Series z-source circuit breaker with pulse-testing capability

Abstract

To provide a series Z-source circuit breaker for cutting power being supplied to a load in response to overcurrent.SOLUTION: A circuit breaker 50 includes a positive bus 22 and a negative bus 24 that can be used for power supply to a load, a breaker switch 26 that is disposed on the positive bus 22 and can operate in order to cut power being supplied to the load in response to overcurrent, an isolation switch 52 that is disposed on the positive bus 22 on the downstream side of the breaker switch 26, a first capacitor 46 that is electrically coupled between the positive bus 22 and the negative bus 24 on the output side of the breaker switch 26, and a second capacitor 48 that is electrically coupled to the positive bus 22 in parallel with the breaker switch 26.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates generally to series-Z power circuit breakers, and more particularly to series-Z power circuit breakers for DC circuits. This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 220,290, filed July 9, 2021, the entire disclosure of which is expressly incorporated herein by reference for all purposes. [Background technology]

[0002] Circuit breakers are often used in medium-voltage DC circuits, such as those used in vehicle charging stations. They open switch contacts, such as vacuum interrupter contacts, in response to large currents, such as fault currents. When the contacts separate and the circuit breaker opens, there is no zero-crossing of the current in the DC circuit that can be used to dissipate the current. Therefore, DC circuit breakers require a mechanism for dissipating the fault current in addition to opening the switch contacts. Furthermore, the very fast rise time of the fault current in DC circuits poses significant challenges for circuit breaker design. Therefore, the prior art has adopted hybrid AC / DC resonant circuits for DC circuit breakers, which generate an oscillating current with a zero-crossing that dissipates the fault current. However, hybrid circuits increase the complexity and cost of the circuit breaker. The prior art has also proposed the use of series-Z power circuit breakers using semiconductor switches in DC circuits. However, as described below, series-Z power circuit breakers have many drawbacks. Summary of the Invention

[0003] SUMMARY OF THE INVENTION A series Z power circuit breaker for a DC circuit is disclosed and described below. In one aspect, a series Z power circuit breaker includes a positive bus and a negative bus usable to supply power to a load, a disconnect switch provided on the positive bus and operable to interrupt power supplied to the load in response to an overcurrent, an isolation switch provided on the positive bus downstream of the disconnect switch, a first capacitor electrically coupled between the positive bus and the negative bus on the output side of the disconnect switch, and a second capacitor electrically coupled to the positive bus in parallel with the disconnect switch.

[0004] In another aspect, a series Z power circuit breaker includes a positive bus and a negative bus usable for supplying power to a load, a shutoff semiconductor switch operable on the positive bus to shut off power supplied to the load in response to an overcurrent, an electromechanical switch electrically coupled to the positive bus in parallel with the shutoff semiconductor switch, a first capacitor electrically coupled between the positive bus and the negative bus on an output side of the shutoff semiconductor switch and a second capacitor electrically coupled to the positive bus in parallel with the shutoff semiconductor switch, and a delay circuit electrically coupled between the positive bus and the negative bus in series with the first capacitor. When no overcurrent is present, the shutoff semiconductor switch is in an open position and the electromechanical switch is in a closed position, allowing supplied power to flow to the load via the electromechanical switch. When an overcurrent is detected, the shutoff semiconductor switch closes and the electromechanical switch opens, and the delay circuit is controlled to delay the time that reverse bias current is sent from the first capacitor to the shutoff semiconductor switch, thereby preventing power from being supplied to the load and allowing the electromechanical switch time to open.

[0005] Further features of the present disclosure will become apparent from the following description and claims, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a circuit diagram of a known series Z power circuit breaker. [Figure 2] FIG. 1 is a circuit diagram of a series Z power circuit breaker including an isolation switch. [Figure 3]FIG. 1 is a circuit diagram of a series Z power circuit breaker including an SCR and a delay circuit. [Figure 4] FIG. 1 is a circuit diagram of a series Z power circuit breaker including an SCR and another type of delay circuit. DETAILED DESCRIPTION OF THE INVENTION

[0007] The following description of disclosed embodiments of a series Z power circuit breaker for a DC circuit is merely exemplary in nature and is not intended to limit the disclosure, its application, or uses.

