GB2417373A

GB2417373A - DC converter with resistive load on input side

Info

Publication number: GB2417373A
Application number: GB0520992A
Authority: GB
Inventors: Peter Kunow; Klaus Biester
Original assignee: Cooper Cameron Corp
Current assignee: Cameron International Corp
Priority date: 2001-09-19
Filing date: 2002-09-18
Publication date: 2006-02-22
Anticipated expiration: 2022-09-18
Also published as: GB2417373B; GB0520992D0

Abstract

A system for supplying power comprises a DC source (2, fig. 1) and a plurality of DC converters 8 where the input side of each converter includes a resistive load 32 to dissipate power when the remote electrical device (3, fig. 1) is not consuming power. The resistive load may be a Zener diode. The plurality of converters may be chosen such that the cooling mechanism that would be required if fewer converters were used may be dispensed with. The system may be used for supplying power from a sea surface to a sub-sea electrical device. The conductor connecting the DC source to the DC converters may be at least one kilometre.

Description

24 1 7373 DC Converter A DC converter is connected to a DC source on its

input side. On the output side, the DC converter delivers a converted DC voltage to at least one electric consumer via a cable connection.

Such DC converters have a wide field of use and are especially used where a DC voltage has to be converted and where the converted DC voltage should be comparatively stable.

Such nerds of use are erg. photovoltalc systems, the field of automotive vehicles, DC trac- tion drives For underground railways and for streetcars, domestic drives for halrdryers, drily ing machines or the like, semiconductor technology and telecommunications.

In the case of high DC voltages on the input side, suitable DC converters are not realizable, since their dielectric strength is determined by the respective dielectric strengths of their components. Components having dielectric strengths of more than 1000 V, e.g. 3000 or 6000 V, are, however, not available or they can hardly be realized technically. If such a converter is nevertheless suitable for such high DC voltages, the whole system Will collapse If the converter fails to operate. In addition, even If the efficiency is comparatively high, the a.

DC converter will have a dissipation power that produces a substantial amount of heat, comparatively locally. This amount of heat may destroy certain components of the con- t: verter. In order to avoid such destnctlon, complicated cooling systems are required which entail high costs.

It is therefore the object of the present invention to improve a DC converter of the type mentioned at the start In such a way that it has a comparatively simple structural design and is able to reliably convert high DC voltages even in the case of high power, and in sucl? a way that the reliability of the converter is Increased and cooling systems entailing high costs can be dispensed with.

In connection With the features of the generic clause of claim 1, this object is achieved In that the DC converter comprises a plurality of DC converter components, each of said [)C converter components being, on the input side, serially connected to the DC source and, on the output side, connected In parallel to the cable connection so as to provide the converted DC voltage for the electric consumer.

Due to the plurality of DC converter components used, each converter component only has to deal with part of the high Input voltage, said high input voltage being converted into a suitable output voltage by the respective converter component. When all the converter components have the same type of structural design, each converter component will con- vert the same percentage of the input voltage if the Input voltage is e.g. 6000 V and If 30 converter components are provided, each converter component only has to convert a volt- age of 200 V into al suitable output voltage. This results from the serial connection oaths input side of the converter components.

On the output side, each converter component delivers the same voltage and feeds this voltage into the cable connection due to the parallel connection.

It is, of course, also possible that the converter components have different structural de- " signs or are utilized to different degrees, so that different proportional parts of the input volts, age are converted by the various converter components into Identical output voltages.

The fact that the voltage conversion is distributed to a plurality of converter components also guarantees that a failure of one, two or more than two converter components will not | lead to a breakdown of the whole supply of the electric consumer on the output side. In" stead, the converter components which are still capable of operating can, when adjusted accordingly, replace the Ineffective converter components fully or at least to a very large extent (redundancy).

In view of the fact that also the dissipation power of the DC converter is distributed to said plurality of converter components, the heat development is distributed over a larger area as well, and can be eliminated by simple cooling systems. When the distance between the respective converter components is sufficiently large in this connect/on, so that the converter components will not mutually heat themselves, cooling by the ambient air or by another medium surrounding the converter components may be sufflclent, so that separate cooling means can be dispensed with.

