阅读说明：本技术 用于固态断路器的电压钳位电路 (Voltage clamping circuit for solid state circuit breaker ) 是由 杜宇 其他发明人请求不公开姓名 于 2019-11-21 设计创作，主要内容包括：公开了固态断路器保护的独特系统、方法、技术和装置。一个示例性实施例是一种固态断路器,该固态断路器包括主开关器件,该主开关器件包括第一端子和第二端子；以及电压钳位电路,该电压钳位电路与主开关器件并联耦合。电压钳位电路包括金属氧化物变阻器(MOV),该MOV被串联耦合在第一端子与辅助半导体器件之间,该辅助半导体器件被布置为选择性地将MOV与第二端子耦合；以及旁路电路,该旁路电路被耦合在第一端子与辅助半导体器件之间。(Unique systems, methods, techniques, and apparatus for solid state circuit breaker protection are disclosed. One exemplary embodiment is a solid state circuit breaker including a main switching device including a first terminal and a second terminal; and a voltage clamp circuit coupled in parallel with the main switching device. The voltage clamping circuit comprises a Metal Oxide Varistor (MOV) coupled in series between the first terminal and an auxiliary semiconductor device arranged to selectively couple the MOV with the second terminal; and a bypass circuit coupled between the first terminal and the auxiliary semiconductor device.)

1. A Solid State Circuit Breaker (SSCB), comprising:

a main switching device including a first terminal and a second terminal; and

a voltage clamp circuit coupled in parallel with the main switching device, the voltage clamp circuit comprising:

a Metal Oxide Varistor (MOV) coupled in series between the first terminal and an auxiliary semiconductor device arranged to selectively couple the MOV with the second terminal, an

A bypass circuit coupled between the first terminal and the auxiliary semiconductor device.

2. The SSCB of claim 1, wherein the voltage clamping circuit is configured to receive a fault current after the main switching device is turned off, and wherein the auxiliary semiconductor device is configured to turn on in response to receiving the fault current by way of the bypass circuit.

3. The SSCB of claim 2, wherein the fault current is commutated from the bypass circuit to the MOV in response to the auxiliary semiconductor device being turned on.

4. The SSCB of claim 3, wherein turning on the auxiliary semiconductor device generates a voltage spike across the auxiliary semiconductor device before the auxiliary semiconductor device is turned on, wherein an MOV voltage increases to an MOV clamp voltage after the auxiliary semiconductor device is turned on, and wherein the voltage clamp circuit is configured such that the combination of the voltage spike and the MOV voltage never exceeds the MOV clamp voltage.

5. The SSCB of claim 1, wherein the bypass circuit is configured to allow a fault current to flow from the first terminal to the auxiliary semiconductor device without flowing through the MOV, thereby effectively turning on the auxiliary semiconductor device before the MOV voltage increases to an MOV clamping voltage.

6. The SSCB of claim 1, wherein the voltage clamp circuit is structured such that a total clamp voltage across the voltage clamp circuit does not exceed an MOV clamp voltage.

7. The SSCB of claim 1, wherein the auxiliary semiconductor device comprises a Transient Voltage Suppression (TVS) thyristor or TVS diode coupled between the MOV and the second terminal, and wherein the bypass circuit comprises a capacitor coupled in parallel with the MOV.

8. The SSCB of claim 1, wherein the auxiliary semiconductor device includes a switching device and a control circuit, wherein the switching device and the control circuit are coupled to the bypass circuit.

9. The SSCB of claim 8, wherein the bypass circuit includes a capacitor coupled to the control circuit and coupled in parallel with the MOV.

10. The SSCB of claim 8, wherein the bypass circuit comprises a capacitor coupled to the switching device and the control circuit and a resistor coupled to the control circuit.

