Patent Publication Number: US-2022231594-A1

Title: Bypass device and method of hvdc sub module

Description:
TECHNICAL FIELD 
     The present invention relates to a device and a method for bypassing a high voltage direct current (HVDC) sub-module, and more particularly, to a bypass function of protecting a capacitor positioned in an HVDC sub-module. That is, the present invention relates to a device and a method for bypassing an HVDC sub-module, which are capable of stably operating an HVDC system by duplicating a bypass circuit of an HVDC sub-module. 
     BACKGROUND ART 
     Recently, there has been an increasing interest in a method of linking a power grid by converting alternating current (AC) power into direct current (DC) power rather than a method of directly linking an AC power system in order to link a power grid. 
     A high voltage direct current (HVDC) system is a system that converts AC power generated in a power plant into DC power, transmits the DC power to a required site, and then reconverts the DC power into AC power to supply the AC power to consumers. Recently, an HVDC system has been developed by constituting a plurality of modular converters in which a plurality of small-capacity sub-modules are connected in series. 
     In this case, a capacitor used in a DC link unit in the HVDC system is mainly used for linking and smoothing a voltage of DC energy and for buffering charge/discharge energy. However, when an accident such as electrolyte ejection due to performance degradation or temperature rise occurs, an increase in use of such a capacitor may cause a very dangerous situation leading to a short circuit accident in an HVDC system, and thus, research on a failure diagnosis system therefor has been continued. 
     As an example, Korean Patent Publication No. 10-2019-0065675 discloses “Apparatus and method for estimating capacitor capacity of HVDC system having modular multi-level converter,” which analyzes a change in capacitor capacity for each sub-module based on data about each sub-module. 
     However, even in this case, when a failure occurs in a circuit controlling a capacitor of the sub-module, the disconnection of the HVDC system may be caused. 
     DISCLOSURE 
     Technical Problem 
     The present invention is directed to providing a device and a method for bypassing a high voltage direct current (HVDC) sub-module, in which, even when a failure occurs in a sub-module controller in an HVDC sub-module, an additional device, which detects a voltage of a capacitor voltage in the sub-module to perform bypass, is used, thereby protecting a capacitor in the sub-module. 
     The present invention is also directed to providing a device and a method for bypassing an HVDC sub-module, in which a function of bypassing an HVDC sub-module is stably performed by duplicating a driving unit of a device for bypassing an HVDC sub-module, thereby preventing an HVDC system from being disconnected due to a failure of the HVDC sub-module. 
     Technical Solution 
     According to one embodiment of the present invention, a device for bypassing a high voltage direct current (HVDC) sub-module includes a sub-module configured to generate a voltage in an HVDC system, a bypass switch driving unit configured to drive a bypass switch positioned at an input of the sub-module, a sub-module controller configured to monitor a state of the sub-module to transmit the monitored state to a system controller and control the sub-module and the bypass switch driving unit according to a command of the system controller, and a voltage monitoring unit configured to monitor a voltage of a capacitor positioned in the sub-module and control the bypass switch driving unit. 
     The sub-module may include the capacitor configured to store and release energy, an insulated gate bipolar transistor1 (IGBT1) and a first diode which are positioned between a P input of the sub-module and a positive terminal of the capacitor, and an insulated gate bipolar transistor2 (IGBT2) and a second diode which are positioned between the P input and a negative terminal of the capacitor connected to an N input of the sub-module. 
     The bypass switch may be connected between the P input and the N input of the sub-module and may bypass the P input and the N input under control of the bypass switch driving unit. 
     The sub-module controller may control both the IGBT1 and the IGBT2 to be turned off to allow input energy of the sub-module to be stored in the capacitor through the first diode in a section in which a P input voltage of the sub-module is higher than an N input voltage thereof. 
     The sub-module controller may control the IGBT1 to be turned on and control the IGBT2 to be turned off to allow energy charged in the capacitor to be released to an input of the sub-module in a section in which a P input voltage of the sub-module is lower than an N input voltage thereof. 
     The sub-module controller may control the IGBT1 to be turned off and control the IGBT2 to be turned on to bypass the P input and the N input of the sub-module. 
     When the voltage of the capacitor exceeds a bypass switch-on voltage by the sub-module controller positioned between an operating voltage and a capacitor limit voltage, the sub-module controller may control the bypass switch driving unit to perform bypass at the input of the sub-module. 
