WO2022125094A1

WO2022125094A1 - Resonant circuit for disconnect switch

Info

Publication number: WO2022125094A1
Application number: PCT/US2020/064217
Authority: WO
Inventors: Christopher Alan Belcastro; Veerakumar Bose
Original assignee: Abb Schweiz Ag
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2022-06-16
Also published as: CN116964939A; EP4260463A1

Abstract

A disconnect switch includes a main switching device including a thyristor configured and operable to selectably close and open a main circuit between a first terminal and a second terminal. A resonant circuit is operatively coupled with the first terminal and the second terminal in parallel with the main switching device and includes a capacitor and switching devices configured and operable to selectably close and open an auxiliary circuit. In a closed state, the auxiliary circuit commutates current from the main circuit through the capacitor and applies a voltage of the capacitor effective to bias the thyristor toward an open circuit state.

Description

RESONANT CIRCUIT FOR DISCONNECT SWITCH

BACKGROUND

[0001] The present disclosure relates generally to disconnect switches. Conventional disconnect switches are structured to interrupt load currents in order to isolate one portion of a power system from another portion. For example, a disconnect switch coupled between a utility grid and a microgrid is structured to isolate the microgrid from the utility grid. Existing disconnect switches suffer from a number of shortcomings and disadvantages. There remain unmet needs including reducing power network stress and increasing disconnect switch response speed. For instance, existing disconnect switches may respond to an isolation command within 20ms, during which components of the power network and the disconnect switch itself are subjected to increased stress, and during which the power network continues to experience a fault condition that may lead to a power system blackout. In view of these and other shortcomings in the art, there is a significant need for the unique apparatuses, methods, systems, and techniques disclosed herein.

DISCLOSURE OF EXAMPLE EMBODIMENTS

[0002] 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.

SUMMARY OF THE DISCLOSURE

[0003] Example embodiments of the disclosure include unique systems, methods, techniques, and apparatuses for resonant-based thyristor commutation. Further embodiments, forms, objects, features, advantages, aspects, and benefits of the disclosure shall become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Fig. 1 illustrates an example power network.

[0005] Figs. 2A-2E illustrates the example power network of Fig. 1 in a series of operational states.

[0006] Fig. 3 illustrates a plurality of graphs depicting electrical characteristics over time of the example power network of Fig. 1.

[0007] Fig. 4 illustrates an example three-phase power network

[0008] Fig. 5 illustrates another example power network.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0009] With reference to Fig. 1, there is illustrated an example electrical power network

10 (also referred to herein as power network 10 or network 10) including a disconnect switch 11. The power network 10 includes two portions electrically coupled to one another by a disconnect switch 11. In the illustrated embodiment, the first portion of the power network 10 comprises a utility grid 1 and the second portion of the power network 10 comprises a microgrid 3. It shall be appreciated that microgrid 3 is a portion of the power network including at least one load and one distributed energy resource structured to distribute power to the loads of the microgrid in the event the microgrid is disconnected from utility grid 1. In other embodiments, disconnect switch

11 may be incorporated into another type of power network, or at another location within a utility grid. Although power network 10 may be structured to transmit single phase or multiphase power. For multiphase power applications, a disconnect switch such as disconnect switch 11 is provided for and coupled with each phase.

[0010] Disconnect switch 11 includes a first disconnect switch terminal 2 (also referred to herein as terminal 2), a second disconnect switch terminal 4 (also referred to herein as terminal 4), a main switching device 12, and a resonant turn-off (RTO) circuit 13. An electronic control system (ECS) 14 is operatively coupled with the disconnect switch 11 and may be considered to be a portion or component of the disconnect switch 11. The ECS may include one or more integrated circuit-based (e.g., microprocessor-based, microcontroller-based, ASICbased, FPGA-based, and/or DSP-based) control units as well as related driver, input/output, signal conditioning, signal conversion, and other circuitry. In certain embodiments, the RTO circuit 13 and the ECS 14 may be housed in a subassembly module or unit structured to be mounted to the main switching device 12. The subassembly module may include a housing structured to enclose ECS 14 and RTO circuit 13, or one or more circuit boards structured to contain ECS 14 and RTO circuit 13 or portions thereof.

[0011] Disconnect switch 11 is structured to open in response to determining a power quality event is occurring. In order to reduce the time between determining the power quality event is occurring and opening main switching device 12, RTO circuit 13 is configured and operable to output a resonant current to main switching device 12 to force the commutation of the main switching device. [0012] Main switching device 12 is structured to selectively conduct bidirectional power between utility grid 1 and microgrid 3. Main switching device 12 is conductively coupled with terminal 2 which is also conductively coupled to utility grid 1. Main switching device 12 is also conductively coupled with terminal 4 which is also conductively coupled with microgrid 3. In the illustrated embodiment, main switching device 12 includes a thyristor Smi coupled in an antiparallel configuration with thyristor Sm2. In other embodiments, the main switching device 12 may include semiconductor switches coupled in different arrangements. Main switching device 12 may include silicon controlled thyristors, gate turn-off thyristors, emitter turn-off thyristors, reverse conducting thyristors, bidirectional triode thyristors, integrated gate commutated thyristors, or reverse-blocking integrated gate commutated thyristors, to name several examples. [0013] RTO circuit 13 is conductively coupled with terminal 2 and terminal 4 in parallel with main switching device 12 and is structured to receive power and output a resonant current to main switching device 12. RTO circuit 13 includes a plurality of legs 31, 33 and, 35 coupled across a bus 36. It shall be appreciated that RTO circuit 13 is one example of a resonant circuit according to the present disclosure. Other embodiments may include a number of additions, modifications, or alternative resonant circuit arrangements including different types and arrangements of legs, switching devices, and capacitors.

