Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-10-04
2002-10-22
Fletcher, Marlon T. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S434000
Reexamination Certificate
active
06469461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a motor control apparatus controlling the operation of a brushless motor through an inverter circuit, and more particularly to a motor control apparatus designed to monitor a malfunction in the apparatus.
2. Background Art
Motor control apparatus are known in the art which are designed to control the operation of a brushless motor through an inverter circuit made up of bridged power switching elements and to control the speed of the motor using PWM (Pulse-Width- Modulated) signals.
A typical motor control apparatus of the above type will be described with reference to
FIGS. 6 and 7
.
FIGS. 6 and 7
show an example where a motor
1
includes three windings (stator coils) L
1
, L
2
, and L
3
having first, second, and third phases (also referred to as U, V, and W phases below) which are connected in a delta form.
The motor control apparatus, as shown in
FIG. 6
, includes a switching circuit
6
that is a three-phase bridge circuit made up of positive switching elements
3
p
,
4
p
, and
5
p
and negative switching elements
3
n
,
4
n
, and
5
n
. The positive switching elements
3
p
to
5
p
are connected between a positive terminal (i.e., a higher voltage side) of a dc power supply
2
and terminals Ju, Jv, and Jw of the windings L
1
to L
3
. Similarly, the negative switching elements
3
n
to
5
n
are connected between a negative terminal (i.e., a lower voltage side) of the power supply
2
and the terminals Ju, Jv, and Jw of the windings L
1
to L
3
. The switching elements
3
p
,
4
p
,
5
p
,
3
n
,
4
n
, and
5
n
are each made by an N-channel MOSFET.
The motor control apparatus also includes a commutation control circuit
7
which provides drive signals Up, Un, Vp, Vn, Wp, and Wn in response to rotor position indicative signals (not shown) of the motor
1
, respectively, to turn on the switching elements
3
p
,
3
n
,
4
p
,
4
n
,
5
p
, and
5
n
in a given sequence. The commutation control circuit
7
forms an inverter circuit
8
together with the switching circuit
6
.
The motor control apparatus also includes a PWM signal generator
9
and AND gates
13
,
14
, and
15
. The PWM signal generator
9
provides a PWM signal for controlling the speed of the motor
1
. The AND gates
13
to
15
receive the drive signals Un, Vn, and Wn outputted from the commutation control circuit
7
and the PWM signal outputted from the PWM signal generator
9
.
The drive signals Up, Vp, and Wp produced by the commutation control circuit
7
are inputted to gates of the switching elements
3
p
,
4
p
, and
5
p
, respectively. Outputs of the AND gates
13
,
14
, and
15
are inputted to gates of the switching elements
3
n
,
4
n
, and
4
n
, respectively.
Each of the switching elements
3
p
,
4
p
, and
5
p
is turned on when a corresponding one of the drive signals Up, Vp, and Wp is at a higher level, while each of the switching elements
3
n
,
4
n
, and
5
n
is turned on when a logical product of the PWM signal from the PWM signal generator
9
and a corresponding one of the drive signals Un, Vn, and Wn is at the higher level (see FIG.
7
).
The commutation control circuit
7
switches, as shown in
FIG. 7
, the drive signals Up, Un, Vp, Vn, Wp, and Wn between the high level and the low level in a cycle to rotate the motor
1
. In
FIG. 7
, each of the drive signals Un, Vn, and Wn to be inputted to the switching elements
3
n
,
4
n
, and
5
n
lying in level on a lower side, as viewed in the drawing, shows the high level. The same is true for
FIG. 2
, as referred to later.
The positive switching element
3
p
and the negative switching element
3
n
connected to the U-phase winding terminal Ju are each turned on for a time period equivalent to an electric angle of 120°, and become active alternately at a time interval of 60° away from each other. The positive switching element
4
p
and the negative switching element
4
n
connected to the V-phase winding terminal Jv and the positive switching element
5
p
and the negative switching element
5
n
connected to the W-phase winding terminal Jw become active at a phase interval of 120° away from the positive switching element
3
p
and the negative switching element
3
n
. Specifically, during a time when the positive and negative switching elements connected to one of the phase winding terminals Ju, Jv, and Jw are both turned off (i.e., an electric angular interval of 60°), another one of the positive switching elements connected to the second one of the phase winding terminals Ju, Jv, and Jw is turned on, while one of the negative switching elements connected to the third one of the phase winding terminals Ju, Jv, and Jw is turned on according to the PWM signal.
FIGS. 6 and 7
illustrate for the case where the negative switching elements
3
n
,
4
n
, and
5
n
are PWM-controlled when the drive signals Un, Vn, and Wn are at the high level, but the positive switching elements
3
p
,
4
p
, and
5
p
, or all the positive and negative switching elements
3
n
,
4
n
,
5
n
,
3
p
,
4
p
, and
5
p
may be PWM-controlled.
If a malfunction occurs in one of the switching elements of the inverter circuit
8
due to a short, turning on of the malfunctioning switching element and a mating one of the switching elements causes an excess current to flow through them. For example, in a case where the U-phase negative switching element
3
n
is short-circuited, when the U-phase positive switching element
3
p
is turned on, it will cause an excess current to flow through both the switching elements
3
n
and
3
p.
In order to detect such a malfunction, the motor control apparatus shown in
FIG. 6
has a current detecting shunt resistor
16
disposed between sources of the negative switching elements
3
n
,
4
n
, and
4
n
and the minus (−) terminal of the dc power supply
2
to monitor the potential difference between terminals of the shunt resistor
16
. When the potential difference becomes greater than a given value, the motor control apparatus determines that any one of the switching elements has been short-circuited and forces all the switching elements into an off-state (as taught in Japanese Patent First Publication Nos. 6-209581 and 7-274580.
Such a system, however, detects occurrence of a malfunction of a switching element after a mating switching element is turned on so that the current flows through the malfunctioning switching element and the mating switching element and has the disadvantage that the current flow may result in a malfunction of the mating switching element that is normally operating. The system has the further disadvantage that the current flows through the shunt resistor
16
even when the system is normally operating, thereby resulting in loss of electric energy.
Japanese Patent First Publication No. 2-266891 teaches a system which determines that a malfunction has occurred when the voltage appearing at winding terminals of a motor does not change cyclically during an operation of the motor and disables all switching elements. The system, however, has also the disadvantages that it is impossible to detect occurrence of the malfunction before the current flows through the switching elements and the current flow may lead to an additional malfunction.
The above Japanese Patent First Publication No. 7-274580 is also designed to compare the voltage at each of the winding terminals Ju, Jv, and Jw with a reference voltage immediately after switching of a corresponding one of the drive signals Up to Wn, determine that a malfunction has occurred when a result of the comparison does not match up with the one of the drive signals Up to Wn, and disables all the switching elements
3
p
to
5
n
. This system, however, the disadvantage that in a case where any one of the switching elements is short-circuited during a time from detection of the malfunction (i.e., the preceding commutation) to the subsequent commutation, a mating one of the switching elements may be short-circuited when turned on. For exa
Konda Shinichi
Ueda Susumu
Fletcher Marlon T.
Law Offices of David G. Posz
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