Abstract:
A high voltage direct current (HVDC) instantaneous power monitoring system is provided. The high voltage direct current (HVDC) instantaneous power monitoring system includes a calculation processing unit receiving three-phase current and voltage, detecting a synchronous phase angle from received three-phase current and voltage, and transforming two-phase data into two-phase data to output two-phase data; and a data processing unit storing data transformed at the calculation processing unit.

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. 10-2014-0051552, filed on Apr. 29, 2014, the contents of which are hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to an HVDC instantaneous power monitoring system. 
         [0003]    There are two power system interconnection methods, one for interconnecting AC power systems as they are, and the other for converting AC power into DC power before interconnection between systems. 
         [0004]    In recent, an interest in the method of converting the AC power into the DC power before interconnection between power systems is more increasing than the method of interconnecting AC power systems as they are. 
         [0005]    A high voltage direct current (HVDC) transmission system using a power converter is also installed between Jeju island and Haenam-gun in Korea to interconnect power systems between Jeju island and Haenam-gun. 
         [0006]    An HVDC transmission method is one of electricity transmission methods and indicates a supply method in which high voltage AC power generated at the power station is converted into DC power, which is transmitted and then re-converted into AC power in a desired power receiving region. 
         [0007]    The DC transmission method has many advantages. 
         [0008]    Firstly, since the size of a DC voltage is just about 70 of the maximum value of an AC voltage, the HVDC transmission system may easily perform device insulation and since there is a low voltage, it is possible to reduce the number of insulators installed in each device and the height of an iron tower. 
         [0009]    Since the DC method has less transmission loss than an AC method when the HVDC transmission system transmits the same power, the best advantage of the HVDC transmission system is that power transmission efficiency may increase. The HVDC transmission system may transmit currents two or more times in the DC method than the AC method. 
         [0010]    Since the HVDC transmission system may reduce wire consumption and the area of a transmission line, it is effective and also possible to enhance the stability of systems by connecting two systems having different voltages or frequencies. 
         [0011]    The HVDC transmission system has no constraint on a power transmission distance and the DC transmission method needs inexpensive construction costs in land power transmission exceeding 450 Km or in submarine power transmission exceeding 40 Km as well. 
         [0012]    Thus, the HVDC transmission system is used for a power system interconnection method of new renewable energy power, especially for power transmission of a large offshore wind farm. 
         [0013]    Since in other countries such as China or India, the distance between a power station and an electricity user is 1000 Km or longer, the prevalence of the HVDC transmission system is rapidly increasing. 
         [0014]    Such an HVDC system is classified into a current type HVDC system using a thyristor valve and a voltage type HVDC system using an insulated gate bipolar mode transistor (IGBT) element. 
         [0015]    A domestic power transmission and distribution system has adopted a method of measuring three-phase current and voltage to monitor instantaneous power for the monitoring of all event situations including a fault current as well as a power flow and for data acquisition. The monitoring of power is performed at the bus-dependent substation of a transmission/distribution point and is also performed on each feeder interconnected to a bus. 
         [0016]    Thus, the HVDC system also monitors AC power on rectifier-side and inverter-side converter stations for the same purpose. 
         [0017]      FIG. 1  is a diagram for explaining a typical HVDC instantaneous power monitoring system. 
         [0018]    Referring to  FIG. 1 , a typical HVDC instantaneous power monitoring system  1  includes a configuration that may measure three-phase voltage and current and the phase difference for the monitoring of AC power to determine all event situations including whether a power transmission system normally operates and a fault situation. 
         [0019]    In particular, a power monitoring and processing unit  10  includes a calculation processing unit  11  and a data processing unit  12 . A design is generally made to store, as data, an event occurrence time and a voltage and current at that time when an event situation occurs, but the data processing unit  12  has a limit in data storage capacity. Thus, data stored for a certain period is deleted automatically or selectively by an operator through a user interface unit  20  to secure a storage space. If an event such as an accident and failure occurs in a power system while the storage space is not secured, there is a difficulty in ensuring an ability for analyzing the reason and solving the situation. Also, it may be difficult to check event data on a past history through random or batch deletion of pre-stored data. 
       SUMMARY 
       [0020]    Embodiments provide a high voltage direct current (HVDC) instantaneous power monitoring system that may efficiently manage a data storage space through an algorithm design for instantaneous power analysis. 
         [0021]    In one embodiment, a high voltage direct current (HVDC) instantaneous power monitoring system includes a calculation processing unit receiving three-phase current and voltage, detecting a synchronous phase angle from received three-phase current and voltage, and transforming two-phase data into two-phase data to output two-phase data; and a data processing unit storing data transformed at the calculation processing unit. 
