An electrical energy storage system

Abstract

This invention provides a hybrid electrical energy storage system for an industrial mining vehicle. The system comprises a plurality of electrical energy storage systems and a corresponding plurality of dual active bridge systems. Each dual active bridge system comprises at least one dual active bridge. A first side of each dual active bridge system is connected to an associated one of the energy storage systems, and a second side of each dual active bridge system is electrically connected in series to the second side of another of the dual active bridge systems. The total output voltage seen across all of the dual active bridge systems connected in series is equal to the sum of the voltages seen at the second side of each individual dual active bridge system.

Description

[0001]SP2951 - 1 - AN STORAGE SYSTEM Field of the Invention This invention relates to an electrical energy storage system. In particular, this invention relates to a hybrid electrical energy storage system for an industrial 5 mining vehicle. Background of the invention Vehicles used in industrial mining operations must be capable of transporting heavy payloads of 200 metric tons or more over rough terrain. Industrial mining 10 vehicles are typically large and heavy, requiring significant power to operate. Historically, industrial mining vehicles have been powered by internal combustion engines. More latterly, hybrid power units comprising both an internal combustion engine and a re-chargeable battery 15 have been employed. Although hybrid power units go some way to reducing carbon and particulate emissions, it is desirable to replace hybrid power units with more environmentally friendly electrical energy storage systems. However, this 20 is challenging, requiring large, heavy, batteries and expensive power transfer equipment to provide the 2000 to 3000 volts required to operate the vehicle. It is an aim of the current invention to overcome at least some of the disadvantages of the known energy 25 storage systems for industrial mining vehicles. Summary of the Invention According to an aspect of the invention, there is provided a hybrid electrical energy storage system for an industrial mining vehicle, comprising a plurality of 30 electrical energy storage systems and a corresponding plurality of dual active bridge systems, wherein each dual active bridge system comprises at least one dual active bridge, wherein a first side of each dual active bridge system is operatively connected to an associated one of the energy storage systems, and a second side of each dual 5 active bridge system is electrically connected in series to the second side of another of the dual active bridge systems such that the total output voltage seen across all of the dual active bridge systems connected in series is equal to the sum of the voltages seen at the second side 10 of each individual dual active bridge system. The invention is advantageous as weight and cost may be saved by the use of multiple lower voltage electrical energy storage systems, and lower rated power transfer equipment, rather than single higher voltage / power rated 15 equivalents. Optionally the total voltage seen across all of the dual active bridge systems connected in series may be greater than or equal to 1500 volts, and the nominal voltage of each energy storage system may be less than or 20 equal to 1500 volts. This allows for the provision of large operational voltages of greater than 1500 volts from smaller and lighter batteries of below 1500 volts. Each dual active bridge system optionally comprises a plurality of dual active bridges connected in parallel. 25 This is advantageous as the power available from each individual energy storage system may be increased. Each energy storage system may comprise a battery or a capacitor as best suits the particular application. In one example, at least one of the energy storage 30 systems differs in type to another one of the energy storage systems. This is advantageous, for example, when one or more of the energy storage systems comprises a battery, and one or more of the energy storage systems comprises a capacitor or supercapacitor. Capacitors and supercapacitors are useful to provide a fast response when there is a rapid increase in power demand, whereas batteries are useful for providing a steady power supply over extended periods. 5 Optionally at least one of the energy storage systems differs in chemistry to another one of the energy storage systems. For example, different battery chemistries may be used in different ones of the energy storage systems. This is beneficial as the mix of battery 10 chemistries may be selected to provide multiple benefits. For example, some battery chemistries (for example, lithium-titanate oxide (LTO) batteries) charge quickly and have high cycle lives (circa 20,000 cycles), but are expensive, while other battery chemistries (for example, 15 nickel manganese cobalt (NMC) batteries) charge more slowly and have lower cycle lives (circa 3000-4000 cycles), but have higher specific energy so the battery can be more compact. Each of the energy storage systems may comprise a20 battery. Each battery may optionally comprise lithium- titanate oxide (LTO) battery chemistry, nickel manganese cobalt (NMC)battery chemistry, or lithium-iron phosphate (LFP) battery chemistry. A transformer located in each dual active bridge may 25 optionally have a turns ratio of 1:1 to help minimise energy loss across the transformer. According to another aspect of the invention, there is provided an industrial mining vehicle comprising the hybrid electrical energy storage system described above 30 and a power distribution bus operatively connected to the hybrid electrical energy storage system. According to another aspect of the invention, there is provided a method of operating an industrial mining vehicle, comprising: supplying power to the power distribution bus from a power supply; and using power from the power supply to charge the plurality of energy storage systems, wherein the power from the power supply is supplied to the plurality of energy storage systems via 5 the plurality of dual active bridge systems. Optionally power may be supplied to the power distribution bus when the vehicle is in motion; and power from the power supply may be used to power an electric traction motor. 