GB2471586A

GB2471586A - Solar cell power management system

Info

Publication number: GB2471586A
Application number: GB1014484A
Authority: GB
Inventors: Anthony John Howard
Original assignee: KENT HOLDINGS INTERNAT Ltd
Current assignee: KENT HOLDINGS INTERNAT Ltd
Priority date: 2008-04-30
Filing date: 2009-04-30
Publication date: 2011-01-05
Also published as: GB201014485D0; GB2471587B; GB201014484D0; GB2471587A

Abstract

A power management system for use in the storage of energy from a solar collector 30 includes an intermediate energy store 32, such as an inductor, to store energy generated by the solar collector 30. A first 44 and second 46 switch regulate the power to the system output 28. Secondary control is applied to the second switch 46 to allow current to flow to the output 28 from the intermediate energy store 32, whilst also limiting the voltage drop and preventing the reverse flow of current into the intermediate energy store 32.

Description

Power Management System

Field of the Invention

In one preferred form, the present invention relates to a power management system for use with a solar power transducer. The power management system advantageously controls the storage of power generated by a solar collector and which supplies current to a load. Further methods and systems are disclosed.

Background to the Invention

The desire to decrease and ultimately eliminate the dependence of society on fossil fuels has stimulated research into clean and renewable ways to produce electricity for io the global marketplace. Solar power has become a viable option because it is a clean form of energy production and there is a potentially limitless supply of solar radiation.

To that end, it is estimated that the solar energy flux from the sun is approximately 2.7 megawatt-hours per square meter per year in certain parts of the world. With this amount of free and clean energy available, together with a desire to reduce the world's is dependence on fossil fuels, solar power production is being reviewed as an important means to help meet energy consumption demands particularly in third world countries.

Solar cells produce direct current electricity from the sun's rays, which can be used to power equipment or recharge a battery. When more power is required than a single solar cell can deliver, solar cells are generally grouped together to form photovoltaic modules and solar panels that may in turn be arranged into larger arrays. Solar arrays have been used in remote areas as a source of power for applications such as roadside emergency telephones, remote sensing and cathodic protection of pipelines. As manufacturing costs decline, the usage of solar cell arrays is expected to increase and to expand to grid-connected electricity generation.

Solar cells are basically current limited sources where the output voltage of the solar cells drops significantly if the current drawn from the solar cells increases. A drop in the output voltage can be problematic especially if the voltage drop causes equipment being powered by the solar cells to stop functioning. In a worst case scenario, this may cause damage to the equipment or a brown out' condition similar to a traditional power grid scenario. The current drawn may also marginally exceed the efficient supply current from the solar cells. This has the disadvantage of causing the solar cells to operate at less than an ideal efficiency.

Solar cell systems must also protect the cells and other components used in the solar s cell system. For this reason, bypass diodes are sometimes used to prevent damaging electrical currents which, if present, are known to heat and damage solar cells.

Referring to Figure 1 there is shown a prior art solar cell system 10'. The solar cell system 10 includes three solar elements 12 that are provided in series in a solar array 14. In the solar array 14 a bypass diode 16 is connected in parallel with each solar io element 12. Each bypass diode 16 is provided to allow current to bypass each corresponding solar element 12 in the event that that solar element produces less power than the other solar elements 12 in the array 14. This may occur when a solar element 12 is exposed to a shaded condition or is defective in some way. By allowing the flow of current past a solar element, the power from the other elements 12 in the is array does not heat the solar element up, but rather flows through the bypass diode 16 instead. In this manner, the bypass diode 16 operates to protect the solar elements 12.

In order to prevent the reverse flow of current, solar cell systems use a reverse block diode such as a diode 18 in Figure 1 that protects the array 14. Figure 2 shows a solar power system 24 having a reverse block diode 20 that protects a parallel arrangement of cells 22.

It would be generally advantageous to provide a solar power system that is relatively simple and compact, while at the same time being capable of efficient energy collection and delivery, with a high temperature capability, and the ability to store collected energy so that electrical energy production is relatively optimized. It is against this background and the problems and difficulties associated therewith that the present invention has been developed.

It is to be recognised that any material discussed in the present specification is intended to explain the context of the invention. It is not to be taken as an admission that the material formed part of the prior art base or relevant general knowledge in any particular country or region.

Summary of the Invention

Described herein is a solar power transducer comprising: at least one solar cell, an intermediate energy store, and a controller, wherein the controller provides a first switch and a second switch for regulating the transfer of energy to and from the intermediate energy store such that the intermediate energy store stores energy generated by the at least one solar cell and the controller recovers energyfrom the intermediate energy store and supplies current to an output of the transducer, wherein the controller includes a switching arrangement for applying secondary control to the second switch of the controller to allow the current to flow to the output, whilst io limiting the voltage drop, and for substantially preventing the reverse flow of current from the output towards the intermediate energy store.

Preferably, the first switch comprises a first MOSFET disposed between the at least one solar cell and the intermediate energy store and the second switch comprises a second MOSFET disposed between the intermediate energy store and the output, the is switching arrangement being adapted to monitor the voltage across the second MOSFET between the intermediate energy store and the output and, on the basis of the monitored voltage, operate the second MOSFET to substantially prevent the reverse flow of current from the output.

The second MOSFET preferably comprises the the only element between the intermediate energy store and the output.

