Electrical protection device for power supply cable of permanent magnet motor

Abstract

The invention relates to a protection device for preventing a short circuit of a high-voltage DC supply line (36, 38) between a DC power source (10) and an active load (20), comprising a bypass circuit consisting of a contactor K3 and a fuse F2 in series, which bypass circuit is arranged in parallel with the active load by means of lines (32, 34) independent of the high-voltage DC supply line, and the bypass circuit is configured such that most of the current passes through the bypass circuit before the fuse F2 is fused.

Description

Technical Field

[0001] The present invention relates to the field of electric propulsion of aircraft, and more specifically to an electrical protection device for permanent magnet motor power supply cables. The device is also used in hybrid platforms, in which the electric drive system cooperates with the thermal drive system to ensure the propulsion of the aircraft. Background Art

[0002] All-electric propulsion systems use an electric propulsion circuit consisting entirely of a power source (usually a battery) and one or more electrical loads (usually electric motors). To minimize weight, these motors are usually permanent magnet motors.

[0003] Similarly, the power distribution system is equipped with electrical protection devices to protect electrical equipment (lines, connectors). These protection devices are designed to cut off the power supply to the short-circuit point when a short circuit occurs.

[0004] In addition, the design of the electrical load should ensure that no regenerative current is generated into the grid to maintain grid stability. If the electrical load (such as a permanent magnet motor or actuator) generates regenerative current, this energy must be dissipated in the motor, actuator or a dedicated resistor device.

[0005] This limitation leads to two situations: one is to increase the size of the load to handle the regenerative energy (in the long run, if the aerodynamic force generated by the propeller driving the motor is too large, the system may be at risk of damage); the other is to add additional equipment, including energy-consuming resistors, which will lead to increased weight and volume, bringing many adverse effects.

[0006] Figure 1 The power distribution architecture for a small vertical take-off and landing (VTOL) platform electric propulsion scenario is schematically shown.

[0007] It is powered by the battery 10 through the distribution box 30 to the motor 20. The battery 10 contains its own protection elements, usually including a power contactor K1, which is used to electrically isolate the battery unit to facilitate maintenance operations; and a power fuse F1, which will blow when a short circuit occurs in the circuit outside the battery 10. The distribution box 30 generally also has its own power contactor K2.

[0008] For example, when a short circuit occurs in the line between the motor 20 and the distribution box 30 (e.g., a cable is damaged), the current provided by the battery will generate an arc (arc current 1), causing the fuse F1 to melt; under the severe action of the short circuit phenomenon, the cable will be damaged and may break (see Figure 2 ).

[0009] like Figure 3Figure 2 shows the battery and motor currents at different states of fuse F1. When the fuse blows, if the motor is still running due to its own inertia or the aerodynamic force on the propeller, the motor will generate electrical energy and provide arc current (arc current 2) to the short circuit point. At this point, there is nothing in the circuit to stop the arc, and the arc will continue as long as the motor is running until the damage is so severe that there is not enough metal material to maintain the arc plasma (this process may last for several seconds).

[0010] Therefore, in electrical systems that power rotating electrical machines in electric or hybrid propulsion systems, there is a need for a dedicated protection device that is able to extinguish the arc by cutting off the current that sustains the arc. Summary of the invention

[0011] The main object of the invention is to provide a device for protecting a distribution network with active loads such as permanent magnet rotating electrical machines by bypassing fault currents. Another object is to avoid excessive use of the motors or their associated control electronics. Still another object is to avoid the installation of large, heavy components in a high voltage direct current (HVDC) distribution network on the load side.

[0012] These objects are achieved by a protection device for preventing a high-voltage DC power supply line between a DC power source and an active load from short circuiting. The device is characterized in that it comprises a bypass circuit formed by a contactor K3 and a fuse F2 connected in series, the bypass circuit is arranged in parallel with the active load through a line independent of the high-voltage DC power supply line, and is configured so that most of the current passes through the bypass circuit before the fuse F2 is blown.

[0013] Therefore, using an independent bypass circuit without any resistive load can achieve a design with simple structure and low component count, which will not cause too much burden in terms of weight and volume.

[0014] Preferably, the rated current of the fuse F2 is low (less than 32 A) and the cross-sectional area of ​​the independent line is small (less than 6 square millimeters).

[0015] Advantageously, the DC power source is a battery and the active load is a permanent magnet motor.

[0016] Preferably, the contactor K3 and the fuse F2 are assembled in a distribution box located between the battery and the permanent magnet motor.