10 Brief Description of the Drawings Figure 1 schematically illustrates a hybrid electrical energy storage system for an industrial mining vehicle; Figure 2 schematically illustrates a dual active 15 bridge; Figure 3 schematically illustrates a hybrid electrical energy storage system connected to an industrial mining vehicle; Figure 4 schematically illustrates another hybrid 20 electrical energy storage system; Figure 5 schematically illustrates a further hybrid electrical energy storage system; Figure 6 schematically illustrates a still further alternative hybrid electrical energy storage system; 25 Figure 7 schematically illustrates a yet further alternative hybrid electrical energy storage system; Figure 8 schematically illustrates the hybrid electrical energy storage system of Figure 7 connected to a charging apparatus; 30 Figure 9 schematically illustrates a control system for controlling the hybrid electrical energy storage system of Figure 8; and Figure 10 schematically illustrates the control system of Figure 9. These drawings depict one or more implementations in accordance with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements. 5 Detailed Description of the Drawings Figure 1 schematically illustrates a hybrid electrical energy storage system 10. The hybrid electrical energy storage system 10 comprises two electrical energy storage systems 12a, 12b and two dual active bridge 10 systems 14a, 14b. Each dual active bridge system 14a, 14b comprises a dual active bridge 30 (see Figure 2). A pair of electrical connectors 17a are located on a first side 16a of the first dual active bridge system 14a, and a pair of electrical connectors 17b are located on a 15 first side 16b of the second dual active bridge system 14b. The pair of electrical connectors 17a located on the first side 16a of the first dual active bridge system 14a are operatively connected to the first energy storage system 12a, and the pair of electrical connectors 17b 20 located on a first side 16b of the second dual active bridge system 14b are operatively connected to the second energy storage system 12b. Filter capacitors 20a, 20b are connected between the respective pairs of electrical connectors 17a, 17b. 25 A pair of electrical connectors 19a are located on the second side 18a of the first dual active bridge system 14a, and a pair of electrical connectors 19b are located on the second side 18b of the second dual active bridge system 14b. Filter capacitors 21a, 21b are connected 30 between the respective pairs of electrical connectors 19a, 19b. A first one of the pair of connectors 19a on the second side 18a of the first dual active bridge system 14a is connected to a first conductor 22a of a power distribution bus 23, and a second one of the pair of connectors 19a is connected to a first one of the pair of connectors 19b on the second side 18b of the second dual active bridge system 14b by connection 24. A second one of 5 the pair of connectors 19b is connected to a second conductor 22b of the bus 23. The dual active bridge systems 14a, 14b are therefore electrically connected in series such that the total output voltage Vt seen across the dual active bridge systems 14a, 14b is equal to the 10 sum of the voltages Va, Vb seen at the second side 18a, 18b - between the pairs of connectors 19a, 19b respectively - of each individual dual active bridge system 14a, 14b. In the example of Figure 1, the first energy storage 15 system 12a may supply a voltage of 1500 volts, and the second energy storage system 12b may supply a voltage of 1500 volts. The total voltage Vt seen across the dual active bridge systems 14a, 14b may be 3000 volts. A dual active bridge 30 is schematically shown in 20 Figure 2. The dual active bridge 30 comprises a DC to AC solid state bridge 32 and an AC to DC solid state bridge 34. The DC to AC solid state bridge 32 is electrically coupled to the AC to DC solid state bridge 34 by transformer 36. In this example the transformer 36 has a 25 1:1 turns ratio such that the voltage Vin on a first side of the dual active bridge 30 is equal to the voltage Vout on a second side of the dual active bridge 30. However, it is not essential that the turns ratio of the transformer 36 be 1:1, and any suitable turns ratio may be used. 30 The dual active bridge 30 is two way such that power may flow in either direction across the dual active bridge 30. A plurality of dual active bridges may be connected in parallel to form a dual active bridge system (as described in greater detail below). Figure 3 schematically illustrates the hybrid electrical energy storage system 10 connected to an industrial mining vehicle 11. In this example the first energy storage system 12a supplies a voltage of 1500 5 volts, and the second energy storage system 12b supplies a voltage of 1500 volts. The dual active bridge systems 14a, 14b each comprise a dual active bridge 30 (as shown in Figure 2) such that the voltages Va, Vb each equal 1500 volts, and the total voltage Vt seen across the conductors 10 22a, 22b of the bus 23 is 3000 volts. Figure 4 schematically illustrates another alternative hybrid electrical energy storage system 10. In this example the first energy storage system 12a comprises a 1000 volt supercapacitor, and the second energy storage 15 system 12 comprises a 1000 volt lithium-ion battery. The dual active bridge systems 14a, 14b each comprise a dual active bride 30 (as shown in Figure 2) such that the total voltage Vt seen across the dual active bridge systems 14a, 14b between the conductors 22a, 22b of the bus 23 is 2000 20 volts. In another example (not shown) both energy storage systems 12a, 12b may comprise a supercapacitor (of any suitable voltage), or both energy storage systems 12a, 12b may comprise a battery (of any suitable chemistry or voltage). 