WO2015000017A1

WO2015000017A1 - A current limit circuit for a supercapacitive device

Info

Publication number: WO2015000017A1
Application number: PCT/AU2014/000686
Authority: WO
Inventors: Phillip Brett Aitchison; David Elliott MCINTOSH; Hao Huang; Pierre Mars
Original assignee: Cap-Xx Limited
Priority date: 2013-06-28
Filing date: 2014-06-30
Publication date: 2015-01-08

Abstract

System (2) includes a supercapacitive device (8) that is electrically connected across a starter (motor7) for supplying current to that motor during a starting sequence of engine (3). Device (8) includes a single sealed housing (9) that contains a plurality six substantially identical individual supercapacitive cells (10) which are connected in series to provide a total capacitance of 150 Farads and an equivalent series resistance(ESR) of 5 mOhms. Also contained within housing (9) is an active balance circuit (11) for maintaining substantially the same voltage across each of cells (10) to protect against overvoltage across the cells (10). In other embodiments circuit (11) is a passive balance circuit.

Description

A CURRENT LIMIT CIRCUIT FOR A SUPERCAPACITIVE DEVICE

FIELD OF THE INVENTION

[0001 ] The present invention relates to a current limit circuit and more particularly to a current limit circuit for a supercapacitive device.

[0002] Embodiments of the invention have been particularly developed for use with a car having an internal combustion engine with a stop/start function and will be described herein with particular reference to that application. However, it will be appreciated that the invention is not limited to such a field of use, and is applicable in broader contexts including, without limitation, cars or other vehicles with hybrid or solely electric engines, other automotive vehicles, electric engines having a stop/start function and non- automotive applications exemplified by grid capacitors (for load smoothing, power factor correction, or otherwise).

BACKGROUND

[0003] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0004] It is known to incorporate stop/start functionality into a car or other vehicle with an internal combustion engine having an electronic engine management system (EMS). This typically involves the EMS being automatically responsive to the car slowing down sufficiently or stopping to turn the internal combustion engine off. That is, to progress the engine to an "off' or "stopped" state. This may occur in heavy traffic, a traffic jam or when a car is stopped at traffic lights. The EMS is also automatically responsive to the driver of the car pressing the accelerator to start the engine and to commence movement once again of the vehicle. That is, the EMS recognises the input from the driver so the driver does not have to be aware the engine stopping and starting as the car comes to a halt or moves from such a halt.

[0005] The rationale for using such stop/start technologies is to minimise the need for the engine to idle when the car is stopped and, hence, to reduce the consumption of fuel and reduce the production of pollution. It has been estimated in some studies that the use of stop/start technology in a car, when applied to typical city driving, may be able to reduce pollution and fuel use by up to 15%.

[0006] Cars include batteries for providing a store of energy to allow starting of the engine. By far the most popular battery for cars is a lead acid battery. A major downside with stop/start technologies is that the battery must start the engine many more times than in a vehicle without such stop/start technology. The conventional solution for cars with stop/start technology is to include either one or more additional lead acid batteries in the car or a much larger capacity lead acid battery. However, to provide sufficient capacity to accommodate stop/start technologies, these batteries add considerable cost and weight to the car. An alternative is to make use of a capacitive device in parallel with the battery, although this has so far proved unpopular due to the relatively high leakage current that is found in capacitors that offer suitable combinations of high capacitance, low volume and low price.

[0007] Whilst in this specification use is made of the term "stop/start" to describe the above and similar functions, it will be appreciated that this is synonymous and interchangeable with any one of the following or like terms: start/stop; stop-start; and start- stop.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0009] According to a first aspect of the invention there is provided a current limit circuit for a supercapacitive device in an electrical system, the electrical system including a first energy source, a second energy source and an electrical load, the current limit circuit including:

a first electrical conductor for allowing a source current to be drawn from at least one of the first energy source and the second energy source;

a second electrical conductor for allowing a charging current to supplied to the supercapacitive device;

a switching device disposed between the first electrical conductor and the second electrical conductor and being responsive to a first and a second control signal for respectively progressing toward a high impedance state and a low impedance state to prevent and allow the drawing of the load current; and

a sensor device for providing:

the first control signal in response to either or both of: the charging current being greater than a predetermined upper threshold; and the voltage at the second electrical conductor being above a predetermined voltage; and the second control signal in response to the charging current falling below a predetermined lower threshold.