Such converter components for an input voltage of e.g. a few hundred volts are nowadays commercially available, whereas converter components for a few thousand or for several thousand volts on the input side are not available at all or are at least very expensive and complicated.

The parallel connection of the converter components on the output side results, depending on the power of the individual converter components, in the total power of the system De- pending on the total power desired, the number and the structural design of the converter components are selected accordingly. The overall system can easily be adapted to given requirements in this way.

In order to satisfy requirements with respect to the control of mains fluctuations and load control, the tendency towards miniaturization and the wish for reducing the dissipation power, the converter components can be implemented as clocked switched mode mains power supplies. Such clocked switched mode mains power supplies have, in comparison with conventional power supply units, an efficiency that is in some cases higher than 90%, a reduction of volume and weight of up to 60 %, a voltage stabilization of less than 1-2 %, they require only a small amount of filtering means and their price-perfonance payoff Is more advantageous. ; There are electric consumers which require both a high voltage and a high power. If the power and the voltage are suddenly demanded, when the electric consumer is switched on, ;,, and are not yet available in the system, the system may collapse due to a feedback to e.g. the DC source. In order to avoid such a collapse and a negative feedback, the clocked switched mode mains power supply has on the input side thereof a load which is connected in parallel to a transmitter of said switched mode mains power supply.

The OC converter according to the present Invention is so conceived that, already prior to switching on or supplying the electric consumer, the voltage and the power in the system are increased to at least the values demanded by the electric consumer. Until the electric consumer actually operates, the voltage drops across the load and the power is converted Into heat as dissipation power. Only when the load will then demand power, this power will be supplied via the various converter components and less voltage will drop across the load and be converted into heat.

For the DC source a stable utilization and a constant load are always discernible, i.e. the respective power distribution takes place in situ and is no longer fed back to the [)C source and the units associated therewith.

The load can be implemented as a Zener diode so that, if necessary, voltage and power can be built up rapidly to desired values only a short time before they are demanded by the electric consumer. Full voltage and full power can in this way be built up within a few milli- seconds and consumed by the Zener diode. The electric consumer is only connected or additionally connected when voltage and power have been built up completely. The voltage and the power are then supplied to the electric consumer, only a residual voltage dropping across the Zener diode and only a small percentage of the power (a few percent) being consumed there. If the electric consumer is then switched off, the whole voltage will again drop across the Zener diode and said Zener diode will consume the full power in the sys- tem. Subsequently, the voltage and the power can be reduced to a lower value. The re- duced values are sufficient for supplying respective components of the system, such a monitoring and control means, which are also active if no electric consumer has been connected or additionally connected.

If a supply of components by the DC converter according to the present invention is not necessary, the voltage and the power can also be switched off completely or reduced to zero.

As soon as there is again a demand from an electric consumer, voltage and power are again built up within a few milliseconds.

Curing application of full voltage and of full power, especially the DC source has always applied thereto a uniform load, since a suitable distribution of voltage and power to the Zener diode and the electric consumer takes place in situ at the DC converter.

The Zener diode can be implemented in the form of field effect transistors or load resistors.

This also permits a control of the voltage drop across the Zener diode so as to adapt the Zener diode to the requirements in question. s

Furthermore, the Zener diode also guarantees in each converter component a good heat dissipation of dissipation power that has there been converted into heat. The heat in ques- tion is no longer generated locally within close limits' but it Is generated at a large number of locations so that the heat can be given off directly Into the air or into water or the like. Sepa- rate cooling systems are not necessary.

Furthermore, the Zener diode may have a very steep limiting characteristic so as to stabilize the output voltage still further, if necessary.

if the Zener diodes and the respective converter components have the same type of struc- tural design, it is also guaranteed that identical current intensities are distributed to each component. The voltage is stabilized up to a range of 2, or % at the most.

It can also be considered to be advantageous when the switched mode mains power supply Is clocked on the primary side so as to galvanically separate the output side and the input side.

