Discharge circuit for discharging a battery

Abstract

A discharge circuit for discharging a battery, wherein the battery includes a positive terminal and a negative terminal, wherein the circuit comprises: a reference voltage source that provides a reference voltage, wherein this voltage source includes a negative terminal and a positive terminal, wherein this voltage source is electrically coupled to the battery, wherein the negative terminal of the voltage source is electrically coupled to the negative terminal of the battery; a load that is electrically coupled to the battery and the voltage source, wherein a current flow generated by the battery through the load discharges the load to the reference voltage; and a mechanical relay-type switch comprising a spring and a coil, wherein the spring holds the switch open, the switch being positioned between the load and the battery pack.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] This invention relates generally to a discharge circuit for discharging a battery according to claim 1. 2. Discussion of the state of the art

[0002] Electric vehicles are becoming increasingly common. These vehicles include hybrid vehicles, such as extended-range electric vehicles (EREVs), which include a battery and a main power source such as an internal combustion engine, a fuel cell system, etc., and pure electric vehicles, such as battery electric vehicles (BEVs). These batteries can be of various types, such as a lithium-ion battery, a nickel-metal hydride battery, a lead-acid battery, etc. A typical high-voltage battery system for an electric vehicle may include multiple battery cells or modules to meet the vehicle's power and energy requirements, with each battery module containing a certain number of battery cells, such as 12 cells.Different vehicle designs include different battery designs, each with different advantages and disadvantages for each application.

[0003] During a vehicle crash or other vehicle damage event, the displacement and / or damage of various vehicle components and components can cause undesirable electrical connections and the leakage of various fluids from the vehicle. Due to the significant electrical power that may be stored in the vehicle battery, these events can potentially lead to hazardous situations, such as the electrification of vehicle components, chemical poisons, combustion fumes, etc. Vehicle battery system designs must consider these potential damage events.

[0004] Fault isolation detection systems are sometimes incorporated into electrical circuits to provide electrical fault detection. Electric vehicles are one electrical system that typically uses fault isolation detection systems to prevent a person from being injured by the high voltage on the vehicle.

[0005] To provide electrical fault isolation, some vehicles are equipped with a battery disconnect unit (BDU), which automatically disconnects or removes battery power from the vehicle after a crash or other incident by opening the battery contactors. It is also known in the art to use a manual service disconnect switch (MSD), which is a device that separates a battery into two parts, allowing a trained emergency responder to remove the MSD after a vehicle crash to isolate the battery. However, these known isolation techniques do not remove the charge from the battery; they only secure it.

[0006] As mentioned above, the integrity of the vehicle battery or other rechargeable energy storage systems (RESS) always becomes an issue when a hybrid electric vehicle experiences a crash or other similar event, regardless of the severity of the vehicle accident. It is desirable to discharge the battery during such an event, for example, reducing the battery voltage by half. Known battery discharge systems can be expensive, costing thousands of dollars, and they are typically heavy and require significant space. One known battery discharge system is an autonomous, embedded, advanced monitoring system with DC / DC buck / boost converters, liquid-cooled load banks, and semi-modern control systems.Furthermore, the compatibility between the different forms of energy storage devices on the market makes battery discharge a complicated task due to the different voltages, chemical compositions and current ranges.

[0007] De 10 2009 055 053 A1 discloses a method and device for discharging an energy storage device in a high-voltage network.

[0008] US 7 427 865 B2 discloses a method for detecting a discharge state fault in an electrical system of a vehicle or machine.

[0009] US 2009 / 0 001 927 A1 discloses systems and methods for intelligent charging and intelligent conditioning of a high-voltage battery. SUMMARY OF THE INVENTION

[0010] In accordance with the teachings of the present invention, a method for discharging a high voltage battery of a vehicle is disclosed according to claim 1.

