Abstract:
The invention relates to a combined AC-DC to DC converter. The converter provides the option of coupling to an AC supply source with at least one phase and the further option of coupling to at least one DC supply source. The converter obtains supply from at least one supply source at a time; and the converter contains controllable contact means that are, upon switching between supply sources, capable of connecting and disconnecting the individual supply sources to/from the converter; whereby a pulse signal is generated. The converter contains at least one coil that is in connection with at least one DC output. The proposed converter distinguishes itself over the prior art in that switching between supply sources is accomplished by means of the contact means over a period of time, where the pulse signal is divided into periods; and wherein the periods alternatingly originate from at least one first supply source and at least one second supply source; and wherein the current pulses from the first supply source is regulated in dependence on the current pulses from the second supply source; and wherein the converter contains means for voltage regulating at least one DC output. Hereby a flexible converter is obtained that can obtain supply from an AC supply source and one or more DC supply sources; and wherein switching between a first supply source and a second supply source can be accomplished without supply failures; and wherein, in overload situations, it is possible to draw on two or more supply sources.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is the National Stage of International Application No. PCT/DK02/0004, filed 22 Jan. 2002. 
   FIELD OF THE INVENTION 
   The invention relates to a combined AC-DC to DC-converter. The converter provides at least one DC output from at least one AC supply with at least one phase and at least one DC supply. The AC supply supplies an AC signal comprising positive and negative half-periods. The converter comprises at least one coil that is in connection with the DC output. The converter contains controllable contact means adapted for connecting and disconnecting the AC supply and the DC supply to and from the converter. 
   BACKGROUND 
   Patent application No. WO 0033451 teaches a converter unit for converting two or more DC voltage levels from the input of the converter unit to a DC voltage on the output of the converter unit, wherein the converter unit comprises controllable switch means that are able to connect and disconnect the individual DC input voltage level for forming an oscillating signal, and wherein the converter unit comprises filtering means for low pass filtering of the oscillating, signal for forming the DC voltage on the output of the converter unit. 
   The converter unit discussed in WO 0033451, however, presents an inconvenience because it cannot connect to an AC supply source. Additionally, the converter unit is not capable of performing a gradual switch of supply source without supply loss, see the below description of a method. Nor is the converter unit capable of performing an adaptive switch in case of overload situations. 
   U.S. Pat. No. 5,751,564 discloses a switching power supply system which is able to connect two or more different power sources with different voltage levels, and can provide power even when the primary power source is low or completely absent. The output voltage is more constant than a conventional switching power supply, and the internal loss is also smaller. As a result, the back-up supply time is longer than that of a conventional UPS system. Finally, when used in a notebook computer, for example, there is no need to use an AC to DC adapter when connecting to an AC power supply, it being possible to connect the switching power supply directly to the AC power supply. 
   The (&#39;564) system, however, is not capable of performing an uninterrupted switching between an AC supply source and a DC supply source. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to provide a converter that can obtain supply from one or more supply sources such as an AC source with one or more phases in combination with one or more DC sources, wherein switching from a first supply source to a second supply source is accomplished gradually without supply failure; and wherein—in overload situations—it is possible to rely on one or more supply sources. 
   This can be accomplished in that the switching between supply sources is accomplished by connecting and disconnecting the supply sources to/from said converter based on phase information of the AC signal, whereby the supply signal fed to said coil is divided into periods, wherein the periods of the supply signal alternatingly originate from either positive or negative half-periods of the AC signal and current pulses from said DC supply; and wherein the current pulses from the DC supply are regulated in dependence of the AC signal; and wherein the converter contains means for voltage regulating said at least one DC output. 
   A flexible converter is achieved that can obtain supply from an AC supply source and one or more DC supply sources; and wherein switching from a first supply source to a second supply source can be accomplished without supply loss; and wherein—in overload situations—two or more supply sources can be relied on. In a typical overload situation with an AC source in the form of a current network from a diesel generator and a DC source in the form of a battery, the advantage of this converter is that the current from the AC source can be maintained on a constant highest value in that supplementary energy is supplied from the DC source. It is possible to use smaller cables and fuses in the AC source without such fuses being blown upon overload. 
   The term ‘supply source’ is used herein to designate either an AC source with one or more phases connected via a common point of reference, or a DC source or two DC sources that are connected in series via a common point of reference, whereby a positive and a negative supply voltage are obtained. 