     When the voltage of the capacitor exceeds a bypass switch-on voltage by the voltage monitoring unit positioned between the bypass switch-on voltage by the sub-module controller and the capacitor limit voltage, the voltage monitoring unit may control the bypass switch driving unit to perform bypass at the input of the sub-module. 
     According to another embodiment of the present invention, a method of bypassing an HVDC sub-module includes a system controller command receiving operation of receiving, by a sub-module controller, a control command from a system controller, an energy storage operation of, when the control command indicates energy storage, controlling, by the sub-module controller, an insulated gate bipolar transistor1 (IGBT1) and an insulated gate bipolar transistor2 (IGBT2) of a sub-module to construct a path through which energy is storable in a capacitor in the sub-module, an energy release operation of, when the control command indicates energy release, controlling, by the sub-module controller, the IGBT1 and the IGBT2 of the sub-module to construct a path through which energy of the capacitor in the sub-module is releasable, a bypass operation of, when the control command indicates bypass, controlling, by the sub-module controller, the IGBT1 and the IGBT2 of the sub-module to block a path with the capacitor in the sub-module and construct a bypass path, a capacitor voltage transmitting operation of, when it is checked whether a voltage of the capacitor in the sub-module is greater than a bypass switch-on voltage by the sub-module controller, and the voltage of the capacitor is less than the bypass switch-on voltage (V 830 ) by the sub-module controller, transmitting the voltage of the capacitor to the system controller, a bypass switch driving unit turning-on operation of, when the voltage of the capacitor in the sub-module is greater than the bypass switch-on voltage by the sub-module controller, comparing the voltage of the capacitor in the sub-module with a bypass switch-on voltage by a voltage monitoring unit and, when the voltage of the capacitor is greater than the bypass switch-on voltage by the voltage monitoring unit, turning a bypass switch driving unit on, and a bypass switch turning-on operation of turning, by the bypass switch driving unit, a bypass switch on. 
     In the energy storage operation, the sub-module controller may control both the IGBT1 and the IGBT2 to be turned off to allow input energy of the sub-module to be stored in the capacitor through a first diode in a section in which a P input voltage of the sub-module is higher than an N input voltage thereof. 
     In the energy release operation, the sub-module controller may control the IGBT1 to be turned on and control the IGBT2 to be turned off to allow energy charged in the capacitor to be released to an input of the sub-module in a section in which a P input voltage of the sub-module is lower than an N input voltage thereof. 
     In the bypass operation, the sub-module controller may control the IGBT1 to be turned off and control the IGBT2 to be turned on to bypass a P input and an N input of the sub-module. 
     The bypass switch-on voltage by the voltage monitoring unit may be positioned between the bypass switch-on voltage by the sub-module controller and the capacitor limit voltage. 
     Advantageous Effects 
     In a device and a method for bypassing a high voltage direct current (HVDC) sub-module according to the present invention, even when a failure occurs in a sub-module controller in an HVDC sub-module, an additional device, which detects a voltage of a capacitor voltage in the sub-module to perform bypass, is used, thereby protecting a capacitor in the sub-module. 
     In addition, in a device and a method for bypassing an HVDC sub-module according to the present invention, a function of bypassing the HVDC sub-module can be stably performed by duplicating a driving unit of the device for bypassing an HVDC sub-module, thereby preventing an HVDC system from being disconnected due to a failure of the HVDC sub-module. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a device for bypassing a high voltage direct current (HVDC) sub-module according to one embodiment of the present invention. 
         FIG. 2  is a simplified circuit diagram illustrating an operation in which the sub-module of  FIG. 1  performs an energy storage function under insulated gate bipolar transistor (IGBT) control. 
         FIG. 3  is a simplified circuit diagram illustrating an operation in which the sub-module of  FIG. 1  performs an energy release function under IGBT control. 
         FIG. 4  is a simplified circuit diagram illustrating a bypass operation under IGBT control in the sub-module of  FIG. 1  in a section in which a P input voltage is higher than an N input voltage. 
         FIG. 5  is a simplified circuit diagram illustrating a bypass operation under IGBT control in the sub-module of  FIG. 1  in a section in which a P input voltage is lower than an N input voltage. 
         FIG. 6  is a graph showing a comparison between various voltages for controlling an operation state of the sub-module by monitoring a voltage of a capacitor of  FIG. 1 . 
         FIG. 7  is a simplified circuit diagram illustrating an operation in which bypass is performed under bypass switch control in the sub-module of  FIG. 1 . 
         FIG. 8  is a flowchart illustrating a method of bypassing an HVDC sub-module according to one embodiment of the present invention. 