[0010] According to a second aspect of the invention there is provided a current limit circuit for a supercapacitive device in an automotive system, the automotive system including a battery, an alternator and a starter motor, the current limit circuit including: a first electrical conductor for allowing a charging current to be drawn from at least one of the battery and the alternator;

a second electrical conductor for allowing the charging current to be supplied to the supercapacitive device;

a switching device disposed between the first electrical conductor and the second electrical conductor and being responsive to a first and a second control signal for respectively progressing toward a high impedance state and a low impedance state to prevent and allow the drawing of the charging current; and

a sensor circuit for providing:

the first control signal in response to either or both of: the charging current being greater than a predetermined upper threshold; and the voltage at the first electrical conductor being above a predetermined voltage; and the second control signal in response to the charging current being supplied to the supercapacitive device falling below a predetermined lower threshold

[001 1 ] In an embodiment the sensor circuit provides the first control signal in response to the voltage at the output being greater than the voltage at the input.

[0012] In an embodiment the current limit circuit includes an inductive device through which the charging current flows downstream of the switching device.

[0013] In an embodiment the inductive device is disposed intermediate the switching device and the sensor circuit.

[0014] In an embodiment the automotive system includes an electrical load that is electrically connected with the first electrical conductor and the current limit circuit selectively allows the load to draw current from the supercapacitive device through the switching device. More particularly, the current limit circuit selectively allows the load to draw current from the supercapacitive device via the second conductor, the switching device and the first conductor. [0015] In an embodiment the automotive system is included in a vehicle and the electrical load is a hotel load for the vehicle.

[0016] According to a third aspect of the invention there is provided a control circuit for a supercapacitive device in an automotive system, the automotive system including a battery, an alternator, a starter motor and a hotel load, the control circuit including:

a first electrical conductor for selectively allowing a source current to be drawn from at least one of the battery and the alternator, the hotel load being electrically connected to the first electrical conductor for selectively drawing at least part of the source current;

a second electrical conductor for supplying selectively a charging current to the supercapacitive device; and

a switching device disposed between the first electrical conductor and the second electrical conductor and being responsive to a first control signal and a second control signal for respectively progressing toward a high impedance state and a low impedance state to maintain the charging current to less than a predetermined maximum amount, the switching device also being responsive to a third control signal for allowing a current to be drawn from the supercapacitive device, via the switching device, to supply the hotel load.

[0017] According to a fourth aspect of the invention there is provided a method of limiting current for a supercapacitive device in an electrical system, wherein the electrical system includes a first energy source, a second energy source and an electrical load, and the method includes the steps of:

providing a first electrical conductor for allowing a source current to be drawn from at least one of the first energy source and the second energy source;

providing a second electrical conductor for allowing a charging current to supplied to the supercapacitive device;

disposing a switching device between the first electrical conductor and the second electrical conductor that is responsive to a first and a second control signal for respectively progressing toward a high impedance state and a low impedance state to prevent and allow the drawing of the load current; and

providing:

[0018] According to a fifth aspect of the invention there is provided a method of limiting current for a supercapacitive device in an automotive system, wherein the automotive system includes a battery, an alternator and a starter motor, and the method includes the steps of:

providing a first electrical conductor for allowing a charging current to be drawn from at least one of the battery and the alternator;

providing a second electrical conductor for allowing the charging current to be supplied to the supercapacitive device;

disposing a switching device between the first electrical conductor and the second electrical conductor that is responsive to a first and a second control signal for respectively progressing toward a high impedance state and a low impedance state to prevent and allow the drawing of the charging current; and

providing:

[0019] According to a sixth aspect of the invention there is provided a method of controlling a supercapacitive device in an automotive system, wherein the automotive system includes a battery, an alternator, a starter motor and a hotel load, and the method includes the steps of:

providing a first electrical conductor for selectively allowing a source current to be drawn from at least one of the battery and the alternator, the hotel load being electrically connected to the first electrical conductor for selectively drawing at least part of the source current;

providing a second electrical conductor for supplying selectively a charging current to the supercapacitive device; and disposing a switching device between the first electrical conductor and the second electrical conductor and being responsive to a first control signal and a second control signal for respectively progressing toward a high impedance state and a low impedance state to maintain the charging current to less than a predetermined maximum amount, the switching device also being responsive to a third control signal for allowing a current to be drawn from the supercapacitive device, via the switching device, to supply the hotel load.

[0020] Reference throughout this specification to "one embodiment", "some embodiments" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment", "in some embodiments" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0021 ] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[0022] As used herein, the term "exemplary" is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment" is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a car including a current limiting circuit according to the invention;

Figure 2 is a schematic view of the current limit circuit included in the car of Figure 1 ; Figure 3 is a more detailed schematic representation of the current limit circuit of Figure 2;

Figure 4 is a current waveform of the current flowing into the input of the circuit of Figure 3;

Figure 5 is a schematic representation of a more general form of the circuit of Figure 2; and

Figure 6 is a further embodiment of the invention making use of a microcontroller and bi-directional current flow through the current limit circuit.

