Hybrid circuit breaker using transient commutation current injection circuit

Abstract

A circuit breaker and operating method. The circuit breaker includes a first current path and a second current path, the first current path includes a mechanical switch, such as an ultrafast mechanical switch, the second current path is connected in parallel with the first current path, and the second current path has a current injector, such as a transient commutation current injection circuit, connected in series with a bidirectional power electronic switch. A short circuit fault current from the mechanical switch path is transmitted to the electronic path by current injection, and then the fault current is interrupted. A pulse current is generated by the electronic switch in the second current path, and the mechanical switch is disconnected during the pulse current. When the mechanical switch is opened, the pulse current and the electronic switch reduce or eliminate arcing.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Application Serial No. 62 / 760,200, filed on November 13, 2018. The entire contents of the pending application are incorporated herein by reference and constitute a part of this application, including but not limited to those parts specifically appearing below. Background Art

[0003] The present invention generally relates to circuit protection devices in electrical power distribution or transmission systems.

[0004] In recent years, DC (direct current) power systems such as MVDC (1,000V to 100,000V) or HVDC (100,000V to 1,000,000V) have attracted much attention due to their higher efficiency and power capacity. However, protecting these DC power systems from short-circuit faults remains a major technical challenge. Due to the lack of zero crossing in DC power supplies, conventional electromechanical circuit breakers cannot reliably interrupt DC fault currents. Figure 1 As shown, the current solution is to use series auxiliary commutation power electronic switches in the main current conduction path under normal operation, but this leads to significant power losses and self-heating. The present invention aims to overcome this basic drawback. Summary of the invention

[0005] A general object of the present invention is to provide a hybrid circuit breaker that can quickly transfer a short-circuit fault current from a mechanical switch branch to an electronic branch and then interrupt the fault current without arcing.

[0006] The general object of the present invention can be achieved at least in part by a circuit breaker including a first current path having a mechanical switch and a second current path connected in parallel with the first current path. The second current path includes a current injector connected in series with an electronic switch. The first current path ideally does not include any electronic switch connected in series with the mechanical switch.

[0007] In an embodiment of the present invention, the mechanical switch is / or comprises an ultrafast mechanical switch, and / or the electronic switch is / or comprises a bidirectional power electronic switch. The current injector may be a transient commutation current injection circuit.

[0008] In an embodiment of the invention, the circuit breaker comprises a current sensor, wherein the current injector generates a pulse current when the sensor detects an overcurrent condition. When the current injector switches the load current from the first current path to the second current path, the mechanical switch opens.

[0009] In an embodiment of the invention, a varistor is connected in parallel with the second current path, wherein the varistor is activated when the electronic switch is open. The varistor may be downstream of the current injector and connected in parallel with the electronic switch.

[0010] The circuit breaker may include, or be used in conjunction with, any suitable control system or circuit to activate the current injector when an overcurrent condition is detected in the first current path. The current state may be monitored by current, voltage and / or temperature sensors. When activated, the current injector generates a current, ideally a calibrated pulse current, to commutate the load current from the first current path to the second current path.

[0011] The circuit breaker according to the embodiment of the present invention may include a power converter. The power converter may include an auxiliary DC power supply combined with a capacitor.

[0012] The present invention also includes a method of DC circuit protection, for example using any of the above circuit breaker embodiments. The method includes transferring a short circuit fault current from a mechanical switch branch to an electronic branch via current injection, and then interrupting the fault current. Under normal operating conditions, the load current flows from the power source to the load through the mechanical current branch / path, rather than the electronic current branch / path.

[0013] In an embodiment of the invention, the method includes: providing a mechanical switch in a first current path and providing an electronic switch in a second current path, the second current path being connected in parallel with the first current path; detecting an overcurrent condition in the first current path; generating a pulse current to the electronic switch in the second current path; and opening the mechanical switch during the pulse current. The pulse current may be substantially equal to the load current and / or the mechanical switch current of the first current path. The pulse current and the electronic switch ideally reduce or eliminate arcing when the mechanical switch is opened. After the mechanical switch is opened, the electronic switch will be closed or otherwise disconnected.

[0014] Other objects and advantages will become apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of a known circuit breaker.

[0016] Figure 2 is a schematic diagram of a hybrid circuit breaker according to an embodiment of the present invention.

[0017] Figure 3A is a schematic diagram of a unidirectional current injector based on a buck converter topology according to an embodiment of the present invention.

[0018] Figure 3Bis a schematic diagram of a bidirectional current injector based on a buck converter topology according to an embodiment of the present invention.

[0019] Figure 4A Schematic diagram of a unidirectional current injector based on a forward converter topology according to an embodiment of the present invention.

[0020] Figure 4B Schematic diagram of a bidirectional current injector based on a forward converter topology according to an embodiment of the present invention.

[0021] Figure 5A -C are each simulation waveform according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention includes a circuit breaker device that detects and interrupts a fault current in an electric power distribution or transmission system to isolate the circuit fault from the rest of the system. The device and method of the present invention are particularly useful in DC power systems such as HVDC grids, solar or wind power generation systems, battery energy storage systems (BESS), EV charging infrastructure, public transportation, ships and subsea power generation systems.

[0023] Embodiments of the present invention include two parallel current paths: a mechanical path and a power electronics path. Figure 2 In the circuit breaker 20 of FIG. 1 , the mechanical path 30 includes an ultra-fast mechanical switch 32. The parallel electronic path 40 includes a main power electronic switch 42. Under normal operating conditions, the load current flows from the power source (to the left of the disconnector 22) to the load (to the right) through the ultra-fast mechanical switch 32. Note that the mechanical path 30 preferably does not include an electronic switch, which can greatly reduce the large power losses associated with the auxiliary solid-state commutation switches used in the above-mentioned prior art (whose resistance is typically 10-100 times higher than that of the mechanical switches).

