Automotive solar cell system and control method for the automotive solar cell system

Abstract

This invention provides an in-vehicle solar cell system and a control method for the in-vehicle solar cell system that can estimate the maximum power point without requiring sensors such as ammeters for charge control. [Solution] The on-board solar cell system comprises a solar cell, a battery, a converter, and a controller. The controller controls the converter based on the maximum power point voltage and controls the charging of the battery from the solar cell. The controller estimates the current maximum power point voltage by estimating a predetermined solar radiation amount corresponding to a pre-recorded calendar and the solar cell temperature from the predetermined solar radiation amount and the ambient temperature. The output voltage of the solar cell is adjusted to follow the estimated maximum power point voltage to charge the battery. Therefore, this on-board solar cell system and charging control method can follow the maximum power point voltage without adding sensors such as an ammeter for charging control.

Description

Technical Field

[0001] The present invention relates to an in-vehicle solar cell system and a control method for an in-vehicle solar cell system.

Background Art

[0002] Since the current that can be extracted from a solar cell is determined by the voltage of the connected load, generally, MPPT control is performed to change the output voltage of the solar cell so that the generated power becomes maximum and to follow the maximum power point voltage.

[0003] Since the maximum power point voltage changes depending on the solar radiation amount and the temperature of the solar cell, in addition to a current sensor for charge control, if a solar radiation meter and a temperature sensor are additionally provided to estimate the maximum power point voltage, the cost of the solar cell system increases.

[0004] Patent Document 1 discloses that by searching for a range including the maximum power point based on control information associated with a calendar and performing power conversion control, the circuit cost can be reduced.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the method described in Patent Document 1 is inefficient because the searched range of the maximum power point is wide and may differ from the actual maximum power point. Therefore, in order to estimate the actual maximum power point from the searched range of the maximum power point, it is necessary to provide sensors such as an ammeter for charge control.

[0007] This invention has been made in view of the problems of the prior art, and its objective is to provide an in-vehicle solar cell system and a control method for an in-vehicle solar cell system that can estimate the maximum power point without requiring sensors such as ammeters for charge control. [Means for solving the problem]

[0008] The inventors of this invention conducted extensive research to achieve the above objectives and discovered that these objectives can be achieved by estimating the temperature of the solar cell in addition to the amount of solar radiation estimated from calendar information, thus completing the present invention.

[0009] In other words, the in-vehicle solar cell system of the present invention comprises a solar cell, a battery, a converter, and a controller. The controller controls the converter based on the maximum power point voltage and controls the charging of the battery from the solar cell. Then, the controller estimates the current maximum power point voltage by estimating the solar cell temperature from a predetermined solar radiation amount corresponding to a pre-recorded calendar and the ambient temperature. The battery is charged by adjusting the output voltage of the solar cell to track the estimated maximum power point voltage.

[0010] Furthermore, the control method for the in-vehicle solar cell system of the present invention reads the solar radiation corresponding to the current time from a predetermined solar radiation corresponding to a calendar that has been recorded in advance, The solar cell temperature is estimated from the solar radiation readings and the ambient temperature, and the maximum power point voltage is then estimated. Furthermore, the battery is charged by adjusting the output voltage of the solar cell to track the estimated maximum power point voltage. [Effects of the Invention]

[0011] According to the present invention, in addition to the amount of solar radiation estimated from calendar information, the temperature of the solar cell is also estimated. Therefore, it is possible to provide an in-vehicle solar cell system and a charging control method that can track the maximum power point voltage without adding sensors such as an ammeter for charging control. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of the configuration of the in-vehicle solar cell system of the present invention. [Figure 2] This is a flowchart for estimating the maximum power point voltage (VMPP). [Figure 3] This graph shows the relationship between solar cell temperature TS, predetermined solar irradiance S, and maximum power point voltage VMPP. [Figure 4] This figure shows another example of the configuration of the in-vehicle solar cell system of the present invention. [Figure 5] This figure shows an example of a typical in-vehicle solar panel system configuration. [Figure 6] This figure illustrates the state of switching between the low-voltage battery charging mode and the high-voltage charging mode of the in-vehicle solar cell system of the present invention. [Figure 7] This diagram illustrates the voltage waveform of a low-voltage battery. [Figure 8] This diagram illustrates how the upper and lower voltage limits VUL of intermittent charging control, which switches between low-voltage and high-voltage battery charging modes, fluctuate in accordance with the maximum power point voltage VMPP_n. [Modes for carrying out the invention]