DETAILED DESCRIPTION

[0024] Referring to Figure 1 there is illustrated a car 1 having stop/start functionality. This functionality is implemented by an automotive system 2 as shown in Figure 2 where connections represented by solid lines and broken lines respectively indicate electrical and mechanical connections.

[0025] System 2 includes an internal combustion engine 3 and an electronic engine management system 4 for controlling and monitoring many aspects of the operation of engine 3. This control includes, for example, fuelling, valve timing, and temperature. The monitoring includes fluid levels and temperatures, voltage levels, and others. It will be appreciated by those skilled in the art that additional or other aspects of the operation of engine 3 are able to be included.

[0026] System 2 includes a 12 Volt 30 Amp. hour lead acid battery 5 for providing an energy store within car 1. This energy store is selectively drawn upon, as will be described in more detail below. In other embodiments different batteries are used. For automotive applications typical batteries are lead acid batteries that are rated from about 15 Amp. hours to 60 Amp. hours.

[0027] An alternator 6 is mechanically driven by engine 3 (when engine 3 is running) for providing up to about 14 Volts of electrical potential that is used, as required, for recharging battery 5. A DC starter motor 7 is selectively actuated to crank engine 3 during a starting sequence for that engine. During this starting sequence (which is part of the stop/start operation) motor 7 will produce several kW for at least about one second. When the starting operation is the first start after a prolonged period of inactivity, motor 7 is usually required to sustain the cranking for longer than during the stop/start operation.

[0028] System 2 includes a supercapacitive device 8 that is electrically connected across motor 7 for supplying current to that motor during the starting sequence. That is, device 8 provides current to a load thai is comprised of motor 7. in this embodiment, device 8 includes a single seated housing 9 having dimension of about 220 mm x 145 mm x 75 mm that contains a plurality six substantially identical individual supercapacitive cells 10 which are connected in series to provide a total capacitance of 150 Farads and an equivalent series resistance (ESR) of 5 mOhrns. Also contained within housing 9 is an active balance circuit 1 for maintaining substantially the same voltage across each of cells 10 to protect against overvoltage across the cells 10, In other embodiments circuit 11 is a passive balance circuit,

[0029] In another embodiment use is made of a supercapacitive device having different characteristics. For example, a further supercapacitive device (not shown) includes a like housing although with a higher surface area carbon coating to provide a capacitance of 230 Farads and an ESR of 3 mOhms.

[0030] in further embodiments, circuit 11 is disposed external to housing 9, Moreover, in still further embodiments, cells 11 are individually housed and electrically connected to circuit 11 , which is separately housed also.

[0031] It will be appreciated by those skilled in the art that cells 10 are able to be placed in parallel and/or series to provide the required capacitance, form factor, ESR and/or voltage required for the specific application.

[0032] System 2 also includes an electrical load 12, which is used to collectively represent ail the electrical loads within car 1 that draw electrical power whether or not car 1 is moving, and whether or not engine 3 is running. For example, load 12 includes one or more of;

• The power assistance for the brakes and steering systems for car 1.

• The headlights, parking lights, tail lights, blinkers, internal lights and other lights or lighting systems used by car 1 ,

• The sound system, radio or other in car entertainment systems that are installed and operating within car 1.

• Any GPS or other navigation system.

EMS 4.

[0033] in other cars different or additional electrical loads will be included. It will also be appreciated that, at different times, load 12 will draw considerably different currents depending upon the nature and manner of use of the loads. [0034] A current limit circuit 15 is provided for supercapacitive device 8 in system 2. Circuit 15 includes a conductive input, in the form of a terminal 17, for drawing a load current l_iN from at least one of battery 5 and alternator 6. A conductive output, in the form of a terminal 18, supplies a charging current Ι₀υτ to supercapacitive device 8. A switching device 19 is disposed between terminals 17 and 18 and is responsive to a first and a second control signal for respectively progressing toward a high impedance state and a low impedance state to prevent and allow the drawing of l|_N.

[0035] A sensor device 20 provides the first control signal in response to either or both of: IOUT being greater than a predetermined upper threshold; and the voltage at the output 18 being above a predetermined voltage. In this embodiment the predetermined voltage is the voltage at input 17. In other embodiments, device 20 also provides the first signal in response to the voltage at input 17 being greater than or equal to the maximum rated voltage of the supercapacitive device. In this embodiment supercapacitive device 8 has a maximum rated voltage of 14 Volts. In other embodiments different maximum rated voltages are provided by the respective supercapacitive device. For electric double layer capacitors (EDLC) of similar form and construction to device 8, the maximum rated voltage is typically in the range of about 14 to 16 Volts.

