JP2015207238A - Solar cell control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To immediately control electric power outputted from a solar cell.SOLUTION: A control section 32 controls a voltage converter 22 until a voltage detection value Vd falls within a target range from a maximum detection value to reduce the voltage detection value Vd by a first change width. The control section 32 reduces the voltage detection value Vd by a second change width smaller than the first change width until the voltage detection value Vd reaches a minimum detection value after the voltage detection value Vd falls within the target range. The control section 32 stores the voltage detection value Vd, a duty ratio α and an electric power detection value each time when reducing the voltage detection value Vd by the first change width or the second change width, in association with each other. On the basis of information about a change range of the voltage detection value Vd, the control section 32 acquires an optimized duty ratio when the electric power detection value is a maximum value, in the change range of the voltage detection value Vd. The control section 32 further controls the voltage converter 22 according to the optimized duty ratio.

Description

  The present invention relates to a solar cell control device, and more particularly to a device that controls electric power output from a solar cell.

  There are power plants such as thermal power plants and nuclear power plants as facilities for supplying power to power consumers such as offices, factories and general households. However, there are various problems in operating these facilities. For example, thermal power plants have problems such as oil depletion and increased carbon dioxide emissions in the future. In addition, nuclear power plants have problems such as enhanced safety management.

  Under such a background, research and development related to solar cells are widely performed. For example, a proposal has been made to reduce the power to be generated at each power plant by providing a solar cell for each power consumer.

  For solar cells, increasing output power, increasing efficiency, and the like are issues. In general, load conditions such as output voltage, output current, and load impedance when the maximum electric power is obtained from a solar cell change according to changes in environmental conditions such as illuminance and temperature of light irradiated on the solar cell. Therefore, as shown in Patent Documents 1 and 2, an apparatus for controlling the load state on the solar cell is considered. In the apparatus described in Patent Document 1, the operating voltage (output voltage) of the solar cell is adjusted stepwise so that the output power of the solar cell increases. When the operating voltage changes only in one of the increasing or decreasing directions for a predetermined number of times, the operating voltage is controlled to increase, and the operating voltage decreases and increases. When the direction is changed so as to repeat, the operation voltage is controlled to be small. In the device described in Patent Document 2, the output voltage of the solar cell is adjusted to the maximum operating voltage that maximizes the output power. The longer the output voltage of the solar cell is from the maximum operating voltage, the shorter the cycle for adjusting the output voltage of the solar cell.

Japanese Patent Laid-Open No. 8-44445 JP2012-13639A

  In the conventional solar cell control device as described in Patent Documents 1 and 2, depending on the magnitude of the change width when adjusting the output voltage of the solar cell, it takes a long time to adjust the output power to the maximum. It may take.

  An object of this invention is to control rapidly the electric power output from a solar cell.

  The present invention includes a voltage adjustment unit that is provided between a solar cell and a load device, adjusts a voltage output from the solar cell by switching, and outputs the voltage to the load device, and the voltage adjustment unit is in a switching state. The output voltage output from the solar cell to the voltage adjustment unit is decreased from the maximum voltage with a predetermined change width, and the output power output from the solar cell to the voltage adjustment unit satisfies the target condition. A control unit that searches for an optimal switching state and sets the switching state to the optimal switching state, and the maximum voltage is a voltage output from the solar cell when the solar cell is in a minimum load state. And the control unit sets the change width based on whether or not the output voltage is included in a target range determined based on the maximum voltage. The features.

  Preferably, when the output voltage is within the target range, the control unit sets the change width to a smaller value than when the output voltage is larger than a value within the target range.

  Preferably, the target condition is a condition that the output power becomes a maximum value in a change range of the output voltage.

  Preferably, the target condition is a condition that the output power becomes a maximum value, and the control unit adjusts the switching state to decrease the output voltage by the change width, and the output power is a maximum value. When the value is reached, the switching state when the maximum value is obtained is set as the optimum switching state.

  Preferably, the voltage adjusting unit includes a voltage converter including a switching element, and the control unit sets a duty ratio for the switching element.

  According to the present invention, the power output from the solar cell can be quickly controlled.

