Patent Description:
For the purposes of clearly, concisely and exactly describing non-limiting exemplary embodiments of the disclosure, the manner and process of making and using the same, and to enable the practice, making and use of the same, reference will now be made to certain exemplary embodiments, including those illustrated in the figures, and specific language will be used to describe the same. It shall nevertheless be understood that no limitation of the scope of the present disclosure is thereby created, and that the present disclosure includes and protects such alterations, modifications, and further applications of the exemplary embodiments as would occur to one skilled in the art with the benefit of the present disclosure.

The present invention is defined in the appended independent claims <NUM> and <NUM>. Embodiments of the invention include systems, methods, techniques and apparatuses for high current protection which are defined in the appended dependent claims. Further embodiments, forms, objects, features, advantages, aspects and benefits of the disclosure shall become apparent from the following description and drawings.

With reference to <FIG>, there is illustrated an exemplary power system <NUM> including a solid-state circuit breaker <NUM> coupled between power networks <NUM> and <NUM>. Solid-state circuit breaker <NUM> is structured to conduct alternating current or direct current between networks <NUM> and <NUM>. In certain embodiments, power networks <NUM> and <NUM> are portions of a utility grid, a microgrid, or a motor control center, to name but a few examples.

Solid-state circuit breaker <NUM> includes a galvanic isolation switching device <NUM> coupled in series with a solid-state switching device <NUM>. Galvanic isolation switching device <NUM> may be structured to open while device <NUM> is not conducting a current. In certain embodiments, galvanic isolation switching device <NUM> is a mechanical disconnector, to name but one example.

Solid-state switching device <NUM> is structured to selectively conduct current from power network <NUM> to power network <NUM>, and from power network <NUM> to power network <NUM>. In the illustrated embodiment, solid-state switching device <NUM> includes two branches coupled in an anti-parallel configuration, each branch including a diode and an integrated gate-commutated thyristor (IGCT). In certain embodiments, the IGCTs may be replaced by a reverse-blocking IGCT (RB-IGCT). In other embodiments, solid-state switching device <NUM> may include a different topology and different components. For example, solid-state switching device <NUM> may include RB-IGCTs, insulated gate bipolar transistors (IGBTs), bipolar junction transistors (BITs), metal-oxide-semiconductor field-effect transistors (MOSFETs), gate turn-off thyristors (GTOs), MOS-controlled thyristors (MCTs), silicon carbide (SiC) switching devices, gallium nitride (GaN) switching devices, or any other type of semiconductor-based switching device structured to block or interrupt the conduction of current.

Solid-state circuit breaker <NUM> includes an energy dissipation branch <NUM> coupled in parallel with solid-state switching device <NUM>. Energy dissipation branch <NUM> is structured to dissipate energy accumulated from toggling solid-state switching device <NUM>. In the illustrated embodiment, energy dissipation branch <NUM> includes a voltage dependent resistor <NUM> which is configured and provided as a metal-oxide varistor (MOV) in the illustrated embodiment, but may comprise a silicon carbide varistor, selenium cells, or other types of voltage-dependent resistors or voltage clamping elements or arrangements.

Solid-state circuit breaker <NUM> includes an assistive branch <NUM> coupled in parallel with solid-state switching device <NUM> and energy dissipation branch <NUM>. Assistive branch <NUM> is structured to conduct current having a reduced magnitude while solid-state switching device <NUM> is open and structured to assist the continuous or intermittent current limiting of the solid-state switching device <NUM>. Assistive branch <NUM> includes a switching device <NUM>, an inductor <NUM>, and a resistor <NUM>. Switching device <NUM> may be any type of switching device structured to selectively conduct current. For example, switching device <NUM> may be a mechanical circuit breaker, to name but one example. The inductor <NUM> is selected to have an inductance on the order of mH, for example, less than 1mH for DC applications and a few mH for AC applications, the inductance of inductor <NUM> being much lower than the system inductance in DC and AC applications. Inductor <NUM> and resistor <NUM> are structured to provide an impedance that share a portion of the current flow with the energy dissipation branch <NUM> when the solid-state switching device <NUM> is off. Inductor <NUM> is structured to provide an AC impedance to limit the time rate of change of current through assistive branch <NUM>. Resistor <NUM> is structured to provide a resistance to dissipate energy and reduce a magnitude of current conducted through assistive branch <NUM>.

