Vehicle-mounted solar power generation system and method for determining operating voltage of vehicle-mounted solar panel

Abstract

To provide a vehicle-mounted solar cell panel capable of maximum power point tracking control that does not require a temperature sensor or an illuminance sensor, and a method for determining an operating voltage.SOLUTION: In a vehicle-mounted solar power generation system that does not require a temperature sensor or an illuminance sensor, a method for determining an operating voltage includes: a solar cell panel 1 formed by connecting a plurality of solar cell modules 11 in parallel; a converter 3 connected to the solar cell panel via a switch 4; a voltmeter 5 connected to the solar cell panel; and a control device 2. The control device turns off the switch and obtains an open-circuit voltage of the solar cell panel from the voltmeter, determines the operating voltage of the vehicle-mounted solar panel from a relation between the open-circuit voltage and the maximum power point voltage of the solar cell panel 1, which is stored in advance, and turns on the switch 4 and controls the converter 3 to generate power at the determined operating voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an in-vehicle solar power generation system and a method for determining an operating voltage of an in-vehicle solar panel, and more particularly to an in-vehicle solar power generation system and a method for determining an operating voltage of an in-vehicle solar panel that do not require sensing of the temperature and illuminance of the solar panel. [Background technology]

[0002] A solar cell system is controlled so as to track a maximum power point at which the output power of the solar cell is maximized, and the maximum power point varies depending on the intensity of solar radiation received and temperature.

[0003] Patent Document 1 discloses a power generation control device that provides a DC / DC converter to each of multiple solar cell modules that make up a solar panel, and performs maximum power point tracking control for each solar cell module when the voltage of the solar cell module is below a predetermined voltage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-199477 A Summary of the Invention [Problem to be solved by the invention]

[0005] Because the optimal operating voltage of a solar cell varies depending on weather conditions, conventional maximum power point tracking control senses the temperature and illuminance of the solar cell module, selects an IV curve corresponding to the measured temperature and illuminance from multiple pre-stored IV curves, and determines the operating voltage based on this IV curve.

[0006] Therefore, it is necessary to provide a temperature sensor and an illuminance sensor in all solar cell modules that make up the solar cell panel, and the large number of such sensors makes it difficult to reduce costs. In addition, controlling each solar cell module is cumbersome and results in large losses.

[0007] The present invention has been made in consideration of the problems associated with the conventional technology, and an object of the present invention is to provide an in-vehicle solar panel capable of maximum power point tracking control without requiring a temperature sensor or an illuminance sensor, and a method for determining an operating voltage. Vehicle-mounted solar power generation system [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned objective, the inventors discovered that by operating all of the solar cell modules that make up a solar cell panel at the maximum power point voltage of the solar cell module that receives the highest solar radiation intensity, it is possible to suppress a decrease in the power generation efficiency of the entire solar cell panel and thereby achieve the above-mentioned objective, thereby completing the present invention.

[0009] That is, the vehicle-mounted solar power generation system of the present invention comprises a solar cell panel formed by connecting a plurality of solar cell modules in parallel, a converter connected to the solar cell panel via a switch, a voltmeter connected to the solar cell panel, and a control device. The control device then turns OFF the switch, obtains the open circuit voltage of the solar cell panel from the voltmeter, determines an operating voltage of the vehicle-mounted solar cell panel from a pre-stored relationship between the open circuit voltage and maximum power point voltage of the solar cell panel, turns ON the switch, and controls the converter to generate power at the determined operating voltage.

[0010] Moreover, the method of determining the operating voltage of an in-vehicle solar cell panel of the present invention is a method of determining the operating point of an in-vehicle solar cell panel composed of a plurality of solar cell modules connected in parallel. The operating voltage of the vehicle-mounted solar cell panel is determined based on a preset relationship between the open circuit voltage and maximum power point voltage of the solar cell panel. Effect of the Invention

[0011] According to the present invention, all of the solar cell modules that make up a solar cell panel are operated at the maximum power point voltage of the solar cell module that receives the greatest solar radiation intensity, thereby making it possible to provide an in-vehicle solar power generation system that does not require a temperature sensor or an illuminance sensor, and a method for determining the operating voltage thereof. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of an in-vehicle solar power generation system. [Diagram 2] FIG. 1 is a diagram showing an example of an arrangement of photovoltaic panels (modules). [Diagram 3] FIG. 13 is a diagram showing an example of IV curves for different illuminances of a photovoltaic power generation module in which unit cells having a rectangular vertical projection image are integrated. [Figure 4] The vertical projection image shows an example of the IV curve for each temperature of a solar power generation module in which rectangular unit cells are integrated. [Diagram 5] FIG. 4 is a chart illustrating an example of a control flow of the control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The vehicle-mounted solar power generation system of the present invention will now be described in detail. The vehicle-mounted solar power generation system of the present invention comprises a solar cell panel, a voltmeter connected to the solar cell panel, a converter connected to the solar cell panel via a switch to adjust the operating voltage of the solar cell panel, and a control device to control the converter.

