Abstract:
A device includes a first thyristor element configured to be coupled to a first voltage line and a second voltage line, wherein the first voltage line is configured to transmit power in a first phase and the second voltage line is configured to transmit power in a second phase. The device includes a second thyristor element configured to be coupled to the second voltage line and a third voltage line, wherein the third voltage line is configured to transmit power in a third phase. The device includes a third thyristor element configured to be coupled to the first voltage line and the third voltage line.

Description:
[0001]    The subject matter disclosed herein relates to a device and system for reducing damages to a voltage converter of a power generation system caused by an overvoltage condition. 
         [0002]    Modern power systems are becoming increasingly interconnected to each other. For example, power generation systems, such as wind or solar power generation plants, may connect to a network or grid to provide power usable by one or more customers. However, voltages from the grid may cause an overvoltage condition on the power generation systems from that same grid, which may lead to damage of the power generation system. Accordingly, a circuit, such as a crowbar circuit, may be implemented between the grid and the power generation system. However, as the crowbar circuit may add overhead, for example, in the form of space and cost, it may be desirable to implement a simplified crowbar circuit that can protect the power generation system from damage caused by overvoltage condition from the grid at the power generation system. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
         [0004]    In one embodiment, a device includes a first thyristor element configured to be coupled to a first voltage line and a second voltage line, wherein the first voltage line is configured to transmit power in a first phase and the second voltage line is configured to transmit power in a second phase, a second thyristor element configured to be coupled to the second voltage line and a third voltage line, wherein the third voltage line is configured to transmit power in a third phase, and a third thyristor element configured to be coupled to the first voltage line and the third voltage line. 
         [0005]    In a second embodiment, system includes a controller configured to transmit a first activation signal to activate a first thyristor element coupled to a first voltage line and a second voltage line, wherein the first voltage line is configured to transmit power in a first phase and the second voltage line is configured to transmit power in a second phase, transmit a second activation signal to activate a second thyristor element coupled to the second voltage line and a third voltage line, wherein the third voltage line is configured to transmit power in a third phase, and transmit a third activation signal to activate a third thyristor element coupled to the first voltage line and the third voltage line. 
         [0006]    In a third embodiment, a non-transitory computer readable medium includes computer-readable instructions to cause a controller to receive input signals related to power passing through a power line, and generate an activation signal configured to activate a first thyristor element coupled to a first voltage line and a second voltage line, wherein the first voltage line is configured to transmit power in a first phase and the second voltage line is configured to transmit power in a second phase, activate a second thyristor element coupled to the second voltage line and a third voltage line, wherein the third voltage line is configured to transmit power in a third phase, and activate the third thyristor element coupled to the first voltage line and the third voltage line; and transmit the activation signal to each of the first thyristor element, the second thyristor element, and the third thyristor element simultaneously. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  is a block diagram of a power network that includes a crowbar circuit, in accordance with an embodiment; 
           [0009]      FIG. 2  is an equivalent block diagram of the power network of  FIG. 1  whereby the crowbar circuit is activated, in accordance with an embodiment; 
           [0010]      FIG. 3  is a block diagram of a power network that includes a second crowbar circuit, in accordance with a second embodiment; and 
           [0011]      FIG. 4  is an equivalent block diagram of the power network of  FIG. 3  whereby the second crowbar circuit is activated, in accordance with the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0013]    When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0014]    The disclosed embodiments relate to a power network that includes a crowbar circuit located between a power generation system, such as wind or solar power generation plant, and a network electricity grid. The crowbar circuit may aid in reducing the propensity an overvoltage or overcurrent condition reaching a power generation system, or of a converter coupled thereto, which might otherwise damage the power generation system and/or the converter. In one embodiment, the crowbar may utilize a thyristor for each voltage line carrying voltage of a distinct phase. For example, three thyristors, such as silicon controlled rectifiers, may be utilized to short circuit voltage being transmitted from a grid to a power generation system in a three-phase power system. This may be accomplished by aligning the thyristors such that every thyristor is connected to two voltage lines carrying voltage of differing phases. In this manner, three-phase voltage being transmitted on separate voltage lines may be transmitted through at least one of the thyristors, regardless of its phase, to short circuit the voltage lines when a fault has been detected. 
