Link capacitor discharge circuit with temperature control

Abstract

To provide a link capacitor discharge circuit with temperature control.SOLUTION: According to at least some embodiments, a discharge circuit for an electric vehicle includes: a link capacitor; a resistance load; a discharge switch that is coupled to the link capacitor and the resistance load, in which the link capacitor is coupled to the resistance load when the discharge switch is closed to enable discharge of the link capacitor; and a discharge interruption assembly. The discharge interruption assembly includes: a detection resistor that is serially connected to the resistance load; and a temperature circuit. The temperature circuit includes an input connected to the detection resistor and an output. A discharge interruption circuit is responsive to a voltage in the output of the temperature circuit in order to open the discharge switch when the voltage from the temperature circuit is higher than a threshold value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates generally to a link capacitor discharge circuit with temperature control. [Background technology]

[0002] An electric vehicle includes a battery that powers one or more motors to drive the wheels. Electric vehicles typically include a large capacitor between the high voltage input positive and negative terminals that must be rapidly discharged while the vehicle is stopped, which may be done through a resistive load. During the initial discharge, the power dissipation in the resistive load is significant and substantial heat is generated. For example, it may be difficult and costly to accurately monitor the temperature of the resistive load and protect against damage to components if the vehicle's battery or batteries are still connected or if too much energy is stored in the capacitor, which may result in a longer discharge event and higher temperatures. Summary of the Invention [Means for solving the problem]

[0003] In at least some implementations, a discharge circuit for an electric vehicle includes a link capacitor, a resistive load, a discharge switch coupled to the link capacitor and the resistive load such that the link capacitor is coupled to the resistive load when the discharge switch is closed to enable discharge of the link capacitor, and a discharge interrupt assembly. The discharge interrupt assembly includes a sense resistor connected in series with the resistive load and a temperature circuit. The temperature circuit has an input coupled to the sense resistor and an output, and the discharge interrupt circuit is responsive to a voltage at an output of the temperature circuit to open the discharge switch when the voltage from the temperature circuit is above a threshold.

[0004] In at least some implementations, the sense resistor is connected in series with the discharge switch.

[0005] In at least some implementations, an amplifier is provided between the sense resistor and the temperature circuit.

[0006] In at least some implementations, the link capacitor, the resistive load, the discharge switch and the sense resistor are connected in series.

[0007] In at least some implementations, the voltage at the output of the temperature circuit is a function of the temperature of the resistive load.

[0008] In at least some implementations, the temperature circuit includes a first resistor, a control capacitor connected in series with the first resistor, and a second resistor coupled in parallel with the control capacitor.

[0009] In at least some implementations, the discharge interrupt assembly includes a comparator coupled to an output of the temperature circuit, the comparator configured to provide a first output when the voltage at the output of the temperature circuit is at a first threshold, hi at least some implementations, the comparator configured to provide a second output when the voltage at the output of the temperature circuit is at a second threshold.

[0010] In at least some implementations, the electric vehicle includes a power supply, a motor driven by electricity from the power supply, an inverter, a link capacitor, a resistive load, a discharge switch, a sensing resistor, a temperature circuit, and a discharge interrupt assembly. The inverter is coupled to the power supply and the motor for converting DC power output from the power supply to AC power and providing the AC power to the motor. The link capacitor is coupled in series between the power supply and the inverter. The discharge switch is coupled to the link capacitor and the resistive load such that the link capacitor is coupled to the resistive load when the discharge switch is closed to enable discharging of the link capacitor. The sensing resistor is configured to receive a current as the current flows from the link capacitor to the resistive load. The temperature circuit has an input coupled to the sensing resistor and the output. And, the discharge interrupt assembly is responsive to a voltage at an output of the temperature circuit for opening the discharge switch when the voltage from the temperature circuit is higher than a threshold value.

[0011] In at least some implementations, the discharge interrupt assembly includes a comparator coupled in series with the output of the temperature circuit, the comparator configured to provide an output when the voltage at the output of the temperature circuit is greater than a threshold value.

[0012] In at least some implementations, an amplifier is coupled between the sense resistor and the temperature circuit.

[0013] In at least some implementations, the temperature circuit includes a first resistor, a control capacitor connected in series with the first resistor, and a second resistor coupled in parallel with the control capacitor.

