Power system for a tethered electric work machine

Abstract

A power system for a tethered electric work machine is provided. The power system includes an input, an AC to DC converter, a DC backbone power bus, a DC to AC converter, and a controller. The input receives AC power from a tether. The AC to DC converter is connected to the input and converts the AC power from the tether to a DC output. In turn the DC backbone power bus receives the DC power from the AC to DC converter and converts it to AC power. The converted AC power is output to a motor of the tethered electric work machine. The controller controls the AC to DC converter and the DC to AC converter to control the power supplied to the motor of the tethered work machine.

Description

[0001] Power System for a Tethered Electric Work Machine

[0002] Field of the disclosure

[0003] The present disclosure relates to work machines, in particular work machines comprising a tether which provides a supply of electrical power to the machine (a “tethered electric work machine”).

[0004] Background

[0005] Electric work machines (i.e. work machines which are driven by electric motors rather than an internal combustion engine) may receive electrical power from one or more batteries provided as part of the work machine, and / or from the electrical grid. Where the electrical grid is used to supply power, the electric work machine may be connected to the electrical grid via a tether (i.e. a power cable).

[0006] For example, JP-B-6752125 discloses an electric construction machine which receives AC power from an external power source via a power feed cable. Three-phase AC power received from the power feed cable is used to directly drive a three phase induction motor of the electric construction machine.

[0007] Against this background, the present disclosures provides an improved, or at least commercially relevant alternative power system for a tethered electric work machine.

[0008] Summary

[0009] According to a first aspect of the disclosure, a power system for a tethered electric work machine is provided. The power system comprises: an input, an AC to DC converter, a DC backbone power bus, a DC to AC converter, and a controller. The input is configured to receive AC power from a tether. The AC to DC converter is connected to the input and configured to receive AC power from the tether and to output DC power. The DC backbone power bus configured to receive DC power from the AC to DC converter. The DC to AC converter is configured to convert DC power from the DC backbone power bus to AC power, and to output said AC power to a motor of the tethered electric work machine. The controller is configured to control the AC to DC converter and the DC to AC converter to control the power supplied to the motor of the tethered work machine.

[0010] According to the first aspect, the power system supplies AC power to an electric motor of the electric work tethered machine. The present inventors have realised that drawing AC power and directly supplying said AC power directly to the electric motor may result in relatively large spikes in current draw. For example, during start-up of an AC motor, the peak current draw experienced by the tether may significantly exceed the peak current draw experienced during normal operation of the tethered work machine. To address this, the power system of the first aspect powers the electric motor from a DC backbone power bus. An AC to DC converter controlled by the controller controls the AC power drawn via the tether and converted to DC power. The converted DC power is in turn converted to AC power by the DC to AC converter. By controlling the power draw in this manner, the variation in the peak AC current draw experienced by the tether may be reduced, particularly during start-up of the tethered electric work machine. This in turn may reduce the impact of the tethered work machine on the local power grid and other electrical devices connected to the local power grid.

[0011] According to a second aspect of the disclosure, a tethered electric work machine is provided. The tethered electric work machine comprises a power system according to the first aspect, and a tether configured to be connected to the input of the power system and configured to receive AC power from an external power supply.

[0012] The second aspect of the disclosure may incorporate any optional features and associated advantages of the first aspect of the disclosure.

[0013] Brief description of the figures

[0014] Embodiments of the disclosure will now be described with reference to the following figures in which:

[0015] Fig. 1 shows a diagram of a tethered electric work machine according to an embodiment of the disclosure;

[0016] Fig. 2 shows a block diagram of a power system for a tethered electric work machine according to an embodiment of the disclosure; Fig. 3 shows a block diagram of a power system for a tethered electric work machine according to a further embodiment of the disclosure;

[0017] Fig. 4 shows a block diagram of a power system including a battery module for a tethered electric work machine according to another embodiment of the disclosure;

[0018] Fig. 5 shows a flow chart for a power system controller which controls the power draw of the tethered electric work machine during operation of the tethered electric work machine;

[0019] Fig. 6 shows a schematic graph of a power supplied to and demanded by a power system of a tethered electric work machine according to this disclosure; and

[0020] Fig. 7 shows a graph of a state of charge of a battery module of a tethered electric work machine according to this disclosure.

[0021] Detailed description

[0022] According to an embodiment of the disclosure, an electric work machine 1 is provided. A diagram of a work machine 1 according to this disclosure is shown in Fig. 1. As shown in Fig. 1 , the tethered electric work machine 1 may be an excavator. In some embodiments, the tethered electric work machine 1 may be any type of work vehicle or work machine which is primarily powered by electrical power. The tethered electric work machine 1 comprises a power system 10 (not shown in Fig. 1). In some embodiments, the tethered electric work machine 1 may be any type of work vehicle or work machine which may is capable of being primarily powered by electrical power. As such, the tethered electric work machine may be a fully electric work machine or a hybrid electric work machine (i.e. the hybrid electric work machine comprises an internal combustion engine in addition to the power system 10).

[0023] The tethered electric work machine 1 is configured to receive electrical power via a tether 3. The tether 3 may comprise a plurality of electrical cables for transferring electrical power from an external power source to the tethered electric work machine 1. In some embodiments, the external power source may be an electrical grid (not shown in Fig. 1) which provides a source of AC electrical power.

[0024] In some embodiments, an off-board power supply 5 may be provided to interface between the tether 3 and the electrical grid. As such, in some embodiments, the power system 10 for the tethered electric work machine 1 may include the off-board power supply and the tether 3. In some embodiments, the off-board power supply 5 may be connected to the electrical grid, and the off-board power supply 5 may be connected to the tether. In other embodiments, the off-board power supply may comprise a generator, or be connected to a generator, wherein the generator generates e.g. AC power. For example in the embodiment of Fig. 1 , the tethered electric work machine 1 is connected to an off-board power supply 5 by a tether 3. The off-board power supply 5 may be configured to receive AC power from the electric grid and may be configured to output AC power to the electric work machine 1 when the tether is connected to the electric work machine 1.

[0025] In some embodiments, the off-board power supply 5 comprises an isolating transformer configured to isolate the electric grid from the tether 3. By isolating the tethered electric work machine 1 from the electrical grid, in the event of a fault in the power system of the tethered electric work machine 1 , the power system may ensure that the off-board power supply 5 operates in a safe manner. The off-board power supply 5 may also comprise one or more circuit breaker circuits which are configured to monitor the power supplied by the off-board power supply 5 and to interrupt the supply of power in the event that an excessive current and / or voltage is detected.

[0026] As shown in Fig. 1, in some embodiments the tethered electric work machine 1 may comprise an upper body 7 and a lower body 9. In some embodiments, the upper body may be configured to rotate relative to the lower body.

[0027] The tethered electric work machine 1 comprises an electric work machine input (not shown in Fig. 1) to which the tether 3 may be connected to supply electrical power to the tethered electric work machine 1. In the embodiment of Fig. 1, the electric work machine input may be provided on the upper body 7 or the lower body 9. In the embodiment of Fig. 1, the electric work machine input is provided on the lower body, such that the tether moves with the motion of the lower body.

[0028] In the embodiment of Fig. 1, one or more other components of the power system may be provided on the upper body 7 of the electric work machine. Where electrical connections between the upper body 7 and the lower body 9 are provided, the power system may comprise one or more slip rings (not shown in Fig. 1). For example, the lower body 9 may comprise a slip ring configured to connect the electric work machine input to the AC to DC converter, wherein the AC to DC converter is provided on the upper body 9 of the electric work machine 1. As such, the slip ring provides for an electrical connection of the power system between the upper body 7 and the lower body 9 of the tethered electrical work machine 1.

[0029] Fig. 2 shows a schematic diagram of the power system 10 for the tethered electrical work machine 1 according to an embodiment of the disclosure. For example, the power system 10 of Fig. 2 may be provided as part of the tethered electric work machine 1 shown in Fig. 1.

[0030] As shown in Fig. 2, the power system 10 comprises an electric work machine input 12, an AC to DC converter 14, a DC backbone power bus 16, a DC to AC converter 18, and a controller 20.

[0031] The electric work machine input 12 is configured to receive AC power from the tether 3. As shown in Fig. 2, the tether 3 is connected to the off-board power supply 5, which is in turn connected to a source of AC power 19, such as an electrical grid.

[0032] In Fig. 2, the flow of power from the electrical grid 19 to the electric work machine input 12 is depicted with a single line. In some embodiments, the tethered electric work machine 1 may be supplied with single-phase AC power via the tether. In some embodiments, the tethered electric work machine 1 may be supplied with three-phase electric power. In embodiments where three phase electrical power is supplied, it will be appreciated that the tether 3 and the off-board power supply 5 may each be adapted to conduct three phase power. For example, Figs. 3 and 4 show schematic diagrams of power systems 10a, 10b according to embodiments of the disclosure in which three phase power is supplied over the tether 3.

[0033] In some embodiments, the three phase power received by the off-board power supply 5 may be in a delta or star (Y) configuration. Typically, three phase power received from electrical grid 19 may be in a delta configuration. In some embodiments, the power transmitted by the tether 3 may be three phase power having a star configuration. In some embodiments, the off-board power supply 5 may be configured to transform the three phase power from a delta configuration to a star configuration. For example, the off-board power supply 5 may comprise a transformer (not shown in Fig. 2) which is configured to transform the three phase power from a delta configuration to a star configuration. In some embodiments, power system 10 may comprise an isolation transformer which is configured to electrically isolate the AC to DC converter 14 from the electrical grid 19 which supplies electrical power to the tether 3. In the embodiments of Figs. 3 and 4, the isolation transformer 30 may be provided as part of the off-board power supply 5. In other embodiments, the isolation transformer 30 may be provided on the tethered electric work machine 1. For example, the isolation transformer 30 may be connected between the electric work machine input 12 and the AC to DC converter 14.

[0034] In some embodiments, the off-board power supply 5 may comprise a safety circuit 32. The safety circuit may be configured to detect a fault in the output of the AC power to the electric work machine input 12 of the power system 10 via the tether 3. For example, the safety circuit 32 of Fig. 3 may be configured to detect a ground fault (i.e. any fault which indicates an unintended connection of a power source to earth, potentially resulting in an excessive draw of current). In some embodiments, the safety circuit 32 may also be configured to detect a fault signal from the tethered electric work machine 1 (e.g. from the controller of the tethered electric work machine 1. Where the safety circuit detects a fault in the output of the AC power (e.g. a ground fault or receives a signal indicative of a fault from the tethered electric work machine 1), the safety circuit 32 may be configured to interrupt the supply of AC power to the tethered electric work machine 1. For example, the safety circuit 32 may comprise one or circuit breaker circuits, such as a relay, which may be configured to interrupt the supply of AC power to the tethered electric work machine 1. It will be appreciated that the safety circuit 32 may also be configured to detect a fault in the operation of the off-board power supply 5, for example a ground fault, and interrupt the supply of power upon detection of the fault. The safety circuit 32 may also comprise one or more sensors (not shown in Figs. 3 and 4) for detecting one or more operating conditions of the off-board power supply 5. The operating conditions of the off-board power supply 5 may comprise a temperature or a one or more parameters of the AC power supplied to the off-board power supply (e.g. line voltage, line current etc.). Where the detected operating condition deviates from an expected behaviour range (e.g. a parameter exceeds or falls below a predetermined threshold or range of acceptable values), the safety circuit may be configured to interrupt the supply of power. For example, where a temperature of the off- board power supply exceeds a predetermined threshold, the safety circuit 32 may determine a fault has occurred.

[0035] 15637015v1 As shown in Fig. 2, the tether 3 may be connected to the tethered electric work machine 1 at electric work machine input 12. As such, the electric work machine input 12 may comprise a connector (not shown in Fig. 2) which is configured to detachably connect the tether 3 to the tethered electric work machine 1. The electric work machine input 12 is configured to receive AC power and to conduct AC power to the AC to DC converter 14.

[0036] In some embodiments, for example as shown in Fig. 2, the AC power received by the tethered electric work machine 1 may be filtered by inductive filter 22 prior to conversion by the AC to DC converter 14. The inductive filter 22 may be configured to filter harmonics from the AC power. As shown in Fig. 2, the inductive filter may be provided between the electric work machine input 12 and the AC to DC converter 14. In some embodiments the inductive filter 22 may comprise an LC filter or an LCL filter. The inductive filter may be configured to filter relatively high frequency harmonics (i.e. harmonic frequencies which are more than double the primary frequency of the AC power) in order to reduce the presence of high frequency harmonics in the power system of the tethered electric work machine 1.

[0037] The AC to DC converter 14 is configured to receive AC power from the tether 3 and to output DC power. As shown in Fig. 2, the AC to DC converter 14 is configured to output DC power to the DC backbone power bus 16. The skilled person is familiar with various AC to DC converter 14 circuits which may be utilised in the power system 10 in order to output the desired DC voltage to the DC backbone power bus 16 and also to output DC power at a level suitable for powering the tethered electric work machine 1.

[0038] The DC backbone power bus 16 may be configured to supply DC power to various electrical actuators and motors of the tethered electric work machine 1. As such, it will be appreciated that the DC backbone power bus 16 may be configured to supply an amount of power which is suitable for driving / operating the tethered electric work machine 1. In some embodiments, the DC backbone power bus 16 may be configured to receive DC power at a bus voltage of at least 250 V. That is to say, the operating voltage of the DC backbone power bus 16 may be at least 250 V. It will be appreciated that such an operating voltage may be significantly higher than a typically operating voltage of a conventional 12V or 24 V battery for a vehicle.

[0039] The DC backbone power bus 16 is configured to receive DC power from the AC to DC converter 14. The DC backbone power bus 16 supplies DC power to various components of the power system 10. For example, as shown in Fig. 2, the DC backbone power bus 16 is configured to supply power to a battery module 30 and also to DC to AC converter 18. It will be appreciated that in some embodiments, the DC backbone power bus 16 may be configured to supply DC power to other components not shown in Fig. 2. For example, the DC backbone power bus 16 may be configured to supply DC power to a DC to DC converter 34 (e.g. as shown in Fig. 3) which is configured to transform the DC bus voltage of the DC backbone power bus 16 to a different voltage (e.g. a lower voltage). As such, in some embodiments, the power system 10 may comprise a DC to DC converter which may be configured to convert a bus voltage of the DC backbone power bus 16 to an auxiliary voltage. The auxiliary voltage may be lower than the bus voltage. For example, the DC to DC converter 34 may be configured to supply the auxiliary voltage to one or more electronics modules of the tethered electric work machine 1.

[0040] The DC to AC converter 18 is configured to convert DC power from the DC backbone power bus 16 to AC power. The DC to AC converter 18 is configured to output said AC power to a motor 24 of the tethered electric work machine 1. As such, the AC power drawn from the tether 3 may be transformed to DC power and then transformed back into AC power before it is utilised to drive the motor 24. Thus, the power system 10 of the present disclosure may control the power drawn from the external power supply (e.g. the electric grid) connected to the tether 3. Furthermore, relative to an AC induction motor which is directly driven by AC power received from a tether, the power system 10 of the present disclosure may control the AC power supplied to the motor 24 by controlling the AC power converted to DC power by the AC to DC converter 14. In particular, when starting an AC induction motor, the current draw of the AC induction motor 24 may be relatively high (relative to steady state operation of the AC induction motor 24). Such high current draw may place a significant stress on the electrical grid 19. To avoid placing a high stress on the electrical grid 19, the AC to DC converter 14 may limit the current drawn from the tether / electrical grid, in particular during start-up of the AC induction motor 24. As such, the controller 20 may be configured to control the AC to DC converter such that an AC current received from the tether 3 does not exceed a predetermined threshold.

[0041] In some embodiments, the controller 20 may control the AC power / AC current drawn by the AC to DC converter 14 during a start-up routine. As such, when the controller 20 receives a demand to supply electrical power to a motor 24 which is currently at rest, the controller may be configured to increase the AC power supplied to the motor 24 from zero to the demanded power over a predetermined time period. That is to say, the controller 20 may control the AC power drawn by the AC to DC converter 14 such that it ramps up over the predetermined time period, rather than an instantaneous demand. In some embodiments, the predetermined time period may be at least 0.1 s, 0.5 s, 1 s or 2 s.

[0042] The DC to AC converter 18 may comprise an inverter which is configured to convert DC power to AC power. The AC power output by the DC to AC converter 18 may be provided at a frequency and amplitude according to the nature of the motor 24 to be driven and any commands from an operator of the tethered electric work machine 1.

[0043] The controller 20 is configured to control the power system 10 to in order to control the flow of power from the tether to the motor 24. As shown in Fig. 2, the controller 20 may be configured to control the AC to DC converter 14 to control the power drawn by the power system 10 from the tether 3. The controller 20 may also be configured to control the DC to AC converter 18 to control the power supplied to the motor 24 of the tethered work machine 1. In particular, where a motor 24 is at rest / stationary and the controller 20 receives a signal indicating a demanded power is to be supplied to the motor 24, the controller 20 may be configured to control the AC power drawn by the AC to DC converter 14 such that it ramps up to the demanded power over a predetermined time period.

[0044] As shown in Fig. 2, the power system 10 may also comprise a battery module 30. The battery module may be configured to supply DC power to the DC backbone power bus 16. The battery module may comprise one or more batteries. Each battery may be configured to store electrical power. The battery module 30 may be configured to output a DC voltage. In the embodiment of Fig. 2 the battery module 30 may be configured to output a DC power at the bus voltage of the DC backbone power bus 16.

[0045] The battery module 30 may be configured to store electrical charge for supplying power to the tethered electric work machine 1. In some embodiments, the battery module 30 may be configured to supply power to the tethered electric work machine 1 when it is not connected to the tether 3. As such, in some embodiments the tethered electric work machine 1 may be able to move between different locations under battery power. Once the tethered electric work machine 1 arrives at a work location, the tethered electric work machine 1 may be connected to a tether 3 for performing a task. In some embodiments, the controller 20 may be configured to control the AC to DC converter 14 in order to control the power supplied to the DC backbone power bus 16 from the input 12 and the battery module 30. That is to say, in some embodiments, the DC power drawn from the DC backbone power bus 16 (e.g. by the DC to AC converter 18) may be provided by a combination of the power supplied from the electric work machine input 12 and the battery module 30. For example, during operation of the power system 10, the majority of the power may be supplied from the electric work machine input 12 / tether 3. The controller 20 may control this flow of power by controlling the operation of the AC to DC converter 14. Where additional power is demanded by the DC to AC converter 18, the battery module 30 may supply additional DC power to the DC to AC converter 18.

[0046] In some embodiments, when the tethered electric work machine 1 is operational (i.e. electrical power is drawn though the tether 3) the battery module 30 may be charged using electrical power drawn from the tether 3 (i.e. electrical power is drawn from the tether 3 via the AC to DC converter 14 and the DC backbone power bus 16). Charging the battery module 30 via the tether may require the AC to DC converter 14 to be operational, and also may require the controller 20 to be operational in order to supply power to the battery module 30 via the DC backbone power bus 16.

[0047] When the tethered electric work machine 1 is not in operation, it may be desirable to allow the battery module 30 to be charged. In order to provide this functionality, the battery module 30 may comprise a charging input (not shown in Fig. 2). The charging input may be provided to allow the battery module 30 to be charged separately from the tether 3. As such, the battery module 30 may be connected directly to an off-board battery charger (not shown in Fig. 2) which is configured to charge battery module. In some embodiments, the off-board battery charger 36 may supply a DC voltage to the battery module 30 in order to charge the battery module 30. By providing a charging input for the battery module 30, the battery module 30 of the tethered electric work machine 1 may be charged without requiring the operation of the AC to DC converter 14 and DC backbone power bus 16 of the power system 10. For example, as shown in Fig. 4, the power system 10 may comprise a charging input 37 connected to the DC backbone power bus 16. A charging cable 38 may be configured to connect to the charging input 37 in order to supply DC power to battery module 30 via the DC backbone power bus 16. In addition to the reduction in power draw upon start-up of the tethered electric work machine 1, the power system 10 of Fig. 2 may also be controlled in to smooth out variation in the power draw during operation of the tethered electric work machine 1. The controller 20 may control the power drawn from the tether 3 and the battery module 30 in order to reduce or eliminate sudden changes in the power draw from the tether 3 in order to reduce stress on the electric grid. Fig. 5 shows a flow diagram for a method of controlling a power system 10 according to an embodiment of the disclosure.

[0048] Thus, in accordance with the embodiments of Figs. 2-4, a power system 10 may be provided for controlling the flow of power to a tethered electric work machine 1.

[0049] In some embodiments, the controller 20 of the tethered electric work machine 1 may also be configured to control the power drawn by the tethered electric work machine 1 during normal operation of the tethered electric work machine 1.

[0050] In addition to the reduction in power draw upon start-up of the tethered electric work machine 1, the power system 10 of Fig. 2 may also be controlled in to smooth out variation in the power draw during operation of the tethered electric work machine 1. The controller 20 may control the power drawn from the tether 3 and the battery module 30 in order to reduce or eliminate sudden changes in the power draw from the tether 3 in order to reduce stress on the electric grid. Fig. 5 shows a flow diagram for a method 100 of controlling a power system 10 according to an embodiment of the disclosure. As shown in Fig. 5, steps 101, 102, and 103 of method 100 may be repeated. As such, method 100 may be performed a plurality of times, over a plurality of timesteps. That is to say, the method 100 may be repeated at regular time intervals (e.g. every 100 ms) in order to control the power system 10 over a period of operating the tethered electric work machine 1.

[0051] As shown in Fig. 5, in step 101 of the method 100 an instantaneous electrical power demand for a motor 24 of the tethered electric work machine 1 is received. For the power system 10 of Fig. 2, the controller 20 may obtain the instantaneous electrical power demand for a motor 24 of the tethered electric work machine 1. For example, the controller 20 may receive a demand for power / motion of the motor 24 from a user of the tethered electric work machine. From this, the controller 20 may determine, or otherwise obtain the instantaneous electrical power demand for the motor 24. As such, for each timestep at which the method 100 is performed, the controller may obtain an instantaneous power to be supplied to the motor 24.

[0052] In step 102, the method 100 comprises determining a moving average power demand for the motor 24 based on a power supplied to the motor 24 over a preceding predetermined time period. In the embodiment of Fig. 2, the controller 20 may determine the moving average power demand. For example, the controller 20 may determine the power supplied to the motor 24 by the DC to AC converter 18 for each repetition (timestep) of the method 100. Alternatively, the controller 20 may determine the moving average power demand based on the instantaneous electrical power demand for the motor 24 from a plurality of previous timesteps. Whichever measure of the power supplied to the motor 24 used by the controller 20, the controller 20 may determine a moving average power demand using at least 5 time steps. Alternatively, the controller 20 may determine the moving average power demand based on the power supplied over timesteps spanning at least the previous: 10 seconds, 30 seconds, 60 seconds, 10 minutes, 60 minutes, or 100 minutes of operation. The predetermined time period may be selected, at least in part based on the battery capacity of the battery module 30. As such, for battery modules 30 having a relatively large battery capacity, the predetermined time period may be increased, relative to smaller capacity battery modules 30.

[0053] In step 103, the method 100 comprises controlling the power system 10 to supply power to the motor 24. For the embodiment of Fig. 2, step 103 comprises the controller 20 controlling the AC to DC converter 14 to draw power from the electric work machine input 12 based on the moving average power demand determined for the timestep.

[0054] In some circumstances, the instantaneous electrical power demand may be different to the moving average power demand. The controller 20 may be configured to control the AC to DC converter 14, the battery module 30 and the DC to AC converter 18 in order manage any excess of power and also to account for any shortfall in power as described further below.

[0055] Where the instantaneous electrical power demand is less than the moving average power demand, the controller 20 may control the AC to DC converter and the battery module such that power is supplied (i.e. the excess power) from the electric work machine input 12 to the battery module 30. As such, the excess power may be stored by the battery module 30 for subsequent use.

[0056] Where the instantaneous electrical power demand is greater than the moving average power demand, the controller 20 may control the battery module 30 to supply power from the battery module 30 to the motor 24. As such, the motor 24 may draw on the energy stored within the battery module 30 to make up for a shortfall in the power supplied from the tether 3 / AC to DC converter 14.

[0057] This effect is indicated schematically in Fig. 6, which shows an instantaneous electrical power demand for the tethered electric work machine 1 (“Machine power requirement”) which varies over time. The power supplied to the tethered electric work machine 1 via the tether (“Grid I tether power supply”) is depicted schematically in Fig. 6 as having little variation over the same time period. As indicated in Fig. 6, there are consequently operating periods where power is discharged from the battery module 30 to supplement the tether power supply and operating periods where the battery module 30 is charged using the excess power.

[0058] In some embodiments, the controller 20 may also control the power drawn by the AC to DC converter based on a state of charge of the battery module 30. For example, for each timestep of the method 100 the controller 20 may be configured to obtain a state of charge of the battery module 30. The controller may then control the AC to DC converter 14 to draw AC power from the electric work machine input 12 based on the moving average power demand and the state of charge of the battery module 30.

[0059] For example, in some embodiments, the controller 20 may specify a minimum state of charge for the battery module 30. Consequently, the controller may control the power system 10 to draw AC power from the electric work machine input 12 based on the moving average power demand and the state of charge of the battery module 30 such that the state of charge of the battery module 30 is above a charge threshold. Fig. 7 shows a schematic diagram of the state of charge of the battery module 30 over a period time. As shown in Fig. 6, the state of charge of battery module 30 may be maintained above a SoC target boundary (a minimum charge threshold). As shown in Fig. 7, as the state of charge approaches the minimum charge threshold, the controller 20 may cause the AC to DC converter 14 to increase the power drawn from tether 3 above what is required to supply the motor 24.

[0060] As also shown in Fig. 7, the controller 20 may also specify a maximum charge threshold for the battery module 30. The controller 20 may control the power system 10 to draw AC power from the electric work machine input 12 based on the moving average power demand and the state of charge of the battery module 30 such that the state of charge of the battery module 30 is below the maximum charge threshold. By specifying a maximum charge threshold and a minimum charge threshold, the controller 20 may prolong the lifetime of the battery module 30 by reducing or avoiding excessively charging / discharging the battery.

[0061] As indicated in Fig. 7, in some embodiments the controller 20 may control the power system 10 to maintain the state of charge of the battery module 30 at about a target state of charge (indicated by central a dashed line in Fig. 7). As such, the controller 20 may be configured to control the AC to DC converter 14 to draw AC power from the electric work machine input 12 based on the moving average power demand and a difference between the state of charge of the battery module 30 and a target state of charge of the battery module 30. For example, the controller 20 may be configured to weight the moving average power demand in order to either increase or decrease the state of charge of the battery module 30. The weighting applied to the calculation of the moving average may be proportional to the difference between the current state of charge of the battery module 30 and the target state of charge. Thus, as shown in Fig. 7, the state of charge of the battery module 30 may be maintained around the target state of charge for a period of operation.

[0062] While in some embodiments the controller 20 may provide absolute minimum and maximum charge thresholds for the battery module 30, in other embodiments, the controller 20 may be configured to control the AC to DC converter to draw AC power from the electric work machine input 12 such that a difference between the state of charge of the battery module 30 and the target state of charge is no greater than a difference threshold. That is to say, the minimum and maximum state of charge may be defined relative to the target state of charge,

[0063] In normal operation, the controller 20 may be configured to control the power drawn from the tether 3 based on the moving average determined. In some embodiments, the controller 20 may receive a signal which indicates that it is desirable to fully charge the battery module 30. In such cases, upon obtaining a charging signal from the tethered electric work machine 1, the controller 20 may be configured to control the AC to DC converter 14 to draw AC power from the input based on the moving average power demand and a state of charge for the battery module 30 such that the state of charge of the battery module 30 is above a charge target state of charge after a predetermined charging time period. For example, as highlighted in Fig. 7, an operator triggered charge signal may be received by the controller 20. In response, the controller 20 may cause the battery module 30 to fully charge (e.g. exceeding the maximum state of charge threshold specified for normal operation). Such a charging operation may be specified in advance of a planned period of time where the tethered electric work machine 1 is to be operated off the tether (i.e. on battery power only). Such battery-only operation may be provided to allow the tethered electric work machine 1 to move to a different work location.

[0064] Following a period of battery-only operation, the tethered electric work machine 1 may be reconnected to a tether 3. As shown in Fig. 7, where the state of charge is below a minimum state of charge for normal operation, the controller 20 may control the power system 10 to draw power from the tether such that the battery module 30 is charged in addition to powering the motor 24.

[0065] As such, it will be appreciated from Fig. 7 that the tethered electric work machine 1 may be operational for an extended period of time whilst substantially maintaining a target state of charge over the operation period. Thus, in contrast to a battery-only work machine which discharges a battery as it operates, the tethered electric work machine 1 may avoid the need to undergo repeated battery charging periods where the tethered electric work machine 1 is not operational. Similarly, where the tethered electric work machine 1 is operating in a battery-only mode (i.e. operation off tether), the tethered electric work machine 1 may charge its battery module back up to the target state of charge during further operation of the tethered electric work machine. That is to say, the operational time of the tethered electric work machine 1 may be improved (i.e. reduced downtime) relative to a battery-only electric work machine.

[0066] While the above description of method 100 describes a method for controlling the electrical power supplied to a single motor 24 of the tethered electric work machine, it will be appreciated that in some embodiments the method 100 may also be applied to the supply of electrical power to a plurality of motors 24 using the power system 10.

[0067] Thus, in accordance with the embodiments of Figs. 2-6, a power system 10 may be provided for controlling the flow of power to a tethered electric work machine 1.

[0068] Industrial applicability

[0069] According to this disclosure, a power system 10 for a tethered electric work machine 1 and a tethered electric work machine 1 is provided. As described herein, the power system 10 may supply AC power to a motor 24 of the tethered electric work machine 1. The power system 10 of this disclosure avoids the motor 24 directly drawing AC power from the electric grid, in order to reduce or eliminate the occurrence of relatively large spikes in current draw, in particular during start-up of the motor 24.

[0070] As such, the power system 10 of this disclosure powers the motor 24 from a DC backbone power bus. An AC to DC converter 14 controlled by the controller 20 controls the AC power drawn via the tether 3 and converted to DC power. The converted DC power is in turn converted to AC power by the DC to AC converter 18. By controlling the power draw in this manner, the variation in the peak AC current draw experienced by the tether may be reduced by way of the controller 20 controlling the AC to DC converter 14. This in turn may reduce the impact of the tethered electric work machine 1 on the local power grid and other electrical devices connected to the local power grid.

[0071] As described herein, the tethered electric work machine 1 may be a tethered electric off- highway machine, for example a tethered electric excavator, of any other type of tethered off-highway electric work machinery.

Claims

CLAIMS:

1. A power system for a tethered electric work machine comprising: an electric work machine input configured to receive AC power from a tether; an AC to DC converter configured to receive AC power from the tether and to output DC power; a DC backbone power bus configured to receive DC power from the AC to DC converter; a DC to AC converter configured to convert DC power from the DC backbone power bus to AC power, and to output said AC power to a motor of the tethered electric work machine; and a controller configured to control the AC to DC converter and the DC to AC converter to control the power supplied to the motor of the tethered work machine.