It is a figure which shows the solar cell control apparatus which concerns on embodiment of this invention. It is a figure which shows a step-down converter. It is a figure which shows the voltage-current characteristic of a solar cell. It is a figure which shows the voltage power characteristic of a solar cell. It is a figure which shows a voltage power characteristic about three cases from which the illumination intensity of the irradiated light differs. It is a figure which shows notionally the process which decreases a voltage detection value by a predetermined change width. It is a figure which shows the voltage power characteristic in which the output voltage corresponding to the maximum power point is lower than the voltage within the target range. It is a figure which shows the voltage-current characteristic when a voltage detection value does not become smaller than a limit value.

  FIG. 1 shows a solar cell control device 10 according to an embodiment of the present invention. The solar cell control device 10 includes a voltage adjustment unit 20 provided between the solar cell 12 and the load device 42. The voltage adjustment unit 20 adjusts the voltage output from the solar cell 12 by switching and outputs the adjusted voltage to the load device 42. The solar cell control device 10 further includes a voltmeter 18 as a voltage detection unit that detects a voltage output from the solar cell 12 to the voltage adjustment unit 20, and a current that detects a current flowing from the solar cell 12 to the voltage adjustment unit 20. An ammeter 16 is provided as a detection unit. The output power of the solar cell 12 is obtained from the product of the voltage detection value Vd by the voltmeter 18 and the current detection value Id by the ammeter 16, and the voltmeter 18 and the ammeter 16 constitute a power detection unit.

  The load impedance when the maximum electric power is obtained from the solar cell 12 changes according to changes in environmental conditions such as the illuminance and temperature of light irradiated on the solar cell 12. Then, the solar cell control apparatus 10 adjusts the load impedance with respect to the solar cell 12 by the voltage adjustment part 20 so that the output electric power of the solar cell 12 becomes appropriate.

  The voltage adjustment unit 20 includes a voltage converter 22 and a control unit 32. The voltage converter 22 performs switching under the control of the control unit 32, adjusts the output voltage of the solar cell 12, and outputs it to the load device 42. As the voltage converter 22, a step-up converter that boosts the output voltage of the solar cell 12 or a step-down converter that steps down the output voltage of the solar cell 12 is used.

  The voltage converter 22 has a function of converting an average load impedance in addition to step-up or step-down. The load impedance for the solar cell 12 is controlled by the operation of the voltage converter 22. Since the current flowing through the solar cell 12 includes a ripple component, the load impedance is defined as, for example, the square of the effective value of the output voltage of the solar cell 12 divided by the output power of the solar cell 12.

  A specific configuration and operation of the solar cell control device 10 will be described. The anode terminal of the battery side diode 14 is connected to the positive terminal of the solar battery 12. The cathode terminal of the battery side diode 14 is connected to the positive input terminal 24 of the voltage converter 22 via the ammeter 16. The negative input terminal 26 of the voltage converter 22 is connected to the negative terminal of the solar cell 12. A voltmeter 18 is connected between the positive input terminal 24 and the negative input terminal 26 of the voltage converter 22. Note that the voltmeter 18 may be connected between the cathode terminal of the battery-side diode 14 and the negative input terminal 26 of the voltage converter 22.

  The anode terminal of the load side diode 34 is connected to the positive output terminal 28 of the voltage converter 22. The cathode terminal of the load side diode 34 is connected to the plus load terminal 38. A negative load terminal 40 is connected to the negative output terminal 30 of the voltage converter 22. A positive terminal and a negative terminal of the battery 36 are connected between the positive load terminal 38 and the negative load terminal 40, respectively. Further, a load device 42 is connected between the plus load terminal 38 and the minus load terminal 40. The battery 36 functions as a backup power supply device for supplying power to the load device 42 when the solar cell 12 does not output power, such as when the solar cell 12 is not irradiated with light. The load device 42 is a power supply destination device, and is, for example, an electric device provided in an office, a factory, a general home, or the like.

