JP6601280B2 - Solar system - Google Patents

Description

  The present invention relates to a solar system that can be mounted on a moving vehicle or the like.

  In general, when the photovoltaic power of a specific cell is reduced due to partial contamination of the solar panel, accumulation of fallen leaves, or the like, the corresponding cell becomes a resistance due to energization, and power loss occurs in the path. There is known a hot spot phenomenon that generates heat when a cell whose photovoltaic power is lowered continues to be energized, and there has been a problem of characteristic deterioration due to panel breakage or deterioration due to heat generation.

  Therefore, in solar power generation MPPT (maximum power point tracking) control, it is known to bypass the solar cell portion where the photovoltaic power is reduced by a bypass diode to solve the above problem (for example, patents). Reference 1).

  Also, when the solar panel is mounted on a vehicle that moves at a certain speed, the shadowed part of the outside building will change every moment due to movement, so let's bypass the shadowed solar cell each time. Then, complicated control is required. In addition, since the influence of the shadow is temporary, it is difficult to consider that the corresponding cell generates heat.

Japanese Patent Laid-Open No. 02-022871

  When a solar panel is mounted on a moving vehicle, etc., the cause of the decrease in photovoltaic power is temporary due to the constantly changing shadow as described above, semi-permanent deposits such as dirt and fallen leaves, and the inside. There are things such as breakdowns that last for a long time. At this time, when the photovoltaic power is lowered for a long time, there is a possibility that it becomes a hot spot due to heat generation, but temporary one does not generate heat.

  However, in general, when the photovoltaic power is lowered, the temporary one and the one over a long time are equivalent as the characteristics of the solar panel and are difficult to discriminate.

  Therefore, in view of the above circumstances, the present invention reduces power loss and suppresses the occurrence of hot spots by avoiding energization to a power generation path including a solar cell whose photovoltaic power has been reduced for a long time. The purpose is to provide a solar system.

In order to solve the above problems, in one aspect of the present invention, a solar system that can be mounted on a vehicle includes a group including a plurality of solar cells connected in series and a bypass diode connected in parallel to the solar cells. A plurality of solar panels; a current sensor for measuring a current value output from the solar panel; a voltage sensor for measuring a voltage value output from the solar panel; and receiving the measured current value and the voltage value And a control unit that performs power generation control using MPPT (maximum operating point tracking) control, wherein the control unit is on an IV curve indicating a correlation between the measured current value and the voltage value. It is comprised so that the voltage which comprises the level | step difference which generate | occur | produces when the differential conductance di / dv is below a threshold value, and the voltage which comprises the level | step difference is stopping Including the first step voltage generated and the second step voltage generated during traveling, and the control unit determines whether the first step voltage and the second step voltage coincide with each other. When the first step voltage and the second step voltage match, the bypass diode is turned on in a group including a solar cell having a voltage lower than the matching voltage and having a reduced photovoltaic power. A voltage that excludes a plurality of solar cells connected in series from the power generation path is set as an operating point voltage, and MPPT control is performed so that the output voltage of the solar panel follows the set operating point voltage.

  By determining whether the voltage value constituting the first step and the voltage value constituting the second step are the same, the decrease in the photovoltaic power in the solar cell is temporary or prolonged. It is possible to determine whether it is to be passed.

  In MPPT control, a voltage smaller than the matching voltage is set as an operating point voltage, and tracking control is performed. Here, the operating point voltage is a voltage smaller than the voltage value constituting the first step and the second step, and in a group including a solar cell in which the photovoltaic power is reduced, the bypass diode is turned on in series. This corresponds to a voltage for excluding a plurality of solar cells to be connected from the power generation path. By performing MPPT control that causes the output voltage of the solar panel to follow the set operating point voltage, it is possible to avoid a solar cell whose photovoltaic power has been lowered for a long time from becoming a hot spot.

  According to one aspect, in a solar system, by avoiding energization to a power generation path including a solar cell whose photovoltaic power has been reduced for a long time, power loss is reduced and generation of hot spots is suppressed. be able to.

1 is an overall view of the present invention. Explanatory drawing of the voltage and electric current of a solar cell. Explanatory diagram of current and voltage in a solar panel with a bypass diode. The control flowchart. The detailed flowchart and calculation graph of calculation of a step voltage.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of a solar system according to an embodiment of the present invention. The present solar system 1000 is required to be mounted for, for example, a vehicle that moves at a certain speed.