   The converter is characterized in that the AC supply source is a single-phase AC source and that at least one DC source is provided. A converter for single-phase systems is obtained that protects against supply failures in case of abrupt switching between the single-phase AC supply source and one, optionally more, DC sources. 
   The converter is characterized in that the AC supply source is a polyphase AC source and that at least one DC source is provided. A converter for polyphase systems is obtained that protects against supply failures in case of abrupt switching between the polyphase AC supply source and one, optionally more, DC sources. 
   The converter is characterized in that, on the basis of a signal from a current detector that measures the current through a coil, a control circuit has means for connecting and disconnecting, respectively, the one terminal of the coil to/from a DC supply source; and means to connect and disconnect, respectively, the second terminal of the coil to/from a common point of reference. The current through the coil flows to the DC output of the converter during periods when the second terminal of the coil is not connected to the common point of reference. The converter is provided with means for connecting and disconnecting, respectively, an AC supply source to the one terminal of the coil, ie that terminal on the coil that can also be connected to the DC source. A converter is obtained that has the smallest possible number of components and that is simultaneously capable of performing a gradual switch between supply sources; wherein the one supply source is an AC supply source; and the second supply source is a DC supply source. The converter protects against supply failures during abrupt switches between supply sources. 
   The converter is characterized in that at least one converter is used to form a DC output that is positive relative to a common point of reference; and at least one converter is used to form a DC output that is negative relative to a common point of reference. A converter is obtained that is able to deliver a positive, optionally more positive, DC output voltages, and one negative, optionally more negative DC output voltages that are protected against supply failures during abrupt switches between supply sources. 
   The converter is characterized in that the AC supply source is shared for the converters that are used to form a positive output voltage and the converters that are used to form a negative output voltage relative to a common point of reference. A converter is obtained that makes requirements to the smallest possible number of AC supply sources. This is a major advantage in that, thus, the converter can also be used where the availability of AC supply sources is scarce. 
   The converter is characterized in that the means for connecting and disconnecting, respectively, the one terminal of the coil to/from a DC supply source is a controllable switch. The controllable switch can be regulated to be connected for-at least a part of every other half-period. It is possible to regulate the period of time when supply is obtained from the DC supply source. This is associated with the advantage that it enables parallel coupling of a number of converters to the same battery. Each converter is then allocated a period of time that is different from that of the other converters, during which the converters obtain energy exclusively from the DC supply source. The option of parallel coupling converters to the same DC supply source also means that supply can be obtained by using as few DC sources as possible. 
   The converter is characterized in that the means for connecting and disconnecting, respectively, the second terminal of the coil to/from a common point of reference is a controllable switch. The controllable switch can be regulated to be connected for at least a part of every other half-period, and the controllable switch is typically connected in burst series. It is possible to regulate the voltage through the coil. On the one hand it makes it possible to perform a gradual switching in consumption of energy from the DC source, and on the other hand it makes it possible to adjust the nominal output voltage on the converter within a field. The option of adjusting the nominal output voltage of the converter within a field means that the same converter design can be used where there is a requirement for several different output voltages. Thereby the number of different converters can be reduced. 
   The converter is characterized in that semi-conducters are used as controllable switches comprising at least one of the types of field effect transistor, bipolar transistor, insulated Gate Bipolar Transistor (IGBT), Gate Turn-Off Tyristor (GTO) and Injection Enhanced Gate Transistor (IEGT). It is possible to select semi-conductor technology while taking into consideration requirements to supply, construction and space.
 
The converter is characterized in that—in an overload situation—the current from the AC supply source is limited to a constant largest value, in that supplementary energy is supplied from the DC supply source.
 
A gentle load of the AC support source is obtained, wherein the converter does not expose the AC supply source to overload.
