Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2002-06-20
2004-01-06
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S254100, C318S132000, C318S599000, C318S801000, C318S802000, C318S803000, C318S804000, C318S805000, C318S806000, C318S807000, C318S808000, C318S809000, C318S810000, C318S811000
Reexamination Certificate
active
06674258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to motor drive technology, and more particularly, to a motor drive technology of a pulse width modulation (PWM) system.
As PWM drive systems for a brushless motor, a triangular wave slicing system and a peak current detecting system are known. In the triangular wave slicing system, a coil current is made to flow through a detection resistance, and the difference between a voltage generated at the detection resistance and a torque command voltage is output as a slice level by an error amplifier. A triangular wave having a constant period is sliced with the slice level, to determine the time period (ON period) during which the current flows to the coil. In the peak current detecting system, which uses no error amplifier, supply of a current to a coil is halted when the voltage generated at the current detection resistance, through which the coil current flows, reaches the torque command voltage, and a regenerative current mode is started.
FIG. 13
is a block diagram of a conventional motor driver of the peak current detecting method. Referring to
FIG. 13
, Hall sensors
21
A,
21
B and
21
C detect the position of a rotor of a motor
10
and output the detection results to a position detection circuit
22
as Hall sensor outputs S
11
, S
12
and S
13
, respectively. The position detection circuit
22
determines position signals S
21
, S
22
and S
23
based on the Hall sensor outputs S
11
, S
12
and S
13
, respectively, and outputs the signals to a phase switch circuit
93
. The position signals S
21
, S
22
and S
23
are signals obtained by shifting the phase of the Hall sensor outputs S
11
, S
12
and S
13
by 30°.
The phase switch circuit
93
determines the phases of currents to pass according to the position signals S
21
, S
22
and S
23
. For easy measurement of the phase currents, the phase switch circuit
93
blocks flow of one of three phase currents. A Logic control circuit
95
, set upon receipt of a reference pulse PI, controls supply of currents to the motor
10
by changing the level of signals output to the phase switch circuit
93
. The reference pulse PI is a periodical pulse.
FIG. 14
is a graph showing changes with time of phase currents for the motor driven by the motor driver of FIG.
13
. In
FIG. 14
, phase currents
11
,
12
and
13
in U, V and W phases, respectively, are shown, and currents flowing from drive transistors
1
to
6
toward the motor
10
are considered positive. As is found from
FIG. 14
, there is always one phase current that becomes zero, and thus there occurs sharp change of any of the phase currents every electrical angle of 60°.
Assume that the logic control circuit
95
has been set with the reference pulse PI. The phase switch circuit
93
turns ON only the W-phase upper side drive transistor
5
and the U-phase lower side drive transistor
2
, for example. In this state, a current flows to a current detection resistance
7
via a W-phase coil
13
and a U-phase coil
11
. The magnitude of this current can therefore be detected as the voltage generated at the current detection resistance
7
. Since this current flows through the inductive coils, the current gradually increases after the conduction of the drive transistors
2
and
5
.
With increase of the current, the voltage generated at the current detection resistance
7
increases, and when it reaches a torque command voltage TI, the level of the output of a comparator
96
changes, causing the logic control circuit
95
to be reset. The reset logic control circuit
95
reverses the level of a signal output to the phase switch circuit
93
. On receipt of this signal, the phase switch circuit
93
turns OFF the drive transistor
2
.
The time period from the setting of the logic control circuit
95
until the reset thereof corresponds to the on-duty period of switching operation. After the reset of the logic control circuit
95
, the current flowing through the coils
11
and
13
still attempts to continue the flow, and this causes a regenerative current to flow through a diode
1
D existing between the source and drain of the drive transistor
1
. Since the regenerative current does not pass through the current detection resistance
7
, the voltage generated at the current detection resistance
7
is zero during the flow of the regenerative current.
The regenerative current gradually decreases. However, upon receipt of the reference pulse PI, the logic control circuit
95
is set again, and the phase switch circuit
93
turns ON the drive transistor
2
. This operation is repeated until the phase switch circuit
93
switches the phases of currents to pass. In this way, as a result of the alternate flow of the drive current flowing when the logic control circuit
95
is set and the regenerative current flowing when the logic control circuit
95
is reset, a phase current roughly corresponding to the torque command voltage TI is allowed to flow through a predetermined coil.
FIG. 15
is a graph showing the current detection resistance voltage (motor current detection signal) MC and the V-phase and W-phase currents
12
and
13
at and around time t=tz in
FIG. 14
, obtained by enlarging the time axis. In
FIG. 15
, a period T
91
is a time period during which a drive current of the U-phase and V-phase currents flows. This drive current flows through the current detection resistance
7
. A period T
92
is a time period during which the U-phase and V-phase currents flow as a regenerative current. A period T
93
is a time period during which a drive current of the U-phase and W-phase currents flows. This drive current flows through the current detection resistance
7
. A period T
94
is a time period during which the U-phase and W-phase currents flow as a regenerative current.
The conventional motor driver shown in
FIG. 13
has the following problem. The phase currents sharply change as shown in FIG.
14
. For this reason, when the phase currents are switched, vibration of the motor and generation of electromagnetic noise tend to occur.
To avoid the above problem, the phase currents may be controlled not to change sharply. However, to detect and control a plurality of phase currents, it is necessary to provide current detection resistances in the same number as the number of phases. It is difficult to incorporate the current detection resistances in an integrated circuit. Therefore, as the number of the current detection resistances is greater, the scale of the device is larger and the cost is higher.
In addition, the properties of resistances generally have variations. Therefore, in the case of using current detection resistances for the respective phases, the current detection properties vary every phase. For example, when two phase currents are actually the same in magnitude, the magnitudes of the detected currents may sometimes be different from each other.
SUMMARY OF THE INVENTION
An object of the present invention is providing a motor driver capable of controlling a plurality of phase currents not to change sharply, using one current detection resistance, to reduce vibration of the motor and electromagnetic noise.
The present invention is directed to a motor driver having a plurality of output circuits each including an upper side switching element and a lower side switching element connected in series, for supplying a current to a motor from a connection point between the upper side switching element and the lower side switching element of each output circuit. The motor driver includes: a current detection resistance connected in series with the plurality of output circuits in common for detecting a current supplied to the plurality of output circuits; a position detection section for outputting a position signal corresponding to the position of a rotor of the motor; a phase switch circuit for selecting one switching element of one of the plurality of output circuits according to the position signal and turning ON the selected switching element for a time period corresponding to a predetermined electrical
Inao Masashi
Iwanaga Taishi
Sakai Hirofumi
Yamamoto Yasunori
Yokouchi Tomoharu
Leykin Rita
Matsushita Electric - Industrial Co., Ltd.
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