Solid-state circuit breaker <NUM> includes a controller <NUM> structured to operate the controllable devices of solid-state circuit breaker <NUM> to prevent overcurrent and overheat damages during faults and transients. Controller <NUM> may include measuring devices structured to measure electrical characteristics of the current conducted by solid-state circuit breaker <NUM>, such as current magnitudes or voltage magnitudes, to name but a few examples. It is important to note that controller <NUM> operates solid-state circuit breaker <NUM> to perform the conventional function of a circuit breaker, i.e. opening in order to interrupt a high current, but also performs additional functions described herein, such operating solid-state circuit breaker <NUM> to limit current conducted by solid-state circuit breaker <NUM> and identifying a source of high current before responding to the high current, to name but a few examples. Controller <NUM> operates solid-state circuit breaker <NUM> in one of four modes: a normal mode, a continuous current limiting mode, an intermittent current limiting mode, and a protection mode.

In normal mode, solid-state switching device <NUM> and galvanic isolation switching device <NUM> are closed, allowing a nominal current to be conducted through solid-state circuit breaker <NUM> by way of solid-state switching device <NUM>. Switching device <NUM> is also closed, but due to resistor <NUM> and inductor <NUM>, only a small portion of the nominal current is conducted through assistive branch <NUM>.

In continuous current limiting mode, solid-state switching device <NUM> is open, galvanic isolation switching device <NUM> is closed, and switching device <NUM> is closed. Current previously conducted through solid-state switching device <NUM> is now conducted by energy dissipation branch <NUM> and assistive branch <NUM>, causing some of the energy of the current to dissipate, thereby reducing the magnitude of the high magnitude current. The maximum current magnitude reduction is determined by the sizing of resistor <NUM>. For example, resistor <NUM> may be structured to limit the magnitude of current conducted through solid-state circuit breaker <NUM> in continuous current limiting mode to <NUM> times the nominal current, to name but one example.

In intermittent current limiting mode, galvanic isolation switching device <NUM> and switching device <NUM> remain closed while solid-state switching device <NUM> is repeatedly toggled, resulting in intermittent current conducted through solid-state switching device <NUM>, energy dissipation branch <NUM>, and assistive branch <NUM>. Controller <NUM> is configured to operate the solid-state switching device <NUM> by transmitting a series of pulses having variable pulse widths and variable pulse rates. The pulse widths and pulse rates are varied in order for the output current of solid-state circuit breaker <NUM> to be conformed to a current reference value. The current reference value is a current magnitude limit and may include both a current magnitude maximum and a current magnitude minimum. As the current reference value decreases, the pulse rate increases. In addition to the current reference value, operating conditions such as system inductance influence the pulse rate and pulse width. For example, as system inductance increases, pulse rate decreases and pulse width increases. Controller <NUM> may also determine the pulse rate and pulse width based on factors including time current curves, total harmonic distortion requirements, power level requirements, and protection level, to give but a few examples.

As a result of the toggling of solid-state switching device <NUM>, controller <NUM> can reduce the magnitude of the current conducted by solid-state circuit breaker <NUM> further than the reduction of magnitude during the continuous current limiting mode. For example, while the continuous current limiting mode might reduce a current to <NUM> times the nominal current, intermittent current limiting mode could reduce the same current to a value between. <NUM> and <NUM> times the nominal current, to give but one example.

During intermittent current limiting mode, current is shared by energy dissipation branch <NUM> and assistive branch <NUM> due to the sizing of resistor <NUM>. For example, resistor <NUM> may be sized so that equal portions of energy of a high magnitude current are dissipated by energy dissipation branch <NUM> and assistive branch <NUM> while operating solid-state switching device <NUM> in the intermittent current limiting mode. In another example, resistor <NUM> may be sized such that both energy dissipation branch <NUM> and assistive branch <NUM> conduct at least <NUM>% of the high magnitude current, to give but one example. In still another example, resistor <NUM> is sized so that the amount of energy dissipated by energy dissipation branch <NUM> is within <NUM>% of the energy dissipated by assistive branch <NUM> while operating solid-state switching device <NUM> in the intermittent current limiting mode.

In protection mode, solid-state switching device <NUM> and switching device <NUM> are opened, interrupting the current being conducted by solid-state circuit breaker <NUM>. Galvanic isolation switching device <NUM> is also opened at a predetermined time after switching devices <NUM> and <NUM> are opened, in order to ensure galvanic isolation switching device <NUM> is not conducting current while it is opening. It shall be appreciated that any or all of the foregoing features of solid-state circuit breaker <NUM> may also be present in the other solid-state circuit breakers disclosed herein.