[0013] The in-vehicle solar cell system of the present invention will be described in detail. As shown in Figure 1, the in-vehicle solar cell system of the present invention comprises a solar cell, a battery, a converter, and a controller, and further includes a voltage sensor for detecting the battery voltage and a reverse current prevention diode for preventing reverse current flow from the battery to the solar cell.

[0014] The solar cells and battery are connected via a converter, and the electricity generated by the solar cells is supplied to the battery, controller, etc., via the converter.

[0015] The controller estimates the maximum power point voltage of the solar cell and controls the converter based on this estimated maximum power point voltage to control charging from the solar cell to the battery.

[0016] In this invention, the maximum power point voltage is estimated as follows. Figure 2 shows a flowchart for estimating the maximum power point voltage.

[0017] First, obtain the current date and time. (Step S101) Then, the default solar radiation amount S corresponding to the current date and time is read from the default solar radiation amount table recorded in the controller. (Step S102)

[0018] The above-mentioned predetermined solar radiation S is the amount of solar radiation at a reference point that has been set in advance based on the sun's trajectory corresponding to the calendar (date and time), and is determined based on the amount of solar radiation on a clear, cloudless day.

[0019] Furthermore, if the vehicle is equipped with a navigation system, the above-mentioned predetermined solar radiation S may be corrected based on the current location's solar altitude (elevation angle) and azimuth calculated from the latitude and longitude obtained from the navigation system.

[0020] Next, the outside temperature T is obtained. (Step S103) This outside air temperature T may be read from a table of default outside temperatures recorded in the controller, similar to the default solar radiation amount, to determine the default outside temperature T corresponding to the current date and time. Alternatively, if the vehicle is equipped with an outside temperature gauge, the outside temperature obtained from the vehicle may be used.

[0021] Note that the above-mentioned predetermined solar radiation amount and predetermined outside air temperature are quite different from the actual solar radiation amount and outside air temperature on cloudy or rainy days, resulting in a decrease in power generation efficiency. However, since the generated power on cloudy or rainy days is originally small, even if the power generation efficiency decreases on cloudy or rainy days, the influence on this power generation efficiency over a long period is small. Therefore, rather than installing sensors such as ammeters and solar radiation meters to obtain the maximum power on cloudy or rainy days, the cost reduction effect obtained by eliminating these sensors is greater.

[0022] From the predetermined solar radiation amount S read in step S102 and the outside air temperature T obtained in step S103, the solar cell temperature T is estimated using the following formula (1). (Step S104) Estimate. (Step S104) Solar cell temperature T S =A × Predetermined solar radiation amount S + Outside air temperature T ··· Formula (1) In the above formula (1), A is a constant specific to the solar cell and is recorded in the controller in advance as 4.

[0023] Using the solar cell temperature T calculated in step S104 and the predetermined solar radiation amount S read in step S102, as shown in FIG. 3, from the relationship between the solar cell temperature T S · Predetermined solar radiation amount S and the maximum power point voltage V S the current maximum power point voltage V MPP is estimated. (Step S105) MPP Estimate. (Step S105)

[0024] As described above, by estimating the maximum power point voltage from the solar cell temperature T S and the predetermined solar radiation amount S, it is possible to accurately estimate the maximum power point voltage without installing sensors such as ammeters on the solar cell for charge control, enabling high-efficiency power generation.

