Current protection circuit and method of using the same

Abstract

A protection device for a vehicle electrical system includes a battery pack having at least one contactor. A microcontroller generates a test pulse at its pulse output and a sense input terminal. The microcontroller has at least one output coupled to a control terminal of at least one contactor. A first capacitor has a terminal coupled to a first terminal of at least one contactor; a second capacitor has a terminal coupled to a second terminal of at least one contactor; and a circuit is coupled between the microcontroller and the first and second capacitors. If each contactor is disconnected when the microcontroller applies a contactor disconnect voltage to the contactor control terminal, the circuit reflects the test pulse to the sense input terminal, and if any contactor is welded closed, the circuit presents a signal different from the reflected test pulse to the sense input terminal of the microcontroller.

Description

Technical Field

[0001] The present invention generally relates to a detection circuit for detecting welded closed contactors in a high voltage battery pack of a vehicle electrical system. Background Art

[0002] High voltage battery packs used in some vehicles, including but not limited to electric vehicles, use two to three sets of contactors to provide safety and protection from potentially harmful currents. The high voltage battery pack is electrically isolated from the chassis ground and the vehicle's 12 volt electrical system. Unfortunately, the contactors have the potential to weld shut due to arcing across the contacts. Summary of the invention

[0003] Exemplary embodiments are generally directed to detection circuits for detecting welded closed contactors in a high voltage battery pack of a vehicle electrical system and alerting a vehicle diagnostic system without violating isolation between the high voltage system and the low voltage system.

[0004] An exemplary embodiment of a protection device for protecting an electrical system in a vehicle is disclosed. The electrical system includes a battery pack having at least one contactor, and a high voltage bus connected to the battery pack. The protection device includes a microcontroller that generates a test pulse at its pulse output terminal and includes a sensing input terminal. The microcontroller has an additional output terminal coupled to a control terminal of at least one contactor. A first capacitor has a first terminal coupled to a first terminal of at least one contactor. A second capacitor has a first terminal coupled to a second terminal of at least one contactor. A circuit is coupled between the microcontroller and the first and second capacitors, the circuit having an input terminal connected to the pulse output terminal of the microcontroller, and an output terminal connected to the sensing input terminal of the microcontroller. If each contactor is disconnected when the microcontroller applies a contactor disconnect voltage to the control terminal of at least one contactor to disconnect it, the circuit reflects the test pulse to the sensing input terminal of the microcontroller, and if any contactor is welded closed when the microcontroller applies the contactor disconnect voltage to the control terminal of at least one contactor, the circuit presents a signal different from the reflected test pulse to the sensing input terminal of the microcontroller.

[0005] In an exemplary embodiment, the circuit is powered by a voltage source. When any contactor is closed, the circuit charges the first and second capacitors, and when each contactor is open, the circuit does not charge the first and second capacitors. The first and second capacitors are coupled to a sense input terminal of a microcontroller such that a voltage at the sense input terminal of the microcontroller corresponds to a voltage across one or more of the first capacitor and the second capacitor.

[0006] In one embodiment, the circuit includes a first transistor having a first conduction terminal coupled to a voltage source, a second conduction terminal coupled to a second terminal of a first capacitor, and a control terminal. A second transistor has a first conduction terminal coupled to a control terminal of the first transistor, a second conduction terminal coupled to a second terminal of the second capacitor, and a control terminal coupled to a pulse output terminal of a microcontroller. A resistor is coupled between the second terminal of the first capacitor and a reference voltage. A voltage appearing at the second terminal of the first capacitor is coupled to a sense input terminal of the microcontroller.

[0007] In this embodiment, when each contactor is open, the first capacitor and the second capacitor are separated from each other, and an open circuit is generated along an electrical path defined along the second conduction terminal of the first transistor, the first capacitor, the second capacitor and the reference voltage. When any contactor is closed, the electrical path is closed.

[0008] The microcontroller is configured such that based on the voltage at the sense input terminal of the microcontroller, the microcontroller determines whether any contactor is welded closed and whether each contactor is open. Based on the voltage at the sense input terminal of the microcontroller, the microcontroller is further configured to determine whether there is any current leakage across at least one contactor. Based on the voltage at the sense input terminal of the microcontroller, the microcontroller is further configured to determine the amount of current leakage across at least one contactor.

