Automotive solar cell system

Abstract

To provide an on-vehicle solar cell system that has specialized in ways how shadows are cast particular to a vehicle, and can prevent significant output drop in a simple circuit configuration.SOLUTION: An on-vehicle solar cell system according of the present invention has a plurality of solar cell modules. Then, one of the solar cell modules has a shape longer in a vehicle width direction than a vehicle length direction of a vehicle, and these are disposed side by side in the vehicle length direction. Each of the solar cell modules has a converter that transmits its power to a vehicle battery, and is independently connected to the vehicle battery. Thereby, even when shadows are cast partially on a front side or a rear side of the vehicle, the on-vehicle solar system can provide a system that can prevent significant output drop by a simple circuit configuration.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an in-vehicle solar cell system, and more particularly to an in-vehicle solar cell system that takes into account the influence when a shadow partially falls during vehicle travel.

Background Art

[0002] In order to maximize the output power of a solar cell, it is necessary to control the voltage so that the product of the current and the voltage is maximized. Since the voltage-current characteristics of a solar cell vary depending on the solar radiation amount, temperature, etc., it is necessary to control the operating point of the solar cell to follow the maximum power point.

[0003] When a solar cell panel is formed of a plurality of solar cell modules connected in series, if a shadow partially falls on this solar cell panel, a difference in solar radiation amount occurs between the solar cell modules, and the output power of the solar cell module with a low solar radiation amount decreases compared to other solar cell modules.

[0004] And since the current value flowing through the entire solar cell panel cannot exceed the current value of the low-output solar cell module with a shadow, the current value of the solar cell module without a shadow is pulled by the current value of the low-output solar cell module, resulting in a decrease in the output power of the entire solar cell panel and a significant reduction in the output power.

[0005] Patent Document 1 discloses a solar cell panel that can capture the maximum power point in a state where a shadow partially falls on the solar cell panel by switching the connection state of the solar cell modules between series connection and parallel connection according to the shadow partially falling on the solar cell panel, bypassing the solar cell module with a shadow, and preventing it from contributing to power generation.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, in the case described in Patent Document 1, the connection state of the solar cell module is changed depending on how the shadow falls, which complicates the circuit configuration and its control.

[0008] Furthermore, development is underway on on-board solar power systems that enable power generation while driving by installing solar panels on the roof of the vehicle. Unlike solar panels fixed to buildings or outdoors, these on-board solar power systems have the characteristic that the shadow is highly likely to move in one direction from front to back as the vehicle moves.

[0009] The objective of the present invention is to provide an in-vehicle solar cell system that is specifically designed to handle the unique shading patterns of such vehicles and can prevent significant power reduction with a simple circuit configuration. [Means for solving the problem]

[0010] The inventors of this invention have conducted extensive research to achieve the above objectives and have found that these objectives can be achieved by arranging multiple solar cell modules in a line along the length of the vehicle and connecting each solar cell module independently to the vehicle battery, thereby completing the present invention.

[0011] In other words, the in-vehicle solar cell system of the present invention comprises multiple solar cell modules It is equipped with a control device. ru. And the above solar cell module, The solar module has multiple solar cells, and these solar cells are arranged in a line in the vehicle width direction and connected in parallel, and this solar module is The shape is such that the width direction is longer than the length direction of the vehicle, and these are arranged side by side in the length direction of the vehicle, and each solar cell module has a converter that transmits its power to the vehicle battery and is independently connected to the vehicle battery. The above control device, The system is characterized by calculating a boost ratio from the maximum power point voltage determined from the temperature and solar irradiance of the solar cell module and the output voltage of the converter, controlling the converter, and controlling each converter with the same duty cycle. . [Effects of the Invention]

[0012] According to the present invention, by arranging multiple solar cell modules in a line along the length of the vehicle and connecting each solar cell module independently to the vehicle battery, it is possible to provide an in-vehicle solar cell system that can prevent a significant decrease in output even if the front or rear of the vehicle is partially shaded, with a simple circuit configuration. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing an example of the vehicle-mounted solar cell system of the present invention installed in a vehicle. [Figure 2] This is a schematic diagram of the in-vehicle solar cell system of the present invention. [Figure 3] This diagram illustrates the power generation state when a shadow falls on the front of the vehicle. [Figure 4] This graph shows the relationship between output voltage and output current when the front of the vehicle is in shadow, and the relationship between output power and output voltage. [Figure 5] This figure shows an example of the connection status of solar cells that make up a solar cell module. [Figure 6] This diagram shows a configuration where bypass diodes are installed in a series-connected solar cell network. [Figure 7] This diagram shows a configuration where reverse current prevention diodes are installed in parallel-connected solar cells. [Figure 8] This graph shows the relationship between the length of the solar cell and the voltage drop rate due to the reverse current blocking diode. [Figure 9] This graph shows the relationship between solar radiation, the temperature of the solar cell module, and the point of maximum power. [Figure 10] This is a flowchart illustrating how to control a converter to generate power at its maximum power point. [Figure 11] This figure shows the maximum power point of the in-vehicle solar cell system of the present invention when there is a difference in the amount of solar radiation between solar cell modules. [Figure 12]It is a diagram showing an example of the maximum power point when there is a difference in solar irradiance between solar cell modules in another solar cell system.

