Abstract:
The present disclosure relates to a reactive power compensation system includes a first measurement unit, a second measurement unit, a reactive power compensation unit, and a controller. The first measurement unit measures impedance of each of at least one load. The second measurement unit measures a voltage and current provided to the at least one load. The reactive power compensation unit compensates the leading reactive power or the lagging reactive power. The controller monitors a change of the impedance in real time, checks a change of the voltage or current according to the change of the impedance, and controls the reactive power compensation unit according to a result of the check to compensate the leading reactive power or the lagging reactive power. 
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Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 10-2016-0067101 filed on May 31, 2016, in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
     1. Technical Field 
       [0002]    The present disclosure relates to a reactive power compensation system and a method thereof. 
       2. Description of the Related Art 
       [0003]    When power is supplied to a receiving end connected to a load, the power is not all used by the load. In other words, the power is not all used as active power by the load and part of the power is lost as reactive power, not contributing to a real work. 
         [0004]    To minimize or compensate the reactive power, a reactive power compensation system is employed. 
         [0005]    The reactive power compensation system adjusts a phase of a voltage or a phase of current and thus the reactive power may be minimized. 
         [0006]    However, in a conventional reactive power compensation system, since real-time compensation according to a load input state or an environmental change is not made, manufactured products may be damaged, for example, due to a temporary blackout state caused by a rapid voltage drop. 
       SUMMARY 
       [0007]    It is an object of the present disclosure to address the above-described problems and other problems. 
         [0008]    It is another object of the present disclosure to provide a reactive power compensation system, which is capable of compensating reactive power in real time by continuously monitoring a change in the impedance of a load, and a method thereof. 
         [0009]    Objects of the present disclosure are not limited to the above-described objects and other objects and advantages can be appreciated by those skilled in the art from the following descriptions. Further, it will be easily appreciated that the objects and advantages of the present disclosure can be practiced by means recited in the appended claims and a combination thereof. 
         [0010]    In accordance with one aspect of the present disclosure, there is provided a reactive power compensation system including a first measurement unit, a second measurement unit, a reactive power compensation unit, and a controller. The first measurement unit measures impedance of each of at least one load. The second measurement unit measures a voltage and current provided to the at least one load. The reactive power compensation unit compensates the leading reactive power or the lagging reactive power. The controller monitors a change of the impedance in real time, checks a change of the voltage or current according to the change of the impedance, and controls the reactive power compensation unit according to a result of the check to compensate the leading reactive power or the lagging reactive power. 
         [0011]    In accordance with one aspect of the present disclosure, there is provided a method of compensating reactive power, which includes measuring impedance of each of at least one load, measuring a voltage and current provided to the at least one load, monitoring a change of the impedance in real time, checking a change of the voltage or current according to the change of the impedance, and compensating leading reactive power or lagging reactive power according to a result of the check. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  illustrates a reactive power compensation system according to an embodiment of the present disclosure. 
           [0013]      FIG. 2  is a flowchart of a method of compensating reactive power according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The above objects, features and advantages will become apparent from the detailed description with reference to the accompanying drawings. Embodiments are described in sufficient detail to enable those skilled in the art in the art to easily practice the technical idea of the present disclosure. Detailed descriptions of well-known functions or configurations may be omitted in order not to unnecessarily obscure the gist of the present disclosure. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Throughout the drawings, like reference numerals refer to like elements. 
         [0015]    As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description, wherein like reference numerals in the drawings denote like elements, and thus their description will not be repeated. The suffix “module” and “unit” for components, which are used in the description below, are assigned and mixed in consideration of only the easiness in writing the specification. That is, the suffix itself does not have different meanings or roles. However, this is not intended to limit the present inventive concept to particular modes of practice, and it is to be appreciated that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of the present inventive concept are encompassed in the present inventive concept. In the description of the present inventive concept, certain detailed explanations of related art are omitted when it is deemed that they may unnecessarily obscure the essence of the inventive concept. 
         [0016]      FIG. 1  illustrates a reactive power compensation system according to an embodiment of the present disclosure. 
