Patent Publication Number: US-2022224110-A1

Title: Asymmetric overvoltage protection apparatus, dc circuit arrangement and dc network

Description:
The invention relates to an asymmetric surge protection device, a DC circuit arrangement and a DC network. 
     Surge protection for power networks or loads is necessary to prevent damage to the loads or circuits in exceptional cases, such as lightning strikes. 
     For DC circuits and DC connections or electronic devices for DC networks, no effective surge protection exists, especially if the DC circuit or the device has no reverse polarity protection, such as a reverse polarity protection diode. 
     It is therefore the object of the invention to provide a surge protection device, a DC circuit arrangement, and a DC network in which damage due to overvoltages can be effectively prevented. 
     The object is achieved by an asymmetric surge protection device for a DC circuit having a current input and a current output, comprising a negative side which can be connected to the current output of the DC circuit, a positive side which can be connected to the current input of the DC circuit, and an asymmetric neutral section. The asymmetric neutral section has a positive protection level for a positive voltage between the positive side and the negative side, and a negative protection level for a negative voltage between the positive side and the negative side, the positive protection level being different from the negative protection level. 
     As the positive protection level and the negative protection level are different, the surge protection can be configured to be asymmetric. In this way, positive and negative overvoltages can be handled separately, as a result of which the asymmetry of the DC circuit or the electrical device and thus the asymmetric sensitivity to overvoltages are taken into account. 
     The negative protection level may be less than the negative freewheeling voltage of the DC circuit. 
     For example, the DC circuit has no reverse polarity protection. 
     The positive side is also called “DC plus” or “L+” for unipolar direct current. Correspondingly, the negative side is also called “DC minus” or “L-” for unipolar direct current. 
     For example, the neutral section includes a discharging component, and the surge protection device includes a drive for the neutral section, the drive being configured so as to release the discharging component accordingly when the voltage between the positive side and the negative side is positive and the magnitude of the voltage is above the positive protection level, or when the voltage is negative and the magnitude of the voltage is above the negative protection level. The drive makes it possible to flexibly adjust the protection levels. 
     The discharging component is in particular capable of withstanding pulse currents. 
     To realize a reliable surge protection device, the discharging component may comprise a spark gap, a gas discharge tube, a varistor, a thyristor, an IGBT and/or a MOSFET, and/or the drive may comprise at least one diode, an IGBT, a thyristor and/or a MOSFET. 
     In one embodiment, the neutral section has a positively discharging branch for reducing a positive voltage and a negatively discharging branch for reducing a negative voltage, in particular wherein the branches are parallel. In this way, the structure of the neutral section can be realized by means of simple components. 
     For an efficient discharge, the positively discharging branch has a first passive discharging component, in particular a varistor, a spark gap and/or a gas discharge tube. 
     The positively discharging branch may be completely passive. The discharging component is in particular capable of withstanding pulse currents. 
     For example, the breakdown voltage or threshold voltage of the positively discharging component is the positive protection level. 
     In one configuration, the negatively discharging branch includes a switchable component, and the surge protection device includes a drive for the switchable component, in particular wherein the switchable component is an IGBT (insulated-gate bipolar transistor), a thyristor, or a MOSFET (metal-oxide-semiconductor field-effect transistor). The drive is configured to switch the switchable component accordingly when the voltage between the positive side and the negative side is negative and the magnitude of the voltage is above the negative protection level. In this way, the negative protection level can be flexibly adjusted. 
     For example, the negatively discharging branch only includes the switchable component. However, it is also conceivable that the negatively discharging branch comprises a further component such as a spark gap, a gas discharge tube and/or a varistor. 
     In one configuration, the negatively discharging branch comprises at least one second passive discharging component, in particular wherein the negatively discharging branch is completely passive, as a result of which the surge protection device can be configured in a particularly simple way. The second passive discharging component is, for example, capable of withstanding pulse currents. 
     The forward voltage or the threshold voltage of the second passive discharging component for the negative voltage may be the negative protection level. In particular, the breakdown voltage for the positive voltage is greater than the positive protection level. 
     For example, the entire neutral section has no active or switching components. 
     To further simplify the surge protection device, the at least one second passive discharging component may be a diode, or the second passive discharging component may be a plurality of series-connected diodes. 