         [0015]    With the foregoing in mind,  FIG. 1  represents a power network  100 . The power network  100  may include a power generation system  102 . The power generation system  102  may represent one or more power plants powered by, for example, wind turbines, solar energy, nuclear fission, burning of fossil fuels (such as coal or natural gas), or the like. Accordingly, power generation system  102  may generate electricity for transmission to the power network  100  via a power grid  104 , which may include, for example, power lines (e.g., high voltage power lines), substations (e.g., to step down voltage of the electricity received), and distribution lines (e.g., power lines that distribute electricity from the substation to residential and/or commercial customers). 
         [0016]    Prior to electricity being transmitted to the power grid  104 , the electricity generated by the power generation system  102  may be transmitted through a converter  106  and through inductance elements  108 ,  110 , and  112  on voltage lines  114 ,  116 , and  116 , respectively. The converter  106  may include, for example, voltage conversion elements, such as one or more step up and/or step down transformers that may alter the voltage generated by the power generation system  102  to a desired voltage for transmission on the grid  104 . Additionally or alternatively, the converter  106  may include an inverter to convert the voltage received from the power generation system  102  from direct current to alternating current. This inverter may be, for example, a three-level bridge inverter utilizing, for example, Neutral-Point-Clamp topology or Neutral-Point-Pivot topology. In another embodiment, the inverter may be, for example, a two-level bridge inverter. Through utilization of an inverter in the converter  106 , power transmitted from the converter  106  may be alternating current (AC) power that may be transmitted at, for example, approximately 50 Hz or 60 Hz at approximately, for example, 1 megawatt, 3 megawatts, 5 megawatts, or more. 
         [0017]    Moreover, the power transmitted from the converter  106  may be, for example, three-phase power. That is, three voltage lines  114 ,  116 , and  118  are present in  FIG. 1  to denote that the power transmitted from the power generation system  102  has been converted by the converter  106  to three-phase power AC power, for example. Three-phase power may include power with three alternating currents (e.g., of the same frequency), such that each of the currents reaches its instantaneous peak value at a time different than the other two currents. For example, the power transmitted on power line  114  may be referred to phase A power, the power transmitted on power line  116  may be referred to phase B power, and the power transmitted on power line  118  may be referred to phase C power. Taking phase A power as a reference, phase B power may be delayed in time by one-third of one cycle. Similarly, Phase C power may be delayed in time by one-third of one cycle from phase B power and two-thirds of one cycle from phase A power. That is, phase A, B, and C power may be out of phase by 120° from each other. 
         [0018]    Returning to  FIG. 1 , inductance elements  108 ,  110 , and  112  may be present on voltage lines  114 ,  116 , and  118 , respectively. These inductance elements  108 ,  110 , and  112  may model line impedances inherently present on voltage lines  114 ,  116 , and  118  and/or may represent transformers for transforming the voltage from the converter  106  prior to transmission on the grid  104 . In one embodiment, the impedance values of the inductance elements  108 ,  110 , and  112  may be approximately, for example, between 20 μH and 200 μH. In another embodiment, the impedance values of the inductance elements  108 ,  110 , and  112  may be approximately, for example, 20 μH, 30 μH, 40 μH, 50 μH, 60 μH, 70 μH, 80 μH, 90 μH, 100 μH, 125 μH, 150 μH, 175 μH, or 200 μH. 
