfer across an extended gap between a primary conductor and a secondary resonant pickup circuit, the means comprising an intermediate resonant loop, resonant at a system-side resonant frequency and capable of being positioned within an inductive power transfer system so that inductive power is capable of being coupled inductively from the primary inductive conductor through the intermediate resonant loop to the at least one secondary resonant pickup circuit capable of collecting the inductive power.
Preferably the invention provides means for coupling inductive power as described in this section, wherein the intermediate resonant loop comprises a capacitance and an inductance, together resonant at the system-side resonant frequency.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the inductance may comprise at least one lumped inductance and at least one extended inductance.
Optionally the at least one element having inductance within the intermediate resonant loop may comprise at least one intermediate lumped inductance comprised of a sub-loop having one or more turns and at least one extended intermediate inductance being the inductance of the loop itself.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the at least one lumped inductance is capable of receiving inductive power from a primary conductor. Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the intermediate resonant loop is extended over a lateral distance so that one or more, spaced-apart, secondary resonant circuits may draw power from the intermediate resonant loop.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the intermediate resonant loop includes means to limit the amount of resonating current flowing.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the means to limit the amount of resonating current flowing includes means for at least partial decoupling of the intermediate loop from the primary conductor.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the secondary resonant circuit provides motive power to an electrically powered vehicle.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the intermediate resonant circuit is extended over a lateral distance beneath at least a part of a route taken by a vehicle, so that the intermediate resonant circuit is capable of providing power to the vehicle when the vehicle is situated adjacent to the position of the intermediate resonant circuit.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the intermediate resonant circuit provides a charging current to one or more battery units within a vehicle when the vehicle is situated adjacent to the position of the intermediate resonant circuit, such as at a bus stop.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the intermediate resonant circuit provides frequency stability to an inductively powered system.
Preferably the invention provides means for coupling inductive power as claimed in the preceding claim, wherein the intermediate resonant circuit includes active frequency-adjusting means or the like to overcome any system instability that may arise.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the intermediate resonant circuit provides a charging current to one or more battery units.
Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the secondary resonant circuit provides electric power to a light source. Preferably the invention provides means for coupling inductive power as described elsewhere in this section, wherein the electrically powered light source is an electroluminescent panel driven with substantially sine-wave alternating current at an effective voltage and at an effective freq
Auckland UniServices Limited
Laxton Gary L.
Wong Peter S.
Young & Thompson
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