  The solar cell 12 applies a voltage between the positive input terminal 24 and the negative input terminal 26 of the voltage converter 22 via the battery-side diode 14. The battery side diode 14 prevents the backflow of current to the solar cell 12. The control unit 32 controls the voltage converter 22 based on the voltage detection value Vd output from the voltmeter 18 and the current detection value Id output from the ammeter 16. The voltage converter 22 performs switching according to the control of the control unit 32, boosts or steps down the voltage applied between the plus input terminal 24 and the minus input terminal 26, and outputs the boosted or stepped down voltage as a plus output. Output to the terminal 28 and the negative output terminal 30. When the converter output voltage output from the plus output terminal 28 and the minus output terminal 30 is larger than the voltage between the terminals of the battery 36, the load side diode 34 is in a forward bias state, and the converter output voltage is changed to the battery 36 and the load device. 42 is applied. The battery 36 is charged with the converter output voltage, and the load device 42 is supplied with electric power based on the converter output voltage. When the converter output voltage is equal to or lower than the voltage between the terminals of the battery 36, the load side diode 34 is in the reverse bias state, and the converter output voltage is not applied to the battery 36 and the load device 42. In this case, power is supplied from the battery 36 to the load device 42.

  FIG. 2 shows a step-down converter 22 </ b> A as an example of the voltage converter 22. One end of a switching element 44 is connected to the positive input terminal 24. One end of the switching element 46 and one end of the inductor 48 are connected to the other end of the switching element 44. The negative input terminal 26 and the negative output terminal 30 are connected to the other end of the switching element 46. A positive output terminal 28 is connected to the other end of the inductor 48. A capacitor 50 is connected between the plus output terminal 28 and the minus output terminal 30.

  As the switching element 44 and the switching element 46, a semiconductor element such as a bipolar transistor or a field effect transistor is used. The switching element 44 and the switching element 46 are alternately turned on / off by the control unit 32.

  When the switching element 44 is on and the switching element 46 is off, a current flows from the positive input terminal 24 to the inductor 48. In this state, when the switching element 44 is turned off and the switching element 46 is turned on, an induced electromotive force is generated in the inductor 48. By this induced electromotive force, an induced current flowing through the inductor 48, the capacitor 50, and the switching element 46 and returning to the inductor 48 flows, and the capacitor 50 is charged. When the switching element 44 is turned on again and the switching element 46 is turned off again, an induced electromotive force is generated in the inductor 48 with the switching element 44 side being positive, and the induced electromotive force and the charging voltage of the capacitor 50 are combined. The voltage becomes equal to the converter input voltage Vi applied to the plus input terminal 24 and the minus input terminal 26. When switching element 44 and switching element 46 are alternately turned on / off, capacitor 50 is charged with a voltage lower than converter input voltage Vi, and the charged voltage is converted from positive output terminal 28 and negative output terminal 30 to the converter. Output as the output voltage Vo. When the duty ratio obtained by dividing the time when the switching element 44 is turned on by one cycle of on / off is α, the converter output voltage Vo is Vo = α · Vi. Since the switching element 44 and the switching element 46 are alternately turned on / off, the duty ratio of the switching element 46 is (1−α). It can be said that the duty ratio α is a value for setting the switching state of the step-down converter 22A.

  When the voltage between the positive output terminal 28 and the negative output terminal 30 is constant, the converter input voltage Vi decreases as the duty ratio α increases, and the current flowing into the positive input terminal 24 increases. As a result, the impedance when the step-down converter 22A side is viewed from the plus input terminal 24 and the minus input terminal 26 is reduced. On the other hand, as the duty ratio α decreases, the converter input voltage Vi increases and the current flowing into the positive input terminal 24 decreases. As a result, the impedance when the step-down converter 22A side is viewed from the plus input terminal 24 and the minus input terminal 26 is increased.

  A diode may be used instead of the switching element 46. In this case, the anode terminal of the diode is connected to the negative input terminal 26 and the negative output terminal 30 side.

  In order to describe the control of the output power of the solar cell, the characteristics of the solar cell will be described here. FIG. 3 shows the voltage-current characteristics of the solar cell. The voltage-current characteristic is a characteristic indicating the relationship between the output voltage of the solar cell and the output current flowing out from the positive terminal of the solar cell. The horizontal axis indicates the output voltage, and the vertical axis indicates the output current. Here, it is assumed that the load device whose impedance changes is connected to the solar cell.

