Unit and method for pre-charging a DC load having an input capacitance

Abstract

The invention relates to a pre-charge unit (10) for pre-charging a DC load (20) having an input capacitance, the unit comprising a magnetoresistive conductor (12) for connecting the DC load to a DC voltage source (30); an electromagnetic arrangement (14) for generating a magnetic field (50) which is applied to the magnetoresistive conductor for controlling a current conducted through the magnetoresistive conductor from the DC voltage source to the DC load; a driver unit (16) for driving the electromagnetic arrangement; and a control unit (18) configured to control the driver unit to drive the electromagnetic arrangement for increasing the impedance of the magnetoresistive conductor by increasing the strength of the magnetic field applied to the magnetoresistive conductor during a pre-charging period.

Description

[0001] power electronic switching elements). The invention also allows for bidirectional charging (from grid to load and from load to grid). Further, the invention can also be used as a current limiter in case of an overload or short circuit event. It is noted that the invention allows to manipulate the current even before a fault current reaches a certain level, since the magnetic field applied to the magnetoresistive conductor - unlike in the current limiter of

[0002] US 2022 / 068527 A1 - is not generated by the fault current itself, allowing to limit the fault current as soon as a fault is detected, resulting in less stress to the grid and in the elimination of a need for a current limiting inductance.

[0003] Preferred embodiments are defined in the dependent claims.

[0004] According to one example, the magnetoresistive conductor is configured to utilize the extraordinary magnetoresistance effect.

[0005] According to one example, the magnetoresistive conductor is galvanically separate from the driver unit and the electromagnetic arrangement.

[0006] According to one example, the magnetoresistive conductor is connected in series via a circuit breaker to the DC voltage source. In particular, the circuit breaker may be connected to the control unit so as to cause the control unit to start a pre-charging period. Further, the circuit breaker may be configured to first connect a first pole of the DC voltage source to the magnetoresistive conductor before causing the control unit to start a pre-charging period and to only thereafter connect a second pole of the DC voltage source to the DC load once the control unit has increased the impedance of the magnetoresistive conductor. For example, the circuit breaker may be an electromechanical circuit breaker, a hybrid circuit breaker (HCB) or a solid state circuit breaker (SSCB).

[0007] According to one example, the control unit is configured to terminate the pre-charging period depending on the charging state of the input capacitance of the load. In particular, the control unit may be configured to terminate the pre-charging period once a voltage at the load has been found to reach a predetermined minimum percentage of a nominal operation voltage. Further, the control unit may be configured to terminate the pre-charging period once the voltage at the load has been found to reach at least 95%, preferably at least 99%, of the nominal operation voltage.

[0008] According to one example, the control unit is configured to control the strength of the magnetic field such that the current through the magnetoresistive conductor is held within a specified range of + / - 10% during the pre-charging period. as a micro grid. Further, a circuit breaker 40 is provided, which is arranged in series with the pre-charge unit 10 between the voltage source 30 and the load 20.

[0009] For example, the DC voltage source 30 may be a DC micro grid, a batery system, a power generator (photovoltaic (PV) supply), etc.

[0010] The pre-charge unit 10 comprises a magnetoresistive conductor 12 for connecting the load 20 to the voltage source 30; more precisely, the magnetoresistive conductor 12 connects a first pole 32 of the voltage source 30 to a first input 22 of the load 20 via a first switch 42 of the circuit breaker 40. A second pole 34 of the voltage source 30 and a second input 24 of the load 20 are connected via a second switch 44 of the circuit breaker 40. For example, the circuit breaker 40 may be an electromechanical circuit breaker, a hybrid circuit breaker (HCB) or a solid state circuit breaker (SSCB).

[0011] In the example of Fig. 1 , all current from the voltage source 30 to the load 20 flows through the magnetoresistive conductor 12.

[0012] The pre-charge unit 10 further comprises an electromagnetic arrangement 14 for generating a magnetic field 50 which is applied to the magnetoresistive conductor 12 for controlling a current conducted through the magnetoresistive conductor 12 from the voltage source 30 to the load 20. The electromagnetic arrangement 14 comprises a coil arrangement, such as a Helmholtz configuration of air coils 14-1 , 14-2, which can apply a homogenous magnetic field to the magnetoresistive conductor 12. In this case, the magnetoresistive conductor 12 may be located between the air coils 14-1, 14-2, as illustrated in Fig. 1. For example, the magnetoresistive conductor 12 may utilize the extraordinary magnetoresistance effect.