 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention will now be described in further detail with reference to the accompanying figures, wherein 
       FIG. 1  shows a single-phase combined AC-DC to DC converter with positive as well as negative output voltage; and 
       FIG. 2  shows curves of a ramp-in course for a single-phase combined AC-DC to DC converter with positive as well as negative output voltage; and 
       FIG. 3  shows a single-phase combined AC-DC to DC converter with positive output voltage; and 
       FIG. 4  shows curves of a ramp-in course for a three-phase combined AC-DC to DC converter with positive as well as negative output voltage; and 
       FIG. 5  shows curves of an overload course for a single-phase combined AC-DC to DC converter with positive as well as negative output voltage; and 
       FIG. 6  shows curves of an overload course for a three-phase combined AC-DC to DC converter with positive as well as negative output voltage; and 
       FIG. 7  shows a three-phase combined AC-DC to DC converter with positive as well as negative output voltage constructed from three converters with shared DC supply; and 
       FIG. 8  shows a three-phase combined AC-DC to Dc converter with positive output voltage constructed from three converters with shared DC supply. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage. The positive terminal on a battery  101  is connected to the anode on a tyristor  106 . The negative terminal on the battery  101  is connected to a common point of reference  104 . The cathode on the tyristor  106  is connected to the cathode on a diode  119 . The gate on the tyristor  106  is connected to an output on a control circuit  108 . The cathode on the tyristor  106  is connected to a coil  112 . A current sensor  114  encloses the connection between the tyristor  106  and the coil  112 . The current sensor  114  is connected to an input on the control circuit  108 . The coil  112  is further connected to collector on a transistor  110 . Collector on the transistor  110  is connected to the anode on a diode  121 . Emitter on the transistor  110  is connected to the common point of reference  104 . An output on the control circuit  108  is connected to the base of the transistor  110 . The cathode on the diode  121  is connected to a capacitor  123  and to a DC output  125 . The capacitor  123  is further connected to the common point of reference  104 . The DC output  125  is connected to the control circuit  108 . The negative terminal on a battery  102  is connected to the cathode on a tyristor  107 . The positive terminal on the battery  102  is connected to the common point of reference  104 . The anode on the tyristor  107  is connected to the anode on a diode  120 . The gate on the tyristor  107  is connected to an output on a control circuit  109 . The anode on the tyristor  107  is connected to a coil  113 . A current sensor  115  encloses the connection between the tyristor  107  and the coil  113 . The current sensor  115  is connected to an input on the control circuit  109 . The coil  113  is further connected to emitter on a transistor  111 . Emitter on the transistor  111  is connected to the cathode on a diode  122 . Collector on the transistor  111  is connected to the common point of reference  104 . An output on the control circuit  109  is connected to the base of the transistor  111 . The anode on the diode  122  is connected to a capacitor  124  and to a DC output  126 . The capacitor is further connected to the common point of reference  104 . The DC output  126  is connected to the control circuit  109 . The anode on the diode  119  is connected to a node  118 . The cathode on the diode  120  is connected to the node  118 . The node  118  is connected to a switch  127 . The switch  127  is further connected to a single-phase AC source  103  and to the input of a synchronizing circuit  105 . The single-phase AC source  103  is further connected to the common point of reference  104 . The first output of the synchronizing circuit  105  is connected to an input on the control circuit  108 , and the second output of the synchronizing circuit  105  is connected to an input on the control circuit  109 , and the third output of the synchronizing circuit  105  is connected to a control input on the switch  127 . 
   It is the task of the synchronizing circuit  105  to register when the AC source  103  is present with a valid voltage with a view to connecting the AC source  102  to the converter  100  via the switch  127 . Besides, the synchronizing circuit  105  serves the purpose of synchronizing to the AC supply by generating synchronous control signals to the control circuits  108 ,  109  with a known phase relative to the AC supply. In the positive half-period of the single-phase AC source  103 , the current flows from the single-phase AC-source  103  through the contact  127 , further through the diode  119 , and further through the coil  112 . If the transistor  110  is interrupted, the current flows from the coil  112  further through the diode  121  to the DC output  125 , and if the transistor  110  is connected, the current flows from the coil  112  to the common point of reference  104 . The tyristor  106  is disconnected for this period. In the negative half-period of the single-phase AC source  103 , the control circuit  108  switches on the tyristor  106 , whereby the current from the battery  101  flows through the tyristor  106  and further through the coil  112 . If the transistor  110  is interrupted, the current flows from the coil  112  to the DC output  125 , and if the transistor  110  is connected, the current flows from the coil  112  to the common point of reference  104 . The control circuit  108  controls the transistor  110  with pulses of varying duty-cycle, and at a frequency that is usually considerably more elevated than the frequency