[0011] Further features of the present invention will become apparent from the following description and the appended claims taken in conjunction with the accompanying figures. SHORT DESCRIPTION OF THE CHARACTERS Fig. Figure 1 is a simple illustration of a vehicle with a high-voltage battery; Fig. 2 is a schematic diagram of a series-configured externally referenced scalable self-discharge circuit; Fig. Figure 3 is a graph with time on the horizontal axis and voltage on the vertical axis showing the voltage discharge of a battery with the self-discharge circuit shown in Fig. 2 shows; Fig. Figure 4 is a graph with time on the horizontal axis and current on the vertical axis showing the current discharge of a battery for the self-discharge circuit from the Fig. 2 shows; Fig. 5 is a schematic diagram of a parallel configured externally referenced scalable self-discharge circuit; Fig. Figure 6 is a graph with time on the horizontal axis and voltage on the vertical axis showing the voltage discharge of a battery for the self-discharge circuit from the Fig. 5 shows; Fig. Figure 7 is a graph with time on the horizontal axis and current on the vertical axis showing the current discharge of a battery for the self-discharge circuit from the Fig. 5 shows; Fig. Figure 8 is a flowchart illustrating a method for discharging a vehicle battery using the self-discharge circuits of Figures Fig. 2 and Fig. 5 shows; Fig. 9 is a schematic diagram of an internally referenced, scalable self-discharge circuit using a soft-switch architecture; Fig. 10 is a schematic diagram of an internally referenced, scalable self-discharge circuit using a hard switch architecture; Fig. Figure 11 is a graph with time on the horizontal axis and voltage on the vertical axis showing the discharge voltage of a battery for the self-discharge circuits from the Fig. 9 and Fig. 10 shows; Fig. Figure 12 is a graph with time on the horizontal axis and current on the vertical axis showing the current discharge of a battery for the self-discharge circuits from the Fig. 9 and Fig. 10 shows; Fig. 13 is a flowchart illustrating a method for discharging a vehicle battery using the self-discharge circuit of the Fig. 9 shows; and Fig. 14 is a flowchart illustrating a method for discharging a vehicle battery using the self-discharge circuit of the Fig. 10 shows. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The following discussion of embodiments of the invention directed to a system and method for discharging a high-voltage vehicle battery using an externally referenced voltage source is merely exemplary in nature and is in no way intended to limit the invention or its applications or uses. For example, the battery discharge technique of the present invention finds particular application in discharging a vehicle battery. However, those skilled in the art can readily recognize that the discharge technique of the invention may have application in other battery systems beyond vehicle battery systems.

[0013] Fig. 1 is a simple illustration of a vehicle intended to represent any electric vehicle or electric hybrid vehicle. The vehicle 10 includes a high-voltage battery 12 mounted on a suitable carrier within the vehicle 10, wherein the battery 12 includes a plurality of battery cells 14. The battery 12 may be any suitable battery for an electric vehicle, such as a lead-acid battery, a lithium-ion battery, a nickel-metal hydride battery, etc. The vehicle 10 may further include an additional power source 16, such as an internal combustion engine, a fuel cell system, etc. for an electric hybrid vehicle. The vehicle 10 further includes an electronic control unit (ECU) 18 that controls various aspects of the operation of the vehicle 10.

[0014] As will be discussed in detail below, the present invention proposes various self-discharge circuits for discharging a vehicle battery on demand, for example, after a crash event or other vehicle damage event by, for example, a suitable emergency responder such as a tow truck driver, or during maintenance by suitable maintenance personnel or by junkyard personnel, etc. In one embodiment, the circuit is part of a unit that the respective person brings to the vehicle and electrically couples to the battery terminals using suitable cables, for example, jumper cables. Each of the various circuits is relatively inexpensive and simple in architecture to be readily available to all interested parties.

[0015] Fig. 2 is a schematic diagram of a scalable self-discharge circuit 30 for discharging a high-voltage battery pack 32 of a vehicle with an external reference. As discussed in detail below, the circuit 30 provides for discharging the battery pack 32 with an external reference using a series-configured architecture. The circuit 30 is provided with an external reference because the reference voltage to which the battery is discharged is located outside the vehicle. Furthermore, the circuit 30 is scalable because the reference voltage is variable and can be changed. The circuit 30 is a self-discharge circuit because the battery pack 32 is automatically discharged relative to the reference voltage once the circuit is connected and powered on.

[0016] The circuit 30 includes a discharge unit 34, which is not part of the electric vehicle but, for example, a portable unit. The unit 34 is connected to the battery pack 32 via terminals 36 and 38 when the situation or need arises to discharge the battery pack 32, which is consistent with the discussion herein. The discharge unit 34 includes a reference DC voltage source 40 that is electrically coupled in series with the battery pack 32 and provides a reference DC voltage to which the battery pack 32 is discharged. In one embodiment, the DC voltage source 40 is a variable source and can be controlled by the operator to set the discharge reference voltage of the battery pack 32.

