Precharge device for a 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 said 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 comprising a pre-charge circuit (208) for said capacitor arranged in parallel with said contactor, wherein the pre-charge circuit comprises, in series from the high-voltage source to the capacitor, a fuse (214), a low-voltage relay (216) housed in a metal casing (217), a transistor (218), and a pre-charge resistor (212), the casing of the low-voltage relay being connected to one terminal of the high-voltage source (102). Figure to be published with the abstract: [Fig. 2]

Description

Title of the invention: Precharging device for a high voltage circuit Technical field of the invention

[0001] The invention relates to high voltage electrical circuits comprising a device for precharging capacitors provided for power converter stages of the electrical circuits. State of the prior art

[0002] High voltage direct current (HVDC) distribution networks. Part of an example of such a circuit 100 is shown in [Fig.l]. The electrical circuit 100 comprises a high voltage direct current source 102 and at least one capacitive storage element, such as a capacitor 106 arranged upstream of a power converter stage. The capacitor is intended for filtering the switching function of the power converter stage.

[0003] When the network is powered up, the capacitors 106 need to be charged because a discharged capacitor behaves like a short circuit. For this, a precharge circuit 108 is generally arranged in parallel with a contactor 104 of the circuit 100, capable of closing or opening the distribution circuit 100. The precharge circuit 108 comprises an auxiliary contactor 110 in series with a precharge resistor 112. The auxiliary contactor 110 must be sized to withstand the voltage of the circuit 100. In addition, this precharge circuit is often designed to guarantee the same galvanic isolation as the main contactor 104.

[0004] The auxiliary contactor 110 is therefore bulky because it is sized to withstand the precharge current and the network voltage delivered by the high voltage source. The auxiliary contactor 110 generally has dimensions greater than 60 mm.

[0005] The invention seeks to remedy one of the aforementioned drawbacks. In particular, the invention seeks to propose a high-voltage electrical circuit with a less bulky and more robust precharging circuit. Summary of the invention

[0006] The invention provides an electrical circuit comprising at least one electrical converter stage and at least one capacitor arranged upstream of said at least one electrical converter stage, the electrical circuit further comprising a high voltage source and a contactor arranged in series between the high voltage source and the electrical converter, the electrical circuit comprising a circuit of precharging said capacitor arranged in parallel with said contactor, wherein the precharging circuit comprises in series in order from the high voltage source to the capacitor, a fuse, a low voltage relay housed in a metal case, a transistor and a precharging resistor, the case of the low voltage relay being connected to a terminal of the high voltage source connected to the fuse.

[0007] The combination of the low voltage relay and the transistor makes it possible to ensure the precharging of the capacitor when the latter are closed and the contactor is open, while resisting the high voltage circulating in the electrical circuit. In addition, such a combination makes it possible to reduce the size of the precharging circuit. Indeed, the low voltage relay has dimensions that are much smaller than the dimensions of the auxiliary contactors of the circuits of the prior art. In addition, the fuse makes it possible to protect the elements of the electrical circuit in the event that an electric arc forms in the housing of the low voltage relay.

[0008] The capacitor may represent the input stage of an energy converter stage. The capacitor may be arranged upstream of the converter stage in a direction of the electric current going from the high voltage source to the converter stage. For example, the converter stage may comprise a direct current bus. The capacitor may be arranged at the input of said direct current bus. The converter stage may also comprise an inverter.

[0009] The high voltage source may be configured to deliver a direct electric current at a voltage between 270 and 1200 V.

[0010] A first terminal of the fuse may be connected to a first polarity of the high voltage source and a second terminal of the fuse may be connected to a first terminal of the low voltage relay. A second terminal of the low voltage relay may be connected to a first terminal of the transistor. A second terminal of the transistor may be connected to a first terminal of the precharge resistor. A second terminal of the precharge resistor may be connected to a first terminal of the capacitor. A second terminal of the capacitor may be connected to a second polarity opposite to the first polarity of the high voltage source.

[0011] The metal housing of the relay can also be connected to the second polarity of the high voltage source.

[0012] A first terminal of the contactor may be connected to the first polarity of the high voltage source and to the first terminal of the fuse. A second terminal of the contactor may be connected to the first terminal of the capacitor and to the second terminal of the precharge resistor.

