US20130119933A1

US20130119933A1 - Ground fault interrupt circuit for electric vehicle

Info

Publication number: US20130119933A1
Application number: US13/651,417
Authority: US
Inventors: Albert Flack; Scott BERMAN
Original assignee: Aerovironment Inc
Current assignee: Aerovironment Inc
Priority date: 2010-04-14
Filing date: 2012-10-14
Publication date: 2013-05-16
Also published as: CN102948029B; WO2011130569A1; US9024685B2; CN103141003A; CN103141003B; US20140176236A1; WO2011130571A1; CN102948029A; US8618877B2; US20130187716A1

Abstract

In one implementation, a ground fault interrupt circuit is provided for a utility power connection to an electric vehicle charging unit. The ground fault interrupt circuit may include a gain amplifier having an input connected to be capable of receiving a differential current from a current sensing transformer and a comparator having an input connect to a reference voltage. It includes a rectifier circuit connected between the gain amplifier and the comparator with a charge accumulator circuit coupled between the rectifier and the comparator.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/US2011/032576 by Flack et al., entitled GROUND FAULT INTERRUPT CIRCUIT FOR ELECTRIC VEHICLE, filed on 14 Apr. 2011, herein incorporated by reference in its entirety, which claims the benefit of the following U.S. Provisional Patent Applications, which are herein incorporated by reference in their entireties:
U.S. Provisional Application 61/324,296, by Albert Flack, filed 14 Apr. 2010, entitled GROUND FAULT INTERRUPT CIRCUIT FOR ELECTRIC VEHICLE; U.S. Provisional Application 61/374,612, Albert Flack, filed 18 Aug. 2010, entitled GROUND FAULT INTERRUPT AUTOMATIC TEST METHOD FOR ELECTRIC VEHICLE; and
U.S. Provisional Application 61/324,293, by Albert Flack, filed 14 Apr. 2010, entitled PILOT SIGNAL GENERATION CIRCUIT.

BACKGROUND

One way to charge an electric vehicle is to supply the vehicle with power so that a charger in the vehicle can charge the battery in the vehicle. If there is a ground fault in the electrical system in the car and someone is touching car while grounded, that person could be shocked.
What is needed to avoid this situation is a ground fault interrupt or GFI circuit to disconnect the power to the vehicle if a ground fault is detected.

SUMMARY

In one implementation, a ground fault interrupt circuit is provided for a utility power connection to an electric vehicle charging unit. The ground fault interrupt circuit may include a gain amplifier having an input connected to be capable of receiving a differential current from a current sensing transformer and a comparator having an input connect to a reference voltage. It includes a rectifier circuit connected between the gain amplifier and the comparator with a charge accumulator circuit coupled between the rectifier and the comparator.
Some embodiments may include an inverter between the gain amplifier and the charge accumulator circuit.
In one possible implementation, a GFI circuit is provided for a utility power connection to an electric vehicle charging unit. The GFI circuit includes a gain amplifier having an input connected to be capable of receiving a differential current from a current sensing transformer. A filter is connected to an output of the gain amplifier. In various embodiments the filter is a half wave rectified dual stage filter. A comparator is connected to an output of the filter. The output of the comparator is connected to a latching circuit. A contactor control circuit is connected to the output of the fault latch. The contactor control circuit may include a contactor control relay. The output of the contactor control circuit is connected to a utility power line contactor so as to be capable of connecting/disconnecting utility power. In various embodiments, a microprocessor is connected to a reset input of the fault latch.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1 shows a schematic view of a cable to connect utility power to an electric vehicle (not shown) along with some associated circuitry.

FIG. 2 shows an enlarged view schematic drawing of the GFI circuit of FIG. 1.

FIG. 3 shows a schematic view of a contactor control circuit.

FIG. 4 shows an enlarged more complete schematic of the pilot circuitry shown in partial schematic in FIG. 1.

FIG. 5 is a partial schematic showing a microprocessor, which may be used to govern the output of the GFI circuit.