[0008] 1 is a schematic diagram of a DC circuit 10 including a known series Z-source circuit breaker 12 for protecting a load 14 from an overcurrent from a DC power source 18, such as a battery, in response to a fast-rising fault 20 between a positive bus 22 and a negative bus 24. The circuit breaker 12 includes a semiconductor switch 26, specifically a silicon controlled rectifier (SCR), an LR circuit 28 located on the positive bus 22 at the input or anode side of the SCR 26 and including an inductor 30, a resistor 32, and a diode 34, and an LR circuit 38 located on the positive bus 22 at the output or cathode side of the SCR 26 and including an inductor 40, a resistor 42, and a diode 44. A reverse-bias capacitor 46 is electrically coupled between the positive bus 22 and the negative bus 24 at the output side of the SCR 26, and a floating capacitor 48 is electrically coupled to the positive bus 22 in parallel with the SCR 26 and the LR circuit 38. To create an artificial fault, a manual switch 36 may be provided between the positive bus 22 and the negative bus 24. It is also known to replace the SCR 26 with a switch using a Thomson coil.

[0009] During normal operation of circuit breaker 12, SCR 26 is gated on and conducting, allowing power from power source 18 to be delivered to load 14. Capacitor 46 charges from positive bus 22 and negative bus 24 to the power source potential, and capacitor 48 discharges to zero potential as current flows through SCR 26 and inductor 40. The impedance provided by inductors 30 and 40 controls the voltage on positive bus 22, thereby controlling current flow. When fault 20 occurs, inductors 30 and 40 limit the increase in fault current, and the voltage polarity across SCR 26 almost instantly reverses, with the cathode potential now greater than the anode potential. Reverse recovery current to SCR 26 is provided from capacitor 46 to the cathode side of SCR 26, charging capacitor 48 to allow current to flow around SCR 26. This turns SCR 26 off, preventing current flow through fault 20 and isolating it from power source 18.

[0010] The series-Z power circuit breaker 12 has a number of drawbacks. Specifically, the use of SCRs 26 with semiconductors in the main current conduction path results in resistive losses and, as a result, the need for a cooling system to dissipate heat. This increases the size and cost of the circuit breaker 12 and may be unsuitable for certain medium-voltage applications. Furthermore, the use of SCRs 26 does not create a substantial physical break in the conduction path from the power source 18 to the load 14 when the SCRs 26 are reverse biased and no longer conduct. Thus, current may still flow. Another significant drawback of the circuit breaker 12 is its inability to immediately interrupt a fault when the SCRs 26 gate on. More specifically, if a fault 20 is present when the SCRs 26 gate on, capacitor 46 has not yet charged to the power source potential, and capacitor 48 has not yet discharged, thereby failing to provide the reverse recovery current or reverse bias necessary to turn the SCRs 26 off. Also, if fault 20 produces a slow rising fault current, capacitor 46 will discharge slowly through fault 20 and inductor 40, which does not present a high impedance while the current is slowly increasing, and capacitor 48 will charge slowly through inductor 30, which does not present a high impedance while the current is slowly increasing, and SCR 26 will not turn off.

[0011] The present disclosure proposes a number of design modifications to the conventional series-Z power circuit breaker 12 that overcome some or all of the above-mentioned drawbacks. Figure 2 is a circuit diagram (schematic) of a series-Z power circuit breaker 50 similar to series-Z power circuit breaker 12, with like components identified by the same reference numerals. To overcome the above drawbacks when a fault 20 is present when power is applied to power source 18, circuit breaker 50 includes an isolation switch 52, such as an electromechanical switch, downstream on positive bus 22 of LR circuit 38. Initially, switch 52 is open, and when power is applied to circuit breaker 50 from power source 18, capacitor 46 has an opportunity to charge before circuit breaker 50 detects the fault current. As soon as capacitor 46 has an opportunity to charge while capacitor 48 is discharged, switch 52 is closed across fault 20, and capacitor 46 is turned off by discharging through the fully discharged capacitor 48 to SCR 26, isolating fault 20.