  As indicated by the point QS, when the solar cell is in an open state and the output current of the solar cell is 0, there is no voltage drop in the solar cell, and the output voltage becomes the maximum voltage VS. At this time, the output power of the solar cell is zero. When the output current increases due to a change in the load impedance to the solar cell, the voltage drop in the solar cell increases and the output voltage decreases as indicated by the arrow 52. The output power of the solar cell is the product of the output voltage and the output current at the point Q on the voltage-current characteristic, and is represented by a hatched rectangular area. The output power of the solar cell is maximized in terms of the voltage-current characteristics where this area is maximized. Such a point is called a maximum power point MPP (Maximum Power Point). When the output current becomes larger than the value at the maximum power point MPP, the output voltage decreases to 0 as indicated by the point QE, and the output power of the solar cell becomes 0.

  Thus, the solar cell has an internal resistance, and when a current flows through the solar cell, the output voltage of the solar cell decreases due to a voltage drop. By adjusting the load impedance for the solar cell so that the maximum power point MPP where the output power is maximum exists on the voltage-current characteristics and the output voltage and the output current are the values at the maximum power point MPP, Maximum output power is obtained.

  FIG. 4 shows a characteristic (voltage power characteristic) of the output power with respect to the output voltage when the output voltage is decreased from the maximum value VS to 0 by changing the load impedance. The horizontal axis indicates the output voltage, and the vertical axis indicates the output power. The output power increases as the output voltage decreases from the maximum value VS, reaches a maximum value at the maximum power point MPP, and then decreases to zero. FIG. 5 illustrates voltage power characteristics 54A, 54B, and 54C for three cases where the illuminance of the irradiated light is different. The voltage power characteristic 54A is a characteristic when the illuminance is larger than the voltage power characteristic 54B, and the voltage power characteristic 54B is a characteristic when the illuminance is larger than the voltage power characteristic 54C. As the illuminance increases, the output power increases, and the output voltage and load impedance corresponding to the maximum power point MPP change according to the change in illuminance.

  The maximum power point MPP is often within a certain target range with the maximum voltage VS as a reference. That is, the maximum power point MPP often exists within a target range of a · VS or more and b · VS or less with respect to the maximum voltage VS. For example, solar cells in which a is 0.7 and b is 0.9 are widely produced. In this case, the maximum power point MPP exists within a target range of 70% or more and 90% or less of the maximum voltage VS.

  Thus, the load impedance at which the output power of the solar cell is maximized changes according to changes in environmental conditions. Therefore, in the solar cell control device 10 according to the embodiment of the present invention, the load impedance for the solar cell 12 is appropriately controlled by the control of the voltage converter 22. Here, the control in the case of using the step-down converter 22A shown in FIG. 2 as the voltage converter 22 will be described.

  Since the switching element 44 and the switching element 46 of the step-down converter 22A are alternately turned on / off, when the duty ratio of the switching element 44 is α, the duty ratio of the switching element 46 is (1−α).

  First, the control unit 32 sets the duty ratio α of the switching element 44 to zero. As a result, the solar cell 12 is opened, and the voltage detection value Vd becomes the maximum detection value VS. The control unit 32 controls the step-down converter 22A to decrease the voltage detection value Vd by a predetermined first change width Δ1 until the voltage detection value Vd reaches a value within the target range from the maximum detection value VS. At this time, the control unit 32 decreases the voltage detection value Vd by the first change width Δ1 by increasing the duty ratio α.

  The control unit 32 obtains the voltage detection value Vd and the current detection value Id and obtains the power detection value W = Id · Vd every time the voltage detection value Vd is decreased by the first change width Δ1. Each time the voltage detection value Vd is decreased by the first change width Δ1, the voltage detection value Vd, the duty ratio α, and the power detection value W are stored in association with each other.

  In FIG. 6, the process of decreasing the voltage detection value Vd from the maximum detection value VS by the first change width Δ1 is conceptually indicated by an arrow on the Vd axis. For each voltage detection value Vd, a power detection value W corresponding to the voltage power characteristic is obtained, and the voltage detection value Vd, the duty ratio α, and the power detection value W are associated with each other.