FIG. 6 shows a simplified plot of an example of possible charge accumulation by the double stage filter leading to a fault detection by the comparator.

FIG. 7 shows a schematic view of an alternate embodiment of a portion of the GFI circuit of FIG. 2.

DESCRIPTION

FIG. 1 shows a schematic view of a cable 100 to connect utility power to an electric vehicle (not shown) along with some associated circuitry. In the embodiment of FIG. 1, the cable 100 contains L1 and L2 and ground G lines. The cable 100 connects to utility power at one end 100 u and to an electric vehicle (not shown) at the other end 100 c. The electric vehicle (not show) could have an onboard charger, or the electric vehicle end 100 c of the cable 100 could be connected to a separate, optionally free standing, charger (not shown). The separate charger (not shown) would in turn be connected to the electric vehicle for charging onboard batteries, or other charge storage devices. In other embodiments not shown, a charger could be integrated into the cable 100.
The cable 100 contains current transformers 110 and 120. The current transformer 110 is connected to a GFI circuit 130 which is configured to detect a differential current in the lines L1 and L2 and indicate when a ground fault is detected. Contactor 140 may be open circuited in response to a detected ground fault to interrupt utility power from flowing on lines L1 and L2 to the vehicle (not shown).
FIG. 2 shows an enlarged view schematic drawing of the GFI circuit 130 of FIG. 1. In the embodiment of FIG. 2, the GFI circuit 130 is designed to trip in the 5-20 mA range for GFI in accordance with the UL 2231 standard.
A signal provided by current transformer 110 (FIG. 1) at pins 3 and 4 of the GFI circuit 130 is amplified by op amp 132 to a voltage reference. That voltage reference is filtered by a double stage RC filter 134 to eliminate spurious noise spikes.
Fault current detected by current transformer 110 (FIG. 1) is converted to voltage by gain amplifier 134 for comparison by comparator 136. The output of the gain amplifier 132 is filtered prior to being supplied to the comparator 136 with the double stage RC filter 134 to remove spurious noise that could cause nuisance shut downs. Output of comparator 136 is latched with flip-flop 138 so that contactor 140 (FIG. 1) does not close after a fault has been detected. The comparator 136 provides a GFI_TRIP signal output, which is an input to the fault latch 138 to produce a latched GFI_FAULT signal.
The double stage filter 134 provides a delay so that the shut-off circuit does not immediately shut off if a fault is detected. The double stage filter 134 is a half-wave rectified circuit that allows an incoming pulse width that is less than 50% in some embodiments, or even as small as about 38% in some embodiments, to accumulate over time so that it will charge at a faster rate than it discharges. The double stage filter 134 accumulates charge and acts as an energy integrator. Thus, the GFI circuit 130 waits a time period before causing shut down. This is because it is not desirable to have an instantaneous shut down that can be triggered by noise in the lines L1 or L2, or in the GFI circuit 130. The GFI circuit 130 should trip only if a spike has some predetermined duration. In the embodiment shown, that duration is one to two cycles.
The filter 134 charges through R102 and R103. When it discharges, it only discharges through R102, so it charges more current than it discharges over time. The double stage filter 134 is a half wave rectified circuit due to diode D25.
Diodes D4 provide surge suppression protection. In typical embodiments, the gain amplifier 132 may actually have surge suppression protection. Despite this, diodes D4 are added to provide external redundant protection to avoid any damage to the gain amplifier 132. This redundant protection is significant, because if the gain amplifier 132 is damaged, the GFI protection circuit 130 may not function, resulting in inadequate GFI protection for the system. For example, without the redundant surge suppressing diodes D4, if a power surge were to damage the gain amplifier 132 so that it no longer provided output, the GFI circuit 130 would no longer be able to detect faults. Since UL 2231 allows utility power L1 and L2 power to be reconnected after a GFI circuit detects a ground fault surge, utility power L1 and L2 could conceivably be reconnected after the gain amplifier 132 had been damaged. It is significant to note that the diodes D4 are connected to the upper and lower reference voltage busses of the circuit, i.e. ground and 3 volts, respectively, so that they can easily dissipate surge current without causing damage to the circuitry. Thus, the redundant surge suppression diodes D4 provide an additional safety feature for the GFI protection circuit 130.
