BATTERY DISCONNECT CIRCUIT

Technical Field

[0001] The present invention relates to battery disconnect circuits and methods for controlling a battery disconnect circuit.

Background

[0002] Electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in HEVs use one or more propulsion systems to provide motive power. The propulsion systems include an electrical system that receives power from power sources such as power grid to charge battery, drives motor to move the vehicle, and energizes accessories to perform functions such as lighting, and a battery pack, that stores electrical power in a chemical manner to run the vehicle in the future. Under certain circumstances, it may be desired to cut off the electrical system from the battery pack.

[0003] US 2011/0133677 discloses a circuit arrangement for supplying an electric drive, to which at least two electric energy sources can be connected. At least one of the at least two electric energy sources supplies at least intermittently the electric drive by way of at least one actuating element. At least one electric energy source can be disconnected from the electric drive by way of a switch.

[0004] US 2012/0306264 discloses a switch load shedding device for a disconnect switch which may be used in electric vehicles. The disconnect switch must perform a galvanic disconnect between the battery and the intermediate circuit. To this end, at least one semiconductor switch is used. The current to be switched off is conducted via the semiconductor switch for disconnecting the electric connection. The disconnect switch is previously or subsequently switched off under reduced voltage buildup. Summary

[0005] According to the present invention, a battery disconnect circuit as claimed in claim 1 is provided. According to the present invention, a method for controlling a battery disconnect circuit as claimed in claim 9 is provided.

Brief Description of the Drawings

[0006] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments are described with reference to the following drawings, in which:

Fig. 1 shows a battery disconnect unit in an electric vehicle (EV) system;

Fig. 2 and FIG. 3 show various battery disconnect units;

Fig. 4A a battery disconnect circuit according to various embodiments;

Fig. 4B shows a flow diagram illustrating a method for controlling a battery disconnect circuit;

Fig. 5 shows an illustration of a system according to various embodiments; and

Fig. 6 shows a diagram illustrating switching control and critical voltage and current waveforms according to various embodiments.

Description

[0007] According to various embodiments, a battery disconnect unit for electric vehicles may be provided.

[0008] Fig. 1 shows a system 100 according to various embodiments. As shown in Figure 1, a battery disconnect unit (BDU) 104 may act as a primary interface between a battery pack 102 and an electrical system (for example including a charger 108 and an inverter 112). The BDU 104 may control both current flows from the charger 108 (which may be connected to a current source, for example an alternating current source 106) to the battery pack 102 and from the battery pack 102 to the inverter 112 (in other words: motor driver), for example configured to drive a motor 114, and accessories (not shown in Fig. 1). A capacitor (C) 110 may be provided between the charger 108 and the inverter 1 12. The BDU 104 may include one or more switches that open or close high current paths between the battery pack 102 and the electrical system, and one controller that controls the switches.

[0009] As the primary interface between the battery pack 102 and the electrical system of a vehicle, the BDU 104 may perform several different functions. These functions may include:

[0010] - Providing a conductive path from the charger 108 to the battery pack 102 by keeping its switches ON to charge the battery pack 102. A vehicle central controller may start or stop to charge the battery pack 102 with its own schedule by controlling the BDU 104 switches ON and OFF in case of that the plugged in charger 108, e.g. from external electric vehicle (EV) charging station, is un-controllable;

[0011] -Performing pre-charging by controlling current flow from the battery pack 102 to other components of the vehicle (e.g., inverter 1 12 connected to an electric motor 114 or to accessories) to protect the components from current surges. Current surges may occur when the components are initially activated (e.g., when the vehicle is turned on);

[0012] - Providing a conductive path from the battery pack 102 to the inverter 112 to drive the electric motor 114 and to accessories to perform functions such as lighting by keeping its switches ON. The vehicle central controller may start or stop energizing the inverter 112 and accessories with instructions from user by controlling the BDU 104 switches ON and OFF;

[0013] - Providing a conductive path from inverter 112 to the battery pack 102 to charge the battery pack 102 during vehicle braking stage by keeping its switches ON. The motor 114 may perform as an electrical generator during braking stage to charge the battery pack 102 by operating the inverter 1 12 in a rectifier mode; [0014] - Protecting the circuit by interrupting the flow of current between the battery pack 102 and the electrical system when a magnitude of the current, or the duration for which the current is at the magnitude, is greater than a predetermined value;

[0015] - Collecting critical parameters such as voltage and current by measuring the BDU 104 input voltage (battery side) and output voltage (DC (direct current)-link side) and current flow through high current paths between the battery pack 102 and the electrical system. The collected parameters may be sent to the vehicle central controller for realizing high level functions.

[0016] Fig. 2 shows an illustration 200 of a system including a BDU 204, a battery 202 (in other words: a battery pack), and an inverter 206. Two high-voltage high-current electromechanical relays 210 and 216, may be configured to connect or disconnect the electrical system from the battery pack 202. A high voltage but low current mechanical relay, for example a pre-charge relay 212, and a power resistor 214, may be used to pre-charge the inverter 206 to avoid high inrush current. A fuse 208, may be used to protect the battery pack 202 from over current discharging by disconnecting the electrical system from battery pack 202 permanently. Since the mechanical relays 210, 216 may need a certain space to suppress arcing during switching off, this solution may result in bulky devices, with low reliability, slow switching, short lifetime and high cost.