[0036] Device 20 also provides the second control signal in response to IOUT falling below a predetermined lower threshold. It will be appreciated that both the first control signal and the second control signal are provided by device 20 to device 19 via a common conductive connector 22. In other embodiments separate connectors are used for each of the first and second control signals.

[0037] Circuit 15 also includes an inductive device 21 through which l|_N flows downstream of switch 19. More particularly, device 21 is disposed directly intermediate switch 19 and the sensor device 20.

[0038] It will be appreciated that EMS 4 controls circuit 15 to be in either an ON state or an OFF state. When in the ON state, circuit 15 operates as set out above and provides a current limiting operation. In the OFF state, circuit 15 does not operate and isolates the circuits including the respective energy storage devices battery 5 and device 8. That is, both I IN and IOUT are effectively zero.

[0039] System 2 includes three states, these being:

1 ) State 1 : where EMS 4 controls engine 3 to run normally.

2) State 2: which commences when EMS 4 automatically turns engine 3 off in response to car 1 slowing down or halting. 3) State 3: which is preceded by State 2 and succeeded by State 1. This includes a starting sequence of engine 3 being initiated by EMS 4.

[0040] During the above three states, the state of circuit 15 is as follows.

[0041] During State 1 , when engine s is being controlled by EMS 3 to run normally, alternator 6 generates a voltage of about 14 Volts and supplies a current that is used to charge battery 5 progressively. That is, terminal 17 is maintained at about 14 Volts.

[0042] EMS 4 also maintains circuit 15 in the ON state so that device 8 is also charged to about 14 Volts, although with the predetermined upper threshold for 1₀υτ being 75 Amps and the lower threshold being 60 Amps. As device s has very low ESR circuit 15 is operable to ensure device 8 does not draw excessive current from battery 5 and/or alternator 6.

[0043] A failure to provide this current limiting will result in damage to either or both of battery 5 and/or alternator 6. As an example, if battery 5 provides 12 Volts and has an interna! impedance of 6 mQ, and the device 8 has an ESR of 4 mQ and is full discharged - that is, if terminal 18 is at zero voltage - then without the operation of circuit 15 device 8 would attempt to draw 1 ,200 Amps. The maximum current limit for lour in the above embodiment is the upper threshold - that is, 75 Amps. However, in other embodiments different upper thresholds are used. Typically, however, the upper threshold is within the range of 50 Amps to 100 Amps.

[0044] Moreover, in different embodiments the lower thresholds are set at Other than 60 Amps.

[0045] When EMS 4 detects a sufficient slowing of car 1 o the halting of car 1 it enters State 2; which is to say that it initiates the stop/start functionality of system 2, This involves EMS 4 automaticall turning off engine 3. With engine 3 turned off, alternator 6 no longer supplies any current to charge battery 5 or device 8. Moreover, in State 2, EMS 4 maintains circuit 15 in the OFF state so that device 8 is isolated from battery 5. At the instant circuit 15 is progressed from the O state (when system 2 is in State 1 ) to the OFF state (when system 2 progresses to State 2} device 8 will be at the voltage it was charged to by alternator 6. in the present embodiment this voltage is about 14 Volts on the assumption that system 2 had been in State 1 (that is, engine 3 had been running) for sufficient time for device 8 to be fully charged,

[0046] it iil be appreciated that in the present embodiment that the time taken to fully charge device 8 from a totally discharged state vvili be about 30 seconds. However, it is usual that device 8 will maintain some level of charge and, as such, the more typical time taken to progress to the fully charged state is less than 10 seconds.

[0047] When alternato 6 is turned off (due to engine s being turned off) the voltage provided by battery 5 - that is,, the voltage at terminal 17 - will drop from about 14 Volts to about 12 to 12.5 Volts (depending upon the type and state of charge of battery 5). As EMS 4 has progressed circuit 15 to the OFF state, device 8 is isolated from terminal 17 and cannot discharge back into battery 5.

[0048] Circuit 15 is an active design that maintains the individual cells 10 at equal voltage while minimising leakage current in device s. This is also advantageous in the present embodiment to slow the discharge of ceils 10 during State 2.

[0049] The above described State 2 is typically initiated when car 1 halts at an intersection or traffic lights. Accordingly, EMS 4 remains responsive to inputs from the driver of car 1 to indicate that there is a desire to move from being halted. Typical inputs to EMS 4 to indicate such a desire include the driver pressing on the accelerator pedal, releasing the brakes or, for manual cars, depressing the clutch pedal. The input, or combinations of inputs, used to assess this desire vary between cars. Once the desire has been assessed, in whatever way, EMS 4 then progresses system 2 to State 3. Particularly, EMS 4 continues to maintain circuit 15 in the OFF state - to continue the electrical isolation of terminals 17 and 18 - whilst initiating a starting sequence for engine 3. This involves, amongst other things, actuating motor 7 to crank engine 3. The current drawn by motor 7 is supplied solely by device 8 for, as mentioned above, terminals 17 and 18 remain electrically isolated from each other.