FIG. 3 shows a schematic view of a contactor control circuit 170. The contactor control circuit 170 opens/closes the contactor 140 (FIG. 1) to disconnect/connect the utility power L1 and L2 from/to the vehicle connector 100 c. As discussed above with reference to FIG. 2, the GFI_TRIP signal is output by the comparator 136 and is an input to the fault latch 138 to produce the GFI_FAULT signal. The GFI_FAULT signal output by the fault latch 138 is an input to the contactor control circuitry 170, shown in FIG. 3, used to control the contactor control relay K1. The contactor control relay K1 is used to open/close the contactor 140 (FIG. 1) to disconnect/connect the utility power L1 and L2 from/to the vehicle connector 100 c. The CONTACTOR_AC signal output by the contactor control relay K1 is connected to the contactor coil 141 (FIG. 1) through pin 1 of the connector 181 (FIG. 1) associated with the utility present circuitry 180 (FIG. 1).
The GFI_TRIP signal output by the comparator 136 (FIG. 2) is not only provided to the contactor control circuit 170 (FIG. 3), but also is provided as an input to the contactor disable latch 152, shown in FIG. 4 to produce a CONTACTOR_FAULT_DISABLE signal. FIG. 4 shows an enlarged more complete schematic view of the pilot circuitry 150 shown in partial schematic in FIG. 1. Additionally, the contactor disable latch 152 (FIG. 4) is an input to the contactor control circuitry 170 (FIG. 3) to control the contactor control relay K1 (FIG. 3). The CONTACTOR_FAULT_DISABLE signal is used to open the contactor control relay K1 (FIG. 3), which opens the contactor 140 (FIG. 1) to open circuit/close circuit the utility power L1 and L2. This provides a redundant circuit for this important safety control circuit. Further, it requires the reset of both latches 138 (FIG. 2) and 152 (FIG. 4) to reconnect L1 and L2 utility power to the vehicle connector 100 c. This provides further software redundancy for this important safety control circuit.
FIG. 5 is a partial schematic showing a microprocessor 500, which may be used to govern the output of the GFI circuit 130 (FIG. 2). Referring to FIGS. 2 and 5, the GFI_FAULT output signal from the fault latch 138 is provided as an input at pin 552 to the microprocessor 500. The microprocessor 500 outputs at pin 538 the GFI_RESET signal to the GFI circuit 130 to control the reset of the GFI_circuit 130, in accordance with a predetermined standard, such as UL 2231. This may be accomplished by outputting the GFI_RESET signal to the fault latch 138, and to the CONTACTOR_RESET to the contactor disable latch 152 (FIG. 4).
Also, the microprocessor 500 may also output at pin 81 the GFI_TEST signal, which causes a GFI test circuit 139 to simulate a ground fault for testing the functionality of the contactor 140 (FIG. 1). The GFI test circuit 139 output AC_1 provides a path via pin 2 of the connector 181 to the contactor coil 141 (FIG. 1) to exercise the contactor 140.
Additionally, the microprocessor 500 provides a CONTACTOR_CLOSE signal output to the contactor close circuit to close the contactor control relay K1 (FIG. 3).
FIG. 6 shows a simplified plot 600 of an example of possible charge accumulation by the double stage filter 134 (FIG. 2) leading to a fault detection by the comparator 136 (FIG. 2). Referring to FIGS. 2 and 6, since the double stage filter 134 discharges slower than it charges, several successive current pulse detections 601, 602, and 603 would be required to cause sufficient charge to accumulate a voltage level that would cause the comparator to indicate a GFI_TRIP. Thus, faults by spurious noise can be minimized. In this simplified example plot, a 1.5 volts pulse of about 38% of the duty cycle for three successive cycles causes sufficient charge to accumulate a GFI TRIP signal. Other embodiments are possible by appropriate selection of the R102, R103, and C51.
FIG. 7 is shows a schematic view of an alternate embodiment 730 of a portion of the GFI circuit 130 of FIG. 2. In this embodiment, the input 730 i of the GFI circuit 730 is connected to gain amplifier 732 via an optional EMI protection circuit 731. Thus, the signal provided by the current transformer 110 is passed through the EMI protection circuit 731, which includes series inductor L7 and resistor R71, of about 50 microHenries and 50 ohms, respectively, with capacitors C34, C33, C20, each about 0.001 microFarads, coupled across the differential input 730 i and coupled to ground.
Further, in this embodiment, the input 730 i is connected to the amplifier 732 via a series capacitor C17, of about 10 microFarads, and series resistor R23 (about 50 ohms) to the inverting input of the amplifier 732. The non-inverting input of the operational amplifier 732 is referenced to 1.5 volts. The output of the amplifier 732 is feed back to the inverting input of amplifier 732 via parallel coupled feedback resistor R24 and an optional feedback capacitor C15, of about 50K ohms and 0.01 microFarads respectively. The optional capacitor C15 provides filtering to reduce noise. The output of the amplifier 733 is provided to the inverting input of amplifier 733 via resistor R18 (about 10K ohms). The non-inverting input of the amplifier 733 is supplied the reference voltage of 1.5 volts. The output of the amplifier 733 is feed back via resistor R15 (about 10K ohms). Thus, the amplifier 733 has a gain of unity so merely provides an inverted output from that of the gain amplifier 732.
