Abstract:
A high voltage direct current (HVDC) transmission system is provided. The high voltage direct current (HVDC) transmission system includes: a first power transceiving part consuming power generated by a power generation part, storing the generated power, and outputting the generated power or stored power to a second power transceiving part; a second power transceiving part consuming power generated by a power generation part, storing the generated power and outputting the generated power or stored power to the first power transceiving part; and a control part controlling the power transmission and reception of the first power transceiving part and the second power transceiving part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Patent Application No. 10-2014-0132200, filed on Oct. 1, 2014, the contents of which are hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to a high voltage direct current (HVDC) transmission system. 
         [0003]    The HVDC transmission system transmits away electricity through an HVDC. 
         [0004]    In general, the HVDC transmission system uses an aerial line or submarine cable to transmit electricity. 
         [0005]    The HVDC transmission system is being widely utilized due to advantages in that an investment cost is low, there is no limitation in cable length and loss in power transmission may be minimized. 
         [0006]    The HVDC transmission system employs a power transmission technique, according to which a transmission site converts alternating current (AC) power generated by a power station into DC power and then transmits the DC power and a reception site re-converts the DC power into the AC power to supply power, so there is a need to efficiently use and distribute generated power. 
       SUMMARY 
       [0007]    Embodiments provide a high voltage direct current (HVDC) transmission system that enables power generated by a power station to be efficiently used and stored at a transmission site and a reception site. 
         [0008]    In one embodiment, a high voltage direct current (HVDC) transmission system includes: a first power transceiving part consuming power generated by a power generation part, storing the generated power, and outputting the generated power or stored power to a second power transceiving part; a second power transceiving part consuming power generated by a power generation part, storing the generated power and outputting the generated power or stored power to the first power transceiving part; and a control part controlling the power transmission and reception of the first power transceiving part and the second power transceiving part. 
         [0009]    According to an embodiment, since generated power may be efficiently utilized at a transmission site and shared with a reception site, it is possible to increase the efficiency of usage. 
         [0010]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram for explaining the configuration of a high voltage direct current (HVDC) transmission system according to an embodiment. 
           [0012]      FIG. 2  is a diagram for explaining the configuration of a mono-polar HVDC transmission system according to an embodiment. 
           [0013]      FIG. 3  is a diagram for explaining the configuration of a bipolar HVDC transmission system according to an embodiment. 
           [0014]      FIG. 4  is a diagram for explaining the connection of a transformer and a three-phase valve bridge according to an embodiment. 
           [0015]      FIG. 5  is a diagram for explaining the configuration of an HVDC transmission system according to an embodiment. 
           [0016]      FIG. 6  is a flowchart for explaining the operation of an HVDC transmission system according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0017]    Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. 
         [0018]    The terms or words used in the detailed description and claims should not be limitatively construed as typical meanings or meanings indicated in dictionaries but should be construed as meanings and concepts matching the technical spirit of the inventive concept based on the principle that the inventor may properly define the concepts of terms in order to describe his or her invention in the best mode. 
         [0019]    Thus, since embodiments described in the detailed description and configurations shown in the drawings are only examples and do not cover all the technical spirits of an embodiment, it should be understood that there may be various equivalents and variations that may replace them upon filing the present application. 
         [0020]      FIG. 1  shows a high voltage direct current (HVDC) transmission system according to an embodiment. 
         [0021]    As shown in  FIG. 1 , an HVDC transmission system  100  according to an embodiment includes a power generation part  101 , a transmission-side alternating current (AC) part  110 , a transmission-side transformation part  103 , a DC power transmission part  140 , a reception-side transformation part  105 , a reception-side AC part  170 , a reception part  180 , and a control part  190 . 
         [0022]    The transmission-side transformation part  103  includes a transmission-side transformer part  120 , and a transmission-side AC/DC converter part  130 . The reception-side transformation part  105  includes a reception-side AC/DC converter part  150 , and a reception-side transformer part  160 . 
         [0023]    The power generation part  101  generates three-phase AC power. The power generation part  101  may include a plurality of power stations. 
         [0024]    The transmission-side AC part  110  transmits the three-phase AC power generated by the power generation part  101  to a DC substation that includes the transmission-side transformer part  120  and the transmission-side AC/DC converter part  130 . 
         [0025]    The transmission-side transformer part  120  isolates the transmission-side AC part  110  from the transmission-side AC/DC converter part  130  and the DC power transmission part  140 . 