[0017] The battery pack 32 is discharged to the reference voltage supplied from the source 40 by a load 42 electrically coupled in series with the source 40 and the battery pack 32. The load 42 may be any load suitable for the purposes discussed herein, such as a resistor bank. The load 42 may have any resistance value or impedance suitable for the desired discharge time and discharge rate for the battery pack 32 to be discharged to the DC reference voltage. This resistance value determines the size and weight of the load 42, which is a matter of design. In this electrical configuration, the negative terminal 38 of the battery pack 32 is electrically coupled to the negative terminal of the voltage source 40, and the positive terminal 36 of the battery pack 32 is electrically coupled to the positive terminal of the load 42 to provide for discharging of the battery pack 32.A start switch 44 is provided to initiate the discharge process upon request. When the switch 44 is closed, the battery pack 32 is discharged to the reference voltage by current flowing through the load 42 at a specific rate that depends on the electrical configuration of the circuit 30 and the size of the load 42. The battery pack 32 is discharged to the reference voltage and will remain at that voltage once discharged.

[0018] Fig. 3 is a graph with time on the horizontal axis and voltage on the vertical axis illustrating the discharging of battery pack 32 using circuit 30. Curve 50 represents the voltage potential of battery pack 32, curve 52 represents the reference voltage potential, which is negative because the negative terminal of source 40 is electrically coupled to the negative terminal 38 of battery pack 32, and curve 54 represents the voltage potential across load 42. In this non-limiting embodiment, the voltage of battery pack 32 is 400 V before it is discharged, and the reference voltage is 200 V, which provides a voltage potential of 200 V across load 42.When switch 44 is closed at time zero, battery pack 32 discharges exponentially to the voltage potential of load 42 in approximately 300 ms and is maintained at this voltage potential by the reference voltage of source 40. Since no potential is developed across load 42 when the battery pack voltage and the reference voltage are equal, no discharge current occurs at battery pack 32 once it reaches the potential of voltage source 40. This can be seen from the graph in FIG. Fig. 4, in which the battery pack 32 discharges exponentially from time zero to 0 A in approximately 300 ms.

[0019] As mentioned above, the series configuration of circuit 30 discharges battery pack 32 to the reference voltage using these example values ​​in approximately 300 ms. This is a relatively long discharge time due to the relatively low voltage potential across the load during discharge. This discharge time can be increased by increasing the voltage potential across load 42, i.e., by allowing greater current flow through load 42, which requires a larger load device. To provide a faster discharge rate at a lower reference voltage, a parallel-configured discharge circuit can be used.

[0020] Fig. 5 is a schematic diagram of a scalable self-discharge circuit 60 with an external reference having a discharge unit 62 for discharging the battery pack 32. The circuit elements common to circuits 60 and 30 are designated by the same reference numerals. In this electrical configuration, the load 42 is electrically coupled in parallel with the battery pack 32 and therefore has the same voltage potential as the battery pack 32. Because the load 42 has the same voltage potential as the battery pack 32, the current flow through the load 42 is higher than when the load 42 is coupled in series with the battery pack 32, as in circuit 30. Specifically, in the series configuration of circuit 30, the difference between the reference voltage and the battery voltage was applied to the load 42. In the parallel configuration of circuit 60, the full voltage of the battery pack 32 is applied to the load 42.

[0021] As discussed above, the load 42 is a larger device because it receives a larger current flow, which adds to the cost of the device but has the advantage of faster voltage decay. In addition, there are greater requirements for heat dissipation because more power is consumed by the load 42. Furthermore, the source 40 in the circuit 60 can be very small because the voltage source 40 in the parallel configuration of the circuit 60 does not conduct current, as does the voltage source 40 in the series configuration of the circuit 30. In the parallel circuit 60, the voltage of the battery pack 32 automatically discharges to the reference voltage as long as the potential across the source 40 is lower than the potential across the battery pack 32. The circuit 60 includes a diode 64 between the DC voltage source 40 and the load 42 to prevent current flow into the positive terminal of the source 40.

[0022] As a result, the battery pack 32 is discharged much faster in the parallel configuration due to the higher current flow through the load 42 when using the same reference voltage and the same starting voltage of the battery pack 32 to the reference potential provided by the source 40. This is due to the Fig. 6 and Fig. 7, which illustrates the graphs shown in the Fig. 3 and Fig. 4 are similar to the graph shown in Figure 4. In the graph of Fig. 6, the reference potential of 200 V with a positive sign is shown by curve 70 and the two voltage potentials across the battery pack 32 and the load 42 are shown by curve 72. As shown, the discharge from 400 V to 200 V takes place linearly in approximately 22 ms. In the graphs in the Fig. 7, the current through the load 42 is shown with the curve 74 and it can be seen that the current decreases linearly from 10 A to 0 A in approximately 25 ms.

