Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
1999-11-05
2001-06-05
Masih, Karen (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S434000, C318S132000, C318S650000, C318S560000, C318S432000
Reexamination Certificate
active
06242875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor driving apparatus which is suited to driving of a polyphase motor.
2. Description of the Background Art
FIG. 22
is a block diagram showing the structure of a conventional motor driving apparatus as a background of the present invention. This apparatus
90
is used to drive a motor
201
which is a sensor-less (having no Hall element for detecting the rotating position) and brush-less three-phase motor. This apparatus
90
includes an output circuit
101
, a selecting circuit
102
, an induced voltage detecting circuit
108
, a commutation control circuit
120
, a starting circuit
121
, terminals SU, SV, SW, and a terminal scom. To drive the motor
201
by using the apparatus
90
, the terminals SU, SV, SW are connected to the three coil terminals of the motor
201
and the terminal scom is connected to the neutral terminal of the motor
201
.
The output circuit
101
has a plurality of switch elements (not shown) interposed between the terminals SU, SV, SW and a power-supply line (not shown) and a ground line. These plurality of switch elements are selectively turned on (conduct) and off (disconnect) to realize a plurality of current-supply patterns. The induced voltage detecting circuit
108
is connected to the terminals SU, SV, SW and the terminal scom to detect points at which the induced voltages at the terminals SU, SV, SW cross the neutral voltage of the motor
201
inputted through the terminal scom.
The commutation control circuit
120
generates and outputs a control signal A
1
for controlling on/off operation of the plurality of switch elements in the output circuit
101
on the basis of a detection signal B
2
outputted from the induced voltage detecting circuit
108
when the motor
201
is operating or when the rotor is rotating. The control signal A
1
is sequentially switched in accordance with the electrical angle of the rotor between a plurality of values corresponding to the plurality of current-supply patterns. When the motor
201
is operating, the selecting circuit
102
sends the control signal A
1
to the plurality of switch elements in the output circuit
101
as control signals C
1
to C
6
. The motor
201
is thus supplied with current in the plurality of current-supply patterns in accordance with the electrical angle of the rotor.
The starting circuit
121
outputs a control signal A
2
when starting the motor
201
, that is, when the rotor at rest starts rotating. When the motor
201
starts rotating, the selecting circuit
102
selects the control signal A
2
and sends it to the output circuit
101
as the control signals C
1
to C
6
. Thus torque for starting is given to the rotor and the rotor starts rotating. When the operation of starting the motor
201
is finished, the selecting circuit
102
selects the control signal A
1
and sends it to the output circuit
101
, as stated above.
FIG. 23
is a timing chart showing signals in individual parts of the apparatus
90
. In the apparatus
90
, when starting the motor
201
, the starting circuit
121
sequentially forces the current-supply pattern to change independently of the position of the rotor (rotating position) in a given period from the beginning of starting (to the point P in
FIG. 23
) to give starting torque to the rotor. As shown in
FIG. 23
, the control signals C
1
to C
6
(equivalent to the control signal A
2
) in the starting period from the beginning of starting to the point P change in the same order as the control signals C
1
to C
6
(equivalent to the control signal A
1
) in the driving period after the point P, with their switching time intervals gradually becoming shorter.
That is to say, in the starting period, the current-supply patterns corresponding to the range from 0 to 360° in electrical angle of the rotor in the driving period are generated irrespective of the position of the rotor. In this way, in the conventional motor driving apparatus, the current-supply patterns for starting are developed in a predetermined order irrespective of the stop position at which the rotor of the motor
201
rested before started, so that the rotor may once reversely rotate and then normally rotate when started.
Further, as shown in
FIG. 23
, in the driving period in which the rotor rotates, spike voltage appears due to switch of the current-supply pattern (i.e. commutation switch) in the induced voltages SU, SV, SW (hereinafter the terminal voltages are simply represented by the same characters as the terminals) induced at the terminals SU, SW, SW (for example, the part surrounded by the dotted circle in FIG.
23
). As has been already stated, the induced voltage detecting circuit
108
detects the points at which the induced voltages SU, SV, SW cross the neutral voltage scom (the parts surrounded by the solid circles in
FIG. 23
) and outputs the detection signal B
2
. Then the commutation control circuit
120
sequentially switches the control signal A
1
between a plurality of kinds corresponding to the plurality of current-supply patterns on the basis of the detection signal B
2
. Accordingly the spike voltage may cause the control signal A
1
to be switched by erroneous timing.
For the purpose of avoiding such erroneous detection in the induced voltage detecting circuit
108
, a mask circuit is provided to prevent the induced voltage detecting circuit
108
from detecting crossing of the induced voltages SU, SV, SW and the neutral voltage scom in the vicinities of spike voltage (mask period). However, the mask period is set to a given length of time for a structural reason of the mask circuit, and therefore the following problems arise. When the rotor of the motor
201
rotates at low speed, the ratio of the mask period to one-turn period is so small that the erroneous detection cannot be prevented sufficiently. When it rotates at high speed, the ratio of the mask period becomes unnecessarily large to possibly prevent normal detection. That is to say, it has been difficult to prevent such erroneous detection at a wide range of rotating speeds.
Also, there is another known motor driving apparatus improved to switch the current-supply pattern not instantaneously but softly in a given time width to reduce acoustic noise caused by switch of the current-supply pattern. However, this improved apparatus realizes the slanted switching by utilizing charge/discharge of a capacitance element, so that the time width for switching remains constant independently of the rotating speed. Accordingly, when the rotor rotates at high speed, the ratio of the time width for switching to one-turn period becomes large, leading to the problem that sufficiently high power cannot be obtained.
Moreover, this improved apparatus has the problem that it cannot make PWM control of the output current. A conventionally known type of motor driving apparatus makes the switching elements in the output circuit
101
perform pulsing operation on the basis of the PWM control to control the effective output current, thereby enabling versatile control of power of the motor
201
. However, the above-mentioned apparatus improved to reduce acoustic noise cannot be adapted for PWM control. In other words, a motor driving apparatus performing PWM control cannot reduce acoustic noise.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a motor driving apparatus for driving a motor by sequentially switching among a plurality of current-supply patterns in accordance with electrical angle of a rotor comprises: an output circuit having a plurality of switch elements individually interposed between a plurality of terminals of the motor, and first and second power-supply lines; a detection control circuit for controlling the plurality of switch elements to sequentially switch among the plurality of current-supply patterns while the rotor is resting; a current detecting circuit for detecting current flowing through the plurality of terminals; a position detecting circuit for detecting stop position of the ro
Kondoh Shunichi
Kusaka Satoshi
Burns Doane , Swecker, Mathis LLP
Masih Karen
Mitsubishi Denki & Kabushiki Kaisha
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