The switched mode mains power supply can be implemented as a push-pull converter so fir as to use a switched mode mains power supply which is also well adapted to high power i values. The push-pull converter can be implemented as a half-bridge or as a full-bridge push-pull converter The switched mode mains power supply can include a switching transistor, especially a power MC)SFET or a power BIMOSFET, so that a transmitter of the switched mode mains power supply, which is clocked on the primary side, can be switched electronically in a sim ple way. In this connect/on, attention should be paid to the fact that, erg. for a ful1-bridge pushpull converter, four such switching transistors are respectively connected in pairs.

The switching transistors can be clocked in a push-pull mode with a clock cycle ratio of 1:1 so as to obtain a low current consumption of the transnnitter in the push-pull converter.

In order to obtain the least possible amount of harmonic waves on the output side, the switched mode mains power supplies of the DC converter can be clocked synchronously.

The switched mode mains power supplies of the DC converter can be clocked in a phase- shiFted mode so as to shift, especially in the case of the communication connection in the direction of the DC source, the cutoff frequency of the system upwards as far as possible so that the signals transmitted for said communication connection will be interfered with as little as possible.

A simple phase shift generating only a minor amount of harmonic waves will occur when the respective phase shin of neighbouring switched mode mains power supplies amounts to An, when n is the number of switched mode mains power supplies of the DC converter. In this way, the n+15' switched mode mains power supply would again be in phase with the first switched mode mains power supply (cyclic phase shift). In addition, the magnitude of the total interfering voltage produced will In this case only be 1/n of the interfering voltage of an individual component In order to realize in this respect a simple cable connection to the DC source, which re- quires only a small cross-section for transmitting the DC voltage and which also permits a reliable and faster transmission through the communication connections, the DC converter can be connected to the DC source via a coaxial cable connection. it.

In order to remove interFerlug frequencies especially from the frequency range required for the communication connection, the DC converter can be provided with a filter means pre- ceding said DC converter on the input side thereof. This filter means filters especially a fre- quency range of up to approx. 50 kHz.

In order to realize suitable communication connection in a simple way and only after the filtering, a means for coupling data signals inlout can be connected upstream of said filter means in the direction of the DC source.

A controller can be associated with at least the DC converter and the components thereof so as to design the DC converter in such a way that said DC converter and, if necessary, also the electric consumer connected thereto can be can be controlled and monitored autarkically. This controller can e.g. detect failure of a converter component and, if desired, also the position of said converter component. This information can be transmitted via the communication connection and the means for coupling data signals in/out to the DC source and the units associated therewith. There, the information can be displayed in a suitable manner on a reproduction device, such as a screen or the like If a relevant number of con- verter components failed, a repair demand can additionally be supplied by the controller Until then, it is possible to readjust the still operational converter components in an appro- priate manner so as to compensate for the failure of the damaged converter components The compensation can be effected e.g. in that, especially in the case of failure of another switched mode mains power supply G' the DC converter, each Zener diode is adapted to be readjusted so as to increase the input voltage of the respective switched mode mains power supply and, consequently, also the output voltage thereof to such an extent that the failure of the damaged switched mode mains power supply or supplies is compensated for by the still operational switched mode mains power supplies.

It is also possible that a suitable readjustment of the output voltage of one switched mode mains power supply is effected directly via a variation of the clock cycle ratio of the switch- ing transistors, if other switched mode mains power supplies fail to operate.

In order to activate the switching means of the various switched mode mains power sup- ; plies while controlling or regulating especially the controller, the switched mode mains >^ power supply can be provided with a pulse modulation means which outputs a series of pulses having variable widths and/or heights andlor frequencies so as to clock the switching means in question or rather the switching transistors defining the same.

It should additionally be pointed out that the filter means between the l:)C converter and the DC voltage source can be realized e.g. by comparatively small capacitors, since, due to the fact that the Individual converter components are clocl<ed in a phase-shifted mode, the cut off frequency of the system is very high.