[0013] The fuse may be configured to continuously pass a limit current that is a function of the capacitor charging current.

[0014] The fuse can be chosen to withstand the high voltage delivered by the source of high voltage.

[0015] The current rating of the fuse can be chosen to protect the wiring of the precharge circuit elements.

[0016] The fuse protects the electrical circuit in the event of a failure of the low voltage precharge relay leading to an insulation fault on the metal part of the latter.

[0017] The transistor may be a bipolar or insulated gate field effect transistor. Alternatively, the transistor may be any other type of transistor.

[0018] The electrical circuit may include discrete elements for controlling the contactor, the low voltage relay and / or the transistor.

[0019] The low voltage relay may have dimensions less than or equal to 26 mm. The low voltage relay may have a cubic shape with a side less than or equal to 26 mm. Alternatively, the low voltage relay may have another shape, for example a parallelepiped.

[0020] The low voltage relay can 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 mentioned above.

[0022] For example, such an electrical circuit may be arranged in association with an electric thruster of said turbomachine.

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

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

[0025] b) when the charge level is below a determined threshold, control the closing of the low voltage relay,

[0026] c) after closing the low voltage relay, control the closing of the transistor.

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

[0028] The determined threshold 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 precharge resistor and the capacitance of the capacitor. Step d) may be executed after a time greater than three times the time constant of the electrical circuit has elapsed.

[0029] The method may comprise a step of delaying a latency time between steps b) and c), said latency time being a function of the closing response time of the low voltage relay.

[0030] The latency time can be between 2 ms and 50 ms, for example equal to 20 ms. Brief description of the figures

[0031] [Fig-1] represents a high voltage direct current electrical circuit according to the art prior,

[0032] [Fig.2] represents an example of embodiment of a high voltage direct current electrical circuit according to the invention,

[0033] [Fig.3] represents an example of a method for controlling the example of the electrical circuit according to [Fig.2]. Detailed description of the invention

[0034] An example of a high voltage direct current electrical circuit 200 is partially shown in [Fig. 2]. The electrical circuit 200 comprises a high voltage direct current voltage source 102 and one or more power converter stages. The electrical circuit 200 comprises a capacitor 106 arranged upstream of one or each power converter stage. A contactor 104 capable of closing or opening the distribution circuit 200 is arranged between the voltage source 102 and the capacitor 106. The voltage source 102 delivers a direct electric current at a high voltage of between 270V and 1200V.

[0035] When the network is powered up, each capacitor 106 needs to be charged because a discharged capacitor behaves like a short circuit. For this, a precharge circuit 208 is arranged in parallel to the contactor 104. The precharge circuit 208 comprises in series from the voltage source 102 to the capacitor 106, a fuse 214, a low-voltage relay 216, a transistor 218 and a precharge resistor 212.

[0036] The capacitor 106 may be any type of capacitive storage element.

[0037] Transistor 218 is an insulated gate field effect transistor (in English Metal Oxide Semiconductor Field Effect Transistor (abbreviated as "MOSFET") but can 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 of type N but can be of type P. The source terminal of transistor 218 is connected to the precharge resistor 212 and the drain terminal of transistor 218 is connected to the low voltage relay 216.

[0038] The low voltage relay 216 comprises a metal housing 217. The low voltage relay 216 therefore has a metal frame. The housing 217 is connected by an electrical wire or cable 220 to an opposite terminal of the voltage source 102 to the terminal of the voltage source 102 connected to the fuses 214 and to the contactor 104.

[0039] The low voltage relay 216 has dimensions less than or equal to 26 mm. For example, the low voltage relay 216 is cubic with a side equal to 26 mm.

[0040] The low voltage relay 216 is configured to support a voltage lower than or equal to 30 V, in particular less than or equal to 28 V.

[0041] The association of the low voltage relay 216 and the transistor 218 makes it possible to ensure the precharging of the capacitor 106 when the latter are closed and the contactor 104 is open, while resisting the high voltage of the electrical circuit 200. Furthermore, such an association makes it possible to reduce the size of the precharging circuit 208.

[0042] The fuse 214 is calibrated to clarify the precharge line after a switching time of the precharge resistor 212 greater than a determined time. The fuse 214 makes it possible to protect the electrical circuit 200 in the event of a failure which does not allow the precharge resistor 212 to be cut.