         [0019]    While power may flow from the power generation system  102  to the converter  106  to the grid  104 , in some circumstances, power may also flow from the grid  104  into the converter  106 . This may lead to damage as well as failures of the converter  106  and/or elements in the power generation system  102 . To avoid these damages from occurring, a crowbar circuit  120  may be implemented. In some embodiments, the crowbar circuit  120  may include switching elements  122 ,  124 , and  126 , crowbar inductance elements  128 ,  130 , and  132 , filter elements  134 ,  136 , and  138 , and thyristor elements  140 ,  142 ,  144 ,  146 ,  148 , and  150 . 
         [0020]    The switching elements  122 ,  124 , and  126  may be switches that cause an open circuit to occur on voltage lines  114 ,  116 , and  118 . For example, the switching circuits  122 ,  124 , and  126  may each include one or more fuses that blow when, for example, excess current is passed through the fuse, causing an open circuit to occur on voltage lines  114 ,  116 , and  118  between the grid  104  and the converter  106 . In another embodiment, the switching elements  122 ,  124 , and  126  may each include a circuit breaker. This circuit breaker may be an electrical switch designed to automatically detect a fault condition and interrupt continuity of the voltage lines  114 ,  116 , and  118 . Alternatively, the circuit breaker may receive a signal that causes the circuit breaker to trip, causing an interrupt continuity of the voltage lines  114 ,  116 , and  118 . By interrupting continuity of the voltage lines  114 ,  116 , and  118 , an open circuit is generated, thus discontinuing electrical flow between the grid  104  and the converter  106 . 
         [0021]    As noted above, the crowbar circuit  120  may also include crowbar inductance elements  128 ,  130 , and  132 . Crowbar inductance elements  128 ,  130 , and  132  may represent, for example, line impedances inherently present in voltage lines  164 ,  166 , and  168 . In one embodiment, crowbar inductance elements  128 ,  130 , and  132  may range from approximately 5 μH to 40 μH. In another embodiment, the impedance values of the inductance elements  128 ,  130 , and  132  may be approximately, for example, 5 μH, 10 μH, 15 μH, 20 μH, 25 μH, 30 μH, 35 μH, or 40 μH. 
         [0022]    Additionally, the crowbar circuit may include filter elements  134 ,  136 , and  138 . Alternatively, filter elements  134 ,  136 , and  138  may instead reside in the converter  106 . The filter elements  134 ,  136 , and  138  may operate to reduce the frequency of the alternating current exiting the converter  106 . For example, the power transmitted from the converter  106  may be alternating current (AC) power at, for example, approximately 50 Hz or 60 Hz. Each of the filter elements  134 ,  136 , and  138  may eliminate higher spectral components from signal spectra provided to it. In this manner, the filtering elements  134 ,  136 , and  138  operate to provide three-phase power at approximately 480V, 690V, 1380V, or another voltage at approximately 60 Hz to the grid  104 . Each of the filter elements  134 ,  136 , and  138  have been modeled as impedances in  FIG. 1  and, in one embodiment, the impedance values for each of the filter elements  134 ,  136 , and  138  may range between approximately, for example, 100 and 300 μH. 
         [0023]    As described above, the crowbar circuit  120  includes switching elements  122 ,  124 , and  126  that may operate to generate an open circuit to cut off the electrical connection between the converter  106  and the grid  104 . However, this process may take, for example, approximately 100 milliseconds to occur. During this time, the converter  106  may be exposed to a power surge that may impair operation of or otherwise damage the converter  106 . Accordingly, the crowbar circuit  120  may also include thyristor elements  140 ,  142 ,  144 ,  146 ,  148 , and  150  to aid in protection of the converter  106  and power generation system  102  from power flowing from the grid  104 . 