     In particular, the diode or diodes have their cathode connected to the positive side and their anode(s) connected to the negative side. 
     In a further embodiment of the invention, the neutral section has at least one unipolar transient-voltage suppression diode which has its cathode connected to the positive side and its anode connected to the negative side, in particular wherein the neutral section has a plurality of parallel-connected unipolar transient-voltage suppression diodes. In this way, the neutral section can be implemented with a single component or with few components. 
     For example, the forward voltage of the transient-voltage suppression diode(s) is the negative protection level, and the breakdown voltage is the positive protection level. 
     In one variant embodiment, the positive protection level is greater than 100 V, in particular greater than  400  V, and/or the negative protection level is less than 100 V, the DC circuit being thus reliably protected. 
     The voltage data refer to the magnitude of the voltage. 
     To protect high-power DC circuits, the DC circuit may be a converter, in particular an inverter or a DC voltage converter. 
     The object is further achieved by a DC circuit arrangement comprising a DC circuit, in particular a converter, such as an inverter or a DC voltage converter, and an asymmetric surge protection device as previously described. The DC circuit has a current input and a current output, and the positive side of the surge protection device is electrically connected to the current input, and the negative side of the surge protection device is electrically connected to the current output. 
     The features and advantages discussed as to the surge protection device apply equally to the DC circuit arrangement and vice versa. 
     In particular, the DC circuit has no reverse polarity protection. 
     To be able to reliably protect the DC circuit, the DC circuit arrangement may have a DC terminal, the surge protection device being arranged between the DC terminal and the DC circuit. 
     The object is further achieved by a DC network comprising a DC circuit arrangement as previously described and a DC source having a positive pole and a negative pole. The positive pole is electrically connected to the positive side of the surge protection device, and the negative pole is electrically connected to the negative side of the surge protection device. 
     The features and advantages discussed as to the surge protection device and the DC circuit arrangement apply equally to the DC network and vice versa. 
     For example, the DC network is a DC network in a building. 
     The surge protection device is for example arranged between the DC source and the DC circuit to reliably protect the DC circuit. 
    
    
     
       Further features and advantages of the invention will become apparent from the description below and from the accompanying drawings, to which reference is made and in which: 
         FIG. 1  shows a block diagram of a DC network according to the invention with a DC circuit arrangement according to the invention which comprises an asymmetric surge protection device according to the invention, 
         FIG. 2  shows a block diagram of a second embodiment of a surge protection device according to the invention, of a DC circuit arrangement according to the invention and of a network according to the invention, 
         FIG. 3  shows a block diagram of a third embodiment of a surge protection device according to the invention, of a DC circuit arrangement according to the invention and of a network according to the invention, 
         FIG. 4  shows a block diagram of a fourth embodiment of a surge protection device according to the invention, of a DC circuit arrangement according to the invention and of a network according to the invention, 
         FIGS. 5 a  to 5 c    show various embodiments of a surge protection device according to the invention as shown in  FIG. 4  in a block diagram, and 
         FIG. 6 a    shows a block diagram of a fifth embodiment of a surge protection device according to the invention, of a DC circuit arrangement according to the invention and of a network according to the invention, and 
         FIG. 6 b    shows a block diagram of a possible configuration of the surge protection device according to  FIG. 6 a   . 
     
    
    
       FIG. 1  shows a DC network  10  with a DC source  12  and a DC circuit arrangement  14  comprising a DC circuit  16  and an asymmetric surge protection device  18  according to the invention. 
     The DC network  10  is, for example, a DC network of a building, of a charging infrastructure for electric vehicles, or any other DC network. For example, the DC network  10  is unipolar. 
     The DC circuit  16  may be a converter  20 , or it may be any other DC circuit, such as a load. 
     The DC source  12  may be any DC source, which in the context of the present invention also includes connections to a higher-level network. Accordingly, the DC source  12  has a first pole  21 , in the described case of a unipolar DC source  12  the positive pole  22 , and a second pole  23 , in this case the negative pole  24 . For the sake of simplicity, reference will be made below only to a positive pole  22  and a negative pole  24 , although this of course also generally means the first pole  21  and the second pole  23 . 
     The DC circuit  16  is operated by means of the current of the DC source  12  and accordingly includes a current input  26  and a current output  28 . 