[0017] Fig. 3 shows an illustration of a system 300 with a battery 302 (in other words: a battery pack), a BDU 304, and an inverter 306. The two high-voltage high-current mechanical relays shown in Fig. 2 are replaced by power electronics switches, e.g. two pairs of IGBTs (insulated-gate bipolar transistors) 308, 310, 312, and 314 which are connected to each other with common emitter configuration, further using a plurality of diodes 316, 318, 320, 322. Thanks to fast and non-arcing switching, this system may be of compact size, high reliability, and long lifetime. In addition, this system may be cheaper than the mechanical relays based solution shown in Fig. 2. However, the system efficiency may be considerable lower due to voltage drop across the semiconductor devices. This voltage drop may lead not only to energy wastage which results in increasing size of battery pack 302, but also to heat generation which might be a problem of thermal dissipation.

[0018] According to various embodiments, a BDU with decreased system cost and system dimension for electric vehicles may be provided.

[0019] According to various embodiments, power electronics switches may be combined with mechanical relays to achieve low cost and small volume.

[0020] According to various embodiments, one high frequency active switch may be used for both a pre-charging circuit and a snubber reset circuit to reduce cost and volume.

[0021] FIG. 4A shows a battery disconnect circuit 400 according to various embodiments. The battery disconnect circuit 400 may include a first semiconductor switch 402 configured to be provided between a battery and an electronics system. The battery disconnect circuit 400 may further include a relay 404 configured to isolate the battery from the electronics system (for example when the electronics system is off). The battery disconnect circuit 400 may further include a pre-charging circuit 406 including a second semiconductor switch; and a snubber circuit 408 including the second semiconductor switch. The first semiconductor switch 402, the relay 404, the pre-charging circuit 406, and the snubber circuit 408 may be coupled with each other, like indicated by lines 410, for example electrically coupled, for example using a line or a cable, and/ or mechanically coupled.

[0022] In other words, a battery disconnect circuit 400 may be provided in which the pre- charging circuit 406 and the snubber circuit 408 jointly use a semiconductor switch.

[0023] According to various embodiments, the first semiconductor switch may be a power semiconductor switch.

[0024] According to various embodiments, the relay 404 may be a mechanical relay, an electromechanical relay, or a contactor. [0025] According to various embodiments, the first semiconductor switch may inlcude two transistors and two diodes.

[0026] According to various embodiments, the pre-charging circuit 406 may include a transistor, two diodes, and an inductor configured as a Buck converter.

[0027] According to various embodiments, the snubber circuit 408 may include a transistor, five diodes, a transformer, an inductor, and a capacitor.

[0028] According to various embodiments, the snubber circuit 408 may be configured to suppress a voltage surge.

[0029] According to various embodiments, the snubber circuit 408 may be configured to transfer energy stored in a capacitor to the battery.

[0030] According to various embodiments, the semiconductor switch may include or may be a MOSFET, or may be an IGBT or may be any other type of semiconductor switches.

[0031] According to various embodiments, the pre-charging circuit 406 may be configured to pre-charge the electronics system.

[0032] According to various embodiments, the pre-charging circuit 406 may further include two diodes, and an inductor.

[0033] According to various embodiments, the snubber circuit 408 may be configured to suppress a voltage surge across the directional power electronics switch.

[0034] According to various embodiments, the power electronics switch 402 may include two further semiconductor switches and two diodes.

[0035] According to various embodiments, the snubber circuit 408 may further include a plurality of diodes, an inductor, and a capacitor.

[0036] According to various embodiments, the power electronics switch 402 may include or may be a bi-directional power electronics switch.

[0037] Fig. 4B shows a flow diagram 412 illustrating a method for controlling a battery disconnect circuit. In 414 a first semiconductor switch configured to be provided between a battery and an electronics system may be controlled. In 416, a relay may be controlled to isolate the battery from the electronics system (for example when the battery is off, or for example when the electronics system is off). In 418, a pre-charging circuit including a second semiconductor switch may be controlled. In 420, a snubber circuit including the second semiconductor switch may be controlled.

[0038] According to various embodiments, the snubber circuit may transfer energy stored in a capacitor to the battery.

[0039] According to various embodiments, the pre-charging circuit may pre-charge the electronics system.

[0040] According to various embodiments, the snubber circuit may suppress a voltage surge across the directional power electronics switch.

[0041] According to various embodiments, the semiconductor switch may include or may be a MOSFET, IGBT or other type of semiconductor switches.

[0042] FIG. 5 shows a system 500 with a battery 502, a BDU 554 (in other words: a battery disconnect circuit), and a motor driver or inverter 558 according to various embodiments.