With reference to <FIG>, there is illustrated an exemplary power system <NUM> including a plurality of exemplary solid-state circuit breakers <NUM>. Power system <NUM> is arranged in a meshed configuration. In other embodiments, power system <NUM> may be arranged in another configuration, such as a ring configuration or a distributed configuration. Power system <NUM> may be structured to conduct AC or DC, or a combination thereof.

The plurality of solid-state circuit breakers <NUM> includes solid-state circuit breaker <NUM> and solid-state circuit breaker <NUM>. In certain embodiments, one or more of the plurality of solid-state circuit breakers <NUM> may be replaced by another type of protection device, such as a mechanical circuit breaker or fuse.

In the illustrated system <NUM>, a short-circuit fault <NUM> is occurring between solid-state circuit breaker <NUM> and solid-state circuit breaker <NUM>. The plurality of solid-state circuit breakers <NUM> includes solid-state circuit breakers both upstream and downstream of fault <NUM>.

Each of the plurality of solid-state circuit breakers <NUM> monitors the current they are conducting. For each solid-state circuit breaker of the plurality of solid-state circuit breakers <NUM> that determine the solid-state circuit breaker is conducting a high magnitude current, the solid-state circuit breaker selects and operates in either the continuous current limiting mode or intermittent current limiting mode. Once the high magnitude current is limited by the selected mode, each controller, either individually or collectively, determines the cause of the high magnitude current and mitigates the high current. For example, since fault <NUM> is a short-circuit fault, solid-state circuit breakers <NUM> and <NUM>, being the closest solid-state circuit breakers to fault <NUM>, enter protection mode and open in order to remove fault <NUM>. Once fault <NUM> is repaired, solid-state circuit breakers <NUM> and <NUM> return to normal mode and power system <NUM> is restored.

In certain embodiments, the controllers of each solid-state circuit breaker coordinate in a distributed fashion in order to determine the cause of the high magnitude current and mitigate the high magnitude current. In other embodiments, a central control system receives information from the controllers of each solid-state circuit breaker to determine a cause of the high magnitude current and transmit commands to the solid-state circuit breakers in order to mitigate the high magnitude current.

With reference to <FIG>, there is a flowchart illustrating an exemplary protection process <NUM> for an exemplary solid-state circuit breaker, such as solid-state circuit breaker <NUM> in <FIG>. Process <NUM> may be implemented in whole or in part in one or more of the controllers of the solid-state circuit breakers disclosed herein. It shall be further appreciated that a number of variations and modifications to process <NUM> are contemplated including, for example, the omission of one or more aspects of process <NUM>, the addition of further conditionals and operations, and the reorganization or separation of operations and conditionals into separate processes.

Process <NUM> begins at start operation <NUM> where a high current condition begins to occur while the solid-state circuit breaker is operating in normal mode. A high current condition occurs when an event, such as a fault or a transient, causes the solid-state circuit breaker to conduct a high magnitude current with a magnitude greater than the nominal current conducted by the solid-state circuit breaker. In certain embodiments, a high magnitude current may be considered a current with a magnitude greater than twice the magnitude of the nominal current.

Process <NUM> proceeds to conditional <NUM>. If the high current condition is an anticipated transient, process <NUM> proceeds to operation <NUM>. An anticipated transient is an event known by the solid-state circuit breaker, which will cause a high magnitude current to be conducted through the solid-state circuit breaker unless the solid-state circuit breaker limits the conducted current. The controller may receive information for anticipating transients from another solid-state circuit breaker controller, or a central control system. The controller may also determine an anticipated transient based on previous transients conducted by the solid-state circuit breaker.

If the high current condition was not anticipated, process <NUM> proceeds to operation <NUM> where the controller determines the solid-state circuit breaker is conducting a high magnitude current. The controller may determine the solid-state circuit breaker is conducting a high magnitude current by measuring the current conducted by the solid-state circuit breaker using a current sensor, to give but one example.

Process <NUM> proceeds to operation <NUM> where the controller selects a current limiting mode. When determining whether to select the continuous current limiting mode or the intermittent current limiting mode, the controller may consider a number of factors, including actual and desired current magnitudes, thermal ratings, and power quality requirements, to give but a few examples.