The switching arrangement is more preferably adapted to switch between a first state and a second state wherein, in the first state, the switching arrangement is configured to allow the flow of current from the intermediate energy store to the output, with a voltage drop of less than O.2V and, wherein, in the second state, the switching arrangement is configured to substantially prevent the reverse flow of current towards the intermediate energy store. In one aspect of the invention, the voltage drop is that of a single mosfet.

Preferably further, there is provided a first path between a positive terminal of the at least one solar cell and a negative terminal of the output. The intermediate energy store is preferably connected across the first path and a second path, wherein the second path extends between a negative terminal of the at least one solar cell and a positive terminal of the output.

In another arrangement, the controller provides a switch regulator with the first switch comprising a main switch, the second switch comprising a synchronous switch and s the switching arrangement of the controller includes a voltage comparator for measuring the voltage across the synchronous switch, further wherein the switching arrangement is adapted to apply secondary control to the synchronous switch to provide an extended synchronous system.

In a preferred embodiment, the comparator is configured to measure the voltage io differential across the synchronous switch with the controller being configured to apply the secondarycontrol by switching the switch on when the differential is of a desired polarity and switching the switch off when the differential is of an undesired polarity. Preferably further, the controller is adapted to proactively maintain the output voltage by varying the duty cycle of the main switch and the synchronous is switch, with the duty cycle being determined solely from the output voltage. The synchronous switch most preferably comprises a mosfet with the comparator being adapted to directly drive the mosfet gate.

In a first aspect of preferred embodiments herein described, there is provided a power management system for use in the storage of energy from a solar collector, the system comprising: an intermediate energy store for storing energy generated by the solar collector and a first switch and a second switch for regulating the power delivered to an output of the power management system wherein the power management system includes a switching arrangement for applying secondary control to the second switch to allow current to flow to the output, as a result of the energy stored in the intermediate energy store, whilst limiting the voltage drop, and for preventing the reverse flow of current from the output towards the intermediate energy store.

Also herein described is a power management system for a solar collector, the system comprising: an input, an output and an intermediate energy store, wherein the intermediate energy store forms part of a voltage boost regulator having a main switch and a synchronous rectifier mosfet with the intermediate energy store being adapted to store energy as a result of the current generated by the solar collector and being adapted to supply the current to the output, wherein the power management system includes a switching arrangement for applying secondary control to the synchronous rectifier mosfet for allowing current generated by the intermediate energy store to flow to the output, whilst limiting the voltage drop therebetween, and s for substantially preventing the reverse flow of current from the output back towards the intermediate energy store.

Further herein described is a power management system for a solar collector, the system comprising: a controller in the form of a voltage boost switching regulator, wherein the controller is adapted to monitor the voltage of an output of the power io management system and to maintain the voltage of the output by varying the duty cycle of the voltage boost switching regulator in accordance with the monitored voltage.

Yet further herein described is a method of managing the transfer of energy from a solar collector to a load, the method comprising: switching a first switch and a second is switch to regulate storing energy in an intermediate energy store as a result of current generated by the solar collector and to allow current to flow to the load, as a result of the energy stored in the intermediate energy store; and applying secondary control of the second switch to substantially prevent the load from supplying current in a direction back towards the intermediate energy store, wherein allowing current to flow to the load includes limiting the voltage drop between the intermediate energy store and the load.

Still further herein described is a method of managing the transfer of energy from a solar collector to a load comprising: using a switching arrangement to store energy generated by the solar collector in an intermediate energy storage device and to recover energy from the storage device in driving a current through the load; monitoring the voltage of the storage device; and monitoring the voltage of the load to change the duty cycle of two switches in the switching arrangement.

The at least one solar cell may comprise a photovoltaic wafer. The wafer may be included substantially within a solid state electronic supporting insolation circuit. The supporting circuit The at least one solar cell may comprise a photovoltaic wafer. The wafer may be included substantially within a solid state electronic supporting insolation circuit. The supporting circuit preferably comprises a reverse inverting topology switching regulator with a microprocessor providing for intelligent backflow prevention across a s single mosfet. In such an arrangement, the voltage across the mosfet switch is preferably monitored and boosted voltage output provided, while at the same time achieving a substantial reduction in the power consumed in operating the solar power transducer.

In preferred embodiments, power handling and voltage management takes an io unspecified negative voltage input and inverts it to a desired positive voltage output, with the output voltage being highly regulated to the design set level. This not only provides the ability to specify an output voltage, but substantially negates the inherent problem of the substrate of the wafer being electrically positive. This is considered to substantially obviate the need for complete electrical isolation of preferred transducers is from the adjacent components of a system in which the transducers may be installed and is considered to substantially eliminate the potential for electrical short-circuiting against a negative earth contact within, or external to, the machine or adjacent cells.

In one preferred embodiment, a switching regulator preferably comprises two mosfet switches comprising a main switch mosfet and a synchronous rectifier mosfet, substantially controlled by a central integrated circuit; one or more inductors connected in parallel to archive suitable power handling; input and output smoothing capacitors; and a feedback network based on a difference amplifier. The switching regulator cycle preferably has two distinct phases, wherein during the first phase the main switch mosfet is preferably conducting while in the second phase the mains switch mosfet is preferably switched off. This allows the negative source voltage to substantially flow into the inductor storing energy in the surrounding magnetic flux.