[0050] The low ESR and high capacitance of device 8 delivers the required power to motor 7 for the required duration. For device 8, where the capacitance is 150 F and the ESR 5 mil, it discharges from 14 Volts to 10.5 Volts after supplying 300 Amps for 1 second to start engine 3. If device 8 is substituted with a similar supercapacitive device having a capacitance of 230 Farads and an ESR of 3 mOhms, this similar device, under the same conditions, will discharge from 14 Volts to 11.8 Volts. [0051 ] Once EMS 4 assesses that engine 3 has started it returns system 2 to State 1. Accordingly, circuit 15 is toggled to the ON state and alternator 6 supplies charge current again.

[0052] The above architecture decouples battery 5 from providing starting current to motor 7. This allows battery 5 to be saved from premature aging that would otherwise result from the increased frequency of discharges required due to the increased number of starts of engine 3.

[0053] It should also be noted that car 1 includes an ignition that is either off or on. When on, EMS 4 controls system 2 as described above. However, when the ignition is off, EMS 4 is substantially inactive and circuit 15 is in the OFF state to minimise current drain from battery 5 due to any leakage currents in device 8. Once the driver activates car 1 after a prolonged stop - for example, by actuating the central locking from a key fob - EMS 4 quickly progresses circuit 15 to the ON state so that device 8 is able to be charged, if required, to a voltage deemed sufficient to allow for a subsequent starting sequence for engine 3. In other embodiments, EMS 4 maintains circuit 15 in the ON state when the ignition is off so that device 8 remains charged and ready to start car 1 for the first start after a period of being parked. For the specific device 8 used in the above described embodiments, where use is made of an active balance system, the leakage current is about 10 mA. Accordingly, battery 5 (which is rated at 30 Amp. hour) only loses 0.8% of its charge in maintaining a full charge on device 8 for 24 hours.

[0054] Reference is now made to a more detailed schematic diagram of circuit 15 in Figure 3, where corresponding features are denoted by corresponding reference numerals. More particularly, switch 19 is implemented with two back-to-back NFETs 31 and 32 that have gates which are commonly connected to the output of a FET gate driver 33. This driver, together with the other associated logic circuits, is part of sensor device 20.

[0055] In addition to driver 33, device 20 includes a high accuracy and low value current sensing resistor 35, an operational amplifier 36 connected across resistor 35 and a comparator 37 for changing state when the output of amplifier 36 exceeds a first voltage reference V_R1. The output of comparator 37 is connected to one of the three inputs of an AND gate 38, while the output of gate 38 is connected to one of the two inputs of an AND gate 39. The output of gate 39 is connected to the input of driver 33.

[0056] It will be appreciated that EMS 4, to maintain circuit 15 in the ON state, holds the relevant input of gate 39 high. Accordingly, in the ON state, if IQUT exceeds a predetermined upper threshold - which, in this embodiment, is 75 Amps - the output of comparator 37 will go low. This will sequentially drive the output of AND gate 38 low and drive the output of AND gate 39 low. This will drive the gates of NFETs 31 and 32 low and, as a result, the NFETs will assume a high impedance state. That is, switch 19 will move from a closed state in which l_!N flows into circuit 15 from terminal 17 to an open state in which l_!N falls to zero. When the later occurs, Ιουτ will fall progressively due to the operation of inductive device 21 (where a return current path is provided by diode 42) until such time as the hysteresis inherent in circuit 15 results in the output of amplifier 36 going low and, consequentially, the output of amplifier 33 going high to progress FETs 31 and 32 to a low impedance state. Accordingly, once again, l_!N will flow. The result is, for those times when device 8 draws significant currents from battery 5 and/or alternator 6, Ιουτ will follow a pseudo-sawtooth pattern between the upper and lower threshold. An example of IOUT during the charging of device 8 by alternator 6 is illustrated in Figure 4. Whilst only three cycles of the current limiting function are illustrated before IOUT decays to zero as device 8 approaches a fully charged state, it will be appreciated that a different number of such cycles will occur depending upon the voltage initially across device 8, the voltage provided by alternator 6, and the capacitance of device 8.

[0057] Diode 42 is a Schottky diode. In other embodiments use is made of a standard power diode.