[0017] The invention also relates to a power distribution network comprising the above-mentioned protection device, and an aircraft equipped with such a power distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings. These drawings illustrate an exemplary embodiment of the present invention, but do not constitute any limitation, wherein:

[0019] Figure 1 A schematic diagram shows the circuit in which the battery powers the electric motor;

[0020] Figure 2 Demonstrates an electrical fault in the motor supply cable Figure 1 Circuit conditions in

[0021] Figure 3 Demonstrates the generation of arc currents between supply cables following an electrical fault;

[0022] Figure 4 The present invention shows a protection device including a low impedance bypass circuit;

[0023] Figure 5 The generation of arc current and the extinction of arc in the circuit are demonstrated;

[0024] Figure 6 The process of gradually eliminating the fault by disconnecting the bypass circuit is demonstrated;

[0025] Figure 7 The control sequence of bypass circuit contactor K3 during the generation and elimination of electrical faults is shown. DETAILED DESCRIPTION

[0026] The principle of the present invention is to add an arc current bypass circuit, which is used to limit the regenerative current that provides energy for the short circuit, thereby extinguishing the arc as quickly as possible.

[0027] Figure 4 The resulting architecture is shown. The battery 10 supplies power to the motor 20 via the distribution box 30. The battery 10 contains a power contactor K1 and a power fuse F1, and the distribution box 30 contains its own protection element, the power contactor K2. The two high-voltage DC power supply lines (-HVDC and +HVDC) between the motor 20 and the distribution box 30 are marked as 32 and 34 respectively. In the electric propulsion system, the voltage of these two power supply lines is usually 270VDC to 540VDC or higher.

[0028] According to the present invention, the distribution box 30 also includes a component composed of a contactor K3 and a fuse F2 connected in series, both of which have a low rated current (i.e., the current is less than 32A), and are arranged in parallel with the motor 20 through two independent wires 36 and 38 with a small cross-sectional area (usually less than 6 square millimeters). The component constitutes an arc current bypass circuit, and its impedance is lower than the impedance of the arc plasma.

[0029] By installing these disconnect elements in the distribution box, the increase in size and weight can be kept to a minimum by utilizing small size and light weight components to bypass and control the short circuit energy (because these components are designed for this function only).

[0030] In this configuration, if Figure 5 As shown, when a short circuit is detected and the voltage downstream of contactor K2 disappears, contactor K3 is controlled to close to consume part of the regenerative energy of the motor. Since the arc requires a certain level of energy to maintain (air ionization energy), it is easy for those skilled in the art to design the parameters of contactor K3 and fuse F2 to just meet the requirements of extinguishing the arc, and the design of the bypass circuit ensures that most of the current passes through the circuit.

[0031] Soon (a few milliseconds at most), the arc will extinguish naturally because there is not enough current to maintain it (arc current 3a). All current will pass through the lower impedance bypass circuit (arc current 3b) until fuse F2 melts (see Figure 6 ). At this point, the main supply circuit from the motor is isolated; the motor can continue to run and produce voltage across its terminals, but once the arc has extinguished, it cannot form again because the main supply circuit has been disconnected.

[0032] Figure 7 The variation of different currents in the circuit depending on the state of contactor K3 is shown in the case of a permanent magnet motor with a power of 30kW to 4.5MW and a 540V high voltage DC power supply.

Claims

1. A protection device for preventing a high voltage DC power supply line (32, 34) between a DC power source (10) and an active load (20) from short circuiting, characterized in that: It comprises a bypass circuit formed by a contactor K3 and a fuse F2 connected in series, the bypass circuit is arranged in parallel with the active load through a line (36, 38) independent of the high-voltage DC power supply line, and is configured so that most of the current passes through the bypass circuit before the fuse F2 is blown.

2. The protection device according to claim 1, wherein: Fuse F2 has a lower rated current and a smaller cross-sectional area for the independent line.

3. The protection device according to claim 2, wherein: Lower current ratings correspond to current values ​​less than 32A.

4. The protection device according to claim 2, wherein: A smaller cross-sectional area corresponds to a cross-sectional area of ​​less than 6 square millimeters.

5. The protection device according to claim 1, wherein: The DC source is a battery and the active load is a motor.

6. The protection device according to claim 5, wherein: The electric motors are permanent magnet motors with power ranging from 30kW to 4.5MW.

7. The protection device according to claim 5 or 6, wherein: The contactor K3 and the fuse F2 are assembled in a distribution box (30) located between the battery and the permanent magnet motor.

8. A power distribution network comprising the protection device according to any one of claims 1 to 7.

9. An aircraft comprising a power distribution network according to claim 8.

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