         [0017]    A plurality of loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  may be connected to a receiving end  11 . In detail, a branch line  12  may be branched from the receiving end  11 , and the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  may be connected to the branch line  12 . 
         [0018]    Although  FIG. 1  illustrates that the branch line  12  is connected to the receiving end  11 , the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  may be directly connected to the receiving end  11  without the branch line  12 . 
         [0019]    The loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  may be connected to a system other than the receiving end  11 . The system may be an AC system, a DC system, or a HVDC system. However, the present disclosure is not limited thereto. 
         [0020]    The loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  may be loads provided in ironworks, for example, arc furnaces  21   a,    21   b,  and  21   c  or smelting furnaces  23   a,    23   b,  and  23   c.  However, the present disclosure is not limited thereto. 
         [0021]    A reactive power compensation unit  30  may be connected parallel to the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  and commonly with the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  to the branch line  12  or the receiving end  11 , but the present disclosure is not limited thereto. Accordingly, power supplied to the receiving end  11  may be supplied not only to the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c,  but also to the reactive power compensation unit  30 . 
         [0022]    The reactive power compensation unit  30 , as illustrated in  FIG. 2 , may include a Thyristor-controlled reactor (TCR)  25 , a Thyristor-switched capacitor (TSC)  27 , and a harmonic filter unit  29 . 
         [0023]    The TCR  25  may include a reactor and a thyristor switch. The number or arrangement of reactors may be implemented by various methods. 
         [0024]    The TSC  27  may include a capacitor and a thyristor switch. The number or arrangement of capacitors may be implemented by various methods. 
         [0025]    The harmonic filter unit  29  may include a plurality of filters. Each filter may include a resistor, a capacitor, and an inductor. Although the resistor and the inductor may be connected in parallel, but the present disclosure is not limited thereto. 
         [0026]    Both the TCR  25  and the TSC  27  may not be necessarily provided. Only one of the TCR  25  and the TSC  27  may be provided, but the present disclosure is not limited thereto. 
         [0027]    Although not illustrated, a fixed compensation unit may be further provided in addition to the TCR  25  or the TSC  27 . The fixed compensation unit may be a fixed capacitor. 
         [0028]    The reactive power compensation unit  30  may control a Thyristor switch provided therein to compensate reactive power The reactive power compensation is described below in detail. 
         [0029]    A second detector  13  may be provided between the receiving end  11  and the branch line  12 . In other words, the second detector  13  may be provided at an input side of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.  The second detector  13  may detect a voltage, a phase of a voltage, current, and a phase of current. In detail, a voltage transformer  13   a  of the second detection unit  13  may detect the voltage and the phase of a voltage applied to the branch line  12 , and a current transformer  13   b  of the second detection unit  13  may detect the current and the phase of current applied to the branch line  12 . The voltage and the phase of a voltage, and the current and the phase of current, detected by the second detection unit  13  are provided to a voltage and current measurement unit  43 . Accordingly, the voltage and current measurement unit  43  may measure voltage and current. 
         [0030]    A phase relation between the voltage and the current may be identified based on the phase of a voltage and the phase of current. For example, when a phase of current is ahead of a phase of a voltage, it may be referred to as leading, and when a phase of a voltage is ahead of a phase of current, it may be referred to as lagging. For example, when a phase angle between the voltage and the current in the leading, is expressed by a positive phase angle (±θ), a phase angle between the voltage and the current in the lagging may be expressed by a negative phase angle (−θ). 
         [0031]    At least one of first detectors  14   a,    14   b,    15   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  may be provided at the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.  The first detectors  14   a,    14   b,    15   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  detect impedance of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  and provide the detected impedance to an impedance measurement unit  41  of the control system  40 . Accordingly, the impedance measurement unit  41  may measure impedance of each of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.    