[0009] The at least one contactor of the battery pack includes a plurality of contactors, each contactor having a first terminal coupled to the first terminal of the first capacitor, and a second terminal coupled to the first terminal of the second capacitor.

[0010] When each contactor is open, the first capacitor and the second capacitor are separated from each other and an open circuit is created along an electrical path defined along a power source for powering the circuit, the first capacitor, the second capacitor, and a ground reference. When any contactor is closed, the electrical path is closed. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will become more fully understood from the detailed description and accompanying drawings, in which:

[0012] Figure 1 is a schematic diagram of a protection circuit for a vehicle electrical system according to an exemplary embodiment;

[0013] Figure 2 Show Figure 1 Voltage waveform of the protection circuit;

[0014] Figure 3 Shows the current leakage of the contactor. Figure 1 Voltage waveform of the protection circuit;

[0015] Figure 4 Shown corresponding to Figure 1 SPICE circuit diagram of the protection circuit. DETAILED DESCRIPTION

[0016] The following description of the exemplary embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0017] refer to Figure 1 , shows a protection circuit 10 for the electrical system of a vehicle. The electrical system includes a high voltage battery pack 20. The protection circuit 10 is powered by a battery V3, which may be a 12V battery, and presents a pulse signal through two capacitors C1 and C2 and across any contactors S1, S2, S3 of the high voltage battery pack 20. The protection circuit 10 maintains electrical isolation from the high voltage system through capacitors C1 and C2. The capacitors C1, C2 are rated for the full voltage of the battery pack 20. The high voltage bus 11 of the electrical system is Figure 1 , and connected to the battery pack 20. The illustrated components of the high voltage bus 11 represent the various loads and capacitances of the components on the high voltage bus, which may include: motor inverters, battery chargers, DC-DC converters (providing high voltage up to 12V), and any other electrical loads. Capacitor C3 and resistor R10 are parasitic bus loads and do not represent specific components on the high voltage bus 11. Resistors R4 and R5 represent voltage dividers used to measure the voltage on the high voltage bus 11.

[0018] The protection circuit 10 includes a microcontroller 12 having a signal generating circuit that generates an output signal 12A that provides a pulse voltage to the capacitor C1 that serves as a test pulse. The microcontroller 12 generates a test pulse of a predetermined voltage and duration, which may be the voltage across the battery V3 or a lower voltage. The microcontroller 12 may be a microcontroller of a vehicle, such as an electrical (or engine) control unit (ECU) of the vehicle. The signal generating circuit of the microcontroller 12 may include or be implemented as a monostable multivibrator circuit that receives a control pulse or signal generated within the microcontroller. The microcontroller 12 may enable or activate the signal generating circuit at a predetermined time during vehicle operation. Monostable multivibrators are well known, so a detailed description of the signal generating circuit 12 will not be provided for reasons of convenience.

[0019] The protection circuit 10 also includes an npn bipolar transistor Q2 having a control or base terminal coupled to an output 12A of the signal generating circuit 12 via a resistor R11. The pnp bipolar transistor Q1 is connected between a battery V3 and transistor Q2. Resistor R2 is connected between the emitter terminal and the base terminal of transistor Q1, and resistor R3 is connected between the base terminal of transistor Q1 and the collector terminal of transistor Q2. The collector terminal of transistor Q1 is connected to capacitor C1, and the emitter terminal of transistor Q2 is connected to capacitor C2. Diode D1 is provided between the emitter terminal and the collector terminal of transistor Q1, wherein the anode of the diode is connected to the emitter of transistor Q1, and the cathode of the diode is connected to the collector of transistor Q1. Diode D2 is connected between the collector of transistor Q1 and the emitter of transistor Q2, wherein the anode of the diode is connected to the emitter of transistor Q2, and the collector of the diode is connected to the collector of transistor Q1. Resistor R8 is coupled between the collector terminal of transistor Q1 and ground, and resistor R13 is connected between resistor R8 and a sense input to microcontroller 12 .

[0020] It should be appreciated that certain implementations of protection circuit 10 may utilize other types of transistors in addition to pnp transistor Q1 and npn transistor Q2 .