         [0026]    The transmission-side AC/DC converter part  130  converts, into AC power, three-phase AC power corresponding to the output of the transmission-side transformer part  120 . 
         [0027]    The DC power transmission part  140  transmits transmission-side DC power to a reception side. 
         [0028]    The reception-side DC/AC converter part  150  converts DC power transmitted by the DC power transmission part  140 , into three-phase AC power. 
         [0029]    The reception-side transformer part  160  isolates the reception-side AC part  170  from the reception-side DC/AC converter part  150  and the DC power transmission part  140 . 
         [0030]    The reception-side AC part  170  provides, to the reception part  180 , three-phase AC power corresponding to the output of the reception-side transformer part  160 . 
         [0031]    The control part  190  may control the turn-on and turn-off timings of a plurality of valves in the power generation part  101 , the transmission-side AC part  110 , the transmission-side transformation part  103 , the DC power transmission part  140 , the reception-side transformation part  105 , the reception-side AC part  170 , the reception part  180 , and the reception-side DC/AC converter part  150 . In this case, the valve may correspond to a thyristor or insulated gate bipolar transistor (IGBT). 
         [0032]      FIG. 2  shows a mono-polar HVDC transmission system according to an embodiment. 
         [0033]      FIG. 2  shows a system transmitting single-pole DC power. 
         [0034]    Although it is assumed in the following description that the single-pole is a positive pole, there is no need to be limited thereto. 
         [0035]    A transmission-side AC part  110  includes an AC power transmission line  111  and an AC filter  113 . 
         [0036]    The AC power transmission line  111  transmits three-phase AC power generated by a power generation part  101 , to a transmission-side transformation part  103 . 
         [0037]    The AC filter  113  removes other frequency components excluding frequency components used by the transformation part  103 , from the transmitted three-phase AC power. 
         [0038]    A transmission-side transformer part  120  includes one or more transformers  121  for the positive pole. For the positive pole, a transmission-side AC/DC converter part  130  includes an AC/positive-pole DC converter  131  generating positive-pole DC power, and the AC/positive-pole DC converter  131  includes one or more three-phase valve bridges  131   a  corresponding to one or more transformers  121 , respectively. 
         [0039]    When one three-phase valve bridge  131   a  is used, the AC/positive-pole DC converter  131  may use AC power to generate positive-pole DC power having six pulses. In this case, the primary and secondary coils of one transformer  121  may have a Y-Y connection or Y-Δ connection. 
         [0040]    When two three-phase valve bridges  131   a  are used, the AC/positive-pole DC converter  131  may use AC power to generate positive-pole DC power having twelve pulses. In this case, the primary and secondary coils of one of two transformers  121  may have a Y-Y connection, and the primary and secondary coils of the other of two transformers  121  may have a Y-Δ connection. 
         [0041]    When three three-phase valve bridges  131   a  are used, the AC/positive-pole DC converter  131  may use AC power to generate positive-pole DC power having 18 pulses. The more the number of pulses of the positive-pole DC power, the price of the filter may decrease. 
         [0042]    The DC power transmission part  140  includes a transmission-side positive-pole DC filter  141 , a positive-pole DC power transmission line  143 , and a reception-side positive-pole DC filter  145 . 
         [0043]    The transmission-side positive-pole DC filter  141  includes an inductor L 1  and a capacitor C 1  and filters positive-pole DC power output by the AC/positive-pole DC converter  131 . 
         [0044]    The positive-pole DC power transmission line  143  may have a DC line for transmission of positive-pole DC power, and earth may be used as a current feedback path. One or more switches may be disposed on the DC line. 
         [0045]    The reception-side positive-pole DC filter  145  includes an inductor L 2  and a capacitor C 2  and DC-filters positive-pole DC power transmitted through the positive-pole DC power transmission line  143 . 
         [0046]    The reception-side DC/AC converter part  150  includes a positive-pole DC/AC converter  151 , which includes one or more three-phase valve bridges  151   a.    
         [0047]    The reception-side transformer part  160  includes one or more transformers  161  corresponding respectively to one or more three-phase valve bridges  151   a  for the positive pole. 
         [0048]    When one three-phase valve bridge  151   a  is used, the positive-pole DC/AC converter  151  may use positive-pole DC power to generate AC power having six pulses. In this case, the primary and secondary coils of one transformer  161  may have a Y-Y connection or Y-Δ connection. 