         [0032]    When a certain load is input or a change occurs in an operating load, impedance of the load may be changed. The change in the impedance of the load may be detected by a corresponding one of the first detectors  14   a,    14   b,    1 . 5   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  and checked by the impedance measurement unit  41 . The impedance measurement unit  41  may be referred to as the first measurement unit, and the voltage and current measurement unit  43  may be referred to as the second measurement unit. 
         [0033]    A voltage may be simultaneously applied to the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c,  and individually to the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  at different times. 
         [0034]    The control system  40  may include the first measurement unit  41 , the second measurement unit  43 , a controller  45 , and a storage unit  47 . 
         [0035]    The first measurement unit  41  may measure the impedance of each of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  detected by the first detectors  14   a,    14   b,    15   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  provided at the respective loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.  While the impedance detected by the first detectors  14   a,    14   b,    15   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  is an analog signal, the impedance measured by the first measurement unit  41  may be a digital signal. However, the present disclosure is not limited thereto. The impedance measured by the first measurement unit  41  may be provided to the controller  45 . 
         [0036]    The second measurement unit  43  may measure the voltage and the current based on the voltage, the phase of a voltage, the current, and the phase of current detected by the second detector  13  provided between the receiving end  11  and the branch line  12 . The voltage may be the voltage applied to the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c,  and the current may be the current flowing from the receiving end  11  to the branch line  12 . While each of the voltage, the phase of a voltage, the current, and the phase of current detected by the second detector  13  is an analog signal, the voltage and the current measured by the second measurement unit  43  may be digital signals, but the present disclosure is not limited thereto. The measured voltage and current may be provided to the controller  45 . 
         [0037]    The controller  45  may check whether the impedance measured by the first measurement unit  41  has changed. The change of the impedance may be checked in real time. 
         [0038]    For example, when the impedance measured at a time point t 1  is Z 1  and the impedance measured at a time point t 2  is Z 2 , and Z 2  is different from Z 1 , it may be determined that the impedance has changed. 
         [0039]    The change of the impedance may be checked for each of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c,  and through the total impedance of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.    
         [0040]    In the present embodiment, for convenience of explanation, the change of the impedance is checked through the total impedance of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c,  but the present disclosure is not limited thereto. 
         [0041]    The change of impedance may signify that a load to which a voltage is applied is changed, an abrupt change, for example, incoming of overcurrent, occurs in the load to which a voltage is currently applied. 
         [0042]    For example, in a state in which a voltage is applied to five loads, when a voltage is additionally applied to two loads, impedance may be changed. 
         [0043]    For example, in a state in which a voltage is applied to five loads, when current abruptly flows to a particular load, impedance may be changed. 
         [0044]    When the impedance is changed, it is necessary to identify the reason of the change of impedance. For example, when a voltage is initially applied to a load or a voltage is applied to a newly added load, it is necessary to identify whether the load to which a voltage is initially applied or the load to which a voltage is additionally applied is a Thyristor-switched load or a Thyristor-controlled load. Performing either leading reactive power compensation or lagging reactive power compensation may be determined according to whether the load is a Thyristor-switched load or a Thyristor-controlled load. For example, when the load is a Thyristor-switched load, leading reactive power compensation may be performed, and when the load is a Thyristor-controlled load, lagging reactive power compensation may be performed, which is described later in detail. 
         [0045]    The voltage or current of power provide from the receiving end  11  to the branch line  12  may vary according to whether the load to which a voltage is initially applied or the load to which a voltage is additionally applied is a Thyristor-switched load or a Thyristor-controlled load. 
         [0046]    In other words, when the impedance is changed, the voltage or current of the power provided from the receiving end  11  to the branch line  12  is changed accordingly. 
         [0047]    The controller  45  may check whether there is a change in the voltage or current detected by the second detector  13  provided between the receiving end  11  and the branch line  12  and measured by the second measurement unit  43 . 
         [0048]    When it is checked that the current is changed and thus the phase of current is ahead of the phase of a voltage, that is, the leading, the controller  45  may determine that the load causing the change of the impedance is a Thyristor-switched load. Since the leading reactive power is present or increased by the Thyristor-switched load, the leading reactive power may be removed or reduced by compensating the leading reactive power. In this case, the controller  45  may generate a first control signal to compensate the leading reactive power and provide the first control signal to the reactive power compensation unit  30 . 
