Control device

Abstract

A control device is described, comprising: an inductor (16) having a small inductance and having an input side and an output side, the input side being connected to an input line (18) which is connected in use to an output from a power source (12), the output side being connected to an output line (20) which is connected in use to a load (14); and a switched capacitor device (22) located on the input side of the inductor (16), the switched capacitor device (22) being configured such that during use of the control device, the average voltage on the input line remains above a predetermined level.

Description

Technical Field

[0001] This invention relates to a control device, and more particularly to a control device suitable for extracting electrical energy from a power source to help increase the level of available extracted electrical energy. The invention is particularly suitable for use in conjunction with photovoltaic panels or the like; however, it should be understood that the invention is not limited in this respect and can be used with certain other forms of power sources. Background Technology

[0002] The reliance on photovoltaic panels for power generation is increasing, and there is a desire to improve the efficiency of such power sources, or to allow for higher levels of usable energy that can be extracted, or to enable continued use under conditions of low light, in situations where there is no way to increase the output of such power sources. Summary of the Invention

[0003] One object of the present invention is to provide a control device that can increase the level of electrical energy that can be extracted from such a power source or supply (e.g., a power source or supply in the form of a photovoltaic panel).

[0004] According to a first aspect of the present invention, a control device is provided, comprising: an inductor having a small inductance and having an input side and an output side, the input side being connected to an input line, the input line being connected to an output from a power source in use, the output side being connected to an output line, the output line being connected to a load in use; and a switched capacitor device located on the input side of the inductor, the switched capacitor device being configured such that during use of the control device, the average voltage on the input line remains above a predetermined level.

[0005] It has been found that the power output of a power source in the form of a photovoltaic panel can be increased by keeping the average voltage on the input lines above a predetermined level. The voltage on the power source can be maintained in a way that enhances the panel's useful output by keeping the average voltage on the input lines above a predetermined level.

[0006] The switched capacitor device preferably includes: a first capacitor and a second capacitor; a charging switch operable to control whether the first capacitor is connected to the input line, thereby controlling whether the first capacitor can be charged; a changeover switch controlling the connection between the first and second capacitors, thereby controlling whether the first capacitor can discharge to charge the second capacitor; and a discharging switch controlling whether the second capacitor is connected to the input line, thereby controlling whether discharge from the second capacitor to the input line is permitted. Preferably, a fourth switch is provided in the input line to control the connection of the inductor to the power supply during use.

[0007] In operation, when both the charging and discharging switches are open, and both the switching and fourth switches are closed, the second capacitor charges from the first capacitor, and the power supply is connected to the load via an inductor. Subsequent switching of all switches disconnects the inductor from the power supply and isolates the second capacitor from the first capacitor. During this operational phase, when the charging switch is closed, the output from the power supply is used to charge the first capacitor. The remaining charge on the first capacitor, as well as the remaining charge on the capacitor associated with the power supply, ensures that the average voltage on the power supply remains at or above a predetermined level. When the discharging switch is closed, the second capacitor discharges through the inductor, storing energy in the inductor. By repeatedly switching the switches between these positions, it should be understood that the average voltage on the power supply can be maintained at or above the desired predetermined level to enhance its output. Therefore, the level of electrical energy that can be extracted from the power supply is increased.

[0008] The first capacitor preferably has a larger capacitance than the second capacitor. For example, it can be 2 to 4 times the capacitance of the second capacitor, and preferably about 3 times the capacitance of the second capacitor.

[0009] Inductors with small inductance preferably have an inductance smaller than the minimum inductance typically used in high-frequency switching circuits operating at a given high frequency. For example, they preferably have an inductance of less than 30 μH, and can be in the range of 15-25 μH.

[0010] The switching frequency for performing the above operation cycle is preferably in the range of 15-25kHz.

