WO2013139373A1

WO2013139373A1 - Switch module and associated method

Info

Publication number: WO2013139373A1
Application number: PCT/EP2012/054873
Authority: WO
Inventors: Franz Wildner; Thorsten STRASSEL
Original assignee: Abb Technology Ltd
Priority date: 2012-03-20
Filing date: 2012-03-20
Publication date: 2013-09-26

Abstract

It is presented a switch module (9) comprising: a first controlled current connection (C); a second controlled current connection (E); a control connection (G); a plurality of switches (21a, 21b, 21c, 21d) connected in parallel between the first controlled current connection (C) and the second controlled current connection (E); fuse elements (3a, 3b, 3c, 3d) respectively provided between each one of the gates of the plurality of switches and the gate connection (G); and a bypass switch (25) arranged between the control connection (G) and the second controlled current connection (E).

Description

SWITCH MODULE AND ASSOCIATED METHOD

TECHNICAL FIELD

The invention relates to a switch module.

BACKGROUND

Switch modules can be used to control a main current, e.g. in a power converter such as an inverter or rectifier. In effect, the switch modules behave like a transistor, where a control signal can alter the state of the switch module between a conducting and a blocking state. The switch module, in turn, can comprise a number of power switches, such as IGBTs (insulated- gate bipolar transistors) arranged in parallel to act on a provided control signal. A gate unit can also be provided to provide a suitable signal to the actual power switches based on the control signal provided to the power module.

A problem occurs if a component, such as a switch, fails. This can in exceptional cases result in propagating errors.

It is desired to manage failures of such switch modules in a more stable way.

SUMMARY

An object of the invention is to improve how failures of switch modules are managed. According to a first aspect, it is presented a switch module comprising: a first controlled current connection; a second controlled current connection; a control connection; a plurality of switches connected in parallel between the first controlled current connection, the second controlled current connection and the control connection; fuse elements respectively provided between each one of the gates of the plurality of switches and the gate connection; and a bypass switch arranged between the control connection and the second controlled current connection. Using the bypass switch, a current flows from a failed switch, to thereby blow a fuse connected to the switch element. This makes it possible to control provide a voltage to the gates of any operating switches. In this way, after a failure, a current through the switch module passes not only through the failed switch, but also the other switches, reducing stress on the switch module and significantly reducing risk of the switching module failing further and becoming blocking. Moreover, by using the fuses, a robust and to a large degree passive control strategy is adopted.

The switch module may further comprise an error signal connection connected to the bypass switch, such that a signal on the error signal connection sets the bypass switch in a conducting state. This is a convenient way to control the bypass switch. The bypass switch may be arranged to stay in a conducting state indefmitely after an error of one of the plurality of switches is detected.

A bypass resistor may be provided to limit any current through the bypass switch. This reduces the required rating of the bypass switch.

Each one of the plurality of switches may comprise an Insulated Gate Bipolar Transistor.

The bypass switch may comprise a transistor. Transistors are easily controllable.

The bypass switch may comprise a low voltage normally off power metal- oxide-semiconductor field-effect transistor. The bypass switch may comprise two antiparallel thyristors. The bypass switch may comprise a single thyristor. Thyristors are cost effective and efficient components.

The plurality of switches maybe arranged such that a current between the first controlled current connection and the second controlled current connection is controllable using a signal on the control connection.

Each one of the fuse elements may comprise a thin film type fuse. According to a second aspect, it is presented a method of controlling a switch module comprising: a first controlled current connection; a second controlled current connection; a control connection; a plurality of switches connected in parallel between the first controlled current connection, the second controlled current connection and the control connection; fuse elements respectively provided between each one of the gates of the plurality of switches and the gate connection; and a bypass switch arranged between the control connection and the second controlled current connection. The method comprises the step of: setting the bypass switch in a conducting state when at least one of the plurality of switches fails.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Figs lA-B are schematic diagrams illustrating an environment where embodiments of the present invention can be applied;

Figs 2A-D are schematic diagrams illustrating how a failure is handled by a switch module according to embodiments presented herein; Figs 3A-C are schematic diagrams illustrating various embodiments of a bypass switch of the switch module of Figs 2A-D; and

Fig 4 is a flow chart illustrating a method performed using the switch module of Figs 2A-D. DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description. Figs lA-B are schematic diagrams illustrating an environment where embodiments of the present invention can be applied. In this example, it is shown a bridge leg for one phase of an inverter. Additional phases (such as for a three phase system) may be configured in the same way. DC power is supplied using a positive DC bus DC+ and a negative DC bus DC-. A valve control unit (VCU) n is connected to a plurality of switch modules 9a-h. An upper part of the bridge leg comprises a first set of switch modules 9a-9d, and a lower part of the bridge leg comprises a second set of switch modules 9e-h. The switch modules 9a-9h are controlled using control signals from the VCU 11. This allows the VCU to e.g. control the voltage and/or current to supply an alternating current on a terminal 40. By placing several switch modules 9a-h in series, high voltage applications can be supported and a more sinusoidal wave form can be generated. It is to be noted that the number of switch modules shown here is only an example and any suitable number of switch modules can be used. If one switch module fails, such as switch module 9c of Fig lB, the circuit can still work as desired if the failed switch module is set to conduct in a short circuit mode. When a failure is detected in a switch module, it is ensured that the failed switch module is set to a short circuit failure mode where it continuously conducts. In other words, regardless of the signal from the VCU 11, the failed switch module 9c will conduct. As long as there is some over- dimensioning in this configuration, the functioning switch modules operate as usual and provides the desired function until the failed switch module 9c is replaced or repaired.