[0058] It will be appreciated that circuit 15 is allows substantially unimpeded flow of l_!N and IOUT for low values of those currents. For the current limiting provided by circuit 15 only operates when the voltage at terminal 17 is sufficiently greater than that at terminal 18 to cause IOUT to be large.

[0059] Circuit 15 also includes other protection functions in addition to the current limiting function described above. A first example of such a protection is provided by a comparator 40, which compares the voltage at terminal 18 with a reference voltage V_R2. In this embodiment V_R2 is set at 14 Volts to ensure that FETs 31 and 32 both progress to a high impedance state if the voltage provided by battery 5 (or more likely alternator 6) exceeds 14 Volts. This protects device 8 from an overvoltage condition. In other embodiments V_R2 is set at other than 14 Volts.

[0060] A further protection function is provided by comparator 41 , which compares a further reference voltage V_R3 with the voltage at terminal 18. In this instance, V_R3 is the voltage at terminal 17. Should the voltage at terminal 18 exceed V_R3, then circuit 15 acts to ensure FETs 31 and 32 are in the high impedance state to prevent discharging of device 8 into battery 5. [0061] Reference is now made to Figure 5, where corresponding features are denoted by corresponding reference numerals. More particularly, there is illustrated a control system 130 for an automotive engine in the form of engine 3. As referred to above, engine s has a starter motor /, an alternator 6, and operates in a variety of states, including a start-up state and a run state. System 130 includes a control circuit, in the form of the combination of EMS 4 and circuit 15, for generating:

a) a first control signal to actuate motor 7 to crank the engine during the startup state, wherein motor ? draws electrical energy from supercapacitive device 8;

b) a second control signal to initiate the supply of electrical energy selectively from battery 5 to device 8 other than during the start-up state; and c) a third control signal to initiate the selective supply of electrical energy during the run state from alternator 6 to device 8.

[0062] It will be appreciated that the second and third control signals are, in this embodiment, while being conceptually distinguished, are provided in the same form. The result of providing those signal varies due to the operation state of system 130.

[0063] EMS 4 and circuit 15 are configured to cooperate and collectively define system 130 to provide the above functionality. In further embodiments (not shown) EMS 4 and circuit 15 are fully integrated, while in further embodiments still (also not shown) one or both of EMS 4 and circuit 15 are configured from disparate cooperating elements.

[0064] The control topology enabled by system 130 in Figure s involves the following steps:

• When engine 3 is operating normally: battery 5 is being charged; circuit 15 is active; device 8 either being charged to 14 Volts or being held at that voltage; hotel loads 12 are supplied from alternator 6; and the boardnet for car 1 is held at 14 Volts.

• When car l has stopped: circuit 15 is OFF (that is, circuit 15 isolates battery 5 from device 8); battery 5 supplies hotel loads 12; and device 8 remains charged at 4 Volts.

• When a restart is initiated: circuit 15 remains OFF; device 8 supplies the cranking current to motor 7 to allowing starting of engine 3 (that is, device 8 supplies all the cranking current and battery 5 provides no cranking current); and battery 5 continues to supply any required current to hotel load 12 at 12 Volts. • Following the restart of engine s, system 130 returns to the first step specified above.

[0065] Points to note about the topology of the control system of Figure 5 include: that battery 5 supplies the hotel load 12; device 8 provides all the cranking current; system 130 provides a current limit between battery 5 and device 8 primarily to ensure device 8 does not draw excessive currents when charging. This allows for superior voltage and current dynamics as the battery voltage remains substantially unchanged during the period in which cranking current is supplied. The voltage provided by battery 5 also remains high as battery 5 provides none of the cranking current, ail of which is supplied by the supercapacitive device. Moreover, engine 3 starts more quickly due to the increased capacity of the supercapacitor device to supply the required cranking current (relative to battery 5 acting alone). As battery 5 is not called upon to provide the cranking current it is able to more reiiabiy supply the hotel foads and therefore more fully contribute to a seamless motoring experience for the operator of the car.

[0066] In another embodiment, as shown in Figure 6, use is made of a topology similar to that of Figure 5, although making use of a control system 140 for providing additional capabilities and functionalities. In this specific embodiment the additional capabilities and functionalities relate to the use of system 140 to manage a micro-hybrid operation of car 1. That is, in this embodiment car 1 is capable of regenerative braking and includes a generator 141 (a starter/generator or alternator) to replace alternator 6 of Figure 10. The current generated by that regenerative braking is supplied by generator 141 to control system 140 and, more specifically, it is supplied to a switch S1. This switch toggles between position 1 and position 2 as illustrated in Figure 6. A furthe difference is that system 140 replaces circuit 15 of Figure s with a converter circuit 142. This converter circuit, in this embodiment, is a bi-directional DC to DC converter and includes both bidirectional conversion of DC voltages and current limiting of those voltages. That is, the topology allows current flow from terminal 18 to terminal 17 and vice versa. This allows device 8 to selectively supply current to hotel load 12.