[0014] In at least some implementations, an electric vehicle includes a power supply, a motor driven by electricity from the power supply, an inverter coupled to the power supply and the motor for converting DC power output from the power supply to AC power and providing the AC power to the motor, a link capacitor coupled in series between the power supply and the inverter, a resistive load, a discharge switch coupled to the link capacitor and the resistive load such that the link capacitor is coupled to the resistive load when the discharge switch is closed to enable discharging of the link capacitor, a sense resistor configured to receive current as it flows from the link capacitor to the resistive load, a resistor-capacitor circuit having an input coupled to the sense resistor and the output, and a comparator coupled to the output of the resistor-capacitor circuit and to the discharge switch and configured to open the discharge switch when a voltage of the resistor-capacitor circuit is higher than a threshold value.

[0015] In at least some implementations, the resistor-capacitor circuit includes a first resistor, a control capacitor connected in series with the first resistor, and a second resistor coupled in parallel with the control capacitor.

[0016] In at least some implementations, the sense resistor is connected in series with the discharge switch.

[0017] In at least some implementations, the link capacitor, the resistive load, the discharge switch and the sense resistor are connected in series.

[0018] In at least some implementations, the voltage at the output of the resistor-capacitor circuit is a function of the temperature of the resistive load.

[0019] In at least some implementations, the comparator is configured to provide a second output when the voltage at the output of the temperature circuit is at a second threshold.

[0020] The following detailed description of the preferred embodiments and best mode is illustrated with reference to the accompanying drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a side view of a vehicle including a power supply and one or more electric motors for propelling the vehicle. [Diagram 2] 1 is a schematic diagram of components and branch circuits within a vehicle's electrical system. [Diagram 3] FIG. 2 is a partial circuit diagram showing an amplifier, a temperature branch circuit, and a comparator. [Figure 4] A partial circuit diagram showing the amplifier, temperature branch circuit and comparator of a larger portion of the circuit including the link capacitor and discharge switch. [Diagram 5] 1 is a flow chart of a method for controlling the discharge of a link capacitor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Referring more particularly to the drawings, FIG. 1 shows a vehicle 10 including a power supply 12 that provides power to one or more motors 14, which drive the vehicle's wheels 16. The power supply 12 may include one or more rechargeable batteries 18 and an inverter 20 coupled to the batteries by a DC link 22. The inverter 20 converts the battery DC power to AC power and includes DC link capacitors 24 (FIG. 2), which are connected in parallel with the batteries 18 to balance the load and store energy in the system. To control the application of power to the motors 14, a controller / control system 26, which may include one or more microcontrollers, is coupled between the power supply 12 and the motors 14 to provide current to the motors to drive them in a desired manner and propel the vehicle 10.

[0023] When vehicle operation is terminated, the link capacitor 24 needs to be discharged somewhat quickly to safely reduce power in the system. To accomplish this, as shown in FIG. 2, a resistive load 28 is selectively connected to the link capacitor 24 by a discharge switch 30. The resistive load 28 may include an array of resistive elements having a desired total resistance. When the discharge switch 30 is open and in a non-conductive state, the link capacitor 24 is not connected to the resistive load 28, and when the discharge switch 30 is closed and in a conductive state, the link capacitor 24 is connected to the resistive load 28 and discharges energy into the resistive load 28. To control the state of the discharge switch 30, the switch is coupled to a control system 26, which provides a signal to close the discharge switch when discharging of the link capacitor 24 is desired.

[0024] The discharge of energy through resistive load 28 is converted to heat, increasing the temperature of the components of resistive load 28 and adjacent components. Resistive load 28 may be designed to handle the normal discharge cycle of link capacitor 24, and power dissipation by resistive load 28 predictably increases the system temperature, e.g., the temperature of resistors, associated circuit board 31 (FIG. 4), and adjacent components. However, a system fault that causes more than the normal amount of energy to be dissipated through resistive load 28 may cause an excessive increase in system temperature. Such a system fault may, for example, cause additional power to be supplied to link capacitor 24 because, for example, battery 18 is still connected to link capacitor 24 due to a disconnect switch failure or other failure. During such a fault, battery 18 continues to supply power to link capacitor 24 as the link capacitor is discharged.