[0025] And the above-mentioned controller estimates the maximum power point voltage V UL_BAT between the battery upper limit voltage V LL_BAT for preventing the battery stored in advance from malfunctioning and the battery lower limit voltage V MPPTo match this, the target voltage V0 of the solar cell is set, and charging is performed by controlling the voltage of the solar cell to V0 using a converter.

[0026] As described above, the in-vehicle solar cell system of the present invention does not require sensors such as ammeters or pyranometers for MPPT control, and can perform highly efficient power generation at low cost.

[0027] This on-board solar cell system, when applied to electric vehicles with directly connected solar cells and batteries, enables not only highly efficient power generation but also low-cost, highly efficient charging by eliminating power losses in the converter.

[0028] This section describes how the in-vehicle solar cell system of the present invention is applied to the above-mentioned electric vehicle, and how power loss in the converter is eliminated.

[0029] As shown in Figure 4, the in-vehicle solar cell system directly connects the solar cells to the low-voltage battery without using a converter, and connects the high-voltage battery to the low-voltage battery and solar cells via a bidirectional converter.

[0030] Furthermore, a reverse current prevention diode is provided between the solar cell and the low-voltage battery to prevent current from flowing back from the low-voltage battery to the solar cell when the amount of sunlight decreases.

[0031] By connecting the devices in this way, the power generated by the solar panels is supplied directly to low-voltage batteries, low-voltage electronic devices, and controllers, and further supplied to high-voltage batteries and motors / inverters via bidirectional converters.

[0032] Generally, when supplying power generated by a solar panel to both a high-voltage battery and a low-voltage battery, as shown in Figure 5, a converter is required to boost the solar panel voltage to the high-voltage battery voltage and another converter is required to step down the solar panel voltage to the low-voltage battery voltage. As a result, power loss in the converter is inevitable when charging either the high-voltage or low-voltage battery.

[0033] In the automotive solar cell system of the present invention, the solar cell and the low-voltage battery are directly connected without a converter, so there is no power loss in the converter when charging the low-voltage battery from the solar cell, enabling highly efficient charging.

[0034] The charging control of the in-vehicle solar cell system of the present invention, in which the solar cell and low-voltage battery are directly connected without a converter, as shown in Figure 4, will be described.

[0035] When a solar panel and a low-voltage battery are directly connected, the output voltage of the solar panel is equal to the terminal voltage V of the low-voltage battery. n Since it is equal to the terminal voltage V of the low-voltage battery measured by the voltage sensor, n Based on this, the power on the low-voltage side of the bidirectional converter is the estimated maximum power point voltage V MPP To achieve this, the power generated by the solar cells is controlled by controlling the power passing through the bidirectional converter to control the voltage of the low-voltage battery.

[0036] Specifically, as shown in Figure 6, the power generated by the solar cells is controlled by intermittent charging control, which switches between a low-voltage battery charging mode, in which the power generated by the solar cells is used to charge a low-voltage battery, and a high-voltage charging mode, in which the power from the low-voltage battery is converted by a bidirectional converter and used to charge a high-voltage battery.

[0037] In the low-voltage battery charging mode described above, the bidirectional converter power is set to 0, the bidirectional converter is stopped, and the low-voltage battery is charged using the power generated by the solar panel. As a result, the terminal voltage of the low-voltage battery increases due to charging, and the voltage of the low-voltage battery reaches the upper limit voltage V UL Once it reaches that point, activate the bidirectional converter and switch to high-voltage battery charging mode.

[0038] In high-voltage charging mode, the power passing through the bidirectional converter is P DCDCWhen this setting is enabled, power from the low-voltage battery is supplied to the high-voltage battery, causing the terminal voltage of the low-voltage battery to drop. And the voltage value of the low-voltage battery is the lower limit voltage V LL Once this is reached, the bidirectional converter power is set to 0 to stop the bidirectional converter, and the system switches back to low-voltage battery charging mode to charge the low-voltage battery.