         [0022]    The calculation processing unit may include a synchronous phase angle detection unit detecting a synchronous phase angle from the three-phase current and voltage. 
         [0023]    The calculation processing unit may include an instantaneous power three-phase to two-phase transformation processing unit performing first and second transformation on the three-phase data. 
         [0024]    The instantaneous power three-phase to two-phase transformation processing unit may transform the three-phase data into two-phase Cartesian coordinate system data through Clarke transformation corresponding to the first transformation, and transform data obtained through the first transformation into a two-phase rotary synchronous coordinate system through Park transformation corresponding to the second transformation. 
         [0025]    The Park transformation may be performed based on the synchronous phase angle detected by the synchronous phase angle detection unit. 
         [0026]    The first transformation may transform the three-phase current into two-phase current, and 
         [0027]    the second transformation may transform the two-phase current obtained through the transformation into two-phase current being a DC. 
         [0028]    The instantaneous power three-phase to two-phase transformation processing unit may inversely perform the first and second transformation on the two-phase current obtained through the first and second transformation to recover initially input three-phase data. 
         [0029]    The instantaneous power three-phase to two-phase transformation processing unit may recover steady-state three-phase current when there is two-line short circuit on the three-phase current. 
         [0030]    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 
         [0031]      FIG. 1  is a diagram for explaining a typical high voltage direct current (HVDC) instantaneous power monitoring system. 
           [0032]      FIG. 2  is a diagram for explaining an HVDC instantaneous power monitoring system to which an embodiment is applied. 
           [0033]      FIGS. 3 ,  4   a  and  4   b  are diagrams for explaining an operation of processing HVDC instantaneous power data according to an embodiment. 
           [0034]      FIGS. 5   a ,  5   b ,  5   c ,  6   a ,  6   b  and  6   c  are exemplary diagrams for explaining HVDC instantaneous power data according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0035]    Particular embodiments are described below in detail with reference to the accompanying drawings. 
         [0036]    The terms used herein are general terms being currently, widely used if possible, but in particular cases, terms arbitrarily selected by the applicant are used and in these cases, since their meanings are described in detail in corresponding parts of the detailed description, it should be noted that an embodiment needs to be understood with the meanings of the terms, not the names of the terms. 
         [0037]    That is, in the following description, the word “including” does not exclude the presence of components or steps other than those enumerated. 
         [0038]      FIG. 2  is a diagram for explaining an HVDC instantaneous power monitoring system to which an embodiment is applied. 
         [0039]    Referring to  FIG. 2 , an HVDC instantaneous power monitoring system  2  to which the embodiment is applied may include a power monitoring and processing unit  100  and a user interface unit  200 . 
         [0040]    The power monitoring and processing unit  100  includes a calculation processing unit  110  and a data processing unit  120 . 
         [0041]    The calculation processing unit  110  may receive a three-phase measurement current and a three-phase measurement voltage and transform them into two-phase DC current and voltage data through data transformation of a received current and voltage. 
         [0042]    The calculation processing unit  110  may include a synchronous phase angle detection unit  111  and an instantaneous power three-phase to two-phase transformation processing unit  112 . 
         [0043]    The synchronous phase angle detection unit  111  may detect a synchronous phase angle from a three-phase current and voltage, and a detected synchronous phase angle may be applied to a first transformation value of instantaneous power to be used as a coefficient calculating a second transformation value. 
         [0044]    The instantaneous power three-phase to two-phase transformation processing unit  112  may perform an operation for transforming two-phase current and voltage data through first and second transformation of the three-phase current and the three-phase voltage according to an embodiment. 
         [0045]      FIGS. 3 to 4   b  are diagrams for explaining the processing operation of the instantaneous three-phase to two-phase transformation processing unit  112  for HVDC instantaneous power data according to an embodiment. 
         [0046]    The transformation operation of instantaneous power monitoring data according to an embodiment is described in detail with reference to  FIGS. 3 to 4   b.    
         [0047]    The instantaneous power three-phase to two-phase transformation processing unit  112  may perform first transformation (e.g., Clarke transformation) and second transformation (e.g., Park transformation) based on three-phase current and three-phase voltage data to transform the data into second-phase instantaneous power data. 
         [0048]    The instantaneous power three-phase to second-phase transformation processing unit  112  may receive three phase currents ia, ib and is and transform the three phase currents at Clarke transformation unit  112   a . In this case, the first transformation for transforming three-phase current and three-phase voltage data into second-phase instantaneous power data may be performed by Clarke transformation. The Clarke transformation transforms three phase currents a, b and c being stators into a stator Cartesian coordinate system having two values α and β based on Equation 1 below and  FIG. 4   a . 
         [0000]    
       
