GB2379345A

GB2379345A - A power module with several power devices controlled through a single galvanically isolated control channel

Info

Publication number: GB2379345A
Application number: GB0215991A
Authority: GB
Inventors: Bernd Winkens
Original assignee: Tyco Electronics AMP GmbH
Current assignee: TE Connectivity Germany GmbH
Priority date: 2001-07-21
Filing date: 2002-07-10
Publication date: 2003-03-05
Anticipated expiration: 2022-07-10
Also published as: GB0117817D0; DE10231996A1; GB0215991D0; GB2379345B

Abstract

A power module for providing electrical power to a load 5 comprises a power unit 2 for supplying power, a control unit 3, and an interface unit 4 for transmitting control signals from the control unit to the power unit while maintaining electrical isolation between the units 2 and 3. The interface unit comprises a serial interface device 42, which may be a transformer, an opto-coupler, an optical fibre, or a radio channel, for serially transmitting control signals for at least two power switching devices 21. The control signals may be sent in digital form, for example in PWM format. It is cheaper to use a single interface channel than use a separate channel for each device (figure 1). Power modules may be used to supply electrical power to loads such as welding apparatus, switchgear, or motors. The power unit 2 may send status information to the control unit 3 through the serial channel 42.

Description

POWER MODULE 2 3 7 9 3 4 5

The present invention relates to a power module. In 5 particular, the present invention relates to a power module for providing electrical power to a load, which power module comprises a power unit for supplying power and having at least two power switching devices capable of receiving control signals, a control unit for 10 controlling the power unit and capable of producing control signals, and an interface unit for transmitting control signals from the control unit to the power unit while maintaining electrical insulation between the control unit and the power unit.

15 Power modules are used to provide electrical power for a variety of devices, such as welding apparatus, switch gear and electrical motors. Examples of power modules are disclosed in WO-A-0074445, WO-A-0074446, US A-5,596,466 and US-A-6,166,464.

20 The power unit of a power module may switch relatively large currents and/or voltages, for example voltages of several hundred volts while the control unit passes relatively low voltage control signals. It is therefore important to keep the power unit and -ate 25 control unit electrically isolated from each other.

To this end, an interface unit is provided. In the prior art, the interface unit often comprises a

transformer arrangement which provides magnetic coupling while maintaining electrical separation. For each 30 switching device of the power unit, a separate pair of windings is provided, each pair comprising a primary and a secondary winding coupled by a common magnetic circuit.

An arrangement of this kind is disclosed in the above mentioned US-A-5, 596,466.

-2- Although such a multiple transformer arrangement functions well, it has the disadvantage of being relatively expensive, in particular when a large number of power switching devices has to be controlled. In 5 addition, the separate winding pairs take up a relatively large space, thus limiting the compactness of the power module. It is an object of the present invention to alleviate these and other disadvantages of the prior art

10 and to provide a power module which is more economical.

It is a further object of the present invention to provide a power module which is compact.

To this end a power module in accordance with the present invention is characterized in that the interface 15 unit comprises a serial interface device for serially transmitting the control signals of at least two power switching devices.

By providing a serial interface device which is capable of transmitting control signals of two or more 20 switching devices, the number of interface devices can be drastically reduced. This, in turn, reduces both the cost and the size of the power module.

Preferably, the interface unit comprises a single interface device. That is, all switching devices of the 25 power unit share a common serial interface device which transmits all control signals to these switching devices.

This reduces the number of interface devices to one only or at least one per power unit. It is however, possible for the interface unit to comprise two serial interface 30 devices, each serving at least two switching devices.

In a preferred embodiment, the interface unit comprises a multiplexer for multiplexing the control signals received from the control unit and a demultiplexer for demultiplexing the serially transmitted

-3- control signals received from the serial interface device. The multiplexer combines any parallel control signals into a serial control signal which can be transmitted over the serial interface device. The 5 demultiplexer then converts the serial control signal back into the constituent control signals and passes these on to the power switching devices of the power unit. Optionally, the control unit produces a combined 10 serial control signal, in which case the multiplexer of the interface unit can be omitted. It is also possible that the power unit is provided with a demultiplexer, thus making the demultiplexer of the interface unit superfluous. 15 In a particularly advantageous embodiment the interface unit is capable of bi-directional transmission.

This enables feedback to the control unit. The feedback may comprise status signals and/or acknowledgement signals. If the interface unit comprises a bi 20 directional serial interface unit, then the same interface device can be used to send feedback signals to the control unit, thus providing feedback without requiring any additional interface device.

In a preferred embodiment, the interface unit 25 comprises an optical interface device. That is, the interface device may comprise an optocoupler, or the combination of a laser, one or more optical fibres and an optical detector/receiver. Alternatively, or additionally, the interface unit may comprise a radio 30 link interface. When this kind of interface is used, there is no need for the power unit and the control unit to be accommodated in the same housing. According to a further aspect of the present invention, therefore, the power unit and the control unit are physically separate.

-4- In such embodiments the interface unit comprises two physical parts, one located at the power unit and the other one at the control unit.