of the single-phase AC source  103 . The auxiliary circuit consisting of the coil  112 , the transistor  110  and the diode  121  constitutes a boost converter. During periods when the transistor  110  is connected the current increases in the coil  112 . During periods when the transistor is disconnected, the current flows on through the diode  121  to the DC output  125  and will simultaneously start to decrease, the voltage above the coil  112  now having opposite polarity sign. Regulation of the duty-cycle for the transistor  110  enables regulation of the current in the coil  112  and thus also the voltage on the DC output  125 . The valid duty cycle for the transistor  110  is determined by the control circuit  108  on the basis of the output voltage that is measured via a return coupling from the DC output  125 . The capacitor  123  smoothens the voltage on the DC output  125  to a DC voltage. In the negative half-period of the single-phase AC source  103 , the current flows to the single-phase AC-source  103  from the switch  127 , further from the diode  120 , and further from the coil  113 . If the transistor  111  is disconnected, the current flows to the coil  113  further from the diode  122  from the DC output  126 , and in case the transistor  111  is connected, the current flows to the coil  113  from the common point of reference  104 . The tyristor  107  is, for this period of time, disconnected. In the positive half-period of the single-phase AC source  103 , the control circuit  109  switches on the tyristor  107 , whereby the current to the battery  102  is caused to flow from the tyristor  107  and on from the coil  113 . If the transistor  111  is disconnected, the current flows to the coil  113 , from the diode  122 , from the DC output, and if the transistor  111  is connected, the current flows to the coil  113  from the common point of reference  104 . The control circuit  109  controls the transistor  111  with pulses of varying duty-cycle and at a frequency that is usually considerably more elevated than the frequency of the single-phase AC source  103 . The auxiliary circuit consisting of the coil  113 , the transistor  111 , and the diode  122  constitutes a boost converter. During periods when the transistor  111  is connected, the current increases in the coil  113 . In periods when the transistor  111  is disconnected, the current flows on from the diode  122  from the DC output  126  and will simultaneously start to decrease, the voltage above the coil  113  now having opposite polarity sign. Regulation of the duty cycle for the transistor  111  enables regulation of the current in the coil  113  and thus the voltage on the DC output  126 , too. The valid duty-cycle for the transistor  111  is determined by the control circuit  109  on the basis of the out-put voltage that is measured via a return coupling from the DC output  126 . 
   The capacitor  124  smooths the voltage on the DC output  126  to a DC voltage. The regulation consists of two independent regulation systems, one for the positive output voltage in the control circuit  108  and another for the negative output voltage in the control circuit  109 . Each of these regulation systems has the object of maintaining a constant output voltage and simultaneously absorbing a current with a predetermined well-defined curve shape, whether the current comes from the AC source or the DC source. This is accomplished in practice by using for each of the two control circuits  108  and  109  two regulator loops, one that maintains the curve-shape on the current, and another whose task it is to maintain the constant output voltage. The regulator loop that determines the current curve shape will usually be the fastest of the two regulator loops. It emits on the output a pulse-width modulated signal to one of the two transistors  110  or  111 . Each time the transistor  110 ,  111  is switched on, the current in the coil  112 ,  113  will increase. 
   Each time it is switched off, the current will decrease, the voltage above the coil  112 ,  113  having in that case the opposite polarity sign. In practice this current control can be performed in accordance with various principles that either keep a constant or variable frequency, or control in accordance with the instantaneous or average value of the current, averaged over several pulses. These various principles must be considered to be prior art and all are able to control the current in the coil  112 ,  113  of a converter  100  to follow optimally the amplitude and the curve-shape on a supplied signal. This is accomplished by comparing the measured value of the current to a signal that corresponds to the desired voltage and continuously adapting the pulse/break-ratio: The current in the coil  112 ,  113  will all the time either increase or decrease, but is regulated continuously with the pulse/break-ratio, such that—averaged over several pulses—it corresponds to the desired curve-shape. The term ‘pulses’ as used in this context is intended to designate control pulses for the transistor  110 ,  111  that will normally be an elevated frequency compared to the current network frequency. This regulator loop receives a signal with a curve-shape and amplitude that corresponds to the current that it is desired that the relevant converter  100  shall draw at a given time. This curve-shape is subsequently referred to as the current reference. The curve-shape of this of the current reference depends on the operating mode of the converter  100 . When it is desired to draw current from the AC source  103  only, the curve-shaped will be positive and negative half-periods, respectively, of a sinusoidal signal, such that the total amount of current that is drawn from the net will become sinusoidal. This is the curve-shape that is seen as curve  231  in  FIG. 1  during the time  236 . When it is desired to draw current