[0023] Fig. 8 is a flowchart 80 showing the general procedure for operating the circuits 30 and 60 described above. In box 84, the operator connects the unit 34 or 62 to the battery pack 32. In box 86, the operator determines the desired voltage to which the battery pack 32 is to be discharged. This can be determined based on various parameters, such as the battery pack type, battery pack size, etc. In box 88, the operator sets the voltage source 40 to the desired discharge voltage of the battery pack 32 and then closes the switch 44 in box 90. The control algorithm controlling the circuits 30 or 60 monitors the terminal voltage of the battery pack 32 and the desired discharge voltage in decision diamond 92. Once the terminal voltage reaches the discharge voltage, the discharge in box 94 is complete, and the unit 34 or 62 can be disconnected from the battery pack 32.Otherwise, the unloading procedure continues in box 96.

[0024] The circuits 30 and 60 described above are circuits that provide an external reference voltage through the voltage source 40 in the units 34 and 62. In other embodiments, it may be desirable to provide the reference voltage internally within the vehicle, specifically using the battery pack 32 itself as the reference voltage to which the battery pack 32 is discharged. This can be achieved by providing a voltage divider circuit electrically parallel to the battery pack 32.

[0025] Fig. 9 is a schematic diagram of a scalable internal reference self-discharge circuit 100 having a discharge unit 102, which may be portable, employing a soft-switch architecture, with similar elements from circuits 30 and 60 being designated by the same reference numerals. As mentioned, the battery pack 32 in the circuit 100 provides the reference voltage to which the battery pack 32 is discharged. In particular, a voltage divider network including resistors 104 and 106, electrically coupled across the battery pack 32 and disposed within the discharge unit 102, divides the voltage of the battery pack 32 to provide the reference voltage. The load 42 is electrically coupled in parallel with the voltage divider network and the battery pack 32.Resistor 104 and / or resistor 106 may be configured to be variable, such that selecting the resistance values ​​of resistors 104 and 106 may selectively adjust the reference voltage, which is consistent with the discussion herein.

[0026] A semiconductor switch 108, such as a MOSFET, IGBT, etc., provides the soft switch architecture discussed in detail below. The voltage potential across resistor 106 provides the reference potential that controls the gate terminal of switch 108 to turn on switch 108 at relatively low currents when a sufficiently high voltage is applied. The values ​​of resistors 104 and 106 are selected to have a high impedance, which prevents large current flow through resistors 104 and 106. The resistance of resistor 106 is selected relative to resistor 104 such that when the voltage of battery pack 32 drops during discharge, the reference voltage drops. As the reference voltage drops, the voltage applied to the gate terminal of switch 108 drops, eventually reaching a threshold voltage of switch 108, resulting in its turn-off.The electrical configuration of circuit 100 is such that when battery pack 32 is discharged and switch 108, which sets the voltage of battery pack 32 to the reference voltage potential, is eventually opened when switch 108 is open, a voltage surge may occur in battery pack 32, causing its voltage to rise, which in turn causes switch 108 to open. Switch 108 may frequently oscillate between on and off at the end of the discharge process until the power in the system is sufficiently dissipated, at which point switch 108 remains open.

[0027] Fig. 10 is a schematic diagram of a scalable, internally referenced self-discharge circuit 110 similar to circuit 100, including a discharge unit 112, where similar elements are designated by the same reference numerals. In circuit 110, soft switch 108 is replaced by a mechanical relay-like switch 114 having a spring (not shown) and coil 116, resulting in a hard-switch architecture, with the spring holding switch 114 open. When switch 114 is closed and the discharge process begins, at which time the voltage potential of battery pack 32 is at its normal high potential, the voltage divided across resistor 106 provides a current flow through coil 116, which is forced against the spring force.The reference voltage is initially not large enough to overcome the spring force, and consequently, additional power from an auxiliary power source 118 must be supplied to coil 116 at the beginning of the discharge process by closing a push-button switch 120. When switch 120 is pressed, the combination of the current flow from source 118 and the current flow from the reference voltage through coil 116 closes switch 114, and releasing push-button 120 returns it to its open position, thus disconnecting power source 118. Once switch 114 is closed, the reference voltage is high enough to maintain switch 114 in the closed position until battery pack 32 is discharged to the desired level.