         [0024]    The thyristor elements  140 ,  142 ,  144 ,  146 ,  148 , and  150  (hereinafter referred to collectively as thyristor elements  140 - 150 ) may operate by generating a short circuit (e.g., a low resistance path) across a voltage source (such as the grid  104 ). In one embodiment, the thyristor elements  140 - 150  may be regenerative gating devices, such as silicon controlled rectifiers (SCRs), integrated gate commutated thyristors (IGCTs), gate turn-off thyristors (GTOs), or other similar semiconductor devices. These thyristor elements  140 - 150  may act as gated bistable switches, whereby the thyristor elements  140 - 150  conduct current when their respective gates receive a current trigger and continue to conduct current while forward biased. 
         [0025]    Accordingly, each of the thyristor elements  140 - 150  is coupled to a gate drive element,  152 ,  154 ,  156 ,  158 ,  160 , or  162  (hereinafter collectively referred to as gate drive elements  152 - 162 ). These gate drive elements  152 - 162  may provide a signal to the gates of the respective thyristor elements  140 - 150  associated therewith to activate the thyristor elements  140 - 150 . Thus, when the thyristor elements  140 - 150  are activated by the gate drive elements  152 - 162 , current may flow through voltage lines  164 ,  166 , and  168 . 
         [0026]    In one embodiment, the activation of the gate drive elements  152 - 162  is controlled by a controller  170 . This controller  170  may include one or more microprocessors, such as one or more “general-purpose” microprocessors, one or more special-purpose microprocessors and/or ASICS, or some combination thereof. Furthermore, the controller  170  may execute one or more algorithms, which may be stored on a tangible non-transitory machine readable medium, such as volatile memory (e.g., random access memory), and/or non-volatile memory (e.g. read-only memory). This memory may be internal to or directly coupled to the controller  170 . 
         [0027]    Moreover, the controller  170  may be coupled to various elements via signal lines  172 ,  174 , and  176 . For example, signal line  172  allows the controller  170  to receive signals from a sensor  178 . These signals received from the sensor  178  may indicate, for example, that power has been measured passing from the grid  104  towards the crowbar circuit  120 . Accordingly, one step of an algorithm that may be executed by the controller  170  is to receive these signals from the sensor  178 . The algorithm may also include instructions for determining if the received signals indicate that power above a threshold has been reached. A subsequent step of the algorithm executed by the controller  170  (subsequent to determining that either signals have been received or that the signals exceed a threshold) may include instructions that cause the controller  170  to send a signal along path  174  to each of the switching elements  122 ,  124 , and  126 . This signal sent to the switching elements  122 ,  124 , and  126  may cause the switching elements  122 ,  124 , and  126  to interrupt the continuous connection (e.g., break) in the electrical path between the grid  104  and the converter  106 . 
         [0028]    Simultaneous to or before sending the signal to the switching elements  122 ,  124 , and  126 , the algorithm executed by the controller  170  may include instructions that cause the controller  170  to send a signal along path  176  to each of the gate drive elements  152 - 162 . This signal sent along path  174  cause the gate drive elements  152 - 162  to activate the thyristor elements  140 - 150  simultaneously. Activation of the thyristor elements  140 - 150  may cause a short circuit to occur in the crowbar circuit  120  faster than the switching elements  122 ,  124 , and  126  may be activated to generate an open circuit. In one embodiment, the activation of the thyristor elements  140 - 150  may be accomplished in approximately, for example, between 50 microseconds and 100 microseconds. In another embodiment, activation of the thyristor elements  140 - 150  may be accomplished in less than or equal to approximately, for example, 50 microseconds, 60 microseconds, 70 microseconds, 80 microseconds, 90 microseconds, 100 microseconds. 