     
    
    
     MODES OF THE INVENTION 
     Detailed embodiments for implementing the present invention will be described with reference to the accompanying drawings. 
     The present invention may be modified in various ways and implemented by various embodiments so that specific embodiments are illustrated in the drawings and will be described in detail below. However, it is to be understood that the present invention is not limited to the specific embodiments but includes all modifications, equivalents, and substitutions included in the spirit and the scope of the present invention. 
     Hereinafter, a device and a method for bypassing a high voltage direct current (HVDC) sub-module according to the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a block diagram illustrating a device for bypassing an HVDC sub-module according to one embodiment of the present invention, and  FIGS. 2 to 7  are detailed circuit diagrams and a graph for describing  FIG. 1  in detail. 
     Hereinafter, the device for bypassing an HVDC sub-module according to one embodiment of the present invention will be described with reference to  FIGS. 1 to 7 . 
     First, referring to  FIG. 1 , the device for bypassing an HVDC sub-module according to one embodiment of the present invention includes a sub-module which generates a voltage in an HVDC system, a bypass switch driving unit  400  which drives a bypass switch  410  positioned at an input of the sub-module, a sub-module controller  200  which monitors a state of the sub-module to transmit the monitored state to a system controller  500  and controls the sub-module and the bypass switch driving unit  400  according to a command of the system controller  500 , and a voltage monitoring unit  300  which monitors a voltage of a capacitor  150  positioned in the sub-module and controls the bypass switch driving unit  400 . 
     Here, the sub-module may include the capacitor  150  which stores and releases energy, an insulated gate bipolar transistor1 (IGBT1)  110  and a first diode  120  which are positioned between a P input of the sub-module and a positive terminal of the capacitor  150 , and an insulated gate bipolar transistor2 (IGBT2)  130  and a second diode  140  which are positioned between the P input and a negative terminal of the capacitor  150  connected to an N input of the sub-module. 
     That is, the sub-module controller  200  transmits a voltage of the capacitor  150  to the system controller  500  and receives an operation command of the sub-module from the system controller  500 . In this case, the sub-module controller  200  receives the control command from the system controller  500  and checks whether the control command indicates energy storage, energy release, or bypass. 
     In this case, when it is checked that the control command indicates the energy storage, the sub-module controller  200  controls the IGBT1  110  and the IGBT2  130  to store energy in the capacitor  150 , when it is checked that the control command indicates the energy release, the sub-module controller  200  controls the IGBT1  110  and IGBT2  130  to release energy stored in the capacitor  150 , and when it is checked that the control command indicates the bypass, the sub-module controller  200  controls the IGBT1  110  and IGBT2  130  to bypass an input thereof. 
     Meanwhile, when a voltage of the capacitor  150  is greater than or equal to a certain voltage, the sub-module controller  200  may control the bypass switch driving unit  400  to perform bypass through the bypass switch  410  at the input of the sub-module, and when bypass is not performed due to malfunction of the sub-module controller  200 , the voltage monitoring unit  300  controls the bypass switch driving unit  400  to perform bypass through the bypass switch  410  positioned at the input of the sub-module. 
     Thus, even when the sub-module controller  200  fails, the capacitor  150  can be protected by the voltage monitoring unit  300 , and a function of bypassing the HVDC sub-module can be stably performed by duplicating protection of the capacitor  150 , thereby preventing the HVDC system from being disconnected due to a failure of the HVDC sub-module. 
       FIG. 2  is a simplified circuit diagram illustrating an operation in which the sub-module of  FIG. 1  performs an energy storage function under IGBT control. 
     As can be seen in  FIG. 2 , the sub-module controller  200  controls both the IGBT1  110  and the IGBT2  130  to be turned off, thereby allowing input energy of the sub-module to be stored in the capacitor  150  through the first diode  120  in a section in which a P input voltage of the sub-module is higher than an N input voltage thereof. 
     Here, a current introduced from the P input does not flow directly to the N input by the second diode  140  because the IGBT2  130  is turned off but may be stored in the capacitor  150  through the first diode  120  because the IGBT1  110  is turned off. 
     Accordingly, whether to store energy in the capacitor  150  can be simply controlled only by controlling the IGBT1  110  and the IGBT2  130 . 
       FIG. 3  is a simplified circuit diagram illustrating an operation in which the sub-module of  FIG. 1  performs an energy release function under IGBT control. 
