Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
1998-08-07
2003-02-04
Nappi, Robert E. (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C307S010100, C191S010000
Reexamination Certificate
active
06515878
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electrical power distribution systems, and more particularly, to methods and apparatus for contactless transfer (especially magnetic transfer) of electric power from primary electric conductors to secondary pick-up coils.
BACKGROUND OF THE INVENTION
In many applications, passenger and cargo transport systems such as trains or monorails carry electric rotating or linear motors to provide propulsion. The motors for such systems generally have brushes for proper distribution of the electric energy within the motors. The electric power is produced by power supplies. In addition, the power supplies for these transport systems usually use either on-board batteries or pantographs that draw electric power to the transport system from conductors that parallel the route of the transport systems. The electric power can also be supplied by means of busbars with sliding contact-type current collectors, flexible-cable festoon systems, or cable reels, as well as other cable handling devices.
Many applications impose extraordinarily strenuous operating conditions. These include the need for higher speed and/or acceleration, complex track configurations, and difficult environmental conditions.
Battery life limits the utility of battery-powered transport systems. Sparking, noise and high installation costs limit the utility of pantographs and/or the motors. Wear and tear and maintenance costs limit the utility of all of the passenger transport systems described above because they are unreliable and maintenance intensive.
The difficult environmental conditions make conventional transport systems vulnerable to water, wind, snow and ice, as well as explosive atmosphere, dirt and other possible ambient situations. In addition, conventional transport systems can be hazardous in operation, producing, for example, arcing and sparking, as well as being electrically charged and, therefore, not touch-proof.
Contactless inductive power transfer offers an attractive alternative to the transport systems described above because it is free of sparking, wear and tear and hazardous operation. Such power transfer is also safe, quiet and marked by a high reliability. Further, contactless inductive power transfer offers unlimited speed and acceleration. Prior art proposals of contactless inductive power transfer systems have not resulted in a wide usage of contactless power transfer because satisfactory inductive transfer of electric power can only be accomplished by taking additional factors into account.
In the prior art, a number of patents have issued to disclosing inductive electric power transfer to moving devices. Generally all of these prior art patents describe the transfer of small quantities of electric power since a relatively high quantity of apparent power is required as a consequence of the large air gap in such prior art systems.
There have also been a number of patents describing motive energy transfer (for example, Tesla, in U.S. Pat. No. 514,972). However, the historic patent that is the most relevant to the present invention is that of Hutin, et al. (U.S. Pat. No. 527,857) which, in 1984, described the use of alternating current induction at approximately 3 kHz. In 1974, Otto (in New Zealand Patent Number 167,422) suggested a practical solution for inductive power transfer using a series resonant secondary winding operating in the range of 4 to 10 kHz for the inductive power transfer to a moving vehicle.
In 1994 Boys and Green (U.S. Pat. No. 5,293,308) suggested another practical system for one-way inductive power transfer, using the results of Otto with regard to the resonant secondary winding and adding some devices to improve the transfer characteristics. The Boys-Green system adds a capacitor in parallel to the primary. This method reduces the required apparent power but has at least two disadvantages. One disadvantage is that the point of compensation varies with the secondary load. The power factor of this and other prior art systems is load-dependent and never equals unity. The other disadvantage of the Boys-Green system is that a large amount of reactive power circulates in the primary, resulting in high primary losses and lower efficiencies which are unfortunately nearly independent of the transferred power. To reduce the effects of these disadvantages, Boys, et al. suggest tuning a primary parallel capacitor at a ringing frequency that depends on, and is disturbed by, the secondary load conditions. Consequently, only limited amounts of real power can be transferred in these prior art systems, leading to their marginal utility. Boys, et al. also suggest using Litz cable for the primary in order to reduce the losses in the primary. Further suggestions reflect the need for special design of control and hardware components to achieve other and less no important power transfer characteristics. For example, complex primary-secondary magnetic decoupling is required for multiple secondaries, and complex primary segmenting and tuning design results in system constraints.
In 1993 Nishino and Boys (New Zealand patent application NZ93/00032) suggested forming the primary from a number of modules that are pre-tuned primary segments connected in series. Linking poles with the same polarity with a non-inductive cable tends to constrain their system, limiting the possible resonant frequencies.
SUMMARY OF THE INVENTION
The present invention provides an improved system for the inductive (magnetic) transfer of large quantities of electric power due to its high efficiency, simple design and low installation costs. It accomplishes this, in part, through its novel pickup coil design, unique power factor compensation and power transfer circuitry, and reverse power flow capability. The invention is applicable to systems which include AC or DC sources and one or more AC and/or DC, active and/or passive secondary loads. The simplified design of the invention accommodates the use of standard components and thereby reduces the installed cost for typical applications.
The inventive contactless power system (CPS) overcomes the following limitations, among others: it provides forward and reverse power transfer capability; it has a unity power factor under all load conditions; it applies only real power to the primary, leading to higher efficiency and greater power transfer capability; the quantity of transferred power is limited only by the primary capacity; primary-secondary magnetic decoupling is not required for multiple secondaries; and it has a simple primary geometry without any system constraints.
The inventive system has a large number of aspects. It is a universal contactless power system which magnetically transfers large quantities of in-phase (i.e., power factor=1) electrical power bidirectionally between an AC or DC primary source and one or more AC and/or DC secondary loads which are active and/or passive.
The inventive system has a distributed-winding pickup coil that improves primary-secondary magnetic coupling, which increases efficiency and permits greater power transfer. The pickup coil has parallel compensation, and consists of either fixed resonant parallel capacitors or parallel capacitors with additional adaptive compensation. This additional adaptive compensation transfers in-phase power to the load at a constant voltage, regardless of the magnetic or state (i.e., consuming or generating) of the load. In contrast to the prior art and as an additional aspect, the present invention uses a new pickup coil design that consists of two windings which are partly magnetically coupled and partly magnetically not coupled. The two windings are each distributed on the middle yoke and a distinct one of the side yokes of a ferromagnetic core, leading to significantly improved magnetic coupling and power transfer efficiency between the primary inductive loop and the pickup coil.
In another aspect of this invention, the two windings of the pickup coil are each connected to a parallel resonant capacitor and compensated to unity power factor.
In another
Meins Jürgen G.
Sinsley John D.
Laxton Gary L.
Nappi Robert E.
Storwick Robert M.
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