Continuous current limiting mode may be selected over intermittent current limiting mode due to power quality requirements since continuous current limiting mode generates less distortion than intermittent current limiting mode. The current oscillations caused by repetitive toggling cause voltage oscillations on the grid side of the solid-state circuit breaker. These oscillations may damage power system components. For example, the controller may select the continuous current limiting mode or the intermittent current limiting mode based on a current reference value and a power quality requirement. The power quality requirement may include a voltage distortion threshold, a current distortion threshold, an overvoltage threshold, and an undervoltage threshold.

Intermittent current limiting mode may be selected over continuous current limiting mode because intermittent current limiting mode is able to reduce the magnitude of the high magnitude current more than continuous current limiting mode. For example, the controller may select the intermittent current limiting mode if operating the solid-state switching device in the continuous current limiting mode would not reduce a magnitude of the high magnitude current to a desired current reference value.

Intermittent current limiting mode may also be selected over continuous current limiting mode if an expected amount of energy dissipated in the assistive branch exceeds an energy dissipation threshold. The energy dissipation threshold may include a thermal rating, to name but one example. The controller may determine the expected amount of energy dissipated in the assistive branch based on an estimated time length of operating the solid-state circuit breaker in the current limiting mode, to name but a one example. In intermittent current limiting mode, the energy dissipated by the solid-state circuit breaker is shared by the assistive branch and the energy dissipation branch, as opposed to the continuous current limiting mode where energy is primarily dissipated in the assistive branch. Therefore, the controller may select intermittent current limiting mode to operate solid-state circuit breaker if the controller determines operating the solid-state circuit breaker in continuous current limiting mode would cause energy dissipation in the assistive branch that is greater than the energy dissipation threshold of the assistive branch.

Process <NUM> proceeds to operation <NUM> where the controller operates the solid-state circuit breaker in the current limiting mode selected in operation <NUM>. By operating the solid-state circuit breaker in the current limiting mode, the controller has sufficient time to identify the cause of the high current condition. Furthermore, operating the solid-state circuit breaker in one of the current limiting modes before the cause of the high current condition is identified avoids opening the solid-state circuit breaker unnecessarily for normal transients, such as transformer inrush and capacitor charging, thereby reducing system downtime.

Process <NUM> proceeds to operation <NUM> where the controller determines whether the cause of the high current condition is a fault or a transient. A fault may include a short circuit fault or another type of condition that requires isolation and removal before the power system can operate normally again. A transient may include an inrush current or another condition that will last for a limited amount of time such that the solid-state circuit breaker may return to normal mode without isolation once the transient terminates.

The controller may receive electrical characteristics of the solid-state circuit breaker before and while operating the solid-state switching device in the selected current limiting mode, and use the received electrical characteristics to determine whether the cause of the high current condition is a fault or a transient. The electrical characteristics may include measured currents and voltages to name but a few examples. The controller may also use electrical characteristics measured at other solid-state circuit breakers in the same power system.

For example, the controller may determine the cause of the high current condition is an inrush transformer transient based on the second harmonics of the measured current. In another example, the controller may determine the cause of the high current condition is a fault based on a decreasing voltage, or a transient based on a steady voltage. In still another example, the controller may determine the cause of the high current condition is a capacitor charging transient based on a measured voltage that increases until it reaches a nominal voltage value.

If the cause of the high current condition is a fault, process <NUM> proceeds to operation <NUM> where the fault is removed. In certain embodiments, the controller removes the fault by entering protection mode opening the semiconductor switching device. For power systems including a plurality of exemplary solid-state circuit breakers, once the fault has been identified and located, the solid-state circuit breaker(s) closest to the fault enter protection mode while the other solid-state circuit breakers that were in a current limiting mode return to normal mode.

In certain embodiments, the power system includes a plurality of solid-state circuit breakers and a plurality of fuses or mechanical circuit breakers. The fuse or mechanical circuit breaker opens at the faulted branch to remove the fault, while the remaining protection devices remain closed. If the fuse or mechanical circuit breaker at the faulted branch fails to open, the solid-state circuit breaker closest to the faulty fuse or mechanical circuit breaker serves as a backup breaker. In response to determining the fuse or mechanical circuit breaker has failed, the switching device on the assistive branch is opened, the solid-state switching device is opened or remains opened, and the galvanic isolation switch is opened.

Process <NUM> proceeds to operation <NUM> where the power system restores operation after the fault is removed. The solid-state circuit breaker in protection mode is returned to normal mode. For solid-state circuit breakers locked under protection mode or a current limiting mode for a predefined period of time, the solid-state circuit breaker returns to normal mode after the time period.

