Abstract:
A DC converter is connected to a DC source on its input side. On the output side, the DC delivers a converted DC voltage to at least one electric consumer via a cable connection. To improve such a DC converter in 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 such a way that the reliability of the converter is increased and cooling systems entailing high costs can be dispensed with, the DC converter comprises a plurality of DC converter components, each of said DC 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.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation of U.S. application Ser. No. 10/489,584 filed Aug. 5, 2004, which claims priority to PCT/EP02/10469 filed 18 Sep. 2002 and to German Application No. DE 201 15 474 filed 19 Sep. 2001, all hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    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. 
         [0003]    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 fields of use are e.g. photovoltaic systems, the field of automotive vehicles, DC traction drives for underground railways and for streetcars, domestic drives for hairdryers, drilling machines or the like, semiconductor technology and telecommunications. 
         [0004]    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 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 converter. In order to avoid such destruction, complicated cooling systems are required which entail high costs. 
       BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS 
       [0005]    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 such a way that the reliability of the converter is increased and cooling systems entailing high costs can be dispensed with. 
         [0006]    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 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. 
         [0007]    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 convert 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 voltage of 200 V into a suitable output voltage. This results from the serial connection on the input side of the converter components. 
         [0008]    On the output side, each converter component delivers the same voltage and feeds this voltage into the cable connection due to the parallel connection. 
         [0009]    It is, of course, also possible that the converter components have different structural designs or are utilized to different degrees, so that different proportional parts of the input voltage are converted by the various converter components into identical output voltages. 
         [0010]    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. Instead, 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). 
         [0011]    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 connection, 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 sufficient, so that separate cooling means can be dispensed with. 
         [0012]    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. 
         [0013]    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. Depending 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. 
         [0014]    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-performance payoff is more advantageous. 
         [0015]    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 transformer of said switched mode mains power supply. 
         [0016]    The DC 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. 
         [0017]    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 DC source and the units associated therewith. 
         [0018]    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 milliseconds 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 system. Subsequently, the voltage and the power can be reduced to a lower value. The reduced values are sufficient for supplying respective components of the system, such as monitoring and control means, which are also active if no electric consumer has been connected or additionally connected. 
         [0019]    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. 
         [0020]    As soon as there is again a demand from an electric consumer, voltage and power are again built up within a few milliseconds. 
         [0021]    During 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. 
         [0022]    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. 
         [0023]    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 question 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. Separate cooling systems are not necessary. 
         [0024]    Furthermore, the Zener diode may have a very steep limiting characteristic so as to stabilize the output voltage still further, if necessary. 
         [0025]    If the Zener diodes and the respective converter components have the same type of structural design, it is also guaranteed that identical current intensities are distributed to each component. The voltage is stabilized up to a range of 2, 3 or 5% at the most. 
         [0026]    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. 
         [0027]    The switched mode mains power supply can be implemented as a push-pull converter so as to use a switched mode mains power supply which is also well adapted to high power values. The push-pull converter can be implemented as a half-bridge or as a full-bridge push-pull converter. 
         [0028]    The switched mode mains power supply can include a switching transistor, especially a power MOSFET or a power BIMOSFET, so that a transformer of the switched mode mains power supply, which is clocked on the primary side, can be switched electronically in a simple way. In this connection, attention should be paid to the fact that, e.g. for a full-bridge push-pull converter, four such switching transistors are respectively connected in pairs. 
         [0029]    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 transformer in the push-pull converter. 
         [0030]    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. 
         [0031]    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. 
         [0032]    A simple phase shift generating only a minor amount of harmonic waves will occur when the respective phase shift of neighbouring switched mode mains power supplies amounts to 1/n, when n is the number of switched mode mains power supplies of the DC converter. In this way, the n+1 st  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. 
         [0033]    In order to realize in this respect a simple cable connection to the DC source, which requires 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. 
         [0034]    In order to remove interfering frequencies especially from the frequency range required for the communication connection, the DC converter can be provided with a filter means preceding said DC converter on the input side thereof. This filter means filters especially a frequency range of up to approx. 50 kHz. 
         [0035]    In order to realize suitable communication connection in a simple way and only after the filtering, a means for coupling data signals in/out can be connected upstream of said filter means in the direction of the DC source. 
         [0036]    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 converter 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 appropriate manner so as to compensate for the failure of the damaged converter components. 
         [0037]    The compensation can be effected e.g. in that, especially in the case of failure of another switched mode mains power supply of 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. 
         [0038]    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 switching transistors, if other switched mode mains power supplies fail to operate. 
         [0039]    In order to activate the switching means of the various switched mode mains power supplies 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 and/or frequencies so as to clock the switching means in question or rather the switching transistors defining the same. 
         [0040]    It should additionally be pointed out that the filter means between the DC 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 clocked in a phase-shifted mode, the cut-off frequency of the system is very high. 
         [0041]    The use of a load on the input side of each converter component is particularly advantageous according to the present invention. The load is important especially when the system is powered up to high voltages, e.g. 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 additionally connected. As long as power is not yet demanded by one of the electric consumers, 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 connection 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 electric 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. 