11. A method for protecting a main switching device of a Solid State Circuit Breaker (SSCB), the main switching device comprising:

coupling a voltage clamp circuit in parallel with the primary switching device, the voltage clamp circuit including a Metal Oxide Varistor (MOV), an auxiliary semiconductor device, and a bypass circuit;

receiving a fault current with the auxiliary semiconductor device by means of the bypass circuit after turning off the main switching device;

switching on the auxiliary semiconductor device using the fault current; and

commutating the fault current from the bypass circuit to the MOV in response to the auxiliary semiconductor device being turned on.

12. The method of claim 11, wherein the MOV is coupled in parallel with the bypass circuit, and wherein the MOV is coupled in series with a switching device of the auxiliary semiconductor device.

13. The method of claim 12, wherein the commutation of the fault current from the bypass circuit to the MOV begins after a switching device of the auxiliary semiconductor device coupled to the MOV closes and ends when MOV voltage increases to a MOV clamp voltage.

14. The method of claim 11, wherein turning on the auxiliary semiconductor device generates a voltage spike across the auxiliary semiconductor device, wherein an MOV voltage of the MOV increases to an MOV clamp voltage after the auxiliary semiconductor device is turned on, and wherein the voltage clamp circuit is configured such that the combination of the voltage spike and the MOV voltage never exceeds the MOV clamp voltage.

15. The method of claim 11, wherein the bypass circuit allows the fault current to flow from the first terminal of the SSCB to the auxiliary semiconductor device without flowing through the MOV, thereby effectively turning on the auxiliary semiconductor device before the MOV voltage reaches the MOV clamp voltage.

16. The method of claim 11, wherein the voltage clamp circuit is configured such that a total clamp voltage across the voltage clamp circuit does not exceed an MOV clamp voltage of the MOV.

17. The method of claim 11, wherein the auxiliary semiconductor device comprises a Transient Voltage Suppression (TVS) thyristor or TVS diode coupled in series with the MOV, and wherein the bypass circuit comprises a capacitor coupled in parallel with the MOV.

18. The method of claim 11, wherein the auxiliary semiconductor device comprises a switching device and a control circuit, and wherein the switching device and the control circuit are coupled to the bypass circuit.

19. The method of claim 18, wherein the bypass circuit comprises a capacitor coupled to the control circuit and coupled in parallel with the MOV.

20. The method of claim 18, wherein the bypass circuit comprises a capacitor coupled to the switching device and the control circuit and a resistor coupled to the control circuit.

Technical Field

The present disclosure relates generally to Solid State Circuit Breaker (SSCB) protection. Metal Oxide Varistors (MOVs) are widely used to protect the main switching devices in the SSCBs from overvoltage damage and to absorb excess energy in the line impedance during overcurrent fault interruption. When choosing an appropriate MOV according to the operating voltage, there are two requirements. First, the peak clamp voltage of the MOV should be lower than the breakdown voltage of the main switching device. Second, the leakage current of the MOV should be low enough to ensure that the resulting power loss is within the power dissipation capability of the MOV. These requirements require the MOV to have a small operating region when the source voltage (or system voltage) approaches the breakdown voltage of the main switching device, as shown in fig. 1, where the MOV operating region 105 is limited by the breakdown voltage 101 of the main switching device and the source voltage 103 of the power flowing through the SSCB during normal operation. There are several drawbacks and disadvantages with existing SSCBs. In some conventional designs, a one-time voltage margin is added to the power supply voltage at the power semiconductor switch due to the larger voltage operating area of the MOV, thereby reducing voltage utilization and increasing the cost of the switch. In view of these and other deficiencies in the art, there is a significant need for unique apparatus, methods, systems, and techniques disclosed herein.

Disclosure of illustrative embodiments

In order to clearly, concisely and accurately describe the non-limiting exemplary embodiments of the present disclosure, the manner and process of making and using the exemplary embodiments, and to enable the practice, making and use of the exemplary embodiments, reference is now made to certain exemplary embodiments, including the embodiments illustrated in the drawings, and specific language is used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby created, and that the disclosure includes and protects such alterations, modifications, and other applications of the exemplary embodiments as would occur to one skilled in the art having the benefit of this disclosure.