[0021] The battery pack 12 includes a stack of cells V1-Vn, which are combined to form a battery. It should be understood that there may be any number of cells that constitute a battery. Contactor S3 is connected between one terminal 11A of the high-voltage bus 11 (via a series resistor R6) and the high-side (positive) terminal of the battery stack. Contactor S3 and resistor R6 represent a pre-charge contactor, which is used to charge the high-voltage bus to prevent arc discharge when contactor S2 is closed. Not all battery systems use pre-charge contactor S3, but a separate circuit can be used to establish the bus voltage before contactor S2 is closed. Contactor S2 is connected between terminal 11A of the high-voltage bus 11 and the high-side terminal of the battery stack. Contactor S1 is connected between the low-side (negative) terminal of the battery stack and the second terminal 11B of the high-voltage bus 11. The second terminal of capacitor C1 is connected to the low-side terminal of the battery stack, and the second terminal of capacitor C2 is connected to the second terminal 11B of the high-voltage bus 11.

[0022] During operation, if all contactors S1-S3 of the battery pack 20 are disconnected, there is an open circuit between C1 and C2, and no current flows through these capacitors. Therefore, this appears as a high impedance to the transistor Q1. When the contactors S1-S3 are disconnected, the voltage pulse of the output signal 12A of the microcontroller 12 is reflected as a voltage pulse at the sensing input of the microcontroller 12. However, if any contactor S1-S3 is closed, such a closure closes the circuit between capacitors C1 and C2 and provides an electrical path from the collector terminal of the transistor Q1 through the capacitors C1 and C2 connected in series to the ground. When the voltage pulse of the output signal 12A is applied, current flows through C1 and C2. Since the transistor Q1 is only a current source path, the capacitors C1 and C2 retain their charge, and the voltage at the sensing input of the microcontroller 12 increases, in this case to a voltage greater than zero volts and less than the voltage at the supply voltage of the battery V3. The microcontroller 12 detects the voltage signal at its sense input at a predetermined time and determines whether there is an open contactor condition (in this case, an undesirable closed contactor condition if the voltage applied to the control terminals of the contactors S1-S3 is the contactor open voltage), a current leakage condition across the contactors, or a loss of isolation of the contactors. Depending on the determined condition, the microcontroller 12 sends a warning to a vehicle diagnostic system (not shown), which can then indicate to the vehicle service provider that the contactors S1-S3 need to be replaced.

[0023] The protection circuit 10 allows any of the contactors S1-S3 in the electrical system to be tested while being operated by an isolated voltage source. The protection circuit 10 always maintains electrical isolation, detects leakage across the contactor, and detects changes in external load capacitance.

[0024] Figure 4 yes Figure 1 PSpice interpretation of the protection circuit 10. Figure 2-3 The waveform shows the output voltage sensed by the microcontroller 12 .

[0025] Figure 2 The top graph of shows the test pulses generated by the microcontroller 12 . Figure 2 The middle graph of shows the control voltage for opening and closing the contactors S1 -S, which may also be generated by the microcontroller 12 . Figure 2 The bottom graph of shows the voltage appearing at the sense input terminal of the microcontroller 12. The high voltage in the middle graph indicates a contactor closing voltage, and the corresponding contactors S1-S3 are closed, while zero volts indicates a contactor opening voltage, and the corresponding contactors are open. When all contactors S1-S3 are open, a voltage pulse appears at the sense input of the microcontroller 12 (as in Figure 2When any of the contactors S1-S3 is closed (seen between 0ms to 20ms and between 25ms to 45ms), the voltage at the sense input is approximately 5 volts.

[0026] Figure 3 The operation of the protection circuit 10 is shown, wherein the current leakage occurs in or through one or more of the contactors S1-S3. The output signal 12A of the microcontroller 12 is described as a voltage spike that occurs every 1.25 ms. The contactors S1-S3 are controlled to be closed between 0-20 ms, 25-45 ms, and 50-70 ms. During these times, the voltage at the sensing input of the microcontroller 12 is at the voltage of the battery V3. As shown in the time between 20-25 ms and between 45-50 ms, when the contactors S1-S3 are controlled to be disconnected, the voltage that appears at the sensing input of the microcontroller 12 corresponds to the voltage spike at the output signal 12A. Therefore, if one or more of the contactors S1-S3 are closed due to unexpected welding, the voltage appearing at the sensing input of the microcontroller 12 is a voltage between ground and the voltage of the battery V3; and if the contactors S1-S3 are not welded closed, then when the contactors are controlled to be open, the voltage at the sensing input of the microcontroller 12 follows the voltage pulses of the microcontroller's output signal 12A.