[0013] The pre-charge unit 10 also comprises a driver unit 16 for driving, i.e., energizing the electromagnetic arrangement 14 and a control unit 18 for controlling the driver unit 16. The control unit 18 receives a signal from the circuit breaker 40 via a line 60 which is indicative of an open / closed state of the circuit breaker. Line 60 may be a single wire or a serial or parallel bus for indicating signals. Thus, line 60 may carry additional signals for communicating other information, like a current or voltage measured in the circuit breaker. Line 60 may be a unidirectional (circuit breaker to control unit) or a bi-directional bus.

[0014] In the example of Fig. 1, the magnetoresistive conductor 12 galvanically separate from the driver unit 16 and the electromagnetic arrangement 14.

[0015] The control unit 18 controls the driver unit 16 in such a manner that during a pre-charging period of the input capacitance of the load 20 the current through the magnetoresistive determined by the pre-charge unit 10. For example, present charging state of the input capacitance of the load 20 may be determined or estimated from a voltage measured at the load 20. Accordingly, the control unit 18 may terminate the pre-charging period once the voltage at the load 20 has been found to reach a predetermined minimum percentage of the voltage of the voltage source 30, i.e., of a nominal operation voltage. For example, the control unit 18 may terminate the pre-charging period once the voltage at the load 20 has been found to reach at least 95%, preferably at 99%, of the nominal operation voltage.

[0016] The control unit 18 may switch off the magnetic field 50 when the pre-charging period is terminated i.e., when the input capacitance of the load 20 has been sufficiently pre-charged, so that the impedance of the magnetoresistive conductor 12 is low or minimal during normal operation of the load 20.

[0017] The pre-charge unit 10 may not only serve for pre-charging of the input capacitance of the load 20; in addition, the pre-charge unit 10, after pre-charging, may act as a fault current limiter (e.g., in case of an overload or short circuit event). To this end, the control unit 18 may cause the driver unit 16 to apply a magnetic field 50 to the magnetoresistive conductor 12 to limit the current through the magnetoresistive conductor 12 once a fault current has been detected by an appropriate current sensor during post-charging operating periods (i.e., when the input capacitance already has been sufficiently pre- charged). A fault current may be reached when the current to the load 20 is more than, e.g., 10 % or 20 % higher than the nominal current of the load. The pre-charge unit 10 can actively manipulate the current through the magnetoresistive conductor 12 even before the current to the load reaches a certain level, since the magnetic field 50 applied to the magnetoresistive conductor 12 is not generated by the fault current itself; this allows the pre-charge unit 10 to limit the fault current as soon as the fault is detected (e.g., within a few ms, or even ps), resulting in less stress to the grid and in the elimination of a need for a current limiting inductance.

Claims

7. The pre-charge unit of one of claims 4 to 6, wherein the circuit breaker (40) is an electromechanical circuit breaker, a hybrid circuit breaker (HCB) or a solid state circuit breaker (SSCB).

8. The pre-charge unit of one of the preceding claims, wherein the control unit (18) is configured to terminate the pre-charging period depending on the charging state of the input capacitance of the load (20).

9. The pre-charge unit of claim 8, wherein the control unit (18) is configured to terminate the pre-charging period once a voltage at the load (20) has been found to reach a predetermined minimum percentage of a nominal operation voltage.

10. The pre-charge unit of claim 9, wherein the control unit (18) is configured to terminate the pre-charging period once the voltage at the load (20) has been found to reach at least 95%, preferably at least 99%, of the nominal operation voltage.

11. The pre-charge unit of one of the preceding claims, wherein the control unit (18) is configured to control the strength of the magnetic field (50) such that the current through the magnetoresistive conductor (12) is held within a specified range of + / - 10% during the pre-charging period.

12. The pre-charge unit of one of the preceding claims, wherein the control unit (18) is configured to control the strength of the magnetic field (50) such that the current through the magnetoresistive conductor (12) is between 1 A and 10 A during the pre- charging period.

13. The pre-charge unit of one of the preceding claims, wherein the control unit (18) is configured to switch off the magnetic field (50) when the pre-charging period is terminated.

14. The pre-charge unit of one of the preceding claims, wherein the electromagnetic arrangement (14) comprises a Helmholtz configuration of two air coils (14-1 , 14-2) configured to apply a homogenous magnetic field (50) to the magnetoresistive conductor (12).

15. The pre-charge unit of claim 14, wherein the magnetoresistive conductor (12) is located between the air coils (14-1 , 14-2) of the electromagnetic arrangement (14).

16. The pre-charge unit of one of the preceding claims, wherein the DC voltage source(30) is a DC micro grid.

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