Disclosure of Invention

Exemplary embodiments of the present disclosure include unique systems, methods, techniques, and apparatuses for solid state circuit breaker protection. Other embodiments, forms, objects, features, advantages, aspects, and benefits of the present disclosure will become apparent from the following description and the accompanying drawings.

Drawings

Fig. 1 is a graph illustrating electrical characteristics of a metal oxide varistor.

Fig. 2 is a circuit diagram illustrating an exemplary solid state circuit breaker.

Fig. 3 is a circuit diagram illustrating current flow through the exemplary solid state circuit breaker of fig. 2.

Fig. 4A is a circuit diagram illustrating an exemplary solid state circuit breaker including a Transient Voltage Suppression (TVS) thyristor-based voltage clamping circuit.

Fig. 4B is a graph illustrating electrical characteristics of a TVS thyristor, such as the TVS thyristor of the exemplary solid state circuit breaker of fig. 4A.

Fig. 5A is a graph illustrating electrical characteristics of a solid state circuit breaker without an exemplary bypass circuit of the solid state circuit breaker of fig. 4A.

Fig. 5B-6B are graphs illustrating electrical characteristics of the example solid state circuit breaker of fig. 4A.

Fig. 7 is a circuit diagram illustrating an exemplary solid state circuit breaker including an Insulated Gate Bipolar Transistor (IGBT) based voltage clamp circuit.

Fig. 8 is a circuit diagram illustrating an exemplary solid state circuit breaker including another IGBT-based voltage clamp circuit.

Detailed Description

Referring to fig. 2, an exemplary Solid State Circuit Breaker (SSCB)200 is shown, the SSCB200 being structured to control current flow through a power system incorporating the SSCB 200. It should be appreciated that the SSCB200 may be implemented in a variety of applications including Direct Current (DC) power systems, low voltage power distribution systems, medium voltage power distribution systems, and high voltage transmission systems, to name a few.

The SSCB200 includes a main switching device 205, the main switching device 205 including a first terminal 201 and a second terminal 203. During normal operation of a power system incorporating the SSCB200, the main switching device 205 is closed, also referred to as on, allowing current to flow between the terminals 201 and 203. In response to a fault condition, the primary switching device 205 opens, also referred to as turning off, thereby interrupting the flow of fault current through the primary switching device 205. The fault condition may include an overcurrent condition in which the fault current exceeds a current threshold, to name one example. The main switching device 205 responds to a fault condition by interrupting the fault current to protect the power system.

The main switching device 205 includes one or more semiconductor switches configured to control current flow, such as Insulated Gate Bipolar Transistors (IGBTs), Bipolar Junction Transistors (BJTs), Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), gate turn-off thyristors (GTOs), MOS Controlled Thyristors (MCTs), Integrated Gate Commutated Thyristors (IGCTs), silicon carbide (SiC) switches, gallium nitride (GaN) switches, or any other type of semiconductor switch. The one or more semiconductor switches of the main switching device 205 may be coupled in series, parallel, anti-series, anti-parallel, or a combination thereof.

The SSCB200 includes a voltage clamp circuit 206, the voltage clamp circuit 206 being structured to protect the main switching device 205 during fault conditions. The voltage clamp circuit 206 includes a Metal Oxide Varistor (MOV)207, an auxiliary semiconductor device 211, and a bypass circuit 209. MOV207 and auxiliary semiconductor device 211 are coupled in series between terminal 201 and terminal 203 such that MOV207 and auxiliary semiconductor device 211 are coupled in parallel with switching device 205. A bypass circuit 209 is coupled to the auxiliary semiconductor device 211 and is coupled in parallel with the MOV 207.