[0011] A changeover switch can form part of a boost circuit between the first and second capacitors. For example, the boost circuit may include an inductor, preferably with a small inductance, a changeover switch connected in series between the first and second capacitors, and a switch ground connection connected to a point between the inductor and the changeover switch in the boost circuit. In this embodiment, the changeover switch is conveniently in the form of a diode. In use, by repeatedly opening and closing the switch ground connection, the boost circuit can be used to boost or increase the voltage on the second capacitor to a level higher than the voltage on the first capacitor and higher than the voltage on the second capacitor. Figure 1 The voltage level obtained in the device results in a larger current flowing through the inductor. In such devices, the switching frequency of the switch grounded connection is typically higher, preferably significantly higher (e.g., 1.5 times or more) than the switching frequency of other switches.

[0012] The present invention also relates to a control method for controlling a control device of the above type, the method comprising the steps of controlling a switched capacitor device such that, in a first operating mode, a first capacitor is charged from a power source and a second capacitor is discharged through an inductor, and in a second operating mode, the first capacitor discharges to the second capacitor, the control device repeatedly switching between the first operating mode and the second operating mode. Attached Figure Description

[0013] The invention will be further described by way of example with reference to the accompanying drawings, wherein:

[0014] Figure 1 A circuit diagram illustrating a control device according to an embodiment of the present invention is provided.

[0015] Figure 2 and 3 To illustrate the graph of inductor current and voltage across the second capacitor; and

[0016] Figure 4 For similar Figure 1 The view shows the modifications to the control unit. Detailed Implementation

[0017] First refer to Figure 1 The diagram illustrates a control device 10 for controlling the extraction of electrical energy from a power source 12, in this case, in the form of a photovoltaic panel, for use by a load 14. While the description herein relates to the extraction of electrical energy from a photovoltaic panel, it should be understood that the invention is not limited in this respect and can be used in conjunction with certain other forms of power source 12.

[0018] In the background, it has been found that the level of electrical energy that can be extracted from a photovoltaic panel can be increased by increasing the size of the inversion layer within the panel, as this improves the panel's quantum efficiency. Increasing the size of the inversion layer can be achieved by applying a voltage or potential difference to the panel, which, if operated using conventional maximum power point tracking methods, is greater than the average potential difference applied to the panel. Therefore, the control device 10 is operable to apply a larger voltage or potential difference to the power supply 12 at all times during its operation, having an average level greater than or equal to a predetermined level. For example, depending on the panel specifications, the average applied voltage on the panel can be maintained at at least 30V.

[0019] like Figure 1 As shown, the control device 10 includes an inductor 16 with a small inductance, whose input side is connected to the input line 18 and its output side is connected to the output line 20. The input line 18 is connected to the output of the power supply 12, and the output line 20 is connected to the load 14.

[0020] A switched capacitor device 22 is connected to the input line 18 between the power supply 12 and the inductor 16. The switched capacitor device 22 includes a first capacitor 24 and a second capacitor 26. The first capacitor 24 is connected to the input line 18 via a charging switch 28 and to the second capacitor 26 via a changeover switch 30. The second capacitor 26 is connected to the input line 18 via a discharging switch 32. As shown, a fourth switch 34 is located at a point midway between the charging switch 28 and the discharging switch 32 on the input line 18.

[0021] The control device 10 also includes input and output capacitors 36 and 38, and first and second boost switches 40 and 42.

[0022] A control unit 44 is provided, and the control unit is operable to control the operation of switches 28, 30, 32, 34, 40, and 42. The switches are controlled by dividing them into a first group consisting of a charging switch 28, a discharging switch 32, and a first boost switch 40, and a second group consisting of a changeover switch 30, a fourth switch 34, and a second boost switch 42. The control unit 44 is configured to control the switches such that in a first operating mode, the first group of switches is in the ON position and the second group of switches is in the OFF position, and in a second operating mode, the second group of switches is in the ON position and the first group of switches is in the OFF position. The control unit 44 repeatedly cycles between the first and second modes at a high frequency, for example, in the range of 15-25 kHz.