from the battery  101 ,  102  only, the reference to both halves of the converter  100  will exclusively be DC signals, since—in that case—it is desired to draw a constant DC current from the battery  101 ,  102 . When it is desired to draw current from both sources, the current reference will have an appearance that corresponds to the curve  231  in  FIG. 2  during the time  235 . This curve-shape consists partly of sinusoidal half-waves and partly of rectangular or trapezoidal pulses. The current reference described can either be generated as a voltage or current curve-shape of an electronic circuit, or it can be a digitally computed curve-shape, generated by, e.g., a microprocessor or a Digital Signal Processor (DSP). In order to know in which of the described operation forms, the run is performed, a detector circuit  105  is present that decides whether the AC source  103  is present and has an acceptable voltage quality. When this has been complied with, AC operation is selected. If the AC source  103  disappears or is in any other way detected to be unacceptable as to either voltage or frequency, switching is performed to battery-operation. When the AC voltage is again present and acceptable, a ramp-in course is made, line in  FIG. 2 . The detector circuit  105  can be shared by both converters. In order to generate the desired curve shapes, a synchronization unit  105  is also used. It also receives the AC signal and synchronizes to this AC signal. It is thereby able to emit phase information to the two control/regulator units  109  and  109  that tells where in time one is relative to the zero transit on the AC signal, e.g., as a degree figure between zero and 360 degrees. Such phase information is subsequently used to determine the course in time of the described curve-shapes. In addition to said signals concerning operating mode and synchronization, it must also be possible to continuously adapt the amplitude on the described current references. By changing the amplitude on the signals, the amount of current to be drawn from the AC source  103  or the DC source  101 ,  102  is changed, and thus how much power is supplied to the converter  100 . This power supply must continuously be adapted to exactly cover the need for power that is drawn from the converter  100  output(s) plus what can be ascribed to loss. In case more power is supplied than needed, it would mean that the voltage on the capacitors  123  or  124  will continue to increase, and correspondingly the voltages will decrease if too little power is supplied. In order to thereby maintain the correct output voltage there is therefore in each of the control/regulator circuits  108  and  109  a regulator loop that measures the voltages on  125  and  126  and compares them to suitable reference values. In case the output voltage deviates from the desired, the amplitudes on the described current reference signals are regulated upwards or downwards. Only one specific maximum value for the current drawn from the AC source  103  is allowed at all times. During a ramp-in course, this maximum value is increased linearly from zero to a predetermined maximum value within a predetermined period, e.g., 10 seconds. If it is desired to supply more current or power than allowed by this maximum value, there is formed, on the one hand, half-wave shaped sinusoidal signals with the maximally allowed value, whereas the remainder of the power need is covered by current pulses from the battery. The distribution between the two pulses is calculated continuously, such that they combine to cover the need for supplied power. Correspondingly, this limitation of AC current pulses is used to delimit the current from a current network or diesel generator during overload. Also in this case it is calculated how much supplement is needed from the battery to deliver the requisite total amount of power. if the node  118  is split and if the AC source  103  and the switch  127  are connected instead to the alternating current inputs of a rectifier bridge, where the positive output of the rectifier bridge is connected to the anode on the diode  119 , and the negative output of the rectifier bridge is connected to the cathode on the diode  120 , it is also possible to obtain supply from the AC source  103  in both half-periods to both the positive half and the negative half of the converter  100 . Hereby the power consumption from the batteries  101 ;  102  can be reduced. 
     FIG. 2  shows curves of a ramp-in course for a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage. A first curve  231  shows the current through the coil  112 . A second curve  232  shows the current through the coil  113 . A third curve  233  shows the total current of the single-phase AC source  103 . To the first curve  231 , and the second curve  232  and the third curve  233  it applies that a first period of time  234  shows supply exclusively from the batteries  101 ,  102  and a second period of time  235  shows a ramp-in course with supply from the batteries  101 ,  102  and the single-phase AC source  103 , where the current from the batteries  101 ,  102  is reduced in pace with the current from the single-phase AC current  103  being increased, and further a third period of time  236  that shows supply exclusively from the single-phase AC source  103 . 
   During the period of time  234 , the batteries  101 ,  102  supply alone the combined AC-DC to DC converter  100 . During the period  235  a ramp-in course takes place, where supply is accomplished from the batteries  101 ,  102  as well as from the single-phase AC source  103 . The strength of the pulse current from the batteries  101 ,  102  is reduced in pace with the pulse current from the single-phase AC source  103  being increased. During the period of time  236  the single-phase AC source  103  delivers exclusively to the combined AC-DC to DC converter  100 . 
