Onboard Powertrain For an Automated Guided Vehicle

Abstract

An onboard powertrain for an automated guided vehicle, AGV, is presented herein. The onboard powertrain includes a split-source inverter, SSI, having at least one middle point pole, a positive DC-link pole, and a negative DC-link pole, a battery and an inductor connected in series between the positive or negative DC-link pole and the middle point pole, and a supercapacitor connected between the positive and negative DC-link poles.

Claims

1. An onboard powertrain for an automated guided vehicle, AGV, the onboard powertrain comprising: a split-source inverter, SSI, having at least one middle point pole, a positive DC-link pole, and a negative DC-link pole; a battery and an inductor connected in series between the positive or negative DC-link pole and the middle point pole; and a supercapacitor connected between the positive and negative DC-link poles.

2. The onboard powertrain according to claim 1, configured to generate a plurality of electrical phases (V.sub.a, V.sub.b, V.sub.c), such as three electrical phases (V.sub.a, V.sub.b, V.sub.c).

3. The onboard powertrain according to claim 2, wherein each electrical phase (V.sub.a, V.sub.b, V.sub.c) is connected to an individual middle point pole.

4. The onboard powertrain according to claim 3, further comprising a battery and an inductor connected in series between the positive or negative DC-link pole and each middle point pole.

5. The onboard powertrain according to claim 2, wherein all electrical phases are connected to a common middle point pole.

6. The onboard powertrain according to claim 5, further comprising a semiconductor element between the common middle point pole and each electrical phase.

7. The onboard powertrain according to claim 6, wherein the semiconductor element is a diode or a MOSFET.

8. The onboard powertrain according to claim 1, wherein the battery is connected closer to the positive or negative DC-link pole than to the inductor.

9. The onboard powertrain according to claim 1, further comprising a supercapacitor per electrical phase (V.sub.a, V.sub.b, V.sub.c) of the SSI, each connected between a common negative DC-link pole for the SSI and a separate positive DC-link pole per phase of the SSI.

10. The onboard powertrain according to claim 1, further comprising an off-board charger with a step-down transformer.

11. The onboard powertrain according to claim 10, wherein the onboard charger is connected to the electrical phases (V.sub.a, V.sub.b, V.sub.c) of the SSI via switches and inductances.

12. The onboard powertrain according to claim 10, wherein the onboard charger is connected separately to individual middle point poles.

13. The onboard powertrain according to claim 10, wherein the onboard charger is connected to a common middle point pole.

14. The onboard powertrain according to claim 1, wherein the capacitance of at least one supercapacitor is at least 1 mJ/mm.sup.3.

15. The onboard powertrain according to claim 14, wherein the capacitance of each supercapacitor is at least 1 farad (F), such as at least 10 F or at least 100 F.

16. The onboard powertrain according to claim 2, wherein the battery is connected closer to the positive or negative DC-link pole than to the inductor.

17. The onboard powertrain according to claim 2, further comprising a supercapacitor per electrical phase (V.sub.a, V.sub.b, V.sub.c) of the SSI, each connected between a common negative DC-link pole for the SSI and a separate positive DC-link pole per phase of the SSI.

18. The onboard powertrain according to claim 2, further comprising an off-board charger with a step-down transformer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0014] FIGS. 1A and 1B are diagrams schematically illustrating known onboard powertrains for an AGV; and

[0015] FIGS. 2A-2B, and 3-6 are diagrams schematically illustrating embodiments of onboard powertrains for an AGV.

DETAILED DESCRIPTION

[0016] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0017] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0018] An embodiment of an onboard powertrain for an AGV is presented with reference to FIGS. 2A and 2B. The embodiment presents an efficient topology to integrate a battery and a supercapacitor with a diode-inductor set to provide a split-source inverter (SSI), utilizing a two-level converter available on the shelf.

[0019] A supercapacitor 20 is connected to a DC-link of the three-phase SSI, i.e. between a positive and negative pole of the DC-link. A battery 21, configured to drive a three-phase AGV, is connected between a middle point of the SSI via an inductor 22 and the negative (FIG. 2A) or positive (FIG. 2B) pole of the DC-link for the motor drive of the AGV.

[0020] The middle point of the SSI is connected to a diode 23 per phase of the three-phase SSI, each phase being connected to a respective AC terminal, V.sub.a, V.sub.b, V.sub.c, of the motor. The SSI further comprises MOSFETs 7-12 arranged to provide the motor voltages V.sub.a-V.sub.c.

[0021] Both the battery current and the supercapacitor current can thus be controlled by the SSI so that only smooth DC-current is taken from/fed to the battery and fluctuating current is buffered by the supercapacitor, which has better cycling capability and less internal loss. The battery lifetime can be extended while the lifetime of the supercapacitor is significantly longer than the battery and is not a concern. Also, the energy from regenerative break can be buffered to extend the recharge mileage. The energy from regenerative break is buffered in the supercapacitor, which voltage will build up and which is designed to handle such case. The energy stored in the supercapacitor is then injected again to the load during acceleration.

[0022] With a battery voltage V.sub.B of 12 V and a supercapacitor rated voltage V.sub.SC of 48 V, the DC-link voltage of the system may vary between 48 V and 24 V in order to allow the high current injection or absorption from the motor.

[0023] Energy flow is thus allowed among the supercapacitor 20, the battery 21 and the motor. There are two main advantages: battery lifetime and recharge mileage can be extended by using the supercapacitor to buffer the load peaks and absorb the regenerated energy; and the cost of the diodes and the inductor is potentially lower than the cost of the DC/DC converter in the conventional solution.