[0014] It shall be appreciated that other embodiments comprise other types of operative couplings associated with terminal 2 or terminal 4. For example, such operative couplings may include one or more transformers providing an electrically isolated coupling between one or more of the utility grid and the terminal 2, the terminal 2 and the main switching device 12, the terminal 2 and the RTO circuit 13, the microgrid 3 and the terminal 4, the terminal 4 and the main switching device 12, and/or the terminal 4 and the RTO circuit 13.

[0015] Leg 31 includes a first RTO switching device Sri coupled in series with a second RTO switching device Sr2 at a midpoint connection 6 (also referred to as an input/output (I/O) port 6) which is coupled to terminal 4. The first RTO switching device Sri is coupled with a first rail 36a of the bus 36 and the second RTO switching device Sr2 is coupled with a second rail of the bus 36. Leg 35 includes a third RTO switching device SB coupled in series with a fourth RTO switching device Sr4 at a midpoint connection 8 (also referred to as input/output (I/O) port 8). The third RTO switching device S is coupled with the first rail 36a of the bus 36 and the fourth RTO switching device Sr4 is coupled with the second rail 36b of the bus 36. In the illustrated embodiment, the RTO switching devices Sri, Sr2, SB, Sr4 comprise thyristors. In other embodiments, the RTO switching devices Sri, SB, S , Sr4 may comprise other types of semiconductor switching devices such as insulated gate bipolar transistors (IGBT). Legs 31 and 35 are structured to receive AC power, convert the received power to DC power, output the DC power to bus 36, and convert the DC power of the bus 36 to AC power.

[0016] Leg 33 includes a first resonant capacitor Cri coupled in series with a second resonant capacitor CB at a midpoint connection 7. The first resonant capacitor Cri is coupled with the first rail 36a of the bus 36 and the second resonant capacitor CB is coupled with the second rail 36b of the bus 36. 133a. A pre-charging circuit 38 is configured and operable to precharge the second resonant capacitor CB to a voltage reference value Vco. A first branch 32 is coupled the second rail 36b of the bus 36 and the midpoint connection 7 and includes an auxiliary switching device Sa coupled in antiparallel with a freewheeling diode D. A second branch 34 is coupled the second rail 36b of the bus 36 and the midpoint connection 7 and includes a voltage clamping device (also referred to herein as a voltage clamp) which provides unipolar voltage clamping across the first resonant capacitor Cri. In the embodiment of Fig. 1, the voltage clamp is a metal oxide varistor (MOV) 9. Other embodiments may include other types or arrangements of voltage clamps. A resonant inductor Lr is coupled between the midpoint connection 8 and the terminal 2 and limits the time rate of change of current (di/dt) for softer commutation. Some forms may additionally or alternatively include another resonant inductor coupled between midpoint connection 6 and terminal 4.

[0017] The ECS 14 is operatively coupled with main switching device 12 and is configured and operable to provide control signals to the thyristor Smi and the thyristor Sm2 to selectably turn each of turn these devices on (e.g., a closed or conductive state) or off (e.g., an open or non-conductive state). The ECS 14 is also operatively coupled with the RTO circuit 13 and is configured and operable to provide control signals to the RTO switching device Sri, RTO switching device SB, RTO switching device SB, and RTO switching device Sr4 to selectably turn each of these devices on (e.g., a closed or conductive state) or off (e.g., an open or non- conductive state). The ECS 14 is also configured and operable to receive one or more inputs 15a indicative of voltage and current values of the utility grid 1, and one or more inputs 15b indicative of voltage and current values of the microgrid 3. The ECS 14 is further configured and operable to determine (e.g, calculate, identify or predict) a power quality in response to the one or more received inputs 15a and/or the one or more received input 15b and, in response to determining a power quality event, initiate or start a turn-off operation of the disconnect switch 11. Power quality events may include utility grid frequency deviation, microgrid frequency deviation, voltage sag, voltage swell, short circuit conditions, and ground fault conditions, to name several examples.

[0018] The ECS 14 operates the RTO circuit 13 to generate and provide a resonant current (IR) configured and operable to force commutation of the main switching device 12. The resonant current (IR) causes the magnitude of the current conducted by main switching device 12 to decrease to zero and causes a reverse voltage bias across the main switching device 12. The ECS 14 is also structured to control pre-charging circuit 38 to pre-charge the second resonant capacitor Cr2 and discharge the second resonant capacitor Cr2 based on a voltage reference value. In certain embodiments, the voltage reference value includes a range with a minimum and maximum threshold. In certain embodiments, the voltage reference value is greater than a nominal RMS voltage of the power received from utility grid 1. In certain embodiments, ECS 14 may adjust the voltage reference value in order to control the peak resonant current.

[0019] The RTO circuit 13 may increase the speed at which the disconnect switch 11 operates to open the main switching device 12 (e.g., 80% faster compared to the same disconnect switch 11 without the RTO circuit 13). In certain embodiments, disconnect switch 11 may open the main switching device 12 within 4-18ms of the beginning of the power quality event. In certain embodiments, disconnect switch 11 may open the main switching device 12 within 5ms of the beginning of the power quality event that caused ECS 14 to activate RTO circuit 13.

[0020] Figs. 2A-2E and 3 shows a series of operational states associated with a turn-off operation of the disconnect switch 11. As further described below, Figs. 2A-2E illustrate current flow paths of a main current (Imain) through the main switching device 12, resonant current (IR) through the RTO circuit 13, and a net load current (Iioad) between the microgrid 3 and the utility grid 1 through the disconnect switch 11.