         [0049]    When two three-phase valve bridges  151   a  are used, the positive-pole DC/AC converter  151  may use positive-pole DC power to generate AC power having 12 pulses. In this case, the primary and secondary coils of one of two transformers  161  may have a Y-Y connection, and the primary and secondary coils of the other of two transformers  161  may have a Y-Δ connection. 
         [0050]    When three three-phase valve bridges  151   a  are used, the positive-pole DC/AC converter  151  may use positive-pole DC power to generate AC power having 18 pulses. The more the number of pulses of the AC power, the price of the filter may decrease. 
         [0051]    A reception-side AC part  170  includes an AC filter  171  and an AC power transmission line  173 . 
         [0052]    The AC filter  171  removes other frequency components excluding the frequency component (e.g., about 60 Hz) used by the reception part  180 , from the AC power generated by the reception-side transformation part  105 . 
         [0053]    The AC power transmission line  173  transmits filtered AC power to the reception part  180 . 
         [0054]      FIG. 3  shows a bipolar HVDC transmission system according to an embodiment. 
         [0055]      FIG. 3  shows a system transmitting two-pole DC power. Although it is assumed in the following description that the two poles are a positive pole and a negative pole, there is no need to be limited thereto. 
         [0056]    A transmission-side AC part  110  includes an AC power transmission line  111  and an AC filter  113 . 
         [0057]    The AC power transmission line  111  transmits three-phase AC power generated by a power generation part  101 , to a transmission-side transformation part  103 . 
         [0058]    The AC filter  113  removes other frequency components excluding frequency components used by the transformation part  103 , from the transmitted three-phase AC power. 
         [0059]    The transmission-side transformer part  120  includes one or more transformers  121  for the positive pole and one or more transformers  122  for the negative pole. A transmission-side AC/DC converter part  130  includes an AC/positive-pole DC converter  131  generating positive-pole DC power and an AC/negative-pole DC converter  132  generating negative-pole DC power, the AC/positive-pole DC converter  131  includes one or more three-phase valve bridges  131   a  corresponding respectively to one or more transformers  121  for the positive-pole, and the AC/negative-pole DC converter  132  includes one or more three-phase valve bridges  132   a  corresponding respectively to one or more transformers  122  for the negative-pole. 
         [0060]    When one three-phase valve bridge  131   a  is used for the positive pole, the AC/positive-pole DC converter  131  may use AC power to generate positive-pole DC power having six pulses. In this case, the primary and secondary coils of one transformer  121  may have a Y-Y connection or Y-Δ connection. 
         [0061]    When two three-phase valve bridges  131   a  are used for the positive pole, the AC/positive-pole DC converter  131  may use AC power to generate positive-pole DC power having 12 pulses. In this case, the primary and secondary coils of one of two transformers  121  may have a Y-Y connection, and the primary and secondary coils of the other of two transformers  121  may have a Y-Δ connection. 
         [0062]    When three three-phase valve bridges  131   a  are used for the positive pole, the AC/positive-pole DC converter  131  may use AC power to generate positive-pole DC power having 18 pulses. The more the number of pulses of the positive-pole DC power, the price of the filter may decrease. 
         [0063]    When one three-phase valve bridge  132   a  is used for the negative pole, the AC/negative-pole DC converter  132  may generate negative-pole DC power having six pulses. In this case, the primary and secondary coils of one transformer  122  may have a Y-Y connection or Y-Δ connection. 
         [0064]    When two three-phase valve bridges  132   a  are used for the negative pole, the AC/negative-pole DC converter  132  may generate negative-pole DC power having 12 pulses. In this case, the primary and secondary coils of one of two transformers  122  may have a Y-Y connection, and the primary and secondary coils of the other of two transformers  122  may have a Y-Δ connection. 
         [0065]    When three three-phase valve bridges  132   a  are used for the negative pole, the AC/negative-pole DC converter  132  may generate negative-pole DC power having 18 pulses. The more the number of pulses of the negative-pole DC power, the price of the filter may decrease. 
         [0066]    The DC power transmission part  140  includes a transmission-side positive-pole DC filter  141 , a transmission-side negative-pole DC filter  142 , a positive-pole DC power transmission line  143 , a negative-pole DC power transmission line  144 , a reception-side positive-pole DC filter  145 , and a reception-side negative-pole DC filter  146 . 