[0025] To limit the temperature of the resistive load 28 during a link capacitor discharge event, a discharge interrupt assembly 32 is provided. As shown in FIGS. 2-4, the discharge interrupt assembly 32 includes a temperature circuit 34 or subcircuit configured to provide an output representative of a system temperature (e.g., of the resistive load and adjacent components). In at least some implementations, the discharge interrupt assembly 32 includes a sense resistor 36, and the temperature circuit 34 includes a resistor-capacitor (RC) subcircuit. The sense resistor 36 is connected in series with the resistive load 28 and to an input of the RC subcircuit 34. The RC subcircuit 34 is configured to provide a voltage at an output of the RC subcircuit 34 that is comparable to the system temperature, as will be described in more detail below. The output voltage of the RC subcircuit may then be used to terminate the link capacitor discharge event when the output voltage of the RC subcircuit exceeds a threshold value, which indicates that the system temperature is at or above the threshold temperature. In this manner, the maximum system temperature during a link capacitor discharge event may be controlled.

[0026] As shown in FIG. 2, the link capacitor 24 is connected in parallel across the terminals of a power supply (e.g., one or more batteries 18). A resistive load 28, a discharge switch 30, and a sense resistor 36 are connected in series with each other and in parallel with the link capacitor 24. When the discharge switch 30 is closed and conductive, the link capacitor 24 discharges into the resistive load 28 and current flows through the discharge switch 30 and the sense resistor 36. The discharge switch 30 may be any type of electronic switch, e.g., a transistor, a MOSFET, and an IGBT, that can be controlled to change state as required, and the state of the discharge switch 30 may be changed by a controller that controls the discharge of the link capacitor 24. Additionally, as shown in FIG. 4, a control interface 38 may be provided to control the discharge of the link capacitor 24 in a desired manner, e.g., using a pulse width modulated signal to provide a desired link capacitor discharge rate in a normal discharge cycle.

[0027] As shown in FIG. 4, the sense resistor 36 may be connected between the discharge switch 30 and ground and connected to the RC branch circuit 34. The sense resistor 36 may have a relatively small resistance compared to the resistive load 28. In at least some implementations, the sense resistor 36 has a resistance between 1 ohm and 10 ohms. The sense resistor 36 may have a low resistance to avoid excessive power / heat dissipation, while having a sufficiently large resistance so that the voltage generated across the sense resistor is detectable by the protection system. Such conditions will typically require a sense resistor value several orders of magnitude lower than the resistive load. When the discharge switch 30 is closed, a current flows through the sense resistor 36, generating a voltage that is at least somewhat proportional to the power dissipated by the resistive load 28. The voltage resulting from the current through the sense resistor 36 is provided as an input to the RC branch circuit 34, as shown in FIGS. 2-4, and the input Vsense is labeled in FIGS. 3 and 4.

[0028] 3, the resulting voltage may be amplified by an amplifier 40, if desired, and the output from the amplifier 40 may be provided to the RC sub-circuit 34. The RC sub-circuit 34 includes one or more resistors and one or more capacitors configured to provide an output that is on the same order as the temperature of the resistive load 28. Thus, the amplifier 40 may provide a larger voltage to the RC sub-circuit 34, which may charge the capacitor(s) in the sub-circuit faster, improving the response from the sub-circuit and allowing the signal to be more easily distinguished from noise or variations within the circuit and in use of the circuit.

[0029] In general, the components of the RC branch circuit 34 are selected to provide an output voltage to the comparator 42 that is comparable to or corresponds to the temperature of the system (e.g., resistive load 28) and can be used to shut off the discharge of the link capacitor 24 and allow further link capacitor discharge. As described in more detail below, during a discharge event, the comparator 42 compares the output voltage to a first set of thresholds corresponding to a maximum temperature threshold, and when the output voltage exceeds the first threshold, the comparator 42 provides an output that is used to shut off the link capacitor discharge event. The comparator 42 then compares the output voltage of the RC branch circuit 34 to a second threshold, which corresponds to a second lower temperature threshold that is lower than the first threshold, and indicates that the system temperature has sufficiently decreased from the maximum temperature. When the output voltage reaches the second threshold, the comparator 42 provides an output that is used to restart the discharge of the link capacitor 24. For example, the comparator 42 may be coupled to an isolation switch 44, as shown in FIGS. 2 and 4, which may be a transistor or other switch as desired, and the comparator 42 may turn the isolation switch 44 off to selectively isolate the link capacitor discharge event and turn the isolation switch 44 back on to allow discharge of the link capacitor 24.