[0021] Fig. 3 illustrates graphs 310, 320, and 330 depicting electrical characteristics of example power network 100 during a turn-off operation the disconnect switch 11 started and controlled by the ECS 14 in response to a power quality event. Graph 310 illustrates “ON” and “OFF” voltage values as a function of time for a main thyristor gate signal 311 (e.g., a signal provided to turn thyristor Smi or thyristor Sm2 on or off), an RTO switching device gate signal 312 (e.g., signals provided to turn RTO switching devices Sri, Sr2, SB, Sr4 on or off), and an auxiliary switching device gate signal 313 (e.g., a signal provided to turn auxiliary switching device Sa on or off). Graph 320 illustrates a curve 321 of load current (Load) e.g., current through the disconnect switch 11 from the microgrid 3 to the utility grid 1) as a function of time, a curve 322 of resonant current (IR) (e.g., current flowing between or through RTO switching device Sri and RTO switching device SB as a function of time, and a curve 323 of a main thyristor current (Imain) e.g., current though thyristor Smi or through thyristor Sm2). Graph 330 illustrates a curve 331 of second resonant capacitor CB voltage (VCB) as a function of time, a curve 332 of auxiliary switch voltage / clamping capacitor voltage (Vsa / Ven) as a function of time, and a curve 333 of main thyristor voltage (Vsmi) as a function of time.

[0022] As shown in Fig. 2A and Fig. 3, before time tl, the main current (Imam) through the thyristor Smi is equal to and constitutes the load current (Iioad) from the microgrid 3 to the utility grid 1. At time tl, the ECS 14 initiates a turn-off operation of the main switching device 12 and, depending on the direction of the load current, controls corresponding auxiliary switching devices of the RTO circuit 13. In the operational state illustrated in Fig. 2A, the thyristor Smi conducts the load current prior to time tl . At time tl, a turn-off operation is started and RTO switching device Sri, RTO switching device Sr4 and auxiliary switching device Sa are controlled to initiate the turn-off sequence. It shall be appreciated that the load current may alternatively flow in the opposite direction from the utility grid 1 to the microgrid 3 through thyristor Sm2, and that operating modes of Figs. 2B-2D may likewise involve load currents and main currents flowing in opposite directions from those illustrated and resonant currents flowing between or through RTO switching devices Sr2 and S , rather than currents flowing between or through RTO switching devices Sri and Sr4 as in the illustrated embodiment.

[0023] As shown in Fig. 3, at time tl, the ECS 14 turns off the main thyristor gate signal 311 and turns on the RTO switching device gate signal 313 and the auxiliary switching device gate signal 315 to initiate the turn-off operation. In response, the resonant current (IR) of curve 322 begins to increase, the main current (Imam) of curve 323 begins to decrease in proportion to the increase in IR, and the load current (Iioad) of curve 321, which is equal to the sum of IR and Imam, remains substantially constant. From time tl to time t2, the proportional decrease in Imain and the increase in IR continues and an increasing portion of Iioad is forced to commutate from the thyristor Smi of the main switching device 12 to the RTO circuit 13 as shown in Fig. 2B. The main thyristor voltage (Vsmi) of curve 333 has also decreased from zero to time tl to a negative voltage at time t2.

[0024] At time t2, the main current (Imain) of curve 323 has decreased to zero and the resonant current (IR) of curve 322 has increased to be equal to the load current (Load) of curve 321. Also, at time t2, a reversed bias voltage from the capacitor Cr2 is applied to the anode of the thyristor Smi to speed up its turning-off or commutation to an off state as shown in Fig. 2C. Between time t2 and time t3, the second resonant capacitor Cr2 discharges and the resonant capacitor voltage (Vcr2) of curve 331 decreases as shown in Fig. 3. The energy in second resonant capacitor Cr2 may be selected to be large enough to maintain the voltage polarity and reverse bias to the thyristor Smi. The time period between time t2 and time t3 may be selected to be sufficient enough to allow enough time for the thyristor Smi to commutate and turn off.

[0025] At time t3, the thyristor Smi is completely turned off and ready to block forward voltage, and auxiliary thyristors Sri, Sr4, and auxiliary switching device Sa are commanded to turn off by ECS 14 changing the value of RTO switching device gate signal 312 and an auxiliary switching device gate signal 313 to off. From time t3 to time t4 the resonant capacitor Cri voltage (Vcri) increases until reaching clamping voltage as shown in Fig. 2D. Loop energy is absorbed by the MOV 9 and capacitor Cri which serve as a snubber circuit to dissipate the resonant current (IR). Accordingly, the load current (Load) is zero and completely interrupted at t4. Resonant switches Sri, Sr4 are off time t4 as shown in Fig. 2E.

[0026] It is contemplated that the various aspects, features, processes, and operations from the various embodiments may be used in any of the other embodiments unless expressly stated to the contrary. Certain operations illustrated may be implemented by a computer including a processing device executing a computer program product on a non-transient, computer-readable storage medium, where the computer program product includes instructions causing the processing device to execute one or more of the operations, or to issue commands to other devices to execute one or more operations.

[0027] In the embodiment of Fig. 1, power network 10 is illustrated in a single-phase form. It shall be appreciated that other embodiment may comprise multi-phase forms. For example, Fig. 4 illustrates a three-phase power network 10a wherein a three-phase utility grid la and a three-phase microgrid 3a are selectably coupled by a three-phase disconnect switch arrangement I la. [0028] Phase Vac-r of the three-phase microgrid 3a is operatively coupled with disconnect switch terminal 4a and phase Vac-u of the three-phase utility grid la is operatively coupled with disconnect switch terminal 2a. An RTO circuit 13a and a main switching device 12a are operatively coupled with disconnect switch terminal 2a and disconnect switch terminal 4a in parallel with one another.