         
           
             
               
                 
                   
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         [0049]    That is, first transformation data transformed at the first transformation unit  112   a  may perform second transformation at the second transformation unit  112   b  by applying a synchronous phase angle θ detected by the phase angle detection unit  111  to the first transformation data. 
         [0050]    The second transformation performed at the second transformation unit  112   b  may be performed by Park transformation. The Park transformation transforms a stator Cartesian coordinate system having two values α and β into a rotary synchronous coordinate system having two values d and q based on Equation 2 below and  FIG. 4   b . In this case, a value θ detected by the synchronous phase angle detection unit  111  may represent the rotor flux location of d and q about α and β. 
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         [0051]    Thus, when three-phase measurement current and three-phase measurement voltage values are input in an embodiment, the values of the three phases may be transformed into two-phase instantaneous power monitoring data through first and second transformation. 
         [0052]    On the contrary, pre-transformed two-phase instantaneous power monitoring data may be transformed into three-phase current and three-phase voltage data through the inverse transformation of the first and second transformation. 
         [0053]    The inverse transformation may be performed by the sequential application of Equations 3 and 4 below. 
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         [0054]    The data processing unit  120  may store the processing result of the calculation processing unit  110  or output pre-stored data to the calculation processing unit  110 . The data processing unit  120  may be a storage unit that stores data processed according to an embodiment and data to be processed. 
         [0055]    HVDC instantaneous power data according to an embodiment is described in detail with reference to  FIGS. 5   s  to  6   c  based on a configuration according to an embodiment as described above. 
         [0056]      FIGS. 5   a  to  6   c  are exemplary diagrams for explaining HVDC instantaneous power data according to an embodiment. 
         [0057]      FIG. 5   a  is an exemplary diagram representing a three-phase current curve in a steady state according to an embodiment. When three phase currents ia, ib and is are input as described above, it is possible to detect the synchronous phase angle θ by the synchronous phase angle detection unit  111  from the three phase currents as described above. The three phase currents experience first transformation at the instantaneous three-phase to two-phase transformation processing unit  112 . When the three-phase currents complete the first transformation, they may be transformed into two phase currents ids and iqs as shown in  FIG. 5   b , and the two phase currents obtained through the first transformation may be output as two phase currents ide and iqe being DC through second transformation as shown in  FIG. 5   c . Thus, since two-phase balanced current data is output as described above, the amount of data decreases and it is easy to analyze, when compared to initially input current and voltage data. 
         [0058]    Also, it is possible to recover initially input data from the two-phase data obtained through transformation as described above, through the inverse transformation of an operation of transforming three-phase data into two-phase data to monitor and analyze the state of data. 
         [0059]      FIG. 6   a  is a three-phase current curve for a two-line short circuit (fault) unlike a steady state in  FIGS. 4   a  and  4   b ,  FIG. 6   b  represents transformation into two phases through first transformation on input three phase currents and in  FIG. 6   c , it is possible to recover steady-state three-phase current easy to analyze through second transformation. 
         [0060]    The HVDC instantaneous power monitoring system according to an embodiment may manage HVDC instantaneous power data and efficiently use a storage space of the monitoring system. 
         [0061]    Also, the HVDC instantaneous power monitoring system according to an embodiment may store all collected data as long as data is not forcibly deleted, and thus may be efficiently used for history management for accidents and events. 
         [0062]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.