Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2002-09-18
2004-09-07
Martin, David (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S362000, C318S375000, C318S434000, C388S903000
Reexamination Certificate
active
06788014
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application, Serial No. 101 46 523.8, filed Sep. 21, 2001, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates, in general, to a drive control system for a multiphase motor powered by a power converter.
Drives for high velocities or rotation speeds are increasingly in commercial use. This is true in particular for the power tool industry. Although rotation speeds of up to 20,000 rpm have already been employed and proven reliable, there is a need for rotation speeds in excess of 20,000 rpm. In particular, when high speeds are involved, motors feed back energy into the system. This is normally realized by a power converter on the mains systems side to feed energy back to the power supply. In case of trouble or a power outage, this energy cannot be fed back, resulting, especially in cases when motors are involved that rotate at high rpm, in significant overvoltages in the voltage intermediate circuit of a converter, which is connected before the motor, and may ultimately lead to the destruction of the converter.
To address this problem, the incorporation of a module has been proposed to reduce encountered overvoltage. A module of the type concerned here is illustrated in FIG.
1
and designated by reference numeral
2
. The module
2
, also called voltage-protection module (VPM), is placed between the input side of a multiphase motor
4
and the output side of a power converter
6
of a converter
8
. In addition, the module
2
is connected via a control line
10
to the output side of a drive control system
12
of the motor-side power converter
6
. The converter
8
includes a voltage intermediate circuit to electrically connect on the DC voltage side the power converter
6
on the motor side and a power converter
14
on the mains systems side. For sake of simplicity, the voltage intermediate circuit is not shown in detail. The power converter
14
on the mains systems side is implemented as a converter that is capable to feed back electric energy so as to enable a return of energy into the power mains supply
16
during braking action of the motor
4
.
An overvoltage-monitoring device checks whether a determined actual voltage value of the voltage intermediate circuit of the converter
8
exceeds a predetermined limit value. As soon as an unacceptable overvoltage is occurs, module
2
is activated and drive control system
12
transmits control signals via the control line
10
. The module
2
has incorporated therein a connection of at least several controllable power semiconductor switches, which can be switched off or disabled and are so controlled and switched together as to short the motor lines that are electrically connected via an electric path through the module
2
. Optionally, the module
2
may also include resistors so that the electric loss power does not occur solely across the power semiconductor switches.
The provision of such a module
2
suffers shortcomings because the module
2
requires space which is approximately the same as the space needed for the motor-side power converter
6
. Moreover, the module
2
has to be connected on the power supply side with the output side of the motor-side power converter
6
and the input side of the multiphase motor
2
, and on the control side with the output side of the drive control system
12
of the power converter
6
. This may lead to circuit failure.
A drive control system
12
of a type involved here is disclosed in European Patent Publication 0 742 637 and shown in more detail in FIG.
2
. The multiphase motor
4
is connected in an electrically conductive manner with phase outputs L
1
, L
2
, L
3
of the motor-side power converter
6
. The power converter
6
includes six valve arms in the form of controllable converter valves or power semiconductor switches T
1
, T
2
, T
3
, T
4
, T
5
, T
6
, which can be switched off or disabled, whereby the power semiconductor switches T
1
, T
3
, T
5
are arranged in the upper bridge side and the power semiconductor switches T
2
, T
4
, T
6
are arranged in the lower bridge side. The power semiconductor switches T
1
, T
2
, T
3
, T
4
, T
5
, T
6
, are configured as insulated gate bipolar transistors (IGBT). Power semiconductor switches T
1
and T
2
of the upper and lower bridge sides of the power converter
6
form a bridge arm as do power semiconductor switches T
3
and T
4
, and power semiconductor switches T
5
and T
6
, and are connected between a positive busbar +Ud and a negative busbar −Ud of a voltage intermediate circuit, not shown in detail. The power semiconductor switches T
1
, T
2
, T
3
, T
4
, T
5
, T
6
are each controlled by a electrically isolating device
18
, of which only two are shown for ease of illustration. An example of such an electrically isolating device
18
includes optocoupler. By means of the electrically isolating devices
18
, the power converter
6
(power component) is connected to the drive control system
12
(control component).
The drive control system
12
includes a control unit
20
, e.g. a pulse width modulator, for providing signals to address the optocouplers
18
and thus to effect a switching of the semiconductor switches T
1
, T
2
, T
3
, T
4
, T
5
, T
6
of the power converter
6
. The signals are sent by the control unit
20
through three signal lines
17
for the upper bridge side and three signal lines
19
for the lower bridge side, whereby the signal lines
17
,
19
include each a diode and a resistor in series.
FIG. 2
illustrates, by way of example, the control for the two optocouplers
18
, shown here. The drive control system
12
further includes a pulse suppressor
22
for cutting the energy supply to the electric drive by suppressing the pulses on the motor-side power converter
6
. The pulse suppressor
22
is activated by a signal S
1
and includes a further optocoupler for indicating the status of the pulse suppressor by means of a status signal S
AKB
which is sent to the control unit
20
, on the one hand, as well as to a device
24
for braking by armature short-circuiting, referred to as “armature short-circuit braking device” in the following description.
In the event of a fault, one of both bridge sides is blocked securely, while the other bridge side is switched on through timed control of the power semiconductor switches T
2
, T
4
, T
6
so that at least two phases of the multiphase motor
4
are shorted. Of course, it is equally possible to block the lower bridge side and to provide a timed control of the upper bridge side of the power converter
6
. In order to implement the required emergency braking in the event of a fault, the armature short-circuit braking device
24
now switches through all transistors T
2
, T
4
, T
6
of the lower bridge side so that the three phases of the electric motor
4
are shorted across the negative busbar −Ud. The remaining kinetic energy of the multiphase motor
4
drives the braking current across the thus-realized shorted bridge. Through the timed control by means of a clock frequency, the power semiconductor switches T
2
, T
4
, T
6
of the lower bridge side of the power converter
6
can be switched through in such a tailored manner that the braking moment generated by the short circuit can be appropriately varied. The armature short-circuit braking device
24
is intended for use solely in emergency situations to shut down the motor as quickly as possible.
It would therefore be desirable and advantageous to provide an improved drive control system, which obviates prior art shortcomings and is so configured as to omit the need for an external voltage-protection module.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a drive control system for a multiphase motor powered by a power converter of a type including a multi-pulsed bridge circuit with a plurality of controllable converter valves, which have an input side,
Kissich Gerwin
Seidner Hans
Feiereisen Henry M.
Martin David
McCloud Renata
Siemens Aktiengesellschaft
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