  The solar system 1000 is a solar system that performs power generation control using MPPT (Maximum Power Point Tracking) control. Since the MPPT control operates while following an optimum operating point (mostly maximum power) that constantly changes according to changes in weather conditions and the like, the maximum power can always be extracted from the solar cell under each weather condition.

  The solar system 1000 includes a solar panel 100, a DC-DC converter 200, a current sensor 210, a voltage sensor 220, and a controller 300.

  The solar panel 100 includes a plurality of solar cells (solar cells) C1, C2,... Cx, and bypass diodes D1, D2.

  In the solar panel 100, the plurality of solar cells C1, C2,... Cx have a string configuration in which they are directly connected. The minimum unit of the string delimited by the bypass diodes D1 and D2 is referred to as clusters (substrings, groups) A and B.

  1 shows an example in which two clusters and corresponding bypass diodes are provided in the solar panel 100, three or more clusters and bypass diodes may be provided.

  The current sensor 210 measures the current output from the solar panel 100. The voltage sensor 220 senses the voltage output from the solar panel 100.

  The controller (control unit) 300 receives the current value measured by the current sensor 210 and the voltage value measured by the voltage sensor 220 and executes a drive command to the DC-DC converter 200. Specifically, the controller 300 includes a step voltage calculation unit 310, a storage unit 320, a comparison / determination unit 330, and a DUTY setting unit 340 in hardware or software by a program.

  The step voltage calculation unit 310 calculates a step voltage from an IV curve indicating a correlation between a current value and a voltage value output from the solar panel 100 measured by the current sensor 210 and the voltage sensor 220.

  The storage unit 320 stores a step voltage (a voltage value of the first step voltage group) during stopping (stopping) and a step voltage (a voltage value of the first step voltage group) during travel.

  The comparison / determination unit 330 compares each voltage value of the stopped step voltage (first step voltage) group with each voltage value of the traveling step voltage (second step voltage) group, and the same step voltage Determine if a value exists.

  When it is determined that the first step voltage and the second step voltage match, the DUTY setting unit 340 controls the DUTY of the signal transmitted to the DC-DC converter 200.

  The DC-DC converter 200 performs voltage conversion from the solar panel to the power supply target. Further, the DC-DC converter 200 controls the voltage of the load connected to the solar panel 100 by controlling the input voltage to the DC-DC converter 200 in accordance with the signal transmitted from the DUTY setting unit 340. become. Thereby, the output voltage from the solar panel 100 is controlled, the output power from the solar panel 100 is maximized and taken out, and supplied to the supply destination 400 such as the electrical equipment of the vehicle.

  In a solar panel, a solar cell (also referred to as a Dark cell) whose electromotive voltage has decreased or is not generating power is a resistor. If a current is forcibly applied to the solar cell, the cell may be damaged or a hot spot may be generated due to heat generation.

  The phenomenon that occurs when the electromotive force of the solar cell decreases will be described in detail. FIG. 2A shows an equivalent circuit of one solar cell.

  In FIG. 2, (b) is an IV curve obtained by a single solar cell of (a), and (c) is a case where the electromotive force of the single solar cell is lowered (when it becomes a Dark cell). The obtained IV curve is shown.

  In FIG. 2C, a broken line indicates that no Dark cell exists, and a solid line indicates that a Dark cell exists. As shown in FIG.2 (c), when the electromotive force of a single solar cell falls, when it is going to send the electric current irr, a voltage will fall (drop).

  Here, changes in voltage and current when a plurality of solar cells are connected without providing a bypass diode in the solar panel (for example, within one cluster in FIG. 1) will be described.

  FIG. 2D shows an IV curve obtained when a plurality of solar cells are connected in series, and FIG. 2E shows an IV curve obtained when one of the plurality of solar cells becomes a Dark cell. , (F) shows an IV curve after transition from the state (e).

  In FIG. 2 (e), a broken line indicates that no Dark cell exists, and a solid line indicates that a Dark cell exists. At this time, since v1 is large, when the electromotive force of one cell decreases, the state changes from (e) to (f), and the overall power generation efficiency decreases.