[0030] In at least some implementations, the capacitance of the RC branch circuit 34 is selected as a function of the thermal mass of any metal enclosure or cover surrounding the conductive elements (e.g., copper) of the circuit board 31, the heat sink, the resistive load 28, and the link capacitor 24. Additionally, in at least some implementations, the resistance of the RC branch circuit 34 may be selected as a function of the thermal resistance from the center of the resistive load 28 (which may be hottest and slowest to cool) to the circuit board 31, and from the circuit board 31 to the ambient environment. Because of the large thermal mass of the system, the temperature rise and fall times may be somewhat long, so the RC branch circuit 34 may include a relatively high capacitance or high resistance. In at least some implementations, the higher capacitance is used as a tolerance, and the reliability of higher value resistors is sometimes poor.

[0031] When configured as described, the RC branch circuit 34 may be used to control the discharge of the link capacitor 24 as a function of the temperature rise caused by the discharge. The rate at which the temperature increases during a discharge event and the rate at which the temperature decreases after a discharge event may be modeled and / or empirically determined. This information may be used in a control strategy to shut off the discharge to allow the desired cooling to the system before allowing further discharge (e.g., a subsequent discharge event). In this manner, system temperature thresholds may be set as an initial or maximum temperature at which the discharge may be terminated / shut off, and a second, lower temperature at which the discharge may be resumed (e.g., after a period of time sufficient to achieve a desired temperature reduction).

[0032] In at least some implementations, the rate of temperature increase during the discharge event is significantly greater than the rate of temperature decrease during the cool down period. In one example, the temperature increase from ambient temperature to the maximum temperature threshold took about 4 seconds, and the temperature decrease cycle from the maximum temperature threshold to the lower second threshold took about 30 seconds. Naturally, these durations will vary as a function of the energy discharge from the link capacitor 24, the resistance of the resistive load 28, and the magnitude of the thermal mass and thermal resistance of the system.

[0033] Referring now to the implementation shown in FIG. 4, the RC branch circuit 34 includes a first resistor R1 coupled in series with the control capacitor C, and a second resistor R2 coupled in parallel with the control capacitor C. As described above, the values ​​of resistors R1 and R2 and the control capacitor C are selected as a function of the thermal mass and thermal resistance of the system. In one implementation, R1 is selected as a function of the thermal resistance from the center of the resistive load 28 to the circuit board 31, which sets the relationship between the power dissipation and the temperature rise in the system during a discharge event. R2 is selected as a function of the thermal resistance from the circuit board 31 to the ambient environment, which sets the relationship between the temperature decrease during a cooldown period. The capacitance of the control capacitor C is selected as a function of the thermal mass of the circuit board 31 and metal components such as heat sinks and the housing in which the circuit board 31 is received.

[0034] One method for determining the values ​​of the components of the RC branch circuit 34 is to empirically test the system and measure the temperature rise to a maximum temperature threshold and the temperature decrease to a lower second threshold over several cycles during a link capacitor discharge event, providing information about the thermal mass and thermal resistance of the system. Furthermore, with a known maximum output voltage from the amplifier 40 and the capacitance value selected for the control capacitor C, the values ​​of resistors R1 and R2 can be calculated.

[0035] In one example, the following equations were used to determine the component values ​​in RC subcircuit 34: To determine the voltage across the capacitor while it is discharging, Vc(t) = V0(e -t / (R2×C) ), To determine the voltage across the capacitor while it is charging, Vc(t)=(V / (R1×C))((R1×R2×C) / (R1+R2)(1-e -t(1 / (R1×C)+(1 / R2×C) ), To determine the voltage output from the RC branch circuit 34, Vh = (V / (R1 x C)((R1 x R2 x C) / (R1 + R2))(1-e -t 0 ×(1 / (R1×C)+1 / (R2×C)) ), where the voltage output corresponds to a maximum temperature threshold at which the discharge event should be shut off / terminated for a period of time to allow the system to cool down, where t0 is the time to reach the maximum temperature from a given temperature (in one example, 90° C., which is the maximum ambient temperature of an assumed resistive load 28) during the discharge event; R2×C=-t c / (ln(Vl / Vh)), where Vl is the voltage output from the RC branch circuit 34 and corresponds to a second lower temperature threshold that may initiate a discharge event, and t c is the predetermined time to cool from the maximum temperature threshold to the second temperature threshold.

