Pre-charging device for high-voltage circuit

Abstract

The invention relates to an electrical circuit (200) comprising at least one electrical converter stage and at least one capacitor (106) arranged upstream of the at least one electrical converter stage, the electrical circuit further comprising a high-voltage source (102) and a contactor (104) arranged in series between the high-voltage source and the electrical converter, the electrical circuit comprises a pre-charging circuit (208) for pre-charging the capacitor, the pre-charging circuit and the contactor are arranged in parallel, and the pre-charging circuit comprises a fuse (214), a low-voltage relay (216) contained in a metal shell (217), a transistor (218) and a pre-charging resistor (212) which are sequentially connected in series from the high-voltage source to the capacitor. The housing of the low voltage relay is connected to a terminal of a high voltage source (102).

Description

Technical Field

[0001] The invention relates to a high-voltage electrical circuit comprising means for precharging a capacitor provided at a power converter stage of the electrical circuit. Background Art

[0002] High voltage direct current distribution system is abbreviated as HVDC distribution system. Figure 1 A portion of an example of such a circuit 100 is shown. The electrical circuit 100 comprises a high voltage DC source 102 and at least one capacitive energy storage element, such as a capacitor 106, arranged upstream of a power converter stage. The capacitor is intended to filter the switching function of the power converter stage.

[0003] When the system is powered on, capacitor 106 needs to be charged because a discharged capacitor behaves like a short circuit. To this end, a pre-charge circuit 108 is typically arranged in parallel with contactor 104 for circuit 100, which can close or open distribution circuit 100. Pre-charge circuit 108 includes an auxiliary contactor 110 connected in series with a pre-charge resistor 112. Auxiliary contactor 110 must be sized to withstand the voltage of circuit 100. Furthermore, the pre-charge circuit is typically designed to provide the same galvanic isolation as main contactor 104.

[0004] Therefore, the auxiliary contactor 110 is bulky because it is sized to withstand the pre-charge current and the system voltage provided by the high voltage source. The auxiliary contactor 110 typically has a size greater than 60 mm.

[0005] The present invention seeks to overcome one of the above disadvantages. In particular, the present invention seeks to provide a high voltage electrical circuit having a smaller and more robust pre-charging circuit. Summary of the Invention

[0006] The present invention provides an electrical circuit comprising at least one electrical converter stage and at least one capacitor, the capacitor being arranged upstream of the at least one electrical converter stage, the electrical circuit further comprising a high-voltage source and a contactor, the contactor being arranged in series between the high-voltage source and the electrical converter, the electrical circuit comprising a precharging circuit for precharging the capacitor, the precharging circuit being arranged in parallel with the contactor,

[0007] The pre-charging circuit includes, in series from the high-voltage source to the capacitor: a fuse, a low-voltage relay housed in a metal shell, a transistor and a pre-charging resistor. The shell of the low-voltage relay is connected to the terminal of the high-voltage source connected to the fuse.

[0008] The combination of a low-voltage relay and a transistor ensures that the capacitor is precharged when the relay is closed and the contactor is open, while also withstanding the high voltage flowing in the electrical circuit. Furthermore, this combination reduces the size of the precharge circuit. In fact, the low-voltage relay is significantly smaller than the auxiliary contactor of conventional circuits. Furthermore, the fuse protects the components of the electrical circuit in the event of an arc within the housing of the low-voltage relay.

[0009] A capacitor may represent the input stage of a power converter stage. The capacitor may be positioned upstream of the converter stage, along the direction of current flow from the high voltage source to the converter stage. For example, the converter stage may include a DC bus. The capacitor may be positioned at the input of the DC bus. The converter stage may also include an inverter.

[0010] The low voltage relay housing may be connected to terminals of a high voltage source connected to the fuse by wires or cables or any other suitable means. The high voltage source may be configured to deliver current at a voltage between 270V and 1200V.

[0011] A first terminal of the fuse may be connected to a first pole of a high-voltage source, and a second terminal of the fuse may be connected to a first terminal of a low-voltage relay. The second terminal of the low-voltage relay may be connected to a first terminal of a transistor. The second terminal of the transistor may be connected to a first terminal of a pre-charge resistor. The second terminal of the pre-charge resistor may be connected to a first terminal of a capacitor. The second terminal of the capacitor may be connected to a second pole of the high-voltage source, the second pole being opposite to the first pole.

[0012] The metal housing of the relay may also be connected to the second pole of the high voltage source.

[0013] The first terminal of the contactor can be connected to the first pole of the high voltage source and the first terminal of the fuse.The second terminal of the contactor can be connected to the first terminal of the capacitor and the second terminal of the pre-charge resistor.

[0014] The fuse can be configured to continuously allow a current limit that depends on the charging current of the capacitor.

[0015] The fuse may be selected to be able to withstand the high voltage delivered by the high voltage source.