[0012] In one embodiment, the isolation switch 52 is a triggered vacuum gap (TVG) device. A TVG device typically includes two stationary main electrodes positioned within a vacuum chamber, defining a main vacuum gap between them. The TVG device also includes a trigger element, such as a trigger electrode, between which a vacuum trigger gap is established. The trigger gap is designed to be much shorter than the main vacuum gap so that its breakdown voltage is much lower than that of the main vacuum gap. To further reduce the breakdown voltage of the trigger gap, it can be bridged with a ceramic insulator. When a sufficiently high trigger voltage impulse is applied across the trigger gap to the main and trigger electrodes, the trigger gap breaks down, generating a plasma cloud that propagates through the main vacuum gap in a fraction of a millionth of a second, causing breakdown of the main vacuum gap. This state of the TVG device indicates a closed switch. Once current begins to flow through the TVG device, it does not stop until the AC current signal on the electrodes passes through a zero-crossing point. When this occurs, the plasma is extinguished by the vacuum and the arc is extinguished. Because the plasma can be ignited inside the vacuum chamber in this way, the timing of the TVG device's conduction can be precisely controlled, i.e., on the order of microseconds. Furthermore, because there is no moving electrode, precise mechanical actuation is not required.

[0013] During normal operation, if fault 20 is present when switch 52 is closed, capacitor 46 is reverse discharged through SCR 26, which will autonomously interrupt fault 20. Once this current is interrupted, switch 52 can be opened. Switch 52 allows fault testing in this embodiment because SCR 26 can be gated on while switch 52 is open, and once capacitor 46 is charged, switch 52 can be pulsed, with the fault let-through current defined by the time capacitor 48 is charged. Once capacitor 48 is charged, any arc across switch 52 will be extinguished.

[0014] A TVG device 56 can be coupled between the positive bus 22 and the negative bus 24 to activate the SCR 26 when a slow-rising fault occurs. When an electronic control (not shown) detects a slow-rising current or low-current threshold fault, the TVG device 56 is commanded to initiate a ground arc fault. This self-induced fault generates both a fault ramp rate and a fault current sufficient for the SCR 26 to isolate the fault. Once the fault is isolated, the arc established at the trigger gap is extinguished.

[0015] 3 is a circuit diagram (schematic) of a series-Z power circuit breaker 60 similar to the series-Z power circuit breakers 10 and 50 described above, with like components identified by the same reference numerals. Circuit breaker 60 includes an electromechanical switch 62 coupled in parallel with SCR 26, which acts as the primary current conduction path to load 14. Circuit breaker 60 also includes a delay circuit 64 having an SCR 66 coupled in series with capacitor 46 between buses 22 and 24, and a diode 68 coupled in parallel with SCR 66. When SCR 66 is open, i.e., gated off, diode 68 allows capacitor 46 to charge, and the open SCR 66 prevents capacitor 46 from discharging.

[0016] During normal operation, switches 52 and 62 are closed, gate-off SCR 26. When fault 20 is detected by a current sensor controller (not shown), the controller simultaneously commands SCR 26 to be gated on and switch 62 to be opened. When switch 62 opens, an arc forms across its contacts, which has an impedance characteristic that allows current to be rectified through SCR 26 rather than switch 62 because SCR 26 is gated on, so switch 62 opens at zero current and near zero voltage. After a short delay before switch 62 opens, the controller gates on SCR 66, causing capacitor 46 to conduct and current to flow in the reverse direction from capacitor 46 through SCR 26 and capacitor 48, reverse-biasing SCR 26 and turning it off. By this time, switch 62 has fully opened, and any residual plasma has been extinguished, preventing re-ignition of an arc across its contacts.