         [0029]    It should be noted that the thyristor elements  140 - 150  of the crowbar circuit  120  are grouped into pairs. For example, thyristor elements  140  and  142  are coupled to voltage line  164  to receive, for example, phase A voltage, thyristor elements  144  and  146  are coupled to voltage line  166  to receive, for example, phase B voltage, and thyristor elements  148  and  150  are coupled to voltage line  168  to receive, for example, phase C voltage. In this setup, regardless of whether the voltage along voltage lines  164 ,  166 , and  168  is positive or negative, when the thyristor elements  140 - 150  are activated by the gate drive elements  152 - 162 , current flows through one of the thyristor elements  140 - 150  in each group. For example, if the phase A voltage on voltage line  164  is positive when gating elements  152  and  154  are activated, voltage passes through thyristor  140  while being resisted by thyristor  142 . Conversely, if the phase A voltage on voltage line  164  is negative when gating elements  152  and  154  are activated, voltage passes through thyristor  142  while being resisted by thyristor  140 . This process occurs for each of the pairs of thyristor elements  140 - 150 , allowing short circuits to be generated regardless of the polarity (e.g., positive or negative) of the voltage transmitted along power lines  164 ,  166 , and  168 . The result of activation of the thyristor elements  140 - 150  may be seen with respect to  FIG. 2 . 
         [0030]      FIG. 2  illustrates an equivalent circuit diagram of the power network  100  after the thyristor elements  140 - 150  have been activated. As illustrated, voltage lines  164 ,  166 , and  168  each carry current generated by equivalent voltage sources  180 ,  182 , and  184  to the crowbar inductance elements  128 ,  130 , and  132 . The currents carried on voltage lines  164 ,  166 , and  168  may be approximately, for example, 10000 amps, 20000 amps, 30000 amps, 40000 amps, 50000 amps, 60000 amps, 70000 amps, 80000 amps, 90000 amps, 100000 amps, or more. In contrast, the current passing through the voltage lines  114 ,  116 , and  118  to the converter  106  may be as small as, for example, approximately 100 amps. This condition may continue until the switching elements  122 ,  124 , and  126  interrupt the continuous connection (e.g., break) the electrical path between the grid  104  and the converter  106  (e.g., approximately 100 milliseconds). Accordingly, during this time, the thyristor elements  140 - 150  discussed in  FIG. 1  operate as shorting devices in crowbar circuit  120 . 
         [0031]      FIG. 3  represents another embodiment of the power network  100 . The power network  100 , similar to that disclosed in  FIG. 1 , may include a power generation system  102 , a grid  104 , a converter  106 , inductance elements  108 ,  110 , and  112  on voltage lines  114 ,  116 , and  116 , controller  170 , signal lines  172 ,  174 , and  176 , and a sensor  178 , each of which operates as previously discussed. 
         [0032]    Additionally,  FIG. 3  includes a crowbar circuit  186 . The crowbar circuit  186  is similar to crowbar circuit  120  in that it includes switching elements  122 ,  124 , and  126 , crowbar inductance elements  128 ,  130 , and  132 , filter elements  134 ,  136 , and  138 , and voltage lines  164 ,  166 , and  168 , each of which operates as previously discussed with respect to the crowbar circuit  120 . However, crowbar circuit  186  differs from crowbar circuit  120  in the number and arrangement of the thyristor elements present therein. 
         [0033]    Crowbar circuit  186  includes a thyristor element  188  coupled to voltage lines  164  and  166 , a thyristor element  190  coupled to voltage lines  166  and  168 , and a thyristor element  192  coupled to voltage lines  164  and  168 . The thyristor elements  188 ,  190 , and  192  may operate by generating a short circuit or low resistance path across a voltage source (such as the grid  104 ). In one embodiment, the thyristor elements  188 ,  190 , and  192  may be regenerative gating devices, such as silicon controlled rectifiers (SCRs), integrated gate commutated thyristors (IGCTs), gate turn-off thyristors (GTOs), or other similar semiconductor devices. As such, the thyristor elements  188 ,  190 , and  192  may act as gated bistable switches, such that they conduct when their gate receives a current trigger and continue to conduct while they remain forward biased. Accordingly, each of the thyristor elements  188 ,  190 , and  192  is coupled to a gate drive element,  192 ,  194 , or  196 , respectively. These gate drive elements  192 ,  194 , and  196  may provide a signal to the respective thyristor elements  188 ,  190 , and  192  associated therewith to activate the thyristor elements  188 ,  190 , and  192  when a signal along path  176  from controller  170  is received at each of the gate drive elements  192 ,  194 , and  196 . Accordingly, when the thyristor elements  188 ,  190 , and  192  are activated, current may flow through voltage lines  164 ,  166 , and  168 . 