[0028] As the battery pack 32 discharges while current is flowing through the load 42, the reference voltage provided by resistor 106 may be reduced to the point where it may no longer be high enough to overcome the spring force. Once this voltage value is reached, the switch 114 opens, causing the battery pack 32 to discharge to the desired voltage. In this embodiment, a voltage surge may occur when the switch 114 is opened. However, this surge will not be high enough to overcome the spring force in the switch 114, causing it to close.

[0029] Fig. 11 is a graph similar to the graphs in the Fig. 3 and Fig. 6 and which shows with the curve 122 the voltage across the battery pack 32 and the voltage across the load 42, wherein in the curve 124 the voltage drops from 400 V to the reference potential of approximately 200 V linearly in approximately 50 ms. Analogously, the Fig. 12 a graph similar to the graphs in the Fig. 4 and Fig. 7, and shows the current consumption with curve 126 for circuits 100 and 110, with the current decreasing from -5 A to 0 A in approximately 50 ms.

[0030] Fig. 13 is a flowchart 130 illustrating a method for discharging battery pack 32 using circuit 100. At box 132, the operator will connect unit 102 to battery pack 32. At box 134, the operator will determine the desired voltage to which battery pack 32 should be discharged. This can be determined based on various parameters, such as battery pack type, battery pack size, etc. At box 136, the operator adjusts the resistance values ​​of resistors 104 and 106 to provide the desired discharge voltage of battery pack 32, and then, at box 90, closes switch 44 to begin the discharge process. The control algorithm controlling circuit 110 monitors the terminal voltage of battery pack 32, and once the terminal voltage reaches the discharge voltage, the discharge in box 144 is complete and unit 104 can be separated from battery pack 32.Otherwise, the unloading procedure continues in box 142.

[0031] Fig.14 is a flowchart 150 illustrating a method for discharging battery pack 32 using circuit 110. At box 152, the operator connects unit 112 to battery pack 32. At box 154, the operator determines the desired voltage to which battery pack 32 is to be discharged. This can be determined based on various parameters, such as battery pack type, battery pack size, etc. At box 156, the operator adjusts the resistance values ​​of resistors 104 and 106 to provide the desired discharge voltage of battery pack 32 and then closes switch 44 at box 90 to begin the discharge process. Furthermore, the operator presses push button 120 at box 158. The control algorithm controlling circuit 110 monitors the terminal voltage of battery pack 32.Once the terminal voltage reaches the discharge voltage, the discharge is complete in box 160, and the unit 112 can be separated from the battery pack 32. Otherwise, the discharge process continues in box 162.

[0032] As will be well understood by those skilled in the art, various or some of the steps and methods discussed herein to describe the invention may be performed by a computer, processor, or other electronic computing device that manipulates and / or transforms data using electrical phenomena. These computers and electrical devices may include various volatile and / or non-volatile memories, including a fixed computer-readable medium having an executable program thereon containing various codes or executable instructions executed by the computer or processor, wherein the memory and / or computer-readable medium may include all forms and types of memory and other computer-readable media.

[0033] The foregoing discussion illustrates and describes purely exemplary embodiments of the present invention. One skilled in the art will readily appreciate from the discussion of the accompanying figures and claims that numerous changes, modifications, and variations may be made without departing from the spirit and scope of the invention as defined by the following claims.

Claims

[1] A discharge circuit for discharging a battery, the battery including a positive terminal and a negative terminal, the circuit comprising: a reference voltage source providing a reference voltage, said voltage source including a negative terminal and a positive terminal, said voltage source being electrically coupled to the battery, said negative terminal of said voltage source being electrically coupled to the negative terminal of the battery; a load electrically coupled to the battery and the voltage source, wherein a current flow generated by the battery through the load discharges the load to the reference voltage; and a mechanical relay-like switch having a spring and a coil, the spring holding the switch open, the switch being arranged between the load and the battery pack. [2] The circuit of claim 1, wherein the battery is a vehicle battery and wherein the battery, the voltage source and the load are electrically coupled in series with each other. [3] The circuit of claim 1, wherein the battery is a vehicle battery and wherein the battery, the voltage source and the load are electrically coupled in parallel. [4] The circuit of claim 1, wherein the voltage source is a variable voltage source so that the reference voltage can be changed. [5] The circuit of claim 1, wherein the voltage source and the load are part of a portable unit that can be selectively coupled to the battery.

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