In the second phase, the synchronous rectifier mosfet is preferably switched on while the main switch mosfet is preferably switched off This allows the stored energy in the inductor to substantially flow out in the reverse direction to which the energy went in, thereby causing a positive output voltage to substantially flow into the output capacitor. This output capacitor is preferably directly connected to the output terminals, making the energy in the capacitor available to power the user's load.

The synchronous rectifier mosfet is preferably under a secondary control to ensure that it does not conduct until the fly-back voltage in the inductor is higher than the voltage already present at the output capacitor, in such a way that a backwards flow from the output terminal back into the inductor is not possible. With this s secondary control, the inclusion in the circuit of an output back-flow prevention diode is obviated, thereby achieving considerable power savings over a conventional solar cell design. In conjunction with the switching regulator, the circuitry preferably includes a central microprocessor which monitors various sensors for light levels around the solar cell for tracking purposes, monitoring thermal conditions and power io input and output statistics.

A reverse block diode in solar power transducer circuit allows for a regulator or DC-DC converter to transfer the power available from a solar cell source, to a load. As discussed, in preferred embodiments, a synchronous rectifier-based design may be employed with a switching arrangement preventing the reverse flow of current from is the output by monitoring the voltage between the intermediate energy store and output of the transducer. In these arrangements, the voltage is preferably monitored across a single high speed switching device in the form of a mosfet which is controlled at its gate.

In this manner, the switching arrangement preferably substantially prevents reverse current from damaging the cell during periods of low power production, such as during cloud cover or at night. Solar power transducers made in accordance with preferred embodiments advantageously provide a significant power improvement, whereby during current flow to the load, a reverse block diode does not dissipate power proportional to a substantial diode voltage drop, that is relatively fixed, and typically in the range of O.3V to O.6V. At high current levels in particular this equates to considerable continuous power loss. In the preferred embodiments, the voltage drop is limited to the voltage drop of a single mosfet having a relatively small internal resistance, while still substantially preventing the risk of a reverse current flow damaging the solar cell.

The switching arrangement is preferably not tuned specifically to a particular cell output. In this manner having to provide an error amplifier to monitor the cell output is obviated. Such an error amplifier is considered to add complexity to the circuit, and to do little to improve the system efficiency. Furthermore, this could mean extensive adjustments or an inability to adjust to cell manufacturing tolerances.

The micro-solar insolation circuit described in US 6,657,419 to Roberts provides an example of such a circuit where the duty cycle of the regulator is controlled by an error-amplifier that is referenced to the cell voltage. In comparison, preferred embodiments described herein are considered to maintain a desired output voltage over a much wider range of insolation conditions with the output voltage being regulated to a stable defined level, on account of the feedback being referenced to the output voltage io In comparison to the solar power transducers of the form of the micro-solar insolation circuit described in U5 6,657,419 and conventional systems (in general), preferred embodiments described herein are considered to have improved characteristics where the voltage drop between the intermediate energy store and the output is substantially limited.

is With the surprising and advantageous use of so lid state electronics and multi-junction wafer technology, preferred embodiments can be used in such a manner that concentrated light can be used more efficiently than traditional systems to generate electrical power. Advantageously, preferred embodiments described herein can utilize marginal gain from a single wafer in power output, rather than allowing any wafer to contribute to a marginal loss. This is achieved using traditional electronic components including microcontrollers that operate switching transistors and inductors to provide an advantageous voltage boosting and/or inverting switching regulator topology.

Typical wafer manufacturing methods produce cells with the reverse face as the positive electrode. A positive earth is created where a positive electrode is directly bonded to a heat-sink, as required for thermal management. In the case of an inverting topology, a wafer can preferably be utilized in the absence of an insulating medium without the problems associated with having a positive earth. An inverting topology arrangement, preferably allows the positive electrode to be connected to the system negative earth, and still allow for a conveniently usable voltage output. In the case where a wafer module with integral electrical insulator is used, a non-inverting boost topology is preferably employed to simplify the output voltage feedback loop.

Solar transducers according to preferred embodiments described herein include a lens system to concentrate sunlight and a solar collector comprising a photovoltaic wafer.

Preferably, the wafer is included substantially withinlnear a solid state electronic supporting insolation circuit. Such systems are described in Australian Patent Application No. 2008902129, which is incorporated herein by reference for all purposes.

Preferred embodiments described herein are considered to provide a number of advantageous systems and methods including: (i) Systems and methods considered to be more efficient, with higher outputs and a greater ability to minimize system losses when used either as a single concentrator cell, or a system of cells used together to create larger amounts of electrical current; is (ii) Systems and methods that provide a reversed inverting topology to protect one or more solar collectors by preventing unwanted effects of differentials in the voltage and power characteristics of each wafer; (iii) Systems and methods in which solar power transducers are efficiently and safely arranged in parallel, thereby relatively maximising collection of insolation; (iv) Systems and methods that are balanced and utilize marginal gain from a single wafer in power output, rather than allowing the wafer to contribute to a marginal loss; and (v) Systems and methods that are reduced in the number of electronic parts and complexity as compared to other systems.

It will be recognised that other preferred forms and advantages will be apparent from the specification including the detailed description, drawings and claims provided below.