MOV207 is configured to dissipate the fault current by converting the fault current into heat. As the fault current continues to flow through the bypass circuit 209, the voltage across the MOV207 (also referred to as MOV207 voltage) increases until the voltage reaches a voltage where the MOV207 is configured to clamp a voltage that prevents the MOV207 voltage from increasing further, also referred to as MOV207 clamping voltage. Auxiliary semiconductor device 211 is configured to control current flow through voltage clamping circuit 206. The auxiliary semiconductor device 211 may include a transient voltage suppression (TSV) thyristor, TVS diode, IGBT, or MOSFET, to name a few. Device 211 may also include control circuitry configured to operate the semiconductor switches of device 211 using the current received from bypass circuit 209.

During normal operation of the power system, the auxiliary semiconductor device 211 is turned off, thereby reducing MOV207 leakage current and blocking a portion of the voltage across the voltage clamp circuit 206. By reducing MOV leakage current, the voltage clamp circuit 206 is arranged to reduce thermal stress and power loss during normal operation. The auxiliary semiconductor device 211 reduces the voltage stress of the MOV207 by blocking a portion of the voltage across the voltage clamp circuit 206.

During a fault condition, the voltage clamp circuit 206 is configured to turn on the auxiliary semiconductor device 211, allowing a fault current to flow through the MOV207 to the terminal 203. A brief delay occurs between auxiliary semiconductor device 211 first receiving the fault current from bypass circuit 209 and auxiliary semiconductor device 211 turning on. For example, where auxiliary semiconductor device 211 comprises a TVS thyristor, turning on auxiliary semiconductor device 211 may take several microseconds (2 μ s to 3 μ s) to build up the device internal carrier modulation. As a result of the delay, a voltage spike is generated across auxiliary semiconductor device 211.

The bypass circuit 209 is configured to allow the fault current to bypass the MOV207 and turn on the auxiliary semiconductor device 211. In some embodiments, the bypass circuit 209 is configured to turn on the auxiliary semiconductor device 211 without a control circuit, thereby simplifying the SSCB200 and reducing cost. By bypassing the MOV207, the voltage clamp circuit 206 is configured to delay the increase in MOV207 voltage so that the combination of the MOV207 voltage and the voltage spike of the auxiliary semiconductor device 211 never exceeds the MOV207 clamp voltage.

Without the bypass circuit 209, the fault current may be commutated from the primary switching device 205 to the MOV207 and the auxiliary semiconductor device 211. The auxiliary semiconductor device 211 may generate a voltage spike when it turns on while the MOV207 voltage reaches the MOV clamp voltage, thereby increasing the total clamp voltage across the main switching device 205. Increasing the total clamping voltage may require increasing the voltage rating of the main switching device 205, thereby reducing the voltage utilization of the main switching device 205.

The bypass circuit 209 may include a capacitor coupled between the terminal 201 and the auxiliary semiconductor device 211, to name one example only. The capacitor may be coupled to the semiconductor switch and the control circuit of the auxiliary semiconductor device 211. In some embodiments, the bypass circuit 209 may include a resistor coupled to the terminal 201 and to the control circuit of the auxiliary semiconductor device 211.

Once the auxiliary semiconductor device 211 is turned on during a fault condition, the fault current is commutated from the bypass circuit 209 to the MOV 207. It will be appreciated that after the fault current commutates from the bypass circuit 209 to the MOV207, most of the fault begins to flow through the MOV207 rather than the bypass circuit, but some of the fault current may continue to flow through the bypass circuit. To give but one example, after the fault current commutates from the bypass circuit 209 to the MOV207, the portion of the fault current that continues to flow through the bypass circuit 209 may be less than 1% of the magnitude of the fault current at the time of the commutation. It should be appreciated that any or all of the foregoing features of the SSCB200 may also be present in other circuit breakers disclosed herein (such as the exemplary solid state circuit breakers shown in fig. 4A, 7, and 8).