The use of a load on the input side of each converter component is particularly advanta geous according to the present invention. The load is important especially when the system is powered up to high voltages, em. from 3000 V to 6000 V, and when the power level made available to the electric consumers Is increased accordingly, since said load permits powering up of the overall system before the electric consumer is actually connected or ad ditionally connected. As long as power is not yet demanded by one of the electric consum x ers, the respective power will be consumed at one of the various loads of the converter components. Hence, a stable utilization of the cable connection or coaxial cable connectio to the DC source already exists. A supply of power to the electric consumer will be effected only afterwards, e.g. by connecting or additionally connecting said electric consumer. Even then, a certain part of the power (a few percent) will still be consumed by the load and by the Zener diode defining said load, whereas most of the power will be supplied to the elec- tric consumer or consumers, i.e. power distribution is effected in situ In the area of the DC converter and a feedback, e.g. to the DC source, does not take place.

The special mode of switching of the DC converter components also guarantees that power, voltage and current can easily be adapted to respective requirements. Depending on the voltage and power required, a smaller or large number of suitably designed con- verter components can be used.

In the following, advantageous embodiments of the present invention will be explained in detail making reference to the figures added as drawings: Fig. 1 shows a schematic representation of an embodiment of DC converter according to the present invention; Fig. 2 shows a schematic circuit diagram of a push-pus converter for use as a switched mode mains power supply in Fig. 1; Fig. 3 shows a circuit for a full-bridge push-pull converter, and Fig. 4 shows a circuit for a half-bridge push-pull converter.

Fig. 1 shows a schematic circuit diagram of an embodiment of a DC converter 1 according to the present invention. This DC converter comprises a number of DC converter compo- nents realized by switched mode mains power supplies 8. The switched mode mains power supplies 8 are preceded by a filter means 7 in the direction of a DC source 2. The DC source 2 is Connally arranged far away from the DC converter 1. The respective coaxial cable connection 6 between the DC source 2 and the DC converter 1 serves to transmit the DC voltage and may have a length of e.g. several kilometres; it may also have a length of 50, 60 or more kliornetres. Due to the transmission of a high DC voltage, only low line losses occur along the coaxial cable connection 6 and, simultaneously' also a communica- tion connection can be realized over this cable connection. Additional attenuation losses, as in the case of an AC voltage, do not occur.

For feeding respective data signals for the communication connection in and out of the co- axial cable connection 6, a means for coupling data signals inlout 16, which is located be- tween the filter means 7 and the DC source 2, Is arranged upstream of the filter means 7.

The various switched mode mains power supplies 8 are each implemented as push-pull converters, cf. Fig. 2-4 These push-pull converters are serially interconnected on the input side via a respective line 27 and they are also connected to the coaxial cable connection 6 On the output side, the respective switched mode mains power supplies are connected parallel to one another and they are connected to a cable connection 4. The cable connec- tion 4 serves to supply at least one electric consumer 3 with DC voltage converted by the converter components 6. Only by way of exernple' a few values are here indicated for the DC voltage supplied by the DC source 2, the power transmitted via the cable connection and the voltage provided on the output side of the DC converter 1. The DC source can, for example, transmit 6000 V via the coaxial cable connection 6 to the DC converter 1. When the VO, converter components have the sanne type of structural design, a voltage of 6000 Vln will drop across each of these components due to the serial connection of the DC: con- verter components 5, n being the number of converter components 5. If n is e.g. 30, a voltage of 200 V will drop across each converter component. This voltage is converted into an output voltage of e.g. 300 V by each of the respective converter components 5 and fed par- allel into the cable connection 4 for supplying the electric consumer or consumers 3.

Such electric consumers are erg. actuators, such as a positioning device, a motor or the like, which serve to operate certain means, such as valves, restrictors, pumps, shut-off de- vices and the like. These means are used erg. for controlling the flow of a fluid Into a line and Within the Itne. If there is e.g. a leak in the line and if a possibly aggressive fluid escapes into the surroundings, an associated fluid source can be shut off against the line by means of a suitable shut-off device whereby further discharge of the fluid Into the sur- roundings can be prevented. Accordingly, the valves and restrictors can control the flow of the fluid as additional units. The respective actuators may also be arranged comparatively far from the DC converter 1, and they are supplied with suitable power and suitable voltage via the cable connection 4 according to requirements.