Embodiments for Carrying Out the Invention

[0014] The in-vehicle solar cell system of the present invention will be described in detail. The in-vehicle solar cell system of the present invention is a system that boosts the power generated by solar cell modules by a converter and supplies it to a vehicle battery. As shown in FIG. 1, it has a plurality of solar cell modules shaped such that the width direction is longer than the length direction of the vehicle, and these solar cell modules are arranged side by side in the length direction of the vehicle. And in each solar cell module, as shown in FIG. 2, a converter is provided at the tip of the black circle in FIG. 1. These converters are independently connected to the vehicle battery to transmit the power generated by each solar cell module to the vehicle battery.

[0015] In the in-vehicle solar cell system of the present invention, since the solar cell modules are shaped such that the width direction is longer than the length direction of the vehicle and are arranged divided in the length direction of the vehicle, there is a high probability that there are solar cell modules that are not shaded at all.

[0016] And in the in-vehicle solar cell system of the present invention, since each solar cell module is independently connected to the vehicle battery, even when a part of the front or rear of the vehicle is shaded, as shown in the left figure of FIG. 3, current does not flow backward from the solar cell module that is not shaded to the solar cell module that is shaded.

[0017] That is, as shown in the right figure of FIG. 3, when the solar cell modules are arranged side by side in the width direction, current flows backward within the solar cell modules and the output power decreases. So, until the shadow completely moves to the rear end of the vehicle and sunlight hits all the solar cell modules, the state where the output power of the solar cell system is decreased continues.

[0018] Figure 4 shows the relationship between output voltage and output current, and the relationship between output power and output voltage, for cases where the solar cell modules are arranged in the length direction of the vehicle (A) and in the width direction of the vehicle (B).

[0019] Thus, the in-vehicle solar cell system can generate electricity while minimizing the effects of shading on the front or rear of the vehicle, and can suppress a significant drop in output voltage.

[0020] A solar cell module may consist of one solar cell or multiple solar cells, provided that its shape is such that the width direction is longer than the length direction of the vehicle.

[0021] When configuring multiple solar cells, as shown in the upper diagram of Figure 5, the solar cells may be connected in series, or as shown in the middle diagram of Figure 5, the series-connected solar cell groups may be connected in parallel to mix series and parallel connections. However, as shown in the lower diagram of Figure 5, it is preferable to connect all solar cells in parallel.

[0022] As shown in the upper and middle diagrams of Figure 5, if solar cells are connected in series, the current value of the solar cells that are not shaded will be limited to the current value of the shaded solar cells. Therefore, as shown in Figure 6, it is necessary to provide a bypass diode connected in parallel to the solar cells to bypass the shaded solar cells.

[0023] Because all solar cells are connected in parallel, bypass diodes are unnecessary, simplifying the circuit configuration.

[0024] Furthermore, because all the solar cells constituting the solar cell module are connected in parallel, the length of the solar cell module in the vehicle-length direction can be shortened, reducing the probability of partial shading within a single solar cell module.

[0025] The length of the solar cell module in the vehicle's longitudinal direction depends on factors such as the required output power and vehicle width, but for example, a length of 10cm to 50cm allows for a balance between reducing the probability of partial shading and achieving sufficient output power.

[0026] In this case, if the shadow falls on part of the left or right side of the vehicle, backflow will occur within the solar cell module, similar to Figure 3(b). However, the probability of the shadow moving in the vehicle's width direction due to vehicle movement is lower than the probability of it moving in the vehicle's length direction, so this does not pose a major problem.

[0027] Furthermore, reverse current flow within the solar cell module, which can occur when a shadow falls on part of the left or right side of the vehicle, can be prevented by providing a reverse current prevention diode connected in series with the solar cell, as shown in Figure 7.

[0028] However, as shown in Figure 8, the voltage drop rate of the solar cell due to the reverse current blocking diode increases as the length of the solar cell in series with respect to the reverse current blocking diode (in the vehicle length direction) decreases.

[0029] In the automotive solar cell system of the present invention, each solar cell module is independently connected to the vehicle battery. Therefore, even if the output power of one solar cell module decreases, the other solar cell modules are not affected, preventing a significant drop in output power. This eliminates the need for reverse current protection diodes, simplifying the circuit configuration.