[0016] The current rating of the fuse may be selected to protect the wiring of the pre-charge circuit elements.

[0017] The fuse allows to protect the electrical circuit in case of failure of the low voltage pre-charge relay leading to insulation failure of its metal parts.

[0018] The transistor may be a bipolar junction transistor or a metal oxide semiconductor field effect transistor. Alternatively, the transistor may be any other type of transistor.

[0019] The electrical circuit may include discrete control elements for controlling contactors, low voltage relays and / or transistors.

[0020] The low-voltage relay may have a size of less than or equal to 26 mm. The low-voltage relay may have a cubic shape with a side length of less than or equal to 26 mm. Alternatively, the low-voltage relay may have another shape, such as a parallelepiped. The low-voltage relay may be configured for a voltage less than or equal to 30 V, in particular less than or equal to 28 V.

[0021] The invention also relates to a turbomachine comprising an electrical circuit as described above.

[0022] For example, such an electrical circuit may be arranged in connection with an electric propulsion unit of the turbomachine.

[0023] The invention also relates to a method for precharging at least one capacitor of an electrical circuit as described above, the method comprising the following steps:

[0024] a) determine the charge level of the capacitor,

[0025] b) When the charge level is lower than the determined threshold, the low voltage relay is controlled to close,

[0026] c) After the low voltage relay is closed, the control transistor is closed.

[0027] The method may comprise a step d) consisting of closing the contactor when the voltage across the capacitor is above a determined threshold or when a time greater than a time constant of the electrical circuit has elapsed and then, in particular after a time delay, opening the transistor and then the low-voltage relay.

[0028] The determined threshold value may be 95% of the voltage delivered by the voltage source.The time constant of the electrical circuit may be the product of the value of the pre-charge resistor and the capacitance of the capacitor.Step d) may be performed after a time greater than three times the time constant of the electrical circuit has elapsed.

[0029] The method may comprise the step of delaying between steps b) and c) by a delay time, the delay time being dependent on the response time of the low voltage relay closing.

[0030] The delay time may be between 2 ms and 50 ms, for example equal to 20 ms. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] [ Figure 1 ] shows a high voltage DC electrical circuit according to the prior art,

[0032] [ Figure 2 ] shows an exemplary embodiment of a high voltage DC electrical circuit according to the present invention,

[0033] [ Figure 3] shows the control Figure 2 An example of a method of illustrating an example electrical circuit is shown. DETAILED DESCRIPTION

[0034] Figure 2 An example of a high-voltage direct current (HVDC) electrical circuit 200 is partially shown in FIG. Electrical circuit 200 includes a high-voltage direct current (HVDC) voltage source 102 and one or more power converter stages. Electrical circuit 200 includes a capacitor 106 positioned upstream of one or each power converter stage. Contactors 104, positioned between voltage source 102 and capacitor 106, are capable of closing or opening distribution circuit 200. Voltage source 102 delivers direct current at a high voltage between 270 V and 1200 V.

[0035] When the system is powered on, each capacitor 106 needs to be charged because a discharged capacitor behaves like a short circuit. To this end, a pre-charge circuit 208 is arranged in parallel with the contactor 104. The pre-charge circuit 208 includes a fuse 214, a low-voltage relay 216, a transistor 218, and a pre-charge resistor 212, which are connected in series from the voltage source 102 to the capacitor 106.

[0036] Capacitor 106 may be any type of capacitive energy storage element.

[0037] Transistor 218 is a metal oxide semiconductor field effect transistor (MOSFET), but may be any other type of transistor. Transistor 218 is sized to withstand a high voltage across its terminals, for example, between 270 and 1200 V. Transistor 218 is an N-type transistor, but may be a P-type. The source terminal of transistor 218 is connected to pre-charge resistor 212, and the drain terminal of transistor 218 is connected to low voltage relay 216.

[0038] The low voltage relay 216 includes a metal housing 217. Thus, the low voltage relay 216 has a metal frame. The housing 217 is connected to a terminal of the voltage source 102 opposite to the terminal of the voltage source 102 to which the fuse 214 and the contactor 104 are connected via a wire or cable 220.

[0039] The size of the low voltage relay 216 is less than or equal to 26 mm. For example, the low voltage relay 216 is a cube with a side length equal to 26 mm.

[0040] The low voltage relay 216 is configured to be able to withstand a voltage less than or equal to 30V, specifically less than or equal to 28V.

[0041] The combination of the low voltage relay 216 and the transistor 218 ensures precharging of the capacitor 106 when they are closed and the contactor 104 is open, while withstanding the high voltage of the electrical circuit 200. Furthermore, this combination reduces the size of the precharging circuit 208.

[0042] The fuse 214 is calibrated to clear the pre-charge line after the switching time of the pre-charge resistor 212 exceeds a determined time. The fuse 214 enables protection of the electrical circuit 200 in the event of a fault that prevents the pre-charge resistor 212 from opening.