[0029] Phase Vac-s of the three-phase microgrid 3b is operatively coupled with disconnect switch terminal 4b and phase Vac-v of the three-phase utility grid lb is operatively coupled with disconnect switch terminal 2b. An RTO circuit 13b and a main switching device 12b are operatively coupled with disconnect switch terminal 2b and disconnect switch terminal 4b in parallel with one another.

[0030] Phase Vac-t of the three-phase microgrid 3c is operatively coupled with disconnect switch terminal 4c and phase Vac-w of the three-phase utility grid 1c is operatively coupled with disconnect switch terminal 2c. An RTO circuit 13c and a main switching device 12c are operatively coupled with disconnect switch terminal 2c and disconnect switch terminal 4c in parallel with one another.

[0031] RTO circuits 13a, 13b, 13c may include the components and functionalities of RTO circuit 13 described above or RTO circuit 130 described below. Main switching devices 12a, 12b, 12c may include the same components and functionalities as main switching device 12 described above or main switching device 120 described below.

[0032] An electronic control system (ECS) 14a is operatively coupled with main switching devices 12a, 12b, 12c, and is configured and operable to provide control signals to selectably turn each of turn their respective thyristors or other main switching components on (e.g., a closed or conductive state) or off (e.g., an open or non-conductive state). The ECS 14 is also operatively coupled with the RTO circuits 13a, 13b, 13c and is configured and operable to provide control signals to selectably turn respective switching devices of each RTO circuit on (e.g., a closed or conductive state) or off (e.g., an open or non-conductive state). The ECS 14 is also configured and operable to receive one or more inputs indicative of voltage and current values of the three-phase utility grid la, and one or more inputs indicative of voltage and current values of the microgrid 3a. During operation, the ECS 14a may control each phase individually in accordance with control operations and functions of ECS 4 and disconnect switch 11 described above. [0033] With reference to Fig. 5, there is illustrated an example power network 100 including a disconnect switch 110. Network 100 includes two portions of the power network coupled together by way of disconnect switch 110. In the illustrated embodiment, the first portion of the power network is utility grid 101 and the second portion of the power network is microgrid 103. It shall be appreciated that microgrid 103 is a portion of the power network including at least one load and one distributed energy resource structured to distribute power to the loads of the microgrid in the event the microgrid is disconnected from utility grid 101. In other embodiments, disconnect switch 110 may be incorporated into another type of power network, or at another location within a utility grid. Although power network 100 is illustrated with a single line diagram, power network 100 may be structured to transmit single phase or multiphase power. For multiphase power applications, a separate disconnect switch such as disconnect switch 110 is coupled to each phase.

[0034] Disconnect switch 110 includes a main switching device 120, a resonant turn-off (RTO) circuit 130, and an ECS 140 (also referred to herein as controller 140). Disconnect switch 110 is structured to open in response to determining a power quality event is occurring. In order to reduce the time between determining the power quality event is occurring and opening main switching device 120, RTO circuit 130 is structured to output a resonant current to main switching device 120 to force the commutation of the main switching device. It shall be appreciated that RTO circuit 130 is one example of a resonant circuit according to the present disclosure. Other embodiments may include a number of additions, modifications, or alternative resonant circuit arrangements including different types and arrangements of legs, switching devices, and capacitors.

[0035] Main switching device 120 is structured to selectively conduct bidirectional power between utility grid 101 and microgrid 103. Main switching device 120 includes a terminal 125 coupled to utility grid 101 and a terminal 127 coupled to microgrid 103. The couplings of these components may conductive couplings or other types of operative couplings such as those described above in connection with Fig. 1.

[0036] In the illustrated embodiment, main switching device 120 includes a thyristor 121 coupled in an anti-parallel configuration with thyristor 123. In other embodiments, the main switching device 120 may include semiconductor switches coupled in different arrangements. Main switching device 120 may include silicon controlled thyristors, gate turn-off thyristors, emitter turn-off thyristors, reverse conducting thyristors, bidirectional triode thyristors, integrated gate commutated thyristors, or reverse-blocking integrated gate commutated thyristors, to name but a few examples.

[0037] RTO circuit 130 is coupled in parallel with main switching device 120 and is structured to receive power and output a resonant current to main switching device 120. RTO circuit 130 includes a plurality of legs 131-135 coupled across a direct current (DC) bus 136. [0038] Leg 131 includes an auxiliary switching device 131a coupled in series with an auxiliary switching device 131b at a midpoint connection 131c. Terminal 125 is coupled to midpoint connection 131c. Leg 135 includes an auxiliary switching device 135a coupled in series with an auxiliary switching device 135b at a midpoint connection 135c. In the illustrated embodiment, the auxiliary switching devices of legs 131 and 135 each include a thyristor. In other embodiments, the auxiliary switching devices of legs 131 and 135 may include an insulated gate bipolar transistor (IGBT) or another type of semiconductor switch. Legs 131 and 135 are structured to receive AC power, convert the received power to DC power, output the DC power to bus 136, receive DC power, and convert the received DC power to AC power.

[0039] Leg 133 includes a resonant capacitor 133a. In certain embodiments, leg 133 includes a plurality of resonant capacitors. A voltage sensor 137 is structured to measure capacitor voltage Vi33a across resonant capacitor 133a. In certain embodiments, voltage sensor 137 may be a voltage divider, or another type of device structured to measure voltage. In order to supply resonant current to main switching device 120, capacitor voltage Vi33ais greater than a voltage of the power conducted through main switching device 120.