     As can be seen in  FIG. 3 , the sub-module controller  200  controls the IGBT1  110  to be turned on and controls the IGBT2  130  to be turned off, thereby allowing energy charged in the capacitor  150  to be released to an input of the sub-module in a section in which a P input voltage of the sub-module is lower than an N input voltage thereof. 
     Here, a current introduced from the N input may flow directly to the P input by the second diode  140  because the IGBT2  130  is turned off, but energy of the capacitor  150  may be released to the P input because a voltage of the capacitor  150  is higher than a voltage of the N input. In this case, since the IGBT1  110  is turned on, the voltage of the capacitor  150  may be released directly to the P input without the influence of the first diode  120 . 
     Accordingly, whether to release energy of the capacitor  150  can be simply controlled only by controlling the IGBT1  110  and the IGBT2  130 . 
       FIG. 4  is a simplified circuit diagram illustrating a bypass operation under IGBT control in the sub-module of  FIG. 1  in a section in which a P input voltage is higher than an N input voltage. 
     As can be seen in  FIG. 4 , in the section in which the P input voltage of the sub-module is higher than the N input voltage thereof, the sub-module controller  200  controls the IGBT1  110  to be turned off and controls the IGBT2  130  to be turned on, thereby allowing a P input current to be bypassed to an N input. 
     Here, a current introduced from the P input may flow directly to the N input because the IGBT2  130  is turned on, and thus, the voltage of the capacitor  150  may be prevented from being released to the P input by the first diode  120 . 
     Accordingly, only by controlling the IGBT1  110  and IGBT2  130 , storage may not be performed in a storage section of the sub-module, and bypass may be simply performed without release of energy of the capacitor  150 . 
       FIG. 5  is a simplified circuit diagram illustrating a bypass operation under IGBT control in the sub-module of  FIG. 1  in a section in which a P input voltage is lower than an N input voltage. 
     As can be seen in  FIG. 5 , in the section in which the P input voltage of the sub-module is lower than the N input voltage thereof, the sub-module controller  200  controls all of the IGBT1  110  and the IGBT2  130  to be turned off or controls the IGBT1  110  to be turned off and controls the IGBT2  130  to be turned on, thereby allowing an N input current to be bypassed to a P input. 
     Here, a current introduced from the N input may flow directly to the P input through the second diode  140  because the IGBT2  130  is turned off, and thus, the voltage of the capacitor  150  may be prevented from being released to the P input by the first diode  120 . 
     Accordingly, only by controlling the IGBT1  110  and IGBT2  130 , release may not be performed in a release section of the sub-module, and bypass may be simply performed without release of energy of the capacitor  150 . 
       FIG. 6  is a graph showing a comparison between various voltages for controlling an operation state of the sub-module by monitoring a voltage of the capacitor  150  of  FIG. 1 . 
     As can be seen in  FIG. 6 , when a voltage of the capacitor  150  exceeds a bypass switch-on voltage V 830  by the sub-module controller positioned between an operating voltage V 840  and a capacitor limit voltage V 810 , the sub-module controller  200  may control the bypass switch driving unit  400  to perform bypass at the input of the sub-module. 
     In addition, in a case in which bypass is not performed due to an error even when the voltage of the capacitor  150  exceeds the bypass switch-on voltage V 830  by the sub-module controller positioned between the bypass switch-on voltage V 830  by the sub-module controller and the capacitor limit voltage V 810 , when the voltage of the capacitor  150  exceeds a bypass switch-on voltage V 820  by the voltage monitoring unit, the voltage monitoring unit  300  controls the bypass switch driving unit  400  to perform bypass at the input of the sub-module. 
     The bypass switch-on voltage V 820  by the voltage monitoring unit may be set to be positioned between the bypass switch-on voltage V 830  by the sub-module controller and the capacitor limit voltage V 810 . 
     That is, even when the sub-module controller  200 , which primarily performs bypass, operates abnormally, the voltage monitoring unit  300  can detect the voltage of the capacitor  150  to perform bypass so that a function of bypassing the HVDC sub-module can be stably performed to prevent the HVDC system from being disconnected due to a failure of the HVDC sub-module. 
       FIG. 7  is a simplified circuit diagram illustrating an operation in which bypass is performed under bypass switch control in the sub-module of  FIG. 1 . 
     As can be seen in  FIG. 7 , the bypass switch  410  may be connected between a P input and an N input of the sub-module, and thus, under control of the bypass switch driving unit  400 , the P input and the N input may be bypassed. 