         [0042]    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 converter components can be used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    In the following, advantageous embodiments of the present invention will be explained in detail making reference to the figures added as drawings: 
           [0044]      FIG. 1  shows a schematic representation of an embodiment of DC converter according to the present invention; 
           [0045]      FIG. 2  shows a schematic circuit diagram of a push-pull converter for use as a switched mode mains power supply in  FIG. 1 ; 
           [0046]      FIG. 3  shows a circuit for a full-bridge push-pull converter, and 
           [0047]      FIG. 4  shows a circuit for a half-bridge push-pull converter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0048]      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 components  5  realized by switched mode mains power supplies  8 . The switched mode mains power supplies  8  are pre-ceded by a filter means  7  in the direction of a DC source  2 . The DC source  2  is normally 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 kilometres. Due to the transmission of a high DC voltage, only low line losses occur along the coaxial cable connection  6  and, simultaneously, also a communication connection can be realized over this cable connection. Additional attenuation losses, as in the case of an AC voltage, do not occur. 
         [0049]    For feeding respective data signals for the communication connection in and out of the coaxial cable connection  6 , a means for coupling data signals in/out  16 , which is located between the filter means  7  and the DC source  2 , is arranged upstream of the filter means  7 . 
         [0050]    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 connection  4  serves to supply at least one electric consumer  3  with DC voltage converted by the converter components  5 . Only by way of example, 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 DC converter components have the same type of structural design, a voltage of 6000 V/n will drop across each of these components due to the serial connection of the DC converter 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 parallel into the cable connection  4  for supplying the electric consumer or consumers  3 . 
         [0051]    Such electric consumers are e.g. actuators, such as a positioning device, a motor or the like, which serve to operate certain means, such as valves, restrictors, pumps, shut-off devices and the like. These means are used e.g. for controlling the flow of a fluid into a line and within the line. 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 surroundings 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. 
         [0052]    The coaxial cable connection  6  may also be very long so that the DC 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 kilometres or more. The DC source and the additional units associated therewith, which are not shown in detail in  FIG. 1 , may e.g. be occupied by operators and arranged at an easily accessible point of the earth&#39;s surface or of the surface of the sea. The DC converter  1  and the electric consumers supplied thereby are, however, arranged at a point which is not easily accessible, such as below ground or below the surface of the sea. 
         [0053]    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 this/these electric consumers  3  on or off, if necessary. 
         [0054]    In  FIG. 1  the respective connections of the controller  17  to the units shown in said figure are indicated by broken lines. 
         [0055]    Reference should be made to the fact that the controller  17  also monitors the means for coupling data signals in/out  16  and thus the communication connection with the DC source  2 . 
         [0056]      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 trans-former  24 . 
         [0057]    The Zener diode  32  can be composed, in a manner known per se, of a number of transistors and load resistors. 
         [0058]    The primary winding of the transformer  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.  FIGS. 3 and 4 ; such switching transistors may be power MOSFETs, BIMOSFETs or thyristors. 
         [0059]    The primary winding is magnetically coupled to a secondary winding of the transformer  24 . The secondary winding is connected to output terminals  29  and  30  of the push-pull converter  9 . A diode  20  and a load  21  are serially connected between the primary winding and the output terminal  29 . The load  21  may e.g. be an inductor  23  according to  FIGS. 3 and 4 . The output terminals  29  of all push-pull converters  9  or switched mode mains power supplies  8  according to  FIG. 1  are connected parallel to one another and to the cable connection  4 . The other output terminals  30  are also connected parallel to one another and to ground  31 . 
         [0060]    On the output side of the push-pull converter  9 , a smoothing capacitor  22  is connected parallel to the secondary winding of the transformer  24 . 
         [0061]    In  FIGS. 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 half-bridge push-pull converter  19 , both push-pull converters  10  and  19  being shown with the respective circuit. 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. 
         [0062]    Furthermore, the Zener diode  32  on the input side of each push-pull converter  9  or  10 ,  19  is connected parallel to the primary winding of the transformer  24 . 
         [0063]    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 converters, and it is only a small percentage of the energy that is still converted into heat by the Zener diode  32 . 
         [0064]    Due to the large number of Zener diodes and the fact that they are arranged in spaced relationship with one another, the electric energy converted into heat in said Zener diodes will not result in overheating of the DC converter  1 , but, depending on the location where the converter is arranged, it can be discharged directly into air or water as waste heat. Complicated and expensive cooling systems can be dispensed with. 
         [0065]    When the electric consumer no longer needs electric energy, it will be switched off, i.e. disconnected from the system. Subsequently, the whole energy is, in situ, again converted into heat by the Zener diode. 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 DC converter  1  which are always in operation. 
         [0066]    In the full-bridge push-pull converter  10  according to  FIG. 3 , a total of four switching transistors  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 transformer  24 , the push-pull clock cycle ratio being 1:1. 
         [0067]    On the output side, respective diodes  20  are provided, and on the input side a plurality of input capacitors  25  is provided. 
         [0068]    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. 
         [0069]    For the sake of clarity, said pulse modulation means  18  is not shown in  FIGS. 2 and 3 .