[0040] Leg 132 includes a pre-charging circuit structured to charge resonant capacitor 133a to increase capacitor voltage Vi33ato a voltage reference value. Leg 132 includes currentlimiting resistors 132a, 132e, and diodes 132b, 132d coupled in series, the diodes 132b, 132d being coupled at a midpoint connection 132c. An auxiliary switching device 132f is coupled between midpoint connection 132c and midpoint connection 131c, and is structured to selectively conduct a charging current through leg 132 to resonant capacitor 133a. In other embodiments, RTO circuit 130 does not include a charging circuit or includes a charging circuit having a topology different from the illustrated leg topology.

[0041] Leg 134 includes a discharge circuit structured to discharge resonant capacitor 133a to decrease capacitor voltage Vi33a to a voltage reference value. Leg 134 includes an auxiliary switching device 134a coupled in series with a discharge resistor 134b. Auxiliary switching device 134a is structured to selectively conduct current from capacitor 133a through discharge resistor 134b in order to decrease capacitor voltage Vi33a. In other embodiments, RTO circuit 130 does not include a discharge circuit or includes a discharge circuit having a topology different from the illustrated leg topology. A resonant inductor 138 is coupled between midpoint connection 135c and terminal 127. Some forms may additionally or alternatively include another resonant inductor coupled between midpoint connection 131c and terminal 125.

[0042] Disconnect switch 110 includes a controller 140 structured to operate the switching devices of main switching device 120 and RTO circuit 130, receive voltage Vi33a measurements from voltage sensor 137, maintain voltage Vi33a with respect to a voltage reference value, and respond to a power quality event by opening main switching device 120 using resonant current IR from RTO circuit 130.

[0043] Controller 140 operates RTO circuit 130 so as to generate and transmit resonant current IR configured to force commutate main switching device 120. Resonant current IR causes the magnitude of the current conducted by main switching device 120 to decrease to zero and causes a reverse voltage bias across the main switching device 120.

[0044] During operation of the RTO circuit, auxiliary switching devices 131b and 135a are turned on during positive half cycles and turned off during negative half cycles and auxiliary switching devices 131a and 135b are turned off during positive half cycles turned on during negative half cycles.

[0045] Controller 140 is also structured to pre-charge capacitor 133a and discharge capacitor 133a based on a voltage reference value. In certain embodiments, the voltage reference value includes a range with a minimum and maximum threshold.

[0046] In response to determining a voltage measurement from voltage sensor 137, which corresponds to voltage Vi33a, is less than the voltage reference value, controller 140 closes auxiliary switching device 132f until the voltage Vi33a increases to the voltage reference value. While auxiliary switching device 132f is closed, power is received by the pre-charging circuit, rectified by diodes 132b and 132d, and output to capacitor 133a.

[0047] In response to determining a voltage measurement from voltage sensor 137 is greater than the voltage reference value, controller 140 closes auxiliary switching device 134a until voltage Vi33a decreases to the voltage reference value. While auxiliary switching device 134a is closed, energy stored in capacitor 133a is dissipated using discharge resistor 134b.

[0048] In certain embodiments, the voltage reference value is greater than a nominal RMS voltage of the power received from utility grid 101. In certain embodiments, controller 140 may adjust the voltage reference value in order to control the peak resonant current.

[0049] Using RTO circuit 130, disconnect switch 110 opens main switching device 120 up to 80% faster compared to the same disconnect switch without RTO circuit 130. In certain embodiments, disconnect switch 110 may open the main switching device 120 within 4-18ms of the beginning of the power quality event. In certain embodiments, disconnect switch 110 opens the main switching device 120 within 5ms of the beginning of the power quality event that caused controller 140 to activate RTO circuit 130.

[0050] In certain embodiments, controller 140 includes a microcontroller. In certain embodiments, disconnect switch 110 includes additional components. For example, disconnect switch 110 may include voltage clamping devices, such as metal oxide varistors (MOVS) or thermally protected MOVs. The voltage clamping devices may be coupled in parallel with main switching device 120 or coupled across bus 136, to name but a few examples. In certain embodiments, RTO circuit 130 and controller 140 are housed in a subassembly module structured to be mounted to main switching device 120. The subassembly module may include a housing structured to enclose controller 140 and RTO circuit 130, or one or more circuit boards structured to house controller 140 and RTO circuit 130.

[0051] One example embodiment is an apparatus comprising: a disconnect switch including: a main switching device including a thyristor operatively coupled with a first disconnect switch terminal and a second disconnect switch terminal, the thyristor being configured and operable to selectably close and open a main circuit between the first disconnect switch terminal and the second disconnect switch terminal in response to main switching device control signals received from an electronic control system; and a resonant circuit operatively coupled with the first disconnect switch terminal and the second disconnect switch terminal in parallel with the main switching device, the resonant circuit including a first switching device, a second switching device, and a capacitor, the first switching device and the second switching device being configured and operable to selectably close and open an auxiliary circuit including the capacitor between the first disconnect switch terminal and the second disconnect switch terminal in response to resonant circuit control signals received from the electronic control system, wherein in a closed state, the auxiliary circuit commutates current from the main circuit through the capacitor and applies a voltage of the capacitor effective to bias the thyristor toward an open circuit state.

