1. Field of the Invention
The instant disclosure relates to a solar energy harvesting device; in particular, to an adaptive solar energy harvesting device.
2. Description of Related Art
The energy which is existed on earth falls into shortage yearly by yearly. Such as coal; petroleum; ethanol; nuclear energy; water energy; geo-thermal energy; wind energy; and renewable bio-energy etc., all encounter different drawbacks and difficult reasons on cost; safety; green; and productivity. Because of the usage and human population are increased rapidly, it is inevitable to have a clean; reliable; and cost effective energy for human being to utilize it daily. There are two candidates which can meet the previous criteria—nuclear fusion and solar energy. The nuclear fusion is good but it still cannot go to commercialize due to technical barrier, while solar is the very candidate to fulfill the determinate role on energy sources. Although solar energy harvesting is a feasible and reasonable energy source as compared to other existed candidates, there are some other issues to be breakthrough to make it become a mighty energy source. The issues are solar cells efficiency and photo-voltaic energy harvest/transfer efficiency. III-V compound cell with new quantum dot technology shows amazing efficiency over 70% photo-voltaic conversion but it can be only used on special applications due to its extraordinary fabrication cost. Currently commercial solar cell is silicon based with about up to 21% photo-voltaic conversion efficiency. Even there are some other type solar cells, for example organic polymer and II-VI compound are announced but the reliability; durability; and cost make it is unable to be a suitable candidate. Lately most of solar cell manufactures invest more and more on the improvement of silicon-based solar cells with light intensity collection; incident light recycling; multiple-path absorption, etc. So far, there is not a good photo-voltaic transfer design to accommodate the harvested solar energy transfer into stored voltaic energy and/or usable electric energy. Most of design needs to be under high light incidence to trigger the harvesting energy transfer, for example more than 30-50K Lux.
Present solutions and their drawbacks are described in the following. Existed solar energy harvesting solutions are unable to do energy harvesting under low-light incidence, thus it always needs sufficient light to trigger energy harvesting. The reason is the loading line problem. The heavy loading line to drain out the current is much more than the supply from solar panel. It results the depletion of solar supply current and boost's output voltage sustainment. The loss strength of converted voltage the energy harvest will be terminated no matter how strong the irradiation of incidence light intensity. Hence the existed harvesting needs a maximum power tracking system which is using the complicated feedback design to have the Maximum Power Point Tracking (MPPT).
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The object of the instant disclosure is to offer an adaptive solar energy harvesting device utilizing the feed-forward control to control the charging current and the charging voltage when charging the electricity storage unit.
In order to achieve the aforementioned objects, according to an embodiment of the instant disclosure, an adaptive solar energy harvesting device is provided. The adaptive solar energy harvesting device comprises a solar energy receiving unit, a voltage converter and a charging power controller. The voltage converter has an input terminal and an output terminal. The input terminal of the voltage converter is coupled to the solar energy receiving unit. The voltage converter receives the electricity from the solar energy receiving unit through the input terminal. The charging power controller is coupled to the output terminal of the voltage converter. The charging power controller senses a supply voltage of the output terminal of the voltage converter and generates a charging voltage and a charging current to charge at least an electricity storage unit. The charging power controller adjusts the charging voltage and the charging current according the feed-forward control related to the supply voltage at the output terminal of the voltage converter.
In summary, the adaptive solar energy harvesting device utilizes feed-forward control to control the charging current and the charging voltage when charging the electricity storage unit, in order to convert and store electricity under low light incidence.
In order to further the understanding regarding the instant disclosure, the following embodiments are provided along with illustrations to facilitate the disclosure of the instant disclosure.
The aforementioned illustrations and following detailed descriptions are exemplary for the purpose of further explaining the scope of the instant disclosure. Other objectives and advantages related to the instant disclosure will be illustrated in the subsequent descriptions and appended drawings.
[An Embodiment of the Adaptive Solar Energy Harvesting Device]
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The voltage converter 11 may be a boost converter or a buck converter. The voltage converter 11 has an input terminal P1 and an output terminal P2. The input terminal P1 of the voltage converter 11 is coupled to the solar energy receiving unit 10. The voltage converter 11 receives the electricity from the solar energy receiving unit 10 through the input terminal P1. The charging power controller 12 is coupled to the output terminal P2 of the voltage converter 11. The charging power controller 12 senses a supply voltage Vo of the output terminal P2 of the voltage converter 11 (wherein the input terminal Vin′ of the charging power controller 12 is also shown in
This embodiment utilizes the charging power controller 12 which has the capability to adaptive adjust the ability of harvesting energy according to the loading. For different intensity of the incident light, each solar cell has itself energy harvesting ability for outputting electricity. If the harvest load is not matched to output generation of solar cells then the output voltage of solar cells would collapse and drop to near ground or lower voltage values under heavy loading drain. To overcome such a problem it is proposed to have the loading forward adjustment to the output (post) stage of the photo-voltaic conversion the energy storage. Every boost or buck clock cycle from the harvested photo-voltaic into voltaic value the post stage which stores the harvested solar energy into electrochemical battery energy is automatically adjusted to accommodate the photo-voltaic output capability from delivered capability of former stage. Referring to
The electricity storage unit 13 usually is a secondary battery, such as the lithium nickel battery or the lithium-ion battery, but the instant disclosure is not so restricted. The electricity storage unit 13 is coupled to the charging power controller 12. The electricity storage unit 13 receives the charging voltage Vo′ and the charging current Io′ to be charged. The electricity storage unit 13 may a temperature sensory device 131. The temperature sensory device 131 senses the temperature of the electricity storage unit 13 and provides a temperature sensing signal TS to the charging power controller 12. The temperature sensory device 131 may provide the temperature sensing signal TS to indicate the charging power controller 12 to stop charging the electricity storage unit 13. Accordingly, over temperature of the electricity storage unit 13 could be avoided for safety.