As such, the series capacitor C17 passes the AC portion of the differential current input 730 i, which is both positive and negative. The input 730 i is referenced to 1.5V by the gain amplifier 732. The output of the gain amplifier 732 is inverted by the inverting amplifier 733.
The output of the amplifier 732 and the output of the amplifier 733 are connected by diodes D2 and D1, respectively, to the charge accumulator 734. The diodes D2 and D1 provide a full wave rectified output (with respect to 1.5V) to the charge accumulator 734. The anode of diode D2 and the anode of diode D1 form a full wave rectifier circuit and are connected to sum at the input of the charge accumulator 734. The cathode of diode D2 is connected to the output of gain amplifier 732 and the cathode of the diode D1 is connected to the output of the inverting amplifier 733. Thus, in this case, as used herein, the charge accumulator 734 actually “accumulates” depleted charge.
The charge accumulator 734 includes a series connected resistor R10 of about 25 k ohms, connected between the diodes D2 and D1 and the non-inverting input of comparator 736. The charge accumulator 734 further includes resistor R7, of about 1M ohm, connected between the reference voltage 1.5V and the non-inverting input to the comparator 736. A capacitor C1, of about 0.1 microFarad is connected between the non-inverting input of the comparator 736 and ground.
A reference voltage of 0.5 volts is provided to the inverting input of the comparator 736 by the R72 and R73 voltage divider. The resistor R72, of about 20K ohms, is connected between the reference 1.5V and the inverting input of the comparator 736. The resistor R73, about 10K ohms is connected between the inverting input of the comparator 736 and ground.
The output of the comparator 736 may be supplied directly/indirectly to the microprocessor 500 (FIG. 5), latch 138 (FIG. 2) or/and latch 152 (FIG. 4), such as discussed above with reference to FIGS. 2-5.
It is worthy to note that any reference to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in an embodiment, if desired. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
The illustrations and examples provided herein are for explanatory purposes and are not intended to limit the scope of the appended claims. This disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the spirit and scope of the invention and/or claims of the embodiment illustrated.
Those skilled in the art will make modifications to the invention for particular applications of the invention.
The discussion included in this patent is intended to serve as a basic description. The reader should be aware that the specific discussion may not explicitly describe all embodiments possible and alternatives are implicit. Also, this discussion may not fully explain the generic nature of the invention and may not explicitly show how each feature or element can actually be representative or equivalent elements. Again, these are implicitly included in this disclosure. Where the invention is described in device-oriented terminology, each element of the device implicitly performs a function. It should also be understood that a variety of changes may be made without departing from the essence of the invention. Such changes are also implicitly included in the description. These changes still fall within the scope of this invention.
Further, each of the various elements of the invention and claims may also be achieved in a variety of manners. This disclosure should be understood to encompass each such variation, be it a variation of any apparatus embodiment, a method embodiment, or even merely a variation of any element of these. Particularly, it should be understood that as the disclosure relates to elements of the invention, the words for each element may be expressed by equivalent apparatus terms even if only the function or result is the same. Such equivalent, broader, or even more generic terms should be considered to be encompassed in the description of each element or action. Such terms can be substituted where desired to make explicit the implicitly broad coverage to which this invention is entitled. It should be understood that all actions may be expressed as a means for taking that action or as an element which causes that action. Similarly, each physical element disclosed should be understood to encompass a disclosure of the action which that physical element facilitates. Such changes and alternative terms are to be understood to be explicitly included in the description.
Having described this invention in connection with a number of embodiments, modification will now certainly suggest itself to those skilled in the art. The example embodiments herein are not intended to be limiting, various configurations and combinations of features are possible. As such, the invention is not limited to the disclosed embodiments, except as required by the appended claims.