         [0067]    The transmission-side positive-pole DC filter  141  includes an inductor L 1  and a capacitor C 1  and DC-filters positive-pole DC power output by the AC/positive-pole DC converter  131 . 
         [0068]    The transmission-side negative-pole DC filter  142  includes an inductor L 3  and a capacitor C 3  and DC-filters negative-pole DC power output by the AC/negative-pole DC converter  132 . 
         [0069]    The positive-pole DC power transmission line  143  may have a DC line for transmission of positive-pole DC power, and earth may be used as a current feedback path. One or more switches may be disposed on the DC line. 
         [0070]    The negative-pole DC power transmission line  144  may have a DC line for transmission of negative-pole DC power, and earth may be used as a current feedback path. One or more switches may be disposed on the DC line. 
         [0071]    The reception-side positive-pole DC filter  145  includes an inductor L 2  and a capacitor C 2  and DC-filters positive-pole DC power transmitted through the positive-pole DC power transmission line  143 . 
         [0072]    The reception-side negative-pole DC filter  146  includes an inductor L 4  and a capacitor C 4  and DC-filters negative-pole DC power transmitted through the negative-pole DC power transmission line  144 . 
         [0073]    The reception-side DC/AC converter part  150  includes a positive-pole DC/AC converter  151  and a negative-pole DC/AC converter  152 , the positive-pole DC/AC converter  151  includes one or more three-phase valve bridges  151   a,  and the negative-pole DC/AC converter  152  includes one or more three-phase valve bridges  152   a.    
         [0074]    The reception-side transformer part  160  includes one or more transformers  161  corresponding respectively to one or more three-phase valve bridges  151   a  for the positive pole and one or more transformers  162  corresponding respectively to one or more three-phase valve bridges  152   a  for the negative pole. 
         [0075]    When one three-phase valve bridge  151   a  is used for the positive pole, the positive-pole DC/AC converter  151  may use positive-pole DC power to generate AC power having six pulses. In this case, the primary and secondary coils of one transformer  161  may have a Y-Y connection or Y-Δ connection. 
         [0076]    When two three-phase valve bridges  151   a  are used for the positive pole, the positive-pole DC/AC converter  151  may use positive-pole DC power to generate AC power having 12 pulses. In this case, the primary and secondary coils of one of two transformers  161  may have a Y-Y connection, and the primary and secondary coils of the other of two transformers  161  may have a Y-Δ connection. 
         [0077]    When three three-phase valve bridges  151   a  are used for the positive pole, the positive-pole DC/AC converter  151  may use positive-pole DC power to generate AC power having 18 pulses. The more the number of pulses of the AC power, the price of the filter may decrease. 
         [0078]    When one three-phase valve bridge  152   a  is used for the negative pole, the negative-pole DC/AC converter  152  may use negative-pole DC power to generate AC power having six pulses. In this case, the primary and secondary coils of one transformer  162  may have a Y-Y connection or Y-Δ connection. 
         [0079]    When two three-phase valve bridges  152   a  are used for the negative pole, the negative-pole DC/AC converter  152  may use negative-pole DC power to generate AC power having 12 pulses. In this case, the primary and secondary coils of one of two transformers  162  may have a Y-Y connection, and the primary and secondary coils of the other of two transformers  162  may have a Y-Δ connection. 
         [0080]    When three three-phase valve bridges  152   a  are used for the negative pole, the negative-pole DC/AC converter  152  may use negative-pole DC power to generate AC power having 18 pulses. The more the number of pulses of the AC power, the price of the filter may decrease. 
         [0081]    A reception-side AC part  170  includes an AC filter  171  and an AC power transmission line  173 . 
         [0082]    The AC filter  171  removes other frequency components excluding the frequency component (e.g., about 60 Hz) used by the reception part  180 , from the AC power generated by the reception-side transformation part  105 . 
         [0083]    The AC power transmission line  173  transmits filtered AC power to the reception part  180 . 
         [0084]      FIG. 4  shows the connection of a three-phase valve bridge and a transformer according to an embodiment. 
         [0085]    In particular,  FIG. 4  shows the connection of two transformers  121  for a positive pole and two three-phase valve bridges  131   a  for the positive pole. Since the connection of two transformers  122  for a negative pole and two three-phase valve bridges  132   a  for the negative pole, the connection of two transformers  161  for the positive pole and two three-phase valve bridges  151   a  for the positive pole, the connection of two transformers  162  for the negative pole and two three-phase valve bridges  152   a  for the negative pole, the connection of a transformer  121  for the positive pole and a three-phase valve bridge  131   a  for the positive pole, the connection of a transformer  161  for the positive pole and a three-phase valve bridge  151   a  for the positive pole and so on may be easily driven from the embodiment in  FIG. 4 , their drawings and descriptions are omitted. 