         [0034]    In contrast to the crowbar circuit  120  of  FIG. 1 , crowbar circuit  186  does not include thyristor elements grouped into pairs. Instead each of the thyristor elements  188 ,  190 , and  192  of the crowbar  186  are connected to two of the voltage lines  164 ,  166 , or  168 . For example, thyristor element  188  may be placed between voltage lines  164  and  166 , such that when phase A voltage on voltage line  164  is negative and/or when phase B voltage on voltage line  166  is positive when gating element  194  is activated, voltage passes through thyristor element  188  to cause a short circuit. Similarly, thyristor element  190  may be placed between voltage lines  166  and  168 , such that when phase B voltage on voltage line  164  is negative and/or when phase C voltage on voltage line  168  is positive when gating element  196  is activated, voltage passes through thyristor element  190  to cause a short circuit. Likewise, thyristor element  192  may be placed in between voltage lines  164  and  168 , such that when phase A voltage on voltage line  164  is positive and/or when phase C voltage on voltage line  168  is negative when gating element  198  is activated, voltage passes through thyristor element  192  to cause a short circuit. In this manner, three phase voltage on separate voltage lines (e.g., voltage lines  114 ,  116 , and  118 ) may be transmitted through at least one of the thyristor elements  188 ,  190 , and  192 , regardless of the phase of the voltage, to short circuit the voltage lines  114 ,  116 , and  118 . That is, regardless of whether the voltage along voltage lines  164 ,  166 , and  168  is positive or negative, activation of the thyristor elements  188 ,  190 , and  192  by the gate drive elements  194 ,  196 , and  198  causes current to flow through the respective thyristor elements  194 ,  196 , and  198 . This process allows short circuits to be generated regardless of the polarity (e.g., positive or negative) of the voltage transmitted along power lines  164 ,  166 , and  168  with a reduced number of thyristor elements  194 ,  196 , and  198  and gate drive elements  194 ,  196 , and  198  relative to the crowbar circuit  120 . The result of activation of the thyristor elements  194 ,  196 , and  198  may be seen with respect to  FIG. 4 . 
         [0035]      FIG. 4  illustrates an equivalent circuit diagram of the power network  100  of  FIG. 3  after the thyristor elements  194 ,  196 , and  198  have been activated. As illustrated, voltage lines  164 ,  166 , and  168  each carry current generated by equivalent voltage sources  180 ,  182 , and  184  to the crowbar inductance elements  128 ,  130 , and  132 . The currents carried on voltage lines  164 ,  166 , and  168  may be approximately, for example, 10000 amps, 20000 amps, 30000 amps, 40000 amps, 50000 amps, 60000 amps, 70000 amps, 80000 amps, 90000 amps, 100000 amps, or more. In contrast, the current passing through the voltage lines  114 ,  116 , and  118  to the converter may be as small as, for example, approximately 100 amps. This condition may continue until the switching elements  122 ,  124 , and  126  interrupt the continuous connection (e.g., break) the electrical path between the grid  104  and the converter  106  (e.g., approximately 100 milliseconds). During this time, the thyristor elements  194 ,  196 , and  198  discussed with respect to  FIG. 3  operate as shorting devices in the power network  100 . In this manner, the crowbar circuit  186  may achieve the same result as crowbar circuit  120  with an overall reduction in the number of thyristors and gate drive circuits, thus leading to less complexity, size, cost, and greater reliability of the crowbar circuit  186  relative to the crowbar circuit  120 . 
         [0036]    This written description uses examples to disclose the invention, including the best mode, and also to allow any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.