Claims

What is claimed is:

1. A ground fault interrupt circuit for a utility power connection to an electric vehicle charging unit, the ground fault interrupt circuit comprising:

a) a gain amplifier having an input connected to be capable of receiving a differential current from a current sensing transformer;

b) a filter having an input connected to an output of the gain amplifier;

c) a comparator having an input connected to an output of the half wave rectified dual stage filter;

d) a fault latch having an input connected to the output of the comparator;

e) a contactor control circuit having an input connected to an output of the fault latch; and

f) a utility power line contactor having a contactor control input connected to an output of the contactor control circuit.

2. The circuit of claim 1, wherein the filter is a half wave rectified dual stage filter.

3. The circuit of claim 1, wherein the gain amplifier comprises a surge protection circuit, and further comprising a redundant surge protection circuit connected to an input of the gain amplifier.

4. The circuit of claim 3, wherein the redundant surge protection circuit comprises a pair of diodes connected to lower and upper reference busses.

5. The circuit of claim 1, further comprising a microprocessor connected to the output of the fault latch so as to detect a fault trip, and to a fault latch reset input of the fault latch.

6. The circuit of claim 1, wherein the contactor control circuit further comprises a contactor control relay, the contactor control relay is connected to the utility power line contactor.

7. The circuit of claim 6, further comprising a contactor disable latch responsive to the output of the comparator, the contactor disable latch being connected to an input of the contactor control circuit in parallel with the output of fault latch so as to provide a redundant control signal for controlling the contactor control relay.

8. The circuit of claim 1, further comprising a differential current sensing transformer coupled to utility power lines.

9. A method for electric vehicle charging for detecting a ground fault comprising:

detecting a differential current in utility power supply;

generating a ground fault signal from the detected differential current;

accumulating the ground fault signal over time; and

comparing the accumulated ground fault signal to a threshold voltage; and

causing a ground fault interrupt when the accumulated ground fault signal exceeds the threshold voltage.

10. The method of claim 9, wherein accumulating the ground fault signal over time comprises filtering the ground fault signal.

11. The method of claim 10, wherein filtering the ground fault signal comprises using a double stage filter.

12. The method of claim 11, wherein filtering the ground fault signal comprises using a half wave rectifying double stage filter.

13. The method of claim 9, wherein accumulating the ground fault signal over time comprises accumulating ground fault signals having a voltage level below the threshold voltage so as to cause the ground fault interrupt at the threshold voltage.

14. The method of claim 9, wherein accumulating the ground fault signal over time comprises accumulating multiple discrete signals having a voltage level below the threshold voltage so as to cause the ground fault interrupt at the threshold voltage.

