Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2002-08-20
2004-03-23
Masih, Karen (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S132000, C318S254100, C318S801000, C318S811000
Reexamination Certificate
active
06710564
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods and apparatus for controlling brushless motors used for driving compressors in automotive air conditioning system. In particular, the present invention relates to methods and apparatus for controlling brushless motors used for driving compressors in automotive air conditioning system. Such compressors are driven by electricity used in electrically driven vehicles, such as hybrid vehicles, fuel-cell vehicles, or the like.
2. Description of Related Art
Electrically driven vehicles including hybrid vehicles, fuel-cell vehicles, or the like, which have electric driving sources, have been developed in order to reduce environmental contamination. Such electrically driven vehicles generally have an air conditioning system including a compressor driven by a brushless motor. An inverter delivers driving power in three-phase current to the brushless motor.
Apparatus for controlling such brushless motors are known in the art. Such known apparatus may include an inverter. For example, known apparatus for controlling brushless motors are disclosed in Japanese Unexamined Patent Publication Nos. 2001-103785, 2001-119984, and 2001-78485. In such known apparatus, direct current (DC) is provided from a DC power source, e.g., a battery, to the inverter. The inverter controls a plurality of switching elements by switching a state on-and-off to achieve phase switching. As such, power output from the inverter is generated in the form of a three-phase-current and is provided to the brushless motor. At the same time, the switching time for each switching element in the on-state is controlled by a known pulse width modulation (PWM) control. An electric power supplied to the brushless motor may be varied, and a rotational speed of the brushless motor may be adjusted. As a result, the rotational speed of the compressor in the air conditioning system for a vehicle may be adjusted, and the temperature in a compartment of the vehicle may be adjusted.
As shown in
FIG. 8
, one example of a known apparatus for controlling a brushless motor using a PWM control is depicted. The known apparatus includes a switching elements group
92
having six switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, and
92
Z, a filter circuit
94
, a controller
95
, a memory
96
, and a voltage detector
97
. Controller
95
detects a rotational position of a brushless motor
93
via filter circuit
94
. Subsequently, controller
95
may drive switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, and
92
Z based on the detected rotational position. A direct current output from a DC power source
91
may be converted to a three-phase current at switching elements group
92
, and the three-phase current may then be provided to motor
93
.
In addition, as shown in a timing chart of
FIG. 9
, switching the state of switching elements
92
X,
92
Y, and
92
Z on and off on a lower side of the inverter is controlled by the PWM control, so that an electric power supplied to motor
93
is varied. As a result, the rotational speed of motor
93
may be adjusted.
Nevertheless, when switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, and
92
Z are switched on and off, due to the influence of stray inductors L
1
and L
2
shown in
FIG. 8
, an upsurging voltage (hereinafter a “transient voltage”) may occur between an emitter and a collector of switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, or
92
Z when switched into the off-state because of the transient voltage phenomena. When the flow of current is increased in motor
93
, a frequency with which the state of each switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, or
92
Z is switched. As a result, the maximum value of the transient voltage may be increased. Therefore, the transient voltage may affect a threshold voltage in selecting each switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, or
92
Z.
As shown in
FIG. 10
, a first transient voltage V
1
occurs between an emitter and a collector of switching elements
92
U,
92
V, and
92
W in the off state, when switching elements
92
U,
92
V, and
92
W at an upper side of the inverter are switched on and off. A second transient voltage V
2
occurs between an emitter and a collector of switching elements
92
X,
92
Y, and
92
Z in off-state, when switching elements
92
X,
92
Y, and
92
Z are switched on and off at the lower side of the inverter by the PWM control. Moreover, both the first transient voltage V
1
and the second transient voltage V
2
are greater than the voltage in a normal condition. This relationship between voltages is known in the art.
In addition, as shown in
FIG. 11
, if duty ratio of the PWM control is varied, the timing of the occurrence of the second transient voltage V
2
is advanced, and waveforms of the first transient voltage V
1
and the second transient voltage V
2
overlap. As a result, the first transient voltage V
1
and the second transient voltage V
2
are combined, and a third transient voltage V
3
may occur. The maximum value of third transient voltage V
3
may be greater than that of first transient voltage V
1
and second transient voltage V
2
. Due to the occurrence of the third transient voltage V
3
, certain problems may arise. First, if the third transient voltage V
3
exceeds a maximum allowable voltage Vmax of switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, or
92
Z, switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, or
92
Z may be damaged or destroyed. Second, in order to avoid damaging switching elements
92
U,
92
V,
92
W,
92
X,
92
Y, or
92
Z, if the switching elements having a greater maximum allowable voltage Vmax are selected, the cost of the switching elements may increase. Third, a noise occurring at the inverter may be increased due to the presence of the third transient voltage V
3
. A malfunction of electric circuits in the inverter may occur due to the noise, and the noise may affect another electrical components. Fourth, in order to suppress the third transient voltage V
3
, a large, transient voltage absorbing circuit may be necessary. As a result, the manufacturing cost and the size of the apparatus for controlling the brushless motor may be increased.
SUMMARY OF THE INVENTION
Therefore, a need has arisen for apparatus for controlling brushless motor and methods of employing such apparatus that overcome these and other shortcomings of the related art. A technical advantage of the present invention is that negative effects due to a transient voltage, occurring at the time during which switching elements are operated or cycled, may be reduced in a low cost.
According to an embodiment of the present invention, a method or apparatus for controlling a brushless motor has an inverter providing a current to the brushless motor. The inverter comprises a first plurality of switching elements, a second plurality of switching elements, and a drive control device. The first plurality of switching elements are connected between a first terminal of a DC power source and a phase terminal of each coil of the brushless motor. The second plurality of switching elements arc connected between a second terminal of the power source and a phase terminal of each coil of the brushless motor. The drive control device selects a state of the first plurality of switching elements and switches either the state of the first plurality of switching elements or the state of the second plurality of switching elements by mean of a pulse width modulation (PWM) control, so that the drive control device controls a rotational speed of the brush less motor. The switching of the state of the first plurality of switching elements by the PWM control is altered, i.e., advanced (made to occur earlier) or delayed (made to occur later), such that a combined voltage of a first transient voltage and a second transient voltage is less than a voltage limit, e.g., a maximum allowable voltage, of the first plurality of switching elements or of the second plurality of switching elements. The first t
Shibuya Makoto
Takano Norimasa
Baker & Botts L.L.P.
Masih Karen
Sanden Corporation
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