The charging power controller 12 may adjust the loading line of charging the electricity storage unit 13 according to the supply voltage Vo when the adaptive solar energy harvesting device 1 charges the electricity storage unit 13. Detailed control manner could be referred to following descriptions.
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In one embodiment, the supply voltage sensing circuit 122 may comprise a transistor MN1 and a resistor R1. One terminal of the resistor R1 is coupled to the control terminal (e.g. the gate electrode) of the power switch MN2 and another terminal of the resistor R1 is coupled to a grounding GND through the transistor MN1, the transistor MN1 is controlled by the supply voltage Vo. The voltage across the transistor R1 is the charging control signal CT. In
In one embodiment, the charging power controller further comprises a current sensing circuit 123 and a loading line control unit 121. The current sensing circuit 123 senses the charging current Io′ of the electricity storage unit 13 to generate a current sensing signal SI. The loading line control unit 121 comprises a current controller 1211. The current controller 1211 is coupled to the supply voltage sensing circuit 122 and the current sensing circuit 123, wherein the current controller 1211 adjusts the charging control signal CT for adjusting the charging current Io′ passing through the power switch MN2. More specifically, the current controller 1211 may generate a first phase signal SA and adjust the charging control signal CT through the first phase signal SA. For example, the first phase signal SA generated by the current controller 1211 is the voltage level of the gate electrode of the power switch MN2, thus the voltage level of the node of connecting the resistor R1 and the gate electrode of the power switch MN2 is adjusted accordingly (for adjusting the charging control signal CT.
In one embodiment, the loading line control signal 121 further comprises a voltage controller 1212. The voltage controller 1212 is coupled to the supply voltage sensing circuit 122 and the current sensing circuit 123. The current controller 1211 generates a first phase signal SA to adjust the charging control signal CT when the charging current Io′ is not less than a threshold. The voltage controller 1212 generates a second phase signal SB to adjust the charging control signal CT when the charging current Io′ is less than a threshold.
The current sensing circuit 123 senses the charging current Io′ of the electricity storage unit 13 to generate a current sensing signal SI which is the basis for determining whether the charging current Io′ is less than the threshold. Generally, the current sensing circuit 123 may be a voltage divider which feedbacks the charging current Io′ to the current controller 1211 and the voltage controller 1212 of the loading line control unit 121 in voltage form, but the instant disclosure is not so restricted. For example, the current sensing signal SI varies according to the charging current Io′ when the current sensing circuit 123 feedbacks the charging current Io′ to the loading line control unit 121 in voltage form. The current controller 1211 and the voltage controller 1212 could determine whether the current signal SI is less than a threshold (in which the threshold may not the same as the threshold of the charging current Io′). Alternatively, the current sensing circuit 123 may trigger the current sensing signal SI when the charging current Io′ is less than a threshold, in which the current sensing signal SI disables the current controller 1211 and enables the voltage controller 1212. An artisan of ordinary skill in the art will appreciate how to implement the voltage controller 1212 and the current sensing circuit 123, thus there is no need to go into details.
Additionally, in order to make the charging power controller 12 have the circuit protection capability, the charging power controller 12 may comprise at least one of an over-voltage protection circuit, an over-current protection circuit, a short protection circuit and an over-temperature protection circuit. Therefore, the charging power controller 12 may have the capability of over-voltage protection, the over-current protection, the short protection and the over-temperature protection. The charging power controller 12 could monitor the charging status of the electricity storage unit 13 and maintain the safety of the electricity storage unit 13. An artisan of ordinary skill in the art will appreciate how to implement the over-voltage protection circuit, the over-current protection circuit, the short protection circuit and the over-temperature protection circuit, thus there is no need to go into detail.
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According to above descriptions, the aforementioned adaptive solar energy harvesting device utilizes feed-forward control to control the charging current and the charging voltage when charging the electricity storage unit, in order to convert and store electricity under low light incidence. The adaptive solar energy harvesting device provides the output capability of the voltage converter for smoothly delivering energy into the storage stage, and transmits the electricity in a full-range and close to maximum power delivery from solar cells into the storage stage.
The descriptions illustrated supra set forth simply the preferred embodiments of the instant disclosure; however, the characteristics of the instant disclosure are by no means restricted thereto. All changes, alternations, or modifications conveniently considered by those skilled in the art are deemed to be encompassed within the scope of the instant disclosure delineated by the following claims.
Number | Date | Country | Kind |
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102141253 | Nov 2013 | TW | national |