Brief Description of the Drawings

In order to facilitate a better understanding of the present invention, several preferred embodiments will now be described with reference to the accompanying drawings, in which: Figure 1 is schematic diagram of a solar cell system according to the prior art, with s the system having a plurality of solar elements arranged in series; Figure 2 is schematic diagram of a solar cell system according to the prior art, with the system having a plurality of solar elements arranged in parallel; Figure 3 is schematic circuit diagram of a solar power transducer according to a first preferred embodiment; io Figure 4 is a schematic circuit diagram of a power management system according to a preferred embodiment of the present invention; Figure 5 is block diagram of a method according to a third preferred embodiment; Figure 6a and 6b schematically show a power management system according to a fourth prefelTed embodiment; is Figure 7 is a top view of a physical layout of a transducer according to a fifth preferred embodiment; and Figure 8 is a schematic circuit diagram of a reverse current protector according to a sixth preferred embodiment.

Description of the Preferred Embodiments

Referring to Figure 1, there is shown a prior art solar cell system 10. In the solar cell system 10, three solar elements 12 are arranged in series in a solar array 14.

Comparatively, in Figure 2, there is shown a prior art solar cell system 24 in which three solar elements 22 are arranged in parallel.

Tuning now to Figure 3, there is shown a solar power transducer 26 according to a first preferred embodiment. The solar power transducer 26 advantageously allows for the relatively efficient conversion of solar power energy into electrical energy to power a connected load 28. The solar power transducer 26 is considered to have several advantages, such as improved electrical energy output to the load 28 in comparison to conventional arrangements of the form shown in Figures 1 and 2.

The solar power transducer 26 includes at least one solar cell 30 and an intermediate energy store 32. The intermediate energy store 32 is provided in the form of an inductor 34 for storing energy as a result of current generated by the at least one solar cell 30. As is known, the voltage of an inductor is proportional to the rate of change of the current through the inductor with the inductor being adapted to store

energy in the inductor's magnetic field.

s The solar power transducer 26 includes a controller 36. In this embodiment, the controller 36 includes a first voltage comparator 38 and a second voltage comparator 40. The controller 36 includes a switching arrangement 42 having a first high speed switch 44 and a second high speed switch 46. As shown in Figure 3, the first high speed switch 44 and second high speed switch 46 are provided as a high frequency mosfet switching transistors.

The controller 36 is adapted to switch the switching arrangement 42 to recover energy from the inductor 34 in the form of current. The controller 36 supplies the current to an output 48 of the solar power transducer 26. The output 48 of the solar power transducer 26 is connected to the load 28. The controller 36 controls the switching is arrangement 42 to allow the at least one solar cell 30 to generate a current and for that current to flow though the inductor 34. As the current flows through the inductor 34,

energy is stored in the magnetic field.

In order to recover the energy, the controller 36 is adapted to control the switching arrangement 42 to allow a flow of current generated by inductor 34 to flow to the output 48. Advantageously, the controller 36 is configured to allow the flow of current generated by the inductor 34, whilst substantially limiting the voltage drop between the inductor 34 and the output 48. This is achieved at the same time as the controller 36 being adapted for preventing the back flow of current from the load and the output 48 back towards the intermediate energy store 32.

Preventing the reverse flow current from the output 48 when the voltage of the inductor drops has, in the past, been achieved using a reverse block diode such as the reverse block diode 18 of the solar cell system 10 in Figure 1. In this embodiment, the switching arrangement 42 advantageously obviates the voltage drop that occurs with the use of such a reverse block diode during forward flow in an advantageous manner.

In order to prevent the reverse flow of current from the output 48 back towards the inductor 34, the controller 36 processes several inputs with the use of a processing unit 52. Furthermore, controller 36 is adapted to monitor the voltage between the intermediate energy store 32 and output 48 and control the mosfet 46, to allow and substantially prevent the flow of current therebetween, using the monitored voltage as the sole parameter.

As shown in Figure 3, the first comparator 38 is connected to a first point 54 and a second point 56. The first point 54 is disposed on the drain side of the mosfet 46 and the second point 56 is disposed on source side of the mosfet 46. The first comparator 38 of the controller 36 advantageously monitors both voltages and produces a comparator output 58 indicative of the difference between the two voltages.

The processing unit 52 is coupled to the comparator 38 and the gate 60 of the mosfet 46. Using the comparator output 58 the processing unit 52 determines when to conveniently switch the mosfet 46 between a first state and a second state to is substantially prevent current from adversely flowing back towards the inductor 34.

In the first state, the switching arrangement 42 is configured to allow the flow of current from the inductor 34 to the output 48 with a voltage drop expected to be less than 0.01 V with say a 10 A current in ordinary use. As discussed, in the second state, the switching arrangement 42 is configured for substantially preventing the flow of current back from output 48 towards the inductor 34 potentially causing possible thermal damage to the at least one cell 30.

It would be apparent that, in the first state, well before any backflow, the voltage drop comprises the voltage drop of a single mosfet 46 between the output 48 and the inductor 34. In addition to providing improved efficiency, the solar power transducer 26 uses an advantageously limited number of components.

One of the advantages of the solar power transducer 26 is derived from the resistance of the mosfet 46 being in the order of milli-Ohms. Comparatively, a reverse block diode will have a voltage drop in the order of about 0.3 to 0.6V and thus provide a much higher resistance. In the solar power transducer 26, this equates to a significant power loss from such a reverse block being obviated while the comparator 36 still protects the system from reverse current flow. The efficiency of the solar power transducer 26 is considered to be significantly increased.