The coaxial cable connection 6 may also be very long so that the no source and other units associated therewith are arranged at a remote site The coaxial cable connection 6 may e.g. have a length of several kilometres, and it may also have a length of 50 or 60 kilome- tres or more. The DC source and the additional units associated therewith, which are not shown in detail in Figs 1, may eggs be occupied by operators and arranged at an easily ac- cessible point of the earth's surface or of the surface of the sea. The DC converter 1 and the electric consumers suppiled thereby are, however, arranged at a point which is not eas- lty accessible, such as below ground or below the surface of the sea.

For controlling the DC converter 1 and for transmitting respective data to the DC source 2 as well as for receiving respective data from said DC source, a controller 17 is provided.

This controller is used for controlling, monitoring and, if necessary, regulating the various components of the DC converter 1, The controller 17 supervises also respective parameters of the electric consumer or consumers 3 and switches thisithese electric consumers 3 on or off, if necessary.

In Fig. 1 the respective connections of the controller 17 to the units shown in said figure are indicated by broken lines Reference should be made to the fact that the controller 17 also monitors the means for coupling data signals inlout 16 and thus the communication connection with the DC source 2.

Fig. 2 shows a simplified embodiment for a push-pull converter 9 used as a switched mode mains power supply 8. This push-pull converter has its input terminals 26 and 28 connected in series with the other push-pull converters 9 or switched mode mains power supplies 8 according to Fig. 1 On the input side, the push-pull converter 9 comprises a Zener diode 32 and an input capacitor 25. These two components are connected parallel to each other and to a primary winding of a transmitter 24.

The Zener diode 32 can be composed, In a manner known per se, of a number of transis- tors and load resistors.

The primary winding of the fransmlffer 24 has associated therewith a switching means 11.

This switching means is shown as a simple switch in Fig. 2. In actual fact, said switching means 11 is, however, realized by one or more switching transistors, cf. e.g. Fig. 3 and 4; such switching transistors may be power MOSFETs, BlMOSFETs or thyristors.

The primary winding is magnetically coupled to a secondary winding of the transmitter 24.

The secondary winding is connected to output terminals 29 and 30 of the push-pull con- verter 9. A diode 20 and a load 21 are serially connected between the primary winding and the output terminal 29. The load 21 nnay e.g. be an inductor 23 according to Fig. 3 and 4.

The output terminals 29 of all pushpull converters 9 or switched mode mains power sup plies 8 according to Fig. 1 are connected parallel to one another and to the cable connec- tion 4. The other output terminals 30 are also connected parallel to one another and to ground 31 ()n the output side of the push-pull converter 9, a smoothing capacitor 22 is connected par- allel to the secondary winding of the transmitter 24.

In Fig. 3 and 4 a respective push-pull converter 9 according to Fig. 2 is shown in detail, in one case as a full-bridge push-pull converter 10 and in another case as a halfbrldge push- pull converter 19, both push-pull converters 10 and 19 being shown with the respective cir- cuit. Such circuits for full-bridge and half-bridge push-pull converters 10, 19 are known per se. The circuits shown differ from known circuits with regard to the respective connection modes of the push-pull converters on the input side and on the output side, i.e. with regard to the fact that respective terminals are serially connected on the input side and connected in parallel on the output side.

Furthermore, the Zener diode 32 on the input side of each pushpull converter g or 10, 19 is connected parallel to the primary winding of the transmitter 24.

This Zener diode 32 serves as an input-side load of the various push-pull converters for powering up the system with regard to voltage and energy already prior to connecting or additionally connecting a respective electric consumer 3. As long as the electric consumer has not yet been connected or additionally connected, the respective energy In the system is consumed and converted into heat by the Zener diode 32 When the electric consumer is then additionally connected, energy distribution takes place in each of the push-pull con- verters, and it is only a small percentage of the energy that Is still converted into heat by the Zener diode 32.