Referring to fig. 3, current paths 301 and 303 through the voltage clamp circuit 206 of the SSCB200 of fig. 2 are illustrated. During a fault condition, a current conduction sequence exists in the voltage clamp circuit 206. After the main switching device 205 is turned off, the fault current flows through a path 301, which path 301 includes the bypass circuit 209 and the auxiliary semiconductor device 211. The auxiliary semiconductor device 211 is turned on using the bypass circuit 209. When the MOV207 voltage rises to the MOV207 clamp voltage, the fault current begins to flow through path 303, thereby commutating from the bypass circuit 209 to MOV 207. When the fault current drops to zero or substantially zero, the auxiliary semiconductor device 211 is turned off to share the blocking voltage with the MOV 207. In one example, the substantially zero may be a current amplitude that is less than a holding current point of the auxiliary semiconductor device. Thus, the leakage current is much smaller compared to a separate MOV.

Referring to fig. 4A, an exemplary SSCB 400 is illustrated, the exemplary SSCB 400 including a main switching device 405 and a voltage clamp circuit 406 coupled in parallel. The main switching device 405 includes terminals 401 and 403. The voltage clamp circuit 406 includes an MOV 407 and a TVS thyristor 411 coupled together in series between the terminal 401 and the terminal 403, and a bypass circuit including a capacitor 409 coupled in parallel with the MOV 407.

Referring to fig. 4B, a graph 420 illustrates the current-voltage characteristics of the TVS thyristor 411. The TVS thyristor 411 is a two-terminal bidirectional device. When the voltage across the terminals of the TVS thyristor 411 is less than the breakdown voltage of the TVS thyristor 411, the TVS thyristor 411 remains off. When the applied voltage increases to the breakdown voltage, the TVS thyristor 411 is turned on. The TVS thyristor 411 remains on as long as the on-current of the TVS thyristor 411 is greater than the hold current point of the TVS thyristor 411, and turns off when the current drops below the hold current point.

With continued reference to fig. 4A, when the TVS thyristor 411 turns off, the TVS thyristor 411 blocks a portion of the voltage across the voltage clamp circuit 406, resulting in a lower leakage current for the MOV 407 as compared to a voltage clamp circuit that does not include an auxiliary semiconductor device (such as the TVS thyristor 411). During a fault condition, the fault current flowing through the capacitor 409 charges the parasitic capacitor of the TVS thyristor 411, thereby increasing its voltage. When the voltage of the TVS thyristor 411 reaches the breakdown voltage, the TVS thyristor 411 is turned on. Since device internal carrier modulation is built, it may take several microseconds (2 μ s to 3 μ s) to turn on the TVS thyristor 411. The capacitor 409 is configured to turn on the TVS thyristor 411 and absorb a voltage spike generated during the turn on of the TVS thyristor 411. Since the voltage across the TVS thyristor 411 is only a few volts when the TVS thyristor 411 is turned on, the total clamping voltage of the voltage clamp circuit 406 is essentially determined by the clamping voltage of the MOV 407. When the fault current decreases below the holding current point of the TVS thyristor 411, the TVS thyristor 411 will turn off and share part of the blocking voltage with the MOV 407.

Referring to fig. 5A-5B, graphs illustrate electrical characteristics of two solid state circuit breakers during a fault condition. Fig. 5A illustrates voltage and current waveforms for a voltage clamp circuit including an MOV and a TVS thyristor coupled in series without a bypass circuit coupled in parallel with the MOV. Fig. 5B illustrates voltage and current waveforms of voltage clamp 406 in fig. 4A. Fig. 5A includes a voltage waveform plot 510 and a current waveform plot 520. Graph 510 includes lines representing the total voltage 511 across the MOV and the TVS thyristor, the voltage 513 across the MOV, and the voltage 515 across the TVS thyristor. Graph 520 includes lines representing the total fault current 521 flowing through the SSCB and the clamp current 523 flowing through the MOV before the MOV voltage reaches the clamp voltage. Fig. 5B includes a voltage waveform plot 530 and a current waveform plot 540. The graph 530 includes lines representing the total voltage 531 across MOV 407 and thyristor 411, the voltage 533 across MOV 407, and the voltage 535 across thyristor 411. Graph 540 includes lines representing total fault current 541 flowing through the SSCB 400, clamp current 543 flowing through the MOV 407, and fault current 545 flowing through the capacitor 409 before the fault current through the capacitor 409 reaches the total fault current.