[0067] This micro-hybrid topology of Figure 6 involves the following steps:

• When engine 3 is operating normally: S1 is maintained in position 1 ; battery 5 is being charged; hotel load 12 is being supplied from generator 141 ; the boardnet for car 1 is held at 14 Volts; device 8 is held at about 9 Volts to leave headroom for energy capture during regenerative braking; and the DC to DC converter circuit 142 is OFF and, hence, device 8 is not being further charged. • When regenerative braking: the DC to DC converter circuit remains OFF; switch S1 is toggled to position 2; battery 5 supplies the boardnet voltage: device 8 is charged up to its maximum voltage (which in this embodiment is 14 Volts) from generator 141 at a current typically in the range of about 150 Amps to 250 Amps, which is much higher than the battery will accept; switch S1 is toggled to position 1 when device 8 is fully charged; and generator 141 supplies the boardnet and charges battery 5.

• When car 1 then stops: device 8 discharges from 14 Voits to supply hotel load 12 at 12.8 Voits through the bi-directional DC to DC converter circuit 142; circuit 142 is turned off when device s discharges to the permitted minimum voltage (set at 9.5 Volts in this embodiment, which has been assessed as the voltage at which device 8 retains enough charge to reliably crank engine 3); and battery 5 then continues to supply hotel load 12. The voltage at which circuit 142 supplies the hotel load - in this embodiment being 12.8 Voits - is chosen so that: a typical lead-acid (such as battery 5) wiil draw very little charge current; and if the current drawn by the hotel load increases beyond the current that can be supplied by circuit 142, then the battery will seamlessly make up the difference. Similarly, when device 8 discharges to its minimum allowed value ~ which in this embodiment is 9.5 Votls - and stops supplying current to hotel load 12, battery 5 seamlessly takes over that supply of current to the hotel load. The output voltage at which circuit 142 supplies the hotel load will vary in other embodiments.

• When the start sequence is initiated: device 8 is initially at 9.5 Volts (which, for this embodiment, is enough to reliably crank the engine with a large safety margin); and the entire cranking current for motor 7 is drawn from device 8. This operation typically results in device 8 discharging to about 9 Volts.

« Following the restart of engine 3, system 140 returns to the first step specified above.

[0068] During regenerative braking, device 8 is able to accept a high charge current and to store considerable amounts of energy. For the specific device 8 used in the above embodiment which is held at 9 Volts prior to the regenerative braking, it is possible to store up to about 14 KJ of recovered energy. The use of a higher capacitance device 8 would allow greater energy storage. By way of example, a 750 Farad supercapacitive device would store about 43 KJ. It will also be appreciated that the supercapacitive module includes EDLC supercapacitive cells, while in other embodiments use is made of other supercapacitive cells, such as hybrid supercapacitive cells.

[0069] The operation of the the DC to DC converter 142 circuit during the period when engine 3 is off during a "stop" of the stop/start cycle, is such that the voltage supplied to terminal 17 is just above the fully charged battery voltage. This ensures that battery 5 does not supply the boardnet for car 1 and also so that battery 5 draws very little current. This operation ensures, for short stops, that battery 5 will not have to supply any current to load 12, which contributes to an extended life of battery 5.

[0070] It will also be appreciated that if, during the stop phase of engine 3, the maximum current that is can supplied by the DC to DC converter circuit 142 is less than the maximum current demanded by the boardnet, then the boardnet voltage will settle to a level where the battery supplies the difference between boardnet requirement and the maximum current provided by circuit 142. In this embodiment the maximum current that can be supplied by circuit 142 to the boardnet is determined by the peak current that can flow through the inductor in circuit 142 without saturating that inductor. In other embodiments, where circuit 142 is implemented differently, another design factor will provide the limit to the maximum current that that circuit can provide to the boardnet.

[0071 ] The topology provided by system 140 makes use of a circuit 142 that is, in this embodiment, a forward direction current limit - that is, when the device 8 is being charged - and a reverse direction DC to DC converter - when device 8 is being discharged to supply hotel load 12. The latter is an important distinction between the functionalities of systems 130 and 140, as system 140 allows device 8 selectively to supply hotel loads 12 while engine 3 is stopped during a stop/start operation. In the above embodiment, the selection is made while the voltage across device 8 remains above 9.5 Volts. In other embodiments a different selection is made, whether that is based upon a different minimum voltage across device 8, another criteria, a combination of criteria, or criteria that are dependent upon the circumstances at that time. For example, the minimum discharge voltage for device 8 is selected such that device 8, upon reaching that voltage, will still be able to reliably start engine 3. This voltage will depend upon a variety of factors, including the starter current profile for engine 3, and may be adjusted according to engine temperature, as a lower temperature will typically require a higher minimum voltage to be maintained on device 8 to provide the same safety margin for reliably cranking engine 3.