If the cause of the high current condition is a transient, process <NUM> proceeds to operation <NUM> where the controller monitors the transient until the transient terminates. Process <NUM> then proceeds to operation <NUM> where the system is restored to normal operation and the solid-state circuit breaker returns to normal mode. For solid-state circuit breakers locked under current limiting mode for a predefined period of time, the solid-state circuit breaker returns to normal mode after the time period.

For anticipated transients, process <NUM> proceeds from conditional <NUM> to operation <NUM> where the controller selects a current limiting mode, just as the controller selected a current limiting mode in operation <NUM>. After selecting the current limiting mode, process <NUM> proceeds to operation <NUM> where the controller operates the solid-state circuit breaker in the selected operating mode, just as in operation <NUM>. Process <NUM> then proceeds to operation <NUM> where the controller continues to monitor the anticipated transient until the transient terminates. Process <NUM> then proceeds to operation <NUM> where the controller operates the solid-state circuit breaker in normal mode.

With reference to <FIG>, there is a plurality of graphs <NUM> illustrating AC conducted by an exemplary solid-state circuit breaker during a fault. The plurality of graphs <NUM> includes graphs <NUM> and <NUM>. Graph <NUM> illustrates AC conducted by the solid-state circuit breaker in continuous current limiting mode. Graph <NUM> includes an output current <NUM> line representing current output from the solid-state circuit breaker. Graph <NUM> also includes a nominal current peak <NUM> line representing the nominal current peak of the current conducted by the solid-state circuit breaker during normal operation, and a high current threshold <NUM> line representing a magnitude of current above which a controller of the solid-state circuit breaker will determine a high magnitude current is being conducted. In the illustrated embodiment, high current threshold <NUM> is twice the magnitude of nominal current peak <NUM>. In other embodiments, high current threshold <NUM> may be a different multiple of nominal current peak <NUM>.

At time instant t<NUM> of graph <NUM>, the high current condition begins and output current <NUM> begins to rise. Without current limiting by the solid-state circuit breaker, output current <NUM> would conform to the waveform illustrated by fault current line <NUM>. Although fault current line <NUM> shows only one cycle, the fault current would continue until the fault is identified and cleared. Instead, the solid-state circuit breaker enters the continuous current limiting mode in response to output current <NUM> exceeding high current threshold <NUM>. By entering continuous current limiting mode, the peaks of output current <NUM> are reduced to one and a half times the magnitude of the nominal current peaks. In other embodiments, the peaks of output current <NUM> may be reduced to a different multiple of the magnitude of the nominal current peaks. The solid-state circuit breaker continues to operate in continuous current limiting mode until time instant t<NUM> where a solid-state circuit breaker or a mechanical breaker in <FIG> closest to the fault location opens in response to determining the high magnitude current is due to a fault. Although time instant t<NUM> is illustrated as a zero-crossing point, the solid-state circuit breaker or the closest breaker may also open while conducting a current.

Graph <NUM> illustrates AC conducted by the solid-state circuit breaker in intermittent current limiting mode. Graph <NUM> includes an output current <NUM> line representing current output from the solid-state circuit breaker. Graph <NUM> also includes a nominal current peak <NUM> line representing the nominal current peak of the current conducted by the solid-state circuit breaker during normal operation, and a high current threshold <NUM> line representing a magnitude of current above which a controller of the solid-state circuit breaker will determine a high magnitude current is being conducted. In the illustrated embodiment, high current threshold <NUM> is twice the magnitude of nominal current peak <NUM>. In other embodiments, high current threshold <NUM> may be a different multiple of nominal current peak <NUM>.

At time instant t<NUM> of graph <NUM>, a high current condition begins to occur and output current <NUM> begins to increase. Without current limiting by the solid-state circuit breaker, output current <NUM> would conform to the waveform illustrated by fault current line <NUM>. Although fault current line <NUM> shows only one cycle, the fault current would continue until the fault is identified and cleared. Instead, the solid-state circuit breaker enters the intermittent current limiting mode in response to output current <NUM> exceeding high current threshold <NUM>. By entering intermittent current limiting mode, the peaks of output current <NUM>, generated by repeatedly toggling the solid-state switching device, are reduced to one and a half times the magnitude of the nominal current peaks. In other embodiments, the peaks of output current <NUM> may be reduced to a smaller multiple of the magnitude of the nominal current peaks. The solid-state circuit breaker continues to operate in intermittent current limiting mode until time instant t<NUM> where a solid-state circuit breaker or a mechanical breaker in <FIG> closest to the fault location opens in response to determining the high magnitude current is due to a fault. Although time instant t<NUM> is illustrated as a zero-crossing point, the solid-state circuit breaker or the closest breaker may also open while conducting a current.