         [0086]    In  FIG. 4 , the transformer  121  having a Y-Y connection is referred to as an upper transformer, the transformer  121  having a Y-Δ connection is referred to as a lower transformer, the three-phase valve bridge  131   a  connected to the upper transformer is referred to as an upper three-phase valve bridge, and the three-phase valve bridge  131   a  connected to the lower transformer is referred to as a lower three-phase valve bridge. 
         [0087]    The upper three-phase valve bridge and the lower three-phase valve bridge have a first output OUT 1  and a second output OUT 2  that are two outputs outputting DC power. 
         [0088]    The upper three-phase valve bridge includes six valves D 1  to D 6  and the lower three-phase valve bridge includes six valves D 7  to D 12 . 
         [0089]    The valve D 1  has a cathode connected to the first output OUT 1  and an anode connected to the first terminal of the secondary coil of the upper transformer. 
         [0090]    The valve D 2  has a cathode connected to the anode of the valve D 5  and an anode connected to the anode of the valve D 6 . 
         [0091]    The valve D 3  has a cathode connected to the first output OUT 1  and an anode connected to the second terminal of the secondary coil of the upper transformer. 
         [0092]    The valve D 4  has a cathode connected to the anode of the valve D 1  and an anode connected to the anode of the valve D 6 . 
         [0093]    The valve D 5  has a cathode connected to the first output OUT 1  and an anode connected to the third terminal of the secondary coil of the upper transformer. 
         [0094]    The valve D 6  has a cathode connected to the anode of the valve D 3 . 
         [0095]    The valve D 7  has a cathode connected to the anode of the valve D 6  and an anode connected to the first terminal of the secondary coil of the lower transformer. 
         [0096]    The valve D 8  has a cathode connected to the anode of the valve D 11  and an anode connected to the anode of the second output OUT 2 . 
         [0097]    The valve D 9  has a cathode connected to the anode of the valve D 6  and an anode connected to the second terminal of the secondary coil of the lower transformer. 
         [0098]    The valve D 10  has a cathode connected to the anode of the valve D 7  and an anode connected to the second output OUT 2 . 
         [0099]    The valve D 1  has a cathode connected to the anode of the valve D 6  and an anode connected to the third terminal of the secondary coil of the lower transformer. 
         [0100]    The valve D 12  has a cathode connected to the anode of the valve D 9  and an anode connected to the second output OUT 2 . 
         [0101]    The reception-side DC/AC converter part  150  may include a modular multi-level converter  200 . 
         [0102]    The modular multi-level converter  200  may use a plurality of sub modules  210  to convert DC power into AC power. 
         [0103]      FIG. 5  is a diagram for explaining the configuration of an HVDC transmission system according to an embodiment. 
         [0104]    The HVDC transmission system according to an embodiment has a structure in which a power transceiving part including both a transmission side and a reception side is connected in plurality. That is, the HVDC transmission system may have a structure in which a first power transceiving part  10  and a second power transceiving part  20  that include a power generation part and a reception part are connected. 
         [0105]    Although as shown in  FIG. 5 , the embodiment defines a left power transceiving part as the first power transceiving part  10  and a right power transceiving part as the second power transceiving part  20 , the connection and arrangement of the first and second power transceiving parts  10  and  20  have no limitations and may vary according to an embodiment. 
         [0106]    In the following, the configuration of the HVDC transmission system according to the embodiment is described in detail with reference to  FIG. 5 . 
         [0107]    A first AC/DC converter part  130  in the first power transceiving part  10  includes an AC/positive-pole DC converter  131  generating positive-pole DC power and the AC/positive-pole DC converter  131  includes dual three-phase valve bridges  131   a  and  131   b  corresponding to transformers  121 . 
         [0108]    Specifically, the first converter part  130  may convert AC power generated by a first power generation part  11  into DC power, and DC power applied from a second converter part  150  into AC power. Also, the first converter part  130  may output the AC power generated by the first power generation part  11  to a first reception part  12  and a first energy storage part  210  or to the second power transceiving part  20 . 