15. The method of claim 14, wherein accumulating the ground fault signal over time and causing the ground fault interrupt comprises causing the ground fault interrupt when the multiple discrete signals have a duration that is less than a duty cycle.

16. The method of claim 9, wherein generating the ground fault signal from the detected differential current comprises using a gain amplifier.

17. The method of claim 9, comprising latching a ground fault interrupt signal when the accumulated ground fault signal exceeds the threshold voltage.

18. The method of claim 9, comprising opening a utility power line contactor when the accumulated ground fault signal exceeds the threshold voltage.

19. The method of claim 9, further comprising generating an inverted ground fault signal, and wherein accumulating further comprises accumulating both the ground fault signal and the inverted ground fault signal over time.

20. The method of claim 19, further comprising rectifying and the ground fault signal and the inverted ground fault signal prior to accumulating.

21. The method of claim 19, wherein generating the ground fault signal comprises generating the ground fault signal about a reference voltage, and wherein generating the inverted ground fault signal comprises generating the ground fault signal about the reference voltage.

22. The method of claim 21, further comprising rectifying and the ground fault signal and the inverted ground fault signal prior to accumulating.

23. A method for electric vehicle charging for detecting a ground fault comprising:

detecting a differential current in utility power supply;

generating a ground fault signal from the detected differential current;

filtering the ground fault signal; and

comparing the filtered ground fault signal to a threshold voltage; and

disconnecting the utility power supply when the filtered ground fault signal exceeds the threshold voltage.

24. The method of claim 23, wherein filtering the ground fault signal comprises using a half wave rectifying double stage filter.

25. The method of claim 23, comprising generating a latched fault signal when the filtered ground fault signal exceeds the threshold voltage.

26. The method of claim 25, comprising opening a utility power contactor to disconnect the utility power supply in response to the latched fault signal.

27. The method of claim 26, wherein generating the latched fault signal comprises generating a ground fault interrupt fault signal and generating a contactor fault disable signal, and further comprising opening the utility power contactor in response to either the ground fault interrupt fault signal or the contactor fault disable signal.

28. A ground fault interrupt circuit for a utility power connection to an electric vehicle charging unit, the ground fault interrupt circuit comprising:

b) a comparator having an input connect to a reference voltage;

c) a rectifier circuit connected between the gain amplifier and the comparator; and

d) a charge accumulator circuit coupled between the rectifier and the comparator.

29. The circuit of claim 28 further comprising an inverter connected between the gain amplifier and the rectifier circuit.

30. The circuit of claim 28, further comprising an inverter having an input connected to an output of the gain amplifier, and wherein the rectifier circuit is a full wave rectifier circuit connected to the output of the gain amplifier and to an output of the inverter, and wherein an output of the full wave rectifier circuit is connected to the charge accumulator circuit.

31. The circuit of claim 28, wherein the charge accumulator comprises the rectifier circuit, and wherein the rectifier circuit is a half wave rectifier circuit connected to the gain amplifier.

32. The circuit of claim 28 further comprising an EMI protection circuit at an input of the ground fault interrupt circuit.

33. The circuit of claim 32 wherein the EMI protection circuit comprises an inductor and a resistor connected in series, and at least one capacitor connected across the differential input and to ground.

34. The circuit of claim 28 further comprising a fault latch having an input connected to an output of the comparator.

35. The circuit of claim 34 further comprising a contactor control circuit having an input connected to an output of the fault latch.

36. The circuit of claim 35, further comprising a utility power line contactor having a contactor control input.

37. The circuit of claim 36 further comprising an inverter having an input connected to an output of the gain amplifier, and wherein the rectifier circuit is a full wave rectifier circuit connected to the output of the gain amplifier and to an output of the inverter, and wherein an output of the full wave rectifier circuit is connected to the charge accumulator circuit.

38. The circuit of claim 36, wherein the charge accumulator comprises the rectifier circuit, and wherein the rectifier circuit is a half wave rectifier circuit connected to the gain amplifier.