[0036] In one example, the voltage of the battery 18 is approximately 900 volts, the capacitance of the link capacitor 24 is 270 μF, the total resistance of the resistive load 28 is 3.9 kΩ, the maximum temperature threshold is set at 140° C., the second temperature threshold is set at 105° C., t0 is 4 seconds, and t cThe time to reset the resistor was 30 seconds. From these values, the resistance of R1 was set at 24.25 kΩ, R2 was set at 74 Ω, and the capacitance of the RC branch circuit 34 was set at 270 μF.

[0037] For these components, the voltage from the RC branch circuit 34 corresponding to a system temperature at the maximum temperature threshold was approximately 3.9 V and the corresponding second temperature threshold was approximately 0.9 V. Accordingly, the comparator 42 is configured to interrupt the discharge event when the output voltage from the RC branch circuit 34 is 3.9 V, where 3.9 V is the upper limit or first threshold corresponding to the maximum temperature threshold. The comparator 42 is also configured to allow continued discharge of the link capacitor 24 when the output voltage decreases to 0.9 V, and may include a resistor configured to provide hysteresis to allow for two voltage thresholds, such as the one shown.

[0038] In use, when the output voltage of the RC branch meets the first threshold, the comparator 42 sends a signal to the disconnect switch 44 to turn it off, stopping the link capacitor discharge event. When the disconnect switch 44 is turned off, the comparator 42 is used to verify that the voltage at the output of the RC branch 34 has decreased to a lower second threshold corresponding to a second temperature threshold. Since the link capacitor discharge event has stopped, energy is now provided by the discharge of the RC branch control capacitor 34, and then, when the voltage at the output of the RC branch 34 reaches the second threshold, the comparator 42 provides an output that turns on the disconnect switch 44, allowing further discharge of the link capacitor 24. As mentioned above, the time for the voltage at the output of the RC branch to decrease from the first threshold to the second threshold via the RC branch control capacitor C is intended to correspond to the time to allow the system to cool sufficiently from the maximum temperature threshold to the second temperature threshold. In other implementations, the output voltage of the RC branch may be provided to a microcontroller to be monitored, but a failure of the microcontroller or a circuit including the microcontroller may prevent proper control of the system.

[0039] In at least some implementations, the resistance of resistor R2 in RC branch circuit 34 may be set higher than the calculated value, for example, to accommodate degradation of the RC branch circuit capacitor that may occur over time. Without the higher value of resistor R2, RC branch circuit 34 may overestimate or overrepresent the temperature of the system, causing premature shutoff of the discharge event, and RC branch circuit 34 may overestimate cooling and allow premature resumption of the link capacitor discharge. Furthermore, the exemplary models and calculations presented herein provide for RC branch circuit 34 where a 0 volt signal occurs at a maximum ambient temperature, and if the actual system temperature is below this temperature, RC branch circuit 34 will overestimate the temperature rise and underestimate the temperature decrease. Other starting / assumed ambient temperatures may be used if desired. In use, such inaccuracies are not an issue as long as they do not interfere with normal link capacitor discharge events where the temperature of the system has not reached the maximum temperature threshold, and shutoff of the discharge event is not necessary.

[0040] Furthermore, the power input to the RC branch 34 is the voltage across the sense resistor 36, which increases linearly with current rather than exponentially as the energy in the link capacitor 24 decreases during discharge, causing the RC branch 34 to underestimate the actual power dissipation and therefore underestimate the increase in system temperature. The system can be designed somewhat conservatively, typically to overestimate the temperature rise, or any such underestimate is within acceptable limits such that the actual temperatures of the system components are below the maximum temperature.

[0041] The comparator 42 may then be of simple design and configured to provide an output to a shutoff switch 44 connected in series with the discharge switch 30 as shown in Figure 4 and shown diagrammatically in Figure 2. During a discharge event, the comparator 42 compares the voltage at the output of the RC branch circuit 34 with a first threshold, and during a shutoff discharge event, the comparator 42 compares the output voltage with a lower second threshold. Thus, simpler and less expensive analog components may be used to control the discharge of the link capacitor 24 as a function of the temperature of the components during a discharge event.