25 Figure 5 schematically illustrates a further alternative hybrid electrical energy storage system 10. In this example first and second energy storage systems 12a and 12b comprise 1000 volt supercapacitors, and third and fourth energy storage systems 12c and 12d comprises 1000 30 volt lithium-ion batteries. The dual active bridge systems 14a, 14b, 14c, 14d each comprise a dual active bridge 30 (as shown in Figure 2) such that the total voltage Vt seen across the dual active bridge systems 14a / 14b, 14c / 14d between the conductors 22a, 22b of the bus 23 is 2000 volts. In another example (not shown) both energy storage systems 12a / 12b, 12c / 12d may comprise a supercapacitor (of any suitable voltage), or both energy storage systems 12a / 12b, 12c / 12d may comprise a battery (of any suitable 5 chemistry or voltage). Figure 6 schematically illustrates a still further alternative hybrid electrical energy storage system 10. In this example the hybrid electrical energy storage system 10 comprises three energy storage systems 12a, 12b, 12c 10 and three dual active bridge systems 14a, 14b, 14c. The three dual active bridge systems 14a, 14b, 14c are electrically connected in series such that the total output voltage Vt seen across the dual active bridge systems 14a, 14b, 14c between the conductors 22a, 22b of 15 the bus 23 is equal to the sum of the voltages Va, Vb, Vc seen at the second side of each individual dual active bridge system 14a, 14b, 14c. In the example of Figure 6, the energy storage systems 12a, 12b, 12c each comprise 800 volt batteries 20 such that the voltage applied to the bus 23 is 2400 volts. The energy storage systems 12a, 12b, 12c may comprise the same battery chemistries, or may differ in battery chemistry. Alternatively, one or more (or all) of the energy storage systems 12a, 12b, 12c may comprise a 25 capacitor or supercapacitor. Figure 7 schematically illustrates a yet further alternative hybrid electrical energy storage system 10. In this example the hybrid electrical energy storage system 10 comprises two energy storage systems 12a, 12b and two 30 dual active bridge systems 14a, 14b. Each dual active bridge system 14a, 14b comprises three dual active bridges 30 connected in parallel. This has the advantage of transmitting more power from the energy storage systems 12a, 12b to the bus 23. The two dual active bridge systems 14a, 14b are electrically connected in series as before such that the total output voltage Vt seen across the dual active bridge systems 14a, 14b between the conductors 22a, 22b of the 5 bus 23 is equal to the sum of the voltages Va, Vb seen at the second side of each individual dual active bridge system 14a, 14b. The energy storage systems 12a, 12b may comprise any suitable battery chemistry or capacitor in any suitable combination. 10 It is not essential that the dual active bridge systems 14a, 14b shown in Figure 7 comprise three dual active bridges 30 connected in parallel, and any suitable number of dual active bridges 30 connected in parallel may be used. In addition, more than two dual active bridge 15 systems - comprising any suitable number of dual active bridges 30 connected in parallel – may be used together with a corresponding number of energy storage systems to increase the total voltage Vt applied to the bus 23. For example, the dual active bridge systems 14a, 14b, 14c 20 shown in the hybrid electrical energy storage system 10 of Figure 6 may comprise a plurality of dual active bridges 30 connected in parallel. Furthermore, it will be understood the dual active bridge systems 14a, 14b, 14c, 14d shown in the hybrid electrical energy storage system 25 10 of Figure 5 may comprise a plurality of dual active bridges 30 connected in parallel. Figure 8 schematically illustrates the hybrid electrical energy storage system 10 of Figure 7 connected to a dynamic power supply 40. In this example the dynamic 30 power supply 40 comprises overhead cables connected to the bus 23 by a pantograph system. However, other dynamic power supplies may be used such as an electrified rail. When the hybrid electrical energy storage system 10 is connected to a dynamic power supply 40, power may be supplied from the dynamic power supply 40 to the power distribution bus 23 to power electrical traction motors (not shown) used to drive the industrial mining vehicle 11. Power may simultaneously be supplied from the dynamic 5 power supply 40 to the energy storage systems 12a. 12b via the dual active bridge systems 14a, 14b to charge the energy storage systems 12a, 12b. It will be understood that the example of Figure 8 is illustrative only, and that more energy storage systems may be used, with a 10 corresponding number of dual active bridge systems, and that the dual active bridge systems my comprise dual active bridges connected in parallel, or may comprise a single dual active bridge. Figure 8 also illustrates charge ports 50a, 50b 15 which may be used to charge the energy storage systems 12a, 12b when the industrial mining vehicle 11 is stationary (and not connected to the dynamic power system 40). In an alternative example, the ports 50a, 50b may be 20 omitted, and the energy storage systems 12a, 12b may be charged by the dynamic power supply 40 when the industrial mining vehicle 11 is stationary or in motion. The hybrid electrical energy storage system 10 may be optimized to maximize power throughput when the industrial mining 25 vehicle 11 is stationary. For example, by coordination between the dynamic power supply 40 and the dual active bridge 30 controller(s). This is beneficial as the costs associated with charging ports 50a and 50b may be avoided, and charging infrastructure costs may be reduced by 30 introducing lower-cost medium voltage chargers / dynamic power supply 40 and locating charging controls with the on-board dual active bridge systems 14a, 14b. Figure 9 schematically illustrates a control system 100 for controlling the hybrid electrical energy storage system 10 of Figure 8. The control system 100 comprises a vehicle energy storage system (ESS) management system 101 5 which communicates with a stationary charger controller 102, a thermal management system 103, a vehicle control unit 104, and a dynamic power system controller 105, first and second battery management systems 106a, 106b, and first and second dual-active bridge system controllers 10 107a, 107b. The vehicle ESS management system 101 communicates with the rest of the control system components via communication channels 108 which may be wired or wireless communication channels. As illustrated in Figure 10, the control system 100 15 is arranged into two levels. Level 1 comprises the vehicle ESS management system 101 which communicates with systems external to the hybrid electrical energy storage system 10 such as the vehicle control unit 104, stationary charger controller 102 and the dynamic power system controller 20 105. The vehicle ESS management system 101 may also communicate with a fleet energy management system (or other aggregate energy management system) as part of the level 1 control. The level 2 systems comprise the battery management 25 systems 106a, 106b, the second dual-active bridge system controllers 107a, 107b and the thermal management system or systems 103a, 103b. While many possible variations of the hybrid electrical energy storage system have been described 30 above, it will be clear to the skilled person that additional variations and modifications can be made without departing from the scope of the invention as claimed in the appended claims.