[0014] As shown in FIG. 1, the solar panel is formed by connecting multiple solar cell modules in parallel, and each solar cell module has the same number of series-connected cells that make up the solar cell module, and is adjusted to have the same output under the same conditions.

[0015] As shown in Figure 2, the solar cell modules of an in-vehicle solar panel may be installed not only on the roof of the vehicle, but also on the hood, back door, and even on the sides of the vehicle body.

[0016] Thus, unlike stationary solar panels, vehicle-mounted solar panels are composed of solar cell modules installed on a curved surface, and one solar cell module that makes up the solar cell panel may be installed at an angle to the other solar cell modules.

[0017] Therefore, the solar cell modules constituting the solar cell panel receive different solar radiation intensities due to different angles relative to the direction of solar radiation, and the maximum power point voltages of the solar cell modules differ.

[0018] As described above, for an in-vehicle solar cell panel having the characteristic that the maximum power point voltages differ between solar cell modules, the present invention operates all of the solar cell modules that make up the in-vehicle solar cell panel at the same operating voltage, rather than performing maximum power point tracking control on the individual solar cell modules that make up the solar cell panel.

[0019] Figure 3 shows an example of the IV curve for a typical solar cell module according to illuminance. As shown in Figure 3, when the solar cell module receives greater solar radiation intensity, the short-circuit current density it outputs increases, and the IV curve at that illuminance moves nearly parallel near the short-circuit state and drops off sharply on the high-voltage side (has a steep slope).

[0020] Therefore, under normal solar radiation conditions, when the operating voltage deviates from the maximum power point voltage, the amount of change in current value when it deviates toward the low voltage side is smaller than the amount of change in current value when it deviates toward the high voltage side, so that the decrease in power generation efficiency can be suppressed more effectively when the operating voltage deviates from the maximum power point voltage toward the low voltage side than when it deviates toward the high voltage side.

[0021] In other words, the conversion efficiency (η) of a solar cell module is determined by the short-circuit current density (Jsc) x open-circuit voltage (Voc) x fill factor (FF), and the increase in current density due to an increase in solar radiation intensity often exceeds the decrease in voltage.

[0022] Therefore, by operating all the solar cell modules that make up the solar cell panel at the maximum power point voltage of the solar cell module that receives the highest solar radiation intensity, the solar cell module that receives a high solar radiation intensity operates at the maximum power point voltage, and the solar cell module that receives a low solar radiation intensity experiences only a slight decrease in power generation efficiency.

[0023] Therefore, it is possible to minimize the decrease in power generation efficiency for a solar cell panel that performs maximum power point tracking control for each solar cell module.

[0024] Furthermore, by operating the entire solar panel at the maximum power point of the solar cell module, which receives the greatest solar radiation intensity, the operating voltage of the solar panel can be adjusted using a single DC-DC converter.This reduces losses due to the DC-DC converter compared to adjusting the operating voltage using multiple DC-DC converters, and improves the power generation efficiency of the solar power generation system as a whole.

[0025] Furthermore, as shown in Figure 4, the open-circuit voltage of a solar cell module tends to decrease as the temperature increases. Since the temperature increase of a solar cell module is mainly due to solar radiation, the higher the solar radiation intensity the solar cell module receives, the higher the temperature and the lower the open-circuit voltage.

[0026] Furthermore, since the solar cell panel of the present invention is formed by connecting a plurality of solar cell modules in parallel, the open-circuit voltage of the entire solar cell panel converges to the open-circuit voltage of the solar cell module that receives the highest solar radiation intensity and becomes low.

[0027] In other words, when solar cell modules with different voltages are connected in parallel, the current of the solar cell module with the higher voltage will flow backwards, and the open-circuit voltage of the module with the lowest open-circuit voltage among the solar cell modules connected in parallel will be detected as the open-circuit voltage of the solar cell panel.

[0028] Therefore, by temporarily disconnecting the DC-DC converter from the solar panel with a switch and measuring the open-circuit voltage of the solar panel at that time, the open-circuit voltage of the solar cell module that received the highest solar radiation intensity can be detected, and the operating voltage of the entire solar cell panel can be determined based on this open-circuit voltage.

[0029] Therefore, control can be performed to approximately track the maximum power point without sensing the temperature and illuminance of the solar cell module, and since no temperature sensor or illuminance sensor is required, costs can be reduced.

[0030] Here, the operation of the control device for the vehicle-mounted solar power generation system and the method for determining the operating voltage of the solar cell panel will be described. FIG. 5 shows the control flow of the control device.

[0031] The control device of the present invention turns off the switch to disconnect the solar panel from the DC-DC converter (S101), and obtains the open circuit voltage (Vo) of the entire solar panel from the voltmeter (S102).