As shown in fig. 5A, the voltage spike generated by turning on the TVS thyristor occurs at the same time the MOV voltage reaches the MOV clamping voltage, so that the total clamping voltage is equal to the sum of the MOV clamping voltage and the TVS thyristor breakdown voltage. In contrast, the graph shown in fig. 5B illustrates the reduction in the total clamping voltage of an exemplary voltage clamping circuit including a bypass circuit. With the capacitor 409 in parallel with the MOV 407, the MOV voltage is limited by the capacitor during the turn on of the TVS thyristor 411. Therefore, the combination of the voltage spike of the TVS thyristor 411 and the voltage of the MOV 407 never exceeds the clamping voltage of the MOV 407.

Referring to fig. 6A and 6B, graphs 610 and 620 illustrate experimental results of the SSCB 400 of fig. 4 at a 700V source voltage and 130A current interruption. Graphs 610 and 620 each include a line 611, which line 611 represents the total voltage across MOV 407 and TVS thyristor 411; a line 613, the line 613 representing the voltage across the TVS thyristor 411; a line 615, the line 615 representing a load current; and line 617, the line 617 representing the current flowing through the voltage clamping circuit 406. In fig. 6A, it can be seen that during the blocking state, the TVS thyristor 411 shares a partial voltage (about 80V) with the MOV 407. When the main switching device 405 is turned off at 130A load current, current is commutated from the device 405 to the voltage clamp 406, thereby charging the voltage across the TVS thyristor 411, as shown in fig. 6B. When the TVS thyristor 411 voltage reaches the breakdown voltage, the TVS thyristor 411 is turned on, and the voltage of the TVS thyristor 411 drops to the on-state voltage. During this period, the MOV 407 voltage is limited by the capacitor 409, the clamp circuit voltage being slightly higher than the breakdown voltage of the TVS thyristor 411. After turning on the TVS thyristor 411, the clamp voltage is determined only by the MOV 407. As shown in fig. 6A, when the fault current drops below the holding current point of the TVS thyristor 411, the TVS thyristor 411 is turned off again and the TVS thyristor 411 starts to block the voltage.

Referring to fig. 7, an exemplary SSCB 700 is illustrated, the exemplary SSCB 700 including a main switching device 705 and a voltage clamp circuit 706 coupled in parallel. Main switching device 705 includes terminals 701 and 703. The voltage clamp circuit 706 includes an MOV 707, a bypass circuit 709 and an auxiliary semiconductor device 711. The bypass circuit 709 includes a capacitor configured to turn on the auxiliary semiconductor device 711. The auxiliary semiconductor device 711 includes an IGBT713, the IGBT713 being coupled between the MOV 707 and the terminal 703; and a control circuit configured to operate the IGBT713 using the fault current received from the bypass circuit 709. The control circuit includes a diode 715, the diode 715 being coupled to the bypass circuit 709 and the gate of the IGBT 713. The control circuit also includes a zener diode 721, a gate capacitor 717, and a resistor 719, all coupled in parallel between the gate of the IGBT713 and the terminal 703.

During a fault condition, fault current first flows through bypass circuit 709 and gate capacitor 717. Once the gate voltage of the IGBT713 exceeds the gate threshold voltage, the IGBT713 is turned on, and a fault current flows through the bypass circuit 709 and the IGBT 713. When the voltage of the bypass circuit 709 rises to the clamp voltage of MOV 707, the fault current commutates from the bypass circuit 709 to MOV 707. Resistor 719 is configured to discharge gate capacitor 717 when MOV 707 sinks a fault current. The IGBT713 is turned off once the voltage across the gate capacitor 717 decreases below the gate threshold voltage.