  After the voltage detection value Vd reaches a value within the target range, the control unit 32 performs the step-down converter until the voltage detection value Vd reaches the first value (minimum detection value) less than the lower limit value a · VS of the target range. The voltage detection value Vd is decreased by a predetermined second change width Δ2 by controlling 22A. The second change width Δ2 is a value smaller than the first change width Δ1. For example, the second change width Δ2 is set to one fifth of the first change width Δ1. At this time, the control unit 32 decreases the voltage detection value Vd by the second change width Δ2 by increasing the duty ratio α.

  The control unit 32 obtains the voltage detection value Vd and the current detection value Id to obtain the power detection value W every time the voltage detection value Vd is decreased by the second change width Δ2. Each time the voltage detection value Vd is decreased by the second change width Δ2, the voltage detection value Vd, the duty ratio α, and the power detection value W are stored in association with each other.

  In FIG. 6, the process of decreasing the voltage detection value Vd with the second change width Δ2 until the voltage detection value Vd reaches the minimum detection value from the value within the target range is conceptually indicated by an arrow on the Vd axis. ing. For each voltage detection value Vd, a power detection value W corresponding to the voltage power characteristic is obtained, and the voltage detection value Vd, the duty ratio α, and the power detection value W are associated with each other.

  Based on the correspondence relationship between the voltage detection value Vd, the duty ratio α, and the power detection value W stored in the change range of the voltage detection value Vd, the control unit 32 detects the power detection value W in the change range of the voltage detection value Vd. Obtain the optimized duty ratio when becomes the maximum value. Then, the duty ratio of switching element 44 of step-down converter 22A is set to an optimized duty ratio, and the duty ratio of switching element 46 is set to a value obtained by subtracting the optimized duty ratio from one. In the example shown in FIG. 6, the duty ratio at the maximum power point MPP is obtained as the optimized duty ratio.

  By setting the duty ratio of each switching element in accordance with the optimized duty ratio, the target condition that the power detection value W becomes the maximum value is satisfied, and the solar cell 12 outputs the maximum power.

  The control unit 32 obtains an optimized duty ratio according to the above process, and repeatedly executes a process of setting the duty ratio of each switching element according to the optimized duty ratio at a predetermined time interval. When a diode is used instead of the switching element 46, the duty ratio may be set only for the switching element 44.

  According to such processing, the change width is set based on whether or not the voltage detection value Vd is included in the target range determined with the maximum detection value VS as a reference. That is, when the voltage detection value Vd is larger than a value within the target range, a first change width larger than the second change width set within the target range is set. As a result, the maximum power point within the target range is quickly searched, and the search resolution of the maximum power point within the target range is improved.

  Some solar cells have an output voltage corresponding to the maximum power point MPP lower than a voltage within a target range, as shown in FIG. In this case, the maximum power point MPP of the voltage power characteristic is not found within the change range of the voltage detection value Vd. As indicated by a point 56 on the voltage power characteristic, when the voltage detection value Vd reaches the minimum detection value, the power detection value W becomes the maximum value in the change range of the voltage detection value Vd. In this case, the duty ratio α when the voltage detection value Vd reaches the minimum detection value is obtained as the optimized duty ratio. By setting the duty ratio of each switching element according to the optimized duty ratio, the target condition that the power detection value W becomes the maximum value in the change range of the voltage detection value Vd is satisfied.

  Further, depending on the state of the circuit on the load side of the step-down converter 22A, such as the output voltage of the battery and the electromotive force generated in the load device, the voltage detection value Vd is not related to the duty ratio α of the switching element 44 of the step-down converter 22A. There is a case where it does not become smaller than a certain limit value VL. In this case, the control unit 32 decreases the voltage detection value Vd from the maximum detection value VS to the limit value VL, and obtains the duty ratio α when the power detection value W reaches the maximum value in this range as the optimized duty ratio. FIG. 8 shows an example of voltage power characteristics when the voltage detection value Vd does not become smaller than the limit value VL. In this example, the limit value VL is a value within the target range, and even if the duty ratio α is increased, the voltage detection value Vd does not become smaller than the lower limit value VL. In this case, the duty ratio α at the point 58 on the voltage power characteristic corresponding to the lower limit value VL is obtained as the optimized duty ratio. By setting the duty ratio of each switching element in accordance with the optimized duty ratio, the target condition that the power detection value W becomes a value at the lower limit value VL is satisfied. Even when the limit value VL is larger than the value within the target range, the optimized duty ratio is obtained by the same processing.