The switching arrangement 42 can be considered to be an extended synchronous diode style system that operates as part of a regulator where the presence of a reverse s block diode is advantageously obviated. In the case of the mosfet 46 having an internal on-resistance as low as 1 milli-ohm and an output current supply of 1 OA- 100A, a substantial power saving in the order of about 6W-SOW can be achieved.

As would be apparent, the power loss in a diode is equivalent to W=Vdrop*I; where Vdrop is the relatively fixed voltage drop of the diode; W is power loss in watts; and I io is current flowing though the diode. Conversely, the active power loss in a mosfet transistor switch can be calculated as: W = 1*1* Rds, where Rds is the relatively fixed drain source resistance of the mosfet.

For current levels from 0 up to a predetermined level, mosfet transistors have significantly lower power loss. Thus, in a micro solar insolation circuit such as that is described, a far better power efficiency is provided at power levels typical of available wafers, and with typically available diodes.

Furthermore, it has been found that by having the switching regulator physically close to the wafer, additional system efficiency gains can be surprisingly achieved on account of the voltage output being higher than the cell output. Advantageously, in the present embodiment, those parts of the solar power transducer 26 associated with current flowing from the at least one solar cell 30 are kept physically close to the wafer with those parts such as the connection 59 associated with less current flow, extending therefrom.

Power loss of the connection 59 to the load 28, shown in Figure 3, can be calculated as: W = 12 * R, where: R is the resistance of the wire carrying the current. The resistance is dependent on the material of the wire, the cross section of the wire, and the length of the wire.

As such, by reducing the current that is flowing in a particular section of wire, the power loss can be significantly reduced. As the switching regulator increases voltage, it decreases current, so by locating this close to the cell any length of wire running between the transducer and the load will lose less power than if the same wire was carrying the power directly from the cell. This embodiment is considered to be advantageous.

It is to be appreciated that the controller 36 does not include an input directly associated or indicative of the voltage of the at least one solar cell 30. This is advantageous as it has been found not to be necessary to tune the controller 36 specifically to a particular cell output. Rather, the duty cycle of the controller 36 is advantageously determined solely from the output voltage.

As shown in Figure 3, the second comparator 40 uses a reference voltage 61 to provide an input 63 representative of the output voltage. The controller 36 uses the io input 63 to proactively maintain the voltage of the output by varying the timing or duty cycle of the switching arrangement 42. This has been found to be particularly advantageous as it becomes possible to efficiently place a number of the solar power transducers 26 in parallel, thereby relatively maximizing the efficiency of the system.

The controller 36 seeks to proactively maintain the output voltage, even if the cell is voltage is varying. In a typical system where multiple cells are placed directly in parallel, any manufacturing differences in cells will cause slightly different cell voltages and cause reverse current flow in the lower voltage cells, resulting in damage and reduced power output. By using the controller 36 to maintain the transducer output voltage accurately, multiple transducers can be placed in parallel and the total power produced by each transducer will be available to the load without any reverse flow to the cell. This advantageously allows large arrays of transducers to be connected together in parallel without substantially compromising the efficiency or stability of any one transducer, or the system as a whole.

Alternatively, solar power transducers may be conveniently arranged in a solar power system in series with other solar power transducers. This serves to amplify the final voltage produced by the solar power system. It is to be appreciated that in such an arrangement, the present embodiment obviates the need for individual bypass diodes with each of the solar power transducers.

In the solar power transducer 26, this arises because of the combination of the mosfet 46 and the inductor 34. This occurs by virtue of the internal parasitic diode integral to the mosfet 46, which provides a path for the rest of the power from the array. In this way, the solar power transducer 26 does not require a bypass diode. This advantageously simplifies the system without impacting system flexibility, as well as adding any marginal power from the at least one solar cell 30 to the system, rather than simply cutting it off as would be the case with a bypass diode. Thus, the combination of the arrangement providing the mosfet 46 and inductor 34 topology is considered to be advantageous as this serves to bypass the at least one solar cell 30, which may be important in times of shade or failure.

As shown in Figure 3, the at least one solar cell 30 has a positive terminal 62 and a negative terminal 64. Similarly, the load 28 has a positive terminal 66 and a negative terminal 68. The solar power transducer 26 includes a first path 70 extending from the positive terminal 62 of at least one solar cell 30 to the negative terminal 68 of the load 28. A second path 72 can be considered as extending from negative terminal 64 of the at least one solar cell 30 to the positive terminal 66 of the load 28. In the embodiment, the inductor 34 extends across the first path 70 and the second path 72.

is It will be appreciated that between the inductor 34 and the output 48, there is provided a single mosfet 46 that forms part of the switching arrangement 42. The switching arrangement comprises the mosfets 44 and the mosfet 46 respectively disposed along a first path 70 on either side of the connection to the inductor 34. The controller 36 is adapted to monitor the voltage across the mosfet 46 and control the state of the mosfet 46 with reference to the monitored voltage to prevent reverse current flow.