[0039] Thus, the controller checks when the voltage of the low-voltage battery reaches the upper voltage V. UL Or lower limit voltage V LL When this is reached, the bidirectional converter is switched on and off to intermittently switch between controlling the charging from the solar cell to the low-voltage battery and controlling the charging from the solar cell and / or the low-voltage battery to the high-voltage battery.

[0040] Next, the upper limit voltage V of the low-voltage battery that switches the bidirectional converter on and off. UL and lower limit voltage V LL This explains the settings.

[0041] In low-voltage battery charging mode, the controller calculates the maximum power point voltage V estimated in steps S101 to S105 above. MPP_n Based on this, the upper voltage limit V of intermittent charging control switches from low-voltage battery charging mode to high-voltage charging mode. UL Set it.

[0042] The upper limit voltage V of the above intermittent charging control UL This is the upper limit voltage V for solar cell control. UL_MPP The target value for preventing low-voltage battery failure is the upper limit voltage V of the low-voltage battery. UL_BAT and auxiliary equipment upper limit voltage V UL_ACC It is the smallest value among them.

[0043] Therefore, the upper limit voltage V for intermittent charging control UL This is the low-voltage battery upper voltage limit V UL_BAT and auxiliary equipment upper limit voltage V UL_ACC With this as the upper limit, the upper limit voltage V for solar cell control UL_MPP To follow suit.

[0044] The upper limit voltage V for the above solar cell control UL_MPP For example, the upper limit voltage V for solar cell control. UL_MPPP = Maximum power point voltage V MPP_n + 1 / 3 × ΔV0, where ΔV0 is the upper limit voltage V for intermittent charging control. UL - Lower limit voltage V LL This is the target value. Also, the low-voltage battery upper limit voltage V UL_BAT and auxiliary equipment upper limit voltage V UL_ACC This is a value that is pre-stored in the controller.

[0045] The controller uses the terminal voltage V of the low-voltage battery. n The upper limit voltage V UL Determine whether it is lower than or equal to the terminal voltage V n The upper limit voltage is V UL If it is lower than, terminal voltage V n The upper limit voltage is V UL Continue the low-voltage battery charging mode until the maximum power point voltage V rises, and repeat steps S101 to S105. MPP_n To estimate the maximum power point voltage V MPP_n Based on this, the upper limit voltage V for intermittent charging control UL Repeat the settings.

[0046] And the terminal voltage V n The upper limit voltage is V UL When the voltage rises, the system switches from low-voltage battery charging mode to high-voltage battery charging mode.

[0047] Furthermore, in high-voltage battery charging mode, the controller calculates the maximum power point voltage V estimated in steps S101 to S105 above. MPP_n Based on this, the lower limit voltage V of intermittent charging control switches from high-voltage charging mode to low-voltage battery charging mode. LL Set it.

[0048] Lower limit voltage V of the above intermittent charging control LL This is the lower limit voltage V for solar cell control. LL_MPPThe target value for preventing low-voltage battery failure is the lower limit voltage V of the low-voltage battery. LL_BAT , and auxiliary equipment V LL_ACC It is the largest value among them.

[0049] Therefore, the lower limit voltage V for intermittent charging control LL This is the lower limit voltage of a low-voltage battery V LL_BAT and auxiliary lower voltage V LL_ACC With the lower limit as the lower limit voltage V for solar cell control, LL_MPP To follow suit.

[0050] The lower limit voltage V of the above solar cell control LL_MPP For example, the lower limit voltage V for solar cell control. LL_MPP = Maximum power point voltage V MPP_n Set to + 2 / 3 × ΔV0. ΔV0 is the upper limit voltage V for intermittent charging control, as described above. UL - Lower limit voltage V LL This is the target value. Also, the lower limit voltage V of a low-voltage battery LL_BAT and auxiliary lower voltage V LL_ACC This value is a target value to prevent the low-voltage battery from failing, and it is a value that is pre-stored in the controller.