Claims

SP2951 - 12 - A I M S 1. A hybrid electrical energy storage system for an industrial mining vehicle, comprising a plurality of electrical energy storage systems and a corresponding plurality of dual active bridge systems, wherein each dual 5 active bridge system comprises at least one dual active bridge, wherein a first side of each dual active bridge system is operatively connected to an associated one of the energy storage systems, and a second side of each dual active bridge system is electrically connected in series 10 to the second side of another of the dual active bridge systems such that the total output voltage seen across all of the dual active bridge systems connected in series is equal to the sum of the voltages seen at the second side of each individual dual active bridge system. 15 2. A hybrid electrical energy storage system as claimed in Claim 1, wherein the total voltage seen across all of the dual active bridge systems connected in series is greater than or equal to 1500 volts, and the nominal 20 voltage of each energy storage system is less than or equal to 1500 volts.

3. A hybrid electrical energy storage system as claimed in any preceding Claim, wherein each dual active 25 bridge system comprises a plurality of dual active bridges connected in parallel.

4. A hybrid electrical energy storage system as claimed in any preceding Claim, wherein each energy storage system 30 comprises a battery or a capacitor.

5. A hybrid electrical energy storage system as claimed in Claim 4, wherein at least one of the energy storage systems differs in type and / or chemistry to another one of the energy storage systems. 5 6. A hybrid electrical energy storage system as claimed in Claim 4 or 5, wherein each of the energy storage systems comprises a battery. 10 7. A hybrid electrical energy storage system as claimed in Claim 6, wherein each battery comprises lithium- titanate oxide battery chemistry, nickel manganese cobalt battery chemistry, or lithium-iron phosphate battery chemistry. 15 8. A hybrid electrical energy storage system as claimed in any preceding Claim, wherein a transformer located in each dual active bridge has a turns ratio of 1:

1. 20 9. An industrial mining vehicle comprising the hybrid electrical energy storage system as claimed in any preceding Claim and a power distribution bus operatively connected to the hybrid electrical energy storage system. 25 10. A method of operating an industrial mining vehicle as claimed in Claim 9, comprising: supplying power to the power distribution bus from a power supply; and using power from the power supply to charge the 30 plurality of energy storage systems, wherein the power from the power supply is supplied to the plurality of energy storage systems via the plurality of dual active bridge systems.

11. A method as claimed in Claim 10, comprising: supplying power to the power distribution bus when the vehicle is in motion; and using power from power supply to power an electric 5 traction motor.

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