[0043] According to various embodiments, a bi-directional power electronics switch with common emitter configuration may include a first transistor 522, a first diode 524, a second transistor 526, and a second diode 528. The first transistor 522 and the second transistor 526 may be IGBTs or MOSFETs (metal oxide semiconductor field-effect transistor) or of any other type of semiconductor switches. The first diode 524 and the second diode 528 may be freewheeling diodes. This bi-directional power electronics switch may be controlled by a BDU controller 520 to start/stop the heavy current flow between battery 502 and the electronics system (for example including the motor driver or inverter 558). [0044] A mechanical relay 542 may be provided. The mechanical relay 542 may be controlled by the BDU controller 520 to isolate the battery pack 502 and the electronics system when it is OFF to avoid static residue voltage at the BDU 554 output.

[0045] A pre-charging cell (in other words: pre-charging circuit) may be provided including a third transistor 540 (which may for example be a MOSFET or an IGBT or any other kind of semiconductor switch), a third diode 548, a fourth diode 530, and an inductor 544 which may be functioning as a Buck converter. The current in the inductor 544 may be controlled to charge the DC-link properly.

[0046] A snubber circuitry may be provided including the third transistor 540, the fourth diode 530, a fifth diode 534, sixth diode 536 (which may be a zener diode), a seventh diode 516, an eighth diode 538, a transformer 518/532 (wherein two coils 518 and 532 may share a common metal core, like indicated by boxes 560 and 562), the inductor 544 and a capacitor 546. This snubber may suppress the voltage surge accrossing the bi-directional power electronics switch 402 when it switches OFF to cut the heavy current flows between battery pack 502 and the electronics system. This snubber may transfer the energy stored in the capacitor 546 back to the battery pack 502 after both the bi-directional power electronics switch 402 and the mechanical relay 542 become OFF. The diode 538 may provide a path for the current in transformer primary 532 to charge the capacitor 546.

[0047] The battery 502 may provide a positive potential 504 and a negative potential 506, which may be connected via resistors 508, 510, wherein the connection of the resistors 508, 510 may be grounded, like indicated by 512.

[0048] A first voltage sensor 514, a second voltage sensor 552 (which may be configured to sense a DC link voltage 556), and a current sensor 550 may be provided. The first voltage sensor 514 may be provided by a resistor in series, by an integrated circuit (IC), by a Hall effect sensor, or by a signal from a battery management system in the battery 502. The second voltage sensor 552 may be provided by a resistor in series, by an integrated circuit (IC), by a Hall effect sensor, or by a signal from the motor driver or inverter 558. The current sensor 550 may be provided by a shunt, by a transformer, or by a Hall effect sensor.

[0049] According to various embodiments, the BDU control system may control all active switches including the first transistor 522, the second transistor 526, the third transistor 540, and mechanical relay 542 by monitoring voltages (battery pack voltage and DC-link voltage) and currents (for example flows between the battery pack and the electronics system, for example in primary side of the transformer 518/532, for example in the inductor 544). Switching control and critical voltage and current waveforms are illustrated in Fig. 6.

[0050] Fig. 6 shows a diagram 600 illustrating switching control and critical voltage and current waveforms of various elements of the circuit shown in Fig. 5. It will be understood that the illustration of the waveforms in Fig. 6 is for illustrative purposes, and therefore, no absolute values are given. For the transistors 522, 526, 540, and the switch 542 a lower value means "off, and a higher value means "on". A vertical axis 604 indicates the respective variable illustrated in the waveforms. The waveforms in Fig. 6 are labeled with the same reference signs as the corresponding elements shown in Fig. 5 for sake of brevity. A horizontal axis 602 indicates the time with the following points of time: (1) initial state, (2) the electromechanical relay 542 ON, (3) pre-charge DC-Link, (4) DC-link is ready, (5) normal operation, (6) DC-link short circuit fault occurred, (7) the transistors 522 and 526 switch OFF, (8) the capacitor 546 fully charged, (9) the mechanical relay 542 OFF, (10) the capacitor 546 discharge, (11) system OFF.

[0051] The devices and methods according to various embodiments may provide an electronics topology and a control strategy for a BDU, which may decrease the system total cost, for example by replacing the high- voltage and high-current electromechanical relay 210 by low cost power electronics switches, by replacing the high-voltage, high-current and fast electromechanical relay 216 by a low- voltage, high-current and slow relay, by omitting the high- voltage, low-current mechanical relay 212 and the power resistor 214 by realizing the pre- charging function through operating part of the snubber circuit as Buck converter, by omitting the fuse 208.

[0052] The devices and methods according to various embodiments may provide an electronics topology and a control strategy for a BDU, which may increase the lifetime. As high operating current may be cut off by the power electronics switches 402, the mechanical relay 404 may be always switching ON and OFF with zero current (off-load operation), and thus, no arcing chute and no fast switching capability may be required, so that the system may use cheaper and smaller relays.

[0053] The devices and methods according to various embodiments may provide an electronics topology and a control strategy for a BDU, which may provide small geometry. The power electronics switches 402 may be non-arcing switches with compact size. The mechanical relay 404 may be always switching ON and OFF with zero current which means no arcing chute thus it can be with small size.

[0054] Various embodiments may be provided to be used for an electronics battery disconnection unit for electric vehicle.

[0055] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.