Referring to fig. 8, an exemplary SSCB 800 is illustrated, the exemplary SSCB 800 including a main switching device 805 and a voltage clamp 806 coupled in parallel. Main switching device 805 includes terminals 801 and 803. The voltage clamp 806 includes an MOV807, a bypass circuit 809, and an auxiliary semiconductor device 815.

Bypass circuit 809 includes a capacitor 811 and a resistor 813 coupled to terminal 801. The capacitor 811 is configured to provide a fault current to the auxiliary semiconductor device 815 to effectively turn on the auxiliary semiconductor device 815. Resistor 813 is configured to provide a fault current to auxiliary semiconductor device 815 to effectively turn auxiliary semiconductor device 815 off.

The auxiliary semiconductor device 815 includes an IGBT 817, the IGBT 817 being coupled between the MOV807 and the terminal 803; and a control circuit configured to operate the IGBT 817 using the fault current received from the bypass circuit 809. The control circuit includes a gate capacitor 819, which gate capacitor 819 is coupled between capacitor 811 and terminal 803. The gate of the IGBT 817 is coupled to the capacitor 811 and the gate capacitor 819. The control circuit also includes an IGBT821 coupled in parallel with a gate capacitor 819, a gate capacitor 823 coupled between resistor 813 and terminal 803, and a zener diode coupled in parallel with gate capacitor 823. The gate of the IGBT821 is coupled to a resistor 813 and a gate capacitor 823.

During a fault condition, a fault current flows through capacitor 811 and gate capacitor 819. Once the gate voltage of the IGBT 817 exceeds the gate voltage threshold, the IGBT 817 turns on and the fault current commutates from the bypass circuit 809 to the MOV 807. When the MOV807 sinks the fault current, a portion of the fault current flows through resistor 813 and gate capacitor 823. When the gate voltage of the IGBT821 exceeds the gate voltage threshold, the IGBT821 is turned on. In response to the IGBT821 being turned on, the gate voltage of the IGBT 817 decreases below the gate threshold, turning off the IGBT 817. The capacitances of capacitors 811, 819 and 823 and the resistance value of resistor 813 are sized such that IGBT 817 is turned on in response to voltage clamp 806 receiving a fault current and IGBT 817 is turned off when the fault current is reduced to zero.

Further written description of several exemplary embodiments is now provided. One embodiment is a Solid State Circuit Breaker (SSCB) comprising a main switching device including a first terminal and a second terminal; and a voltage clamp circuit coupled in parallel with the primary switching device, the voltage clamp circuit comprising a Metal Oxide Varistor (MOV) coupled in series between the first terminal and an auxiliary semiconductor device arranged to selectively couple the MOV with the second terminal; a bypass circuit is coupled between the first terminal and the auxiliary semiconductor device.

