Electricity: motive power systems – Plural – diverse or diversely controlled electric motors – Series-parallel connected motors
Patent
1982-04-30
1985-07-30
Shoop, William M.
Electricity: motive power systems
Plural, diverse or diversely controlled electric motors
Series-parallel connected motors
318113, 318733, 318734, 318748, 318244, H02P 774
Patent
active
045324581
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrical machines which can be operated over a range of speeds.
Variable-speed electrical machines exist in various forms but in general to achieve a variable speed a machine has to have a more complicated construction, and often associated complex control circuits, than a machine for single speed operation. Examples include d.c. machines with commutators and brush gear and field and/or armature current control equipment and a.c. machines with complex inverters to provide reliable commutation of s.c.r. devices under a range of operating conditions. Compound machines or machine sets, such as the Ward-Leonard arrangement, are also known. Other approaches include pole-switching, e.g. a 2/16 pole induction motor, and the pole amplitude modulation technique. The pole-switching technique while simple and robust has the penalty that a larger machine frame is needed as in effect the windings for both a 2 pole and a 16 pole machine have to be accommodated.
With the present requirements to save both energy and materials there is a need for electrical machines which are economical in power and material consumption while a simple and inexpensive variable speed capability for a machine with the rugged construction of the induction motor type is also desirable. Generators with the ability to operate well at a range of speeds are also in demand, particularly for wind or water power drive.
Speed control for machines of the induction type, in practical terms, is preferably at constant efficiency or constant torque and varies the synchronous speed of the machine, that is the speed, V.sub.s, of the electromagnetic wave along the air gap periphery where V.sub.s =2T.sub.p f. T.sub.p is the pole pitch and f the supply frequency. Clearly the pole switching technique varies T.sub.p. The variable-frequency inverter or mechanical commutator techniques vary f. The pole amplitude modulation technique varies the value of V.sub.s by using a specific form of winding and external switches. Where some form of power conversion, e.g. an inverter, is used it is also possible to achieve speed control by varying the voltage supplied to the machine.
It is an object of the invention to provide an improved electrical machine arrangement for economic operation over a range of speeds.
In the Specification of UK Published Patent Application 2058478 and corresponding Applications in other countries including U.S. Ser. No., 179,781, incorporated herein by reference, there is described an electrical machine having a space-transient in the field conditions. Such a transient is there described as being provided in various ways including the use of some poles with shorter pitch than the remainder. The existence of the space-transient enables a motor form of the machine to recover energy from the rotor in a beneficial phase relation with the energy supplied to the machine. The recovered energy can be applied to improve the power factor or efficiency or other operating parameter of the machine, as described in the above mentioned specifications.
According to the present invention there is provided an electrical machine arrangement having an air gap and a winding in separate parts to create in the air-gap, in operation, a machine air-gap moving flux having a space-transient the arrangement including means to alter a current in a part of the winding to vary the effective speed of movement of the flux along the air-gap, whereby the adjustment provides continuously variable control of at least one of the machine operating parameters including speed, torque and efficiency.
Some of the separate parts of the winding may be connected to an electrical power network and others of the separate parts to a variable impedance.
Some of the separate parts of the winding may be connected to an electrical power network in a specific phase arrangement and others of the separate parts connected thereto in a different phase arrangement to apply rotor induced voltage to said some winding parts in parallel with a power network voltage but with a phase
REFERENCES:
patent: 2018287 (1935-10-01), Sousedik
patent: 2341095 (1944-02-01), Hansen
patent: 2500595 (1950-03-01), James et al.
patent: 3161795 (1964-12-01), Bekey
patent: 4189654 (1980-02-01), Mourier
patent: 4208620 (1980-06-01), Ringland
Kuznetsov Stephen B.
Laithwaite Eric R.
Ip Paul Shik Luen
National Research Development Corporation
Shoop William M.
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