[0024] The SSI, battery and supercapacitor can all each be made of standard commercial products. The inductor with diodes may alternatively be integrated as one piece instead of being a standard product connected to a standard SSI. The topology can be realized with minimum design modification of a typical onboard powertrain of an AGV.

[0025] FIG. 3 illustrates an embodiment with a topology where the diodes 23 and 24 of FIGS. 2A and 2B are replaced by MOSFETs 25 to allow a bi-directional power flow. When pushing energy into the battery, the MOSFET 25 work in synchronized rectification mode and switches at the fundamental frequency according to the motor requirements.

[0026] FIG. 4 illustrates an embodiment with a topology in which the battery 21 of FIG. 3 is divided into 3 modules, V.sub.B1, V.sub.B2, V.sub.B3, wherein each module is connected between the negative DC-link pole and one of the AC terminals V.sub.a, V.sub.b, V.sub.c, via switches 26.sub.a, 26.sub.b, 26.sub.c. Switches 26.sub.a, 26.sub.b, 26.sub.c can be diodes, MOSFETs, or diodes with MOSFETs in series for full controllability. Switches 26.sub.a, 26.sub.b, 26.sub.c may also be relays to enable only one of these batteries.

[0027] FIG. 5 illustrates an embodiment with a topology in which also the supercapacitor 20 is split into 3 modules V.sub.SC1, V.sub.SC2, V.sub.SC3 in the same way as the battery illustrated in FIG. 4, so that each phase of the motor is connected to a half-bridge.

[0028] FIG. 6 illustrates an embodiment with an onboard charger for the topology of FIG. 3. An external AC-source is via a step-down transformer 29 connectable to the phases V.sub.a, V.sub.b, V.sub.c of the SSI via switches 28 and inductances 27. The motor is connectable via switches 30. The motor is disconnected when the battery 21 is charged via the external AC-source. The onboard charger is illustrated as connected to the three-phase terminals but can alternatively be connected to the common middle point pole as a single-phase charger instead. A relay or contactor can be used to avoid direct connection between the transformer and the motor. The switched may be MOSFETs as one alternative option, under which the onboard charger can be just a step-down transformer without much complexity, resulting in reduced system cost.

[0029] Selection of topology for a specific implementation may be dependent on the internal layout design of the AGV (i.e., space requirement) and required functionality.

[0030] An embodiment of an onboard powertrain for an AGV is presented with reference to FIGS. 4 and 5. The onboard powertrain comprises an SSI, a middle point pole per electrical phase of the SSI, a positive DC-link pole, and a negative DC-link pole, a battery 21 and an inductor 22 connected in series between the positive or negative DC-link pole and the middle point pole, and a supercapacitor 20 connected between the positive and negative DC-link poles.

[0031] The onboard powertrain may be configured to generate a plurality of electrical phases. There may be three electrical phases V.sub.a, V.sub.b, V.sub.c.

[0032] Each electrical phase V.sub.a, V.sub.b, V.sub.c is connected to an individual middle point pole.

[0033] The onboard powertrain may further comprise a battery 21 and an inductor 22 connected in series between the positive or negative DC-link pole and each middle point pole.

[0034] The battery(ies) may be connected closer to the positive or negative DC-link pole than to the inductor.

[0035] The onboard powertrain may further comprise a supercapacitor per electrical phase V.sub.a, V.sub.b, V.sub.c of the SSI, each connected between a common negative DC-link pole for the SSI and a separate positive DC-link pole per phase of the SSI.

[0036] The onboard powertrain may further comprise an off-board charger with a step-down transformer.

[0037] The onboard charger may be connected to the electrical phases V.sub.a, V.sub.b, V.sub.c of the SSI via switches and inductances.

[0038] The onboard charger may be connected separately to individual middle point poles.

[0039] The capacitance of at least one supercapacitor 20 may be at least 1 mJ/mm3.

[0040] The capacitance of each supercapacitor 20 may be at least 1 farad (F), or may be at least 10 F, or may be at least 100 F.

[0041] An embodiment of an onboard powertrain for an AGV is presented with reference to FIGS. 2, 3 and 6. The onboard powertrain comprises an SSI having a common middle point pole, a positive DC-link pole, and a negative DC-link pole, a battery 21 and an inductor 22 connected in series between the positive or negative DC-link pole and the common middle point pole, and a supercapacitor 20 connected between the positive and negative DC-link poles.

[0042] The onboard powertrain may be configured to generate a plurality of electrical phases. There may be three electrical phases V.sub.a, V.sub.b, V.sub.c.

[0043] All electrical phases are connected to the common middle point pole.

[0044] The onboard powertrain may further comprise a semiconductor element 23, 24, 25 between the common middle point pole and each electrical phase V.sub.a, V.sub.b, V.sub.c.

[0045] The semiconductor element may be a diode 23, 24 or a MOSFET 25.

[0046] The battery 21 may be connected closer to the positive or negative DC-link pole than to the inductor 22.

[0047] The onboard powertrain may further comprise a supercapacitor 20 per electrical phase V.sub.a, V.sub.b, V.sub.c of the SSI, each connected between a common negative DC-link pole for the SSI and a separate positive DC-link pole per phase of the SSI.

[0048] The onboard powertrain may further comprise an off-board charger with a step-down transformer 29.

[0049] The onboard charger may be connected to the electrical phases V.sub.a, V.sub.b, V.sub.c of the SSI via switches 28 and inductances 27.

[0050] The onboard charger may be connected to a common middle point pole.

[0051] The capacitance of at least one supercapacitor 20 may be at least 1 mJ/mm3.

[0052] The capacitance of each supercapacitor 20 is at least 1 F, or may be at least 10 F, or may be at least 100 F.

[0053] The aspects of the present disclosure have mainly been described above with reference to a few embodiments and examples thereof. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.