[0027] Figure 3 The effect of current leakage across contactors S1-S3 is shown. The voltage labeled "1 MOhm" appearing at the sense input terminal shows the leakage of 1 MOhm leakage across contactors S1-S3. The row labeled "10 MOhm" corresponds to the effect of 10 MOhm leakage across the contactors. Figure 3 As can be seen in FIG. 1 , as leakage increases, the voltage at the sense input terminal gradually rises to a voltage corresponding to closing contactors S1-S3. By observing the voltage level during each test pulse applied to the protection circuit 10, the microcontroller 12 is able to determine the amount of leakage through the leakage contactors S1-S3.

[0028] In another embodiment, the protection circuit 10 is disposed within the battery pack 20 and is powered by a high voltage battery. The warning signal provided by the microcontroller 12 is sent to a diagnostic system such as an on-board diagnostic system of the vehicle through an isolation barrier such as an optocoupler.

[0029] The description of the present invention is merely exemplary in nature and thus variations that do not depart from the gist of the present invention are intended to be within the scope of the present invention. Such variations should not be regarded as a departure from the spirit and scope of the present invention.

Claims

1. A protection device for protecting an electrical system in a vehicle, the electrical system comprising a battery pack having at least one contactor and a high voltage bus connected to the battery pack, the protection device comprising: a microcontroller generating a test pulse at a pulse output terminal thereof and comprising a sense input terminal, the microcontroller having an additional output terminal coupled to a control terminal of the at least one contactor; a first capacitor having a first terminal coupled to the first terminal of the at least one contactor; a second capacitor having a first terminal coupled to the second terminal of the at least one contactor; as well as A circuit is coupled between the microcontroller and the first capacitor and the second capacitor, the circuit having an input terminal connected to a pulse output terminal of the microcontroller and an output terminal connected to a sensing input terminal of the microcontroller, if each contactor is disconnected when the microcontroller applies a contactor disconnection voltage to the control terminal of the at least one contactor to disconnect the at least one contactor, the circuit reflects the test pulse to the sensing input terminal of the microcontroller, and if any contactor is welded closed when the microcontroller applies the contactor disconnection voltage to the control terminal of the at least one contactor, the circuit presents a signal different from the reflected test pulse to the sensing input terminal of the microcontroller.

2. The protection device according to claim 1, wherein: The circuit is powered by a voltage source, and the circuit charges the first capacitor and the second capacitor when any contactor is closed, and does not charge the first capacitor and the second capacitor when each contactor is opened, and the first capacitor and the second capacitor are coupled to the sensing input terminal of the microcontroller so that the voltage at the sensing input terminal of the microcontroller corresponds to the voltage across one or more of the first capacitor and the second capacitor.

3. The protection device according to claim 2, wherein: The circuit comprises: a first transistor having a first conduction terminal coupled to the voltage source, a second conduction terminal coupled to the second terminal of the first capacitor, and a control terminal; a second transistor having a first conduction terminal coupled to a control terminal of the first transistor, a second conduction terminal coupled to a second terminal of the second capacitor, and a control terminal coupled to a pulse output terminal of the microcontroller; and A resistor is coupled between a second terminal of the first capacitor and a reference voltage, and a voltage appearing at the second terminal of the first capacitor is coupled to a sense input terminal of the microcontroller.

4. The protection device according to claim 3, wherein: When each contactor is open, the first capacitor and the second capacitor are separated from each other and an open circuit is created along an electrical path defined along the second conduction terminal of the first transistor, the first capacitor, the second capacitor and the reference voltage, and when any contactor is closed, the electrical path is closed.

5. The protection device according to claim 2, wherein: The microcontroller is configured such that based on a voltage at a sense input terminal of the microcontroller, the microcontroller determines whether any contactor is welded closed and whether each contactor is open.

6. The protection device according to claim 5, wherein: Based on the voltage at the sense input terminal of the microcontroller, the microcontroller is further configured to determine whether there is any current leakage across the at least one contactor.

7. The protection device according to claim 6, wherein: Based on a voltage at a sense input terminal of the microcontroller, the microcontroller is further configured to determine an amount of current leakage across at least one contactor.