  In order to solve this problem, in the solar panel 100, the bypass diode is connected in parallel for each cluster with respect to the solar cells connected in series. The function of the bypass diode in the solar panel will be described with reference to FIG.

  3A shows a current flow in the solar panel 100 of FIG. (B) shows an IV curve (voltage / current characteristic graph) of the A portion of the solar panel, (c) shows an IV curve of the B portion of the solar panel, and (d) shows a cluster A of the solar panel. The total IV curve of B and B is shown, and (e) shows the IV curve after transition from the state of (d).

  Here, in FIG. 3E, the breakdown voltage Vfall is negatively output in the cluster A. Specifically, since the solar cells constituting the string are connected in series, the current is common to each solar cell. When a cell having low generation current capability is present in the string, if the operating point current value corresponding to the maximum operating point determined by MPPT is larger than the short-circuit current value of the cell, the operating point of the cell is balanced on the negative voltage side. Since the voltage is negative, it is not power generation but power consumption (heat generation).

  Since the corresponding solar cell has a negative voltage, if the current is forced to flow, the solar cell may be damaged. Further, since the current consumed by the other solar cells is consumed by the cell, the efficiency of the entire cluster A including the Dark cell is reduced as in FIG.

  Here, when the voltage in the cluster A becomes equal to or lower than the forward voltage Vf of the bypass diode, it is passed in the forward direction of the bypass diode.

  In order for the bypass diode to be turned on, the voltage across the solar cell having a low current capability as described above needs to be higher than the voltage generated by the solar cells constituting the cluster other than the cell. For example, when one cluster is composed of 20 cells in series, if the terminal voltage of one cell is not higher than the total voltage of the forward voltages of the other 19 cells, the bypass diode is not turned on and is hot. Become a spot.

  Therefore, in order to make the bypass diode of cluster A function, it is preferable to control the operating point voltage to be tracked to be equal to or less than (total voltage of portion B) + (forward voltage Vf of bypass diode D1) (FIG. 4). , S3).

  In this way, when there is a cell that does not generate power (Dark cell), the voltage of the substring including that cell becomes negative, so that it bypasses in units of string and passes through the bypass diode instead of the solar cell that does not generate power. Current flows. Thereby, the energization to the Dark cell is excluded, the temperature of the solar cell rises, and the occurrence of a hot spot that leads to breakage or ignition can be avoided.

  Hereinafter, control in the solar system 1000 of the present invention will be described. FIG. 4 shows a schematic flowchart of control in the present invention.

  FIG. 5 shows a detailed flowchart and calculation graph of the step voltage calculation. 5A is a voltage / current characteristic graph (IV curve), FIG. 5B is a voltage / power characteristic graph (PV curve), and FIG. 5C is a voltage / differential conductance characteristic graph (di / (dv-V curve), (d) shows a detailed flowchart of the step voltage calculation used in the determination of S2 of FIG.

  In S1 of the flowchart of FIG. 4, when the vehicle travels, when the vehicle reaches a predetermined speed (Sth), the process proceeds to S2.

  In S <b> 2, the comparison / determination unit 330 of the controller 300 calculates the stored voltage values of the stopped step voltage (first step) group and the voltage values of the traveling step voltage (second step) group. Are matched (whether there is a match).

  Here, the step voltage {vstop [i]} calculation / storage during stopping (when the vehicle is stopped at zero speed) used in the determination of S2 in FIG. 4 will be described with reference to FIG.

  First, in S11 of FIG. 5D, the step voltage calculation unit 310 of the controller 300 receives (acquires) the output current and output voltage from the solar panel 100 measured by the current sensor 210 and the voltage sensor 220 ( S11).

  From the received current value and voltage value, (a) voltage / current characteristics (IV curve), (b) voltage / power characteristics (PV curve), and (c) voltage / differential conductance. The characteristic (di / dv-V curve) is calculated (S12).

Here, when the mountain climbing method, which is a general MPPT method, is used, the power peak value Pmax is set as the maximum operating point to be tracked, as indicated by the dotted line in the PV curve in FIG. . Then, the power is changed while inverting the sign of the voltage change amount ΔV so that the voltage value fluctuates around the voltage value (Vmax) corresponding to the peak value Pmax of the power (for example, between V _{P1 and} V _P2 ). adjust.