[0043] Furthermore, if the low voltage relay 216 is commanded to open while the precharge circuit 208 is still powered, an arc in the breaking chamber of the low voltage relay 216 can propagate to the housing 217, the latter being connected to said opposite terminal of the voltage source 216, the fuse 214 makes it possible to protect the elements of the electrical circuit 200 from this insulation fault.

[0044] Thus, the electrical circuit 200 allows the following advantages: • a high degree of integration and compactness of the precharge function in the high voltage circuit, • galvanic isolation by low voltage relay, and • a clarification of two failure modes: • low voltage relay insulation fault, and • low voltage relay opening fault during charging of the capacitor.

[0045] The electrical circuit 200 may comprise discrete 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.

[0046] Figure 3 shows a method 300 for controlling the electrical circuit 200 capable of precharging the capacitor 106. The method 300 comprises a preliminary step of detecting whether the capacitor 106 is discharged. For example, the capacitor 106 is considered to be discharged if the voltage across the capacitor 106 is less than 95% of the voltage delivered by the voltage source 102. In the case where the capacitor 106 is discharged, the method 300 comprises a first step 302 for controlling the closing of the low voltage relay 216, which consists of sending an instruction to close the low voltage relay 216. In order to ensure that the low voltage relay 216 is properly closed, the method 300 comprises a time delay step 304. For example, the waiting time is determined as a function of the response time for closing the low voltage relay 216.At step 304, a delay of between 2 ms and 50 ms, for example equal to 20 ms, is expected before step 306 of controlling the . closing of transistor 218. The low voltage relay 216 and the transistor 218 are kept closed until the capacitor 106 is charged. In step 308, the charge level of the capacitor 106 is determined. For this purpose, the voltage across the capacitor is measured and the capacitor 106 is considered to be charged when this voltage is greater than 95% of the voltage delivered by the voltage source 102. Alternatively, the capacitor 106 is considered to be charged when a time greater than three times the time constant of the electrical circuit 200, denoted T, has elapsed. The time constant is equal to the product of the value of the precharge resistor, denoted R, and the capacitance of the capacitor 106, denoted C. The time constant is therefore determined by the following formula: { = R x C.

[0047] At the end of step 308, the contactor 104 is commanded to be closed at step 310. Then, at the end of a time delay corresponding to the response time of the contactor 104, the method 300 comprises a step 312 of opening the transistor 218 then the opening of the low voltage relay 216, when the precharging of the capacitor 106 is finished.

Claims

Claims

1. An electrical circuit (200) comprising at least one electrical converter stage and at least one capacitor (106) arranged upstream of said 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 comprising a precharging circuit (208) for said capacitor arranged in parallel with said contactor, wherein the precharging circuit comprises in series in order from the high voltage source to the capacitor, a fuse (214), a low voltage relay (216) housed in a metal case (217), a transistor (218) and a precharging resistor (212), the case of the low voltage relay being connected to a terminal of the high voltage source (102) connected to the fuse (214).

2. An electrical circuit (200) according to claim 1, wherein the fuse (214) is configured to continuously pass a limiting current dependent on the current of the capacitor (106).

3. An electrical circuit (200) according to any preceding claim, wherein the transistor (218) is an insulated gate field effect transistor.

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

5. Electrical circuit (200) according to one of the preceding claims, in which the low voltage relay (216) has dimensions less than or equal to 26 mm.

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

7. Method (300) for precharging at least one capacitor of the electrical circuit (200) according to one of claims 1 to 5, the method comprising the steps of: a) determining a charge level of the capacitor, b) when the charge level is lower than a determined threshold, controlling (302) the closing of the low voltage relay (216), c) after closing the low voltage relay (216), controlling (306) the closing of the transistor (218).

8. Method (300) according to the preceding claim, comprising a step

9. d) consisting of closing (310) the contactor (104) then opening (312) the transistor (218), then opening the low voltage relay (216), when the voltage across the capacitor is greater than a determined threshold or when a time greater than a time constant of the electrical circuit has elapsed. Method (300) according to claim 7 or 8, comprising a step (304) of timing a latency time between steps b) and c), said latency time being a function of the closing response time of the low voltage relay (216).

Images