In all embodiments, it is preferred that the control 5 unit comprises a microprocessor. Preferably, the interface unit is arranged for transmitting the control signals in digital form. In particular, said digital form may include a PAM (pulse width modulation)data word.

The present invention will now be further explained 10 with reference to exemplary embodiments illustrated in the accompanying drawings, in which: Figure l schematically shows a power module according to the prior art;

Figure 2 schematically shows a power module 15 according to the present invention; and Figure 3 schematically shows an interface unit according to the present invention.

The power module l according to the prior art shown

in Fig. l comprises a power unit 2, a control unit 3 and 20 an interface unit 4. The power unit 2 contains power switches 21 which receive electrical power from a power source 6 which is external to the module 1. In response to appropriate control signals, the power switches 2l pass electrical current to the loads 5. To this end, the 25 switches 2l may each be provided with at least one power transistor or similar device. If such semiconductor devices are used, it is often possible to gradually control the current passing through the power switches 21, in addition to switching the current on or off.

30 Each power switch 2l is connected to the control unit 3, via the interface unit 4, by an individual control line. Control signals A, B. C are transmitted in parallel over these control lines. The interface unit 4 consists of a plurality of interface devices 42, one for

-5 each control line. Each interface device 42 comprises a transformer. In this way, the control signals can be transmitted while electrically separating the electrical circuits of the control unit from those of the power 5 unit.

The power module 1 according to the present invention shown in Fig. 2 also comprises a power unit 2, a control unit 3 and an interface unit 4. In contrast to the power module according to the prior art, however, the

10 power module of the present invention has an interface unit 4 which is provided with a serial interface device 42. In addition, the interface unit 4 may have a multiplexer 41 and a demultiplexer 43, as shown in Figure 15 3. Parallel primary control signals A, B. C received from the control unit 2 are combined by the multiplexer 41 so as to form a single multiplexed control signal X which is serially transmitted over the serial interface device 42. The demultiplexer 43 converts the serial 20 control signal X into parallel secondary control signals A', B', C' which correspond with the original control signals A, B. C. Preferably, these secondary control signals A', B', C' are identical to their respective primary counterparts, but this is not essential.

25 Although the primary control signals A, B. C can be time or frequency multiplexed into a combined signal, it is also possible to convert any combination of primary signals into one code word which is digitally transmitted. In that case the multiplexer would act as a 30 coding device and the demultiplexer as a decoding device.

The interface device 42 may consist of a transformer having only one pair of windings. Preferably, however, the interface device is a commercial opto-coupler or a combination of a laser, one or more optical fibres and an

optical detector/receiver. The use of optical fibres has the advantage that the multiplexer 41 and the demultiplexer 42 may be located at a distance from each other. It is then possible for the power module to 5 consist of two parts, one part comprising the control unit 3 and the multiplexer 41, and the other part comprising the power unit and the demultiplexer 42, the parts being connected by the interface device 42, that is, the optical fibre(s).

10 In the above, it has been assumed that the interface unit 4 is unidirectional, that is, control signals pass from the control unit to the power unit only. It is advantageous for status signals to be fed from the power unit to the control unit. To make this possible the 15 interface unit 4 has to be bi-directional. This can be accomplished by having either a bi-directional serial interface device, or two serial interface devices operating in opposite directions. In both options r a multiplexer and a demultiplexer is to be provided at 20 either end of the interface device 42.

It will be understood by those skilled in the art that the present invention is not limited to the embodiments shown and that many additions and modifications are possible without departing from the 25 scope of the present invention as defined by the appended claims.

Claims

-7- CLAIMS

1. A power module for providing electrical power to a load, comprising: 5 i) a power unit for supplying power and having at least two power switching devices capable of receiving control signals, ii) a control unit for controlling the power unit and capable of producing control signals, and 10 iii) an interface unit for transmitting control signals from the control unit to the power unit while maintaining electrical insulation between the control unit and the power unit, said interface unit comprising a serial interface 15 device for serially transmitting the control signals of the power switching devices.

2. The power module according to claim l, wherein the interface unit comprises a single interface device.

20

3. The power module according to claim l or 2, wherein the interface unit comprises a multiplexer for multiplexing the control signals received from the control unit and a demultiplexer for demultiplexing the-

serially transmitted control signals received from the 25 serial interface device.

4. The power module according to any one of the preceding claims, wherein the interface unit is capable of bi-directional transmission.

5. The power module according to claim 4, wherein the 30 interface unit comprises a bi-directional serial interface device.

6. The power module according to any one of the preceding claims, wherein the interface device is optical.

-8

7. The power module according to any one of the preceding claims 1-5, wherein the interface unit comprises a radio link interface.

8. The power module according to claim 6 or 7, wherein 5 the power unit and the control unit are physically separate.

9. The power module according to claim 8, comprising at least two power units.

10. The power module according to any one of the 10 preceding claims, wherein the or each power unit comprises more than two power switching devices.

11. The power module according to any one of the preceding claims, wherein the control unit comprises a microprocessor. 15

12. The power module according to any one of the preceding claims, wherein the interface unit is arranged for transmitting the control signals in digital form.

13. The power module according to claim 12, wherein the digital form involves a data word in PWM format.

20

14. A power module constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.