     FIG. 3  shows a single-phase combined AC-DC to DC converter  300  with positive output voltage. The positive terminal on a battery  301  is connected to the anode on a tyristor  306 . The negative terminal on the battery  301  is connected to the anode on a tyristor  306 . The negative terminal on the battery  301  is connected to a common point of reference  304 . The cathode on the tyristor  306  is connected to the cathode on a diode  319 . The gate on the tyristor  306  is connected to an output on a control circuit  308 . The cathode on the tyristor  306  is connected to a coil  312 . A current sensor  314  encloses the connection between the tyristor  306  and the coil  312 . The current sensor  314  is connected to an input on the control circuit  308 . The coil  312  is further connected to a collector on a transistor  310 . Collector on the transistor  310  is connected to the anode on a diode  321 . Emitter on the transistor  310  is connected to the common point of reference  304 . An output on the control circuit  308  is connected to the base of the transistor  310 . The cathode on the diode  321  is connected to a capacitor  323  and to a DC output  325 . The capacitor  323  is further connected to the common reference point  304 . The DC output  325  is connected to the control circuit  308 . The anode on the diode  319  is further connected to switch  327 . The switch  327  is further connected to a single-phase AC source  303  and to the input of a synchronization circuit  305 . The single-phase AC source  303  is further connected to the common reference point  304 . The one output of the synchronization circuit  305  is connected to an input on the control circuit  308 , and the second output of the synchronization circuit  305  is connected to a control input on the switch  327 . 
   The indication of functionality for a single-phase combined AC-DC to DC converter  300  with positive output voltage, in accordance with  FIG. 3 , follows the indication of functionality for the positive half of a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, in accordance with  FIG. 1 . Like the single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, the AC source  303  and the switch  327  can instead be coupled to the alternating-current inputs of a rectifier bridge, where the positive output of the rectifier bridge is connected to the anode on the diode  319 , and the negative output of the rectifier bridge is connected to the reference point  304 . Hereby it is possible to obtain supply from the AC source  303  in both half-periods to the converter  300 . Hereby the power consumption from the battery  301  can be reduced. 
     FIG. 4  shows curves of a ramp-in course for a three-phase combined AC-DC to DC converter  700 ,  740 ,  780  with positive as well as negative output voltage. A first curve  431  shows the current through the coil in the positive half of the converter for a phase (phase  1 ). A second curve  432  shows the current through the coil in the negative half of the converter for the same phase (phase  1 ). A third curve  433  shows the total amount of current of the AC source  703  for the same phase (phase  1 ). A fourth curve  437  shows the total amount of current from the battery  701  to the positive half of the converter for all three phases (phase  1 , phase  2  and phase  3 ). A fifth curve  438  shows the total amount of current to the battery  702  from the negative half of the converter for all three phases (phase  1 , phase  2  and phase  3 ). To the first curve  431 , and the second curve  432 , and the third curve  433 , and the fourth curve  437 , as well as the fifth curve  438  it applies that a first period of time  434  shows supply exclusively from the batteries  701 ,  102 , and a second period of time  435  shows a ramp-in course with supply from the batteries  701 ,  702  and the AC source  703 , where the current from the batteries  701 ,  702  is reduced in pace with the current from the AC source  703  being increased, and also a third period of time  436  that shows supply exclusively from the AC source  703 . 
   The indication of functionality for the ramp-in course for a three-phase combined AC-DC to DC converter  700 ,  740 ,  780  with positive as well as negative output voltage, in accordance with  FIG. 4 , follows the indication of functionality for the ramp-in course for a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, in accordance with  FIG. 2 . It is noted that the batteries  701 ,  702  are shared (and identical) for converters  700 ,  740 ,  780  for all three phases (phase  1 , phase  2  and phase  3 ). Batteries  701 ,  702  deliver to three otherwise independent circuits  700 ,  740 ,  780  that each corresponds to a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, in accordance with  FIG. 1 . This means that the battery  701  is connected to three tyristors in each their circuit  700 ,  740 ,  780 , and the battery  702  is connected to three tyristors in each of the same three circuits. The three circuits  700 ,  740 ,  780  use each their phase, where the common point of reference  704  is shared for the three phases. 