With reference to <FIG>, there is a plurality of graphs <NUM> illustrating DC conducted by an exemplary solid-state circuit breaker during a fault. The plurality of graphs <NUM> includes graphs <NUM> and <NUM>. Graph <NUM> illustrates DC conducted by the solid-state circuit breaker in continuous current limiting mode. Graph <NUM> includes an output current <NUM> line representing current output from the solid-state circuit breaker. Graph <NUM> also includes a high current threshold <NUM> line representing a magnitude of current above which a controller of the solid-state circuit breaker will determine a high magnitude current is being conducted. In the illustrated embodiment, high current threshold <NUM> is twice the magnitude of nominal current I<NUM>. In other embodiments, high current threshold <NUM> may be a different multiple of nominal current I<NUM>.

At time instant t<NUM> of graph <NUM>, a high current condition begins to occur and output current <NUM> begins to increase. Without current limiting by the solid-state circuit breaker, output current <NUM> would conform to the waveform illustrated by fault current line <NUM> until the fault is identified and the solid-state circuit breaker would open, interrupting output current <NUM>. Instead, the solid-state circuit breaker enters the continuous current limiting mode in response to output current <NUM> exceeding high current threshold <NUM>. By entering continuous current limiting mode, the magnitude of the output current <NUM> is reduced to one and a half times the magnitude of the nominal current magnitude. In other embodiments, the magnitude of output current <NUM> may be reduced to a different multiple of the magnitude of the nominal current. The solid-state circuit breaker continues to operate in continuous current limiting mode until time instant t<NUM> where a solid-state circuit breaker or a mechanical breaker in <FIG> closest to the fault location opens in response to determining the high magnitude current is due to a fault.

Graph <NUM> illustrates DC conducted by the solid-state circuit breaker in intermittent current limiting mode. Graph <NUM> includes an output current <NUM> line representing current output from the solid-state circuit breaker. Graph <NUM> also includes a high current threshold <NUM> line representing a magnitude of current above which a controller of the solid-state circuit breaker will determine a high magnitude current is being conducted. In the illustrated embodiment, high current threshold <NUM> is twice the magnitude of nominal current I<NUM>. In other embodiments, high current threshold <NUM> may be a different multiple of nominal current I<NUM>.

At time instant t<NUM> of graph <NUM>, a high current condition begins to occur and output current <NUM> begins to increase. Without current limiting by the solid-state circuit breaker, output current <NUM> would conform to the waveform illustrated by fault current line <NUM> until the fault is identified and the solid-state circuit breaker would open, interrupting output current <NUM>. Instead, the solid-state circuit breaker enters the intermittent current limiting mode in response to output current <NUM> exceeding high current threshold <NUM>. By entering intermittent current limiting mode, the peaks of output current <NUM>, generated by repeatedly toggling the solid-state switching device, are one and a half times the magnitude of nominal current I<NUM>. In other embodiments, the peaks of output current <NUM> may be a smaller multiple of the magnitude of the nominal current peaks. The solid-state circuit breaker continues to operate in intermittent current limiting mode until time instant t<NUM> where the solid-state circuit breaker or another breaker in <FIG> closest to the fault location opens in response to determining the high magnitude current is due to a fault.

With reference to <FIG>, there is a graph <NUM> illustrating energy dissipation of an exemplary solid-state circuit breaker while operating in continuous current limiting mode, wherein the solid-state device of the solid-state circuit breaker includes an IGCT, the energy dissipation branch includes an MOV, and the assistive branch includes a resistor having a resistance of <NUM> Ohms. Graph <NUM> includes energy dissipation values for each parallel branch of the solid-state circuit breaker over a range of system inductances between <NUM>-<NUM> H to <NUM>-<NUM> H. As illustrated in graph <NUM>, energy dissipation in the assistive branch is significantly higher than the energy dissipation in either the solid-state switching device or the energy dissipation branch, due to the single turnoff of the solid-state switching device during continuous current limiting mode.