Another risk with a failed switch module is that an arc can occur if the failed switch module breaks the circuit, which can lead to additional failed components and even fires.

So even in cases where a failed switch module defaults to a short circuit state, it is valuable to handle such a short circuit failure mode with sufficient stability to reduce the risk of failures propagating or the failed switch module failing to conduct. There are many other topologies, such as H-bridge, half bridge, etc. where the same idea is useful, i.e. when a switch module fails it should be set to a conducting state.

Figs 2A-D are schematic diagrams illustrating how a failure is handled by a switch module 9 according to embodiments presented herein. In Fig 2A, the switch module 9 is shown in a state of normal operation. The switch module 9 comprises a plurality (in this example four) switches 2ia-d connected in parallel between a first controlled current connection C, a second controlled current connection E and a control connection G. The switch module can comprise any number of switches connected in parallel, as long as there are at least two switches. Each switch 2ia-d can comprise a chip comprising one or more IGBTs, power MOSFETs (Metal-Oxide- Semiconductor Field-Effect Transistors) or any other controllable power switch capable of being controlled between a conducting and a blocking state. Hereinafter to make it easier to understand, terminology of IGBTs are used, i.e. gate connection for the control connection, and collector and emitter for the first and second controlled current connections, respectively. However, it is to be noted that the embodiments presented are not limited to the use of IGBTs. The switch module 9, and thereby the switches 21-d, is controlled using the gate connection G, to thereby affect a controlled current I (also known as load current) between the collector C and the emitter E.

During normal operation, and when the switch module 9 is in conducting state, a bypass switch 25 is in a non-conducting state, whereby all of the controlled current is divided between the switches 2ia-d. Since, in this example, there are four switches, the controlled current I is shared between the switches 2ia-d, so that each one of the switches 2ia-d handles a current of about I/4. Between the gate connection G and the gates of each switch 2ia-d, respective fuse elements 3a-d are provided. The term fuse element is to be interpreted as any element which is set in a blocking state when a current over a threshold current is applied. For example, each fuse element 3a-d can comprise a thin film type fuse. The function of the fuse elements 3a-d will be explained in more detail below.

An optional gate resistor 12 is provided between the gate connection G and the fuse elements 3a-d. The bypass switch 25 is provided between the emitter E and the fuse elements 3a-d. Additionally, a bypass resistor 13 is provided between the bypass switch 25 and the fuse elements 3a-d, to limit any current through the bypass switch 25, when this is in a conducting state.

In Fig 2B, a single switch 21a has failed, leading to an equivalent circuit of 21a'. The functioning switches 2ib-d are electrically blocking, since the failed switch shortcuts the gates of the functioning switches to the emitter E. This prevents the gates of the functioning switches 2ib-d from keeping a sufficient voltage to set the functioning switches 2ib-d in a conducting state, whereby the gate control G becomes inoperative. The failed switch 21a then has to handle full load current I at this stage.

There is some, albeit low, resistance within the failed switch 21a, whereby the equivalent circuit 21a' comprises an upper resistor 26a and a lower resistor 26b. The size of each of the upper and lower resistors 26a-b can be in the region of a few milliohms or a few tenths of milliohms. Due to the failed switch, there is a shortcut between a gate unit 5, connected to the gate connection G, and the emitter E.

In Fig 2C, the shortcut from the gate unit 5 to the emitter E results in a control signal to the error signal connection 19, whereby the bypass switch 25 is set in conducting state. This will result in the load current I being divided between a first current Ii passing straight through the failed switch 21a' and a second current I₂, passing through the first fuse element 3a, the bypass resistor 13, and the bypass switch 25 to the emitter connection E. Essentially, the size of the bypass resistor 13 in relation to the lower resistor 26b will determine the size of the second current I₂ in relation to the load current I. By dimensioning the bypass resistor 13 appropriately, the second current I₂ will be sufficiently large to blow the first fuse element 3a.

In Fig 2D, the switch module 9 is shown at a state where the first fuse element 3a has blown, which disconnects the gate of the failed switch 21a' from the gate connection G. After the first fuse element 3a has blown, the bypass element 25 is optionally set to a blocking state again. Alternatively, the bypass element 25 can remain in a conducting state indefinitely.