     FIG. 5  shows curves of an overload course for a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage. A first curve  539  shows the current load in percentages relative to an allowable upper current threshold. A second curve  531  shows the current through the coil  112 . A third curve  532  shows the current through the coil  113 . A fourth curve  533  shows the total amount of current of the single-phase AC source  103 . To the first curve  539 , and the second curve  531 , and the third curve  532 , and the fourth curve  533  it applies that a first and third period of time  536  show normal operation with supply exclusively from the single-phase AC source  103 , and a second period of time  540  shows an overload course with supply from both the batteries  101 ,  102  and the single-phase AC source  103 , where the current from the batteries  101 ,  102  are of such magnitude that the current from the single-phase AC source  103  is kept constant and also within certain allowable current thresholds. 
   During the two periods  536  normal operations take place, where the single-phase AC source  103  alone delivers to the combined AC-DC to DC converter  100 . During the period of time  540  an overload course occurs, where supply takes place from both the batteries  101 ,  102  and the single-phase AC source  103 . The pulse current from the batteries  101 ,  102  is adjusted to such magnitude that compensation is fully made for the overload, whereby the current from the single-phase AC source  103  is kept constant and within certain allowable thresholds. 
     FIG. 6  shows curves of an overload course for a three-phase combined AC-DC to DC converter  700 ,  740 ,  780  with positive as well as negative output voltage. A first curve  639  shows the current load as percentages on all three phases relative to an allowable upper current threshold. A second curve  631  shows the current through the coil in the positive half of the converter for a phase (phase  1 ). A third curve  632  shows the current through the coil in the negative half of the converter for same phase (phase  1 ). A fourth curve  633  shows the total amount of current of the AC source  703  for the same phase (phase  1 ). A fifth curve  637  shows the total amount of current from the battery  701  to the positive half of the converter to all three phases (phase  1 , phase  2  and phase  3 ). A sixth curve  638  shows the total amount of current to the battery  702  from the negative half of the converter from all three phases (phase  1 , phase  2  and phase  3 ). To the first curve  639 , and the second curve  631 , and the third curve  632 , and the fourth curve  633  it applies that a first and third period of time  636  show normal operation with supply exclusively from the AC source  703 , and a second period of time  640  that shows an overload course with supply from both the batteries  701 ,  702  and the AC source  703 , where the current from the batteries  701 ,  702  is of such magnitude that the current from the AC source  703  is kept constant and further within given allowable current thresholds. 
   The indication of functionality for the overload course for a three-phase combined AC-DC to DC converter  700 ,  740 ,  780  with positive as well as negative output power, in accordance with  FIG. 6 , follows the indication of functionality for the overload course for a single-phase combined AC-DC to DC converter  100  with positive as well as negative output load, in accordance with  FIG. 5 . It is noted that the batteries  701 ,  702  are shared (and identical) for converters  700 ,  740 ,  780  for all three phases (phase  1 , phase  2  and phase  3 ). Batteries  701 ,  702  deliver to three otherwise independent circuits  700 ,  740 ,  780 , that each corresponds to a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, in accordance with  FIG. 1 . This means that the battery  701  is connected to three tyristors in each their circuit  700 ,  740 ,  780  and the battery  702  is connected to three tyristors in each of the same three circuits. The three circuits  700 ,  740 ,  7809  use each their phase, wherein the common point of reference  704  is shared for the three phases. 
     FIG. 7  shows a three-phase combined AC-DC to DC converter with positive as well as negative output voltage constructed by means of three converters  700 ,  740 ,  80  with shared DC supply  701 ,  702 . The positive terminal on a battery  701  is connected to the anode on a tyristor in each of the three converters  700 ,  740 ,  780  corresponding to the tyristor  106  in  FIG. 1 . The negative terminal on the battery  701  is connected to a common point of reference  704 . The negative terminal on a battery  702  is connected to the cathode on a tyristor in each of the three converters  700 ,  740 ,  780 , corresponding to the tyristor  107  in  FIG. 1 . The positive terminal on the battery  702  is connected to the common point of reference  704 . A switch in each of the three converters  700 ,  740 ,  780 , corresponding to the switch  127  in  FIG. 1 , is connected to each their phase on an AC source  703 . The AC source  703  is further connected to a common point of reference  704 . The positive outputs of the three converters  700 ,  740 ,  780  are all connected to an output  725 . The negative outputs of the three converters  700 ,  740 ,  780  are all connected to an output  726 . The references of the three converters  700 ,  740 ,  780  are all connected to the point of reference  704 . 
