Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Reexamination Certificate
2002-09-24
2004-03-09
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
C361S021000
Reexamination Certificate
active
06704182
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for protecting a matrix converter having nine bidirectional power switches, which are arranged in a 3×3 switch matrix, against overvoltages, and to an active overvoltage protection device.
A matrix converter is a self-commutating direct converter. This self-commutating direct converter is a converter without an intermediate circuit. The arrangement of the electronic power switches in a 3×3 switch matrix results in the three input phases being connected to the three output phases. This self-commutating direct converter has the advantage that its topology allows a feedback capability, and appropriately applied control results in sinusoidal power supply system currents. A semiconductor switch integrated in a diode bridge, on the one hand, and two back-to-back series-connected semiconductor switches on the other hand may be used as the bidirectional switches in the switch matrix. The two back-to-back series-connected semiconductor switches in a bidirectional power switch in the switch matrix are configured using either the common emitter mode or common collector mode topology. The embodiment of the bidirectional power switch with a semiconductor switch being embedded in a diode bridge is referred to as an embedded switch.
FIG. 1
shows a circuit diagram of a conventional bidirectional switch
2
in the common collector mode topology. For comparison,
FIG. 2
shows a conventional bidirectional power switch
2
in the common emitter mode topology. These two bidirectional power switches
2
each have two semiconductor switches
4
and
6
, which are connected back to back in series. In
FIG. 1
, these two semiconductor switches
4
and
6
are connected back-to-back in series such that the two collector terminals are electrically conductively connected to one another. This back-to-back series circuit formed by the two semiconductor switches
4
and
6
is therefore also referred to as the common collector mode. In
FIG. 2
, the two semiconductor switches
4
and
6
are connected back-to-back in series such that their emitter terminals are electrically conductively connected. Since the emitter terminals are linked, this circuit is referred to as the common emitter mode. Semiconductor switches which can be turned off, in particular Insulated Gate Bipolar Transistors (IGBT), are used as the semiconductor switches
4
and
6
, and each have a reverse diode. The internal topology can be seen from the accessible terminals of the bidirectional power switch
2
. In the bidirectional power switch
2
in the common collector mode topology as shown in
FIG. 1
, the terminals E
1
, E
2
, G
1
and G
2
are accessible on the power switch
2
. In contrast to this, in the bidirectional power switch
2
in the common emitter mode topology as shown in
FIG. 2
, the terminals C
1
, C
2
, G
1
and G
2
are accessible. In addition, these bidirectional power switches
2
have auxiliary terminals EH
1
and EH
2
, which each form a control terminal.
FIG. 3
shows in more detail a circuit diagram of a conventional bidirectional power switch
2
in the embedded switch topology. This bidirectional power switch
2
has a semiconductor switch
5
which can be turned off, in particular an Insulated Gate Bipolar Transistor (IGBT), which is arranged in a diode bridge. The collector side of this semiconductor switch
5
is electrically conductively connected to cathode terminals of two diodes, and its emitter side is electrically conductively connected to anode terminals of two further diodes in the diode bridge. The free terminals of these diodes each form an input and output terminal for the bidirectional power switch
2
.
Driving of the semiconductor switches
4
and
6
and of the semiconductor switch
5
in the bidirectional power switch
2
in the matrix converter in each case switches on one current path in a specific direction. If both the semiconductor switches
4
and
6
are actuated, then this allows current to flow in both directions, so that a reliable electrical connection is produced between one input phase and one output phase. If only one semiconductor switch
4
or
6
in the bidirectional power switch
2
in the matrix converter is actuated when the bidirectional power switch
2
is in the common collector mode or common emitter mode topology, respectively, then this results in a connection for only one preferred current direction. One phase of the matrix converter is an arrangement of three bidirectional power switches, which produces a connection from the three power supply system phases to in each case one of the output phases.
Since the matrix converter has no passive freewheeling circuits, in the same way as a voltage intermediate circuit converter, then, particularly in the case of a pulse inhibitor generated on the basis of an EMERGENCY OFF (with the actuate pulses to all the semiconductor switches being switched off), a high reverse voltage occurs across the semiconductor switches owing to the inductances in the circuit. These overvoltages can also occur as a result of a failure of the actuate for the bidirectional power switches. The output current is interrupted in each of these situations that have been mentioned. The interruption in the output circuit in conjunction with the inductances in the circuit causes the overvoltages, which can lead to destruction of the semiconductor switches.
A general overvoltage protection device is known from the publication “Novel Solutions for Protection of Matrix Converter to Three Phase Induction Machine”, printed in the Proceedings of the “IEEE Industry Applications Society” New Orleans, La., October 5-9, 1997, pages 1447 to 1454. This overvoltage protection device has two 6-pulse diode bridges, which are linked to one another on the DC voltage side by means of a capacitor. On the AC voltage side, one of the 6-pulse diode bridges is connected to the input terminals of the matrix converter. The other diode bridge is connected on the AC voltage side to the output terminals of the matrix converter. A resistor is connected electrically in parallel with the capacitor, and discharges the capacitor. The input terminals of the matrix converter are also connected to an LC filter, whose input side is connected to a three-phase power supply system. This LC filter, which is also referred to as an input filter, keeps pulse-frequency harmonics away from the power supply system. The size of this filter depends on the pulse repetition frequency of the matrix converter.
Any overvoltages are rectified by the diode bridges and passed to the capacitor. A precharging circuit is required for the capacitor for this overvoltage protection device, which is also disclosed in U.S. Pat. No. 4,697,230. This precharging circuit is required in order that no inrush current surges or overvoltages occur at twice the power supply system voltage when the matrix converter is switched on. Overvoltages such as these cause high surge currents, which have to be carried by the diodes in the diode bridge. The resistor is designed such that its resistance ensures that a predetermined amount of energy is discharged from the capacitor.
An overvoltage protection device with two 6-pulse diode bridges is also known from the publication “Performance of a two Steps Commutated Matrix Converter for AC-Variable-Speed Drives” printed in the Proceedings of EPE'99, Lausanne, September 1999, pages 1 to 9. Each of these two diode bridges has a capacitor on the DC voltage side. These two capacitors are electrically connected in parallel. A Zener diode and a pulse resistor are electrically connected in parallel with these two capacitors, thus limiting the voltage on the capacitors to a predetermined value. Furthermore, each bidirectional power switch has a varistor and two back-to-back series-connected Zener diodes, which limit the overvoltages across the bidirectional power switch.
A number of varistors are provided as an overvoltage protection device in the publication “A Matrix Converter without Reactive Clamp Elements
Bruckmann Manfred
Simon Olaf
Feiereisen Henry M.
Kitov Z
Siemens Aktiengesellschaft
Sircus Brian
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