The solar power transducer 26 further includes a capacitor 76 and a capacitor 78. The capacitors 76, 78 operate as smoothing capacitors to limit rapid fluctuations in voltage. An inductor 80 is connected to the at least one solar cell 30 so that the capacitor 78 and inductor 80 operate as a low pass filter. The operation of low pass filters is generally known in the field of power electronics 26. The use of this phenomenon has not been generally considered in the use of solar power handling; however, it has been found that using this phenomenon on the input side of a switching regulator allows a more efficient power system, while maintaining peak power output from any given photovoltaic cell due to the limited nature of available peak current and the corresponding relationship between this current and peak available power. When the mosfet 44 is on and the mosfet 46 is off, the inductor 34 stores energy in its magnetic field as a result of current generated by the at least one solar cell 30. As described, the switching arrangement 42 is used to allow the flow of current from the intermediate energy store to the output 48, whilst limiting the voltage drop therebetween to the voltage drop produced by the mosfet 46, and to substantially prevent the flow of current from the load 28 at outlet 48 towards the inductor 34. This is considered to be advantageous as it serves to protect the at least one solar cell 30 from reverse flow and thus thermal damage while providing the system with relatively improved power conversion efficiency.

Furthermore, by connecting the positive terminal 62 of at least one solar cell 30 to the negative terminal 68 of the load 28, several power handling and voltage management io advantages are provided, in the embodiment, with an advantageous switching regulator design. The design will take an unspecified negative voltage input and invert it to a desired positive voltage output, with the output voltage being highly regulated to the design set level. This not only has the ability to specify an output voltage, but also negates the inherent problem of the substrate of the wafer being is electrically positive.

The positive substrate is an outcome of the typical manufacturing process of a solar cell. This inversion shown in Figure 3 is considered to advantageously negate the need for complete electrical isolation of the transducer system from the adjacent components of any system in which it may be installed and eliminates the potential for electrical short-circuiting against a negative earth contact within, or external to, the machine or adjacent cells.

Referring to Figure 4, there is shown a power management system 100 according to a preferred embodiment of the present invention. The power management system 100 is provided for advantageous use in the storage of energy from a solar collector. The system includes an intermediate energy store 102 in the form of an inductor 104. The inductor 104 is arranged for storing energy generated by the solar collector connected to a terminal 105. The power management system 100 includes a switching arrangement 106 for allowing the current to flow to an output terminal 107 as a result of the energy stored in the inductor 104, whilst limiting the voltage drop, and for substantially preventing any reverse flow of current from the output. The power management system 100 includes a synchronous diode mosfet 108, a main switch 110, a backflow comparator 112 and a feedback error amplifier 114. A capacitor 116, a capacitor 118 and an inductor 120 are also provided.

The power management system 100 operates to switch between a first state and a second state. In the first state, the flow for current is allowed from the inductor 104 to s a load with a voltage drop of less than 0. 1V, when the load is connected to the output terminal 107. In the second state, the power management system 100 is configured for preventing the reverse flow of current from the load when connected to the output 107. Advantageously, between the inductor 104 and output 107 there is provided a single mosfet 108.

io The power management system 100 is advantageous in that it allows for the relatively efficient transfer of power from a solar collector in the form of a plurality of solar cells to a load when connected to the output 107. The solar collector is preferably insolated to limit the possibility of short circuit damage.

Referring to Figure 5, there is shown a method 150 according to a further preferred is embodiment. The method 150 advantageously manages the transfer of energy from a solar collector 152 to a load 154. At block 156, the method 150 includes storing energy in an intermediate energy store 158 as a result of current generated by the solar collector 152. Subsequently, at block 160 a switching arrangement 162 allows current to flow to the load 154, as a result of the energy stored in the intermediate energy store 158. As the current to the load 154 reduces, the switching arrangement 162 operates to substantially prevent the load from supplying current in a direction back towards the intermediate energy store 158. In the method 150, this is achieved by monitoring the voltage across a mosfet of the switching arrangement 162 that is the sole device disposed between the intermediate energy store 158 and the load 154.

Advantageously, allowing current to flow to the load 154 at block 160 includes limiting the voltage drop between the intermediate energy store and the load to less than 0.1 volts.

According to a further preferred embodiment as illustrated in Figures 6a and 6b, there is shown a power management system 170 connected to a solar collector 172 and a load 174. The power management system 170 is similar to the system used in the solar power transducer 26, in that an output 176 of a comparator 178 drives a gate 180 of a first mosfet 182 in a similar manner to the gate 60 of the mosfet 46 being driven by the processing unit 52 in the transducer 26.

As would be apparent, the comparator 178 provides an intelligent backflow prevention unit 184. The comparator 178 is configured to measure the voltage s differential across the mosfet 182 drain and source pins, and will switch the mosfet 182 on when the differential is of the desired polarity and switch the mosfet 182 off when it is of the undesired polarity. In such an arrangement, the mosfet conducts or blocks current flow. The comparator is set for this purpose. As shown previously, the mosfet 182 can carry the desired current much more efficiently than a diode. When io the mosfet 182 is on there is a small but measurable resistance across the mosfet 182 when it is conducting. This resistance causes a small but measurable voltage drop, and this drop is measured by the comparator 176 to switch the mosfet 182 off when the polarity of the voltage is undesired. In this arrangement, the comparator 178 is of sufficient drive capacity and is used to directly drive the mosfet gate 180. Other is arrangements may of course trigger a mosfet drive buffer or other circuitry which would result in the appropriate mosfet gate drive signal.

A switching regulator 188 includes the first mosfet switches 182 and a second mosfet switch 190 substantially controlled by a central integrated circuit 194; at least one inductor 192 connected in parallel to archive suitable power handling; output; output smoothing capacitor 196; and a feedback network based on a difference amplifier 198.

