Motor control unit

Details Motor control unit Motor control unit

1999-10-20

2001-07-31

Sherry, Michael J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Motor protective condition responsive circuits

C361S025000

Reexamination Certificate

active

06268986

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor control unit which drives a motor using a power converting semi-conductor, and more particularly to the overheat protection of the power converting semi-conductor and the temperature control of the motor control unit.
2. Description of the Prior Art
A first example of a conventional motor control unit provided therein with overheat protection function is shown in FIG.
14
. In the first example as shown in
FIG. 14
, a three-phase alternating current motor is used as a motor and an inverter is used as a power converter, respectively.
In
FIG. 14
, reference numeral
1
A is a motor control unit, reference numeral
2
is a motor,
3
A a control computing unit and
4
A a power converting semi-conductor. The power converting semi-conductor
4
A is provided with three-phase switching arms (U phase arm, V phase arm and W phase arm), an overheat identification means
8
A and an overheat protection means
9
A. The U phase arm that is one of the switching arms consists of an upper arm switching element
5
a
, a lower arm switching element
5
b
, an upper arm freewheeling element
6
a
, a lower arm freewheeling element
6
b
, an upper arm gate switching element
7
a
, a lower arm gate switching element
7
b
and thermistors
10
and
11
. The V phase arm and the W phase arm have the same structure as the U phase arm. A bipolar transistor is used here as the switching element. In the drawing, C, G and E show a collector, a gate and an emitter, respectively.
The motor control unit
1
A generally converts direct-current power from an electric power unit (not shown) into alternating-current power and supplies it to the motor
2
. The conversion from direct-current power to alternating-current power is carried out by switching the switching elements consisting of a power element of the power converting semi-conductor
4
A. The power elements consist of the switching elements and the freewheeling elements. A gate driving signal which is generated in the control computing unit
3
A for switching is connected to gates G of the switching elements through the gate switching elements. When the switching elements are electrified by switching, they generate heat due to internal loss. Overheating may destroy the switching elements. To avoid the possible destruction of the switching elements, overheat protection is provided by monitoring the temperature of the switching elements, cutting off (gate cut) the signal flowing from the control computing unit
3
A to the gates of the switching elements when the temperature reaches a predetermined level, and breaking the electric current sent to the switching elements. A protection function operation alarm signal is transmitted to the control computing unit
3
A when the overheat protection is carried out. In the drawing, an overheat identification means
8
A determines by a signal from the thermisitor
10
whether the temperature sensing and gate-cut are necessary or not. The signal for gate cutting is generated in the overheat protection means
9
A to effect the gate cutting by gate switching elements
7
a
and
7
b
. The thermistor
10
is disposed near the switching elements to reflect the temperature of the switching elements correctly.
Another thermistor
11
is disposed on the periphery of the switching elements as a means of informing the control computing unit
3
A of the temperature of the switching elements. In the control computing unit
3
A, the temperature information of the switching elements is obtained from the thermistor
11
by, for example, a microcomputer or an A/D converter. With this temperature information (signal), a gate driving signal is operated so that the temperature of the switching elements us not raised excessively.
As a second conventional example, Japanese laid-Open Patent Application (Kokai) No. Hei 10-21079 discloses a control unit for protecting switching elements from overheating by using a temperature signal from a power converting semi-conductor. In this second conventional example, a motor control unit for proving overheat protection is applied to an electric vehicle.
FIG. 15
shows this second conventional example.
In
FIG. 15
, reference numeral
2
is a motor, reference numeral
12
is a battery,
13
a power converter,
14
wheels,
15
a power converter ECU (an electronic control unit),
16
an accelerator pedal, and
17
a temperature sensor, respectively.
The power converter
13
is connected to the battery
12
serving as a power unit and the motor
2
for driving the vehicle is connected to the power converter
13
. The driving force of the motor
2
is transmitted to the wheels
14
through a rotation axis and a differential gear to serve as the propulsive force of the vehicle. The power converter
13
is provided with the power converting semi-conductor. Also, the power converter
13
is controlled by the power converter ECU
15
, and the power converting semi-conductor within the power converter
13
starts a switching operation according to a gate driving signal input from the power converter ECU
15
. With this switching operation, the direct-current power supplied from the battery
12
is converted to alternating-current power to be supplied to the motor
2
.
The power converter ECU
15
is connected to an accelerator pedal
16
and adapted to detect an amount of pressure as an accelerator opening A% when a driver depresses the accelerator pedal
16
. It is however noted that the accelerator opening is 100% when the accelerator pedal is fully pressed.
The power converter ECU
15
is also connected to the temperature sensor
17
disposed within a case of the power converter
13
to gain the temperature INV-T of the switching elements. Further, the power converter ECU
15
determines the amount of change of the element temperature per unit time based on the element temperature INV-T to allow the temperature change rate to be &Dgr;T/&Dgr;t.
The power converter ECU
15
determines a torque to be output from the motor
2
according to the accelerator opening A% and converts the torque found to a torque command*. Further, the following two kinds of limiting rates (a first limiting rate &agr;, a second limiting rate &bgr;) multiplied by the torque command T make the regulated torque command T*. This first limiting rate &agr; is determined based on the element temperature INV-T. The first limiting rate &agr; is 100% when the element temperature INV-T is below a limitation start temperature T
1
. When the element temperature INV-T is higher than the limitation start temperature T
1
, the first limiting rate &agr; corresponding to the element temperature INV-T at that time is multiplied by the torque command T*. When the element temperature INV-T reaches a zero-power temperature T
2
, the first limiting rate &agr; is 0 and the torque command T* is also 0.
The second limiting rate &bgr; is determined based on the temperature change rate &Dgr;T/&Dgr;t. The second limiting rate is used when the element temperature INV-T is above the limitation start temperature T
1
. When the temperature change rate &Dgr;T/&Dgr;t is below a first reference value &dgr;1, the second limiting rate &agr; is 100%. When the temperature change rate &Dgr;T/&Dgr;t is higher than the first reference value &dgr;1, the second limiting rate &bgr; corresponding to the temperature change rate &Dgr;T/&Dgr;t at that time is multiplied by the torque command T*. When the temperature change rate &Dgr;T/ &Dgr;t is above a second reference &dgr;2, the second limiting rate &bgr; is 0 and the torque command T* is also The power converter ECU
15
obeys the regulated torque command T* found by the above and a command value I* of a motor electrifying current corresponding to the regulated torque command T* . The generating torque of the motor
2
is controlled to coincide with the regulated torque command T* by switching the switching elements of the power converting semi-conductor based on this current command value I*.
As described above, the switching element

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