Electronically commutated motor

Details Electronically commutated motor Electronically commutated motor

2000-12-12

2001-10-23

Nappi, Robert E. (Department: 2837)

Electricity: motive power systems

Switched reluctance motor commutation control

C318S434000, C318S132000

Reexamination Certificate

active

06307338

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an electronically commutated motor having at least two stator winding strands or phases, each of which can be actuated by means of an associated power transistor. Such motors are often referred to as “two-phase” motors and are used in great quantities, above all in fans.
FIG. 6
shows one of the circuits presently used by the Applicant for controlling such motors.
BACKGROUND
Often, such motors must be capable of being operated on very differing voltages, e.g. a fan with a nominal voltage of 24 V is, in practice, operated with voltages ranging between 12 V and 32 V, which represents a voltage deviation range from −50% to +30%. Depending upon voltage, such a fan runs at a desired speed (RPM), i.e. slowly at lower voltages, and fast at higher voltages.
Upon commutation of the motor current from one stator winding phase to another, the switchover can occur in a “hard” or in a “soft” manner. A hard switchover offers good efficiency, but high structure-borne noise levels caused by commutation noise and, additionally, EMC problems (EMC=Electro-Magnetic Compatibility). Further, protective measures must be taken for the end-stage transistors, so that the critical limit values of the components (permissible collector voltages etc.) are not exceeded. This can be accomplished by internal Z-diodes contained in the end-stage transistors or by external Z-diodes (for limiting these voltages) or by recovery diodes which feed back the shutoff energy of the windings to an operating voltage link circuit containing a capacitor capable of receiving this shutoff energy.
FIG. 6
shows a motor
10
with two stator winding strands or phases
12
,
14
and a (schematically indicated) permanent magnet rotor
16
, in whose vicinity a Hall generator
18
is located. Hall generator
18
is also shown in the left portion of FIG.
6
. Ohmic resistors of phases
12
and
14
are designated
20
and
22
, respectively. Phase
12
is connected in series with an npn Darlington transistor
24
with built-in recovery diode
26
, and phase
14
is connected in series with an npn Darlington transistor
28
with built-in recovery diode
30
. The emitters of transistors
24
,
28
are connected via a common emitter resistor
32
to a negative conductor
34
. Phases
12
,
14
are connected to a positive conductor
36
, as shown. Conductors
34
,
36
are, during operation, connected to a power supply device
38
which contains a storage capacitor
40
. This serves to take up the shutoff energy of phases
12
,
14
, which is fed back via recovery diodes
26
,
30
into this capacitor
40
. To the extent that the motor is supplied from an accumulator, the shutoff energy is fed back into the accumulator.
Hall generator
18
is connected via a resistor
42
with positive conductor
36
and via a resistor
44
with negative conductor
34
. Its output signal U
H
(
FIG. 7A
) is applied to both inputs IN
1
and IN
2
of an IC (Integrated Circuit)
46
which generates signals OUT
1
and OUT
2
for controlling transistors
24
,
26
and simultaneously serves as blocking or stall protection for motor
10
, i.e. when it is unable to turn, it is switched off by IC
46
.
This IC is preferably the ROHM BA6406.
FIG. 7A
shows the signal U
H
,
FIG. 7B
shows the signal OUT
1
of IC
46
and
FIG. 7C
shows the signal OUT
2
. Signals OUT
1
and OUT
2
run in phase opposition to each other. FIG. OUT
1
is fed via a resistor
50
(e.g. 8.2 k&OHgr;) to the base of transistor
24
, which is connected via a capacitor
52
(e.g. 1 Nf) to the collector and via a base drain-off resistor
54
(e.g. 1.2 k&OHgr;) to negative conductor
34
. In the same manner, signal OUT
2
is fed via a resistor
56
to the base of transistor
28
, which is connected via a capacitor
58
with its collector and via a base drain-off resistor
60
with negative conductor
34
.
During operation, transistors
24
,
28
are alternately switched on by signals OUT
1
, OUT
2
. Through the combination of resistor
50
and capacitor
52
and the common resistor
32
, a soft switching of transistor
24
is achieved. Similarly, resistor
56
, in combination with capacitor
58
and common resistor
32
, effects a soft switching of transistor
28
. However, these measures cause an increased warming of transistors
24
,
28
and therefore a reduction in efficiency. Furthermore, the circuit can be optimally configured only for a single operating point, i.e. for a specified RPM and a specified torque. This results in many compromises, especially with respect to voltage overruns and temperature overruns. One also obtains, in practice, a voltage range only of ±15%.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a new electronically commutated motor.
In accordance with the invention, this object is achieved by adding latching circuitry, including two transistors, to prevent simultaneous conduction of both power transistors. By the alternate biasing of the power transistors, one achieves that such a motor is usable over a large range of its operating voltage U
B
; and further, that, during commutation, both power transistors are briefly blocked, which minimizes braking torques and improves efficiency, and that the kind of commutation can be adapted to the rotation speed (soft commutation at low RPM, hard commutation at higher RPM). This can be achieved by making the kind of ascent and descent of the commutation signal dependent upon the RPM. Such a solution is also very economical.


REFERENCES:
patent: 4356437 (1982-10-01), Saito et al.
patent: 4542323 (1985-09-01), Doemen
patent: 4626751 (1986-12-01), Doemen
patent: 4734627 (1988-03-01), Koerner
patent: 4748386 (1988-05-01), Nakanishi et al.
patent: 5349275 (1994-09-01), Muller
patent: 5563480 (1996-10-01), Okada
patent: 5731674 (1998-03-01), Jeske
patent: 23 46 380 (1974-11-01), None
patent: 28 22 315 C2 (1979-12-01), None
patent: 33 48 986 A1 (1985-06-01), None
patent: 36 28 306 (1988-02-01), None
patent: 0 722 214 A1 (1996-07-01), None
Zetex Corp. datasheet: ZTX600 NPN Silicon Planar Medium Power Darlington Transistors, Jun. 1994.
Philips datasheet: BC846; BC847 NPN general purpose transistors, Apr. 23, 1999, 8 pp.
Rohm Co. Ltd. datasheet: 2-phase half-wave motor predriver BA6406F, pp. 696-699, Aug. 2000.
WPI English abstract of Müller/Papst DE 36 28 306, publ. Feb. 25, 1988.
WPI English abstract of Papst FR 2,244,290 publ. May 16, 1975 & DE 23 46 380 filed Sep. 14, 1973.

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