[0072] The DC to DC converter function of circuit 142 - that is, when current is being discharged from device 8 and supplied to load 12 - selectively acts in either a linear mode (when the voltage at terminal 18 is greater than the required voltage at terminal 17) and a boost mode (when the voltage at terminal 18 is less than the required voltage at terminal 17). As mentioned above, In this embodiment the voltage at terminal 18 during the stop of a stop/start operation is 12.8 Volts, Circuit 142 operates to maintain the voltage by selectively operating in the linear and boost mode as the voltage on device 8 falls from greater than 12.S Volts to less than 12.8 Volts, in other embodiments the voltage to be maintained at terminal 17 is less than or greater to 12.8 Volts.

[0073] It will be appreciated that switch S1 is able to implemented in a variet of ways. In this automotive embodiment use is made of two pairs of back-to-back FETS. However, in other embodiments different components are used such as high current relays.

[0074] A exemplary embodiment of circuit 142 and switch S1 is provided in Figure 18 of co-pending PCT application No. ... filed on 30 June 2014 (Attorney docket number 80584WGPG0) and is incorporated herein by way of cross reference. The illustrated circuit operates both as a current limit - for current flowing from battery 5 to device 8 - and selectively as a boost converter - for current flowing from device 8 to battery 5,

[0075] in broad terms the current limit function of the circuit of Figure 18 in the above PCT application follows that of circuit 15 of Figure 2 of this application. The main difference is that the control logic hardware used in circuit 15 is replaced by a microcontroller and associated hardware. That is, while the current limit function operates on the same principles, the hardware and software control is differently implemented to provide that operation.

[0076] The operation of the current limit functionality of the circuit 142 and its constituent components are described in the abovementfoned PCT application and are expressly incorporated herein by way of cross reference.

[0077] The major advantages of the above embodiments include:

» A cost effective and relatively simply current limiting function for automotive applications.

* Maintaining a relatively high average charging current during the charging of the supercapacitive device.

» Ease of including additional protection features within the current limiting circuit. » Ease of retrofitting to existing engine management systems.

• Ease of integrating with an engine management system. • Supportive of stop/start architectures that make use of different energy storage devices,

• Supportive of stop/start architectures that provide specific electrical isolation between the different energy storage devices.

[0078] it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment. Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention thai the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than ail features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[0079] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as wouid be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0080] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0081] Similarly, it is to be noticed that the term connected, when used in the claims, should not be interpreted as being limited to direct connections or couplings only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device S should not be limited to devices or systems wherein an output of devtce A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet stiil co-operate or interact with each other. [0082] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks.

Claims

1. A current limit circuit for a supercapacitive device in an automotive system, the automotive system including a battery, an alternator and a starter motor, the current limit circuit including:

a first electrical conductor for allowing a source current to be drawn from at least one of the battery and the alternator;

a second electrical conductor for allowing a charging current to be supplied to the supercapacitive device;

a switching device disposed between the first electrical conductor and the second electrical conductor and being responsive to a first and a second control signal for respectively progressing toward a high impedance state and a low impedance state to prevent and allow the drawing of the source current; and

a sensor device for providing:

2. A current limit circuit according to claim 1 wherein the sensor device provides the first control signal in response to the voltage at the second electrical conductor being greater than the voltage at the first electrical conductor.

3. A current limit circuit according to claim 1 or claim 2 including an inductive device through which the charging current flows downstream of the switching device.

4. A current limit circuit according to claim 3 wherein the inductive device is disposed intermediate the switching device and the sensor device.

5. A current limit circuit according to any one of the preceding claims wherein the charging current is substantially equal to the load current.

6. A current limit circuit according to any one of the preceding claims wherein the automotive system includes an electrical load that is electrically connected with the first electrical conductor and the current limit circuit selectively allows the load to draw current from the supercapacitive device through the switching device.

7. A current limit circuit according to claim 6 wherein the automotive system is included in a vehicle and the electrical load is a hotel load for the vehicle.

8. A current limit circuit for a supercapacitive device in an electrical system, the electrical system including a first energy source, a second energy source and an electrical load, the current limit circuit including:

a second electrical conductor for supplying a charging current to the supercapacitive device;

a sensor device for providing:

9. A control circuit for a supercapacitive device in an automotive system, the automotive system including a battery, an alternator, a starter motor and a hotel load, the control circuit including: