FIELD OF THE INVENTION

[0001 ] The present invention relates to a power supply.

[0002] The invention has been developed primarily as a power supply for use in a CubeSat satellite and will be described herein with reference to that application. However, the invention is not limited to that particular field of use and is also suitable for many other uses, including as a power supply for other standalone devices or as a power supply for wearable systems such as a soldier system, space suit or health monitoring system or as a power supply relying upon intermittent energy sources.

BACKGROUND OF THE INVENTION

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

[0004] Electrically powered standalone devices, such as CubeSat satellites, typically include a power supply system capable of supplying power to the electrical load presented by the satellite. Such a power supply system usually includes an array of solar panels to generate in combination a supply current and a power supply for drawing the supply current and converting it into a load current to supply to the load. The power supply typically includes a battery and a battery charging regulator. The battery charging regulator receives the supply current to generate a charging current for the battery which, in turn, acts as an electrochemical store of energy that is drawn upon to generate the load current.

[0005] All of the above components present performance and risk issues for the satellite and can compromise its operation and shorten its operational lifetime. For example, a common cause of CubeSat satellite failure arises from a failure of the battery in the power supply. Although batteries are able to be designed with a high energy density and can be well suitable to supplying loads of the type presented by a satellite, the hostile and harsh environmental conditions encountered by satellites make many battery types unsuitable or compromised for this application. [0006] Moreover, it is usual for each of the solar panels in the array to have different orientations to accommodate a range of orientations of the satellite without completely compromising the generation of the supply current by the array. This results in different ones of the panels generating, at different times to each other, different voltages. In response to this, it is known for the individual panels to be connected to the battery charging regulator via respective diodes to prevent an underperforming panel becoming an unintentional energy sink. However, as the diode for an underperforming panel is held in a reverse bias configuration, that underperforming panel or panels will not at all contribute to the charging of the battery when in that state.

[0007] Accordingly, there is a need in the art to provide an improved power supply.

SUMMARY OF THE INVENTION

[0008] It is an object of the preferred embodiments 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 power supply for a standalone device having a common power rail, the power supply including a plurality of power supply units each including:

an input for receiving source energy from an energy source; an output for providing output energy to the common power rail; an energy storage device; and a control unit for selectively allowing: the source energy to be stored in the energy storage device; and the output energy to be drawn from the energy storage device.

[00010] In some embodiments the power source, includes a plurality of sub- sources.

[00011 ] In some embodiments, each of the plurality of sub-sources is connected, and provides source energy, to a corresponding input.

[00012] In some embodiments a subset of the plurality of sub-sources include photovoltaic panels. [00013] In some embodiments, each sub-source includes a photovoltaic panel.

[00014] In some embodiments each photovoltaic panel includes at least one photovoltaic cell.

[00015] In some embodiments, at least a subset of the energy storage devices each include a rechargeable direct current (DC) energy storage unit.

[00016] In some embodiments the energy storage device includes a rechargeable direct current (DC) energy storage unit.

[00017] In some embodiments, the energy storage unit includes a battery.

[00018] In some embodiments the battery is a lithium-polymer battery.

[00019] In some embodiments, the battery is a single cell lithium-polymer battery.

[00020] In some embodiments the energy storage device includes a supercapacitor.

[00021 ] In some embodiments, at least a subset of the energy storage devices include a vibration energy harvesting device.

[00022] In some embodiments at least a subset of the energy storage devices preferably include a radio isotope thermal generator.

[00023] In some embodiments, at least a subset of the energy storage devices include a thermoelectric generation device.

[00024] In some embodiments the standalone device is selected from the group including: a space satellite; a space craft other than a satellite; an aircraft; a drone; a watercraft; an earthbound vehicle; and a wearable system.

[00025] In some embodiments, the each input receives the source energy at a respective first DC voltage and the respective control units draw the output energy such that it is provided to the common rail at a second DC voltage.

[00026] In some embodiments the first DC voltages are different to the second DC voltage.

[00027] In some embodiments, in operation, the first DC voltages are always different to the second DC voltage. [00028] In some embodiments the converter units includes a boost function and the first DC voltages are lower than the second DC voltage.

[00029] In some embodiments the power supply includes a controller for controlling at least one of the control units.

[00030] In some embodiments the controller preferably controls all of the control units.

[00031 ] In some embodiments the controller individually controls all of the control units.

[00032] In some embodiments the controller controls at least one of the control units to regulate the output energy supplied to the common rail.

[00033] In some embodiments, the controller controls at least one of the control units to regulate the output energy supplied to the common rail by the respective power supply units.

[00034] In some embodiments, the controller controls at least one of the control units by selectively connecting and disconnecting the respective outputs to and from the common rail.

[00035] In other embodiments, the controller controls at least one of the control units by selectively activating and deactivating the respective control units.

[00036] In some embodiments, the plurality of sub-sources include at least two different power sources.

[00037] In one embodiment, at least one of the control units obtains operational data for the respective power supply unit.

[00038] In some embodiments, the operational data is derived from one or more characteristics of the source energy and/or the output energy.

[00039] In some embodiments, at least one of the control units selectively transmits the operational data.

[00040] In one embodiment the control unit transmits the operational data wirelessly to a base station.

[00041 ] In some embodiments the controller includes the base station.

[00042] In one embodiment the power supply units are modular. [00043] In some embodiments the energy source is intermittent.

[00044] In one embodiment, the energy source includes a plurality of sub-sources, all of which are intermittent.

[00045] In one embodiment each input is configured to receive source energy from a respective sub-source.

[00046] According to a further aspect of the invention there is provided a power supply for supplying electrical energy to a load, the power supply including a plurality of power supply units, wherein each unit includes:

an input for connecting to and drawing energy from an intermittent energy source; an output for connecting to the load; an energy storage device; a charging unit for selectively connecting the energy storage device to the input to draw energy from the energy source; and a switching unit for selectively connecting the energy storage device to the output to supply electrical energy to the load.

[00047] In some embodiments the energy source includes a plurality of sub- sources and the input for each unit is connected with a respective one of the sub sources

BRIEF DESCRIPTION OF THE DRAWINGS

[00048] A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a modular power supply;

Figure 2 is a schematic representation of a modular power supply;

Figure 3 is a schematic representation of a single modular power supply unit;

Figure 4 is a schematic representation of a modular power supply; Figure 5 is a schematic representation of a modular power supply;

Figure 6 is a perspective view of a front face of a power generator; and

Figure 7 is a perspective view of a rear face of a power generator.

PREFERRED EMBODIMENT OF THE INVENTION

[00049] Referring initially to Fig. 1 , there is illustrated a modular power supply 1 for a standalone device in the form of a CubeSat satellite 2. Power supply 1 has a common 28 Volt DC power rail 3 for connecting to an electrical load 4 presented by the relevant components of satellite 2. Supply 1 also includes a plurality of modular power supply units 5 that operate in parallel. Units 5 include respective DC inputs 6 for receiving source energy directly from an energy source in the form of respective independent photovoltaic panels 7. An output 9 of each of units 5 provides output energy to rail 3.

[00050] In this embodiment, supply 1 includes eight separate units 5 that receive the source energy from respective panels 7 that are located on the exterior of satellite 2 at different locations and having differing orientations. In other embodiments a different number of units 5 are included. Preferably, the number of units 5 corresponds with the number of panels 7 to provide maximum redundancy and adequate supply of the source energy. However, in further embodiments the number of units 5 exceeds the number of panels 7. In still further embodiments, the number of units 5 is less than the number of panels 7.

[00051 ] Units 5 are modular in that they are substantially identical and swappable with each other. In further embodiments use is made of a plurality of power supply units that are not modular, or which include a subset which is modular and a subset which is not.

[00052] In another embodiment, such as that illustrated in Figure 2, where corresponding features are denoted by corresponding reference numerals, a power supply 13 further includes a common battery bus 11 which can be used for selectively powering the most critical functions of the system when total functionality is not required. This may occur when operating in a standby mode, when available energy is low, for isolating critical functionality from cascading failures in the rest of the system or for battery current sharing and charging between units 5. [00053] One of the units 5 of Figure 2 is illustrated in more detail in Figure 3. In particular, unit 5 includes an output 12 for electrically connecting with bus 1 1 . Unit 5 also includes an energy storage device, in the form of a single cell 4.2 Volt 1000 mAh lithium battery 15. A control unit 17, including a charging controller 18, selectively allows the source energy received from the relevant ones of panels 7 to be stored in battery 15. The output energy, which is supplied to rail 3, is then drawn from battery 15 via a boost converter unit 19 which receives energy/power from battery 15 at a first DC voltage VBatt - typically in the range of 3.0 Volts to 4.2 Volts - and delivers it to rail 3 at a second DC voltage VBUS which, in this embodiment, is highly regulated at 28 Volts. It will be appreciated that VBUS is highly regulated to 28 V DC to provide stability of operation for load 4.

[00054] In other embodiments VBUS is provided at a voltage other than 28 Volts. Moreover, in further embodiments, each of units 5 has a plurality of outputs 9 for providing a corresponding plurality of regulated voltages of different values to respective power rails. In still further embodiments, such as those where unit 5 is optimised for operational efficiency, VBUS is unregulated.

[00055] In other embodiments converter 19 is substituted with another type of converter, for example a buck converter or a boost/buck converter to accommodate different operational voltages at input 6 and rail 3.

[00056] Unit 5 also includes a heater 20 that draws energy from battery 15 for maintaining battery 15 in an operable temperature range should the ambient temperature drop to sufficiently low levels.

[00057] Unit 5 also includes a protection system 21 which, in this embodiment, comprises two resettable fuses 23 and 24 for outputs 9 and 12 respectively. In other embodiments alternative or additional components are included in system 21 to provide different or additional protection functions. For example, in some embodiments, system 21 includes a protection device (not shown) at input 6 and/or between battery 15 and either or both of unit 19 and heater 20.

[00058] In other embodiments battery 15 is substituted with an alternative energy storage device or combination of energy storage devices. For example, in one such embodiment use is made of a bank of tantalum capacitors. In another embodiment, use is made of one or more supercapacitors, while in a further embodiment use is made of a hybrid energy storage device. In further embodiments use is made of an electrochemical storage device other than that based upon lithium polymer chemistry and with a different number of cells. It will be appreciated that combinations of such devices are also able to be used to provide the required energy and power density dictated by the requirements of load 4.

[00059] It will be appreciated that the architecture of power supply 5 is such as to offer redundancy between the supply of the source energy and the output energy. That is, there are a number of paths between the generation of the source energy and the supply of the output energy to the common rail 3, each of which includes an energy storage device such as battery 15.

[00060] Figure 4 illustrates a further embodiment of a modular power supply, being power supply 29, where corresponding features are denoted by corresponding reference numerals. In this embodiment, supply 29 includes a plurality of power supply units 30 which provide base-level functionality similar to that of units 5. Units 30 each include a monitoring and control unit (discussed below) for generating data signals in the form of serial data. A controller 31 receives the serial data from units 30 via serial data links 32 (represented by broken lines). In this embodiment the serial data is indicative of: operational data from individual units 30 relating to the energy being received from the respective power sources (not shown); the energy stored in the energy storage device included in each unit 30; and the power delivered to common DC rail 3 for consumption by load 4. In other embodiments different or additional data is provided to controller 31. Moreover, in further embodiments, links 32 transmit the data other than as a serial signal.

[00061 ] Controller 31 is further configured to transmit control signals to units 30 to allow the independent control of those units to conform to an optimised operation of supply 29. These control signals are able to be communicated via links 32 or by other communications paths. For example, in this specific embodiment one of the control signals is a power toggle signal that is transmitted through a separate communications link 35 to enable or disable individual units 30. When a given unit 30 is enabled, it supplies power to rail 3 and when a given unit 30 is disabled it does not supply power to rail 3. In this embodiment, controller 31 is responsive to the operational data received by links 32 for determining if the power toggle signal is required for each unit 30. [00062] In the Figure 4 embodiment, links 32 and 35 are wired communications links. However, in other embodiments, either or both of links 32 and 35 are wireless links. Moreover, it will be appreciated that links 32 and 35 are, in some embodiments, the same, in that one link provides for two-way communications between controller 31 and unit 30. It will also be appreciated that controller 31 , in some embodiments, communicates with different units 30 via different links. For example, in some embodiments, units 30 and controller 31 are in a daisy chained network.

[00063] One of the units 30 of Figure 4 is illustrated in more detail in Figure 5. In particular, control unit 17 of unit 30 includes a monitoring and control unit 37 and an output switch 38. Switch 38 is configured to receive the power toggle signal from controller 31 through link 35 and to selectively connect battery 15 to rail 3 based on the power toggle signal. It will be appreciated that the power toggle signal allows controller 31 to remotely enable or disable individual units 30 independently of each other. In another embodiment, the power toggle signal is not independently addressable to individual units 30. This function is of greater utility, for example, for those satellites having a plurality of power supplies according to embodiments of the invention. That is, each of the power supplies is able to be toggled independently between an enabled and disabled state. Preferentially, controller 31 cooperates with all the power supplies to allow this functionality. However, in other embodiments, each power supply includes its own controller 31. In some embodiments use is made of a master controller (not shown) for communicating with the individual controllers 31 for providing overall control of the operation of the individual power supplies.

[00064] Unit 37 is configured to collect operational data from unit 30 by monitoring the electrical energy flowing into input 6, into battery 15 and out of unit 19 via monitoring lines 39, 40 and 41 respectively. Unit 37 is further configured to communicate the operational data to controller 31 via a serial data link 32. It will be appreciated that the operational data allows controller 31 to determine the energy being received from the respective power sources (not shown); the energy stored in each unit 30; and the power delivered to common DC rail 3 by each unit 30. It will also be appreciated that in embodiments of power supply 29 where more than one storage technology is used for storage units 15, that controllers 37 and controller 31 can be configured to work cooperatively to maximise the cycle life of each unit 5 for the particular storage technology of that unit 5. This can be achieved whilst still providing energy on bus 3 by regulating the flow of current into and out of each unit 5 of supply 29 to provide optimal charge current, optimal end of charge voltage, optimal discharge current and optimal depth of discharge for each individual storage unit 15 of units 5. For example, one embodiment contains both supercapacitors and Lithium-Ion batteries as energy storage devices.

[00065] Unit 37 is further configured to operate heater 16 to maintain the battery temperature within a specified operational range by cycling the operational state of the heater 16. By cycling the operation state of the heater rather than operating the heater constantly, minimal power is used to control the temperature within a small, specific range, optimised for best performance of the battery.

[00066] A further embodiment relating to a power generator unit 42 is illustrated in Figures 6 and 7. Unit 42 is generally prismatic in form and includes a substantially planar front face 43 to which a solar panel 44 is mounted. Panel 44 includes an array of individual photovoltaic (PV) cells, which in this embodiment is exemplarily illustrated as being a 3 x 4 array of cells grouped in connected triplets that provide four separate and independent supplies of source energy. In other embodiments use is made of a different number of arrays, or cells within an array. In other embodiments the cells may be angled to increase density and maximise the energy collection area.

[00067] Unit 42 also includes a substantially planar rear face 45 upon which is mounted a modular power supply 46 having four power supply units (not shown) for receiving the source energy from the respective triplets referred to above. Figure 6 is a perspective view of the front side of generator 42 illustrating panel 44. Figure 7 provides a perspective view of the rear of generator 42 where supply 46 is mounted. Power supply 46 is able in other embodiments to represent any one of power supplies 1 , 13 and 29. It will be appreciated that generator 42 is capable of functioning as a standalone power generator for mounting to any platform, such as a CubeSat satellite. Furthermore, in some embodiments the front face 43 and rear face 45 represent opposed faces of a single printed circuit board (PCB) such that generator 42 is produced as a unitary device.

[00068] In the above embodiments the power supplies receive the source energy as direct current (DC) electrical energy and store and provide energy to load 4 also in a DC form. This is done to minimise conversion losses and, all else being equal, reduce the weight and size of the circuitry required to construct the power supply. However, in other embodiments where the design parameters require different optimisation paths, other forms of energy are used. More particularly, in some embodiments, units 5 and 30 are configured to convert between DC and AC forms of electrical energy.

[00069] The power source is illustrated above as an array of panels 7. That is, the source includes a plurality of sub-sources, wherein each of the sub-sources is connected to a corresponding input 6 of a respective unit 5 or 30. Although the exemplary embodiments described above utilise solar panels as the sub-sources, it will be appreciated that any suitable power source is able to be used, and not all the sub- sources need be the same. Other embodiments include different power sources and sub-sources, such as a vibration energy harvesting device, a radio isotope thermal generator, a thermoelectric generation device, a fuel cell, a wave generator, a wind generator and any other device capable of generating electric power. It is also possible that different units 5 or 30 in the same power supply utilise different power sources. This allows the power supplies of the embodiments to be able to generate power from a diverse range of sources.

[00070] Remote electronic devices such as CubeSat satellites conventionally use solar panels to charge a single battery which is used to power the onboard electronics. The inventor of the present application has identified power supply failure as a common cause of satellite failure, often as a result of battery failure. The power supplies of the above embodiments do not suffer from the prior art problem of a single point of failure and therefore provide a far more robust and reliable power supply.

[00071 ] The power supplies of the above embodiments are able to be designed to include a predetermined degree of redundancy, allowing for the overall reliability of the system to be finetuned and optimised for the given application. That is, if one or more of the batteries fails, the system as a whole will still be able to store and supply a usable amount of power onto bus 11 and rail 3, allowing the electronics of the satellite or other platform to continue functioning. These power supplies are therefore far more tolerant to component failure when compared with the conventional topology and hence allow for increased operational lifetime of the remote electronic devices which they power. [00072] In another embodiment (not shown) a mobile platform includes two or more such power supplies in combination to supply the required power. The two or more supplies, in some embodiments, function independently of each other, while in other embodiments the power supplies are centrally controlled by a controller analogous to the controller 31 of supply 29. The latter also includes a controller that allows, at least during one mode of operation, the independent operation of the power supplies.

[00073] By utilising a plurality of power supplies in combination, a greater degree of redundancy is able to be achieved in the overall power supply for the platform, thereby further increasing the tolerance to individual component failure.

[00074] In another embodiment, controller 31 of power supply 29 is configured to detect faulty modular units 30 via the operation data received from the respective monitoring and control units 37. In response to the detection of a faulty module 30, controller 31 is configured to switch the power source 7 connected to the faulty module 30 to another module 30 in which no fault has been detected. In this way, the power source 7 will be able to provide power to the supply 29 even though the module to which it was connected has failed. For example, if the battery 15 of a first module 30 fails, such that the first module 30 no longer stores energy, controller 31 will connect a first power source 7 of the first unit 30 to the input 6 of a second unit 30. In this way, energy generated by the first power source 7 will be stored in the battery of the second unit 30 and hence the first power source 7 will still contribute energy to rail 3 and bus 11. It will be appreciated that this embodiment allows for maximum collection and storage of energy in the event that a subset of the modular units 30 have failed. This feature increases the reliability of power supply 29.