[0052] In some forms, the resonant circuit comprises: a bus including a first rail and a second rail, a first leg coupled across the first rail and the second rail of the bus including the first switching device and a third switching device coupled in series at first midpoint connection, a second leg coupled across the first rail and the second rail of the bus including said capacitor and an additional capacitor coupled at a second midpoint connection, and a third leg coupled across the first rail and the second rail of the bus including the second switching device and a fourth switching device coupled in series at a third midpoint connection. In some forms, the second leg of the resonant circuit comprises: a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including an auxiliary switching device, and a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including voltage clamp. In some forms, the auxiliary switching device is configured and operable in combination with the first switching device and the second switching device to selectably close and open the auxiliary circuit including in response to the resonant circuit control signals. In some forms, the voltage clamp and the additional capacitor are configured to operable to dissipate current through the auxiliary circuit. In some forms, the resonant circuit comprises: an inductor coupled between the third midpoint connection and one of the first disconnect switch terminal and the second disconnect switch terminal. In some forms, the resonant circuit includes a pre-charge circuit configured to charge said capacitor prior to said voltage of the capacitor effective to bias the thyristor toward an open circuit state. In some forms, the main switching device includes a second thyristor operatively coupled with the first disconnect switch terminal and the second disconnect switch terminal and in anti-parallel with the thyristor. Some forms comprise the electronic control system operatively coupled with the main switching device and the resonant circuit. In some forms, the first disconnect switch terminal is operatively coupled with one of a microgrid and a utility grid and the second disconnect switch terminal is operatively coupled with the other of the microgrid and the utility grid. [0053] A further example embodiment is a method of operating a disconnect switch including a main switching device operatively coupled with a first terminal and a second terminal, a resonant circuit operatively coupled with the first terminal and the second terminal in parallel with the main switching device, and an electronic control system operatively coupled with the main switching device and the resonant circuit, the method comprising: operating the disconnect switch so that the main switching device transmits power between the first terminal and the second terminal through a thyristor of the main switching device and the resonant circuit does not transmit power between the first terminal and the second terminal; operating a first switching device and a second switching device of the resonant circuit with the electronic control system to close an auxiliary circuit of the resonant circuit including the first switching device, the second switching device, and a capacitor, effective to commutate current from the main switching device through the capacitor and to apply a voltage of the capacitor to bias the thyristor toward an open circuit state; and operating the thyristor in the open-circuit state with the electronic control system so that the main switching device does not transmit power between the first terminal and the second terminal. In some forms, the act of operating the first switching device and the second switching device of the resonant circuit with the electronic control system to close the auxiliary circuit of the resonant circuit further includes operating an auxiliary switching device of the resonant circuit with the electronic control system to close the auxiliary circuit of the resonant circuit. In some forms, the resonant circuit comprises: a bus including a first rail and a second rail, a first leg coupled across the first rail and the second rail of the bus including the first switching device and a third switching device coupled in series at first midpoint connection, a second leg coupled across the first rail and the second rail of the bus including said capacitor and an additional capacitor coupled at a second midpoint connection, and a third leg coupled across the first rail and the second rail of the bus including the second circuit switching device and a fourth switching device coupled in series at a third midpoint connection. In some forms, the second leg of the resonant circuit comprises: a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including an auxiliary switching device, and a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including voltage clamp. Come forms comprise, with the thyristor in the opencircuit state, operating the auxiliary switching device with the electronic control system to dissipate current with the voltage clamp and the additional capacitor. In some forms, one or more of: (a) the main switching device includes a second thyristor operatively coupled with the first disconnect switch terminal and the second disconnect switch terminal and in anti-parallel with the thyristor; (b) the first terminal is operatively coupled with one of a microgrid and a utility grid and the second terminal is operatively coupled with the other of the microgrid and the utility grid; (c) said capacitor is pre-charged with a pre-charging circuit to said voltage of the capacitor effective to bias the thyristor toward an open circuit state; and (d) an inductor is coupled between the resonant circuit and at least one of the first disconnect switch terminal and the second disconnect switch terminal.

[0054] Another example embodiment is a system comprising: a disconnect switch including: a first terminal operatively coupled with one of a microgrid and a utility grid and a second terminal operatively coupled with the other of the microgrid and the utility grid; a main switch including a thyristor operatively coupled with a first terminal and a second terminal, the thyristor being configured and operable to selectably turn on and off a main circuit between the first terminal and the second terminal; a resonant circuit operatively coupled with the first terminal and the second terminal in parallel with the main switch, the resonant circuit including a first switch, a second switch, and a capacitor, the first switch and the second switch being configured and operable to selectably turn on and off an auxiliary circuit including the capacitor between the first terminal and the second terminal, wherein in a closed state, the auxiliary circuit commutates current from the main circuit through the capacitor and applies a voltage of the capacitor effective to bias the thyristor toward an off state; and an electronic control system operatively coupled the main switch and the resonant circuit. In some forms, the resonant circuit comprises: a bus including a first rail and a second rail, a first leg coupled across the first rail and the second rail of the bus including the first switch and a third switch coupled in series at first midpoint connection, a second leg coupled across the first rail and the second rail of the bus including said capacitor and an additional capacitor coupled at a second midpoint connection, and a third leg coupled across the first rail and the second rail of the bus including the second switch and a fourth switch coupled in series at a third midpoint connection. In some forms, the second leg of the resonant circuit comprises: a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including an auxiliary switch, and a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including voltage clamp. In some forms, the auxiliary switch is configured and operable in combination with the first switch and the second switch to selectably turn on and off the auxiliary circuit including in response to the resonant circuit control signals. In some forms, the voltage clamp and the additional capacitor are configured to operable to dissipate current through the auxiliary circuit. In some forms, the resonant circuit comprises: an inductor coupled between the third midpoint connection and one of the first terminal and the second terminal. In some forms, the resonant circuit includes a precharge circuit configured to charge said capacitor prior to said voltage of the capacitor effective to bias the thyristor toward an open circuit state. In some forms, the main switch includes a second thyristor operatively coupled with the first terminal and the second terminal and in antiparallel with the thyristor.