         [0049]    Although the first control signal may be, for example, a signal controlling the phase of current to be synchronized with the phase of a voltage, the present disclosure is not limited thereto. The leading reactive power may be compensated as a Thyristor switch of the TCR  25  included in the reactive power compensation unit  30  is switch-controlled in response to the first control signal. As such, when the impedance is changed by the Thyristor-switched load, the leading reactive power is compensated by means of the TCR  25 . Accordingly, the power factor may be improved, that is, the active power may be increased, as the phase angle of the current and the voltage becomes 0° or approaches 0°. 
         [0050]    When it is checked that the voltage is changed and thus the phase of a voltage is ahead of the phase of current, that is, the lagging, the controller  45  may determine that the load causing the change of the impedance is a Thyristor-controlled load. Since lagging reactive power is present or increased by the Thyristor-controlled load, the lagging reactive power may be removed or reduced by compensating the lagging reactive power. In this case, the controller  45  may generate a second control signal to compensate the lagging reactive power and provide the second control signal to the reactive power compensation unit  30 . 
         [0051]    Although the second control signal may be, for example, a signal controlling the phase of a voltage to be synchronized with the phase of current, the present disclosure is not limited thereto. The lagging reactive power may be compensated as a Thyristor switch of the TSC  27  included in the reactive power compensation unit  30  is switch-controlled in response to the second control signal. As such, when the impedance is changed by the Thyristor-controlled load, the lagging reactive power is compensated by means of the TSC  27 . Accordingly, the power factor may be improved, that is, the active power may be increased, as the phase angle of the current and the voltage becomes 0° or approaches 0°. 
         [0052]    According to the present disclosure, when a change occurs in the impedance of a load impedance by monitoring the impedance change in real time, whether the load is a Thyristor-switched load or a Thyristor-controlled load is identified based on the change in the voltage or current according to the change of impedance and thus compensation is performed accordingly. Thus, the damage of a product due to the addition of a load or overcurrent flowing to the load may be prevented. For example, when the load is a refining furnace, and a flicker is generated due to a change of the load causing a temporary blackout, impurities in iron may not be appropriately removed and thus defective iron may be produced. In this case, when the load is determined to be a Thyristor-switched load based on the change of impedance, a flicker is regarded to be generated. When a flicker is generated, the leading reactive power in which the phase of current is ahead of the phase of a voltage may increase. Accordingly, the controller  45  may control the TSC  27  to compensate the leading reactive power, thereby removing the flicker. 
         [0053]    The storage unit  47  may store various pieces of setting information, for example the type of work or the amount of work processed by each of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.    
         [0054]    The storage unit  47  may store a work temperature sensed at a place where the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  are provided. 
         [0055]    The storage unit  47  may store various pieces of information needed to embody the present disclosure that is not described above. 
         [0056]      FIG. 2  is a flowchart of a method of compensating reactive power according to an embodiment of the present disclosure. 
         [0057]    Referring to  FIGS. 1 and 2 , a voltage, current, and impedance may be measured (S 111 ). 
         [0058]    In detail, the impedance may be measured by the first measurement unit  41 , and the voltage and current may be measured by the second measurement unit  43 . The impedance may be measured from signals detected by the first detectors  14   a,    14   b,    15   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  provided at the respective loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c.  The voltage and current may be measured from a signal detected by the second detector  13  provided between the receiving end  11  and the branch line  12 . 
         [0059]    The second detector  13  may detect the voltage, the phase of a voltage, the current, and the phase of current. The second measurement unit  43  may check whether the leading reactive power is present or the lagging reactive power is present, based on the relation between the phase of a voltage and the phase of current. In addition, the second measurement unit  43  may calculate a phase angle based on the relation between the phase of a voltage and the phase of current. The second measurement unit  43  may provide the controller  45  with the measured voltage and current, information about the leading reactive power or the lagging reactive power, and the phase of angle. 