     In particular, the DC circuit  16  has no reverse polarity protection. 
     The surge protection device  18  has a positive side  30 , a negative side  32 , and a neutral section  34 . 
     Within the surge protection device  18 , the positive side  30  and the negative side  32  are connected to each other by means of the neutral section  34 . 
     The positive side  30  and the negative side  32  are each formed by a line electrically connecting the positive pole  22  of the DC source  12  to the current input  26  of the DC circuit  16 , and the current output  28  of the DC circuit  16  to the negative pole  24  of the DC source  12 , respectively. 
     Thus, the surge protection device  18  is arranged between the DC source  12  and the DC circuit  16 . 
     In other words, the DC circuit arrangement  14  has a DC terminal  36  connected to the DC source  12 . The surge protection device  18  is arranged between the DC terminal  36  and the DC circuit  16 . 
     It is also conceivable that the terminals of the positive side  30  or the negative side  32  facing the DC source  12  form the DC terminal  36  of the DC circuit arrangement  14 . 
     During regular operation of the DC network  10 , the DC source  12  provides a positive voltage. 
     As a result, the positive side  30  of the surge protection device  18  is at a higher potential than the negative side  32 , so that the voltage V between the positive side  30  and the negative side  32  is positive. In the context of the present invention, this is referred to as a positive voltage in this case. 
     In exceptional cases, the negative side  32  may be at a higher potential than the positive side  30 . This situation may occur, for example, in case of a lightning strike in the DC network  10 . In this case, the voltage V is negative, and this is referred to as a negative voltage in the context of the present invention. 
     The neutral section  34  is now configured to provide two different protection levels, namely a positive protection level V p  and a negative protection level V n . 
     “Different” in this case means different magnitudes. 
     The positive protection level V p  relates to positive voltages V, and the negative protection level V n  relates to negative voltages V. 
     This means that positive voltages V above the positive protection level V p  and negative voltages V the magnitude of which is greater than the negative protection level V n  are reduced through the neutral section  34 . 
     In other words, the positive protection level V p  and the negative protection level V n  define the operating range of the DC circuit  16  by: −V n &lt;V&lt;V p . 
     For example, the positive protection level V p  is greater than 100 V, for example 400 V, and the negative protection level V n  is less than 100 V, for example 80 V, resulting in a safe operating range of −80 V to 400 V. It is of course also conceivable that the positive protection level V p  is greater than 400 V and the negative protection level V n  is less than 80 V. 
     In this way, the DC circuit  16  is reliably protected from current pulses with both positive voltage and negative voltage, taking the different sensitivities of the DC circuit  16  to negative and positive voltage into account. 
       FIGS. 2 to 5  illustrate and describe further embodiments of the DC network  10 , the DC circuit arrangement  14  and the surge protection device  18 , respectively, which are substantially the same as the first embodiment according to  FIG. 1 . Therefore, only the differences will be discussed below, and identical and functionally identical parts are provided with the same reference signs. 
     In the embodiment according to  FIG. 2 , the DC circuit  16  is an inverter  38 . 
     In this embodiment, the neutral section  34  has a discharging component  40  and a drive  42  for the discharging component  40 . 
     The discharging component  40  is capable of withstanding current pulses, particularly with a symmetrical protection level for positive and negative voltages. For example, the discharging component  40  is a gas discharge tube, a spark gap, or a varistor. 
     Drives  42  for discharging components  40  are sufficiently known. 
     In the second example embodiment shown, the drive  42  includes a switching element  44 , a diode  45 , and a control unit  46  arranged to control the switching element  44 . 
     The discharging component  40  is directly connected to the positive side  30  and, by means of the switching element  44  and the diode  45 , to the negative side  32 . The diode  45  and the switching element  44  are arranged in parallel. 
     The diode  45  has its anode connected to the negative side  32  and its cathode connected to the discharging component  40 . 
     The switching element  44  is, for example, an IGBT (insulated-gate bipolar transistor), a thyristor and/or a MOSFET (metal-oxide-semiconductor field-effect transistor). 
     The control unit  46  is connected to the switching element  44 , for example to the gate electrode of the switching element  44 , for control, and to the positive side  30  and the negative side  32  for measuring the voltage V. 