[0055] A further example embodiment is a power network or a disconnect switch thereof comprising a resonant circuit including a direct current (DC) bus, a first leg coupled across the DC bus and including a first second auxiliary switching device and a second auxiliary switching device coupled in series at an input terminal, a second leg coupled across the DC bus including a resonant capacitor, a third leg coupled across the DC bus including a third auxiliary switching device and a fourth auxiliary switching device coupled in series at a midpoint connection, and a resonant inductor coupled between the midpoint connection and an output terminal; and a main switching device including a first terminal coupled to the input terminal, and a second terminal coupled to the output terminal. Some forms comprise a controller structured to operate the first, second, third, and fourth auxiliary switching devices based on a voltage of the resonant capacitor so as to output a resonant current at the output terminal, the resonant current being configured to force commutate the main switching device. In some forms, the resonant circuit includes a precharge circuit coupled to the input terminal and the DC bus, and wherein the controller is structured to operate the pre-charge circuit in response to determining a voltage of the resonant capacitor is less than a voltage reference value. In some forms, the resonant circuit includes a discharge circuit coupled to the DC bus, and wherein the controller is structured to operate the discharge circuit in response to determining a voltage of the resonant capacitor is greater than a voltage reference value. In some forms, the controller is structured to adjust a voltage reference value corresponding to a voltage of the resonant capacitor. In some forms, the controller and the resonant circuit are housed in a subassembly module coupled to the first terminal and the second terminal. In some forms, the controller is structured to operate the first, second, third, and fourth auxiliary switching devices so as to output the resonant current in response to a power quality event. In some forms, the resonant current is configured to force commutate the main switching device within 5ms of a beginning of a power quality event.

[0056] Another example embodiment is a power network or a subassembly module thereof comprising a resonant circuit including a direct current (DC) bus, a first leg coupled across the DC bus including a first auxiliary switching device and a second auxiliary switching device coupled in series at an input terminal, a second leg coupled across the DC bus including a resonant capacitor, a third leg coupled across the DC bus including a third auxiliary switching device and a fourth auxiliary switching device coupled in series at a midpoint connection, and a resonant inductor coupled between the midpoint connection and an output terminal; and a controller structured to operate the resonant circuit effective to receive power at the input terminal and output a resonant current at the output terminal. In some forms, the controller is structured to operate the first, second, third, and fourth auxiliary switching devices based on a voltage of the resonant capacitor so as to output the resonant current at the output terminal, the resonant current being configured to force a magnitude of current conducted by a main switching device to zero and cause a reverse voltage bias across the main switching device. In some forms, the resonant circuit includes a pre-charge circuit coupled to the input terminal and the DC bus, and wherein the controller is structured to operate the pre-charge circuit in response to determining a voltage of the resonant capacitor is less than a voltage reference value. In some forms, the resonant circuit includes a discharge circuit coupled to the DC bus, and wherein the controller is structured to operate the discharge circuit in response to determining a voltage of the resonant capacitor is greater than a voltage reference value. In some forms, the controller is structured to adjust a voltage reference value corresponding to a voltage of the resonant capacitor. In some forms, the resonant circuit is structured to be coupled to a first terminal of a main switching device and a second terminal of the main switching device. In some forms, the controller is structured to operate the first, second, third, and fourth auxiliary switching devices so as to output the resonant current in response to a power quality event. In some forms, the resonant current is configured to force commutate a main switching device within 5ms of a beginning of the power quality event. [0057] While the present 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 example embodiments have been shown and described, and that all changes and modifications that come within the spirit of the present disclosure are desired to be protected. It should be understood that while the use of words such as “preferable,” “preferably,” “preferred” or “more preferred” utilized in the description above 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 present disclosure, the 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 one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. The term “of’ may connote an association with, or a connection to, another item, as well as belonging to, or a connection with, the other item as informed by the context in which it is used. The terms “coupled to,” “coupled with” and the like include indirect connection and coupling, and further include but do not require a direct coupling or connection unless expressly indicated to the contrary. 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.

Claims

CLAIMS What is claimed is:

1. An apparatus comprising: a disconnect switch including: a main switching device including a thyristor operatively coupled with a first disconnect switch terminal and a second disconnect switch terminal, the thyristor being configured and operable to selectably close and open a main circuit between the first disconnect switch terminal and the second disconnect switch terminal in response to main switching device control signals received from an electronic control system; and a resonant circuit operatively coupled with the first disconnect switch terminal and the second disconnect switch terminal in parallel with the main switching device, the resonant circuit including a first switching device, a second switching device, and a capacitor, the first switching device and the second switching device being configured and operable to selectably close and open an auxiliary circuit including the capacitor between the first disconnect switch terminal and the second disconnect switch terminal in response to resonant circuit control signals received from the electronic control system, wherein in a closed state, the auxiliary circuit commutates current from the main circuit through the capacitor and applies a voltage of the capacitor effective to bias the thyristor toward an open circuit state.

2. The apparatus of claim 1, wherein the resonant circuit comprises: a bus including a first rail and a second rail, a first leg coupled across the first rail and the second rail of the bus including the first switching device and a third switching device coupled in series at first midpoint connection, a second leg coupled across the first rail and the second rail of the bus including said capacitor and an additional capacitor coupled at a second midpoint connection, and a third leg coupled across the first rail and the second rail of the bus including the second switching device and a fourth switching device coupled in series at a third midpoint connection.

3. The apparatus of claim 2, wherein the second leg of the resonant circuit comprises: a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including an auxiliary switching device, and a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including voltage clamp.

4. The apparatus of claim 3, wherein the auxiliary switching device is configured and operable in combination with the first switching device and the second switching device to selectably close and open the auxiliary circuit including in response to the resonant circuit control signals.

5. The apparatus of claim 4, wherein the voltage clamp and the additional capacitor are configured to operable to dissipate current through the auxiliary circuit.