     Thus, the capacitor  150  is prevented from being overcharged, and a function of bypassing the sub-module is stably performed when the sub-module fails, thereby preventing the HVDC system from being disconnected due to a failure of the HVDC sub-module. 
       FIG. 8  is a flowchart illustrating a method of bypassing an HVDC sub-module according to one embodiment of the present invention. 
     As can be seen in  FIG. 8 , the method of bypassing an HVDC sub-module according to the present invention includes receiving, by a sub-module controller  200 , a control command of a sub-module from a system controller  500  (S 100 ), controlling, by the sub-module controller  200 , an IGBT1  110  and an IGBT2  130  of the sub-module to construct a path through which energy is storable in a capacitor  150  in the sub-module when the control command indicates energy storage (S 210 ), controlling, by the sub-module controller  200 , the IGBT1  110  and the IGBT2  130  of the sub-module to construct a path through which energy of the capacitor  150  in the sub-module is releasable when the control command indicates energy release (S 220 ), controlling, by the sub-module controller  200 , the IGBT1  110  and the IGBT2  130  of the sub-module to block a path with the capacitor  150  in the sub-module and construct a bypass path when the control command indicates bypass (S 230 ), transmitting the voltage of the capacitor  150  to the system controller  500  when it is checked whether a voltage of the capacitor  150  in the sub-module is greater than a bypass switch-on voltage V 830  by the sub-module controller (S 310 ) and the voltage of the capacitor  150  is less than the bypass switch-on voltage V 830  by the sub-module controller (S 300 ), comparing the voltage of the capacitor  150  in the sub-module with a bypass switch-on voltage V 820  by a voltage monitoring unit when the voltage of the capacitor  150  in the sub-module is greater than the bypass switch-on voltage (V 830 ) by the sub-module controller (S 410 ), and turning a bypass switch driving unit  400  on when the voltage of the capacitor  150  is greater than the bypass switch-on voltage V 820  by the voltage monitoring unit (S 400 ), and turning, by the bypass switch driving unit  400 , a bypass switch  410  on (S 500 ). 
     In this case, in energy storage operation S 210 , the sub-module controller  200  may control both the IGBT1  110  and the IGBT2  130  to be turned off, thereby allowing input energy of the sub-module to be stored in the capacitor  150  through a first diode  120  in a section in which a P input voltage of the sub-module is higher than an N input voltage thereof. 
     In addition, in energy release operation S 220 , the sub-module controller  200  controls the IGBT1  110  to be turned on and controls the IGBT2  130  to be turned off, thereby allowing energy charged in the capacitor  150  to be released to an input of the sub-module in a section in which the P input voltage of the sub-module is lower than the N input voltage thereof. 
     In addition, in bypass operation S 230 , the sub-module controller  200  controls the IGBT1  110  to be turned off and controls the IGBT2  130  to be turned on, thereby allowing a P input and an N input to be bypassed. 
     Here, the bypass switch-on voltage V 820  by the voltage monitoring unit may be positioned between the bypass switch-on voltage V 830  by the sub-module controller and a capacitor limit voltage V 810 . 
     According to the method of bypassing an HVDC sub-module of the present invention as described above, when a voltage of the capacitor  150  is greater than or equal to a certain voltage, the sub-module controller  200  may control the bypass switch driving unit  400  to perform bypass through the bypass switch  410  at an input of the sub-module, and even when bypass is not performed due to malfunction of the sub-module controller  200 , the voltage monitoring unit  300  controls the bypass switch driving unit  400  to perform bypass through the bypass switch  410  positioned at the input of the sub-module. 
     As described above, in a device and a method for bypassing an HVDC sub-module according to the present invention, even when a failure occurs in a sub-module controller in an HVDC sub-module, an additional device, which detects a voltage of a capacitor voltage in the sub-module to perform bypass, is used, thereby protecting a capacitor in the sub-module. In addition, a function of bypassing the HVDC sub-module can be stably performed by duplicating a driving unit of the device for bypassing an HVDC sub-module, thereby preventing an HVDC system from being disconnected due to a failure of the HVDC sub-module. 
     What has been described above includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purpose of describing the above-described embodiments but it can be perceived that those skilled in the art may make many additions and replacements of various embodiments. Accordingly, the described embodiments include all alternatives, modifications, and changes without departing from the spirit and scope of the present invention as defined in the following claims. 
     INDUSTRIAL AVAILABILITY 
     The present invention relates to a device and a method for bypassing an HVDC submodule and is available in an HVDC field.