Due to the large number of Zener diodes and the fact that they are arranged In spaced rela tlonship with one another, the electric energy converted into heat in said Zener diodes will not result In overheating of the l:)C converter 1, but, depending on the location where the converter is arranged, it can be discharged directly into air or water as waste heat. Compli- cated and expensive cooling systems can be dispensed the When the electric consumer no longer needs electric energy, it will be switched off, i.e. dis- connected from ale system. Subsequently, the whole energy is, In situ, again converted into heat by the Zener diodes If the electric consumer in question or another electric consumer is then not connected or additionally connected once more, the system as a whole can be run down to a lower voltage, such as 3000 V or even less than that. The reduced voltage is then still required for the function of the controller and of other units of the DO converter 1 which are always in operation.

in the full-bridge push-pull converter 10 according to Fig. 3, a total of tour switching tran- sistors 12, 13, 14, 15 are integrated in the switching means 11. The switching transistors 12, 13, 14, 15 co-operate in pairs for effecting a push-pull activation of the transmitter 24, the push-pull clock cycle ratio being 1:1.

On the output side, respective diodes 20 are provided, and on the input side a plurality of input capacitors 25 is provided.

For activating the various switching transistors 12, 13, 14, 15, a pulse modulation means 18 is shown in Fig 4. This pulse modulation means outputs a series of pulses whose widths and/or heights and/or frequencies are variable so as to clock the switching transistors 12, 13,14 and 15 and the switching means 11, respectively.

For the sake of clarity, said pulse modulation means 18 is not shown in Fig. 2 and 3.