  However, when a partial shadow (Dark cell) is generated, the power does not reach the peak value Pmax as indicated by the solid line of the PV curve in (b).

  In S13, the step voltage calculation unit 310 (c) in the di / dv-V curve, when the differential conductance di / dv falls below the threshold Th1, the electromotive force decreases in the solar panel 100 due to shadows or the like ( a) It is determined that a step has occurred in the IV curve.

  At this time, when the threshold Th1 of the differential conductance di / dv falls below, the point with the largest change (that is, the lowest point in the graph (c)) is stored as the corresponding voltage (step voltage) (S14). .

  Here, in the solar panel, in the example shown in FIG. 1, two groups (clusters) are shown. However, when three or more clusters are connected, in the di / dv-V curve, di There may be a plurality of step voltages that cause a change such that / dv (voltage differentiation of current, differential conductance) falls below the threshold Th1. In this case, all voltage values corresponding to the set of step voltage are stored in the storage unit 320.

  In this way, the i step voltages (first step voltages) v1, v2, v3,... Vi generated while the vehicle is stopped are collectively referred to as a first step voltage group vstop [i].

  The calculation and storage of the step voltage shown in FIG. 5 (d) can also be applied to the calculation and storage of the step voltage during traveling (when the vehicle is operating at a certain speed or more). When calculating the step voltage during travel, the current value and voltage output from the solar panel in S11 after the travel speed of the vehicle has exceeded a predetermined value (Sth) as shown in S1 of FIG. The difference is that the measurement of the output value starts. Other operations are the same as those in FIG.

  The j step voltages (second step voltages) v1, v2, v3,... Vj generated during traveling are collectively referred to as a second step voltage group vmov [j].

  In S2 of FIG. 4, when it is determined that the voltage value constituting the first step calculated and stored by the method of FIG. 5D matches part or all of the voltage value constituting the second step, It is determined whether a common voltage Vhotspot exists. Specifically, a set of voltages Vstop [i] corresponding to a generation point below the threshold Th1 of the differential conductance di / dv while stopped and a voltage corresponding to a generation point below the threshold Th1 of the running di / dv It is determined whether or not the set Vmove [j] matches (whether there is a match).

  The presence of a step in the IV curve indicating the output characteristics of the solar panel 100 both when the vehicle is running and when it is stopped means that the photovoltaic power in the solar cells C1, C2,. However, it means that it is not temporary, it is something that lasts for a long time. For example, it can be said that it is not the influence of an external building but a partial shadow (semi-permanent shadow) over a long period of time due to an object attached to a solar panel and moving at the same speed as the vehicle.

  For this reason, when it is determined that there is a match between the first step voltage and the second step voltage, it means that the decrease in photovoltaic power is over a long period of time, so a hot spot occurs. Or a hot spot may be generated (S2). Therefore, the following S3 control is performed to avoid the occurrence of hot spots.

  In S3, when the voltage to the solar panel 100 is input, the control position is moved (the operating point voltage to be followed is changed), and the MPPT is controlled. That is, the operating point voltage is changed to a lower voltage so that the bypass diode works in the group including the cell in which the photovoltaic power is lowered.

  In this case, the user (vehicle crew) is notified (S4).

  On the other hand, if it is determined in S2 that the first step voltage and the second step voltage do not match and no hot spot is generated (NO), normal MPPT control is performed (S5).

  Specifically, in the normal maximum power point tracking (MPPT) control, the voltage Vmax corresponding to the maximum point Pmax of the power indicated by the mountain-shaped dotted line shown in FIG. 5B is set as the optimum operating point voltage. Then, power is generated while controlling the output voltage of the solar panel 100 to follow the operating point voltage (S5 in FIG. 4).

  On the other hand, in S3, in order to avoid the occurrence of a hot spot, not the voltage corresponding to the maximum value Pmpp of the electric power indicated by the solid line in FIG. 5B, but common during stopping and traveling in FIG. 5B. Follow-up control is performed at an operating point (optimal operating point Vop) of a voltage equal to or lower than the step voltage Vhotspot (if there are a plurality of step voltages Vhotspot, for example, v1 in the figure).