[0017] Because switch 62 operates much slower, on the order of milliseconds, than SCR 26, which operates on the order of microseconds, it may be desirable to delay the timing of conduction through capacitor 48 when fault 20 is detected and SCR 26 becomes reverse biased. To create this delay, a delay circuit 72 having SCR 74 can be coupled in series with capacitor 48, and a diode 76 can be coupled in parallel with SCR 74. When SCR 74 is open, i.e., gated off, diode 76 allows capacitor 48 to discharge, while the open SCR 74 prevents capacitor 48 from charging. Delaying the time it takes for the reverse bias of SCR 26 to conduct through capacitor 48 allows time for switch 62 to open.

[0018] While circuit breaker 60 required the controller to turn on SCR 66 to create the delay, it may be desirable to use a passive delay circuit to provide the delay. FIG. 4 is a circuit diagram (schematic) of a series-Z power circuit breaker 80 similar to series-Z power circuit breakers 10, 50, and 60 described above, with like components identified by the same reference numerals. Circuit breaker 80 includes a delay circuit 82 having an inductor 84 coupled in series with capacitor 46 between buses 22 and 24, with a diode 86 and resistor 88 coupled in series across inductor 84. Delay circuit 82 delays the discharge of capacitor 46 so that switch 62 opens while SCR 26 is conducting fault 18. The dynamic impedance of inductor 84 allows sufficient time for capacitor 46 to discharge enough current through SCR 26 to reverse the bias voltage and turn it off.

[0019] The foregoing disclosure and description disclose and describe merely exemplary embodiments of the present invention. Those skilled in the art will readily recognize from the foregoing description and the accompanying drawings and claims that various changes, modifications, and variations can be made without departing from the spirit and scope of the present disclosure, as defined in the following claims. [Explanation of symbols]

[0020] 10 DC circuit 12 Series Z Power Circuit Breaker (Prior Art) 14 Load 18 DC power supply 20 Malfunction 22 positive busbar 24 negative bus 26 Semiconductor Switch / SCR 28 LR circuit 30 Inductor 32 Resistance 34 Diode 36 Manual Switch 38 LR circuit 40 Inductor 42 Resistance 44 Diode 46 reverse bias capacitor 48 Floating Capacitor 50 Series Z Power Circuit Breaker 52 Isolation Switch 56 TVG equipment 60 Series Z Power Circuit Breaker 62 Electromechanical Switch 64 Delay Circuit 66 SCR 68 Diode 72 Delay Circuit 74 SCR 76 Diode 80 Series Z Power Circuit Breaker 82 Delay Circuit 84 Inductor 86 Diode 88 Resistance

Claims

1. a positive busbar and a negative busbar available for supplying power to a load; a cutoff switch provided on the positive bus and operable to cut off power supplied to the load in response to an overcurrent; an isolation switch provided on the positive bus downstream of the cutoff switch; a first capacitor electrically coupled between the positive bus and the negative bus on the output side of the isolation switch; a second capacitor electrically coupled to the positive bus in parallel with the isolation switch; A series Z power supply circuit breaker comprising:

2. 2. The series Z power circuit breaker according to claim 1, wherein the cutoff switch and / or the isolation switch is an electromechanical switch.

3. 2. The series Z power circuit breaker of claim 1, wherein the isolation switch is a vacuum triggered gap (TVG) device.

4. 2. The series Z power circuit breaker of claim 1, wherein the interrupt switch is a silicon controlled commutator.

5. 10. The series-Z power circuit breaker of claim 1, further comprising a vacuum trigger gap (TVG) device coupled between the positive bus and the negative bus downstream of the isolation switch.

6. 2. The series Z power circuit breaker according to claim 1, wherein the series Z power circuit breaker is used in a DC circuit.

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