[0042] The control system may include one or more controllers, which may be coupled to the motor(s), battery, inverter 20, vehicle electrical system, and other vehicle components in any desired manner and configuration. To perform the functions and desired processing and calculations illustrated herein, the controller may include, but is not limited to, processor(s), computer(s), DSP(s), memory, storage, register(s), timing devices, circuit breaker(s), communication interface(s), and input / output signal interfaces, and the like, as well as combinations comprising at least one of the above. For example, the controller may include input signal processing and filtering to enable accurate sampling and conversion or acquisition of such signals from the communication interfaces and sensors.

[0043] As used herein, the terms control system or controller may refer to one or more processing circuits, such as application specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated or groups) and memory that execute one or more software or firmware programs, combinatorial logic circuits, and / or other suitable components that provide the described functionality.

[0044] A general method 46 for controlling the discharge of the link capacitor 24 is shown in FIG. 5. The method 46 begins at 48 by determining in step 50 whether the vehicle is stopped, which may be determined, for example, by the state of the ignition switch 51 (shown diagrammatically in FIG. 2). If the vehicle is stopped, the discharge switch 30 is closed in step 52 to initiate a discharge event. The system temperature is then checked against a maximum temperature threshold in step 54. As explained above, the system temperature may be estimated via the RC subcircuit 34, which may provide an output voltage representative of the system temperature. If the output voltage of the RC subcircuit falls below a first threshold, indicating that the system temperature is below the maximum temperature threshold, the method continues to step 56, which determines whether the link capacitor 24 is fully or completely discharged, and if this occurs, the method ends at 58.

[0045] If, in step 54, it is determined that the system temperature is at or exceeds the maximum temperature threshold, the method continues to step 60 where the discharge event is interrupted (e.g., by comparator 42 turning off interrupt switch 44). Thereafter, in step 62, the output voltage of the RC branch is checked to determine whether the output voltage has decreased to a second threshold indicating that the system temperature has decreased to the second temperature threshold, and if this has occurred, the method returns to step 52 to resume discharging link capacitor 24. A further discharge interruption can occur if the temperature rises again to the maximum temperature threshold, or link capacitor 24 is discharged if the temperature does not rise again to that threshold.

[0046] In this manner, link capacitor 24 may discharge while maintaining the system temperature below the threshold, limiting or preventing damage to components that may occur at higher temperatures. If the output voltage of the temperature subcircuit is still below the upper threshold, link capacitor 24 may discharge completely without shutting off. That is, in at least some implementations, shutting off occurs only when the voltage of the temperature subcircuit rises above the upper threshold, indicating that the system temperature is at the maximum temperature threshold.

[0047] The temperature circuit may include a simple RC branch circuit 34 with one or more resistors and one or more capacitors, and need not include a temperature sensor such as a thermistor or thermocouple. Such a temperature sensor would need to be coupled to the circuit board 31, creating manufacturing costs as well as high voltage creepage and clearance issues, since the temperature sensor is on the low voltage control side of the circuit, but must be physically mounted in fairly close proximity to the high voltage active discharge resistor(s) in order to accurately monitor the temperature. Furthermore, due to the difficult physical location of the sensor, response times may be slow, causing resistors to operate above their power ratings for longer periods of time before a temperature rise is detected. This may require oversized cooling features to manage the system temperature, increasing cost and weight. Such complexity and associated problems are avoided by the temperature circuit described herein, resulting in a robust, easy to implement, low cost solution to the problem of excessive temperature conditions during link capacitor discharge events.

[0048] All terms used in the claims are intended to be given their broadest reasonable construction and ordinary meaning as understood by one of ordinary skill in the art, unless otherwise indicated herein. In particular, the use of singular articles such as "a," "the," "said," etc., should be construed as referring to one or more of the indicated elements, unless the claim recites an express limitation otherwise. [Explanation of symbols]

[0049] 10 Electric Vehicles 28 Resistive Load 30 Discharge switch 34 Link Capacitor 36 Sensing resistor 40 Amplifier 42 Comparator C Control capacitor

Claims

1. 1. A discharge circuit for an electric vehicle, the discharge circuit comprising: A link capacitor; A resistive load, a discharge switch coupled to the link capacitor and the resistive load, the discharge switch coupling the link capacitor to the resistive load when the discharge switch is closed to enable discharging of the link capacitor; a discharge interruption assembly having a sensing resistor and a temperature circuit connected in series with the resistive load; the temperature circuit having an input connected to the sense resistor and an output, the discharge cutoff circuit responsive to a voltage at the output of the temperature circuit to open the discharge switch when a voltage from the temperature circuit is above a threshold.