         [0109]    Also, the second converter part  150  may also include dual three-phase valve bridges  151   a  and  151   b  for the positive pole. 
         [0110]    Specifically, the second converter part  150  in the second power transceiving part  20  may convert AC power generated by a second power generation part  11  into DC power, and DC power applied from the first converter part  130  into AC power. Also, the second converter part  150  may output the AC power generated by the second power generation part  21  to a second reception part  22  and a second energy storage part  220  or to the first power transceiving part  10 . 
         [0111]    The energy storage parts  210  and  220  may be connected respectively to the first converter part  130  and the second converter part  150 . In the embodiment, the energy storage part connected to the first converter part  130  is described as the first energy storage part  210  and the energy storage part connected to the second converter part  150  is described as the second energy storage part  220 , for example. 
         [0112]    The first energy storage part  210  and the second energy storage part  220  may store power generated by the first and second power generation parts  11  and  21  respectively or mutually. 
         [0113]    The control part  190  may calculate power to be consumed by the first reception part  12  with respect to power generated by the first power generation part  11  and check the power consumption and the generated power so that surplus power may be stored in the first energy storage part  210 . Also, the control part  190  may check power to be supplied to the second reception part  22  with respect to the power stored in the first energy storage part  210  and output corresponding power to the second energy storage part  220 . The control part  190  may store power excluding that supplied to the second reception part  22  in the second converter part  150  to the second energy storage part  220  and transmit it to the first converter part  130 . That is, the first and second energy storage parts  210  and  220  may check power generated by the first and second power generation parts  11  and  21  connected respectively thereto and consumed by the first and second reception parts  12  and  22  and store surplus power. Also, stored power may be transmitted to a transmission side or reception side under the control of the control part  190 . 
         [0114]    In the following, the operation of the HVDC transmission system according to an embodiment is described in detail with reference to  FIG. 6 . 
         [0115]      FIG. 6  is a flowchart for explaining the operation of an HVDC transmission system according to an embodiment. 
         [0116]    Referring to  FIG. 6 , a control part  190  according to an embodiment may check the power generated by a first power generation part  11  in step  5602 . 
         [0117]    The control part  190  may check the generated power and check power to be discharged by a first reception part  12  and power to be transmitted to a second power transceiving part  20  in step  5604 . 
         [0118]    When the power to be discharged by the first reception part  12  is less than or equal to the generated power, the control part  190  may store power corresponding to the difference in an energy storage part. The energy storage part may be a first storage part  210  connected to a first converter part  130 . 
         [0119]    The control part  190  may check whether a power demand signal is received from the other side, i.e., a second converter part  150  in a second power transceiving part  20 . That is, the control part  190  may check whether power pre-transmitted from the second power transceiving part  20  or pre-stored has been discharged. 
         [0120]    The control part  190  may check power demanded from the second power transceiving part  20  and transmit energy stored in the first energy storage part  210  to the second power transceiving part  20 , in step  5614 . 
         [0121]    On the contrary, if the generated power is less than charged power, the control part  190  may request energy stored in a second energy storage part  220  connected to a second transformer part  150  of the second power transceiving part  20  and store corresponding energy in the first energy storage part  210 , in step  616 . That is, the power pre-transmitted to the second power transceiving part  20  may be received and used as power for a first power transceiving part  10 . In this case, the control part  190  may enable surplus power excluding the power consumption of the first power transceiving part  10  to be re-transmitted. 
         [0122]    Also, the control part  190  may enable power generation, reception and transmission to the second power transceiving part  20  performed by the first power transceiving part  10  to be performed by the second power transceiving part  20 . That is, since the converter part of each of the first and second power transceiving parts  10  and  20  includes dual three-phase valve bridges and the first and second power transceiving parts include the power generation parts  11  and  21  respectively and the reception parts  12  and  22  respectively, bidirectional power transmission and reception are possible. 
         [0123]    Also, if a trouble is sensed in transmission and reception operations of the HVDC transmission system, the control part  190  may output power generated or stored by each of the first and second power transceiving parts  10  and  20  to perform self-discharging (consumption). 
         [0124]    Exemplary embodiments are mainly described above. However, they are only examples and do not limit the inventive concept. A person skilled in the art may appreciate that many variations and applications not presented above may be implemented without departing from the essential characteristic of embodiments. For example, each component specifically represented in embodiments may vary. In addition, it should be construed that differences related to such a variation and such an application are included in the scope of the inventive concept defined in the following claims.