   The indication of functionality for a three-phase combined AC-DC to DC converter with positive as well as negative output voltage constructed from three converters  700 ,  740 ,  780  with shared DC supply  701 ,  702 , in accordance with  FIG. 7 , follows the indication of functionality for a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, in accordance with  FIG. 1 . 
     FIG. 8  shows a three-phase combined AC-DC to DC converter with positive output voltage constructed from three converters  800 ,  840 ,  880  with shared DC supply  801 . The positive terminal on a battery  801  is connected to the anode on a tyristor in each of the three converters  800 ,  840 ,  880 , corresponding to the tyristor  306  in  FIG. 3 . The negative terminal on the battery  801  is connected to a common point of reference  804 . A switch in each of the tree converters  800 ,  840 ,  880 , corresponding to the switch  327  in  FIG. 3 , is connected to each their phase on an AC source  803 . The AC source  803  is further connected to a common point of reference  804 . The negative outputs of the three converters  800 ,  840 ,  880  are all connected to an output  825 . The references of the three converters  800 ,  840 ,  880  are all connected to the point of reference  804 . 
   The indication of functionality for a three-phase combined AC-DC to DC converter with positive as well as negative output voltage constructed from three converters  800 ,  840 ,  880  with common DC supply  801 , in accordance with  FIG. 8 , follows the indication of functionality for the positive half of a single-phase combined AC-DC to DC converter  100  with positive as well as negative output voltage, in accordance with  FIG. 1 . 
   The converter ( 100 ,  300 ,  700 ,  740 ,  780 ,  800 ,  840 ,  880 ) can be characterized, e.g., in that—at a given load, typically full load—on at least one DC output ( 125 ,  126 ,  325 ,  725 ,  726 ,  825 ) switches occur adaptively from a DC supply source ( 101 ,  102 ,  301 ,  701 ,  702 ,  801 ) to an AC supply source ( 103 ,  303 ,  703 ,  803 ), typically a diesel generator, while taking into consideration stability of frequency and voltage on the AC supply source ( 103 ,  303 ,  703 ,  803 ). By such adaptive switch of source, gradual switching from the DC supply source to the AC supply source will occur, where supply from both supply sources takes place during the switching time. The adaptive switch of source optionally comprises that there are several, consecutive periods with supply from both supply sources. Finally, the adaptive switching of source means that it is possible to switch completely or partially back to the DC supply source. Hereby a gentler coupling onto the AC supply source is obtained, where the converter does not expose the AC supply source to abrupt and forceful loading couplings. Hereby the AC source is protected against overload with ensuing fluctuation of, e.g., frequency and voltage. If the AC source is, e.g., a diesel generator, it is important to avoid abrupt and forceful loading couplings, since they translate onto the rotor current, whereby the diesel generator becomes instable with regard to both frequency and voltage. In a worst-case scenario, the instability may result in self-oscillation with ensuing supply failures. 
   The converter ( 100 ,  300 ,  700 ,  740 ,  780 ,  800 ,  840 ,  880 ) can be, e.g., characterized in that—upon supply from an AC supply source ( 103 ,  303 ,  703 ,  803 ), typically a diesel generator, dynamic load changes are compensated, where the current from at least one DC output ( 125 ,  126 ,  325 ,  725 ,  726 ,  825 ) is increased adaptively. The adaptive compensation of dynamic load changes occurs with due regard to stability of frequency and voltage on the AC supply source ( 103 ,  303 ,  703 ,  803 ) by obtaining supplementary energy from a DC supply source ( 101 ,  102 ;  301 ,  701 ,  702 ,  801 ). By such adaptive compensation of dynamic load changes, a supplementary supply from the DC supply source will occur, in that supply will—for a period of time—take place from both supply sources. Optionally there may be several consecutive periods with supply from both supply sources. Hereby a gentler load onto the AC supply source is obtained, where the converter does not expose the AC supply source to abrupt and forceful loading couplings. Hereby the AC source is protected against overload with ensuing fluctuation of, e.g., frequency and voltage. If the AC source is, e.g., a diesel generator, it is important to avoid abrupt and forceful loading couplings, since they translate onto the rotor current. 
   Hereby the diesel generator becomes instable with regard to both frequency and voltage, and in a worst-case scenario, the instability may result in self-oscillation with ensuing supply failures.