[0030] In this invention, the "length of the solar cell module" refers to the length from one end of the solar cell group to the other, including the gaps between the solar cells constituting the solar cell module, as shown in Figure 5.

[0031] Next, the maximum power point tracking control of the in-vehicle solar cell system of the present invention will be described. As described above, the in-vehicle solar cell system of the present invention boosts the power generated by the solar cell module using a converter and supplies it to the vehicle battery.

[0032] As shown in Figure 9, the maximum power point of a solar cell module changes not only with the amount of sunlight but also with the temperature of the solar cell module. Therefore, the control device uses a converter to control the output voltage of the solar cell module so that power can be generated at the maximum power point.

[0033] As shown in Figure 10, the control device acquires the amount of solar radiation and the temperature of the solar cell module. From these values, it determines the maximum power point voltage of the solar cell module based on the relationship between the solar radiation and the temperature of the solar cell module, which is stored in advance, as shown in Figure 9.

[0034] The above solar radiation can be obtained from a solar radiation sensor, and the solar cell module temperature can be obtained from a temperature sensor. Solar radiation sensors and temperature sensors may be provided on each solar cell module, or solar radiation sensors and temperature sensors provided on one solar cell module may be applied to all solar cell modules.

[0035] The control unit calculates the converter boost ratio required to raise the voltage from the maximum power point voltage to the vehicle battery voltage (converter output voltage) using the acquired vehicle battery voltage and the maximum power point voltage of the solar cell module. Then, it determines the converter duty cycle that results in this converter boost ratio and controls the converter accordingly.

[0036] In this way, high-speed control is possible by determining the converter duty cycle from the vehicle battery voltage and the maximum power point voltage.

[0037] The relationship between the converter boost ratio and the converter duty cycle is stored in the control unit beforehand. For example, if the converter is a non-inverting buck-boost converter, the converter duty cycle can be calculated as converter boost ratio / (1 + converter boost ratio).

[0038] The converter may perform the voltage boost in a single step or in multiple steps.

[0039] Furthermore, as shown in Figures 11 and 12, we will explain the tracking control of the maximum power point when the shadow is cast at an angle.

[0040] As shown in the left diagram of Figure 11, the in-vehicle solar cell system of the present invention ensures that even when there are differences in the amount of sunlight between solar cell modules, multiple solar cell modules are equipped with converters and are independently connected to the vehicle battery, so that a shaded solar cell module does not affect other solar cell modules.

[0041] Furthermore, since the solar cells in each solar cell module are connected in parallel, the voltage fluctuation of the solar cell module is small, as shown in the right-hand diagram of Figure 11.

[0042] Therefore, even when there are differences in the amount of sunlight between solar cell modules, all converters can be controlled with the same duty cycle and the current can be adjusted according to the amount of sunlight to generate power at the maximum power point. This reduces the load on the control device while preventing a decrease in output power.

[0043] In contrast, as shown in the left diagram of Figure 12, when solar cell modules, which are connected in series, are connected in parallel and multiple solar cell modules are controlled by a single converter, the output voltage of each solar cell module will be different, as shown in the right diagram of Figure 12.

[0044] Therefore, if the current is controlled so that the solar cell module (a), which is most shaded, reaches its maximum power point, the current to the other solar cell modules must also be reduced, making it impossible to generate power at the maximum power point. Conversely, if the voltage is adjusted to match the solar cell module (f), which is least shaded, power cannot be drawn from the other solar cell modules, resulting in a decrease in the overall output power of the solar cell system.

[0045] Thus, the in-vehicle solar cell system of the present invention has a high probability of having solar cell modules that are not shaded at all, even if a part of the front or rear of the vehicle is partially shaded. Furthermore, since the solar cell modules are independently connected to the vehicle battery, a decrease in power generation can be suppressed with a simple circuit configuration. [Explanation of Symbols]

[0046] 1. Solar cell module 11 Large-capacity battery cells 2 Converters 3. Control device 4. Vehicle Battery 5. Solar radiation sensor 6. Temperature sensor 7 Bypass diode 8. Reverse current protection diode

Claims

[Claim 1] An in-vehicle solar cell system comprising multiple solar cell modules and a control device, The above-mentioned solar cell module has multiple solar cells, which are arranged in a row in the vehicle width direction and connected in parallel, and the solar cell module is longer in the vehicle width direction than in the vehicle length direction, and these are arranged side by side in the vehicle length direction, and each solar cell module has a converter that transmits its power to the vehicle battery and is independently connected to the vehicle battery. The above control device, An in-vehicle solar cell system characterized by calculating a boost ratio from the maximum power point voltage obtained from the temperature and solar irradiance of the solar cell module and the output voltage of the converter, controlling the converter, and controlling each converter with the same duty cycle.

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