Advantageously, the first mosfet switch 182 is the same switch used for the intelligent backflow prevention. It also preferably includes a low pass filter comprising of one or more inductors (not shown) and one or more capacitors 199 to further smooth the current waveform from the cell, to better maintain the cell at maximum power output, rather than having an input current ripple that only peaks at maximum power.

The switching regulator 188 runs in a continuous cycle, switching between two distinct phases. During the first phase, the main switch mosfet 190 is preferably conducting while the synchronous rectifier mosfet 182 is preferably switched off This allows the source voltage from the cell to substantially flow into the inductor 192, thereby storing energy in a surrounding magnetic flux. During this phase, no current is flowing from the solar collector 172 to the load 174, and as such the load is being powered by energy previously stored in the output capacitor 196 In the second phase, the synchronous rectifier mosfet 182 is preferably switched on while the main switch mosfet 190 is preferably switched off. This allows the stored energy in the inductor 192 to substantially flow out in the reverse direction to which the energy went in, thereby causing a positive output current (fly-back current) to substantially flow through the synchronous diode mosfet 182 into the output capacitor 196. This output capacitor 196 is preferably directly connected to the output terminals 197, making the energy in this capacitor available to power the load.

The speed at which the cycles change is preferably fixed at a rate that seeks to optimize the efficiency of the mosfets and the size of the inductors and output capacitor. The ratio of time spent in each phase controls the output voltage. Higher percentages of time spent in the first phase results in higher output voltages. This ratio, or duty cycle, is preferably controlled by the input from the feedback error amplifier 198 such that the duty cycle is dependent on the difference between the output voltage and the desired voltage, and as such the system will automatically is adjust the duty cycle to maintain the desired output voltage.

The switching regulator cycles has been described for an inverting case. Nonetheless, the cycles are identical for both the inverting and non-inverting cases; only the physical configuration of the mosfet switches, the inductor/s and the feedback error amplifier is different. In the case where an inverting topology is used, the switching regulator controller is referenced to ground with a positive output voltage identical to the positive output voltage from the non-inverting topology. The input voltage is inverted, such that the positive electrode of the wafer is connected to system ground alleviating the problems discussed above. This is unlike traditional inverting topologies where the input voltage to the switching regulator is positive and the output is negative, which would not alleviate issues associated with the positive cell substrate.

With an inverting topology as described, two or more transducers may be readily used in a unit which results in a significant increase in the collecting power of the system.

This additional collecting power would under normal conditions result in the possibility of back flows of electricity and a subsequent loss thereof However, by utilising this arrangement, the wafers in flat, multi-wafer photovoltaic panel (such as described in AU2008902129) are preferably electrically aligned in parallel, with possible cell degradation due to unwanted back flows of current being substantially reduced. Notably, an inverting topology with a negative load earth is provided in the transducer 26 shown in Figure 1. The transducer 26 is also considered advantageous for this reason.

s Thus, in the embodiment there is provided a power management system where, the synchronous rectifier mosfet is under the secondary control of a control unit that ensures that it does not conduct until the fly-back voltage in the inductor is higher than the voltage already present at the output capacitor, in such a way that a backwards flow from the output terminal back into the inductor is not possible. With io this arrangement, power savings over a conventional solar cell design are provided.

In conjunction with the switching regulator, the circuitry preferably includes a central microprocessor which monitors various sensors for light levels around the solar cell for tracking purposes, monitoring thermal conditions and monitoring power input and output statistics. This microprocessor preferably comprises means for substantially is conducting this gathered information to a wider system, preferably via a multi-drop serial bus on which all other system devices can communicate. This microcontroller can preferably also undertake the role of the central integrated circuit of the switching regulator. In further embodiments, the comparator 178 shown in Figure 6b is omitted.

Such an embodiment does of course not have the reverse current protection, however the advantageous inverting topology is provided.

Referring to Figure 7, there is shown a circuit layout 200 according to a further preferred embodiment. The circuit layout 200 provides a power management system according to an embodiment which is designed around Spectrolab CDO-100 or similar characteristic photovoltaic cells and uses commercially available components.

The preferred embodiment utilises Concentrated Photovoltaic Cells, but the invention is applicable to any current limited supply source, where maximum power occurs at a fixed relationship between voltage and drawn current that may not necessarily have a fixed relationship to the rated nominal voltage of the device. In the preferred embodiment, the circuit 200 includes a synchronous rectifier mosfet 201, at least one photosensor's 202 to assist in the tracking system, inductor/s 203 for power handling, the main mosfet switch 204, switching regulator controls 205, a microprocessor 206, a communications interface 207 and the photovoltaic wafer 208. The centrally located photovoltaic wafer 208 is preferably substantially surrounded by four photosensors 202. The circuit 200 utilizes a standard switching regulator controller chip 205 preferably including additional backflow detection circuitry to coordinate both the main switch 204 and the synchronous rectifier 201, both of which are s preferably N-channel mosfets selected for suitable power handling and switching speed required for high efficiency power handling. Power savings of up to 5W are achieved, compared to a high efficiency Schottky diode as typically used for backflow prevention with a possible 1 OA load. Integrating the circuit 200 with boost regulation, enables many applications to be substantially powered by a single transducer unit.

Otherwise, insufficient voltage may be generated to say charge a mobile phone.