2. A power system according to claim 1, further comprising: a battery module configured to supply DC power to the DC backbone power bus.

3. A power system according to claim 2, wherein the controller is configured to control the AC to DC converter in order to control the power supplied to the DC backbone power bus by the tether and the battery module.

4. A power system according to any of claims 1 to 3, further comprising: a DC to DC converter configured to convert a first voltage of the DC backbone power bus to a second voltage lower than the first voltage, wherein the DC to DC converter is configured to supply the second voltage to one or more electronics modules of the tethered electric work machine.

5. A power system according to any of claims 1 to 4, wherein the DC backbone power bus is configured to receive DC power at a first voltage of at least 250 V.

6. A power system according to any of claims 1 to 5, further comprising an inductive filter configured to filter harmonics from the AC power between the electric work machine input and the AC to DC converter, wherein optionally the inductive filter is an LC filter or an LCL filter.

7. A power system according to any of claims 1 to 6, further comprising an off-board power supply; and a tether, wherein the off-board power supply is configured to receive AC power from an electric grid and to output AC power to the electric work machine input of the power system via the tether when the tether is connected to the electric work machine input.

8. A power system according to claim 7, wherein the off-board power supply comprises an isolating transformer configured to transfer AC power from the electric grid to the tether while isolating the electric grid from the tether.

9. A power system according to claim 7 or claim 8, wherein the off-board power supply comprises a safety circuit which is configured: to detect a fault in the output of the AC power to the electric work machine input of the power system via the tether; and upon detecting a fault in the output of the AC power, the safety circuit is configured to interrupt the output of AC power to the tethered electric work machine.

10. A power system according to any of claims 7 to 9, further comprising a battery module configured to supply DC power to the DC backbone power bus; and a charging cable, the off-board power supply configured to supply electrical power to the battery module via the charging cable.

11. A power system according to claim 10, further comprising a charging input connected to the DC backbone power bus, wherein the charging cable is configured to connect to the charging input in order to supply DC power to battery module via the DC backbone power bus.

12. A power system according to claim 10 or claim 11 , wherein the controller is configured to: receive an instantaneous power demand for the motor; determine a moving average power demand for the motor based on the power supplied to the motor over a preceding predetermined time period;15637015v1control the AC to DC converter to draw AC power from the input based on the moving average power demand; and control the AC to DC converter to supply power from the electric work machine input to the battery module, or control DC to AC converter to supply power from the battery module to the motor, based on a difference between the moving average power demand and the instantaneous electrical power demand for the motor.

13. A power system according to claim 12, wherein where the instantaneous power demand is lower than the moving average power demand, the controller is configured to cause the battery module to draw DC power from the AC to DC converter via the DC backbone power bus.

14. A power system according to any of claims 12 to 13, wherein the controller is configured to: obtain a state of charge of the battery module, wherein the controller is configured control the AC to DC converter to draw AC power from the input based on the moving average power demand and the state of charge of the battery module.

15. A power system according to claim 14, wherein the controller is configured to control the AC to DC converter to draw AC power from the input based on the moving average power demand and the state of charge of the battery module such that the state of charge of the battery module is above a charge threshold.

16. A power system according to claim 14 or claim 15, wherein the controller is controller is configured to control the AC to DC converter to draw AC power from the input based on the moving average power demand and a difference between the state of charge of the battery module and a target state of charge of the battery module.

17. A power system according to claim 16, wherein the controller is controller is configured to control the AC to DC converter to draw AC power from the input such that a difference between the state of charge of the battery module and the target state of charge is no greater than a difference threshold.

18. A power system according to any of claims 14 to 17, wherein upon obtaining a charging signal from a user, the controller is configured to control the AC to DC converter to draw AC power from the input based on the moving average power demand and the state of charge for the battery module such that the state of charge of the battery module is above a charge target state of charge after a predetermined charging time period.

19. A tethered electric work machine comprising: a power system according to any of claims 1 to 18.

20. A tethered electric work machine according to claim 19, wherein the tethered electric work machine comprises an upper body and a lower body, the upper body being configured to rotate relative to the lower body; wherein the lower body comprises the electric work machine input configured to be connected to the tether21. A tethered electric work machine according to claim 20, wherein the lower body comprises a slip ring configured to connect the electric work machine input to the AC to DC converter, wherein the AC to DC converter is provided on the upper body of the electric work machine, wherein optionally a battery module of the tethered electric work machine is provided on the upper body of tethered electric work machine.15637015v1

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