With reference to <FIG>, there is a graph <NUM> illustrating energy dissipation of an exemplary solid-state circuit breaker while operating in intermittent current limiting mode, wherein the solid-state device of the solid-state circuit breaker includes an IGCT, the energy dissipation branch includes an MOV, and the assistive branch includes a resistor having a resistance of <NUM> Ohms. Graph <NUM> includes energy dissipation values for each parallel branch of the solid-state circuit breaker over a range of system inductances between <NUM>-<NUM> H to <NUM>-<NUM> H. As illustrated in graph <NUM>, energy dissipation in the assistive branch and the energy dissipation branch is equal for one system inductance and shared for the illustrated range of system inductances. The resistance of the assistive branch may be resized in order for the energy dissipation of the energy dissipation branch and the assistive branch to be equal at a different system inductance.

With reference to <FIG>, there are exemplary control algorithms of an exemplary solid-state circuit breaker controller for determining switch toggling patterns during intermittent current limiting mode. For hysteresis algorithm <NUM> illustrated in <FIG>, the controller determines a current reference value <NUM> and receives a current magnitude measurement <NUM>. Using reference <NUM> and measurement <NUM>, the controller calculates an adjustment <NUM> to the switch-toggling pattern to move the output current magnitude closer to the current reference value.

For feedback control algorithm <NUM> illustrated in <FIG>, the controller determines a current reference value <NUM> and receives a current magnitude measurement <NUM>. Operator <NUM> calculates the difference between reference <NUM> and measurement <NUM>. Proportional-integral-derivative (PID) controller <NUM> receives the difference from operator <NUM> and outputs a pulse width <NUM>. PID controller <NUM> receives the difference from operator <NUM> and outputs a pulse rate <NUM>.

For two-level feedback control algorithm <NUM> illustrated in <FIG>, the controller determines a current reference value <NUM> using variable time current curves. Operator <NUM> calculates the difference between a previous time current curve and an adjusted time current curve <NUM>. The controller adjusts the time current curve based on operating conditions of the solid-state circuit breaker. The controller allows a different let-through energy to be conducted by the solid state circuit breaker with the adjusted time current curve. A higher let-through energy is allowed when the time current is adjusted upwards. Proportional-integral-derivative (PID) controller <NUM> receives the calculated difference from operator <NUM> and outputs current reference value <NUM>. Operator <NUM> calculates the difference between reference <NUM> and a received current magnitude measurement <NUM>. PID controller <NUM> receives the difference from operator <NUM> and outputs a pulse width <NUM>. PID controller <NUM> receives the difference from operator <NUM> and outputs a pulse rate <NUM>.

Further written description of a number of exemplary embodiments shall now be provided. One embodiment of the present invention is a power system comprising a solid-state circuit breaker including a solid-state switching device, an energy dissipation branch coupled in parallel with the solid-state switching device, the energy dissipation branch including an energy dissipation device, an assistive branch coupled in parallel with the solid-state switching device, the assistive branch including a resistor, an inductor, and a switching device coupled together in series, and a controller configured to determine the solid-state circuit breaker is conducting a high magnitude current, select a continuous current limiting mode or an intermittent current limiting mode, and operate the solid-state switching device in the selected current limiting mode.

In certain forms of the foregoing power system and of the present invention, operating the solid-state switching device in the intermittent current limiting mode includes repeatedly toggling the solid-state switching device using a series of pulses. In certain forms, operating the solid-state switching device in the continuous current limiting mode includes opening the solid-state switching device and not closing the solid-state switching device. In certain forms, the controller selects the intermittent current limiting mode if operating the solid-state switching device in the continuous current limiting mode would not reduce a magnitude of the high magnitude current to a current reference value. In certain forms, the controller selects the continuous current limiting mode or the intermittent current limiting mode based on a current reference value and a power quality requirement, including at least one of a voltage distortion threshold and a current distortion threshold. In certain forms, the controller is configured to update a time current curve of the solid-state circuit breaker based on operating conditions of the solid-state circuit breaker, wherein the controller is configured to determine a pulse width of one pulse of the series of pulses based on the updated time current curve, and wherein the controller is configured to determine a pulse rate for a portion of the series of pulses based on the updated time current curve. In certain forms, the resistor is sized so that equal portions of energy of the high magnitude current are dissipated by the energy dissipation branch and the assistive branch while operating the solid-state switching device in the intermittent current limiting mode. In certain forms, the resistor is sized so that a first amount of energy dissipated by the energy dissipation branch is within <NUM> percent of a second amount of energy dissipated by the assistive branch while operating the solid-state switching device in the intermittent current limiting mode. In certain forms, the power system includes a plurality of solid-state circuit breakers, wherein the controller is configured to determine a cause of the high magnitude current is a fault, and wherein the controller is configured to determine the solid-state circuit breaker is closer to the fault than the plurality of solid-state circuit breakers and begin to operate the solid-state circuit breaker in a protection mode in response to determining the solid-state circuit breaker is closer to the fault than the plurality of solid-state circuit breakers. In certain forms, the controller is configured to determine a cause the high magnitude current is a transient, and wherein the controller is configured to continue to operate the solid-state switching device in the selected current limiting mode until the transient terminates.