[0043] Furthermore, if the low-voltage relay 216 is controlled to open while the pre-charge circuit 208 is still energized, the arc in the arc extinguishing chamber of the low-voltage relay 216 may propagate to the housing 217 connected to the opposite terminal. The fuse 214 allows the components of the electrical circuit 200 to be protected from such insulation failures.

[0044] Therefore, the electrical circuit 200 provides the following advantages:

[0045] The high integration and compactness of the pre-charge function in the high voltage circuit,

[0046] Galvanic isolation via low voltage relays, and

[0047] The fuse clears two fault modes:

[0048] Insulation failure of the low voltage relay, and

[0049] The low voltage relay failed to open during capacitor charging.

[0050] The electrical circuit 200 may include discrete control elements for controlling the contactor 104, the low voltage relay 216, and / or the transistor 218. The discrete control elements may be configured to open / close the contactor 104, the low voltage relay 216, and / or the transistor 218.

[0051] Figure 3A control method 300 for an electrical circuit 200 capable of precharging a capacitor 106 is shown. Method 300 includes a preliminary step of detecting whether capacitor 106 has discharged. For example, if the voltage across capacitor 106 is less than 95% of the voltage delivered by voltage source 102, capacitor 106 is considered discharged. If capacitor 106 has discharged, method 300 includes a first step 302 of controlling the low-voltage relay 216 to close, which includes sending a close command to low-voltage relay 216. To ensure that low-voltage relay 216 closes properly, method 300 includes a delay step 304. For example, the delay time is determined based on the response time required for low-voltage relay 216 to close. In step 304, a delay between 2 ms and 50 ms, for example, equal to 20 ms, is applied before step 306 of controlling transistor 218 to close. Low-voltage relay 216 and transistor 218 remain closed until capacitor 106 is charged. In step 308, the charge level of capacitor 106 is determined. To this end, the voltage across the capacitor is measured, and capacitor 106 is considered charged when this voltage is greater than 95% of the voltage delivered by voltage source 102. Alternatively, capacitor 106 is considered charged when a time greater than three times the time constant of electrical circuit 200 has elapsed. The time constant is equal to the product of the resistance of the pre-charge resistor (denoted by R) and the capacitance of capacitor 106 (denoted by C). Therefore, the time constant is determined by the following formula:

[0052] At the end of step 308, the contactor 104 is controlled to close in step 310. Then, after a delay corresponding to the response time of the contactor 104, the method 300 includes the step of opening the transistor 218 and then the low voltage relay 216 in step 312 when the pre-charging of the capacitor 106 is completed.

Claims

1. An electrical circuit (200) comprising at least one electrical converter stage and at least one capacitor (106), the at least one capacitor (106) being arranged upstream of the at least one electrical converter stage, the electrical circuit further comprising a high-voltage source (102) and a contactor (104), the contactor (104) being arranged in series between the high-voltage source and the electrical converter, the electrical circuit comprising a precharging circuit (208) for precharging the capacitor, the precharging circuit being arranged in parallel with the contactor, in, The pre-charging circuit includes, in series from the high-voltage source to the capacitor, a fuse (214), a low-voltage relay (216) contained in a metal housing (217), a transistor (218) and a pre-charging resistor (212), wherein the housing of the low-voltage relay is connected to a terminal of the high-voltage source (102) connected to the fuse (214).

2. The electrical circuit (200) according to claim 1, characterized in that The fuse (214) is configured to continuously allow a current limit to flow that is dependent on the current of the capacitor (106).

3. The electrical circuit (200) according to any one of the preceding claims, characterized in that The transistor (218) is a metal oxide semiconductor field effect transistor.

4. The electrical circuit (200) according to any one of the preceding claims, comprising discrete control elements for controlling the contactor (104), the low voltage relay (216) and / or the transistor (218).

5. The electrical circuit (200) according to any one of the preceding claims, characterized in that The size of the low voltage relay (216) is less than or equal to 26 mm.

6. Turbomachine comprising an electrical circuit (200) according to any one of the preceding claims.

7. A method (300) for precharging at least one capacitor of an electrical circuit (200) according to any one of claims 1 to 5, the method comprising the steps of: a) determine the charge level of the capacitor, b) controlling (302) the low voltage relay (216) to close when the charge level is below a determined threshold, c) After the low voltage relay (216) has closed, the transistor (218) is controlled (306) to close.

8. The method (300) according to the preceding claim, comprising a step d) consisting of: When the voltage across the capacitor is above a determined threshold or when a time greater than a time constant of the electrical circuit has elapsed, the contactor (104) is closed (310), the transistor (218) is then opened (312), and the low voltage relay (216) is then opened.

9. The method (300) according to claim 7 or 8, comprising a step (304) of delaying between steps b) and c) by a delay time, the delay time being dependent on the response time of the closing of the low voltage relay (216).

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