8. The protection device according to claim 1, wherein: The at least one contactor of the battery pack includes a plurality of contactors, each contactor having a first terminal coupled to the first terminal of the first capacitor and a second terminal coupled to the first terminal of the second capacitor.

9. The protection device according to claim 1, wherein: When each contactor is open, the first capacitor and the second capacitor are separated from each other and an open circuit is created along an electrical path defined by a power source powering the circuit, the first capacitor, the second capacitor and a ground reference, and the electrical path is closed when any contactor is closed.

10. A protection device for protecting an electrical system in a vehicle, the electrical system comprising a battery pack having at least one contactor and a high voltage bus connected to the battery pack, the protection device comprising: a microcontroller generating a test pulse at a pulse output terminal thereof and comprising a sense input terminal, the microcontroller having an additional output terminal coupled to a control terminal of the at least one contactor; a first capacitor having a first terminal coupled to the first terminal of the at least one contactor; a second capacitor having a first terminal coupled to the second terminal of the at least one contactor; as well as A circuit is coupled between the microcontroller and the first capacitor and the second capacitor, the circuit having an input terminal connected to a pulse output terminal of the microcontroller and an output terminal connected to a sensing input terminal of the microcontroller, if each contactor is disconnected when the microcontroller applies a contactor disconnection voltage to the control terminal of the at least one contactor to disconnect the at least one contactor, the circuit reflects the test pulse to the sensing input terminal of the microcontroller, and if any contactor is welded closed when the microcontroller applies the contactor disconnection voltage to the control terminal of the at least one contactor, the circuit presents a signal different from the reflected test pulse to the sensing input terminal of the microcontroller, the first capacitor and the second capacitor are connected in series, and the at least one contactor provides an electrical connection between the first capacitor and the second capacitor when the at least one contactor is closed, and provides a disconnection between the first capacitor and the second capacitor when each contactor is disconnected.

11. The protection device according to claim 10, wherein: The circuit is powered by a voltage source, and the circuit charges the first capacitor and the second capacitor to or near the voltage source when any contactor is closed, and does not charge the first capacitor and the second capacitor when each contactor is opened, and the first capacitor and the second capacitor are coupled to the sensing input terminal of the microcontroller so that the voltage at the sensing input terminal of the microcontroller corresponds to the voltage across one or more of the first capacitor and the second capacitor.

12. The protection device according to claim 11, wherein: The circuit comprises: a first transistor having a first conduction terminal coupled to the voltage source, a second conduction terminal coupled to the second terminal of the first capacitor, and a control terminal; a second transistor having a first conduction terminal coupled to a control terminal of the first transistor, a second conduction terminal coupled to a second terminal of the second capacitor, and a control terminal coupled to a pulse output terminal of the microcontroller; and A resistor is coupled between a second terminal of the first capacitor and a reference voltage, and a voltage appearing at the second terminal of the first capacitor is coupled to a sense input terminal of the microcontroller.

13. The protection device according to claim 12, wherein: When each contactor is open, the first capacitor and the second capacitor are separated from each other and an open circuit is created along an electrical path defined along the second conduction terminal of the first transistor, the first capacitor, the second capacitor and the reference voltage, and when any contactor is closed, the electrical path is closed.

14. The protection device according to claim 11, wherein: The microcontroller is configured such that based on a voltage at a sense input terminal of the microcontroller, the microcontroller determines whether any contactor is welded closed and whether each contactor is open.

15. The protection device according to claim 14, wherein: Based on the voltage at the sense input terminal of the microcontroller, the microcontroller is further configured to determine whether there is any current leakage across the at least one contactor.

16. The protection device according to claim 15, wherein: Based on a voltage at a sense input terminal of the microcontroller, the microcontroller is further configured to determine an amount of current leakage across at least one contactor.

17. The protection device according to claim 10, wherein: The at least one contactor of the battery pack includes a plurality of contactors, each contactor having a first terminal coupled to the first terminal of the first capacitor and a second terminal coupled to the first terminal of the second capacitor.

18. The protection device according to claim 10, wherein: When each contactor is open, the first capacitor and the second capacitor are separated from each other and an open circuit is created along an electrical path defined by a power source powering the circuit, the first capacitor, the second capacitor and a ground reference, and the electrical path is closed when any contactor is closed.

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