  In the above, after the voltage detection value Vd, the duty ratio α, and the power detection value W are stored in association with each other in the change range of the voltage detection value Vd, the optimized duty ratio when the power detection value W becomes the maximum value is calculated. The processing to be obtained has been described. In addition to such processing, when the maximum value of the power detection value W is found in the process of decreasing the voltage detection value Vd, processing for setting the duty ratio α corresponding to the maximum value as the optimized duty ratio is performed. May be executed.

  In this case, the control unit 32 compares the power detection value W before and after the voltage detection value Vd is decreased by a predetermined change width. When the power detection value W2 after the voltage detection value Vd is decreased is smaller than the power detection value W1 before the voltage detection value Vd is decreased, the power detection value W1 is the maximum value of the power detection value W. And the duty ratio α corresponding to the detected power value W1 is obtained as the optimized duty ratio.

  According to such processing, it is not always necessary to decrease the voltage detection value Vd over the entire range from the maximum detection value VS to the minimum detection value. Therefore, an optimized duty ratio is quickly required.

  In the above description, the voltage detection value Vd when the solar cell 12 is in the open state is the maximum detection value VS. The maximum detection value VS is defined as the voltage detection value Vd when the output power of the solar cell 12 becomes a predetermined minimum value, that is, when the solar cell 12 is in the minimum load state (including the open state). May be.

  In the above description, the example in which the step-down converter 22A is used as the voltage converter 22 has been described. Even when a boost converter is used as the voltage converter 22, the optimized duty ratio can be obtained by the same processing. In this case, by changing the duty ratio of the switching element included in the boost converter, the voltage detection value Vd is decreased from the maximum detection value VS by a predetermined change width, and the duty when the power detection value W satisfies the target condition. The ratio is determined as the optimum duty.

DESCRIPTION OF SYMBOLS 10 Solar cell control apparatus, 12 Solar cell, 14 Battery side diode, 16 Ammeter, 18 Voltmeter, 20 Voltage adjustment part, 22 Voltage converter, 22A Buck converter, 24 Plus input terminal, 26 Negative input terminal, 28 Plus output terminal , 30 Negative output terminal, 32 Control unit, 34 Load side diode, 36 Battery, 38 Positive load terminal, 40 Negative load terminal, 42 Load device, 44, 46 Switching element, 48 Inductor, 50 Capacitor, 52 Arrow, 54A, 54B , 54C Voltage power characteristics, 56 Points on voltage power characteristics corresponding to the minimum value of the detection voltage change range, 58 Points on voltage power characteristics corresponding to the lower limit value VL.

Claims (5)

A voltage adjustment unit is provided between the solar cell and the load device, and adjusts a voltage output from the solar cell by switching and outputs the voltage to the load device.
The voltage regulator is
By adjusting the switching state, the output voltage output from the solar cell to the voltage adjustment unit is decreased from the maximum voltage with a predetermined change width, and the output power output from the solar cell to the voltage adjustment unit is a target condition. A control unit that searches for an optimal switching state when satisfying and sets the switching state to the optimal switching state;
The maximum voltage is a voltage output from the solar cell when the solar cell is in a minimum load state,
The said control part sets the said change width based on whether the said output voltage is contained in the target range defined on the basis of the said maximum voltage, The solar cell control apparatus characterized by the above-mentioned. In the solar cell control apparatus according to claim 1,
The control unit, when the output voltage is within the target range, makes the change width smaller than that when the output voltage is larger than a value within the target range. Battery control device. In the solar cell control device according to claim 1 or 2,
The target condition is a condition that the output power becomes a maximum value in a change range of the output voltage. In the solar cell control device according to any one of claims 1 to 3,
The target condition is a condition that the output power becomes a maximum value,
The controller reduces the output voltage by the change width by adjusting the switching state, and when the output power reaches a maximum value, the switching state when the maximum value is obtained is the optimum A solar cell control device characterized by being in a switching state. In the solar cell control apparatus according to any one of claims 1 to 4,
The voltage adjusting unit includes a voltage converter including a switching element,
The said control part sets the duty ratio with respect to the said switching element, The solar cell control apparatus characterized by the above-mentioned.

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