  The voltage at this operating point is a voltage that excludes a plurality of solar cells connected in series from the power generation path when a bypass diode is turned on in a group including solar cells whose photovoltaic power has decreased for a long time. As a result, control that does not generate a loss that is a source of a hot spot is performed.

  In this way, by setting a voltage smaller than the voltage value that coincides with the first step and the second step as the operating point voltage, and causing the output voltage of the solar panel 100 to follow the operating point voltage, the bypass diode The power generation control is executed while avoiding the power generation path on which dirt or the like is attached. Therefore, power loss can be suppressed by performing such MPPT control.

  Here, in MPPT control, in order to operate the solar panel 100 at an operating point voltage equal to or lower than Vhotspot, the DUTY setting unit 340 of the controller 300 only changes the DUTY of the signal applied to the DC-DC converter 200. Well, it does not require a special configuration.

  As described above, in the control of the invention, by determining whether or not the step voltage during the stop and the step voltage during traveling coincide with each other, the decrease in photovoltaic power in the solar cell is temporary, It is possible to determine whether it is for a long time. Furthermore, when it is determined that the decrease in photovoltaic power is long-lasting, the operating point voltage, which is the MPPT control follow-up position, is moved to a voltage that activates the bypass diode. The cell can be excluded from the power generation path, and the occurrence of hot spots can be avoided.

  In the di / dv-V curve calculated from the IV curve as shown in FIG. 5 (d), there is a change that di / dv (voltage differential of current, differential conductance) is lower than the threshold Th1. It is preferable to periodically perform the operation of storing the generated step voltage sets (v1, v2,... Vi) and (v1, v2,... Vj). Further, it is preferable that the entire operation of FIG. 4 for determining whether or not the first step voltage and the second step voltage match and determining whether or not to adjust the set value in the MPPT is also performed periodically.

  This is because even a Dark cell that has not changed between stopping and traveling may change due to external factors when the solar panel is mounted on a moving vehicle. For example, it may be assumed that a new dark cell is generated, fallen leaves are deposited, foreign matter (insects, bird droppings, etc.) is attached, the cell itself is broken, or the dark cell is eliminated, and the fallen leaves and attached matter are removed by rain. As described above, in the solar panel, by periodically detecting and comparing the characteristics during stopping and traveling, it is possible to detect the change in the generation state of the Dark cell and reflect it in the MPPT control.

  As mentioned above, although the solar system was demonstrated by embodiment, this invention is not limited to the said embodiment, A various deformation | transformation and improvement are possible within the scope of the present invention.

1000 System 100 Solar Panel 200 DC-DC Converter 210 Current Sensor 220 Voltage Sensor 300 Controller (Control Unit)
310 Step voltage calculation unit 320 Storage unit 330 Comparison / determination unit 340 DUTY setting unit 400 Power supply destination A, B Cluster (substring, operation unit, group)
C1, C2, C3, ... Cx solar cells (solar cells)
D1, D2 Bypass diode vstop [m] First step voltage set (step voltage while stopped)
vmove [n] second step voltage set (step voltage during travel)
Vhotspot common step voltage (minimum value)
Vmax Maximum operating point Vop Operating point voltage

Claims (1)

A solar system that can be mounted on a vehicle ,
A solar panel comprising a plurality of groups comprising a plurality of solar cells connected in series and one bypass diode connected in parallel to the solar cells;
A current sensor for measuring a current value output from the solar panel;
A voltage sensor for measuring a voltage value output from the solar panel;
A control unit that receives the measured current value and the voltage value and performs power generation control using MPPT (maximum operating point tracking) control, and
The control unit is configured to calculate a voltage constituting a step generated when the differential conductance di / dv is equal to or less than a threshold value on an IV curve indicating a correlation between the measured current value and the voltage value. And
The voltage constituting the step includes a first step voltage generated while the vehicle is stopped and a second step voltage generated during traveling,
The control unit determines whether the first step voltage and the second step voltage match,
When the first step voltage and the second step voltage coincide with each other, the bypass diode is turned on in a series including a solar cell having a voltage lower than the matching voltage and having a reduced photovoltaic power. A voltage that excludes a plurality of solar cells to be connected from the power generation path is set as an operating point voltage, and MPPT control is performed to cause the output voltage of the solar panel to follow the set operating point voltage. system.

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