Since there is no shortcut from the gate connection G to the emitter E, the gate unit 5 connected to the gate connection G is again able to control the remaining, functioning, switches 2ib-d. If the bypass switch 25 is still conducting, the bypass resistor 13 needs to be sufficiently large to allow the gate unit 5 to keep a voltage on the gates of the functioning switches 2ib-d to make the functioning switches 2ib-d conduct. When the functioning switches 2ib-d conduct again, the load current I is divided between a third current I₃ through the failed switch 21a' and a fourth current I₄, which is divided between the functioning switches 2ib-d. In this example, since there are three functioning switches 2ib-d, whereby each one of the functioning switches handles a current of I₄/3. In other words, with the structure of this switch module 9, it is ensured that it is not only the failed switch which has to take care of the load current I;

instead the load current is divided between all switches. This is a significant advantage since the switch module 9 can then be cooled properly, etc., and the switches are under less thermal and electrical stress.

The switch module 9 is thus safely set in a short circuit failure mode. By dividing the load current through the switch module 9 between all switches 2ia-d, less stress is put on the switches. Cooling of the switch module also functions more like in a normal state. This short circuit failure mode is thus a stable state and there is a low risk of propagating errors or the failed switch becoming blocking. In some instances, switch module 9 can continue in the short circuit failure mode for months or even years, whereby any failed switch modules can be replaced during normal service intervals.

Moreover, the structure of the switch module can function without active, complicated control algorithms, whereby the failure handling is robust and cost effective.

Figs 3A-C are schematic diagrams illustrating various embodiments of a bypass switch of the switch module of Figs 2A-D.

In Fig 3A, the bypass switch 25 comprises a transistor 28, e.g. an IGBT or a power MOSFET. Transistors have the advantage of being easy to control between conducting and blocking states. In one embodiment, the transistor 28 is a low voltage normally off power MOSFET.

In Fig 3B, the bypass switch 25 comprises two antiparallel thyristors 29. Thyristors are cost effective and efficient components. Since the direction of a current passing through switch module comprising the bypass switch will alternate, any fired thyristors 29 will eventually be turned off.

In Fig 3C, the bypass switch 25 comprises a single thyristor 30. Since the direction of a current passing through switch module comprising the bypass switch will alternate, a fired thyristor 30 will eventually turned off. Fig 4 is a flow chart illustrating a method performed using the switch module of Figs 2A-D. The method comprises a single step 41 of set bypass switch to conduct. This step can be performed by the gate unit when there is a shortcut from the gate G to the emitter E. The bypass switch is set in a conducting state by providing an appropriate control signal (e.g. voltage) to the error signal connection.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A switch module (9) comprising:

a first controlled current connection (C);

a second controlled current connection (E);

a control connection (G);

a plurality of switches (2ia-d) connected in parallel between the first controlled current connection (C), the second controlled current connection (E) and the control connection (G);

fuse elements (3a-d) respectively provided between each one of the gates of the plurality of switches and the gate connection (G); and

a bypass switch (25) arranged between the control connection (G) and the second controlled current connection (E).

2. The switch module (9) according to claim 1, further comprising an error signal connection (19) connected to the bypass switch, such that a signal on the error signal connection sets the bypass switch (25) in a conducting state.

3. The switch module (9) according to claim 2, wherein the bypass switch is arranged to stay in a conducting state indefinitely after an error of one of the plurality of switches (2ia-d) is detected.

4. The switch module (9) according to any one of the preceding claims, wherein a bypass resistor (13) is provided to limit any current through the bypass switch (25).

5. The switch module (9) according to any one of the preceding claims, wherein each one of the plurality of switches (2ia-d) comprises an Insulated Gate Bipolar Transistor.

6. The switch module (9) according to any one of the preceding claims, wherein the bypass switch (25) comprises a transistor (28).

7. The switch module (9) according to any one of the preceding claims, wherein the bypass switch (25) comprises a low voltage normally off power metal-oxide-semiconductor field-effect transistor.

8. The switch module (9) according to any one of the preceding claims, wherein the bypass switch (25) comprises two antiparallel thyristors (29).

9. The switch module (9) according to any one of claims 1 to 7, wherein the bypass switch (25) comprises a single thyristor (30).

10. The switch module (9) according to any one of the preceding claims, wherein the plurality of switches (2ia-d) are arranged such that a current between the first controlled current connection (C) and the second controlled current connection (E) is controllable using a signal on the control connection (G).

11. The switch module (9) according to any one of the preceding claims, wherein each one of the fuse elements (3a-d) comprise a thin film type fuse.

12. A method of controlling a switch module (9) comprising: a first controlled current connection (C); a second controlled current connection (E); a control connection (G); a plurality of switches (2ia-d) connected in parallel between the first controlled current connection (C), the second controlled current connection (E) and the control connection (G); fuse elements (3a-d) respectively provided between each one of the gates of the plurality of switches and the gate connection (G); and a bypass switch (25) arranged between the control connection (G) and the second controlled current connection (E), the method comprising the step of:

setting the bypass switch in a conducting state when at least one of the plurality of switches (2ia-d) fails.