         [0060]    A voltage may be applied to at least one of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  (S 113 ). The at least one of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  may be a load to which a voltage is initially applied or a load to which a voltage is newly applied while a voltage is applied to other load(s). 
         [0061]    The controller  45  may check whether impedance is changed while a voltage is applied to the at least one of the loads  21   a,    21   b,    21   c,    23   a,    23   b,  and  23   c  (S 115 ). 
         [0062]    The change of impedance may be changed based on the impedance detected in real time by the first detectors  14   a,    14   b,    15   a,    15   b,    16   a,    16   b,    17 ,  18 , and  19  and measured by the first measurement unit  41 . 
         [0063]    When the impedance change is checked, the controller  45  may check whether a voltage or current is changed (S 117 ). 
         [0064]    The change of a voltage or current may be checked based on the voltage, current and phase angle detected in real time by the second detector  13  and measured by the second measurement unit  43 . 
         [0065]    The impedance may be changed due to the newly added load or the load into which current abruptly flows. When the impedance is changed, the voltage or current may be changed according to whether the load is a Thyristor-switched load or a Thyristor-controlled load. 
         [0066]    For example, when the load is a Thyristor-switched load, for example, current changed and thus the leading reactive power in which the phase of current is ahead of the phase of a voltage may be present. Unlike the above, when the load is a Thyristor-switched load, for example, a voltage is changed and thus the leading reactive power in which the phase of a voltage is behind the phase of current may be present. 
         [0067]    For example, when the load is a Thyristor-controlled load, for example, a voltage is changed and thus the lagging reactive power in which the phase of a voltage is ahead of the phase of current may be present. Unlike the above, when the load is a Thyristor-controlled load, for example, current is changed and thus the lagging reactive power in which the phase of current is behind the phase of a voltage may be present. 
         [0068]    The controller  45  may determine whether the leading reactive power is present or the lagging reactive power is present, based on the change of the current or voltage. 
         [0069]    As a result of the determination, when the leading reactive power is present (S 119 ), the controller  45  may control compensation of the Thyristor-controlled reactive power (S 121 ). 
         [0070]    In detail, when the leading reactive power is present, the controller  45  may generate a first control signal to compensate the leading reactive power and provide the first control signal to the reactive power compensation unit  30 . The first control signal may be a signal to adjust, for example, the phase of current, to be synchronized with the phase of a voltage, but the present disclosure is not limited thereto. As the Thyristor switch of the TCR 25  included in the reactive power compensation unit  30  is switch-controlled in response to the first control signal, the leading reactive power may be compensated. 
         [0071]    As a result of the determination, when the lagging reactive power is present, the controller  45  may control compensation of the Thyristor-switched reactive power (S 123 ). 
         [0072]    In detail, when the lagging reactive power is present, the controller  45  may generate a second control signal to compensate the lagging reactive power and provide the second control signal to the reactive power compensation unit  30 . Although the second control signal may be a signal to adjust, for example, the phase of a voltage, to be synchronized with the phase of current, the present disclosure is not limited thereto. As the Thyristor switch of the TSC  27  included in the reactive power compensation unit  30  is switch-controlled in response to the second control signal, the lagging reactive power may be compensated. 
         [0073]    As such, according to the present disclosure, whenever the impedance is changed, compensation may be performed according to the change of the impedance. 
         [0074]    According to the present disclosure, by monitoring a change of impedance in real time, the leading reactive power or the lagging reactive power that is present according to whether the load causing the impedance change is a Thyristor-switched load or a Thyristor-controlled load may be identified based on the change in the voltage or current. Since the leading reactive power or the lagging reactive power is compensated in real time according to a result of the identification, the damage of a product due to a change of the load may be prevented. 
         [0075]    The present disclosure described above may be variously substituted, altered, and modified by those skilled in the art to which the present inventive concept pertains without departing from the scope and sprit of the present disclosure. Therefore, the present disclosure is not limited to the above-mentioned exemplary embodiments and the accompanying drawings.