Electricity: motive power systems – Limitation of motor load – current – torque or force
Patent
1998-10-21
2000-12-19
Martin, David
Electricity: motive power systems
Limitation of motor load, current, torque or force
318254, 318138, 310184, H02K 1300
Patent
active
061631221
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to a high-efficiency electric motor of electronic commutation type.
2. Discussion of the Background
High-efficiency electrical machines of electronic commutation type, hereinafter known as ECMs, operate with pulse modulation and generally at ultrasonic frequencies, with absorption of very high ripple current pulses. Without the use of a costly and bulky L-C filter in the feed line, the conducted and radiated electrical disturbance levels would be greater than allowed by current regulations. To reduce costs, the filter can be replaced by one of active type able to decouple the current absorbed by the electric motor from the battery current. A known and particularly effective implementation, in terms both of cost and performance, is to interpose between the battery and the ECM a step-up converter current-controlled by means of R.sub.FB on the basis of control information C.sub.FB originating from the ECM, which is compared with a velocity input V.sub.set by known methods. This converter is characterised by operating with an output voltage V.sub.c greater than the battery voltage V.sub.b and by absorbing from the battery an essentially continuous current (of constant delivered power) with a ripple as small as desired, achieved by dimensioning the inductor L and the switching frequency by known methods. The waveform of the battery current i.sub.b is shown in FIG. 2, which shows the typical times associated with the operation: 1/T is the switching frequency, T.sub.on and T.sub.off are the on and off times of the electronic power switch P (FIG. 1); also shown are the ripple superimposed on the mean absorbed current and the composition of i.sub.b, consisting of the sum of i.sub.P and i.sub.D, this latter being integrated by the capacitor C to provide a mean current i.sub.2 (from an essentially continuous V.sub.c) which powers the ECM.
SUMMARY OF THE INVENTION
The object of the invention is to achieve the operability of the schematic of FIG. 1 essentially in terms of the waveform of the current absorbed from the battery, while significantly reducing cost and bulk by eliminating the inductance L and the switch P. As it is not possible to eliminate these components from an operational viewpoint, the invention proposes a solution which utilises certain switches and certain windings of the ECM, already present for its normal operation, to also perform the function of switch P and inductance L.
This object is attained according to the invention by a high-efficiency electric motor of electronic commutation type, having a single stator unit and a single rotor unit, including a first electrical submachine and a second electrical submachine, in which: with a sensor for measuring the current absorbed from the feed; said first submachine including at least two windings characterised by an inductance, a resistance, an induced electromotive force and a switch connected in series; charged at a controlled voltage; its poles connected to the end of the respective winding, which is connected to said switch, and the remaining pole connected to one of the ends of the capacitor thus charged at a controlled voltage; current absorption from said voltage source with harmonics content as low as desired and, by charging the capacitor at the voltage via the diodes, said first submachine provides the unique power supply for said second submachine.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a schematic block diagram of an electric motor of known type;
FIG. 2 shows the waveforms of the current through the motor of FIG. 1;
FIG. 3 is a schematic block diagram of the electric motor according to the invention;
FIGS. 4 and 5 are illustrations of two electromagnetic structures forming the electric
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Bitron S.P.A.
Leykin Rita
Martin David
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