[0024] like Figure 2As shown, the electronic path 40 includes a current injector 50 in series with the electronic switch 42. For example, the electronic path of an embodiment of the present invention has a bidirectional power electronic switch (e.g., an IGBT or a diode) and a power electronic transient commutator current injector (TCCI) circuit in series, which does not conduct load current under normal operation due to its much higher resistance. When the current sensor 62 detects an overcurrent condition, the control system or circuit 55 activates the TCCI 50 to generate, for example, a pulse current equal to the load current (and the mechanical switch current) within tens of microseconds. The electronic path 40 now conducts 100% of the load (fault) current, and the mechanical switch 32 can be opened with little or no arcing. After a short period of time (e.g., hundreds of microseconds), the main power electronic switch 42 is disconnected, driving the parallel varistor 60 to activate and absorb the residual electromagnetic energy in the circuit loop. The interruption action is now completed.

[0025] In embodiments of the present invention, the TCCI circuit ideally does not operate at all under normal conditions, resulting in no power loss. Once invoked by the control circuit, it rapidly generates a switch-mode pulse current to commutate the load current from the mechanical branch to the electronic branch. Current-mode control methods can be used to precisely match its current to the load current. The TCCI operates for only a short period of time (e.g., <200 microseconds, preferably <100 microseconds), and then once the commutation between the mechanical and electronic paths is complete, the load current is allowed to flow freely through itself. For illustrative purposes, several exemplary designs of the TCCI are shown here. Computer simulations have been performed to verify the designs, and the simulated waveforms are also included. Figure 5A -C.

[0026] Figure 3A An embodiment of a unidirectional TCCI 50 based on a buck converter formed between Q3, D7 and L1 is shown. An auxiliary off-line DC source DC2 is used to charge a shunt capacitor 52. After receiving a commutation control signal, Q3 turns on to discharge capacitor 52 through L1, ramping the current up to approach the load (fault) current. When the TCCI current reaches the load current, Q3 turns off and remains in PWM (bang-bang current control mode) to ensure accurate tracking of the load current. See Figure. Figure 3B An embodiment of a bidirectional TCCI 50 via a full bridge 55 is shown. Figure 4A -B is based on a forward converter via a transformer 58 and operates in a similar manner to a buck converter. Throughout the figures, reference numerals are used consistently for identical or similar components.

[0027] Therefore, the present invention provides a hybrid circuit breaker that can quickly transfer a short-circuit fault current from a mechanical switch branch to an electronic branch and then interrupt the fault current without an arc.

[0028] The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component or ingredient which is not specifically disclosed herein.

[0029] Although certain preferred embodiments of the present invention have been described in the foregoing detailed description and many details have been set forth for illustrative purposes, it will be apparent to those skilled in the art that the present invention is susceptible to other embodiments and that certain details described herein may vary considerably without departing from the basic principles of the invention.

Claims

1. A circuit breaker, characterized in that: include: a first current path including a mechanical switch; a second current path connected in parallel with the first current path, the second current path comprising a current injector connected in series with the electronic switch; When the current injector is activated when an overcurrent condition is detected in the first current path, the current injector generates a calibrated pulse current, and when the pulse current of the current injector switches the load current from the first current path to the second current path, the mechanical switch opens; The pulse current is substantially equal to a load current and / or a mechanical switch current of the first current path.

2. The circuit breaker according to claim 1, characterized in that: The mechanical switch comprises an ultrafast mechanical switch.

3. The circuit breaker according to claim 1, characterized in that: The electronic switch comprises a bidirectional power electronic switch.

4. The circuit breaker according to claim 1, characterized in that: The current injector is operated with pulse width modulation (PWM) to provide a calibrated pulse current.

5. The circuit breaker according to claim 1, characterized in that: The first current path does not include any electronic switch in series with the mechanical switch.

6. The circuit breaker according to claim 1, characterized in that: Also included is a current sensor configured to detect an overcurrent condition.

7. The circuit breaker according to claim 1, characterized in that: Also included is a varistor downstream of the current injector and connected in parallel with the electronic switch.

8. The circuit breaker according to claim 1, characterized in that: Also included is a control circuit combined with the current injector, the control circuit being configured to activate a pulse width modulation (PWM) signal for activating the current injector when an overcurrent condition is detected in the first current path.

9. The circuit breaker according to claim 8, characterized in that: The current injector includes a power converter.

10. The circuit breaker according to claim 9, characterized in that The power converter includes providing an auxiliary DC power supply in conjunction with a capacitor.

11. The circuit breaker according to claim 1, characterized in that: The calibrated pulsed current comprises a switch-mode pulsed current.

12. The circuit breaker according to claim 1, characterized in that The current injector is configured to operate in a bang-bang current control mode to provide a calibrated pulse current.

13. A method for protecting a DC circuit, characterized in that: The method includes: providing a mechanical switch for a first current path and an electronic switch for a second current path, the second current path being connected in parallel with the first current path; detecting an overcurrent condition in a first current path; generating a switch-mode pulsed current to the electronic switch in a second current path; The mechanical switch is opened during the pulse current; The pulse current is substantially equal to a load current and / or a mechanical switch current of the first current path.

14. The method according to claim 13, characterized in that The pulsed current and the electronic switch reduce or eliminate arcing when the mechanical switch is opened.

15. The method according to claim 13, characterized in that Also included is closing the electronic switch when the mechanical switch is opened.

16. The method according to claim 13, characterized in that Also includes: Residual electromagnetic energy in a varistor connected in parallel with the electronic switch is absorbed.

17. The method according to claim 13, characterized in that Under normal operating conditions, the load current flows from the power source to the load through the first current path rather than the second current path.

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