2. 2. The circuit of claim 1, wherein the sense resistor is connected in series with the discharge switch.

3. 2. The circuit of claim 1, further comprising an amplifier between said sensing resistor and said temperature circuit.

4. 2. The circuit of claim 1, wherein the link capacitor, the resistive load, the discharge switch and the sense resistor are connected in series.

5. 2. The circuit of claim 1, wherein the voltage at the output of the temperature circuit is a function of the temperature of the resistive load.

6. 2. The circuit of claim 1, wherein the temperature circuit includes a first resistor, a controlled capacitor connected in series with the first resistor, and a second resistor coupled in parallel with the controlled capacitor.

7. 2. The circuit of claim 1, wherein the discharge interrupt assembly includes a comparator coupled to the output of the temperature circuit, the comparator configured to provide a first output when a voltage at the output of the temperature circuit is at a first threshold.

8. The circuit of claim 7 , wherein the comparator is configured to provide a second output when the voltage at the output of the temperature circuit is at a second threshold.

9. An electric vehicle, the electric vehicle comprising: A power supply device; a motor driven by electricity from the power supply; an inverter coupled to the power supply and to the motor for converting DC power output from the power supply to AC power and providing the AC power to the motor; a link capacitor coupled in series between the power supply and the inverter; A resistive load, a discharge switch coupled to the link capacitor and the resistive load, the discharge switch coupling the link capacitor to the resistive load when the discharge switch is closed to enable discharging of the link capacitor; a sense resistor configured to receive current as current flows from the link capacitor to the resistive load; a temperature circuit having an input connected to the sense resistor and an output; a discharge interrupt assembly responsive to a voltage at the output of the temperature circuit for opening the discharge switch when a voltage from the temperature circuit is above a threshold value; An electric vehicle comprising:

10. 10. The vehicle of claim 9, wherein the discharge interrupt assembly includes a comparator coupled in series with an output of the temperature circuit, the comparator configured to provide an output when a voltage at the output of the temperature circuit is above a threshold value.

11. 10. The vehicle of claim 9, also including an amplifier coupled between the sense resistor and the temperature circuit.

12. 10. The vehicle of claim 9, wherein the temperature circuit includes a first resistor, a controlled capacitor connected in series with the first resistor, and a second resistor coupled in parallel with the controlled capacitor.

13. An electric vehicle, the electric vehicle comprising: A power supply device; a motor driven by electricity from the power supply; an inverter coupled to the power supply and to the motor for converting DC power output from the power supply to AC power and providing the AC power to the motor; a link capacitor coupled in series between the power supply and the inverter; A resistive load, a discharge switch coupled to the link capacitor and the resistive load, the discharge switch coupling the link capacitor to the resistive load when the discharge switch is closed to enable discharging of the link capacitor; a sense resistor configured to receive current as current flows from the link capacitor to the resistive load; a resistor-capacitor circuit having an input connected to the sense resistor and an output; a comparator coupled to the output of the resistor-capacitor circuit and to the discharge switch, the comparator configured to open the discharge switch when a voltage of the resistor-capacitor circuit is higher than a threshold; An electric vehicle comprising:

14. 14. The vehicle of claim 13, wherein the resistor-capacitor circuit includes a first resistor, a controlled capacitor connected in series with the first resistor, and a second resistor coupled in parallel with the controlled capacitor.

15. 14. The vehicle of claim 13, wherein the sense resistor is connected in series with the discharge switch.

16. 14. The vehicle of claim 13, wherein the link capacitor, the resistive load, the discharge switch and the sense resistor are connected in series.

17. 14. The vehicle of claim 13, wherein the voltage at the output of the resistor-capacitor circuit is a function of the temperature of the resistive load.

18. 14. The vehicle of claim 13, wherein the comparator is configured to provide a second output when the voltage at the output of the temperature circuit is at a second threshold.

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