[00075] An additional benefit of the power supplies of the above embodiments is that significant increases in efficiency are able to be realised over conventional power supply topologies. In conventional topologies, the solar panels in the array are connected together to provide a single source of electrical energy to a charging controller. However, this topology requires the use of isolation diodes, or some other combination of semiconductors ensuring unidirectional current flow, for each panel to prevent those panels from becoming energy sinks when not in operation or when a sufficient voltage difference between the individual panels exists. That is, the isolation diodes are used to prevent the battery or other solar panels from pushing electric energy into non-operational or low voltage panels. A consequence of this is that if one of the panels is underperforming compared to the others in the array (that is, producing power at a lower voltage), its isolation diode will be in a reverse bias configuration preventing any generated energy from leaving that panel. In this way, the underperforming panel at that time makes no contribution to the overall power generated by the array. By contrast, the power supplies in the above embodiments include a plurality of independent solar panels or solar panel arrays, each connected to a respective power supply unit with a dedicated charging controller 18 and battery 15. As a result, if one of the panels or arrays connected to one of the power supply units is underperforming compared to the rest - for example, if it is partially shaded when the other panels are not - it will still be able to contribute source energy to the power supply. That is, even if there is an isolation diode used on the shaded panel, it will be able to be forward biased even if not operating at its peak voltage. Hence, the shaded panel will be able to provide source energy to the relevant one of the power supply units that it is connected to and allow charging of the respective battery 15 in that unit. Although the charging of that battery 15 will be at a reduced rate compared to the corresponding batteries in those power supply units connected to better performing panels, it is still storing energy from that underperforming solar panel or solar panel array. This presents a clear improvement in efficiency compared to the traditional topology which would not be able to store the energy generated by the underperforming panel. This is of great benefit in a CubeSat satellite for example, where at given times some of the solar panels will be in full sunlight, while others are only receiving light scattered from the Earth due to its albedo. The panels receiving only the scattered light will be underperforming and producing power at a lower voltage compared to the panels in full sunlight. Using the conventional topology these underperforming, low voltage panels will make negligible or no contribution to the overall energy stored. In the modular power supply of the above embodiments, however, the panels receiving the scattered light will still contribute to the overall energy stored.

[00076] A further consequence of this is that the power supply as a whole, when supplied by solar panels, is less affected by orientation. As mentioned above, the efficiency of conventional solar array power supplies suffer when light of differing intensity falls on different parts of the array. Such a situation frequently occurs on land- based moving platforms or vehicles which constantly change their orientation and position with respect to the sun and other environmental objects (which may reflect or block light). However, as described above with regard to receiving light from the earth’s albedo, the power supply 1 , 13 or 29 is far less sensitive to receiving varied light intensity across the solar panel array. Accordingly, the power supply as a whole is less sensitive to changes in orientation and hence better suited to mobile applications.

[00077] Thus, although the embodiments have been described primarily with reference to mobile platforms such as CubeSat satellites it will be appreciated that other embodiments are suitable for a wide range of remote electronic devices and mobile platforms which cannot be easily serviced or which are specifically designed to have low maintenance requirements. Examples of such applications include manned boats or other vehicles in remote locations, autonomous vehicles performing surveys in remote areas such as autonomous boats or“rover” type devices or remote weather or communication stations.

[00078] Furthermore, in the conventional topology, the solar panel array is connected to a charging controller which includes a maximum power point (MPPT) tracker. The MPPT holds the solar panel array at or near its maximum power point voltage allowing for an efficient transfer of power from the array. It is an important distinction however that the MPPT will hold the array at the maximum power point for the array, which is not necessarily the maximum power point of each of the individual panels in that array. Therefore it is likely that the individual panels in the array will not be operating at their maximum power point and hence not delivering power efficiently. In the power supplies of the above embodiments, however, each power supply unit includes a dedicated charging controller 18 which is able to utilise a maximum power point for the panel or panel array connected to that power supply unit. By utilising the appropriate maximum power point, all of the solar panels are able to be operated at or close to their maximum power point voltage thereby further increasing efficiency of the overall system in comparison to conventional topologies.

[00079] Thus, by utilising a plurality of energy storage devices and charging controllers, the power supply described in the above embodiments is able to achieve significant increases in the overall reliability and efficiency of the power system. [00080] In some embodiments, power supply 29 is used as a communication relay. In these embodiments, communication signals are able to be transmitted to the power supply via modulated optical signals such as a modulated laser beam. The modulated laser beam is directed toward a receiving solar panel connected to the power supply, causing a corresponding modulated signal in the electric power received at input 6 of unit 30 connected to the receiving solar panel. Monitoring and control unit 37 detects the modulated electrical signal via monitoring line 39. The detected signal is then relayed onward toward a target location. The signal is able to be first transmitted to system controller 31 before being transmitted to a target location or monitoring and control unit 37 is able to be configured to directly transmit to the target location. In either instance it will be appreciated that power supply 29 is able to be used as a target for communications, or as a communication relay.

[00081 ] Although the invention has been described with reference to a specific example, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.