[0051] The controller uses the terminal voltage V of the low-voltage battery. n The lower limit voltage V LL Determine whether it is higher than or equal to the terminal voltage V n The lower limit voltage V LL If it is higher than, terminal voltage V n The lower limit voltage V LL The high-voltage battery charging mode continues until the voltage drops to V, and steps S101 to S105 are repeated to return to the maximum power point voltage V. MPP_n To estimate the maximum power point voltage V MPP_n Based on this, the lower limit voltage V for intermittent charging control LL Repeat the settings.

[0052] And the terminal voltage V n The lower limit voltage V LL When the battery decelerates, it switches from high-voltage battery charging mode to low-voltage battery charging mode.

[0053] In this way, by switching between the low-voltage battery charging mode and the high-voltage battery charging mode, the estimated maximum power point voltage V can be obtained, as shown in Figure 8. MPP_n With the update, the upper limit voltage V of intermittent charging control UL However, the maximum power point voltage V MPP_n It follows the lower limit voltage V of intermittent charging control. UL Similarly, the estimated maximum power point voltage V MPP_n With the update, the maximum power point voltage V MPP_n It changes in accordance with the situation.

[0054] Therefore, even when the solar cell and the low-voltage battery are connected directly without a converter, maximum power point voltage tracking control is possible, and highly efficient charging is possible by eliminating power loss due to the converter.

Claims

1. It consists of a solar cell, a battery, a converter, and a controller. The above controller controls the converter based on the maximum power point voltage and controls the charging from the solar cell to the battery in an in-vehicle solar cell system, The above controller estimates the current maximum power point voltage by estimating the solar cell temperature from a predetermined solar radiation amount corresponding to a pre-recorded calendar and the ambient temperature, An in-vehicle solar cell system characterized by charging the battery by making the output voltage of the solar cell track the estimated maximum power point voltage.

2. The vehicle-mounted solar cell system according to claim 1, characterized in that the predetermined solar radiation is the amount of solar radiation determined based on the amount of solar radiation on a sunny day.

3. The in-vehicle solar cell system according to claim 1, characterized in that the above-mentioned outside temperature is an outside temperature obtained from a predetermined outside temperature corresponding to a calendar that has been recorded in advance.

4. The in-vehicle solar cell system according to claim 1, characterized in that the above-mentioned outside temperature is the outside temperature obtained from the vehicle.

5. The above battery has a high-voltage battery and a low-voltage battery, The above converter is a bidirectional converter, The solar cell and the low-voltage battery are directly connected, and the high-voltage battery is connected to the solar cell and the low-voltage battery via the bidirectional converter. The above controller performs intermittent charging control based on the voltage of the low-voltage battery. The above intermittent charging control stops the above bidirectional converter and controls charging from the above solar cell to the above low-voltage battery, The in-vehicle solar cell system according to claim 1, characterized in that the above-mentioned bidirectional converter is operated to intermittently switch between charging control from the solar cell and / or the low-voltage battery to the high-voltage battery.

6. The above controller operates the bidirectional converter at the upper limit voltage of the intermittent charging control and stops the bidirectional converter at the lower limit voltage of the intermittent charging control to perform intermittent charging control of the high-voltage battery. The automotive solar cell system according to claim 5, characterized in that the upper limit voltage and the lower limit voltage of the intermittent charging control change in accordance with the estimated maximum power point voltage.

7. The solar radiation corresponding to the current time is read from a predetermined solar radiation corresponding to a previously recorded calendar. The solar cell temperature is estimated from the solar radiation read out above and the ambient temperature, and the maximum power point voltage is then estimated. A control method for an in-vehicle solar cell system, characterized by charging the battery by adjusting the output voltage of the solar cell to track the estimated maximum power point voltage.

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