In some forms of the above-described SSCB, the voltage clamping circuit is configured to receive the fault current after the main switching device is turned off, and wherein the auxiliary semiconductor device is configured to turn on in response to receiving the fault current by way of the bypass circuit. In some forms the fault current is commutated from the bypass circuit to the MOV in response to the auxiliary semiconductor device being turned on. In some forms turning on the auxiliary semiconductor device generates a voltage spike across the auxiliary semiconductor device before turning on the auxiliary semiconductor device, wherein the MOV voltage increases to an MOV clamp voltage after turning on the auxiliary semiconductor device, and wherein the voltage clamp circuit is configured such that the combination of the voltage spike and the MOV voltage never exceeds the MOV clamp voltage. In some forms the bypass circuit is configured to allow the fault current to flow from the first terminal to the auxiliary semiconductor device without flowing through the MOV to effectively turn on the auxiliary semiconductor device before the MOV voltage increases to the MOV clamp voltage. In some forms the voltage clamp circuit is configured such that the total clamp voltage across the voltage clamp circuit does not exceed the MOV clamp voltage. In certain forms the auxiliary semiconductor device comprises a Transient Voltage Suppression (TVS) thyristor or TVS diode coupled between the MOV and the second terminal, and wherein the bypass circuit comprises a capacitor coupled in parallel with the MOV. In some forms the auxiliary semiconductor device includes a switching device and a control circuit, wherein the switching device and the control circuit are coupled to the bypass circuit. In some forms the bypass circuit includes a capacitor coupled to the control circuit and coupled in parallel with the MOV. In some forms the bypass circuit includes a capacitor coupled to the switching device and the control circuit, and a resistor coupled to the control circuit.

Another exemplary embodiment is a method for protecting a main switching device of a Solid State Circuit Breaker (SSCB), the main switching device comprising: coupling a voltage clamp circuit in parallel with the primary switching device, the voltage clamp circuit including a Metal Oxide Varistor (MOV), an auxiliary semiconductor device, and a bypass circuit; after turning off the main switching device, the auxiliary semiconductor device receives a fault current by means of the bypass circuit; switching on the auxiliary semiconductor device using the fault current; the fault current is commutated from the bypass circuit to the MOV in response to the auxiliary semiconductor device being turned on.

In some forms of the above method, the MOV is coupled in parallel with a bypass circuit, wherein the MOV is coupled in series with a switching device of the auxiliary semiconductor device. In some forms the commutation of the fault current from the bypass circuit to the MOV begins after a switching device coupled to an auxiliary semiconductor device of the MOV closes and ends when the MOV voltage increases to an MOV clamp voltage. In some forms turning on the auxiliary semiconductor device generates a voltage spike across the auxiliary semiconductor device, wherein upon turning on the auxiliary semiconductor device, the MOV voltage of the MOV increases to an MOV clamp voltage, wherein the voltage clamp circuit is configured such that the combination of the voltage spike and the MOV voltage never exceeds the MOV clamp voltage. In some forms the bypass circuit allows a fault current to flow from the first terminal of the SSCB to the auxiliary semiconductor device without flowing through the MOV to effectively turn on the auxiliary semiconductor device before the MOV voltage reaches the MOV clamp voltage. In certain forms the voltage clamp circuit is configured such that a total clamp voltage across the voltage clamp circuit does not exceed an MOV clamp voltage of the MOV. In some forms the auxiliary semiconductor device comprises a Transient Voltage Suppression (TVS) thyristor or TVS diode coupled in series with the MOV, and wherein the bypass circuit comprises a capacitor coupled in parallel with the MOV. In some forms the auxiliary semiconductor device includes a switching device and a control circuit, wherein the switching device and the control circuit are coupled to the bypass circuit. In some forms the bypass circuit includes a capacitor coupled to the control circuit and coupled in parallel with the MOV. In some forms the bypass circuit includes a capacitor coupled to the switching device and the control circuit, and a resistor coupled to the control circuit.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain exemplary embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. It should be understood that while the use of words such as "preferred," "preferably," "preferred," or "more preferred," etc. utilized in the foregoing description indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the disclosure, that scope being defined by the claims that follow. In reading the claims, it is intended that when words such as "a," "an," "at least one," or "at least a portion" are used, it is not intended that the claims be limited to only one item unless specifically recited in the claim. The term "of" may imply an association or connection with another item and also belong to or be connected with another item as the context in which it is used dictates. Unless expressly stated to the contrary, the terms "coupled to," "coupled with … …," and the like include indirect connections and couplings, and also include but do not require direct couplings or connections. When the language "at least a portion" and/or "a portion" is used, the item can include a portion and/or the entire item unless specifically stated to the contrary.