     During operation, the control unit  46  measures the voltage V continuously or at regular intervals. If the voltage V measured by the control unit  46  is positive and its magnitude is above the positive protection level V p , the control unit  46  switches the switching element  44  to reduce the voltage V via the discharging component  40 . 
     The positive protection level V p  is thus stored in the control unit  46  as a threshold value and can be adapted to the DC circuit  16 . 
     The negative protection level V n  is provided by the forward voltage of the diode  45 . When the voltage V is negative and the magnitude of the voltage V is above the negative protection level V n , the diode  45  becomes conductive and releases the discharging component  40 . The negative voltage is then reduced through the diode  45  and the discharging component  40 . 
     It is of course possible that the switching element  44  and the diode  45  are arranged between the discharging component  40  and the positive side  30 , as shown in dashed lines in  FIG. 2 . 
     It is also conceivable that instead of the diode  45 , a further switching element  47  is used, which is switched by the control unit  46 . The further switching element  47  can be designed like the switching element  44  but be antiparallel. In this case, the control unit  46  switches the further switching element  47  to reduce the voltage V via the discharging component  40  when the voltage V measured by the control unit  46  is negative and its magnitude is above the negative protection level V n . Thus, both the positive and negative protection levels V p , V n  may be stored as threshold values in the control unit  46 . 
     In the third embodiment shown in  FIG. 3 , the DC circuit  16  is a DC voltage converter  48  which is shown schematically. 
     In the third example embodiment shown, the DC voltage converter  48  has a half-bridge circuit  50  having two substrate or freewheeling diodes  52  which define a freewheeling voltage V F  of the DC voltage converter  48  and of the DC circuit  16 , respectively. 
     Similarly, the DC circuits  16  have all of the example embodiments shown, or all of the DC circuits  16  have a freewheeling voltage V F . A negative voltage with a magnitude greater than the freewheeling voltage V F  will cause damage to the DC circuit  16 , especially at high voltages. 
     Therefore, the negative voltage level V n  is always selected to be smaller than the freewheeling voltage VF. 
     In the third embodiment according to  FIG. 3 , the neutral section  34  has a unipolar transient-voltage suppression diode  54  the cathode of which is connected to the positive side  30  and the anode of which is connected to the negative side  32 . 
     It is also conceivable that a plurality of unipolar transient-voltage suppression diodes  54  are connected in parallel, as indicated by the illustration in dashed lines in  FIG. 3 . 
     The forward voltage of the unipolar transient-voltage suppression diode  54  represents the negative protection level V n , and the breakdown voltage of the unipolar transient-voltage suppression diode  54  represents the positive protection level V p . Thus, in this third embodiment, the neutral section  34  is entirely passive as no switching or active components are required. In particular, the neutral section  34  includes only one or more unipolar transient-voltage suppression diodes  54 . 
     In the fourth embodiment shown in  FIG. 4 , the neutral section  34  has two parallel branches, namely a positively discharging branch  56  and a negatively discharging branch  58 . 
     The positively discharging branch  56  serves to discharge the voltage V if the voltage V is positive, and the negatively discharging branch  58  serves to discharge the voltage V if the voltage V is negative. 
     For example, in the fourth embodiment, the positively discharging branch  56  has only a first passive discharging component  60  which is capable of withstanding current pulses and has a high breakdown voltage which forms the positive protection level V p . The breakdown voltage of the first passive discharging component  60  or the positively discharging branch  56  may also be symmetrical. 
     The negatively discharging branch  58  is configured to be asymmetric. This means that the breakdown voltage of the negatively discharging branch  58  for positive voltages is above the breakdown voltage of the positively discharging branch  56 . However, the forward voltage for negative voltages of the negatively discharging branch  58  is significantly smaller and represents the protection level V n . 
     The forward voltage for negative voltages, and hence the negative protection level V n , is less than the freewheeling voltage V F  of the DC circuit  16  and is also less than the symmetrical breakdown voltage of the positively discharging branch  56 . 
       FIGS. 5 a , 5 b  and 5 c    show various configurations of the discharging branches  56 ,  58 , the combinations of configurations of the discharging branches  56 ,  58  being merely exemplary. 
     The discharging branches  56 ,  58  may of course be combined in any combination to form the neutral section  34 . 
     In the example embodiment shown in  FIG. 5 a   , the first passive discharging component  60  is a varistor  62 . 