[0023] In the first mode, inductor 16 is disconnected from power supply 12, and the output from power supply 12 is used to charge the first capacitor 24. The second capacitor 26 discharges through inductor 16 and the first boost switch, storing energy within inductor 16. The charging of the first capacitor 24 and the input capacitor 36 maintains the voltage or potential difference on power supply 12 at or above a predetermined level to enhance its operation, as described above.

[0024] Upon subsequent switching to the second operating mode, the closing of the fourth switch 34 and the second boost switch 42 connects the power supply 12 to the output 14 via the inductor 16. The inductor 16 generates a reverse current, transferring charge from the output capacitor 38 to the input capacitor 36, sufficient to maintain the required voltage or potential difference on the power supply 12 to enhance its operation. Simultaneously, the changeover switch 30 opens, causing partial discharge of the first capacitor 24 and charging of the second capacitor 26, preparing for a return to the first mode. By repeatedly switching between these operating modes, it should be understood that electrical energy can be extracted from the power supply 12 while maintaining a sufficiently high average voltage or potential difference on the power supply 12 to improve its efficiency, thereby allowing additional electrical energy to be available for extraction.

[0025] Figure 2 and Figure 3 The diagram shows the inductor current and the charging of the second capacitor during these operating modes, demonstrating that by repeatedly switching between these operating modes, electrical energy can be extracted from the power supply while maintaining a sufficient voltage or potential difference on power supply 12 to keep its operation at an enhanced level.

[0026] The size of the second capacitor 26 should be sufficient to ensure that once it discharges to charge the inductor 16, enough charge remains on the second capacitor 26, thus avoiding negative voltage on the device. To ensure that the charging of the second capacitor 26 can occur quickly and efficiently, and to charge the second capacitor 26 to an appropriate level, the first capacitor 24 should be larger than the second capacitor, for example, 2-4 times the capacitance of the second capacitor 26, and preferably approximately 3 times the capacitance of the second capacitor 26. Similarly, the capacitance of the output capacitor should be larger than that of the input capacitor. Conveniently, to minimize the number of component sizes present in the circuit, the input and output capacitors can have the same size as the charging and discharging capacitors. For example, in one device, the inductor 16 can have an inductance of approximately 21 μH, the second capacitor 26 can have a capacitance of approximately 10 μH, and the first capacitor 24 can have a capacitance of 29 μH. In an alternative device, the inductance can be 16 μH, and the capacitances can be 8 μH and 23 μH, respectively. Obviously, these are merely examples, and other component sizes can be used if desired.

[0027] The circuit preferably operates at a switching speed in the range of 15-25 kHz. For example, using the first set of component dimensions described above, it can operate at a switching frequency of 17 kHz, and using the second set of component dimensions, it can operate at a switching frequency of 22 kHz. It has been found that, in this way, an average voltage or potential difference of at least 30 V can be maintained on the power supply.

[0028] As described above, by maintaining the voltage or potential difference on power supply 12 at or above a predetermined level, it has been found that the energy extracted can be increased by an average of, for example, about 5%. Therefore, the use of this invention demonstrates a significant improvement compared to conventional control devices.

[0029] Figure 4 Showing the Figures 1 to 3The device is modified in that the changeover switch 30 forms part of a boost circuit 50 between the first and second capacitors 24, 26, such that when the second capacitor 26 is charged from the first capacitor 24, the boost circuit 50 can be used to boost the voltage on the second capacitor 26 to a higher level than a voltage otherwise obtained. The boost circuit 50 includes an inductor 52 (conveniently, in this embodiment, in the form of a diode 30a) connected in series with the changeover switch 30 between the first and second capacitors 24, 26, and a switch ground connection 54 connected to a point between the inductor 52 and the changeover switch 30.