Claims

I. A system for supplying power to an electrical device, the system comprising: a DC source; a plurality of DC/DC converters, wherein inputs of the DC/DC converters are connected to the DC source via an electrical conductor and wherein outputs of the DC/DC converters are connected to the electrical device, wherein the plurality of DCIDC converters receive a high DC voltage from the DC source via the electrical conductor and convert the high DC voltage to a lower DC lO voltage without a cooling mechanism that is needed when an amount of DCIDC converters less than the plurality of DCIDC converters are implemented to convert the high DC voltage to the lower DC voltage, and wherein an input side of each DC/DC converter comprises a resistive load to dissipate power when the electrical device is not consuming power.
2. 'I'he system according to claim I, wherein the resistive load is a zoner diode.
3. The system according to claim I or 2, wherein the electrical conductor is at least one kilometer in length.
4. The system according to any preceding claim, further comprising a controller coupled to each of the DC/DC converters, wherein the controller is operable to regulate one or more functions of each DCIDC converter.
5. The system according to claim 4, wherein the controller is further coupled to the remote electrical consumer, wherein the controller is operable to regulate one or more functions of the electrical device.
6. The system according to claim 4 or 5, further comprising a data coupling device coupled to the electrical conductor and the controller, wherein the data coupling device is operable to decouple data from the electrical conductor and provide the data to the controller while power is supplied to the electrical device.
7. The system according to claim 6, wherein the data coupling device is operable to couple data from the controller to the electrical conductor while power is supplied to the electrical conductor.
8. The system according to claim 7, wherein the data decoupled from the electrical conductor is used to control the electrical device.
9. The system according to claim 7 or 8, wherein the data coupled to the electrical conductor is used to monitor the electrical device.
10. The system according to any of claims 7 to 9, wherein the data coupled to the electrical device is used to monitor the DC/OC converters.
11. The system according to any of claims 4 to 10, wherein the controller is operable to detect failure of a DC/)C converter and cause functioning DC/DC converters to compensate for the tailed DC/DC converter.
12. The system according to any of claims 4 to 11, wherein the controller independently a? controls an output power of each DC/DC converter.
13. The system according to claim 12, wherein each DC/DC converter comprises a switching mechanism that permits the output power of each DC/I)C converter to be controlled using a pulse width modulated signal.
14. The system according to any preceding claim, wherein the electrical device is an actuator.
15. The system according to any preceding claim, wherein the electrical conductor is a coaxial cable.
16. The system according to any preceding claim, wherein the electrical device is located below ground.
17. The system according to any preceding claim, wherein the electrical device is located under water.
18. A DC converter for connection to a DC source on the input side and which, on the output side, delivers a converted voltage to at least one electric consumer via a cable connection, wherein the DC converter comprises: a plurality of DC converter components, each of said DC converter components being, on the input side, serially connected to the DC source and, on the output side, connected in parallel to the cable connection so as to provide the converted DC voltage for the electric consumer.
19. A DC converter according: to claim 18, wherein the DC converter component is Implemented as a clocked switched mode power supply.
20 A DC converter according to claim 19, wherein the switched mode power supply is clocked on the primary side.
21. A DC converter according to claim 19 or 20, wherein the switched mode power supply is implemented as a push-pull converter.
22. A DC converter according to claim 21, wherein the switched mode power supply includes as a switching means at least one switching transistor.
23. A L)C converter according to claim 22, wherein the or each switching transistor of the push-pull converter is clocked in a push-pull mode with a clock cycle ratio of 1:1.
24. A DC converter according to claim 22 or 23, wherein a clock cycle ratio of the or each switching transistor can be varied by readjusting the output voltage of the switched mode power supply.
25. A DC converter according to any of claims 22 to 24, wherein, for a clocked activation of the switching transistors, the switched mode power supply is provided with a pulse modulation means which outputs a series of variable pulses to clock the or each switching transistor.
26. A DC converter according to any of claims 19 to 25, wherein the switched mode power supplies of the DC converter are clocked synchronously.
27. A DC converter according to any of claims 19 to 26, wherein the switched mode power supplies of the DC converter are clocked in a phaseshifted mode.
28. A DC converter according to any of claims] 9 to 27, wherein a respective clock phase shift of neighboring switched mode power supplies amounts to 1/n, where n is the number of switched mode power supplies ofthe OC converter.
29. A DC converter according to any of claims] 9 to 28, wherein the switched mode power supply has on the input side thereof a load which is connected in parallel to a transmitter of said switched mode power supply.
30. A DC converter according to any of claims 19 to 29, wherein the load is a Zener diode.
31. A DC converter according to claim 30, wherein when a failure of a switched mode power supply of the DC converter occurs, the voltage of each Zener diode is adapted to be varied so as to readjust the output voltage of the non-failed switched mode power supplies.
32. A DC converter according to claim 30 or 31, wherein the Zener diode comprises semiconductor elements.
33. A DC converter according to any of claims 18 to 32, wherein the DC converter is connected to the DC source via a coaxial cable connection.
34. A DC converter according to any of claims 18 to 33, wherein the 1)C converter is provided with a filter means between the DC converter and the DC source.
35. A DC converter according to claim 34, wherein a means for coupling data signals in/out is connected upstream of said filter means in the direction of the DC source.
36. A DC converter according to any of claims 18 to 35, wherein a controller is associated with at least the DC converter and the components thereof.
37. A system for supplying power from a sea surface to a subsea location, the system comprising: a DC source for disposal at the sea surface; a subsea electrical device; and a plurality of DC voltage converters for disposal subsea, each having an input side connected to the DC source via an electrical conductor and an output side connected to the subsea electrical device; wherein an input side of each DC voltage converter includes a resistive load to dissipate power when the subsea electrical device is not consuming power.
38. The system according to claim 37, wherein the electrical conductor extends subsea to the subsea electrical device.
39. The system according to claim 37 or 38, wherein the resistive load is a zoner diode.
40. The system according to any of claims 37 to 39, wherein the DC converters are in a spaced relationship with each other such that heat from the DC converters is dissipated without the need of a cooling component.
41. The system according to any of claims 37 to 40, further including a controller which detects a failure of a DC converter and causes other DC converters to compensate for the failed DC converter.
42. A system for supplying power to a remote electrical device, the system comprising: a DC source; a plurality of DC voltage converters each having an input serially connected to the DC source via a conductor and each having an output connected to the remote electrical device, wherein an input side of each DC converter includes a resistive load to dissipate power when the remote electrical device is not consuming power; and wherein the length ofthe conductor is at least one kilometer.
43. A DC converter substantially as hereinbefore described having reference to any of the accompanying figures.
44. A system for supplying power to an electrical device substantially as hereinbefore described having reference to any of the accompanying figuecs.
45. A system for supplying power from a sea surface to a subsca location substantially as hereinbcfore described having reference to any of the accompanying figures.

lo
46. Use of a DC converter as claimed in any of claims 18 to 36 or 43, or a system as claimed in any of claims I to 17, 37 to 42, 44 or 45 for supplying power to an electrical device.
47. Use according to claim 46, wherein the electrical device is underground or underwater. At,