The microprocessor 206 preferably contains a temperature sensor (not shown) which is thermally connected to the same base as the cell, such that it is used to measure cell temperature. The microprocessor 206 allows the at least one sensor/s 202 to be calibrated such that any off-the-shelf sensors can be used interchangeably.

is The circuit 200 provides a supporting circuit having a switching regulator. The supporting circuit couples one or more photovoltaic wafers to a load or battery. The circuit utilises photovoltaic wafers for collecting the solar insolation, at least one smoothing capacitor, a power output, a synchronous rectifier mosfet, at least one inductor, a main switch mosfet, a difference amplifier and a switching regulator controller. The switching regulator controller coordinates both switches to sequentially charge power from the supplying cell into an inductor and discharge the inductor into the output smoothing capacitor. The switching regulator controller integrates backflow detection to disable the synchronous rectifier switch, if necessary.

The switching rate is determined based on the difference amplifier output, such that the output is regulated to a design set level.

A device 210 according to a further preferred embodiment is shown in Figure 8.

Unlike the other preferred embodiments, the device 210 does not include a boost regulation circuit. Rather, the device 210 provides a reverse current protector 210 for at least one solar cell 212. With the arrangement, the reverse current protector 210 includes a mosfet 214 and a control unit 216. The mosfet 214 is disposed between an input and an output of the reverse current protector 210. The control unit 216 includes a monitoring unit and a switching unit in the form of a comparator 218. The monitoring unit is provided for determining the nature of the voltage across the mosfet and the switching unit is provided for switching the mosfet 214 between a first state and a second state. The control unit 216 is adapted such that the switching unit operates in response to the monitoring unit to prevent the flow of s current through the mosfet in a reverse direction toward the at least one solar cell.

In providing the preferred embodiments described, it will be recognised that several realisations have been made and that a number of advantages have been provided.

For example, it has been surprisingly found that it is possible to provide a solid state electronic supporting insolation circuit having intelligent backflow substantially io prevented using a synchronous rectifier switch in combination with a switching regulator to provide boosted voltage output, while at the same time achieving a substantial reduction in the power consumed in operating the transducer.

It has also been found that by utilizing the above-described configuration of solid state components for the conversion of sunlight to electricity, destruction of the wafer or the supporting circuit due to reverse current flow can be substantially prevented.

Several power handling and voltage management advantages are provided, in the embodiments, with an advantageous switching regulator design, which will take an unspecified negative voltage input and invert it to a desired positive voltage output, with the output voltage being highly regulated to the design set level. This not only has the ability to specify an output voltage, but also negates the inherent problem of the substrate of the wafer being electrically positive. The positive substrate is an outcome of the typical manufacturing process of a solar cell.

Generally with the preferred embodiments described, conventional solid state electronics and multi-junction wafer technology can be organized in such a manner such that concentrated light can be used far more efficiently for creating electrical power than systems that have been used traditionally. The output voltage in embodiments of the present invention is regulated to a stable defined level.

Furthermore, it is possible to efficiently place a number of solar power transducers in parallel, thereby relatively maximising the power generation.

It is to be recognised that various alterations and equivalent forms may be provided without departing from the spirit and scope of the present invention. This includes modifications within the scope of the appended claims along with all modifications, alternative constructions and equivalents.

In the present specification, where the terms "comprise", "comprises", comprised", "comprising", "including" and "having" are used in this specification, they are to be interpreted as specifiying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof Background material on the art as discussed in the present specification is intended to explain the context of the present invention, and is not to be taken as an admission io that the material forms part of the prior art base or relevant general knowledge in any particular country or region.

Claims

Claims 1. A power management system for use in the storage of energy from a solar collector, the system comprising: an intermediate energy store for storing energy generated by the solar collector and a first switch and a second switch for regulating the power delivered to an output of the power management system wherein the power management system includes a switching arrangement for applying secondary control to the second switch to allow current to flow to the output, as a result of the energy stored in the intermediate energy store, whilst limiting the voltage drop, and for substantially preventing the reverse flow of current from the output towards the intermediate energy store.
2. A power management system as claimed in claim 1, wherein between the intermediate energy store and the output there is provided a single mosfet, the mosfet forming the second switch of the switching regulator.
3. A power management system as claimed in claim 2, wherein the switching arrangement includes a controller for monitoring the voltage across the mosfet and for controlling the is state of the mosfet based on the monitored voltage.
4. A power management system as claimed in any one of claims 1 to 3, wherein the switching arrangement is adapted to switch between a first state and a second state wherein, in the first state, the switching arrangement is configured for allowing the flow of current from the intermediate energy store to the output with a voltage drop of less than O.2V, and wherein, in the second state, the switching arrangement is configured to substantially prevent the flow of current back towards the intermediate energy store.
5. A power management system for a solar collector, the system comprising: an input, an output and an intermediate energy store, wherein the intermediate energy store forms part of a voltage boost regulator having a main switch and a synchronous rectifier mosfet with the intermediate energy store being adapted to store energy as a result of the current generated by the solar collector and being adapted to supply the current to the output, wherein the power management system includes a switching arrangement for applying secondary control to the synchronous rectifier mosfet for allowing current generated by the intermediate energy store to flow to the output, whilst limiting the voltage drop therebetween, and for substantially preventing the reverse flow of current from the output back towards the intermediate energy store.