     In this example embodiment, the negatively discharging branch  58  includes a switchable component  64 , and the surge protection device  18  includes a control unit  66  which forms a drive  65  for the switchable component  64 . 
     The switchable component  64  has a high breakdown voltage for positive voltages and is in particular capable of withstanding current pulses. In particular, the negatively discharging branch  58  includes only the switchable component  64 . 
     The switchable component  64  is, for example, an IGBT, a thyristor, or a MOSFET. 
     Similar to the drive  42 , the control unit  66  is connected to the positive side  30 , the negative side  32 , and also to the switchable component  64  for control. 
     The control unit  66  measures the voltage V continuously or at regular intervals, and as soon as the voltage V is negative and above the negative protection level V n  in terms of magnitude, the control unit  66  switches the switchable component  64  so that the voltage V is reduced via the negatively discharging branch  58 . 
     In the embodiment shown in  FIG. 5 b   , the first passive discharging component  60  is a gas discharge tube  63 . 
     In this embodiment, the negatively discharging branch  58  does not have a switchable component  64 , but is completely passive. Thus, the negatively discharging branch  58  has a second passive discharging component  68 . Thus, the entire neutral section  34  is passive. 
     The second passive discharging component  68  is also capable of withstanding pulse currents. 
     Here, the numeral word “second” is used to differentiate from the first passive discharging component  60 . The use does not imply that the negatively discharging branch  58  also includes a first passive discharging component. 
     In the example embodiment shown in  FIG. 5 b   , the second passive discharging component  68  is a diode  70  having its cathode connected to the positive side  30  and its anode connected to the negative side  32 . 
     In the example embodiment of  FIG. 5 c   , which is substantially the same as the example embodiment of  FIG. 5 b   , the first passive discharging component  60  is a spark gap  72 . 
     In this embodiment, the second passive discharging component  68  includes a plurality of series-connected diodes  74 . 
     Though three diodes  74  are shown in  FIG. 5 c   , any number of diodes  74  can of course be used to achieve the desired breakdown voltage and/or forward voltage. 
       FIGS. 6 a  and 6 b    show a fifth embodiment. In this fifth embodiment, the DC network  10  is not a unipolar DC network but a multipolar DC network, in this case a bipolar DC network. 
     Accordingly, the DC source  12  in this embodiment is also a multipolar DC source  12 , in this case a bipolar DC source. 
     Similarly, the other components of the DC network  10  are also configured to be multipolar, in particular the DC circuit arrangement  14 , the DC circuit  16  and the surge protection device  18 . 
     The mode of operation will be described below with reference to a bipolar DC network, but can of course be extended to DC networks having more than three poles. 
     In addition to the first pole  21  and the second pole  23 , the DC source  12  has a third pole  76 . For example, the first pole  21  is referred to as L+, the second pole is referred to as L−, and the third pole  76  is referred to as M. The third pole  76  may also be referred to as the common zero pole. 
     The regular operating voltage between the first pole  21  and the third pole  76  may be 400 V and may also be 400 V between the third pole  76  and the second pole  23  (see  FIG. 6 b   ). The first pole  21  and the second pole  23  then have a potential difference of 800 V. 
     Accordingly, the DC circuit  16  has three current inputs or current outputs  26 ,  27 ,  80 . 
     In this embodiment, the surge protection device  18  has two neutral sections  34  and three sides, namely a third side  78  in addition to the positive side  30  and the negative side  32 . 
     The first neutral section  34  is provided between the positive side  30  and the third side  78 , and the second neutral section  34  is provided between the negative side  32  and the third side  78 . 
     The neutral sections  34  of this fifth embodiment may be formed in accordance with the previous embodiments. 
     In the example shown in  FIG. 6 b   , the neutral sections  34  correspond to the neutral section of the embodiment of  FIG. 5 b   . However, all other embodiments are also conceivable. 
     Accordingly, the mode operation of the neutral sections  34  of the fifth embodiment is also the same as that of the neutral section  34  of the preceding embodiments. For the first neutral section  34 , the third side  78  corresponds to the negative side of the previous embodiments, and for the second neutral section  34 , the third side  78  corresponds to the positive side. 
     In this way, DC circuits  16  can be reliably protected even in multipolar DC networks  10 .