6. The apparatus of claim 2, wherein the resonant circuit comprises: an inductor coupled between the third midpoint connection and one of the first disconnect switch terminal and the second disconnect switch terminal.

7. The apparatus of claim 1, wherein the resonant circuit includes a pre-charge circuit configured to charge said capacitor prior to said voltage of the capacitor effective to bias the thyristor toward an open circuit state.

8. The apparatus of claim 1, wherein the main switching device includes a second thyristor operatively coupled with the first disconnect switch terminal and the second disconnect switch terminal and in anti-parallel with the thyristor.

9. The apparatus of claim 1 comprising the electronic control system operatively coupled with the main switching device and the resonant circuit.

10. The apparatus of claim 1 wherein the first disconnect switch terminal is operatively coupled with one of a microgrid and a utility grid and the second disconnect switch terminal is operatively coupled with the other of the microgrid and the utility grid.

11. A method of operating a disconnect switch including a main switching device operatively coupled with a first terminal and a second terminal, a resonant circuit operatively coupled with the first terminal and the second terminal in parallel with the main switching device, and an electronic control system operatively coupled with the main switching device and the resonant circuit, the method comprising: operating the disconnect switch so that the main switching device transmits power between the first terminal and the second terminal through a thyristor of the main switching device and the resonant circuit does not transmit power between the first terminal and the second terminal; operating a first switching device and a second switching device of the resonant circuit with the electronic control system to close an auxiliary circuit of the resonant circuit including the first switching device, the second switching device, and a capacitor, effective to commutate current from the main switching device through the capacitor and to apply a voltage of the capacitor to bias the thyristor toward an open circuit state; and operating the thyristor in the open-circuit state with the electronic control system so that the main switching device does not transmit power between the first terminal and the second terminal.

12. The method of claim 11, wherein the act of operating the first switching device and the second switching device of the resonant circuit with the electronic control system to close the auxiliary circuit of the resonant circuit further includes operating an auxiliary switching device of the resonant circuit with the electronic control system to close the auxiliary circuit of the resonant circuit.

13. The method of claim 12, wherein the resonant circuit comprises: a bus including a first rail and a second rail, a first leg coupled across the first rail and the second rail of the bus including the first switching device and a third switching device coupled in series at first midpoint connection, a second leg coupled across the first rail and the second rail of the bus including said capacitor and an additional capacitor coupled at a second midpoint connection, and a third leg coupled across the first rail and the second rail of the bus including the second circuit switching device and a fourth switching device coupled in series at a third midpoint connection.

14. The method of claim 13, wherein the second leg of the resonant circuit comprises: a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including an auxiliary switching device, and a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including voltage clamp.

15. The method of claim 13, comprising: with the thyristor in the open-circuit state, operating the auxiliary switching device with the electronic control system to dissipate current with the voltage clamp and the additional capacitor.

16. The method of claim 11, wherein one or more of:

(a) the main switching device includes a second thyristor operatively coupled with the first disconnect switch terminal and the second disconnect switch terminal and in anti-parallel with the thyristor;

(b) the first terminal is operatively coupled with one of a microgrid and a utility grid and the second terminal is operatively coupled with the other of the microgrid and the utility grid;

(c) said capacitor is pre-charged with a pre-charging circuit to said voltage of the capacitor effective to bias the thyristor toward an open circuit state; and

(d) an inductor is coupled between the resonant circuit and at least one of the first disconnect switch terminal and the second disconnect switch terminal.

17. A system comprising: a disconnect switch including: a first terminal operatively coupled with one of a microgrid and a utility grid and a second terminal operatively coupled with the other of the microgrid and the utility grid; a main switch including a thyristor operatively coupled with a first terminal and a second terminal, the thyristor being configured and operable to selectably turn on and off a main circuit between the first terminal and the second terminal; a resonant circuit operatively coupled with the first terminal and the second terminal in parallel with the main switch, the resonant circuit including a first switch, a second switch, and a capacitor, the first switch and the second switch being configured and operable to selectably turn on and off an auxiliary circuit including the capacitor between the first terminal and the second terminal, wherein in a closed state, the auxiliary circuit commutates current from the main circuit through the capacitor and applies a voltage of the capacitor effective to bias the thyristor toward an off state; and an electronic control system operatively coupled the main switch and the resonant circuit.

18. The system of claim 17, wherein the resonant circuit comprises: a bus including a first rail and a second rail, a first leg coupled across the first rail and the second rail of the bus including the first switch and a third switch coupled in series at first midpoint connection, a second leg coupled across the first rail and the second rail of the bus including said capacitor and an additional capacitor coupled at a second midpoint connection, and a third leg coupled across the first rail and the second rail of the bus including the second switch and a fourth switch coupled in series at a third midpoint connection.

19. The system of claim 18, wherein the second leg of the resonant circuit comprises: a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including an auxiliary switch, and a first branch coupled with the first rail of the bus and the second midpoint connection in parallel with the additional capacitor and including voltage clamp.

20. The system of claim 19, wherein the auxiliary switch is configured and operable in combination with the first switch and the second switch to selectably turn on and off the auxiliary circuit including in response to the resonant circuit control signals.

21. The system of claim 20, wherein the voltage clamp and the additional capacitor are configured to operable to dissipate current through the auxiliary circuit.

22. The system of claim 18, wherein the resonant circuit comprises: an inductor coupled between the third midpoint connection and one of the first terminal and the second terminal.

23. The system of claim 17, wherein the resonant circuit includes a pre-charge circuit configured to charge said capacitor prior to said voltage of the capacitor effective to bias the thyristor toward an open circuit state.

24. The system of claim 17, wherein the main switch includes a second thyristor operatively coupled with the first terminal and the second terminal and in anti-parallel with the thyristor.