[0032] Then, the control device compares the obtained open-circuit voltage (Vo) with the open-circuit voltages of a plurality of IV curves stored in advance, estimates the IV curve of the solar cell module with the highest solar radiation intensity that receives the IV curve with the closest open-circuit voltage (S103), and obtains the optimum operating point voltage (Vmpp) from this IV curve (S104).

[0033] The optimum operating point voltage does not necessarily have to be obtained from the IV curve stored in the control device, but may be obtained from the ratio or difference with the obtained open circuit voltage (Vo).

[0034] Then, the obtained optimum operating point voltage is compared with a threshold voltage (Vth) previously stored in the control device (S105). If the optimum operating point voltage is equal to or greater than the threshold voltage, the command voltage to the DC-DC converter that controls the voltage of the solar cell module is set to the optimum operating point voltage (Vmpp) (S106). If the optimum operating point voltage is less than the threshold voltage, the command voltage is set to the threshold voltage (Vth) (S107).

[0035] This is because when there is a solar cell module in an ultra-low illuminance environment where the received solar radiation intensity is extremely low, the open circuit voltage of the solar cell module is smaller than that of a solar cell module in a high illuminance environment, and therefore the amount of power that can be extracted is reduced when the solar cell module is operated at its optimal operating point voltage in the ultra-low illuminance environment.

[0036] For example, if the open circuit voltage threshold is set to 8 V and an open circuit voltage of less than 8 V is detected, the device can be operated at the above threshold voltage regardless of the open circuit voltage to prevent a reduction in the power that can be extracted.

[0037] The open circuit voltage threshold value may be, for example, ¼ of the operating voltage at the maximum rated output recorded in the control device.

[0038] Then, the switch is turned On to connect the solar panel and the DC-DC converter (S108), and the duty ratio of the DC-DC converter is adjusted so as to achieve the determined command voltage (S109) to cause the solar panel to generate power.

[0039] The control device preferably changes the frequency at which the open-circuit voltage of the solar panel is obtained depending on the vehicle speed. Specifically, when the vehicle speed is fast, the frequency at which the open-circuit voltage is obtained is increased, and when the vehicle speed is slow, the frequency at which the open-circuit voltage is obtained is decreased, thereby enabling power generation in accordance with changes in solar radiation conditions.

[0040] The solar cell module constituting the solar cell panel of the present invention can have an integrated structure in which unit cells having a rectangular vertical projection image are connected by a transparent conductive film, and examples of materials for forming the unit cells include conventionally known thin film materials such as CIS, a-Si, CdTe, perovskite and organic materials. [Explanation of symbols]

[0041] 1. Solar Panel 11. Solar cell module 12 Unit Cell 2. Control device 3 DC-DC Converter 4 Switch 5. Voltmeter

Claims

1. A solar cell panel formed by connecting a plurality of solar cell modules in parallel; A converter connected to the solar panel via a switch; A voltmeter connected to the solar panel; A vehicle-mounted solar power generation system including a control device, The control device turns off the switch and obtains an open circuit voltage of the solar panel from the voltmeter, determining an operating voltage of the vehicle-mounted solar cell panel from a relationship between an open circuit voltage and a maximum power point voltage of the solar cell panel, the relationship being stored in advance; an in-vehicle solar power generation system, characterized in that the switch is turned on and the converter is controlled to generate power at the determined operating voltage.

2. The vehicle-mounted solar power generation system according to claim 1, characterized in that the control device compares the open-circuit voltages of multiple IV curves stored in advance with the acquired open-circuit voltage, and estimates the IV curve as the IV curve of the solar cell module that receives the highest solar radiation intensity.

3. 2. The vehicle-mounted solar power generation system according to claim 1, wherein the control device changes the frequency at which the open-circuit voltage of the solar cell panel is obtained depending on the vehicle speed.

4. 2. The vehicle-mounted solar power generation system according to claim 1, wherein the control device causes the solar panel to generate power at a threshold voltage when an open-circuit voltage of the solar panel is less than a pre-stored threshold voltage.

5. 2. The vehicle-mounted solar power generation system according to claim 1, wherein at least one of the plurality of solar cell modules is installed at an angle to the other solar cell modules.

6. 6. The vehicle-mounted solar power generation system according to claim 5, wherein the solar cell module is installed on a curved surface.

7. 2. The vehicle-mounted solar power generation system according to claim 1, wherein a unit cell constituting the solar cell module has a vertical projection image that is rectangular.

8. The vehicle-mounted solar power generation system according to claim 7, characterized in that the unit cell is formed of a thin film material selected from the group consisting of CIS-based, a-Si-based, CdTe-based, perovskite-based and organic-based materials.

9. A method for determining an operating point of an on-vehicle solar panel composed of a plurality of solar cell modules connected in parallel, comprising: Detects the voltage of an open solar panel, A method for determining an operating voltage of the solar panel for vehicle installation from a predetermined relationship between an open circuit voltage and a maximum power point voltage of the solar panel.

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