Another exemplary embodiment of the present invention is a method comprising operating a solid-state circuit breaker including a solid-state switching device, an energy dissipation branch coupled in parallel with the solid-state switching device and including an energy dissipation device, an assistive branch coupled in parallel with the solid-state switching device and including a resistor, an inductor, and a switching device coupled together in series; determining the solid-state circuit breaker is conducting a high magnitude current; select a continuous current limiting mode or an intermittent current limiting mode; and operate the solid-state switching device in the selected current limiting mode.

In certain forms of the foregoing method and of the present invention, operating the solid-state switching device in the intermittent current limiting mode includes repeatedly toggling the solid-state switching device. In certain forms, operating the solid-state switching device in the continuous current limiting mode includes opening the solid-state switching device and not closing the solid-state switching device. In certain forms, selecting the continuous current limiting mode or the intermittent current limiting mode includes selecting the intermittent current limiting mode if operating the solid-state switching device based on the continuous current limiting mode would not reduce a magnitude of the high magnitude current to a current reference value. In certain forms, selecting the continuous current limiting mode or the intermittent current limiting mode is based on a current reference value and a power quality requirement including at least one of a voltage distortion threshold and a current distortion threshold. In certain forms, operating the solid-state switching device in the intermittent current limiting mode updating a time current curve of the solid-state circuit breaker based on operating conditions of the solid-state circuit breaker, determine a pulse width of one pulse of a series of pulses based on the updated time current curve, and determining a pulse rate for a portion of the series of pulses based on the updated time current curve. In certain forms, the resistor is sized so that equal portions of energy of the high magnitude current are dissipated by the energy dissipation branch and the assistive branch while operating the solid-state switching device in the intermittent current limiting mode. In certain forms, the resistor is sized so that a first amount of energy dissipated by the energy dissipation branch is within <NUM> percent of a second amount of energy dissipated by the assistive branch while operating the solid-state switching device in the intermittent current limiting mode. In certain forms, the method comprises determining a cause of the high magnitude current is a fault; determining the solid-state circuit breaker is closer to the fault than a plurality of solid-state circuit breakers of the power system; and operating the solid-state circuit breaker in a protection mode in response to determining the solid-state circuit breaker is closer to the fault than the plurality of solid-state circuit breakers. In certain forms, the controller is configured to determine a cause the high magnitude current is a transient, and wherein the controller is configured to continue to operate the solid-state switching device in the selected current limiting mode until the transient terminates.

Claim 1:
A power system (<NUM>) comprising:
a solid-state circuit breaker (<NUM>) including:
a solid-state switching device (<NUM>),
an energy dissipation branch (<NUM>) coupled in parallel with the solid-state switching device (<NUM>), the energy dissipation branch (<NUM>) including an energy dissipation device (<NUM>),
an assistive branch (<NUM>) coupled in parallel with the solid-state switching device (<NUM>), the assistive branch (<NUM>) including a resistor (<NUM>), an inductor (<NUM>), and a switching device (<NUM>) coupled together in series, the solid-state circuit breaker is characterised in that it further includes:
a controller (<NUM>) configured to determine the solid-state circuit breaker (<NUM>) is conducting a high magnitude current, select a continuous current limiting mode or an intermittent current limiting mode, and operate the solid-state switching device (<NUM>) and the switching device (<NUM>) based on the selected current limiting mode;
wherein operating the solid-state switching device (<NUM>) in the intermittent current limiting mode includes repeatedly toggling the solid-state switching device using a series of pulses;
wherein operating the solid-state switching device (<NUM>) in the continuous current limiting mode includes opening the solid-state switching device (<NUM>) and not closing the solid-state switching device (<NUM>)