[0030] In use, when the second capacitor 26 is charging from the first capacitor 24, by repeatedly opening and closing the ground connection 54, it should be understood that the boost circuit 50 operates to raise the voltage on the second capacitor 26 to a level exceeding the voltage on the first capacitor 24. As a result, when the second capacitor 26 discharges, the current supplied to the inductor 16 can increase, and therefore the circuit output can increase.

[0031] The switching frequency of the grounding connection 54 is preferably greater than the switching frequency of other switches, conveniently and significantly greater. For example, it can be 1.5 times or more the switching frequency of other switches.

[0032] If necessary, the boost function can be turned off (by keeping the switch grounded) if the voltage on the second capacitor 26 is monitored appropriately.

[0033] While specific embodiments of the invention have been described herein, it should be understood that these are merely exemplary embodiments and many modifications or alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.

Claims

1. A control device (10) comprising: a first inductor (16) having a small inductance and having an input side and an output side, the input side being connected to an input line (18) which in use is connected to an output from a power supply (12), the output side being connected to an output line (20) which in use is connected to a load (14); a switched capacitor arrangement (22) located at the input side of the first inductor (16), the switched capacitor arrangement being arranged such that the average voltage on the input line is maintained above a predetermined level during use of the control arrangement; wherein the switched capacitor arrangement (22) comprises a first capacitor (24) and a second capacitor (26), a charging switch (28) operable to control whether the first capacitor (24) is connected to the input line (18) and thereby whether the first capacitor (24) can be charged, a transfer switch (30) controlling connection between the first capacitor (24) and the second capacitor (26) and thereby whether the first capacitor (24) can be discharged to charge the second capacitor (26), and a discharging switch (32) controlling whether the second capacitor (26) is connected to the input line (18) and thereby whether discharge from the second capacitor (26) to the input line (18) is permitted, and wherein the capacitance of the first capacitor (24) is greater than the capacitance of the second capacitor (26).

2. An arrangement according to claim 1, further comprising a fourth switch (34) provided in the input line (18) to control connection of the first inductor (16) to the power supply (12) in use.

3. The apparatus of claim 1, wherein, The capacitance of the first capacitor (24) is 2-4 times the capacitance of the second capacitor (26).

4. The apparatus of claim 3, wherein, The capacitance of the first capacitor (24) is 3 times the capacitance of the second capacitor (26).

5. The apparatus of claim 1, wherein, The transfer switch (30) forms part of a boost circuit (50) interposed between the first capacitor (24) and the second capacitor (26).

6. The apparatus of claim 5, wherein, The boost circuit comprises a second inductor (52) and the transfer switch (30) connected in series between the first capacitor (24) and the second capacitor (26) and a switch (54) connected to a point between the second inductor (52) and the transfer switch (30) of the boost circuit (50).

7. The apparatus of claim 6, wherein, The second inductor (52) has a small inductance.

8. The apparatus of claim 6 or 7, wherein, The transfer switch (30) comprises a diode (30a).

9. The apparatus of claim 6, wherein, The switching frequency of the ground connected switch (54) is higher than the switching frequency of the charging switch (28), the transfer switch (30), the discharging switch (32).

10. The apparatus of claim 1, wherein, The inductance of the first inductor (16) having a small inductance is less than the minimum inductance used in high frequency electrical conversion circuits operating at a given high frequency.

11. The apparatus of claim 10, wherein, The inductance of the first inductor (16) is less than 30µH.

12. The apparatus of claim 11, wherein, The inductance of the first inductor (16) is in the range 15-25µH.

13. The apparatus of the preceding claim 1, operating with a switching frequency in the range of 15-25 kHz.

14. A control method for controlling a control apparatus (10) according to any of the preceding claims, the method comprising the step of controlling a switched capacitor apparatus (22) such that in a first operating mode its first capacitor (24) is charged from a power supply (12) and its second capacitor (26) is discharged through a first inductor (16), and in a second operating mode of the apparatus the first capacitor (24) discharges to the second capacitor (26), the control apparatus (10) repeatedly switching between the first operating mode and the second operating mode.

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